What photosynthesis is ?
The process by which green plants prepare their own food with the help of water, CO2 and sunlight is known as photosynthesis. Green plants are known as autotrophs or producers as they can prepare their own food. This mode of nutrition is known as autotrophic nutrition. CO2 is absorbed through stomata and roots help in the absorption of water. Oxygen which is produced through the process of photosynthesis is used by all living organisms for breathing. Plants store extra food in the form of starch.Photosynthesis is the only natural process that supplies pure oxygen.
It is one of the important topic for class 7 biology chapters ICSC.
Photosynthesis reaction
Sunlight
Carbon dioxide + Water ➡ Glucose + Oxygen
Water + Water
Structure of Stomata
Tiny pores present in the upper and lower surface of the leaves that help in the exchange of gases are known as stomata. Stomata also help in the process of transpiration.
Each stroma consists of two guard cells that are bean shaped that contain chloroplast. The outer walls of guard cells are thinner than the outer walls.The guard cells swell when they are full of water, they bulge outwards and the stomata open. They lose turgidity as they lose water and stomata close. Stomata generally open during the day and close during the night.
What are the materials required for photosynthesis?
Photosynthesis raw materials include -
* CO2 - Atmosphere is the main source of CO2 for plants. The atmosphere consists of 0.03% to 0.04% of carbon dioxide.
* Light - The principal source of light on the earth is sun.Plants can't perform photosynthesis without light. They convert the light energy of the sun into the chemical energy of food.
* Water - Water is absorbed by the roots from the soil which is then carried to different parts of the plant by xylem vessels.
* Chlorophyll - Chlorophyll helps in absorbing energy from the sun. It imparts green colour to the leaves.
Why are leaves considered as most suitable organs to carry out the process of photosynthesis?
Leaves are considered as most suitable organs for photosynthesis as they consist of chlorophyll. They are arranged at right angle to the source of light so that help them to absorb maximum light to carry on the process of photosynthesis. They have stomata to absorb CO2 and give out oxygen.
What are chloroplasts?
Chloroplasts are the organelles that provide chlorophyll to the leaves. Their diameter ranges between 4-6 micrometer. Chloroplasts are concentrated mostly in the upper layer of the leaves. They consist of a double membrane.The inner membrane of chloroplasts is folded in the form of disc shaped sacs known as thylakoids. Thylakoids consist of chlorophyll and some other pigments. They are arranged in stacks known as granum.
Photosynthesis equation -
Sunlight
6CO2 + 12H2O ➡ C6H12O6 + 6O2 + 6H2O
Water
Photosynthesis process
Firstly, plants absorb water with the help of root hair and CO2 with the help of stomata.Chlorophyll on absorbing sunlight gets excited and splits the water molecule to release oxygen. The above process occurs in the thylakoids that are present in the chloroplasts and is a light dependent process or reaction.
Secondly, CO2 gets split into sugar. This process doesn't depend upon light and is a light independent reaction. It takes place in stroma. Complex sugars are formed by the combination of simple sugars.
What are the factors that affect photosynthesis?
The factors that affect photosynthesis are -
1. Light - The rate of photosynthesis increases as the intensity of light increases. Very high intensity of light may retard the process of photosynthesis by bleaching chlorophyll.
2. Temperature - The most suitable temperature for the process of photosynthesis ranges between 20°C to 40°C.The rate of photosynthesis increases with the increase in temperature. The process of photosynthesis stops above 40°C.
3. Carbon dioxide - An increase in carbon dioxide concentration increases the rate of carbon dioxide.
4. Chlorophyll - Chlorophyll helps in absorbing sunlight and helps in the process of photosynthesis.
5.Water - Plants don't use all the water by the roots in the process of photosynthesis. The percentage of water used in this process is even less than 1% .
What is the significance of photosynthesis?
1. It provides food to all the organisms. It takes place in green plants which are the primary producers in the food chain.
2. It helps in providing oxygen to all the organisms.
3. It plays an important role in the growth and development of the plants.
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