Photosynthesis in autotrophic organisms helps to meet which of the following basic requirements? I. Carbon source II. Water III. Energy

Introduction / Context:

Autotrophic organisms such as green plants are able to synthesise their own food using inorganic raw materials and sunlight. Photosynthesis is the key process that allows them to fix carbon dioxide into organic molecules and store energy in chemical form. To answer questions about what photosynthesis fulfills, students must distinguish between raw materials consumed and outputs produced by the process. This question lists carbon, water, and energy and asks which of these requirements are fulfilled for autotrophs through photosynthesis.

Given Data / Assumptions:

• Autotrophic organisms carry out photosynthesis using carbon dioxide and water in the presence of light and chlorophyll.
• The options refer to three items: carbon source, water, and energy.
• We assume the standard simplified equation of photosynthesis: 6 CO2 + 6 H2O with light and chlorophyll gives C6H12O6 + 6 O2.
• We also assume that water is primarily an input taken from soil rather than a requirement fulfilled as an output.

Concept / Approach:

Photosynthesis allows plants to fix inorganic carbon from atmospheric carbon dioxide into organic compounds such as glucose, which provides both a carbon skeleton for building biomolecules and a stored form of chemical energy. Thus, photosynthesis fulfills the requirement of a carbon source and an energy source for the plant. Water, on the other hand, is a reactant drawn from the soil and is used up in the process rather than produced for the plant as a new supply. While some water is formed in biochemical reactions, the basic requirement of water for the plant is met primarily by absorption through roots, not by photosynthesis. Therefore, the best description is that photosynthesis fulfills the needs for carbon (I) and energy (III) for autotrophic organisms.

Step-by-Step Solution:

Step 1: Identify carbon dioxide as the source of carbon for photosynthesis and note that plants convert it into sugars. Step 2: Recognise that glucose and other carbohydrates produced by photosynthesis store chemical energy derived from sunlight. Step 3: Understand that water is taken up from the soil and is a raw material consumed, not primarily a requirement that photosynthesis itself supplies. Step 4: Match the statements with these facts: carbon requirement is fulfilled (I), energy requirement is fulfilled (III), while water requirement is mainly met by root uptake rather than by the photosynthetic reaction. Step 5: Select I and III as the combination of requirements fulfilled by photosynthesis.

Verification / Alternative check:

Textbooks explain that photosynthesis is the process by which plants manufacture food and store energy. The carbohydrate produced provides both building material and energy for respiration. Many diagrams show carbon dioxide entering leaves as a raw material and carbohydrates leaving as outputs. Water is consistently shown coming from the soil into the roots and up the xylem. This presentation supports the view that photosynthesis secures a carbon source and energy, while water remains an external requirement obtained from the environment.

Why Other Options Are Wrong:

Option A, Only I, ignores the fact that energy stored in carbohydrates is also a key requirement satisfied by photosynthesis. Option B, Only III, omits the role of carbon fixation. Option D, All I, II and III, treats water as if photosynthesis supplies it, which is misleading because water is mostly an input for the process. Option E, Only II and III, incorrectly emphasises water while overlooking the carbon fixation role as a requirement for organic synthesis.

Common Pitfalls:

Students may misinterpret the phrase fulfills requirements and assume that because water appears in the chemical equation, photosynthesis somehow generates the water supply. Others may treat all reactants and products without distinguishing what the plant needs to obtain from the environment versus what it can produce. To avoid confusion, it is helpful to remember that photosynthesis turns carbon dioxide and water plus light into food and oxygen, and the key benefits for an autotroph are a carbon rich food source and stored chemical energy.

Final Answer:

Photosynthesis mainly fulfills the requirements of carbon source and energy (I and III) for autotrophic organisms.