Photosynthesis

      

     What is photosynthesis?

Photosynthesis is the amazing process by which plants and some other organisms capture the sun's energy and transform it into food! Here's a quick rundown:

Ingredients:

1) Sunlight: The energy source, captured by chlorophyll (the green pigment in plants).

2) Water: Taken in from the soil.

3) Carbon dioxide: Absorbed from the air.

Process:

1. Light Capture: Chlorophyll absorbs specific wavelengths of sunlight, exciting its electrons.

2. Electron Transport Chain: These excited electrons move through a series of molecules, generating energy (ATP) and releasing some as heat.

3. Carbon Fixation: Using ATP, plants convert carbon dioxide into organic molecules like glucose (sugar).

4. Oxygen Production: As a byproduct, water is split, releasing oxygen gas into the atmosphere.

Products:

1) Glucose: The plant's food, used for growth, reproduction, and energy.

2) Oxygen: Released into the atmosphere, essential for animal life.

Importance:

1) Food for all: Photosynthesis is the base of all food chains, as plants are eaten by herbivores, who are then eaten by carnivores.

2) Oxygen production: Photosynthesis replenishes the oxygen we breathe.

3) Climate regulation: Plants absorb carbon dioxide, a greenhouse gas, helping to regulate Earth's climate.

Additional facts:

* Different types of photosynthesis exist, adapted to different environments.

* Photosynthesis is a complex process with many intricate steps.

* Scientists are still studying the full potential of photosynthesis for various applications.

Photosynthesis in higher plants involves additional process which is not happens in smaller plants.

Photosynthesis in Higher Plants is the process by which green plants convert light energy into chemical energy, producing carbohydrates from carbon dioxide and water, with oxygen released as a by-product.

Equation:-

$6CO_2 + 6H_2O + light\ energy \rightarrow C_6H_{12}O_6 + 6O_2$

Site of photosynthesis

* Occurs in chloroplast of plant cells.

* Chloroplast contain:- 

Grana (stacks of thylakoids): site of light reactions.

Stroma: site of carbon fixation (Calvin cycle).

Pigments Involved

• Chlorophyll a – primary photosynthetic pigment.
• Chlorophyll b
• Carotenoids (carotenes and xanthophylls)

Difference between Chlorophyll A and chlorophyll B

Chlorophyll a absorbs around 430 nm (blue-violet) and 662 nm (red). Chlorophyll b absorbs b absorbs more around 455nm (blue) and 642 nm (orange red). 

Phases of Photosynthesis

1. Light Reaction (Photochemical Phase)

Occurs in the thylakoid membranes.

Main events:

• Absorption of light by pigments.
• Splitting of water (photolysis).
• Release of oxygen.
• Formation of ATP and NADPH.

2. Dark Reaction (Biosynthetic Phase / Calvin Cycle)

Occurs in the stroma.

Main events:

• Fixation of CO₂.
• Reduction of CO₂ to carbohydrates using ATP and NADPH.
• Regeneration of RuBP.

Photosystems

Two photosystems participate in light reactions:

1. Photosystem II (PS II) – P680

   • Initiates electron flow.
   • Splits water.
   Photosystem I (PS I) – P700
   • Produces NADPH.

Photophosphorylation

Formation of ATP using light energy.

Types:

• Cyclic photophosphorylation: produces ATP only.
• Non-cyclic photophosphorylation: produces ATP, NADPH, and O₂.

Calvin Cycle (C₃ Pathway)

Three stages:

1. Carboxylation
2. Reduction
3. Regeneration

Key enzyme:

• RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase)

Photorespiration

• Occurs when RuBisCO acts as an oxygenase.
• Consumes oxygen and releases CO₂.
• Reduces photosynthetic efficiency.
• Prominent in C₃ plants.

C₄ Pathway

Examples:

• Sugarcane
• Maize
• Sorghum

Features:

• Initial CO₂ fixation by PEP carboxylase.
• Kranz anatomy present.
• Minimizes photorespiration.
• More efficient under high temperature and light intensity.

CAM Pathway

Examples:

• Cactus
• Pineapple
• Agave

Features:

• Stomata open at night.
• CO₂ fixed at night and used during the day.
• Adaptation to arid conditions.

Factors Affecting Photosynthesis

External Factors

• Light intensity
• Carbon dioxide concentration
• Temperature
• Water availability

Internal Factors

• Chlorophyll content
• Leaf anatomy
• Age of leaf
• Enzyme activity

Importance of Photosynthesis

• Primary source of food on Earth.
• Produces atmospheric oxygen.
• Maintains carbon cycle.
• Converts solar energy into chemical energy.
• Supports nearly all ecosystems.

Do you know how plant transport water from root to leaves in plants ?

Plants move water upwards against the force of gravity through a complex system of biological and physical mechanisms, primarily involving a specialized vascular tissue called xylem. This upward movement is referred as transportation stream. It relies on following process.

1. Transpiration and the Transpiration Pull

When leaves comes in direct contact with sunlight evaporation of water started from the leaves through microscopic pore called stomata. As soon as water starts evaporate from mesophyll cell walls into air it create a negative pressure or suction known as Transportation Pull. This transportation pull is transmitted through all way down to the roots, drawing water up to replace water they have lost.

2. Cohesion-Tension Theory

Water Molecule are polar in nature they have a unique properties that allow them to form a continuous, unbreakable chain of water from root to leaves.

Cohesion:- Each water molecule connected with each other through hydrogen bonds. This ensures that when one molecule is pulled up by transpiration at the top, the entire "chain" of molecules follows.

Adhesion:- Water molecules also stick to the cellulose in the xylem walls. This prevents the water column from pulling away from the walls or falling back down due to gravity.

3. Capillary Action

In the very narrow tubes of the xylem (vessels and tracheids), the combined forces of cohesion and adhesion create capillary action. This allows water to climb up the sides of the tubes, further aiding its upward movement.

4. Root Pressure

Plants also generate an upward push from the bottom called root pressure.

* Root cells actively transport mineral ions from the soil into the xylem, which lowers the water potential inside the root.

* Water follows these minerals into the root by osmosis, increasing the internal water pressure and steadily pushing the water column upwards.

* While root pressure helps move water into the xylem, it is generally considered a secondary force compared to the much stronger transpiration pull.