Definitions [2]
Define the following term:
Photolysis of water
Releasing electrons and dividing the water molecule (H2O) into its two components (Hydrogen and Oxygen). Photolysis is the term used to describe this reaction, which is characterised by the fracturing of molecules by light (photo = light, lysis = breaking).
Definition: Photosynthesis
Photosynthesis is the process by which living plant cells, containing chlorophyll, produce food substances (glucose and starch) from carbon dioxide and water by using light energy. Plants release oxygen as a byproduct during photosynthesis.
Key Points
Key Points: Concept of Photosynthesis
- Photosynthesis converts sunlight into chemical energy using CO₂ and water, producing glucose and releasing oxygen as a byproduct.
- Green plants are autotrophs (make their own food); all other organisms are heterotrophs. All life depends on sunlight for energy.
- Three essentials for photosynthesis: chlorophyll, light, and CO₂.
- Experiment 1 - Variegated leaf tested for starch showed that photosynthesis occurs only in green parts in the presence of light.
- Experiment 2 - Leaf part enclosed with KOH-soaked cotton (absorbs CO₂) tested negative for starch → proved CO₂ is necessary for photosynthesis.
Key Points: Factors Affecting Photosynthesis
- Blackman’s Law of Limiting Factors states that the rate of photosynthesis is controlled by the factor in the least supply.
- Light affects photosynthesis through intensity, quality, and duration; it shows a linear increase at low intensity and saturation at about 10% of full sunlight.
- Carbon dioxide is the major limiting factor; increasing CO₂ concentration increases photosynthesis up to a limit, after which it may become harmful.
- Temperature controls enzymatic reactions (dark reactions); C₄ plants work better at higher temperatures, while C₃ plants have a lower optimum temperature.
- Water affects photosynthesis indirectly; water stress causes stomatal closure, reducing CO₂ availability and decreasing photosynthesis.
- All factors work together, but usually one limiting factor determines the overall rate of photosynthesis.
Concepts [15]
- Photosynthetic Pigments
- Spectrum of Electromagnetic Radiation
- Photosynthetic Unit (Quantasome)
- Absorption Spectrum and Action Spectrum
- Emerson’s Experiments and Hill’s Reaction
- Concept of Photosynthesis
- Photo-oxidation Phase of Light Reaction
- Photo Chemical Phase of Light Reaction
- Photophosphorylation
- Dark Reaction or C3 Cycle or Biosynthetic Phase or Photosynthetic Carbon Reduction (PCR)Cycle
- Hatch and Slack Pathway or C4 Cycle or Dicarboxylic Acid Pathway or Dicarboxylation Pathway
- Crassulacean Acid Metabolism or CAM Cycle
- Photorespiration or C2 Cycle or Photosynthetic Carbon Oxidation (PCO) Cycle
- Factors Affecting Photosynthesis
- Photosynthesis in Bacteria
