Unit 3 Biology

Study Guide

cell membrane

A selectively permeable barrier that regulates what enters and exits the cell; made of a phospholipid bilayer with embedded proteins.

cell wall

A rigid outer layer made of cellulose that provides structure and protection (only in plant cells)

capsule

A protective outer layer found in some prokaryotic cells (bacteria); helps prevent dehydration and shields the cell from the host's immune system

centriole

Structures involved in cell division; found in animal cells

chloroplast

The organelle in plant cells where photosynthesis occurs, converting sunlight into chemical energy (glucose).

cytoplasm

The jelly-like substance inside the cell that holds organelles and is the site of many chemical reactions

cytoskeleton

A network of protein fibers that provide shape, support, and movement for the cell

endoplasmic reticulum

A network of membranes involved in protein and lipid synthesis

flagellum

A long, whip-like structure that helps a cell move; found in some animal cells (e.g., sperm cells) and many prokaryotic cells like bacteria

Golgi apparatus

Modifies, packages, and ships proteins and lipids to their destinations in vesicles.

lysosome

A vesicle filled with digestive enzymes that break down waste, worn-out cell parts, and invading bacteria (mainly in animal cells)

mitochondria

The powerhouse of the cell; organelle responsible for producing ATP through cellular respiration.

nucleoid

The region in a prokaryotic cell where the DNA is located; not surrounded by a membrane, unlike the nucleus in eukaryotic cells

nuclear membrane

A double-layered membrane that surrounds the nucleus in eukaryotic cells; contains nuclear pores that regulate the movement of materials in and out of the nucleus

nucleolus

A dense region inside the nucleus where ribosomes are made

nucleus

The control center of the cell; contains DNA and directs cell activities

organelle

A specialized structure within a cell that performs a specific function (e.g., nucleus, mitochondria, ribosomes)

pilus

Hair-like structures on the surface of some prokaryotic cells that help with attachment to surfaces and the transfer of genetic material during conjugation

plasmid

A small, circular piece of DNA in prokaryotic cells that is separate from the main chromosome; often contains genes for antibiotic resistance and can be transferred between bacteria

plastid

A group of organelles found in plant cells and some protists; includes chloroplasts (photosynthesis), chromoplasts (pigment storage), and leucoplasts (starch storage)

ribosome

The site of protein synthesis; found in the cytoplasm or attached to the rough ER

vacuole

A membrane-bound sac is used for storage of water, nutrients, and waste. Plant cells have a large central vacuole, while animal cells have smaller vacuoles

vesicle

A small sac that transports materials within the cell

diffusion

The movement of molecules from an area of high concentration to an area of low concentration without energy input

osmosis

The diffusion of water across a selectively permeable membrane from an area of low solute concentration to high solute concentration

active transport

The movement of molecules across a membrane using energy (ATP), often against the concentration gradient (low to high)

Passive Transport

The movement of molecules across a membrane without energy input, including diffusion, facilitated diffusion, and osmosis

endocytosis

A process where the cell engulfs material into a vesicle to bring it inside

exocytosis

The process of releasing substances from the cell by fusing a vesicle with the membrane

ATP

The main energy carrier of the cell, providing energy for cellular processes

cellular respiration

The process that breaks down glucose to produce ATP; occurs in mitochondria

photosynthesis

The process by which plants convert sunlight into chemical energy

enzyme

A protein that speeds up chemical reactions by lowering activation energy

substrate

The specific reactant that an enzyme acts upon

Hypotonic Solution

A solution with a lower solute concentration than the cell, causing water to enter and the cell to swell

Hypertonic Solution

A solution with a higher solute concentration than the cell, causing water to leave and the cell to shrink

Isotonic Solution

A solution where the solute concentration is equal inside and outside the cell, resulting in no net water movement

Facilitated Diffusion

the passive movement of molecules across a membrane through protein channels

prokaryotic cell

A simple cell without a nucleus or membrane-bound organelles (e.g., bacteria)

eukaryotic cell

A complex cell with a nucleus and membrane-bound organelles (e.g., plant and animal cells)