Photosynthesis and Cellular Respiration

Cumulative Final Exam Preparation

The final exam is cumulative.
Noted that students should review past material, especially detailed lessons from chapters leading to the exam.

Photosynthesis is the process by which plants convert solar energy into chemical energy.
The basic equation for photosynthesis is:
- ext{6 CO}2 + ext{6 H}2 ext{O}
  ightarrow ext{C}6 ext{H}{12} ext{O}6 + ext{6 O}2
Carbon dioxide is fixed, and glucose is produced as the main energy source for the plant.

Photosynthesis occurs in chloroplasts, which contain:
- Thylakoids: Membrane-bound compartments where the light reactions happen.
- Stroma: The fluid that contains enzymes for the Calvin cycle.

The process is divided into two main stages:
1. Light Reactions
2. Calvin Cycle (Dark Reactions)

Occur in the thylakoid membranes.
Require solar energy to initiate the conversion of light energy into chemical energy.
Key Components:
- Photons: Discrete packets of light energy absorbed primarily by chlorophyll (particularly chlorophyll a and b).
- Chlorophyll: Major pigment involved in capturing sunlight.
Water Splitting: Water is split, releasing oxygen as a byproduct.
ATP and NADPH: Produced as energy carriers for the Calvin cycle.

During light reactions:
- Light energy is captured by chlorophyll, exciting electrons.
- Electrons pass through an electron transport chain where:
- ATP is generated via photophosphorylation.
- NADP+ accepts the electrons, becoming NADPH.

Occurs in the stroma of chloroplasts.
Does not require light directly but depends on ATP and NADPH produced in the light reactions.
Key Steps:
1. Carbon Fixation: Incorporates carbon dioxide into organic molecules using the enzyme rubisco.
- Three CO2 molecules are used to yield one G3P (glyceraldehyde-3-phosphate).
1. Reduction Phase: ATP and NADPH convert three PGA (3-phosphoglycerate) into G3P.
2. Regeneration of RuBP: The remaining G3P molecules regenerate ribulose bisphosphate (RuBP) using ATP.
G3P: The final product that can be converted into glucose and other carbohydrates.

Important Connection: The process of photosynthesis helps mitigate carbon dioxide levels in the atmosphere, affecting global warming.
Discussion about ozone and its significance related to the effects of greenhouse gases.

Autotrophs: Organisms that can produce their own food through processes like photosynthesis (e.g., plants).
Photoautotrophs: A subtype of autotrophs that specifically use light energy to produce glucose.
Chemoautotrophs: Organisms that use inorganic chemicals to create food, differing from photoautotrophs.
Heterotrophs rely on other organisms for energy and food, contrasting with autotrophs.

Each type of chlorophyll absorbs different wavelengths of light, which is essential for maximizing energy capture.
Light reactions convert light energy to chemical potential energy, producing ATP through a hydrogen gradient, similar to processes in cellular respiration.
Each nutrient and energy product from the light reactions feeds directly into the Calvin cycle for sugar production.

Photosynthesis is crucial for life on Earth, providing oxygen and organic material for living organisms.
Understanding photosynthesis can lead to insights into agricultural practices and improving crop yields.