Cells and Membranes

Active transport

Movement of molecules across a membrane using energy, usually from ATP.

Cell wall

Rigid outer layer that provides structure and protection for plant cells.

Central vacuole

Large storage sac in plant cells that holds water, nutrients, and waste.

Centriole

Cylinder-shaped organelle that helps organize cell division in animal cells.

Chloroplast

Organelle in plant cells that captures sunlight to make food by photosynthesis.

Cilia

Short, hairlike structures that move the cell or move substances around the cell.

Concentration gradient

Difference in the amount of a substance across a space or membrane.

Cotransport

Transport of two substances together across a membrane using one transport protein.

Cytoplasm

Gel-like material inside the cell where organelles are suspended.

Cytoskeleton

Network of protein fibers that gives the cell shape and helps with movement.

Cytosol

The fluid part of the cytoplasm where cell reactions occur.

Desmosomes

Strong connections that hold animal cells together like spot welds.

Diffusion

Movement of molecules from high concentration to low concentration.

Endocytosis

Process by which the cell takes in large materials by forming vesicles.

Endomembrane system

Group of membranes and organelles that work together to modify, package, and transport lipids and proteins.

Eukaryotic cell

Cell with a nucleus and membrane-bound organelles.

Exocytosis

Process where cells release materials by fusing vesicles with the cell membrane.

Extracellular matrix

Network of proteins and carbohydrates outside animal cells that provides support.

Facilitated diffusion

Movement of molecules through membrane proteins without using energy.

Flaccid

When a plant cell loses water and becomes soft or limp.

Flagella

Long, whip-like tails that help cells move.

Fluid mosaic model

Describes the flexible structure of the cell membrane made of proteins and lipids.

Gap junctions

Channels that allow communication and transport between animal cells.

Glycoprotein

Protein with attached carbohydrate chain used for cell recognition.

Golgi apparatus

Stack of membranes that modifies, sorts, and ships proteins and lipids.

Hypertonic

Solution with a higher solute concentration causing cells to lose water.

Hypotonic

Solution with a lower solute concentration causing cells to gain water.

Integral proteins

Proteins that span across the cell membrane.

Isotonic

Solution with equal solute concentration; no net water movement.

Membrane potential

Electrical charge difference across a cell membrane.

Microfilaments

Thin protein fibers that support the cell’s shape and help with movement.

Microtubules

Thick hollow tubes that help the cell maintain shape and move organelles.

Mitochondrion

Organelle that makes energy (ATP) from food.

Nucleoid region

Area in a prokaryotic cell where DNA is located.

Nucleolus

Small dense area inside the nucleus that makes ribosomes.

Nucleus

Control center of the cell that holds DNA.

Osmosis

Movement of water through a membrane from low to high solute concentration.

Passive transport

Movement of molecules without using energy.

Peripheral proteins

Proteins attached to the surface of the cell membrane.

Peroxisome

Organelle that breaks down fatty acids and detoxifies harmful substances.

Phagocytosis

“Cell eating” — cell engulfs large particles or other cells.

Pinocytosis

“Cell drinking” — cell takes in small droplets of fluid.

Plasma membrane

Flexible barrier that controls what enters and leaves the cell.

Plasmodesmata

Openings between plant cells that allow materials to pass through.

Prokaryotic cell

Cell without a nucleus or membrane-bound organelles.

Ribosome

Small structure that makes proteins.

Rough endoplasmic reticulum (ER)

Membrane system with ribosomes that makes and transports proteins.

Selective permeability

Property of membranes that lets some substances pass but not others.

Smooth endoplasmic reticulum (ER)

Membrane system without ribosomes that makes lipids and detoxifies.

Tight junctions

Seals between animal cells that prevent leakage.

Turgid

When a plant cell is full of water and firm.