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

Study Guide - Smart Notes

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Cell Structure and Membrane Function

Phospholipid Bilayer Structure

The phospholipid bilayer forms the fundamental structure of cell membranes, providing a semi-permeable barrier between the cell and its environment.

Phospholipids have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
Bilayer arrangement: Hydrophobic tails face inward, hydrophilic heads face outward.
Provides fluidity and flexibility to the membrane.

Fluid Mosaic Model

The fluid mosaic model describes the structure of cell membranes as a mosaic of components that move fluidly within the lipid bilayer.

Fluid: Lipids and proteins can move laterally within the layer.
Mosaic: Diverse proteins, cholesterol, and carbohydrates are embedded in the bilayer.

Membrane Transport Mechanisms

Cells exchange substances with their environment through various transport mechanisms.

Simple diffusion: Movement of small, nonpolar molecules down their concentration gradient without energy or proteins.
Facilitated diffusion: Movement of molecules down their gradient via membrane proteins (channels or carriers); no energy required.
Active transport: Movement of molecules against their gradient using energy (usually ATP) and transport proteins.

Osmosis and Solutions

Isotonic, Hypotonic, and Hypertonic Solutions

Osmosis is the movement of water across a semi-permeable membrane in response to solute concentration differences.

Isotonic solution: Solute concentration is equal inside and outside the cell; no net water movement.
Hypotonic solution: Lower solute concentration outside the cell; water enters the cell, which may swell or burst (lysis in animal cells, turgid in plant cells).
Hypertonic solution: Higher solute concentration outside the cell; water leaves the cell, causing shrinkage (crenation in animal cells, plasmolysis in plant cells).

Osmotic lysis occurs when a cell bursts due to excessive water intake in a hypotonic environment.

Plasmolysis is the shrinking of the cytoplasm away from the cell wall in plant cells in a hypertonic environment.

Enzymes and Metabolism

Endergonic and Exergonic Reactions

Chemical reactions in cells can either require energy or release energy.

Endergonic reactions: Absorb energy; products have more energy than reactants (e.g., photosynthesis).
Exergonic reactions: Release energy; products have less energy than reactants (e.g., cellular respiration).

Anabolism and Catabolism

Metabolism consists of two main types of reactions:

Anabolism: Building complex molecules from simpler ones; usually endergonic.
Catabolism: Breaking down complex molecules into simpler ones; usually exergonic.

Enzyme Activity and Inhibition

Enzymes are biological catalysts that speed up chemical reactions.

Enzyme activity: Influenced by temperature, pH, substrate concentration, and inhibitors.
Competitive inhibition: Inhibitor competes with substrate for the active site.
Non-competitive inhibition: Inhibitor binds elsewhere, changing enzyme shape and reducing activity.
Allosteric sites are regulatory sites on enzymes where molecules can bind to modulate activity.

Cellular Respiration

Redox Reactions

Cellular respiration involves a series of oxidation-reduction (redox) reactions.

Oxidation: Loss of electrons.
Reduction: Gain of electrons.
In the reaction , glucose is oxidized and oxygen is reduced.

Aerobic Respiration Steps

Aerobic respiration is the process by which cells convert glucose and oxygen into ATP, carbon dioxide, and water.

Major steps: Glycolysis, Pyruvate oxidation, Citric acid cycle (Krebs cycle), Electron transport chain, and Oxidative phosphorylation.
Electron carriers: NADH, FADH2 transport electrons to the electron transport chain.
ATP is produced mainly during oxidative phosphorylation.
Oxygen acts as the final electron acceptor in the electron transport chain.
Total ATP yield per glucose: ~30-32 ATP (most from oxidative phosphorylation).

Fermentation

Fermentation is an anaerobic process that allows ATP production without oxygen.

Occurs when oxygen is absent; pyruvate is converted to lactate (in animals) or ethanol and CO2 (in yeast).
Produces much less ATP than aerobic respiration (2 ATP per glucose).
Final electron acceptor: organic molecules (not oxygen).

Photosynthesis

Light and Dark Reactions

Photosynthesis converts light energy into chemical energy in plants, algae, and some bacteria.

Light reactions: Occur in the thylakoid membranes; use light to produce ATP and NADPH, and release O2.
Dark reactions (Calvin cycle): Occur in the stroma; use ATP and NADPH to fix CO2 into glucose.
Chlorophyll absorbs light energy, exciting electrons.
Electron flow: Water → Photosystem II → Electron transport chain → Photosystem I → NADP+ → NADPH.
Rubisco catalyzes carbon fixation in the Calvin cycle.

Photosynthesis Steps and Locations

Key events and their cellular locations:

Oxygen production: Thylakoid membrane (light reactions).
ATP production: Stroma (Calvin cycle in plants), cytoplasm (animal cells).
Electron transport: Thylakoid membrane (plants), mitochondria (animals).

Order of Photosynthesis Events

The main steps in photosynthesis, in order:

CO2 fixation
ATP production
Glucose production
Chlorophyll excitation and electron transfer
Water splitting to produce oxygen
NADPH production

Key Terms Table

Term	Definition	Example/Application
Phospholipid Bilayer	Double layer of phospholipids forming cell membranes	Plasma membrane of animal cells
Osmosis	Diffusion of water across a semi-permeable membrane	Water uptake in plant roots
ATP	Energy currency of the cell	Produced during cellular respiration
NADH/NADPH	Electron carriers in metabolism	NADH in respiration, NADPH in photosynthesis
Rubisco	Enzyme for carbon fixation in Calvin cycle	Photosynthesis in plants

Additional info: Some explanations and order of events were inferred from standard biology curriculum to ensure completeness and clarity.