Photosynthesis: Food Making Process in Plants | Science Class 7 (Old NCERT) PDF Download

Leaves: The Chefs of Plants

Leaves are like the kitchen factories of plants. They make food for the plants through a process called photosynthesis. Just like chefs cook food, leaves create food for the entire plant.

Leaves: Chef for Plants

What Do Leaves Need to Make Food?

• To make food, leaves need water and minerals. These are found in the soil. The roots of the plant act like straws, sucking up the water and minerals from the soil and sending them up to the leaves.
• Sunlight is also very important for photosynthesis.

Once the leaves have all the ingredients they need, they start the process of photosynthesis to make food for the plant!

Process of making food in Green Plants: Photosynthesis

Leaves possess chlorophyll, a green pigment that aids in capturing sunlight's energy and gives color to the leaves. This energy is utilized to produce food by combining carbon dioxide and water. As this food synthesis process relies on sunlight, it is known as photosynthesis.

Definition of Photosynthesis: The process of making food by green plants in the presence of sunlight and chlorophyll is known as photosynthesis.

Photosynthesis is the combination of two words- Photo + Synthesis. ‘Photo’ means light and ‘Synthesis’ means to make.

Green plants make their food through PhotosynthesisOur earth is the only unique planet where photosynthesis takes place. In the absence of photosynthesis, life would not be possible on earth.

Hence, for taking place of photosynthesis carbon dioxide, water, and sunlight must be present in the green leaves in addition to the presence of chlorophyll. Leaves have several tiny pores on their lower surface. These are called stomata, through which leaves absorb carbon dioxide from the air. 

Let's understand the Plant's Nose:

What is Stomata?

• Plants have special tiny openings on their leaves called stomata. These stomata act like little doors that let the plant take in something very important for its survival: carbon dioxide from the air. Just like we breathe in oxygen, plants breathe in carbon dioxide. 
• These stomata are like the plant's nose, and they are surrounded by special cells called guard cells that protect and control the opening and closing of the stomata. 

Stomata

So, the stomata are like little windows that help the plant get the carbon dioxide it needs to survive.

• After absorbing CO₂, water is transported to the leaves through hair-like pipelines from the roots. These pipelines are present throughout the plant, i.e., from roots to branches and leaves.
  

Let's understand how Roots send water to leaves?

Think of plants like a big network of pipes that carry water and minerals to all parts of the plant, including the leaves. These pipes are called vessels, and they run through the roots, stems, branches, and leaves just like pipes run through a building. 

They create a pathway for the water and minerals to travel and reach the leaves. So, it's like the plant has its own plumbing system to deliver all the important nutrients to every part of its body.

• These pipelines are known as Xylem. Xylem is a type of tissues. 

Xylem: Works as pipeline for plants

• Chlorophyll, a green pigment, is found in green leaves. Chlorophyll absorbs sunlight and gives energy. Chlorophyll absorbs sunlight, carbon dioxide and water and convert them to carbohydrate and oxygen. Carbohydrate is used as food and oxygen is emitted out to the atmosphere. 
• This whole process of making food by plants is called photosynthesis.

Complete process of Photosynthesis

• The reaction that takes place in the process of photosynthesis can be written as:
  

• Carbohydrate which is produced in the process of photosynthesis is ultimately converted into starch and stored into leaves. From leaves, it is transported to the parts of plants. Starch is a type of carbohydrate. The oxygen so produced is released into the atmosphere through the stomata.
• Besides leaves, photosynthesis takes place in other green parts of the plant also, such as in green stems. Chlorophyll is necessary for photosynthesis; hence photosynthesis takes place only in green plants.
• The leaves of plants that grow in desert areas are modified in spine-like structure or scales to reduce the loss of water in the course of transpiration. In such plants, photosynthesis takes place in green stems.
• Photosynthesis helps to maintain a balance between oxygen and carbon dioxide in the atmosphere as it absorbs carbon dioxide and release oxygen.
• Sunlight is necessary for photosynthesis. Thus, the sun is the ultimate source of energy for all living organism.

Photosynthesis in Algae 

Photosynthesis in Algae

• Green patches in ponds or near stagnant water are easily noticeable. These green patches are made up of algae. 
•  Algae are simple, self-feeding organisms. They typically thrive in shallow, damp areas, like around tube wells and taps. One must be careful, as it can be slippery. Algae appear green due to the presence of chlorophyll and make their own food through photosynthesis using sunlight. 

Synthesis of Plant Food Other Than Carbohydrates

• Plants need proteins and fats in addition to carbohydrates for their growth and development. Proteins are made up of substances that contain nitrogen.
• Although nitrogen is abundant in the atmosphere, plants cannot directly take it in. Instead, they obtain nitrogen from the soil. 
• Certain bacteria in the soil, called rhizobium, play a crucial role in converting atmospheric nitrogen into forms that plants can use. These bacteria release the converted nitrogen into the soil, where plants can absorb it along with water and other minerals through their roots.
• To ensure that plants receive enough nitrogen along with other nutrients, farmers sometimes add nitrogenous fertilizers to the soil. Once plants have all the necessary nutrients, they can synthesize proteins and fats, which are essential for their growth and development.