AP Bio Unit 2

Cell Membrane

The cell membrane (plasma membrane) is primarily made of a phospholipid bilayer with proteins, cholesterol, and carbohydrates embedded or attached.

Phospholipid Bilayer

Two layers of phospholipids with hydrophilic (water-attracting) heads facing outwards and hydrophobic (water-repelling) tails facing inward.

Integral (Transmembrane) Proteins

Proteins that span the membrane and are involved in transport.

Peripheral Proteins

Proteins attached to the surface of the membrane, used for signaling or support.

Cholesterol

Embedded in the bilayer; maintains fluidity and stability of the membrane.

Glycoproteins

Proteins with carbohydrate chains; used in cell recognition.

Glycolipids

Lipids with carbohydrate chains; also involved in recognition.

Channel Proteins

Proteins that allow specific ions/molecules to pass through the membrane.

Carrier Proteins

Proteins that change shape to transport substances across the membrane.

Receptor Proteins

Proteins that bind to signaling molecules and trigger responses in the cell.

Passive Transport

Diffusion of a substance across a membrane with no energy investment.

Active Transport

Process that uses energy to move solutes against their gradients.

Bulk Transport

Transport across the membrane that occurs by exocytosis and endocytosis.

Eukaryotic Cells

Cells that have internal membranes that compartmentalize their functions.

Endomembrane System

System that regulates protein traffic and performs metabolic functions within the cell.

Mitochondria

Organelles that change energy from one form to another.

Chloroplasts

Organelles that change energy from one form to another, specifically in photosynthesis.

Cytoplasm

Network of fibers that organizes structures and activities in the cell.

Extracellular Components

Components and connections between cells that help coordinate cellular activities.

Cell Structure

The organization and arrangement of various components within a cell.

Carbohydrates (glycoproteins/glycolipids)

Help with cell recognition and communication.

Selective permeability

Biological membranes are selectively permeable due to the hydrophobic core of the phospholipid bilayer, which blocks polar or charged molecules, but allows small nonpolar molecules (like O₂, CO₂) to pass easily.

Transport proteins

Proteins that facilitate transport of specific ions and molecules (like glucose, Na⁺, K⁺) across the membrane.

Osmosis

Movement of water across membranes toward higher solute concentration.

Contractile vacuoles

In protists, they expel excess water.

Kidneys

In animals, they regulate water and salt through filtration and reabsorption.

Stomata regulation

In plants, it controls water loss via transpiration.

Aquaporins

Channel proteins that speed up water transport.

Endocytosis

Cell engulfs materials via vesicles.

Phagocytosis

'Cell eating' (e.g., engulfing bacteria).

Pinocytosis

'Cell drinking' (liquids).

Receptor-mediated endocytosis

Selective uptake using receptor proteins.

Exocytosis

Vesicles fuse with the membrane to export materials (e.g., hormones, neurotransmitters).

Water (H₂O)

Small and polar; moves via osmosis or through aquaporins.

Ions (Na⁺, K⁺)

Charged and hydrophilic; require channel or carrier proteins to cross the membrane.

Small nonpolar molecules (O₂, CO₂)

Can diffuse freely through the lipid bilayer.

Concentration gradients

Molecules naturally move from high concentration to low concentration (down their gradient) via simple diffusion, facilitated diffusion (through proteins), and active transport.

Osmoregulation

Ensures cells don't swell or shrink excessively.

Freshwater organisms

Expel water since their environment is hypotonic.

Saltwater organisms

Conserve water and excrete excess salts.

Terrestrial animals

Use kidneys and hormones (ADH, aldosterone) to balance water/salt.

Nucleus

Stores genetic material; site of RNA synthesis.

Ribosomes

Made of rRNA and proteins; free in cytoplasm or bound to ER.

Rough ER (RER)

Network of membranes with ribosomes.

Smooth ER (SER)

Membrane network without ribosomes.

Golgi Apparatus

Flattened membrane sacs; modifies, sorts, and packages proteins and lipids.

Chloroplasts (plants)

Double membrane; contains thylakoids and stroma; photosynthesis.

Lysosomes

Membrane-bound vesicles with enzymes; digest macromolecules and old cell parts.

Peroxisomes

Membrane-bound; contains enzymes; breaks down fatty acids, detoxifies hydrogen peroxide.

Vacuoles

Large vesicles; large central vacuole in plants; storage of water, ions, waste; plant turgor pressure.

Cytoskeleton

Protein fibers (microtubules, microfilaments); structure, transport, cell division, movement.

Plasma Membrane

Phospholipid bilayer with proteins; controls movement in/out of the cell.

Cell Wall (plants, fungi, bacteria)

Rigid structure outside plasma membrane; protection, structure, prevents overexpansion.

Surface area-to-volume ratio

A low surface area-to-volume ratio limits the rate of exchange of materials (like oxygen, nutrients, waste).

Compartmentalization

Internal membranes increase efficiency by isolating reactions; allows for simultaneous processes.

Endosymbiotic theory

Explains that mitochondria and chloroplasts were once free-living prokaryotes engulfed by a larger ancestral cell.

Supporting Evidence for Endosymbiotic theory

Mitochondria and chloroplasts have their own DNA (circular, like bacteria), have double membranes, replicate via binary fission, and have prokaryote-like ribosomes.