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Biology X - Photosynthesis Cheat Sheet by

Important Notes On the Chapter- Photosynthesis for Exams

Important Terms

The process by which green plants make glucose or food with the help of Carbon dioxide and water in presence of sunlight and chloro­phyll is called Photos­ynt­hesis
+ 12H
O --> C
+ 6O
+ 6H
NADP- Nicoti­namide Adenine Dinucl­eotide Phosphate
Chloro­phyll is the green pigment found in plants.
Chloro­plasts are minute oval bodies bounded by a double membrane, and their interior contains closely packed flattened sacks (thylakoids) arranged in piles (grana) lying in a colourless ground substance called stroma.
The Carbon Cycle is a series of chemical reactions in which carbon as a chemical element is removed from the air, used by living organisms in their body processes and is finally returned to air.
Photolysis of water: Chemical decomp­osition of water induced by light or other radiant energy. Photolysis plays an important role in photos­ynt­hesis, during which it produces energy by splitting water molecules into gaseous oxygen and hydrogen ions.
In the process of photos­ynt­hesis, the phosph­ory­lation of ADP to form ATP using the energy of sunlight is called photop­hos­pho­ryl­ation.

Stomatal Opening and Closing


Adapta­tions in Leaf For Photos­ynt­hesis

Large Surface Area - for maximum light absorption
Leaf Arrang­ement - at the right angle to the light source to obtain maximum light
Cuticle and Upper Epidermis - are transp­arent and waterproof to allow light to enter freely
Numerous Stomata - allow rapid exchange of gases
Thinness of Leaves - reduces distance between cells facili­tating rapid transport
Chloro­plasts - concen­trated in the upper layers of leaf to obtain light energy quickly
Extensive Vein System - for rapid transport to and from the mesophyll cells.

Stomatal Transp­iration

The following steps are involved in stomatal transp­ira­tion:
Osmotic diffusion transports water from the leaf’s xylem to the interc­ellular space above the stomata.
The stomata open and close.
Through stomata, water is transp­orted from the interc­ellular space to the external enviro­nment.

Factors Affecting Photos­ynt­hesis

Light Intensity
Carbon Dioxide Concen­tration
Water Content
Structure Of Leaf

Importance Of Photos­ynt­hesis

Provides Food
Provides Oxygen

Stages in Photos­ynt­hesis:

Light Reaction: Light reaction occurs in the thylakoids during daytime in the presence of sunlight. Since it results in the formation of chemical energy from radiant energy, it is called a photoc­hemical reaction and it is divided into 4 stages.
Dark Reaction: This reaction occurs in the stroma. Since this reaction results in the formation of biomol­ecules, it is called a biosyn­thetic phase. There are three stages identified in the Calvin cycle.
Absorption of light energy: Chloro­phyll pigments present in Photos­ynt­hetic units in the thylakoids absorb a photon of energy. This results in electrons being excited into a higher energy level.
Carbox­ylation: CO2 is covalently linked to a 5 carbon sugar (RuBP) and converted to 2 three carbon compounds.
Photolysis of water: The excess energy is used to split a molecule of water into H+ and OH– ions. Oxygen is formed as a byproduct and is released into the atmosp­here. 4H₂O → 4H⁺ + 4(OH) ⁻ (i) 4(OH) ⁻→ 2H₂O + O₂ + 4e⁻ (ii) 2H₂O→ 4H⁺ + O₂ + 4e⁻ (adding i + ii)
Reduction: In the presence of the energy stored in the NADPH₂ and ATP, the two 3-carbon molecules combine to form a six carbon glucose molecule. NADP is got back from NADPH₂ and ADP is obtained from ATP. These are used in the next cycle of the light reaction. (The hydrogen released is used to reduce carbon dioxide into sugar molecule).
Reduction of NADP: 2NADP + 4e⁻ + 4H⁺ → NADPH
Regene­ration: The CO2 acceptor RuBP reforms at the expense of ATP.
Photop­hos­pho­ryl­ation: In the presence of sunlight, ADP binds with inorganic phosphate to form ATP. (ADP + Pià ATP)
The ATP and NADPH formed in the reaction are used to reduce CO₂ to carboh­ydrates in the dark reaction.


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