Why do living organisms need nutrients in their food, and what is the main purpose these nutrients serve in the body?

Introduction / Context:
Nutrition is a core concept in biology that explains why organisms must eat and what happens to the food they consume. Nutrients are the useful chemical substances present in food that the body can absorb and utilise. This question asks for the main purpose that nutrients serve in living organisms, which connects directly to topics such as metabolism, growth, and maintenance of health.

Given Data / Assumptions:

• The question refers to all living organisms, including humans, animals, and plants.
• Nutrients include carbohydrates, proteins, fats, vitamins, minerals, and water.
• The options suggest different possible roles, such as breaking down food, recycling wastes, or supporting life processes.
• We assume standard school level understanding of nutrition and metabolism.

Concept / Approach:
Nutrients are required to supply energy, build and repair body tissues, and regulate chemical reactions in the body. Carbohydrates and fats provide energy, proteins help build new cells and repair damaged tissues, and vitamins and minerals act as regulators in metabolic pathways. Without nutrients, organisms could not grow, maintain their structures, or carry out processes such as respiration, circulation, or reproduction. Therefore, the main purpose of nutrients is not just to physically break down food or to recycle waste but to enable energy production and all vital life processes.

Step-by-Step Solution:
Step 1: Recall what happens after food is eaten: it is digested into simpler molecules like glucose, amino acids, and fatty acids. Step 2: These smaller molecules are absorbed into the bloodstream and transported to cells, where they are used as nutrients. Step 3: Nutrients provide energy through processes like cellular respiration, allowing muscles to work and organs to function. Step 4: Nutrients also supply raw materials for building and repairing body tissues, such as muscles, skin, and organs. Step 5: Vitamins and minerals, as part of the nutrient group, help regulate enzyme activity, hormone function, and immunity, supporting all vital life processes. Step 6: From the options, the statement that best summarises these roles is that nutrients are needed to obtain energy, grow, repair tissues, and carry out vital life processes.

Verification / Alternative check:
Health science and biology textbooks describe three main functions of nutrients: providing energy, building body structures, and regulating body processes. For example, carbohydrates and fats are described as energy yielding nutrients, proteins as both energy sources and body building nutrients, and vitamins and minerals as regulators. None of these functions is limited to mere mechanical breakdown of food or recycling waste. When you match these textbook descriptions with the options, the comprehensive option about energy, growth, repair, and vital processes clearly fits best.

Why Other Options Are Wrong:
Only to break down food into smaller pieces in the mouth is wrong because chewing is mainly mechanical digestion and does not describe why nutrients are needed; digestion is a preliminary step, not the purpose of nutrients. Only to recycle waste materials is incorrect, because nutrients primarily provide new materials and energy rather than simply reusing wastes. Purely to change the taste and colour of food is clearly wrong; taste and colour may influence food choice but are not the biological purpose of nutrients.

Common Pitfalls:
Students sometimes confuse the process of digestion with the purpose of nutrition, thinking that breaking down food is itself the goal. Another mistake is to focus on a single role of nutrients, such as energy, and forget growth and repair. To avoid such errors, remember that nutrients are essential for three broad reasons: they provide energy, build and maintain body structures, and regulate biochemical reactions. Seeing nutrition in this complete way helps you pick the most comprehensive and accurate option in multiple choice questions.

Final Answer:
The correct choice is To obtain energy, grow, repair tissues and carry out vital life processes, because these are the main purposes that nutrients serve in living organisms.