PHOTOSYNTHESIS-TEXT

PHOTOSYNTHESIS

BIOLOGY

CBSE-VII

Leaves are the food factories of plants. The synthesis of food in plants occurs in leaves. Therefore, all the raw materials must reach there.

Water and minerals present in the soil are absorbed by the roots and transported to the Paheli wants to know why our body cannot make food from carbon dioxide, water and minerals like plants do.

CELLS:
You have seen that buildings are made of bricks. Similarly, the bodies of living organisms are made of tiny units called cells. Cells can be seen

only under the microscope. Some organisms are made of only one cell. The cell is enclosed by a thin outer boundary, called the cell membrane.

Most cells have a distinct, centrally located spherical structure called the nucleus (Fig. 1.1).

The nucleus is surrounded by a jelly-like substance called cytoplasm. leaves. Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves. These pores are surrounded by ‘guard cells’. Such pores are called stomata.

Water and minerals are transported to the leaves by the vessels which run like pipes throughout the root, the stem, the branches and the leaves. They form a continuous path or passage for the nutrients to reach the leaf.

You will learn about transport of materials in plantsThe leaves have a green pigment called chlorophyll. It helps leaves to capture the energy of the sunlight. This energy is used to synthesise (prepare) food from carbon dioxide and water.

Since the synthesis of food occurs in the presence of sunlight, it is called

photosynthesis (Photo: light; synthesis : to combine). So we find that chlorophyll, sunlight, carbon dioxide and water are necessary to carry out the process of photosynthesis. It is a unique process on the earth.

The solar energy is captured by the leaves and stored in the plant in the form of food. Thus, sun is the ultimate source of energy for all living organisms.

Can you imagine life on earth in the absence of photosynthesis!

In the absence of photosynthesis there would not be any food. The survival of almost all living organisms directly or indirectly depends upon the food made by the plants.

Besides, oxygen which is essential for the survival.Besides leaves, photosynthesis also takes place in other green parts of the Plant- in green stems and green branches. The desert plants have scale- or spine-like leaves to reduce loss of water by transpiration. 

These plants have green stems which carry out photosynthesis of all living organisms is produced during photosynthesis. In the absence of photosynthesis, life would be impossible on the earth.

During photosynthesis, chlorophyll containing cells of leaves in the presence of sunlight, use carbon dioxide and water to synthesise

carbohydrates. 

The process can be represented as an equation: during the process oxygen is released. The carbohydrates ultimately get converted into starch. 

The presence of starch in leaves indicates the occurrence of photosynthesis. The starch is also a carbohydrate. Synthesis of plant food other than carbohydrates.

You have just learnt that plants synthesise carbohydrates through the process of photosynthesis. The carbohydrates are made of carbon, hydrogen and oxygen. 

These are used to synthesise other components of food such as proteins and fats. But proteins are nitrogenous substances which contain nitrogen. From where do the plants obtain nitrogen?

Recall that nitrogen is present in abundance in gaseous form in the air.

However, plants cannot absorb nitrogen in this form. Soil has certain bacteria that convert gaseous nitrogen into a usable form and release it into the soil.

These soluble forms are absorbed by the plants along with water. Also, you might have seen farmers adding fertilisers rich in nitrogen to the soil. 

In this way the plants fulfil their requirements of nitrogen along with the other constituents. Plants can then synthesise components of food other than carbohydrates such as proteins and fats.

THANKYOU,
NANDITHA AKUNURI