Why We Need Food
State one reason why living things need food.
To get energy for daily activities.
Name the green substance in leaves that helps in photosynthesis.
Chlorophyll
Animals cannot make their own food. How do they get energy?
By eating plants or other animals.
What is the main source of energy for all living things on Earth?
The Sun
Which organelle in plant cells carries out photosynthesis?
Chloroplast
Which two things in our body does food help to repair and build?
Cells and tissues
Write the word equation for photosynthesis.
Carbon dioxide + Water → Glucose + Oxygen
State one example of a herbivore and one example of a carnivore.
Herbivore – cow, Carnivore – lion
State one way plants depend on the Sun.
Photosynthesis
A rabbit eats grass. Which type of consumer is the rabbit?
Primary consumer
Food gives us energy in the form of ______ energy.
Chemical energy
State two raw materials plants need for photosynthesis.
Carbon dioxide and water
Describe how energy flows from plants to humans using an example.
Sunlight → wheat plant → bread → human eats bread and gains energy
How do humans indirectly depend on the Sun for energy?
By eating plants or animals that got energy from plants.
During a very cloudy week, a farmer noticed his crops were weak and growing slowly. Explain why this happened.
With less sunlight, plants cannot photosynthesize effectively, so less glucose is produced, leading to weak growth.
Explain why a child needs more food energy than an elderly person.
A child is still growing and needs energy for growth and activities.
Why do plants release oxygen during photosynthesis?
Because oxygen is a by-product of photosynthesis.
Compare how a lion and a cow obtain their energy.
Lion eats other animals for energy, while a cow eats plants for energy.
If the Sun stopped shining, what would happen to plants? State two consequence.
They cannot make food and would die.
A child eats rice and eggplant every day. Explain how the Sun’s energy is involved in giving the child energy to run and play.
The Sun’s energy is captured by plants through photosynthesis to make glucose. Rice and vegetables store this chemical energy, which the child eats and converts into energy for movement.
Predict (three predictions) what might happen to a person’s body if they eat too little food for a long time.
They may feel weak, fall sick easily, and not grow properly.
A plant is placed in a sealed glass jar with plenty of sunlight. After 3 days, the plant begins to wilt and eventually dies.
The plant used up the carbon dioxide in the sealed jar. Without carbon dioxide, photosynthesis could not continue, and the plant could not make food. Oxygen build-up may also have affected survival.
In every food chain, not all the energy from food is passed on. Give two reasons why energy is lost between each level.
Energy is lost as heat during respiration, and as waste materials (e.g., undigested food, waste removal, urination).
Explain the chain reaction that would happen if there was no Sun at all.
Plants die → herbivores die → carnivores die → life on Earth cannot survive.
Compare the energy flow in these two food chains:
Sun → Grass → Rabbit → Eagle
Sun → Algae → Small Fish → Large Fish → Human
Food chain 1, provides more energy because it is shorter. In chain 2, more energy is lost at each extra level before reaching humans.