Photosynthesis

Photosynthesis: Converts light energy to a usable form.
Respiration: Releases stored energy.
Importance: Facilitates growth, development, and reproduction.
Metabolism: Sum of all interrelated biochemical processes in living organisms.
Context: Animals rely on green plants for oxygen, food, shelter, and other products.

Enzymes: Regulate metabolic activities.
Anabolism:
- Definition: Forming chemical bonds to build molecules.
- Relation to photosynthesis: Photosynthesis reactions store energy by constructing carbohydrates by combining carbon dioxide (CO₂) and water (H₂O).
Catabolism:
- Definition: Breaking chemical bonds.
- Relation to respiration: Cellular respiration reactions release energy held in chemical bonds by breaking down carbohydrates, producing CO₂ and H₂O.
Photosynthesis-Respiration Cycle: Involves transfer of energy via oxidation-reduction reactions.

Oxidation: Loss of electron(s).
Reduction: Gain of electron(s).
Coupling: Oxidation of one compound is usually coupled with the reduction of another compound, catalyzed by the same enzyme or enzyme complex.
Hydrogen Atom:
- Lost during oxidation.
- Gained during reduction.
Final Electron Acceptor: Oxygen is usually the final acceptor of electrons.

Essence of Photosynthesis: Energy for most cellular activities uses adenosine triphosphate (ATP).
ATP Production: Plants make ATP using light as an energy source.
Location: Takes place in chloroplasts and other green parts of the organisms.
Chemical Equation for Photosynthesis:
$6CO_2 + 12H_2O + ext{light} <br>ightarrow C_6H_{12}O_6 + 6O_2 + 6H_2O$
Process Specifics:
- Many intermediate steps are involved, and glucose is not the immediate first product.

Transportation to Chloroplasts: CO₂ reaches chloroplasts in mesophyll cells by diffusing through stomata into leaf interior.
Human Impact: Use of fossil fuels, deforestation, and other human activities add more CO₂ to the atmosphere than is removed, with potential to cause global warming and enhance photosynthesis.

Usage in Photosynthesis: Less than 1% of all water absorbed by plants is used in photosynthesis; most is transpired or incorporated into plant materials.
Role in Photosynthesis: Water serves as the source of electrons, and oxygen is released as a by-product.
Conditions Affecting Water Supply: If water is in short supply or light intensities are too high, stomata close, reducing the supply of CO₂ available for photosynthesis.

Visible Light: About 40% of radiant energy received on Earth is in the form of visible light.
Wavelengths Used: Violet to blue and red-orange to red wavelengths are more extensively utilized, whereas green light is reflected.

Variation in Light Intensity: Plants require different light intensities for optimal photosynthesis.
Limiting Factors: Temperature and availability of CO₂ can also limit photosynthesis.

Adverse Conditions:
- High light and temperature can alter the ratio of CO₂ to oxygen inside leaves, leading to increased photorespiration, which uses oxygen and releases CO₂.
- Photorespiration can help some plants survive under adverse conditions.
- High light intensity can cause photooxidation, resulting in the destruction of chlorophyll.

Chlorophyll Types: Various types exist with the magnesium end capturing light; most plants contain chlorophyll a (blue-green color) and chlorophyll b (yellow-green color).
Function: Chlorophyll b transfers energy from light to chlorophyll a, allowing photosynthesis to occur over a broad spectrum of light.