General Biology: Cell Structure, Metabolism, and Photosynthesis Study Guide

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

Cells are classified as either prokaryotic or eukaryotic based on their structural features.

• Prokaryotic cells lack a nucleus and membrane-bound organelles. Their DNA is located in the nucleoid region.

• Eukaryotic cells possess a true nucleus and various membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum).

• Examples: Bacteria are prokaryotes; plants and animals are eukaryotes.

Structure and Function of Organelles

Organelles perform specialized functions that contribute to overall cellular activity.

• Nucleus: Stores genetic material and coordinates cell activities.

• Mitochondria: Site of cellular respiration and ATP production.

• Chloroplasts: Site of photosynthesis in plant cells.

• Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

Endosymbiosis Theory

The endosymbiosis theory explains the origin of mitochondria and chloroplasts as formerly free-living prokaryotes engulfed by ancestral eukaryotic cells.

• Evidence includes double membranes, circular DNA, and similarities to prokaryotic ribosomes.

Cellular Metabolism and Energy

Potential vs. Kinetic Energy in Chemical Reactions

Potential energy is stored energy (e.g., chemical bonds), while kinetic energy is energy of motion (e.g., movement of molecules).

• Chemical reactions convert potential energy in molecules to kinetic energy and vice versa.

Endergonic vs. Exergonic Reactions & Gibbs Free Energy

Reactions are classified by their energy changes, described by Gibbs free energy ($riangle G$).

• Endergonic reactions: Require energy input; $riangle G > 0$.

• Exergonic reactions: Release energy; $riangle G < 0$.

• Equation: $\triangle G = \triangle H - T\triangle S$

Enzyme Catalysis

Enzymes are biological catalysts that lower the activation energy of reactions.

• They increase reaction rates without being consumed.

• Enzyme activity is affected by factors such as pH and temperature.

Cellular Respiration

Stages of Cellular Respiration

Cellular respiration consists of four interconnected stages:

1. Glycolysis

2. Pyruvate oxidation

3. Citric acid cycle (Krebs cycle)

4. Electron transport chain (ETC) and oxidative phosphorylation

Glycolysis

Glycolysis occurs in the cytoplasm and consists of two phases:

• Energy investment phase: ATP is used to phosphorylate glucose.

• Energy payoff phase: ATP and NADH are produced.

Citric Acid Cycle

The citric acid cycle completes the oxidation of glucose derivatives, generating NADH, FADH2, and ATP.

• Occurs in the mitochondrial matrix.

• Key role: Provides high-energy electrons for the ETC.

Electron Transport Chain (ETC) and Oxidative Phosphorylation

The ETC uses electrons from NADH and FADH2 to create a proton gradient, driving ATP synthesis.

• Occurs in the inner mitochondrial membrane.

• Oxygen is the final electron acceptor.

Aerobic vs. Anaerobic Respiration & Fermentation

• Aerobic respiration: Uses oxygen, produces more ATP.

• Anaerobic respiration: Does not use oxygen, less ATP produced.

• Fermentation: Allows ATP production without oxygen (e.g., lactic acid or alcohol fermentation).

Photosynthesis

Inputs and Outputs of Photosynthesis

Photosynthesis occurs in two major stages in the chloroplast:

• Light-dependent reactions: Occur in the thylakoid membranes; produce ATP and NADPH.

• Calvin cycle (light-independent reactions): Occur in the stroma; use ATP and NADPH to fix CO2 into sugars.

Pigments and Light Absorption

Chlorophyll and other pigments absorb light energy, which is used to drive photosynthesis.

• Absorption spectrum determines which wavelengths are absorbed.

• Chlorophyll appears green because it reflects green light.

Z-Scheme and Electron Transport

The Z-scheme describes the flow of electrons through photosystems II and I, generating ATP and NADPH.

• ATP is generated via a proton gradient (chemiosmosis).

• NADPH is produced via electron transport.

Calvin Cycle: Phases and Enzyme

The Calvin cycle consists of three phases:

1. Fixation: CO2 is attached to RuBP by the enzyme RuBisCO.

2. Reduction: ATP and NADPH are used to convert 3-PGA to G3P.

3. Regeneration: RuBP is regenerated for the cycle to continue.

C4 and CAM Plants

C4 and CAM plants have adaptations to minimize photorespiration by separating carbon fixation from the Calvin cycle.

• C4 plants: Spatial separation; CO2 fixation occurs in mesophyll cells, Calvin cycle in bundle sheath cells.

• CAM plants: Temporal separation; CO2 fixation at night, Calvin cycle during the day.

Type	Adaptation	Example
C3	No separation	Wheat
C4	Spatial separation	Corn
CAM	Temporal separation	Cactus

*Additional info: Table inferred for comparison of C3, C4, and CAM plants; examples added for clarity.*