Photosynthesis

Study Notes

Light Reactions

Occur in the thylakoid membranes of chloroplasts.
Convert light energy into chemical energy (ATP and NADPH).
Key steps:
- Light absorption by chlorophyll boosts electrons.
- Water (H₂O) is split (photolysis) to release oxygen (O₂).
- Electron transport chain generates ATP via chemiosmosis.

Calvin Cycle

Takes place in the stroma of chloroplasts.
Converts CO₂ into glucose using ATP and NADPH from light reactions.
Phases:
1. Carbon Fixation: CO₂ combines with ribulose bisphosphate (RuBP).
2. Reduction Phase: ATP and NADPH convert 3-phosphoglycerate (3-PGA) into glyceraldehyde-3-phosphate (G3P).
3. Regeneration of RuBP: Some G3P is used to regenerate RuBP, allowing the cycle to continue.

Chlorophyll Function

Primary pigment involved in photosynthesis, absorbs light energy.
Main types: Chlorophyll a (mainly absorbs blue and red light) and Chlorophyll b (assists by capturing additional light wavelengths).
Located in thylakoid membranes, essential for exciting electrons during light reactions.

Photosynthetic Organisms

Types:
- Plants: Autotrophic, perform photosynthesis to produce their own food.
- Algae: Aquatic organisms, can be unicellular or multicellular; major contributors to oxygen production.
- Cyanobacteria: Photosynthetic bacteria that perform oxygenic photosynthesis.
Role in ecosystems: Serve as primary producers, forming the base of food chains.

Environmental Impact

Photosynthesis reduces atmospheric CO₂ levels, helping mitigate climate change.
Produces oxygen, essential for aerobic life forms.
Deforestation and habitat destruction can impact photosynthetic rates and biodiversity.
Algal blooms, often fueled by nutrient runoff, can disrupt aquatic ecosystems, leading to dead zones.

Photosynthesis Overview

Photosynthesis is the process by which organisms convert light energy into chemical energy stored in glucose.
It consists of two main stages: Light Reactions and the Calvin Cycle, occurring in chloroplasts.

Light Reactions

Occur in thylakoid membranes of chloroplasts, converting light energy into ATP and NADPH.
Light absorption by chlorophyll excites electrons, initiating the process.
Photolysis splits water (H₂O), releasing oxygen (O₂) as a byproduct.
An electron transport chain generates ATP through chemiosmosis, using the proton gradient created.

Calvin Cycle

Takes place in the stroma of chloroplasts, utilizing ATP and NADPH produced in light reactions.
Carbon Fixation: CO₂ integrates with ribulose bisphosphate (RuBP), forming an unstable 6-carbon compound.
Reduction Phase: ATP and NADPH convert 3-phosphoglycerate (3-PGA) to glyceraldehyde-3-phosphate (G3P), a sugar molecule.
Regeneration of RuBP: Some G3P is used to regenerate RuBP, allowing the cycle to continue and fix more CO₂.

Chlorophyll Function

Chlorophyll is the primary pigment in photosynthesis, critical for absorbing light energy.
Two main types:
- Chlorophyll a: Primarily absorbs blue and red light.
- Chlorophyll b: Helps capture additional light wavelengths, maximizing energy absorption.
Located in thylakoid membranes, chlorophyll plays a key role in exciting electrons during light reactions.

Photosynthetic Organisms

Plants: Autotrophic organisms that perform photosynthesis to create their own energy sources.
Algae: Aquatic photosynthetic organisms, contributing significantly to global oxygen production; can be unicellular or multicellular.
Cyanobacteria: Photosynthetic bacteria that conduct oxygenic photosynthesis and are crucial in various ecosystems.
These organisms serve as primary producers, foundational to food chains and energy flow in ecosystems.

Environmental Impact

Photosynthesis lowers atmospheric CO₂ levels, contributing to climate change mitigation.
Produces oxygen, vital for the survival of aerobic life forms.
Deforestation and habitat destruction can diminish photosynthetic rates and biodiversity, adversely affecting ecosystems.
Algal blooms, driven by nutrient runoff, disrupt aquatic ecosystems, potentially creating dead zones due to depleted oxygen.

Description

Test your knowledge on the process of photosynthesis, focusing on the light reactions occurring in the thylakoid membranes and the Calvin Cycle in the stroma. Understand the key components, including chlorophyll function, ATP production, and carbon fixation.