In Depth Notes on Photosynthesis

Key Terms

• Autotrophs: Organisms that can produce their own food using light, water, carbon dioxide, or other chemicals.
• Photoautotrophs: A type of autotroph that uses light energy to synthesize organic compounds from carbon dioxide.
• Photosynthesis: A process used by plants, algae, and some bacteria to convert light energy into chemical energy stored in glucose, involving the transformation of carbon dioxide and water into glucose and oxygen.
• Producers of the biosphere: Organisms (primarily plants) that produce organic compounds from carbon dioxide, thus forming the basis of the food chain.
• Consumers: Organisms that depend on other organisms for food.
• Heterotrophs: Organisms that cannot produce their own food and rely on consuming other organisms for energy.

Examples of Producers

• Land Environment: Trees (e.g., oak, pine), shrubs, grasses.
• Aquatic Environment: Phytoplankton, seaweed, and aquatic flowering plants.

Location of Photosynthesis

• In Plant Cells: Photosynthesis primarily occurs in the chloroplasts, mainly located in the mesophyll cells of leaves.
• In Photosynthetic Bacteria: Photosynthesis occurs in the cytoplasm or in specialized membranes.

Requirements for Photoautotrophs

• Light, water, and carbon dioxide from the environment to create food (glucose).

Chloroplast Structure

• Mesophyll: Leaf tissue where chloroplasts are concentrated.
• Stomata: Small openings on leaf surfaces for gas exchange.
• Stoma: A fluid-filled space inside the chloroplast where the Calvin cycle occurs.
• Thylakoids: Membrane systems within chloroplasts where light reactions take place.
• Grana: Stacked structures of thylakoids.

Photosynthesis Equation

• Basic summary: 6CO2 + 6H2O + light
  ightarrow C6H{12}O6 + 6O2

Oxygen Release

• The oxygen produced in photosynthesis originates from the splitting of water molecules (photolysis) during the light reactions.

Photosynthesis as a Redox Process

• Photosynthesis involves the reduction of carbon dioxide to glucose and oxidation of water to oxygen.

Comparison with Cellular Respiration

• Photosynthesis converts light energy into chemical energy, while cellular respiration breaks down glucose to release energy.

Nature of Reaction

• Endergonic Reaction: Photosynthesis requires energy input (light).

Stages of Photosynthesis

1. Light Reactions: Occur in the thylakoid membranes, converting light energy into chemical energy.
2. Calvin Cycle: Occurs in the stroma, using ATP and NADPH to fix carbon dioxide into glucose.

Light Reactions Details

• Energy is stored in ATP and NADPH.
• Electron Acceptors: NADP+ is reduced to NADPH during these reactions.

Carbon Fixation

• The process of converting inorganic CO2 into organic molecules (glucose) during the Calvin cycle.

Electromagnetic Spectrum

• Range of all types of electromagnetic radiation, including visible light, which is the portion of the spectrum that photosynthesis utilizes.

Wavelength of Visible Light

• Roughly 400 nm to 700 nm.

Photon

• A particle of light that has specific energy and can be absorbed by pigments in plants.

Photosynthetic Pigments

• Chlorophyll a: Absorbs blue-violet and red light.
• Chlorophyll b: Assists chlorophyll a and absorbs light in other wavelengths (mainly blue and orange-red).
• Carotenoids: Accessory pigments that absorb excess light energy and protect plants from photodamage.

Leaf Color

a. Green Appearance: Due to high chlorophyll content that reflects green light and absorbs blue and red light.

Light Reaction Processes

• Involves photophosphorylation to generate ATP, with ATP synthase providing the enzyme required for ATP creation.

The Calvin Cycle Stages

1. Carbon Fixation: Catalyzed by the enzyme Ribulose bisphosphate carboxylase/oxygenase (RuBisCO).
2. Reduction: ATP and NADPH are used to convert 3-phosphoglycerate into glyceraldehyde-3-phosphate (G3P).
3. Regeneration: RuBP is regenerated from G3P.

C3, C4, and CAM Plants

• C3 Plants: Use the Calvin cycle directly for carbon fixation; susceptible to photorespiration (e.g., wheat, rice).
• C4 Plants: Modify fixation with an additional step to minimize photorespiration (e.g., corn, sugarcane).
• CAM Plants: Open stomata at night to fix carbon, thereby reducing water loss (e.g., succulents, cacti).

Impact of Photosynthesis

• Provides food and oxygen, essential for life forms.
• Glucose Storage: Stored as starch in plants.

Environmental Considerations

• Higher CO2 levels can boost plant productivity.
• Greenhouse Effect: Increase in gas emissions leading to climate change. Reducing fossil fuel usage and deforestation is crucial to mitigate impacts.