Question 1

The type of bone fracture in which the bone is broken into several fragments at multiple places along its length is called what?

Accepted Answer

Introduction / Context: Fractures are breaks in bones caused by trauma, stress, or disease. Medical professionals classify fractures into different types based on the pattern and severity of the break. Knowing these terms is important for understanding treatment and healing. This question asks which term refers to a fracture in which a bone is broken into several fragments or pieces at multiple sites. Given Data / Assumptions: The bone is broken at several places, with multiple fragments. Options include complicated fracture, greenstick fracture, impacted fracture, comminuted fracture, and simple fracture. We assume standard orthopaedic definitions. We focus on the fragmentation pattern rather than whether the skin is broken. Concept / Approach: A comminuted fracture is defined as a fracture in which the bone is broken into three or more fragments. It often occurs in high energy injuries such as road accidents or severe falls. In contrast, a greenstick fracture is an incomplete fracture seen in children where the bone bends and cracks on one side. An impacted fracture occurs when one fragment is driven into another. A complicated fracture involves damage to surrounding structures, and a simple fracture means the bone is broken but does not penetrate the skin. Since the question emphasises several places and multiple fragments, comminuted fracture is the correct term. Step-by-Step Solution: Step 1: Identify the key phrase: bone is broken at several places, implying multiple fragments. Step 2: Recall that comminuted fracture means the bone is shattered or broken into three or more pieces. Step 3: Compare this with a greenstick fracture, which is partial and incomplete, not multi fragment. Step 4: Note that an impacted fracture involves one part of the bone being driven into another, often with fewer larger fragments. Step 5: Recognise that complicated fractures focus on associated injury to nerves or blood vessels rather than fragmentation pattern. Step 6: A simple fracture is closed, with no break in the skin, but it may still be a single clean break, not necessarily many fragments. Step 7: Therefore, comminuted fracture is the correct term for a bone shattered into several pieces. Verification / Alternative check: Orthopaedic and first aid manuals list comminuted fractures as fractures with multiple bone fragments, often requiring more complex treatment such as surgical fixation with plates, screws, or rods. Diagrams show bones broken into many irregular pieces rather than a single clean line. This matches the description in the question, confirming the choice of comminuted fracture. Why Other Options Are Wrong: Complicated fracture: Usually refers to a fracture with additional complications such as injury to blood vessels, nerves, or internal organs, not specifically many fragments. Greenstick fracture: An incomplete fracture common in children where the bone bends and partially breaks on one side only. Impacted fracture: One fragment is driven into another, often seen in falls, but not necessarily involving numerous small fragments. Simple (closed) fracture: The bone is broken but the skin remains intact; the number of fragments is not specified. Common Pitfalls: Some learners may choose complicated fracture simply because the injury sounds severe. Others may not differentiate between types based on the pattern of breakage. To avoid such errors, remember the key word associated with comminuted: it implies the bone has been crushed or shattered into multiple pieces. Final Answer: The correct answer is Comminuted fracture.

Question 2

Which hormone produced by the female reproductive system plays the key role in preparing and maintaining the uterine lining for implantation of the embryo?

Accepted Answer

Introduction / Context: Successful pregnancy depends on proper coordination between hormones and reproductive organs. After fertilisation, the embryo must implant into the prepared lining of the uterus. A specific hormone produced mainly by the ovaries is essential for thickening, maintaining, and stabilising this uterine lining so that the embryo can attach and grow. This question asks you to identify that hormone. Given Data / Assumptions: The focus is on implantation of the embryo in the uterus. Options are testosterone, insulin, prolactin, progesterone, and adrenaline. We assume normal female reproductive physiology. We seek the hormone primarily responsible for preparing and maintaining the endometrium. Concept / Approach: Progesterone is the main hormone responsible for preparing the endometrium (uterine lining) after ovulation and maintaining it for possible implantation. It is secreted by the corpus luteum in the ovary and later by the placenta if pregnancy occurs. Progesterone makes the endometrium thick, glandular, and well supplied with blood, creating a suitable environment for the embryo. Testosterone is a male sex hormone, insulin regulates blood glucose, prolactin stimulates milk production, and adrenaline prepares the body for fight or flight. None of these have the central role in implantation that progesterone has. Step-by-Step Solution: Step 1: Recall that after ovulation, the ruptured follicle in the ovary forms the corpus luteum. Step 2: The corpus luteum secretes progesterone, which acts on the uterine lining. Step 3: Progesterone causes the endometrium to thicken, become more vascular, and secrete nutrients, making it receptive to an implanting embryo. Step 4: If fertilisation and implantation occur, progesterone levels remain high to maintain the uterine lining and prevent its shedding. Step 5: Testosterone is primarily a male hormone, insulin controls blood sugar, prolactin regulates milk secretion, and adrenaline affects heart rate and alertness. Step 6: Therefore, the hormone that helps in implantation of the embryo is progesterone. Verification / Alternative check: Reproductive physiology texts describe the menstrual cycle in phases: follicular, ovulatory, and luteal. The luteal phase is dominated by progesterone, during which the endometrium becomes secretory and ready for implantation. Clinical practice also uses progesterone supplementation in some cases of infertility to support implantation. These consistent references confirm progesterone as the hormone most directly associated with implantation. Why Other Options Are Wrong: Testosterone: Primarily a male sex hormone involved in development of male secondary sexual characters and spermatogenesis. Insulin: Regulates blood glucose and metabolism, not directly involved in implantation. Prolactin: Stimulates milk production in mammary glands after childbirth, not responsible for preparing the uterus. Adrenaline: A stress hormone affecting heart rate and blood pressure, unrelated to uterine implantation. Common Pitfalls: Some students may confuse progesterone with estrogen, another important female hormone. While estrogen helps build up the uterine lining earlier in the cycle, progesterone is the hormone that stabilises and prepares it specifically for implantation. Remember the association: progesterone preserves pregnancy by preparing and maintaining the endometrium. Final Answer: The correct answer is Progesterone.

Question 3

The innermost delicate membrane of the meninges that directly covers the surface of the brain and spinal cord is called what?

Accepted Answer

Introduction / Context: The brain and spinal cord are extremely delicate organs that need protection from mechanical injury and infection. In addition to the skull and vertebral column, they are covered by three protective membranes collectively called meninges. Each meningeal layer has a specific position and structure. This question asks you to identify the innermost membrane that lies directly on the surface of the brain and spinal cord. Given Data / Assumptions: The question refers to the innermost membrane covering the brain. Options include pleura, dura mater, pia mater, arachnoid membrane, and pericardium. We assume standard anatomical knowledge of meningeal layers. We focus on the layer that closely follows the contours of the brain and spinal cord. Concept / Approach: The three meningeal layers from outermost to innermost are dura mater, arachnoid mater, and pia mater. Dura mater is thick and tough, attached to the skull. Arachnoid mater is a web like middle layer. Pia mater is the innermost delicate membrane that adheres closely to the brain and spinal cord, following all their folds and grooves. The pleura is the membrane around the lungs, and the pericardium surrounds the heart, so they are unrelated to the central nervous system meninges. Therefore, the correct answer is pia mater. Step-by-Step Solution: Step 1: Recall the names of the three meninges: dura mater, arachnoid mater, and pia mater. Step 2: Understand their order: dura mater is outermost, arachnoid mater is in the middle, and pia mater is innermost. Step 3: Recognise that pia mater lies directly on the brain and spinal cord, closely following their surface. Step 4: Dura mater is tough and fibrous, providing strong outer protection, not the innermost membrane. Step 5: Arachnoid membrane is between dura and pia and contains the subarachnoid space with cerebrospinal fluid, but it does not directly adhere to the brain surface. Step 6: Pleura and pericardium are protective membranes of lungs and heart respectively, not parts of the meninges. Step 7: Therefore, the innermost membrane covering the brain is the pia mater. Verification / Alternative check: Anatomy textbooks consistently display cross sectional diagrams of the skull and brain, labelling the meninges in the order dura, arachnoid, and pia from outside to inside. They describe the pia mater as vascular and delicate, providing a supportive covering that accompanies the brain into all sulci and fissures. This description matches the innermost membrane requested in the question and confirms the answer. Why Other Options Are Wrong: Pleura: A double layered membrane surrounding the lungs, unrelated to brain coverings. Dura mater: The outermost tough meningeal layer, not the innermost. Arachnoid membrane: The middle meningeal layer, separated from pia by the subarachnoid space. Pericardium: A fibrous sac surrounding the heart, not part of the meninges. Common Pitfalls: Students sometimes confuse the order of the meningeal layers or mix up pia and dura because of similar sounding names. Others may not distinguish between meninges and other body membranes such as pleura. An easy memory aid is to think of the pia mater as the tender mother right on the brain, while dura mater is the tough mother on the outside. Final Answer: The correct answer is Pia mater.

Question 4

In the spectrum of electromagnetic radiation, which of the following has a greater wavelength than visible light?

Accepted Answer

Introduction / Context: Electromagnetic radiation includes a wide range of waves with different wavelengths and frequencies, from very short wavelength gamma rays to very long wavelength radio waves. Visible light occupies only a small portion of this spectrum. Understanding which regions lie just beyond the visible range is a common physics and general science question. This question asks you to identify which type of radiation has a wavelength greater than that of visible light. Given Data / Assumptions: We compare different types of electromagnetic radiation with visible light. Options include ultraviolet rays, infrared rays, cosmic rays, X-rays, and gamma rays. We assume standard ordering of the electromagnetic spectrum by wavelength. Greater wavelength means longer wavelength and therefore lower frequency than visible light. Concept / Approach: In the electromagnetic spectrum, gamma rays have the shortest wavelengths, followed by X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves with the longest wavelengths. Ultraviolet rays have shorter wavelengths than visible light. Infrared rays have wavelengths longer than visible light and are felt as heat. Cosmic rays are extremely high energy particles and are associated with very short effective wavelengths, not longer ones. Gamma rays and X-rays also have shorter wavelengths than visible light. Therefore, the type of radiation with wavelength greater than visible light among the given options is infrared. Step-by-Step Solution: Step 1: Recall the approximate order of the electromagnetic spectrum from short to long wavelengths: gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, radio waves. Step 2: Compare ultraviolet and infrared with visible light. Ultraviolet is just beyond visible violet and has shorter wavelength, while infrared is just beyond visible red and has longer wavelength. Step 3: Recognise that gamma rays, X-rays, and most cosmic radiation are very high energy, very short wavelength forms of radiation. Step 4: Since the question is asking for greater wavelength than visible light, eliminate ultraviolet, X-rays, gamma rays, and cosmic rays, which all have shorter wavelengths. Step 5: The remaining option, infrared rays, lies on the long wavelength side of visible light. Step 6: Therefore, infrared rays have greater wavelength than visible light and are the correct answer. Verification / Alternative check: Physics textbooks often show diagrams of the electromagnetic spectrum marking the visible band between about 400 nanometres and 700 nanometres. They place ultraviolet below 400 nanometres and infrared above 700 nanometres. They also explain that humans perceive infrared mostly as heat radiation. This positional relationship confirms that infrared has longer wavelength than visible light. Why Other Options Are Wrong: Ultraviolet rays: Lie just beyond the violet end of visible light and have shorter wavelengths than visible light. Cosmic rays: Very high energy radiation with extremely short effective wavelengths, shorter than even gamma rays. X-rays: Also shorter in wavelength than visible light and used in medical imaging. Gamma rays: Shortest wavelength and highest energy in the electromagnetic spectrum. Common Pitfalls: Students sometimes reverse the order of ultraviolet and infrared or assume that all names that sound more exotic, like cosmic rays, must have larger wavelengths. To avoid confusion, memorise the proper order and remember that infrared is associated with heat and longer wavelengths, whereas ultraviolet is associated with higher energy and shorter wavelengths than visible light. Final Answer: The correct answer is Infrared rays.

Question 5

Cretinism, a condition characterised by stunted physical growth and mental retardation in children, is due to a disorder of which endocrine gland?

Accepted Answer

Introduction / Context: Endocrine glands secrete hormones that regulate growth, metabolism, and development. When these glands malfunction, characteristic diseases arise. Cretinism is a disorder seen in children due to lack of a specific hormone that is crucial for normal growth and brain development. This question asks which gland, when underactive or defective during early life, leads to cretinism. Given Data / Assumptions: Cretinism is associated with stunted physical and mental development. Options list thymus, parathyroid, thyroid, adrenal, and pituitary glands. We assume standard endocrine disease associations used in textbooks. We focus on congenital or early life hormone deficiency. Concept / Approach: The thyroid gland produces thyroid hormones, mainly thyroxine (T4) and triiodothyronine (T3). These hormones are essential for growth, brain development, and metabolic regulation. If thyroid hormone production is severely deficient from birth or early childhood, the child may develop cretinism, characterised by dwarfism, delayed milestones, and intellectual disability. Thymus is involved in immune cell maturation, parathyroids regulate calcium, adrenal glands secrete stress and metabolic hormones, and the pituitary is a master gland but its deficiency causes different syndromes. Thus, thyroid gland disorders cause cretinism. Step-by-Step Solution: Step 1: Recall that the thyroid gland lies in the neck and secretes thyroxine, which controls metabolism and growth. Step 2: Understand that in children, thyroxine is especially important for normal development of bones and the nervous system. Step 3: Recognise that lack of thyroid hormone in early life leads to cretinism, with symptoms like retarded growth, mental retardation, and characteristic facial features. Step 4: Check other gland functions: the thymus is linked to T cell maturation, parathyroids regulate calcium, adrenals secrete cortisol and adrenaline, and pituitary controls many glands but is not directly named in the definition of cretinism. Step 5: Therefore, identify the thyroid gland as the endocrine gland whose disorder results in cretinism. Verification / Alternative check: Endocrinology and paediatrics references consistently define cretinism as congenital hypothyroidism. They highlight the importance of early screening and thyroid hormone replacement in newborns to prevent permanent damage. While pituitary disorders can lead to secondary hypothyroidism, the classical exam question directly associates cretinism with thyroid gland failure, confirming this answer. Why Other Options Are Wrong: Thymus gland: Plays a role in immune system development, not directly in body growth and cognitive development in the same way. Parathyroid glands: Control blood calcium and phosphate; disorders cause tetany or bone problems, not classic cretinism. Adrenal glands: Involved in stress response and metabolism, but their disorders result in conditions such as Addison disease or Cushing syndrome, not cretinism. Pituitary gland: Although it influences thyroid activity, exam questions on cretinism point to the thyroid gland as the main associated organ. Common Pitfalls: Some learners confuse cretinism with dwarfism due to pituitary hormone deficiency. While both involve short stature, cretinism also includes severe mental retardation and is directly tied to thyroid hormone deficiency. Remember the association: cretinism equals congenital hypothyroidism and therefore involves the thyroid gland. Final Answer: The correct answer is Thyroid gland.

Question 6

Which cell organelle plays the most important role in carrying out photosynthesis by capturing light energy and converting it into chemical energy in plant cells?

Accepted Answer

Introduction / Context: Photosynthesis is the fundamental biological process by which green plants, algae and some bacteria capture light energy from the sun and convert it into chemical energy stored in food molecules. To perform this complex reaction, plant cells rely on specialised internal structures. This question asks you to identify the specific cell organelle that is central to the process of photosynthesis in higher plants. Given Data / Assumptions: We are dealing with photosynthesis in typical plant cells. The options list various cellular structures: chloroplast, centrosome, tonoplast, nematoblast and mitochondrion. We assume a basic understanding of plant cell organelles and their functions. The task is to pick the organelle that directly carries out photosynthesis. Concept / Approach: Chloroplasts are double membrane bound organelles found mainly in the green parts of plants, such as leaves. They contain the green pigment chlorophyll, which absorbs light energy, especially in the blue and red regions of the spectrum. Inside chloroplasts, stacks of thylakoid membranes host the light dependent reactions, while the surrounding stroma hosts the light independent (Calvin cycle) reactions. Together, these reactions convert light energy, water and carbon dioxide into glucose and oxygen. None of the other listed structures is the primary site of photosynthesis in plant cells. Step-by-Step Solution: Step 1: Recall that photosynthesis requires chlorophyll, a green pigment that captures sunlight. Step 2: Remember that chlorophyll molecules are embedded in the thylakoid membranes of chloroplasts. Step 3: Identify chloroplasts as the only organelles that contain both chlorophyll and the complete enzyme machinery for photosynthesis. Step 4: Recognise that centrosomes are involved in organising spindle fibres during cell division, not in light capture. Step 5: Note that the tonoplast is the membrane of the vacuole, nematoblasts are stinging cells in some animals, and mitochondria are responsible for respiration, not photosynthesis. Verification / Alternative check: If you think about the overall energy flow in plants, chloroplasts perform photosynthesis to make food, while mitochondria perform respiration to break down that food for usable energy. This division of labour is emphasised in all standard biology textbooks. Diagrams of plant cells clearly label chloroplasts as the green organelles responsible for photosynthesis, confirming that they play the central role in this process and matching the wording of the question precisely. Why Other Options Are Wrong: Centrosome helps in organising microtubules and spindle formation during cell division and is not involved in photosynthesis. Tonoplast is simply the membrane surrounding the vacuole, mainly related to storage and turgor, not light capture. Nematoblasts are specialised stinging cells found in cnidarians like jellyfish and hydra, not in plants. Mitochondria are sites of aerobic respiration and ATP production, using oxygen and food produced by photosynthesis, rather than capturing light themselves. None of these structures performs the primary photosynthetic role of chloroplasts. Common Pitfalls: Students sometimes confuse chloroplasts with mitochondria because both are double membrane bound organelles with their own DNA and internal membrane systems. Another pitfall is to overthink tonoplast or centrosome simply because these names sound technical. To avoid such errors, always associate chlorophyll, thylakoids and light capture with chloroplasts, and respiration and ATP production with mitochondria. This simple association helps you quickly identify the correct organelle for questions related to photosynthesis. Final Answer: The organelle that plays the most important part in photosynthesis is the chloroplast.

Question 7

The biogenetic law, often summarised as “ontogeny recapitulates phylogeny”, was originally proposed by which biologist?

Accepted Answer

Introduction / Context: The biogenetic law is a historical concept in evolutionary biology that attempted to link the development of an individual organism with the evolutionary history of its species. It is commonly summarised by the phrase “ontogeny recapitulates phylogeny”. Although modern biology recognises that this statement is an oversimplification, the idea remains important from a historical perspective. This question tests your knowledge of which biologist first formulated and popularised this law. Given Data / Assumptions: The term biogenetic law refers to a relationship between individual development (ontogeny) and evolutionary history (phylogeny). The famous phrase associated with it is “ontogeny recapitulates phylogeny”. Options list several key figures in biology and evolution: Wallace, Darwin, Haeckel, Lamarck and Mendel. We assume standard historical attributions used in evolutionary biology. Concept / Approach: Ernst von Haeckel, a German biologist of the nineteenth century, formally proposed the biogenetic law. He suggested that the embryonic development of an organism passes through stages that resemble the adult forms of its evolutionary ancestors. While modern embryology has shown that this is not literally true, Haeckel's idea stimulated significant research in comparative embryology. Darwin and Wallace jointly proposed the theory of natural selection, Lamarck is associated with inheritance of acquired characters, and Mendel is the father of genetics; none of them specifically proposed the biogenetic law. Step-by-Step Solution: Step 1: Link the phrase “ontogeny recapitulates phylogeny” with the name Haeckel, as often mentioned in textbooks. Step 2: Recall that Darwin and Wallace are best known for natural selection, not for detailed embryological laws. Step 3: Recognise that Lamarck preceded Darwin and proposed use and disuse theory and inheritance of acquired characters. Step 4: Remember that Mendel worked on pea plants and elucidated the laws of inheritance, becoming the father of genetics. Step 5: Conclude that Ernst von Haeckel is the correct match for the biogenetic law. Verification / Alternative check: Another check is to think about typical exam tables that pair scientists with their contributions. Haeckel is always mentioned with the biogenetic law and the statement that an organism's development reflects its evolutionary history. Darwin is listed with the book On the Origin of Species and natural selection, Lamarck with his theory of use and disuse, Wallace as co discoverer of natural selection, and Mendel with Mendelian laws. Since only Haeckel is consistently associated with the biogenetic law, this confirms your choice. Why Other Options Are Wrong: Alfred Russel Wallace independently arrived at the idea of natural selection but did not propose the biogenetic law. Charles Darwin made only cautious comments about embryology and never stated that ontogeny literally repeats phylogeny. Lamarck’s main idea centred on the inheritance of acquired traits, not on embryonic recapitulation. Gregor Mendel focused on genetic inheritance patterns in pea plants and did not formulate laws about developmental stages mirroring evolutionary history. Therefore, none of these alternatives fits the description given in the question. Common Pitfalls: A common mistake is to attribute almost every evolutionary idea to Darwin because of his central role in biology. Another pitfall is mixing up Haeckel with Lamarck or Wallace due to unfamiliarity with nineteenth century scientists. To avoid this, remember a simple association: Haeckel equals biogenetic law and ontogeny recapitulates phylogeny, Darwin and Wallace equal natural selection, Lamarck equals acquired characters and Mendel equals genetics. Having these key links clear in your mind makes such matching questions much easier. Final Answer: The biogenetic law was proposed by Ernst von Haeckel.

Question 8

In humans, which hormone is primarily responsible for rapidly accelerating the rate of heartbeat during situations of fear, stress or excitement?

Accepted Answer

Introduction / Context: The human body responds quickly to stress, fear and excitement through changes such as increased heart rate, faster breathing and heightened alertness. These changes are coordinated by the autonomic nervous system and specific hormones. This question asks you to identify the hormone that most directly and rapidly accelerates the heartbeat in such “fight or flight” situations. Given Data / Assumptions: The focus is on acceleration of heart rate, not slow long term changes in metabolism. The context is acute stress, fear or excitement, typical of the fight or flight response. Options include adrenaline, acetylcholine, thyroxine, pituitrin and insulin. We assume standard physiology of the autonomic nervous and endocrine systems. Concept / Approach: Adrenaline, also known as epinephrine, is secreted by the adrenal medulla in response to signals from the sympathetic nervous system. It prepares the body for sudden action by increasing heart rate, strengthening cardiac contractions, dilating airways and mobilising glucose. Acetylcholine is mainly associated with parasympathetic activity and can slow the heart. Thyroxine is a thyroid hormone that increases basal metabolic rate and can affect heart rate over longer periods, but it is not the main acute stress hormone. Pituitrin is an old term often used for posterior pituitary extract containing vasopressin and oxytocin, which do not primarily speed up heartbeat. Insulin regulates blood glucose levels, not heart rate. Step-by-Step Solution: Step 1: Identify the situation described as fear, stress or excitement, characteristic of the fight or flight response. Step 2: Recall that the adrenal medulla releases adrenaline during such situations. Step 3: Remember that adrenaline binds to receptors in the heart, increasing heart rate and the force of contraction. Step 4: Compare this with acetylcholine, which is associated with the parasympathetic system and can slow heart rate. Step 5: Recognise that thyroxine, pituitrin and insulin have other major functions and are not the primary acute accelerators of heartbeat. Verification / Alternative check: Think about common descriptions in textbooks: adrenaline is often called the emergency hormone or fight or flight hormone. Diagrams of stress response typically show the sympathetic nervous system stimulating the adrenal medulla to secrete adrenaline, which then causes tachycardia (increased pulse), raised blood pressure and increased blood flow to muscles. These characteristic effects confirm that adrenaline, not the other listed hormones, is primarily responsible for the rapid acceleration of heart rate under stress. Why Other Options Are Wrong: Acetylcholine acts at parasympathetic nerve endings, particularly the vagus nerve, and tends to slow down the heart, not speed it up. Thyroxine increases metabolic rate and can raise heart rate over time, but it is not the rapid emergency hormone released in acute stress. Pituitrin (vasopressin and oxytocin extract) mainly influences water balance and uterine contraction. Insulin works to lower blood glucose and does not primarily affect heart rate. Therefore, choosing any of these would not correctly answer the question about rapid heartbeat acceleration in stressful situations. Common Pitfalls: Students sometimes pick thyroxine because they recall that thyroid disorders can affect heart rate. However, the question emphasises immediate acceleration during fear or stress, which clearly points to the fight or flight response and adrenaline. Another pitfall is confusion between sympathetic and parasympathetic neurotransmitters; remember that acetylcholine generally slows the heart through the vagus nerve, whereas adrenaline speeds it up. Keeping sympathetic equals adrenaline and parasympathetic equals acetylcholine in mind helps avoid these mistakes. Final Answer: The hormone that primarily accelerates the rate of heartbeat during fear, stress or excitement is adrenaline (epinephrine).

Question 9

When food items are wrapped directly in old newspaper, they are most likely to become contaminated by which toxic metal present in printing inks?

Accepted Answer

Introduction / Context: In many places, street food or snacks are still wrapped in old newspapers despite repeated health warnings. Printing inks used in newspapers can contain various chemicals, including heavy metals. Over time, these substances can migrate from the ink onto oily or moist foods, creating a health risk. This question asks you to identify the main toxic metal of concern when food is wrapped directly in newspaper. Given Data / Assumptions: Food is wrapped directly in printed newspaper. Printing inks may contain heavy metals and other harmful chemicals. Options list metals: magnesium, aluminium, lead, copper and mercury. We focus on the metal commonly associated with ink toxicity and food contamination in this context. Concept / Approach: Lead is a toxic heavy metal historically used in various pigments and inks. Chronic exposure to lead can cause neurological damage, especially in children, along with anaemia and kidney problems. Although many countries now regulate or restrict lead in inks, old or low quality printing materials may still contain it. When hot, oily or moist food is wrapped in newspaper, lead and other chemicals from the ink can leach onto the food surface and then be ingested. Magnesium and aluminium are not typically highlighted as serious contaminants from newspaper ink in this context, and copper or mercury are less commonly associated with standard printing inks used for papers. Step-by-Step Solution: Step 1: Recognise that the health concern discussed in public advisories about wrapping food in newspapers mainly mentions heavy metal contamination. Step 2: Recall that lead is one of the most widely known toxic metals historically used in pigments and inks. Step 3: Consider that magnesium is an essential nutrient and not a typical ink contaminant causing such alarms. Step 4: Note that while aluminium and copper can be present in the environment, they are not the classic example linked to newspaper ink. Step 5: Conclude that lead is the specific toxic metal most likely to contaminate food wrapped directly in newspaper. Verification / Alternative check: You can verify this by recalling health warnings from food safety authorities, which often emphasise that newspapers are not safe for direct contact with food because ink may contain lead and other harmful substances. Lead poisoning is a major public health issue worldwide, and eliminating avoidable sources of exposure, including contaminated food packaging, is a key priority. Since the other listed metals do not appear as prominently in such warnings about newspaper wrapping, this supports lead as the correct answer. Why Other Options Are Wrong: Magnesium is a vital mineral nutrient and is not considered a toxic metal in small quantities; it is not the primary concern in printing inks. Aluminium can be present in cookware and cans but is not the classic contamination risk from newspaper wrapping. Copper is an essential trace element, and although excessive amounts can be harmful, it is not typically cited in this specific context. Mercury is highly toxic but is mainly associated with industrial pollution and certain thermometers or fluorescent lamps, rather than routine newspaper inks. Thus, none of these alternatives fits the standard explanation for food contamination from newspaper wrapping as directly as lead does. Common Pitfalls: Students may be tempted to choose mercury because it is widely recognised as a dangerous metal, even though it is not usually linked to printing ink in everyday newspapers. Others might pick aluminium due to ongoing debates about aluminium cookware, which again is a different issue. To avoid confusion, remember that lead has a long historical association with paints and inks and is the classic example of a toxic contaminant in situations like this. Linking newspaper ink contamination specifically with lead will help you answer similar public health questions accurately. Final Answer: Food wrapped directly in old newspaper is most likely to be contaminated by lead from the printing ink.

Question 10

In which of the following kinds of organisms is a dramatic phenomenon observed in which, after copulation, the female often kills and eats the male partner?

Accepted Answer

Introduction / Context: In the animal kingdom, mating behaviour can be extremely diverse. One striking and much discussed behaviour is sexual cannibalism, where one partner, usually the female, kills and sometimes eats the male after or even during copulation. This question asks you to identify the type of organism in which this phenomenon is classically and widely observed. Given Data / Assumptions: We are focusing on a phenomenon where the female kills the male after copulation. Options list different kinds of animals: dragonfly, honey bee, spider, pit viper and earthworm. We assume typical textbook and documentary examples used to illustrate sexual cannibalism. The question refers to a well known, not rare, example. Concept / Approach: Sexual cannibalism is most famously documented in certain spiders, such as the black widow and some orb weavers. In these species, the female may attack, kill and even eat the male during or after mating. This behaviour is thought to provide nutritional benefits to the female and sometimes to increase the chances of successful fertilisation. While other groups, like some mantises, also show sexual cannibalism, spiders are the classic and commonly cited example in basic biology courses. The other listed animals do not typically show this extreme post mating killing of the male in the same way. Step-by-Step Solution: Step 1: Recall well known examples of sexual cannibalism from biology textbooks and nature documentaries. Step 2: Identify spiders, particularly black widows and some garden spiders, as classic examples where the female may kill the male after mating. Step 3: Check dragonflies, which have complex mating behaviours but do not usually involve the female killing the male. Step 4: Remember that in honey bees, the male drone may die after mating due to loss of reproductive organs, but the queen does not actively kill and eat him. Step 5: Recognise that pit vipers and earthworms do not show this type of post mating cannibalistic behaviour as a standard pattern. Verification / Alternative check: To verify, think about how sexual cannibalism is introduced in ecology and behaviour chapters. The first examples almost always include female spiders and preying mantises. Among the options provided, only spiders match this conventional illustration. Honey bees do have dramatic mating deaths for males, but caused by physical damage rather than deliberate killing by the female and there is no cannibalism. Dragonflies, pit vipers and earthworms are not associated with this specific behaviour in standard teaching material, which confirms spiders as the correct answer. Why Other Options Are Wrong: Dragonflies show elaborate courtship and mating flights, but females do not routinely kill and eat males after copulation. Honey bee drones die after mating because their endophallus is torn away, not because the queen kills them, and there is no feeding on the male. Pit vipers are solitary reptiles whose mating behaviour does not include regular sexual cannibalism by females. Earthworms are hermaphroditic animals that exchange sperm and separate again; they do not kill each other after mating. Thus, these options do not fit the description of female driven post mating killing and cannibalism. Common Pitfalls: A common mistake is to focus on the fact that honey bee drones die after mating and assume that this means the queen kills them, which is not accurate. Another pitfall is to forget that the question emphasises both killing and, typically, feeding on the male, which is characteristic of sexual cannibalism. To answer correctly, always associate classic sexual cannibalism examples with spiders, especially the black widow, whenever such questions appear in exams. Final Answer: The phenomenon where the female often kills the male after copulation is most famously observed in spiders.

Question 11

Which of the following is not an endocrine gland, that is, it does not primarily secrete hormones directly into the bloodstream?

Accepted Answer

Introduction / Context: Endocrine glands are specialised organs that secrete hormones directly into the bloodstream, where these chemical messengers travel to target tissues and regulate many body functions. Distinguishing between endocrine and non endocrine organs is a basic skill in human physiology. This question asks you to identify which listed organ is not primarily an endocrine gland. Given Data / Assumptions: We are comparing organs on the basis of whether they function as endocrine glands. Options include spleen, pituitary, thyroid, adrenal and pancreas. Endocrine glands secrete hormones directly into blood without ducts. We assume standard human anatomy and physiology terminology. Concept / Approach: The pituitary gland, thyroid gland and adrenal glands are classic endocrine glands. The pituitary is often termed the master gland because it secretes many hormones that regulate other endocrine organs. The thyroid secretes thyroxine and other hormones that control metabolism. Adrenal glands produce hormones like cortisol and adrenaline. The pancreas has both endocrine parts (islets of Langerhans) that secrete insulin and glucagon and exocrine parts that secrete digestive enzymes. In contrast, the spleen is primarily a lymphoid organ involved in filtering blood, recycling old red blood cells and participating in immune responses; it is not an endocrine gland. Step-by-Step Solution: Step 1: Identify which organs in the list are clearly known endocrine glands. Step 2: Recognise the pituitary, thyroid and adrenal glands as standard endocrine glands found in all textbooks. Step 3: Recall that the pancreas, although mixed in function, has a well known endocrine role via insulin and glucagon secretion. Step 4: Consider the spleen, which is involved mainly in blood filtration and immune functions, not hormone secretion. Step 5: Conclude that spleen is the only option that is not an endocrine gland. Verification / Alternative check: You can verify your answer by recalling the list of major endocrine glands usually taught: pituitary, thyroid, parathyroids, adrenals, pancreas (endocrine part), gonads and sometimes thymus and pineal. The spleen does not appear in this list. Anatomy diagrams show the spleen in the left upper abdomen as a blood reservoir and immune organ, not connected with hormone pathways. These observations confirm that the spleen is not classified as an endocrine gland, while the others have recognised endocrine functions. Why Other Options Are Wrong: The pituitary gland secretes hormones such as growth hormone, TSH, ACTH and others, clearly marking it as endocrine. The thyroid gland releases thyroxine and triiodothyronine, controlling metabolic rate. The adrenal glands secrete cortisol, aldosterone and adrenaline, which are critical for stress response and salt balance. The pancreas has endocrine islets that produce insulin and glucagon, directly regulating blood glucose. Therefore, all these organs function as endocrine glands, unlike the spleen, which primarily filters blood and supports immunity rather than hormone secretion. Common Pitfalls: Students may be confused by the pancreas because it also has exocrine functions, leading them to doubt its endocrine status. However, its hormone secreting islets of Langerhans make it an important endocrine organ. Another pitfall is to assume the spleen might secrete some substances into blood and therefore call it endocrine, but its main recognised roles are immune and haematological, not hormonal. To avoid mistakes, keep a clear mental list of classic endocrine glands and remember that the spleen does not belong to that group. Final Answer: Among the options given, the organ that is not an endocrine gland is the spleen.

Question 12

In the DNA double helix, what type of chemical bonds hold together the sugar–phosphate units along each strand, forming the “sides” of the DNA ladder?

Accepted Answer

Introduction / Context: The structure of DNA is often compared to a twisted ladder, where the sugar–phosphate backbones form the two sides and paired nitrogenous bases form the rungs. Understanding which bonds hold together different parts of this structure is crucial for grasping DNA stability, replication and function. This question focuses specifically on the bonds that connect the sugar and phosphate groups along each strand, forming the sides of the ladder. Given Data / Assumptions: We are considering the sugar–phosphate backbone of DNA, not the base pairs between strands. The options include polar covalent bonds, ionic bonds, metallic bonds, general covalent bonds and hydrogen bonds. We assume standard knowledge of DNA's double helix structure. The question refers to bonds holding the sides of the ladder together along each strand. Concept / Approach: Within each DNA strand, nucleotides are linked by strong covalent bonds called phosphodiester bonds. These bonds connect the phosphate group of one nucleotide to the sugar of the next, forming the sugar–phosphate backbone that makes up each side of the ladder. Covalent bonds are strong and stable, ensuring that the sequence of nucleotides does not easily break. In contrast, hydrogen bonds hold the complementary base pairs together between the two strands, forming the rungs, not the sides. Ionic and metallic bonds are not involved in the primary structure of DNA, and while phosphodiester bonds are polar covalent in nature, the broad correct category is covalent bonds. Step-by-Step Solution: Step 1: Visualise the DNA double helix as a twisted ladder with two backbones and base pair rungs. Step 2: Recall that each backbone is made of alternating deoxyribose sugars and phosphate groups. Step 3: Remember that these sugar and phosphate units are joined by phosphodiester bonds, a type of covalent bond formed during DNA synthesis. Step 4: Distinguish these strong covalent bonds from the weaker hydrogen bonds that connect adenine with thymine and cytosine with guanine across the two strands. Step 5: Recognise that ionic and metallic bonds are not relevant to the primary structure of DNA, making covalent bonds the correct choice. Verification / Alternative check: If you examine any standard diagram of the DNA molecule, the legend or explanation usually labels the sugar–phosphate backbone as being linked by covalent phosphodiester bonds. At the same time, it labels the base pairs in the centre as being joined by hydrogen bonds, typically two between A and T and three between G and C. The fact that textbooks consistently describe the backbone bonds as covalent, not hydrogen or ionic, confirms that covalent bonds are responsible for holding the sides of the DNA ladder together along each strand. Why Other Options Are Wrong: Polar covalent bonds is a partially correct description because phosphodiester bonds do have polar character, but this option is too vague compared with the clearer term covalent bonds used in most exam keys. Ionic bonds involve the attraction between oppositely charged ions and do not form the sugar–phosphate backbone in DNA. Metallic bonds occur in metals, where electrons are delocalised across a lattice, and are not found in DNA. Hydrogen bonds do play a crucial role, but they hold the two strands together at the base pairs, not the sugar–phosphate sides of each strand, which is what this question is asking about. Common Pitfalls: A very common mistake is to confuse the bonds that hold the strands together with the bonds that hold the backbone together. Students often remember that DNA has hydrogen bonds and may choose hydrogen bonds for any question about DNA stability. To avoid this, always separate the ideas clearly: covalent phosphodiester bonds link nucleotides along a strand (sides of the ladder), while hydrogen bonds link complementary bases between strands (rungs of the ladder). Keeping this distinction in mind will help you correctly answer many structural questions about DNA. Final Answer: The sugar–phosphate sides of the DNA ladder are held together along each strand by strong covalent bonds (phosphodiester bonds).

Question 13

In diet planning, which of the following statements best describes the concept of “nutrient density” when choosing foods?

Accepted Answer

Introduction / Context: Modern nutrition guidelines emphasise not just how many calories you eat, but also how many useful nutrients you get from those calories. The term “nutrient density” is used to compare foods based on how rich they are in vitamins, minerals, fibre and other beneficial substances relative to their energy content. This question asks you to identify which statement most accurately captures the meaning of nutrient density in practical diet planning. Given Data / Assumptions: We are choosing among several statements about healthy eating. The key concept is nutrient density, not just variety or fat reduction. One option emphasises nutrients per kilocalorie, while others mention variety or general healthy habits. We assume standard definitions used by nutritionists and dietary guidelines. Concept / Approach: A food is called nutrient dense if it provides a large amount of vitamins, minerals, fibre and other beneficial components relative to the number of calories it contains. For example, vegetables, fruits, whole grains and lean proteins are usually more nutrient dense than sugary drinks or fried snacks. The defining idea is “more nutrition for fewer calories”. Variety in the diet, while important, is a separate principle and does not by itself define nutrient density. Similarly, focusing only on reducing fat or eating from all food groups does not fully capture the concept if nutrient content per calorie is ignored. Step-by-Step Solution: Step 1: Identify the option that explicitly mentions nutrients relative to calories. Step 2: Notice that option b states that you should consume foods that have the most nutrition for their kilocalories. Step 3: Recognise that this matches the core definition of nutrient density used in nutrition science. Step 4: Understand that option a (eat a variety of foods) is a general healthy eating guideline but does not define nutrient density. Step 5: See that option c (choose different foods within a group) and option e (only reduce fat) also describe other aspects of diet, not nutrient density itself, so option d, which says all the above, cannot be correct. Verification / Alternative check: You can verify this definition by looking at common textbook examples. A glass of orange juice and a glass of sugary soft drink may have similar calories, but orange juice provides vitamin C and other nutrients, so it is more nutrient dense. Leafy greens give many vitamins and minerals for very few calories, making them highly nutrient dense. In contrast, sweets with lots of sugar and fat but few vitamins are energy dense but nutrient poor. These examples all use the idea of nutrients per calorie, confirming that option b best describes nutrient density. Why Other Options Are Wrong: Option a encourages variety across food groups, which is good advice but does not express the nutrient per calorie concept. Option c encourages variety within a food group, also beneficial but still not a definition of nutrient density. Option d (all of the above) cannot be correct because options a and c are only indirectly related. Option e focuses solely on reducing fat, which might reduce calories but says nothing about improving vitamin or mineral intake; some low fat foods may still be low in essential nutrients. Therefore, only option b clearly and directly captures the key idea behind nutrient density. Common Pitfalls: A common mistake is to equate “healthy eating” in general with nutrient density and choose “all of the above” whenever several statements sound positive. Another pitfall is focusing only on calories and fat without considering vitamins, minerals and fibre. To avoid this, remember that nutrient density always involves a ratio: nutrients divided by calories. The higher this ratio, the more nutrient dense the food is. This simple mental formula helps you identify the correct definition even when options are worded in different ways. Final Answer: Nutrient density means choosing foods that provide the most vitamins, minerals and beneficial nutrients for the fewest kilocalories.

Question 14

Regarding the valves of the human heart, which of the following statements is correct?

Accepted Answer

Introduction / Context: The human heart contains four main valves that ensure one way flow of blood through its chambers and into the great arteries. Understanding the correct positions and functions of these valves is crucial for learning cardiovascular anatomy and physiology. This question asks you to pick the one correct statement from several descriptions about heart valves and their roles. Given Data / Assumptions: Options mention aortic, pulmonary, atrioventricular, tricuspid and mitral valves, as well as chordae tendineae and semilunar valves. We are asked to identify which statement accurately describes normal human heart anatomy and function. We assume a standard four chambered heart with two atria, two ventricles and four principal valves. Statements involve both location and role of the valves. Concept / Approach: The two atrioventricular (AV) valves are the tricuspid valve on the right side and the mitral (bicuspid) valve on the left side. They lie between atria and ventricles. These valves are attached to papillary muscles inside the ventricles by fibrous cords called chordae tendineae. During ventricular contraction, the chordae tendineae prevent the valve leaflets from inverting back into the atria and thereby reduce regurgitation of blood. The aortic and pulmonary valves are semilunar valves that control blood flow out of the heart into the aorta and pulmonary artery, not into the heart chambers. The tricuspid valve is between the right atrium and right ventricle, and the mitral valve is between the left atrium and left ventricle, not on the right side. Step-by-Step Solution: Step 1: Evaluate option a, which says aortic and pulmonary valves control blood flow into the heart. This is incorrect; they control flow out of the heart from the ventricles into arteries. Step 2: Examine option b, which states that AV valves are supported by chordae tendineae to prevent regurgitation into the atria during ventricular contraction. This is a standard textbook description and is correct. Step 3: Check option c, which incorrectly places the tricuspid valve between the left atrium and left ventricle; in reality, it is between the right atrium and right ventricle. Step 4: Check option d, which incorrectly claims the mitral valve separates the right atrium from the right ventricle; actually, the mitral valve lies between the left atrium and left ventricle. Step 5: Evaluate option e, which incorrectly positions semilunar valves between atria and ventricles, whereas they are at the exits of the ventricles into the aorta and pulmonary artery. Verification / Alternative check: A simple verification method is to recall a labelled diagram of the heart. You will see the tricuspid valve on the right side and the mitral valve on the left side, both with chordae tendineae attaching their leaflets to papillary muscles. When the ventricles contract, these cords keep the valves from flipping backward. The semilunar valves sit at the base of the aorta and pulmonary artery and open only when ventricular pressure exceeds arterial pressure. Since only option b correctly captures this anatomical and functional detail, it must be the correct statement. Why Other Options Are Wrong: Option a reverses the direction of control; aortic and pulmonary valves regulate blood leaving, not entering, the heart. Option c misplaces the tricuspid valve; it belongs to the right side, not the left. Option d misplaces the mitral valve; it is on the left side, not between the right atrium and ventricle. Option e incorrectly locates semilunar valves between atria and ventricles, whereas atrioventricular valves occupy that position. Each of these errors conflicts with established heart anatomy. Common Pitfalls: Students often mix up right and left side valves or confuse the names tricuspid and bicuspid (mitral). Another frequent confusion is between atrioventricular valves and semilunar valves. To avoid these mistakes, remember a simple association: tricuspid right, bicuspid left, both with chordae tendineae; semilunar valves guard the exits into the aorta and pulmonary artery. Keeping this mental map in mind will help you quickly identify correct statements about heart valves in exams. Final Answer: The correct statement about heart valves is that the atrioventricular (AV) valves are supported by chordae tendineae, which help prevent regurgitation of blood into the atria during ventricular contraction.

Question 15

Which of the following is considered an abnormal constituent of urine in a healthy human being?

Accepted Answer

Introduction / Context: The kidneys filter blood and form urine to remove metabolic wastes while conserving useful substances. Normal urine composition includes water, urea and certain other waste products, but some substances should be present only in very small amounts or not at all. Detecting abnormal constituents in urine is an important diagnostic tool. This question asks you to identify which listed substance is considered abnormal when found in significant quantity in the urine of a healthy person. Given Data / Assumptions: We are considering urine composition of a healthy individual. Options include creatinine, uric acid, glucose, urea and sodium ions. We assume normal kidney function without disease. We focus on substances whose presence at noticeable levels signals a problem. Concept / Approach: Normal urine contains water, urea, creatinine, uric acid, various ions (such as sodium, potassium and chloride) and small amounts of other dissolved substances. Glucose, however, is normally reabsorbed completely in the proximal tubule and should not appear in significant amounts in the urine. The presence of glucose in urine, known as glycosuria, often indicates uncontrolled diabetes mellitus or other conditions affecting renal glucose handling. Therefore, glucose is considered an abnormal constituent when found in measurable quantities in routine urine tests for healthy individuals. Step-by-Step Solution: Step 1: Recall the main nitrogenous wastes excreted in urine: urea, creatinine and uric acid. Step 2: Recognise that these wastes are normal final products of protein and nucleic acid metabolism. Step 3: Note that urine also normally contains various electrolytes such as sodium ions, depending on diet and body needs. Step 4: Remember that glucose is almost completely reabsorbed in the kidney tubules and does not usually appear in urine in healthy individuals. Step 5: Conclude that glucose, if present in measurable amounts, is an abnormal constituent indicating a possible disorder like diabetes. Verification / Alternative check: Urine analysis reports for healthy people list urea as the major nitrogenous waste and mention creatinine and uric acid as normal findings. Clinical textbooks emphasize that the renal threshold for glucose is such that blood glucose must rise above a certain level before any glucose spills into urine. Therefore, routine detection of glucose in urine is considered abnormal and prompts further testing for diabetes. By contrast, the presence of urea, creatinine, uric acid and sodium ions is expected, although their levels may vary. Why Other Options Are Wrong: Creatinine is a normal waste product formed from creatine in muscles and is regularly excreted by the kidneys. Uric acid is produced from the breakdown of purine nucleotides and also appears normally in urine. Urea is the main nitrogenous waste formed from ammonia in the liver and is the largest solid component of urine. Sodium ions are part of the body's normal electrolyte balance and are excreted in varying amounts depending on intake and kidney function. None of these are considered abnormal constituents when present within normal ranges. Common Pitfalls: Some students may think that any nitrogenous waste product is abnormal simply because it is a waste. However, normal urine is supposed to contain these waste materials. Others might focus on ions like sodium due to concerns about high salt intake, forgetting that sodium excretion is a normal function. The key to this question is recognising that glucose is a valuable energy source that the kidneys normally conserve. Its appearance in urine in significant amounts is a red flag rather than a usual finding. Final Answer: Among the given options, glucose is considered an abnormal constituent of urine in a healthy human being.

Question 16

Descriptions a–f refer to different types of RNA. Which classification correctly matches each description with tRNA, mRNA or rRNA? a) contains an anticodon b) specifies the amino acid sequence of a protein c) contains exons d) has amino acids covale…

Accepted Answer

Introduction / Context: Cells use three main types of RNA to express genetic information: messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA). Each type has distinct structural features and specific roles in protein synthesis. This question gives a series of descriptions labelled a to f and asks you to correctly assign them to tRNA, mRNA or rRNA. It tests your detailed understanding of RNA structure and function in the central dogma of molecular biology. Given Data / Assumptions: Description a: contains an anticodon. Description b: specifies the amino acid sequence for a protein. Description c: contains exons. Description d: has amino acids covalently attached. Description e: is a component of ribosomes. Description f: is the most abundant form of RNA. We must match each description with tRNA, mRNA or rRNA and select the option that does so correctly. Concept / Approach: tRNA molecules carry amino acids to the ribosome and possess an anticodon loop that base pairs with codons on mRNA. Each tRNA can be charged with a specific amino acid, forming a covalent bond between the amino acid and the tRNA's 3' end. Therefore, descriptions a (contains an anticodon) and d (has amino acids covalently attached) clearly refer to tRNA. mRNA is the transcript copy of a gene that carries the coded information for the amino acid sequence of a protein; after processing in eukaryotes, it contains only exons. Thus, b (specifies amino acid sequence) and c (contains exons) describe mRNA. rRNA is a structural and functional component of ribosomes and is the most abundant RNA in cells, matching e and f. Step-by-Step Solution: Step 1: For description a (contains an anticodon), recall that only tRNA has an anticodon loop to recognise mRNA codons. Step 2: For description d (has amino acids covalently attached), remember that aminoacyl tRNA synthetases attach specific amino acids to tRNA, so this also points to tRNA. Step 3: For description b (specifies the amino acid sequence of a protein), recognise that mRNA carries the codon sequence that determines the order of amino acids, so this describes mRNA. Step 4: For description c (contains exons), understand that in eukaryotes, processed mRNA contains exons after introns are removed; tRNA and rRNA are not described in terms of exons in basic exam questions. Step 5: For description e (is a component of ribosomes) and f (is the most abundant RNA), recall that rRNA molecules form the core of ribosomes and are the most abundant type of RNA in cells, so both refer to rRNA. Step 6: Combine these matches: a and d – tRNA; b and c – mRNA; e and f – rRNA. This corresponds exactly to option a. Verification / Alternative check: To double check, think of some standard facts: tRNA is often illustrated with a cloverleaf structure showing an anticodon and an amino acid attachment site. mRNA is depicted as a linear strand with codons that determine protein sequence, and in eukaryotes it is processed to remove introns, leaving exons. rRNA is drawn as part of the large and small ribosomal subunits and is repeatedly described as the most abundant RNA. Since these textbook descriptions line up perfectly with the mapping in option a, we can be confident that option a is correct. Why Other Options Are Wrong: Option b misassigns anticodons or exons to the wrong RNA types and therefore cannot be correct. Option c incorrectly links anticodons with rRNA and exons with tRNA, which contradicts standard definitions. Option d mixes up roles of tRNA, mRNA and rRNA in a way that does not match actual cell biology. Option e states that none of the classifications is correct, which is clearly false because we have found a consistent and accurate mapping in option a. Thus, options b, c, d and e all fail to match descriptions a–f correctly. Common Pitfalls: Students sometimes confuse mRNA and tRNA because both are involved in translation at the ribosome. A typical error is to forget that anticodons belong to tRNA, not mRNA, and that exons are a feature of processed mRNA, not of tRNA or rRNA. Another pitfall is to forget which RNA type is most abundant; many assume mRNA, but rRNA actually dominates by mass. To avoid these mistakes, remember three key associations: tRNA equals anticodon plus amino acid, mRNA equals codons plus exons and rRNA equals ribosome plus most abundant. These simple links help you quickly sort such descriptions correctly. Final Answer: The correct classification is a and d – tRNA; b and c – mRNA; e and f – rRNA, which is given in option a.

Question 17

In a healthy adult human at rest, what is considered the normal arterial blood pressure (systolic/diastolic) measured in millimetres of mercury (mmHg)?

Accepted Answer

Introduction / Context: Blood pressure is a key vital sign that reflects the force of blood against the walls of arteries as the heart pumps. It is usually expressed as systolic pressure over diastolic pressure, measured in millimetres of mercury (mmHg). Knowing the typical normal value for a healthy adult at rest is important both for general health awareness and exam preparation. This question asks you to identify that standard normal value. Given Data / Assumptions: We are considering an average healthy adult at rest, not a child or an athlete. Blood pressure is given as systolic/diastolic in mmHg. Options include common approximate values such as 120/80 mmHg and others. We assume standard clinical guidelines used in introductory physiology. Concept / Approach: Systolic pressure is the higher value, measured when the heart's ventricles contract and eject blood into the arteries. Diastolic pressure is the lower value, recorded when the ventricles relax and the heart refills. For a typical healthy adult at rest, the normal arterial blood pressure is often quoted as around 120/80 mmHg. Although individual values can vary slightly, and modern guidelines may refine what counts as optimal, 120/80 remains the classic textbook example and is widely used in general knowledge questions. Step-by-Step Solution: Step 1: Recall the standard textbook value for normal blood pressure: approximately 120/80 mmHg. Step 2: Recognise that the first number represents systolic pressure and should be higher than the diastolic pressure. Step 3: Examine option a (80/120), which reverses the order and places a lower value first, making it incorrect. Step 4: Check other options like 80/110 and 110/90, which may occur in some individuals but are not the standard reference values. Step 5: Confirm that 120/80 mmHg, with a higher systolic and lower diastolic number, matches the widely accepted normal reference. Verification / Alternative check: You can verify by recalling how blood pressure readings are written in medical reports and health articles. Whenever normal blood pressure is mentioned, 120/80 mmHg is given as the typical example. Health education posters and school textbooks also highlight this number when teaching about hypertension and hypotension. While there is a range of normal values, and guidelines may discuss ideal lower targets, for exam purposes 120/80 mmHg is the expected answer and the only option that fits the classic pattern. Why Other Options Are Wrong: Option a (80/120 mmHg) reverses systolic and diastolic values, which is physiologically incorrect because systolic pressure should be higher. Option c (80/110 mmHg) and option d (110/90 mmHg) represent possible readings but are not the standard normal adult reference. Option e (100/60 mmHg) may be seen in some healthy individuals, especially athletes, but again is not the typical textbook value quoted as normal for the general adult population. Therefore, these alternatives do not match the established normal reference of 120/80 mmHg. Common Pitfalls: A common mistake is to confuse the order of systolic and diastolic pressures or to assume that any combination of two plausible numbers could be called normal. Another pitfall is to overthink small variations and forget that exams usually expect the standard textbook value. To avoid these errors, remember the mnemonic that the higher number (about 120) is systolic and comes first, while the lower number (about 80) is diastolic and comes second. This simple pattern reinforces 120/80 mmHg as the classic normal blood pressure reading. Final Answer: The normal arterial blood pressure in a healthy adult human at rest is approximately 120/80 mmHg.

Question 18

Which observation most clearly proves that a cell is eukaryotic rather than prokaryotic?

Accepted Answer

Introduction / Context: Cells are broadly classified into prokaryotic and eukaryotic types. Prokaryotic cells, such as bacteria, are simpler and lack a membrane bound nucleus, while eukaryotic cells, such as plant and animal cells, have a true nucleus and various membrane bound organelles. This question asks you to identify which specific observation would most clearly demonstrate that a cell is eukaryotic rather than prokaryotic. Given Data / Assumptions: We must differentiate eukaryotic cells from prokaryotic cells based on observable features. Options mention DNA, ribosomes, cell membrane, a nucleus and a circular chromosome. We assume standard textbook definitions of prokaryotes and eukaryotes. The question asks for an observation that proves the cell is eukaryotic. Concept / Approach: Both prokaryotic and eukaryotic cells contain DNA, ribosomes and a cell membrane, so these features cannot be used alone to definitively distinguish them. The key distinguishing feature is that eukaryotic cells have their genetic material enclosed in a membrane bound nucleus, whereas prokaryotes have DNA located in a nucleoid region without a surrounding membrane. Therefore, the observation that DNA is enclosed inside a distinct nucleus proves the cell is eukaryotic. Having a single circular chromosome in the cytoplasm is characteristic of many prokaryotes, not eukaryotes. Step-by-Step Solution: Step 1: Evaluate option a: containing DNA. Since all known cells contain DNA, this does not distinguish eukaryotes from prokaryotes. Step 2: Evaluate option b: containing ribosomes. Prokaryotes also have ribosomes (although they are smaller), so this is not unique to eukaryotes. Step 3: Evaluate option c: having a cell membrane. Again, both cell types possess a plasma membrane, so this feature is not diagnostic. Step 4: Evaluate option d: DNA enclosed inside a distinct membrane bound nucleus. This is the defining feature of eukaryotic cells and is absent in prokaryotes. Step 5: Evaluate option e: single circular chromosome in the cytoplasm. This actually indicates a typical prokaryotic organisation, not a eukaryotic one. Verification / Alternative check: You can verify by recalling the word roots: prokaryote literally means “before nucleus” and eukaryote means “true nucleus”. Diagrams of bacterial cells show DNA as a loop in the nucleoid region with no surrounding nuclear envelope. In contrast, diagrams of animal or plant cells clearly depict a nucleus enclosed by a nuclear membrane. Therefore, observing DNA inside a well defined membrane bound nucleus is sufficient proof that the cell is eukaryotic. Why Other Options Are Wrong: Option a is wrong because prokaryotic cells also contain DNA. Option b is wrong because ribosomes are universal in cells, though they differ in size between prokaryotes and eukaryotes. Option c is wrong because the presence of a cell membrane is a basic feature of all cells, not just eukaryotes. Option e describes a typical prokaryotic arrangement of genetic material (single circular chromosome in the cytoplasm), which actually suggests the cell is not eukaryotic. Thus, only option d clearly and uniquely indicates a eukaryotic cell. Common Pitfalls: Students sometimes pick features that all cells share, such as DNA or ribosomes, mistakenly assuming they are unique to eukaryotes. Another pitfall is to think that any complex looking structure implies a eukaryote without focusing on the nucleus. To avoid these errors, always remember that the hallmark of eukaryotic cells is the presence of a “true” nucleus with a nuclear envelope. Whenever a question asks you to prove a cell is eukaryotic, look for that specific feature. Final Answer: The observation that proves a cell is eukaryotic is that its DNA is enclosed inside a distinct membrane bound nucleus.

Question 19

Organisms that obtain their food by feeding specifically on the faeces (excreta) of other animals are known by which term?

Accepted Answer

Introduction / Context: Animals and microorganisms obtain food through a wide range of feeding strategies. Some species have evolved to feed on unusual materials that other organisms discard. One such strategy is consuming faeces or excreta of other animals. This question asks you to recall the specific term used in biology for organisms that feed on the excreta of other organisms as an important part of their diet. Given Data / Assumptions: The food source is faeces or excreta of other animals. We need a precise term, not just the general category of being a heterotroph. Options include autotrophs, heterotrophs, coprophagous organisms, saprotrophs and omnivores. We assume standard ecological terminology. Concept / Approach: Autotrophs are organisms that synthesise their own food from inorganic substances, usually using light or chemical energy. Heterotrophs obtain food from other organisms or organic material in general, which includes many feeding behaviours. Saprotrophs feed on dead and decaying organic matter, such as fallen leaves or carcasses, by external digestion. Omnivores eat both plant and animal matter. Organisms that specifically feed on faeces are called coprophagous (or coprophages). Dung beetles, some rodents and certain insects are classic examples of coprophagous organisms in ecology. Step-by-Step Solution: Step 1: Recognise that the question focuses on excreta or faeces as the primary food source. Step 2: Recall that the prefix copro refers to dung or faeces, and phagous refers to eating, giving coprophagous for dung eating organisms. Step 3: Note that autotrophs do not rely on excreta; they produce their own food. Step 4: Remember that while all coprophagous organisms are heterotrophs, the term heterotroph is too broad and not specific enough for this behaviour. Step 5: Recognise that saprotrophs and omnivores may consume various organic materials, but the technical term for faeces feeding is coprophagous. Verification / Alternative check: To verify, think about dung beetles rolling and burying animal droppings; these are always described in ecology texts as coprophagous insects. Similarly, some rodents such as rabbits practice coprophagy by re ingesting faecal pellets to extract more nutrients. In each of these examples, the term coprophagous is used rather than heterotroph or saprotroph, confirming that it is the correct and specific term for this feeding behaviour. Why Other Options Are Wrong: Autotrophs obtain energy from light or chemical reactions and build their own organic molecules, so they do not feed on excreta. Heterotrophs is a broad term for any organism that relies on external organic sources for food; it includes predators, herbivores, scavengers and coprophages, but does not specifically describe faeces feeding. Saprotrophs typically feed on dead and decaying matter, not on fresh faeces, which still contains undigested nutrients. Omnivores consume both plant and animal tissues but are not defined by eating excreta. These terms therefore do not accurately capture the specialised behaviour described in the question. Common Pitfalls: A common mistake is to choose heterotrophs or saprotrophs because they sound like general terms for non self feeding organisms. However, exam questions often look for the most specific term that fits the description. Another pitfall is not recognising the meaning of the prefix copro. Learning common biological prefixes and suffixes (such as auto, hetero, sapro and copro) can greatly help you decode unfamiliar terms and answer such questions correctly without rote memorisation. Final Answer: Organisms that feed on the excreta of other organisms are called coprophagous organisms.

Question 20

Organisms that synthesise their own organic food from simple inorganic substances (such as carbon dioxide and water) are known by which term?

Accepted Answer

Introduction / Context: Living organisms can be broadly divided into those that produce their own food and those that must obtain food from other sources. This fundamental distinction lies at the heart of ecology and energy flow in ecosystems. The question asks for the correct term used to describe organisms that can synthesise their own organic food from simple inorganic raw materials using an external energy source such as sunlight or chemical reactions. Given Data / Assumptions: The organisms in question can make their own food from inorganic substances. Typical examples include green plants and certain bacteria. Options include autotrophs, heterotrophs, auxotrophs, saprotrophs and parasites. We assume standard ecological and nutritional definitions. Concept / Approach: Autotrophs are organisms that can synthesise organic compounds from inorganic substances. Photoautotrophs, such as green plants, use light energy to drive photosynthesis, while chemoautotrophs, such as some bacteria, use energy from chemical reactions. In contrast, heterotrophs cannot make their own food and must consume organic material produced by other organisms. Auxotrophs are mutant organisms that require a specific additional nutrient that the wild type does not need. Saprotrophs feed on dead and decaying organic matter, and parasites live on or in a host, deriving nutrients from it. Only autotrophs match the description of synthesising their own food from inorganic sources. Step-by-Step Solution: Step 1: Focus on the phrase “synthesise their own food from inorganic substances”. Step 2: Recall that auto means self and troph means feeding, so autotroph literally means self feeding. Step 3: Recognise that green plants, algae and some bacteria are classic autotrophs producing sugars from carbon dioxide and water. Step 4: Distinguish this from heterotrophs, which must obtain ready made organic food from external sources. Step 5: Note that auxotrophs, saprotrophs and parasites are all specific types of heterotrophs, not organisms that create food from purely inorganic materials. Verification / Alternative check: Check familiar examples: a green plant using sunlight to produce glucose from carbon dioxide and water is always described as an autotroph. A lion eating other animals is a heterotroph, not an autotroph. A mushroom decomposing dead wood is a saprotroph, feeding on pre existing organic matter. A tapeworm living in a host intestine is a parasite. Textbooks and ecological pyramids always place autotrophs at the base as producers, reinforcing that this is the correct term for organisms that synthesise their own food from inorganic raw materials. Why Other Options Are Wrong: Heterotrophs cannot synthesise all their food from inorganic substances and instead rely on consuming organic materials produced by other organisms. Auxotrophs are genetically altered organisms that require additional specific nutrients and are still heterotrophic. Saprotrophs obtain food by secreting enzymes on dead and decaying matter and absorbing the digested nutrients, not by making organic molecules from inorganic carbon dioxide. Parasites feed on living hosts and depend on host derived nutrients. None of these categories fit the description of independent food synthesis from inorganic sources as directly as autotrophs do. Common Pitfalls: A common mistake is to mix up autotrophs with heterotrophs because both ends in trophs and sound similar. Another pitfall is to think of saprotrophs as self sufficient simply because they can digest dead matter externally. To avoid confusion, remember that autotrophs build organic molecules from inorganic ones, while all other trophic types rely on pre formed organic substances. Associating autotrophs with producers at the base of the food chain can help you quickly recall the correct term in exam questions. Final Answer: Organisms that synthesise their own food from inorganic substances are called autotrophs.

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