Chapter 10 — Life Processes in Plants

Chapter 10 is titled 'Life Processes in Plants.' It covers how plants grow, how they make food through photosynthesis, how they transport water and food through xylem and phloem, and how they release energy through respiration.

Photosynthesis is the process by which plants prepare food in the presence of sunlight and chlorophyll. The raw materials are carbon dioxide (from air) and water. The products are glucose and oxygen. The word equation is: Carbon dioxide + Water → (Sunlight/Chlorophyll) → Glucose + Oxygen.

Leaves are called the 'food factories' of plants because they are the primary site for photosynthesis. Their broad, flat shape and green chlorophyll pigment help them capture sunlight efficiently to produce food (glucose) for the plant.

Chlorophyll is a green pigment present in leaves. It helps in capturing sunlight efficiently and is essential for the preparation of starch (food) in plants. Without chlorophyll, photosynthesis cannot take place.

First, boil the leaf in water for five minutes, then dip it in alcohol placed in a beaker of boiling water until the leaf becomes colourless (decolourised). Then place a few drops of diluted iodine solution on the leaf. A blue-black colour change indicates the presence of starch.

Carbon dioxide from the air is essential for plants to prepare starch. When a leaf is placed inside a bottle containing caustic soda (sodium hydroxide), which absorbs carbon dioxide, that part of the leaf cannot produce starch even in the presence of sunlight, water, and chlorophyll.

Oxygen is released during photosynthesis. It can be detected by collecting the gas produced by a water plant in an inverted test tube placed in sunlight — when a lit matchstick is inserted into the collected gas, it produces an intense flame, confirming the gas is rich in oxygen.

Stomata are tiny pores present on the surface of leaves. They help in the exchange of oxygen and carbon dioxide during photosynthesis and respiration.

Xylem is a set of thin tube-like structures that transport water and dissolved minerals from the roots upward to all parts of the plant. Phloem is another set of thin tube-like structures that transport food (prepared in the leaves by photosynthesis) to all other parts of the plant, where it may be used or stored.

Yes, all parts of a plant — green and non-green — carry out respiration. During respiration, glucose is broken down in the presence of oxygen, releasing carbon dioxide, water, and energy. The word equation is: Glucose + Oxygen → Carbon dioxide + Water + Energy. The energy released is used for the plant's growth and development.

Plants require both sunlight and water for growth. An experiment with three pots shows that the plant in direct sunlight with adequate water grows best; the plant in direct sunlight without water may die; and the plant in the dark with water shows the least growth.

Some plant leaves appear red, violet, or brown because they contain more of those coloured pigments than the green-coloured chlorophyll, which hides the green colour. Some of these pigments also help in photosynthesis, and an iodine test can confirm that starch is still produced in such leaves.

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