Cell Biology: Key Concepts and Structures for Biology Students

Cell theory

The theory that all living things are made of cells, cells are the basic units of life, and all cells come from pre-existing cells.

Homeostasis

Maintenance of stable internal conditions in an organism or cell despite external changes.

Ribosome

Structure that builds proteins by linking amino acids together.

Metabolism

All of the chemical reactions that occur within an organism to maintain life.

Adenosine triphosphate (ATP)

Main energy-carrying molecule used by cells for work.

Nucleus

Organelle in eukaryotic cells that contains DNA and controls cell activities.

Cytoplasm

Jelly-like material inside a cell that holds organelles and supports chemical reactions.

Prokaryotic

Cells without a nucleus or membrane-bound organelles.

Eukaryotic

Cells that have a nucleus and membrane-bound organelles.

Domain

Highest taxonomic rank; includes Bacteria, Archaea, and Eukarya.

Bacteria

Single-celled prokaryotes that can live in diverse environments.

Archaea

Single-celled prokaryotes that often live in extreme environments.

Eukarya

Domain containing all eukaryotic organisms (animals, plants, fungi, protists).

Organelle

Specialized structure within a cell that performs a specific function.

Cytosol

Fluid portion of the cytoplasm where many metabolic reactions occur.

Surface area

Total outer area of a cell; important for nutrient and waste exchange.

Vesicle

Small membrane-bound sac that transports substances within or outside the cell.

Endomembrane system

Network of membranes (ER, Golgi, vesicles) that modify, package, and transport molecules.

Nuclear envelope

Double membrane surrounding the nucleus that controls material flow in and out.

Endoplasmic reticulum (ER)

Network of membranes; rough ER makes proteins, smooth ER makes lipids and detoxifies.

Enzyme

Protein that speeds up chemical reactions.

Golgi apparatus

Modifies, sorts, and packages proteins and lipids for storage or export.

Lysosome

Organelle containing digestive enzymes that break down waste or damaged parts.

Mitochondria

Organelle that produces ATP through cellular respiration; the cell's "powerhouse."

Cellular respiration

Process of breaking down glucose and oxygen to produce ATP, carbon dioxide, and water.

Mitochondrial matrix

Inner space of the mitochondrion where part of cellular respiration occurs.

Chloroplast

Organelle in plant cells that performs photosynthesis.

Photosynthesis

Process by which plants convert light energy into chemical energy (glucose).

Thylakoid

Flattened sacs inside chloroplasts where light reactions of photosynthesis occur.

Grana

Stacks of thylakoids inside a chloroplast.

Chlorophyll

Green pigment in chloroplasts that absorbs sunlight for photosynthesis.

Cytoskeleton

Network of protein fibers that gives cells shape, support, and movement.

Turgor pressure

Pressure of water pushing against the cell wall in plant cells, keeping them firm.

Vacuole

Storage organelle; large in plant cells (for water), small in animal cells (for waste or nutrients).

Lipid bilayer

Double-layered structure of cell membranes made of phospholipids.

Transport protein

Protein that helps substances cross the cell membrane.

Receptor protein

Protein that receives chemical signals from outside the cell.

Integral membrane protein

Protein embedded within the lipid bilayer.

Peripheral membrane protein

Protein attached loosely to the surface of the membrane.

Transmembrane protein

Protein that spans the entire cell membrane.

Glycolipid

Lipid with a carbohydrate attached; involved in cell recognition.

Glycoprotein

Protein with a carbohydrate attached; used for signaling or identification.

Fluid mosaic model

Model describing the cell membrane as a flexible layer of lipids and proteins that move freely.

Concentration gradient

Difference in concentration of a substance across a space or membrane.

Passive transport

Movement of substances across a membrane without energy input.

Facilitated diffusion

Passive transport using transport proteins to move large or charged molecules.

Channel protein

Protein that forms a pore allowing specific molecules (like ions) to pass through.

Carrier protein

Protein that changes shape to move molecules across the membrane.

Aquaporin

Channel protein that specifically allows water to move through membranes.

Active transport

Movement of substances against their concentration gradient using energy (ATP).

Primary active transport

Uses ATP directly to pump molecules across a membrane.

Secondary active transport

Uses energy stored in gradients created by primary active transport.

Exocytosis

Process where vesicles fuse with the membrane to release materials outside the cell.

Endocytosis

Process where the cell membrane engulfs materials to bring them inside.

Solute

Substance dissolved in a solution.

Molarity

Measure of solute concentration in moles per liter of solution.

Osmosis

Diffusion of water across a selectively permeable membrane.

Water potential

Potential energy of water; determines the direction water will move.

Osmotic pressure

Pressure needed to stop water from moving across a membrane by osmosis.

Tonicity

Relative concentration of solutes in two fluids separated by a membrane.

Hypertonic

Solution with higher solute concentration; water moves out of the cell.

Hypotonic

Solution with lower solute concentration; water moves into the cell.

Isotonic

Solutions with equal solute concentrations; no net water movement.

Contractile vacuole

Organelle in some protists that pumps excess water out to maintain balance.

Pressure potential

Physical pressure on water in a cell; part of total water potential.

Solute potential

Effect of solute concentration on water potential; more solute means lower potential.

Osmoregulation

Control of water and solute balance in an organism.

Symbiosis

Close relationship between two different species that live together.

Endosymbiosis

Theory that mitochondria and chloroplasts originated from free-living bacteria engulfed by early eukaryotes.

Autophagy

Process by which cells recycle or break down their own damaged components.