Which one of the following life processes cannot be performed by animals, even though they carry out other essential activities such as respiration, reproduction, and digestion?

Introduction / Context:
Animals and plants are both living organisms, but they differ in how they obtain energy and carry out basic life processes. General biology questions often compare these processes to highlight the fundamental differences between the two kingdoms. This question asks you to identify which specific process animals are not capable of performing, even though they can carry out many other vital activities such as respiration, reproduction, digestion, and excretion.

Given Data / Assumptions:

• The focus is on common life processes: respiration, photosynthesis, reproduction, digestion, and excretion.
• The organism group in question is animals.
• We assume a school level understanding of how animals and plants obtain energy and nutrients.
• We assume that only one of the listed processes is impossible for animals to perform under normal biological conditions.

Concept / Approach:
Animals are heterotrophic organisms. They cannot manufacture their own food from inorganic substances using sunlight. Instead, they must consume organic material produced by plants or other animals. In contrast, green plants and some microorganisms are autotrophic and can perform photosynthesis, the process of using light energy to convert carbon dioxide and water into glucose and oxygen. Animals do perform respiration to release energy from food, digestion to break down complex food, excretion to remove wastes, and reproduction to produce offspring. Therefore, the key is to recognise that photosynthesis is a plant and certain microbe specific process, not carried out by animals.

Step-by-Step Solution:
Step 1: List the processes that animals definitely perform: respiration, digestion, excretion, and reproduction. Step 2: Recall that respiration occurs in animal cells to release energy from glucose using oxygen. Step 3: Recall that digestion in animals breaks down complex food into simpler, absorbable molecules. Step 4: Remember that animals excrete metabolic waste and also reproduce sexually or asexually depending on the species. Step 5: Identify photosynthesis as the process where chlorophyll containing organisms manufacture food using light energy, which animals do not do because their cells lack chloroplasts and chlorophyll. Step 6: Conclude that photosynthesis is the only process in the list that animals cannot perform.

Verification / Alternative check:
A quick verification comes from thinking about cell structure. Animal cells have mitochondria for respiration but do not have chloroplasts. Chloroplasts containing chlorophyll are essential for photosynthesis. Since animals lack chloroplasts, they cannot convert light energy directly into chemical energy. Instead, they rely on consuming food produced by plants and other organisms. This structural difference between plant cells and animal cells confirms that photosynthesis is not an animal process, whereas respiration, digestion, excretion, and reproduction clearly occur in animals.

Why Other Options Are Wrong:
Option A: Respiration definitely occurs in animals as they break down glucose to release usable energy in the form of ATP. Option C: Reproduction is a basic life process of animals, allowing the continuation of species through sexual or asexual means. Option D: Digestion is essential for animals to break down complex food into simpler nutrients for absorption. Option E: Excretion is the removal of metabolic waste products from the animal body and is a vital process, not absent in animals.

Common Pitfalls:
Some learners confuse respiration with breathing and may think that only lungs are involved, but respiration actually occurs in all living cells. Another mistake is to assume that any green coloured animal or symbiotic association might be performing photosynthesis. Even if some animals associate with photosynthetic organisms, the animal cells themselves do not carry out photosynthesis. Remember that photosynthesis requires chloroplasts, which are not present in animal cells. This distinction helps to correctly identify photosynthesis as the process animals cannot perform.

Final Answer:
Among the processes listed, animals cannot perform photosynthesis, even though they do carry out respiration, digestion, excretion, and reproduction.