What this chapter is about
Plants are living things, and like all living things, they carry out certain activities to stay alive. These activities are called life processes. This chapter introduces how plants make their own food, take in water and minerals, transport materials inside their body, and get rid of waste.
You already know that animals eat food to get energy. But plants cannot move around to find food. So how do they survive? Plants have a special ability to make their own food using sunlight. This process is one of the most important things happening on Earth because it produces oxygen and food for almost all other living things.
After studying this chapter, you should be able to explain how plants make food, describe how water moves from roots to leaves, and understand how plants respire and excrete. You will also learn why leaves are green and what happens inside a leaf during the day.
Key ideas
- Photosynthesis is the process by which green plants make their own food using sunlight, carbon dioxide from air, and water from soil.
- Photosynthesis takes place mainly in leaves because they contain a green pigment called chlorophyll, found in tiny structures called chloroplasts.
- During photosynthesis, plants release oxygen as a by-product, which is essential for most living things to breathe.
- Plants absorb water and dissolved minerals from the soil through their roots, specifically through tiny root hairs.
- Water and minerals move upward through tube-like structures called xylem, while food made in leaves moves to other parts through phloem.
- Plants also respire like animals — they take in oxygen and release carbon dioxide to get energy from food.
- Plants get rid of waste products through their leaves, bark, and by storing some waste in old leaves that fall off. This is called excretion.
- The process of water loss from leaves through tiny pores called stomata is known as transpiration.
Formulas and facts to remember
- Photosynthesis equation in words: Carbon dioxide + Water (in presence of sunlight and chlorophyll) → Glucose + Oxygen
- Chlorophyll is the green pigment that traps sunlight energy.
- Stomata are small openings on the lower surface of leaves that allow gases to enter and exit.
- Xylem carries water upward from roots to leaves.
- Phloem carries food from leaves to other plant parts.
- Respiration in plants happens all the time (day and night), while photosynthesis happens only in sunlight.
- Transpiration creates a pulling force that helps water rise in tall plants and trees.
Worked examples
Example 1: Why do leaves look green?
Question: Meera noticed that most plant leaves are green. Why is this so?
Solution:
- Leaves contain chloroplasts, which have a pigment called chlorophyll.
- Chlorophyll absorbs red and blue light from sunlight for photosynthesis.
- It reflects green light, which reaches our eyes.
- That is why leaves appear green to us.
Example 2: Direction of transport in plants
Question: Ravi watered a plant in the morning. Trace the path of water in the plant.
Solution:
- Water enters the plant through root hairs in the roots.
- It then moves into the xylem tubes.
- Xylem carries water upward through the stem.
- Finally, water reaches the leaves and other parts of the plant.
- Some water is used in photosynthesis, and some is lost through stomata as transpiration.
Example 3: Day and night processes
Question: Does a plant carry out photosynthesis at night? What about respiration?
Solution:
- Photosynthesis needs sunlight. At night, there is no sunlight.
- So, photosynthesis does not happen at night.
- Respiration provides energy to the plant for its activities.
- Respiration happens all the time — both day and night.
Common mistakes
- Thinking plants only respire at night → Plants respire continuously, day and night; photosynthesis happens only during the day.
- Believing plants get food from soil → Plants make their own food through photosynthesis; they only absorb water and minerals from soil.
- Confusing xylem and phloem → Xylem carries water upward; phloem carries food in all directions.
- Thinking oxygen is produced during respiration → Oxygen is released during photosynthesis; respiration uses oxygen and releases carbon dioxide.
- Assuming stomata are only for releasing water → Stomata also allow carbon dioxide to enter and oxygen to leave during photosynthesis.
Quick revision
- Photosynthesis = making food using sunlight, carbon dioxide, water, and chlorophyll.
- Chlorophyll in leaves gives them their green colour and traps light energy.
- Xylem moves water up; phloem moves food around.
- Transpiration is water loss from leaves through stomata.
- Respiration in plants happens all the time; photosynthesis needs light.
- Plants excrete waste through leaves, bark, and by shedding old leaves.