Cellular Respiration, Photosynthesis, and the Cell Cycle: Study Guide (Chapters 9, 10, 12)

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Cellular Respiration (Chapter 9)

Redox Reactions in Cellular Respiration

Cellular respiration is driven by redox reactions, where electrons are transferred between molecules, resulting in energy release.

Oxidation: Loss of electrons from a substance.
Reduction: Gain of electrons by a substance.
Oxidizing agent: Accepts electrons (is reduced).
Reducing agent: Donates electrons (is oxidized).
Electron donor: The molecule that loses electrons.
Electron acceptor: The molecule that gains electrons.
Net equation of respiration:

NAD+ and Its Role

NAD+ (nicotinamide adenine dinucleotide) is an electron carrier.
It cycles between oxidized (NAD+) and reduced (NADH) states, shuttling electrons to the electron transport chain.

Stages of Cellular Respiration

Glycolysis: Occurs in the cytosol; splits glucose into two pyruvate molecules. Has an investment phase (uses ATP) and a payoff phase (produces ATP and NADH).
Pyruvate oxidation and Citric Acid Cycle: Occurs in the mitochondrial matrix; completes the breakdown of glucose, producing CO2, NADH, and FADH2.
Oxidative phosphorylation: Includes the electron transport chain and chemiosmosis; occurs in the inner mitochondrial membrane; produces most ATP.

Cellular Locations of Respiration Steps

Glycolysis: Cytosol
Pyruvate oxidation & Citric Acid Cycle: Mitochondrial matrix
Electron Transport Chain & Chemiosmosis: Inner mitochondrial membrane

Role of Oxygen

Oxygen acts as the final electron acceptor in the electron transport chain, forming water.
Without oxygen, the chain stops, and ATP production is severely reduced.

Proton-Motive Force and ATP Generation

The electron transport chain pumps protons (H+) across the inner mitochondrial membrane, creating a proton-motive force.
ATP synthase uses this gradient to synthesize ATP as protons flow back into the matrix.
If protons cannot cross, ATP synthesis halts.

Fermentation

Alcohol fermentation: Converts pyruvate to ethanol; releases CO2.
Lactic acid fermentation: Converts pyruvate to lactate; no CO2 released.
Both regenerate NAD+ for glycolysis but yield less ATP than aerobic respiration.

Aerobic vs. Anaerobic Respiration

Aerobic respiration: Uses oxygen as the final electron acceptor.
Anaerobic respiration: Uses other molecules (e.g., sulfate, nitrate) as final electron acceptors.

Feedback Mechanisms in Respiration

Respiration is regulated by feedback inhibition.
ATP and citrate are inhibitors; AMP is an activator of phosphofructokinase (key glycolysis enzyme).

Photosynthesis (Chapter 10)

Autotrophs vs. Heterotrophs

Autotrophs: Organisms that produce their own food (e.g., plants).
Photoautotrophs: Use light energy to synthesize organic molecules.
Heterotrophs: Obtain food by consuming other organisms.
Producers: Autotrophs; Consumers: Heterotrophs; Decomposers: Break down dead matter.

Chloroplast Structure and Function

Found mainly in leaf cells.
Thylakoids: Membranous sacs; site of light reactions.
Stroma: Fluid surrounding thylakoids; site of Calvin cycle.
Veins: Transport water and nutrients.

Photosynthesis Equation and Redox

Net equation:
CO2 is reduced to glucose; H2O is oxidized to O2.
O2 comes from water, not CO2.

Stages of Photosynthesis

Light reactions: Occur in thylakoid membranes; convert light energy to ATP and NADPH; split water, releasing O2.
Calvin Cycle: Occurs in stroma; uses ATP and NADPH to convert CO2 to G3P (a sugar).
NADP+: Electron carrier reduced to NADPH in light reactions.
Photophosphorylation: ATP synthesis using light-driven chemiosmosis in chloroplasts.

Calvin Cycle Details

CO2 is fixed in the stroma; three phases: carbon fixation, reduction, regeneration of RuBP.
Rubisco: Enzyme that fixes CO2.
For every 3 CO2 molecules, 1 G3P is produced.

Pigments and Spectra

Chlorophyll a: Main pigment; absorbs blue-violet and red light.
Chlorophyll b: Accessory pigment; broadens absorption spectrum.
Carotenoids: Accessory pigments; protect against excess light.
Absorption spectrum: Wavelengths absorbed by pigments.
Action spectrum: Wavelengths most effective for photosynthesis.

Electron Flow in Photosynthesis

Linear electron flow: Both photosystems; produces ATP and NADPH.
Cyclic electron flow: Only photosystem I; produces ATP but not NADPH or O2.
Photosystem II functions first; electrons excited by light, transferred to primary electron acceptor.

Chemiosmosis: Chloroplasts vs. Mitochondria

Feature	Chloroplasts	Mitochondria
Energy Source	Light	Food molecules
Location of H+ Gradient	Thylakoid space	Intermembrane space
ATP Synthesis Site	Stroma	Matrix
Final Electron Acceptor	NADP+	O2

Stomata and Plant Types

Stomata: Pores on leaf surface; allow gas exchange.
C3 plants: Use Calvin cycle directly; susceptible to photorespiration.
C4 plants: Use spatial separation to minimize photorespiration.
CAM plants: Use temporal separation; open stomata at night.
Photorespiration: Process where Rubisco adds O2 instead of CO2, reducing efficiency.

The Cell Cycle and Mitosis (Chapter 12)

Phases of the Cell Cycle

Interphase: G1 (growth), S (DNA synthesis), G2 (preparation for mitosis).
M phase: Mitosis and cytokinesis.

Mitosis Stages and Spindle Movements

Prophase: Chromosomes condense; spindle forms.
Prometaphase: Nuclear envelope fragments; spindle attaches to kinetochores.
Metaphase: Chromosomes align at metaphase plate.
Anaphase: Sister chromatids separate to opposite poles.
Telophase: Nuclear envelopes reform; chromosomes decondense.

Cytokinesis

Animals: Cleavage furrow forms; cell pinches in two.
Plants: Cell plate forms; new cell wall divides cell.

Binary Fission

Prokaryotic cell division; DNA replicates, cell splits in two.

Cell Cycle Checkpoints

Checkpoints: Control points where stop/go signals regulate the cycle (e.g., G1, G2, M).
Failure can lead to uncontrolled division (cancer).
Cyclins and Cdks (cyclin-dependent kinases): Proteins that regulate progression through the cycle.

Cancer and Cell Cycle Regulation

Cancer: Uncontrolled cell division due to checkpoint failures.
Density-dependent inhibition: Normal cells stop dividing when crowded; lost in cancer cells.
Anchorage-dependent inhibition: Normal cells must be attached to a substrate to divide; lost in cancer cells.

Additional info: For visualizing mitosis, refer to Figure 12.15 in your textbook or online animations for a step-by-step depiction of chromosome and spindle dynamics.