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

Cell Structure and Function

Microscopy

Microscopy is essential for studying cells and their components. It allows visualization of structures not visible to the naked eye.

• Light Microscopy: Uses visible light to magnify specimens up to ~1000x.

• Electron Microscopy: Uses electron beams for much higher resolution, revealing ultrastructure.

Prokaryotic vs Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their structure.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles (e.g., bacteria).

• Eukaryotic Cells: Have a nucleus and organelles (e.g., plants, animals, fungi).

Cell Size and Surface Area to Volume Ratio

Cell size is limited by the surface area to volume ratio, which affects nutrient uptake and waste removal.

• Smaller cells have a higher ratio, facilitating efficient exchange.

Structure and Function of Cell Membrane and Cell Wall

The cell membrane controls movement of substances; the cell wall provides structural support (in plants, fungi, bacteria).

• Fluid Mosaic Model: Describes the membrane as a dynamic structure of lipids and proteins.

• Cell Wall: Composed of cellulose in plants, peptidoglycan in bacteria.

Animal vs Plant Cells

Animal and plant cells share many features but differ in some organelles.

• Plant Cells: Have cell walls, chloroplasts, and large central vacuoles.

• Animal Cells: Lack cell walls and chloroplasts, have smaller vacuoles.

Compartmentalization in Eukaryotic Cells

Eukaryotic cells have membrane-bound organelles that compartmentalize functions.

• Nucleus: Contains genetic material.

• Mitochondria: Site of cellular respiration.

• Endoplasmic Reticulum: Protein and lipid synthesis.

Structure and Function of Nucleus and Ribosomes

• Nucleus: Stores DNA, coordinates cell activities.

• Ribosomes: Synthesize proteins.

Endomembrane System

The endomembrane system includes the ER, Golgi apparatus, lysosomes, and vesicles, coordinating synthesis and transport.

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

• Lysosomes: Digest cellular waste.

Cytoskeleton

The cytoskeleton provides structural support and facilitates movement.

• Microtubules, Microfilaments, Intermediate Filaments: Each has distinct roles in cell shape and transport.

Extra-cellular Matrix

The extracellular matrix surrounds animal cells, providing structural and biochemical support.

• Composed of proteins like collagen and glycoproteins.

Membrane Transport and Homeostasis

Functions of the Plasma Membrane

The plasma membrane regulates entry and exit of substances, maintaining homeostasis.

• Selective permeability allows specific molecules to pass.

Major Functions of Membrane Proteins

• Transport: Channels and carriers move substances.

• Enzymatic Activity: Catalyze reactions.

• Signal Transduction: Relay signals from outside.

• Cell Recognition: Identify cells.

• Intercellular Joining: Connect cells.

• Attachment: Anchor cytoskeleton and ECM.

Types of Membrane Transport

• Passive Transport: Movement down concentration gradient (no energy).

• Active Transport: Movement against gradient (requires energy).

Types of Passive Transport

• Simple Diffusion: Direct movement of small molecules.

• Facilitated Diffusion: Uses transport proteins.

Types of Bulk Transport

• Endocytosis: Intake of large particles.

• Exocytosis: Release of substances.

Osmosis and Water Balance

Osmosis is the diffusion of water across a membrane.

• Cells regulate water balance to prevent lysis or shrinkage.

Tonicity in Plant vs Animal Cells

• Isotonic: No net water movement.

• Hypotonic: Water enters cell; plant cells become turgid, animal cells may burst.

• Hypertonic: Water leaves cell; cells shrink.

Concentration Gradients and Potential Energy

Gradients store potential energy used for transport and cellular work.

• Active transport uses energy to maintain gradients.

Na+/K+ Pumps and Membrane Potential

The sodium-potassium pump maintains membrane potential by moving Na+ out and K+ in.

• Uses ATP to transport ions against their gradients.

Example Equation:

$\text{3 Na}^+ \text{ out} / \text{2 K}^+ \text{ in per ATP hydrolyzed}$

Cellular Metabolism and Energy

Catabolic vs Anabolic Reactions

Metabolism includes catabolic (breakdown) and anabolic (synthesis) reactions.

• Catabolic: Release energy by breaking down molecules.

• Anabolic: Consume energy to build molecules.

Exergonic vs Endergonic Reactions

• Exergonic: Release energy ($\Delta G < 0$).

• Endergonic: Require energy input ($\Delta G > 0$).

Kinetic vs Potential Energy

• Kinetic Energy: Energy of motion.

• Potential Energy: Stored energy (e.g., in gradients).

First and Second Laws of Thermodynamics

• First Law: Energy cannot be created or destroyed.

• Second Law: Entropy (disorder) increases in closed systems.

Gibbs Free Energy

Gibbs free energy ($G$) determines spontaneity of reactions.

$\Delta G = \Delta H - T\Delta S$

• Negative $\Delta G$ indicates a spontaneous reaction.

ATP Structure and Function

ATP is the cell's energy currency, powering cellular work.

• Hydrolysis of ATP releases energy.

Enzyme Structure and Function

Enzymes are biological catalysts that speed up reactions by lowering activation energy.

• Specificity due to active site shape.

• Affected by temperature, pH, and inhibitors.

Environmental Effects on Enzymes

• Extreme conditions can denature enzymes, reducing activity.

Cellular Respiration and Photosynthesis

Relationship Between Respiration and Photosynthesis

Photosynthesis converts light energy to chemical energy; respiration releases energy from food.

• Photosynthesis: Occurs in chloroplasts, produces glucose and O2.

• Respiration: Occurs in mitochondria, uses glucose and O2 to produce ATP.

Summary Equation for Cellular Respiration

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Oxidation vs Reduction

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

Function of NAD+ in Cellular Respiration

NAD+ acts as an electron carrier, becoming NADH when reduced.

• Transfers electrons to the electron transport chain.

Stages of Cellular Respiration

• Glycolysis

• Krebs Cycle (Citric Acid Cycle)

• Electron Transport Chain and Oxidative Phosphorylation

Substrate-Level vs Oxidative Phosphorylation

• Substrate-Level: Direct transfer of phosphate to ADP.

• Oxidative: Uses electron transport chain and ATP synthase.

Aerobic vs Anaerobic Metabolism

• Aerobic: Requires oxygen, yields more ATP.

• Anaerobic: No oxygen, less ATP (e.g., fermentation).

Energy Yields: Aerobic Respiration vs Fermentation

Process	ATP Yield (per glucose)
Aerobic Respiration	~30-32
Fermentation	2

Photosynthesis

Location and Structure of Chloroplasts

Photosynthesis occurs in chloroplasts, which contain thylakoids and stroma.

• Thylakoids: Site of light reactions.

• Stroma: Site of Calvin cycle.

Summary Equation for Photosynthesis

$6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

Redox Equations for Photosynthesis

• CO2 is reduced to glucose.

• H2O is oxidized to O2.

Stages of Photosynthesis

• Light Reactions: Convert light energy to chemical energy (ATP, NADPH).

• Calvin Cycle: Uses ATP and NADPH to fix CO2 into glucose.

Roles and Structures of Leaves

• Leaves maximize light absorption and gas exchange.

Light's Wave and Particle Nature

• Light behaves as both waves and particles (photons).

Electromagnetic Spectrum and Visible Light

• Visible light: 400-700 nm, used in photosynthesis.

Functions and Types of Pigments

• Chlorophyll a: Main pigment.

• Chlorophyll b, Carotenoids: Accessory pigments.

Light Reactions of Photosynthesis

• Involve photosystems (PSII and PSI), electron transport, and ATP/NADPH production.

P680 vs P700

• P680: Reaction center of PSII.

• P700: Reaction center of PSI.

Cyclic vs Non-Cyclic Electron Flow

• Non-Cyclic: Produces ATP and NADPH.

• Cyclic: Produces only ATP.

Oxidative vs Photophosphorylation

• Oxidative: In mitochondria, uses O2.

• Photophosphorylation: In chloroplasts, uses light.

Calvin Cycle Phases and Functions

• Carbon Fixation: CO2 attached to RuBP.

• Reduction: ATP/NADPH used to form G3P.

• Regeneration: RuBP regenerated.

Role of RuBP and Rubisco

• RuBP: CO2 acceptor.

• Rubisco: Enzyme catalyzing carbon fixation.

Roles of ATP and NADPH in Calvin Cycle

• Provide energy and reducing power for synthesis of sugars.

Fate of Reactants of Photosynthesis

• CO2 becomes glucose.

• H2O provides electrons and protons.

Producers vs Consumers

• Producers: Autotrophs (plants, algae) make their own food.

• Consumers: Heterotrophs (animals, fungi) eat other organisms.

Photorespiration

Photorespiration occurs when Rubisco binds O2 instead of CO2, reducing photosynthetic efficiency.

C3 vs C4 vs CAM Plants

Type	CO2 Fixation	Adaptation
C3	Directly via Calvin cycle	Most plants; less efficient in hot, dry climates
C4	CO2 fixed in mesophyll, Calvin cycle in bundle sheath	Adapted to high light, temperature
CAM	CO2 fixed at night, Calvin cycle during day	Adapted to arid environments

Example: Corn is a C4 plant; cactus is a CAM plant.