Energy In Food

In this article, you will learn about how we obtain energy from food according to the Singapore Primary 6 Science Syllabus. You will understand that living things need energy to carry out life processes and they obtain energy from the food they eat.  We will also examine the conditions required for photosynthesis and the products formed during the process of photosynthesis.

Energy In Food

Energy is the ability to do work.  Energy is important for all living things as it is needed to carry out life processes such as growth, reproduction and movement.

The Sun is the main source of energy for living things. However, not all living things are able to use light energy directly. Plants are examples of living things that are able to use light energy via photosynthesis to obtain energy that they need to carry out their life processes. The other organisms which cannot make use of light energy to make their own food will consume other organisms to obtain energy for their survival. Thus, the energy in plants is being passed down to other organisms when the organisms eat the plants.

Plants are also known as food producers as they are able to make their own food.  The organisms that feed on other organisms are known as food consumers. 

How do plants make their own food?

Plants make their own food during the process of photosynthesis. Photosynthesis is the process whereby plants use sunlight, water and carbon dioxide to produce food (sugar) and oxygen.

\( \text{carbon dioxide + water} \quad\xrightarrow[\qquad\text{chlorophyll}\qquad]{\qquad\text{light energy}\qquad} \quad\text{food (sugar) + oxygen} \\ \)

 

Carbon dioxide is taken in by the plants via gaseous exchange through the tiny openings (stomata) that are mainly found on the underside of the leaves.

Water is absorbed through the roots and transported up the stem via the water-carrying tubes (xylem tubes) to the leaves.

Chlorophyll is found in the chloroplasts of leaf cells. They help to trap / absorb light energy that is required for photosynthesis.  As chlorophyll is green, this gives the leaves its green colour.  Plants with coloured leaves have hidden chlorophyll under their coloured pigments.

Products Of Photosynthesis

Plants convert carbon dioxide and water into food (sugar) and oxygen in the presence of light energy.  Food (sugar) that is being produced provides the energy for the plants to carry out their life processes such as growth and reproduction. The food produced is also being transported through the food-carrying tubes to the other parts of the plant. Excess food made by the plants is stored as starch in the various parts of the plants such as fruits and underground stems.  When the plants need more energy, starch from the storage parts will be converted back into sugar for the plant to use.

Oxygen is a byproduct of photosynthesis that is being released through the tiny openings into the atmosphere. This helps to replenish the oxygen in the atmosphere for other living things.

Conclusion

In this article, we learnt that living things need energy to carry out life processes. We also understood that plants are able to make their own food while other organisms depend on other organisms for food. Plants undergo photosynthesis to make food for themselves to obtain the energy they need. We also recognised the materials and conditions required for photosynthesis to occur and what the products of photosynthesis are.

Test Your Concepts

Answer the following questions based on the concepts that we have covered in this article. If you are unclear, you may want to revisit the relevant section to revise the concepts.

Question 1:

Timothy conducted an experiment on a green plant. He covered both the upper and lower surfaces of two leaves with cardboard. A week later, he observed that leaves covered by the cardboard withered and died.

Explain why the leaves covered with cardboard withered and died.

Solution:

As cardboard does not allow light to pass through, the leaves covered by the cardboard were not able to receive light energy (sunlight) to make food. Thus, they withered and died.

Explanation:

Sunlight is needed for photosynthesis to take place.

Question 2:

Some water plants were placed under bright sunlight for 5 hours. It was noted that the water plants produced gas bubbles and the gas was collected in the test tube as shown in the diagram below.

1. What was the gas produced by the water plants?

Solution:

oxygen

Explanation:

The water plants were being exposed to bright sunlight and were able to photosynthesise and produce oxygen.

2. What would happen to the amount of gas produced by the water plant if the set-up were moved under a shady tree?

Solution:

The amount of gas produced would be less.

Explanation:

There would be less sunlight under a shady tree. Thus, the water plants would obtain less light energy for photosynthesis and produce less oxygen.

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