Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is a metabolic process by which cells convert biochemical energy from nutrients into adenosine triphosphate (ATP), releasing waste products. It is essential for energy production in both plants and animals.

• Aerobic respiration: Occurs in the presence of oxygen and produces more ATP.

• Anaerobic respiration: Occurs without oxygen, producing less ATP and different byproducts.

Types of Phosphorylation

• Chemiosmosis/Oxidative phosphorylation: ATP is produced using energy from electrons transferred through the electron transport chain, creating a proton gradient across the mitochondrial membrane. Definition: The process by which ATP is synthesized as protons flow back into the mitochondrial matrix through ATP synthase. Where it occurs: Inner mitochondrial membrane. Products: ATP, water.

• Substrate-level phosphorylation: ATP is formed directly in metabolic pathways by transferring a phosphate group from a substrate to ADP. Where it occurs: Glycolysis and Krebs cycle. Products: ATP.

Fermentation

Fermentation is an anaerobic process that allows cells to produce ATP without oxygen. It regenerates NAD+ for glycolysis.

• Alcoholic fermentation: Saccharomyces cerevisiae (yeast) converts pyruvate to ethanol and CO2.

• Lactic acid fermentation: Lactobacillus and muscle cells convert pyruvate to lactic acid.

Catabolic vs. Anabolic Pathways

• Catabolic pathways: Break down molecules to release energy (e.g., cellular respiration).

• Anabolic pathways: Build complex molecules from simpler ones, requiring energy (e.g., photosynthesis).

Redox Reactions in Respiration

Redox (reduction-oxidation) reactions transfer electrons between molecules, crucial for energy production.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• NADH and FADH2: Electron carriers reduced during glycolysis and Krebs cycle, oxidized in the electron transport chain.

Events in the Intermediate Step

The intermediate step (pyruvate oxidation) links glycolysis to the Krebs cycle.

• Pyruvate is transported into the mitochondrion.

• Converted to acetyl-CoA, producing NADH and CO2.

Purpose of Citric Acid Cycle (Krebs Cycle)

The citric acid cycle completes the breakdown of glucose, generating electron carriers for the electron transport chain.

• Produces NADH, FADH2, ATP, and CO2.

ATP Production in Cellular Respiration

• Glycolysis: 2 ATP (net)

• Krebs cycle: 2 ATP

• Oxidative phosphorylation: ~26-28 ATP

• Total: ~30-32 ATP per glucose molecule

Equations of Cellular Respiration

• Overall equation:

Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen.

• Occurs in chloroplasts.

• Consists of light-dependent and light-independent (Calvin cycle) reactions.

Light-Dependent Reactions

These reactions capture light energy to produce ATP and NADPH.

• Occur in the thylakoid membranes.

• Water is split, releasing oxygen.

• ATP and NADPH are produced for use in the Calvin cycle.

Light-Independent Reactions (Calvin Cycle)

The Calvin cycle uses ATP and NADPH to fix carbon dioxide into glucose.

• Occurs in the stroma of the chloroplast.

• Produces G3P (glyceraldehyde-3-phosphate), which is used to form glucose.

Equation of Photosynthesis

• Overall equation:

Origin of Oxygen Released by Plants

• Oxygen released during photosynthesis comes from the splitting of water molecules in the light-dependent reactions.

Absorption Spectrum and Action Spectrum

These spectra describe how different wavelengths of light are absorbed and used in photosynthesis.

• Absorption spectrum: Shows which wavelengths are absorbed by pigments (e.g., chlorophyll).

• Action spectrum: Shows the rate of photosynthesis at different wavelengths.

Thylakoid Membrane Events

• Light excites electrons in chlorophyll.

• Electrons pass through the electron transport chain, producing ATP and NADPH.

• Oxygen is produced as a byproduct.

Photorespiration

Photorespiration is a process where oxygen is consumed and carbon dioxide is released, reducing the efficiency of photosynthesis.

• Occurs when Rubisco binds O2 instead of CO2.

• More common in hot, dry conditions.

C3, C4, and CAM Pathways

Plants have evolved different mechanisms to fix carbon and minimize photorespiration.

Stomata and Photosynthetic Rate

• Stomata regulate gas exchange and water loss.

• Closing stomata reduces water loss but also limits CO2 uptake, affecting photosynthesis.

Evolutionary Adaptations

• C4 and CAM plants have adaptations to reduce photorespiration and conserve water.

Summary Table: Cellular Respiration vs. Photosynthesis

Additional info: Some explanations and examples have been expanded for clarity and completeness.