Photosynthesis,Std-10
➤ Photosynthesis
:- This word splits into two parts - photo + synthesize, photo means 'sunlight' and synthesize means - combine together.
:- Green plants make their food by this process.
:- It is a biochemical, endothermic process in which heat is utilized and carbon dioxide reduced to form carbohydrates.
:- Site of photosynthesis is chloroplast in leaves of the plant that is why the leaf is considered as a photosynthetic organ or kitchen room of the plants.
:- Chlorophyll plays a crucial role in this process ( because chlorophyll is a green pigment and absorbs sunlight ).
* Definition:- The process of making food by the plants with the help of Carbon dioxide( Co2 ) and Water( H2O )in the presence of sunlight and chlorophyll is called photosynthesis.
:- Solar energy gets converted into chemical energy.
*Requirements for photosynthesis are as follows - Carbon dioxide, water, and minerals.
:- Plants obtain Carbon dioxide from the atmosphere by the process of diffusion through tiny pores I.e stomata, which are present at the undersurface of leaves.
:- Plants obtain water and minerals from soil by roots ( through the process Osmosis).
* Reaction:-
* Significances of photosynthesis:-
:- It provides food for all.
:- It is essential for sustaining life and it is the ultimate source of Oxygen, Energy.
:- It helps in the growth and development of plants.
:- It is necessary for the synthesis of organic compounds from inorganic compounds.
:- It converts Carbon dioxide back to Oxygen.
* Phases of photosynthesis:-
:- There are mainly two phases in photosynthesis -
1. Light phase or Light reaction and
2. Dark phase or Dark reaction
1. Light Reaction
:- It is a photochemical phase of photosynthesis and light dependent reaction ( means it takes place in the presence of sunlight )
:- It occurs in the thylakoids of grana in the chloroplast.
Que. What happens during the light reaction?
Ans:- A couple of steps occur during light reaction.
Step - 1. Excitation of chlorophyll
:- The chlorophyll absorbs light energy in the form of photons.
:- The chlorophyll molecule gets excited and is converted to chemical energy.
Step - 2. Formation of ATP from ADP
:- In this step ATP synthesized from ADP and inorganic Phosphate.
:- ADP + Pi + energy ⟶ ATP
:- This ATP is used during dark reaction.
Note:- ADP - Adenosine diphosphate
ATP - Adenosine triphosphate and
Pi - Inorganic Phosphate.
Step - 3. Splitting of water
:- Photolysis of water takes place in this step.
:- H2O ⟶ 2H+ + O2 + 2e-
( The free oxygen is the O2 gas given off during photosynthesis. )
Step -4. NADP reduced to NADPH
:- The released hydrogen ion ( H+ ) reduce NADP into NADPH.
:- NADP + 2e- + H+( ion ) ⟶ NADPH
( NADPH - Nicotinamide Adenine Dinucleotide Phosphate. )
2. Dark reaction
:- It is light independent reaction I.e this reaction doesn't require light energy, but it doesn't mean that it occurs during dark only.
:- It occurs simultaneously with the light reaction.
:- it is biosynthetic phase of photosynthesis means the reduction of carbon dioxide takes place and form carbohydrate.
:- It occurs in the stroma of the chloroplast.
:- This reaction utilizes NADPH and ATP ( formed during the light reaction ) to form sugar i.e carbohydrate(C6H12O6 )
(Note:- More about the dark reaction you will study in Higher classes, it is till std - X only. )
* Factors affecting Photosynthesis
:- There is a number of factors which affect photosynthesis.
1. Light intensity
:- The rate of photosynthesis increases with an increase in the intensity of light.
(But, extremely high intensity of light do not increase the rate of photosynthesis )
2. CO2 concentration
:- The rate of photosynthesis increases with an increase in the CO2 concentration.
3. Temperature
:- The maximum suitable temperature when photosynthesis occurs best is 35°C after which the rate falls.
:- The process of photosynthesis stops above 40°C as the enzymes are destroyed.
:- Low temperature also inhibits enzymatic activities and the rate of photosynthesis is reduced.
4. Water
:- It acts as a limiting factor in photosynthesis.
:- This word splits into two parts - photo + synthesize, photo means 'sunlight' and synthesize means - combine together.
:- Green plants make their food by this process.
:- It is a biochemical, endothermic process in which heat is utilized and carbon dioxide reduced to form carbohydrates.
:- Site of photosynthesis is chloroplast in leaves of the plant that is why the leaf is considered as a photosynthetic organ or kitchen room of the plants.
:- Chlorophyll plays a crucial role in this process ( because chlorophyll is a green pigment and absorbs sunlight ).
* Definition:- The process of making food by the plants with the help of Carbon dioxide( Co2 ) and Water( H2O )in the presence of sunlight and chlorophyll is called photosynthesis.
:- Solar energy gets converted into chemical energy.
*Requirements for photosynthesis are as follows - Carbon dioxide, water, and minerals.
:- Plants obtain Carbon dioxide from the atmosphere by the process of diffusion through tiny pores I.e stomata, which are present at the undersurface of leaves.
:- Plants obtain water and minerals from soil by roots ( through the process Osmosis).
* Significances of photosynthesis:-
:- It provides food for all.
:- It is essential for sustaining life and it is the ultimate source of Oxygen, Energy.
:- It helps in the growth and development of plants.
:- It is necessary for the synthesis of organic compounds from inorganic compounds.
:- It converts Carbon dioxide back to Oxygen.
* Phases of photosynthesis:-
:- There are mainly two phases in photosynthesis -
1. Light phase or Light reaction and
2. Dark phase or Dark reaction
1. Light Reaction
:- It is a photochemical phase of photosynthesis and light dependent reaction ( means it takes place in the presence of sunlight )
:- It occurs in the thylakoids of grana in the chloroplast.
Que. What happens during the light reaction?
Ans:- A couple of steps occur during light reaction.
Step - 1. Excitation of chlorophyll
:- The chlorophyll absorbs light energy in the form of photons.
:- The chlorophyll molecule gets excited and is converted to chemical energy.
Step - 2. Formation of ATP from ADP
:- In this step ATP synthesized from ADP and inorganic Phosphate.
:- ADP + Pi + energy ⟶ ATP
:- This ATP is used during dark reaction.
Note:- ADP - Adenosine diphosphate
ATP - Adenosine triphosphate and
Pi - Inorganic Phosphate.
Step - 3. Splitting of water
:- Photolysis of water takes place in this step.
:- H2O ⟶ 2H+ + O2 + 2e-
Step -4. NADP reduced to NADPH
:- The released hydrogen ion ( H+ ) reduce NADP into NADPH.
:- NADP + 2e- + H+( ion ) ⟶ NADPH
( NADPH - Nicotinamide Adenine Dinucleotide Phosphate. )
2. Dark reaction
:- It is light independent reaction I.e this reaction doesn't require light energy, but it doesn't mean that it occurs during dark only.
:- It occurs simultaneously with the light reaction.
:- it is biosynthetic phase of photosynthesis means the reduction of carbon dioxide takes place and form carbohydrate.
:- It occurs in the stroma of the chloroplast.
:- This reaction utilizes NADPH and ATP ( formed during the light reaction ) to form sugar i.e carbohydrate(C6H12O6 )
(Note:- More about the dark reaction you will study in Higher classes, it is till std - X only. )
* Factors affecting Photosynthesis
:- There is a number of factors which affect photosynthesis.
1. Light intensity
:- The rate of photosynthesis increases with an increase in the intensity of light.
(But, extremely high intensity of light do not increase the rate of photosynthesis )
2. CO2 concentration
:- The rate of photosynthesis increases with an increase in the CO2 concentration.
3. Temperature
:- The maximum suitable temperature when photosynthesis occurs best is 35°C after which the rate falls.
:- The process of photosynthesis stops above 40°C as the enzymes are destroyed.
:- Low temperature also inhibits enzymatic activities and the rate of photosynthesis is reduced.
4. Water
:- It acts as a limiting factor in photosynthesis.
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