Biology: Cells and Passage of Substances

This set of vocabulary flashcards covers the fundamental concepts of cell biology, organizational levels of living organisms, and the primary methods of substance transport including diffusion, osmosis, and active transport.

Cell

The basic structural and functional unit of all known living organisms; the smallest unit of life and the "building block of life."

Unicellular Organism

An organism made up of only one cell that carries out all the functions needed by the organism.

Multicellular Organism

An organism composed of many cells.

Tissue

A group of similar cells working together to perform a particular function.

Organ

A group of different tissues working together to perform a particular function.

Organ System

A group of organs performing several closely related functions.

Diffusion

The random movement of molecules, atoms, and ions from a region of their higher concentration to a region of their lower concentration, down a concentration gradient until an equilibrium is achieved.

Concentration Gradient

The difference in concentration of a particular substance in one region compared to another region.

Equilibrium

A state reached when molecules are evenly distributed throughout a solution.

Selectively Permeable Membrane

A membrane that allows some substances to move through while others cannot pass; the cell membrane is described as being "picky" about what enters and leaves.

Osmosis

The passage of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

Water Potential ($\Psi$)

A measure of the tendency of water molecules to move; represented by the symbol $\Psi$, where a dilute solution has a high water potential and a concentrated solution has a low water potential.

Hypotonic Solution

A weak or dilute solution characterized by a high water potential ($\Psi$).

Hypertonic Solution

A strong or concentrated solution characterized by a low water potential ($\Psi$).

Endosmosis

The process where water moves into a cell by osmosis, occurring when a cell is placed in a hypotonic solution.

Exosmosis

The process where water moves out of a cell by osmosis, occurring when a cell is placed in a hypertonic solution.

Turgid

A state in plant cells where the vacuole swells and gains water, making the cell firm, while the rigid cell wall prevents it from bursting.

Active Transport

The movement of ions or substances from a region of their lower concentration to a region of their higher concentration against a concentration gradient.

Stomata

Pores at the surface of leaves through which carbon dioxide ($CO_2$) and oxygen ($O_2$) diffuse for photosynthesis and gaseous exchange.

Alveoli

Structures in the lungs where oxygen ($O_2$) diffuses from a high concentration into the blood and carbon dioxide ($CO_2$) diffuses from the blood into the air.

Root Hair Cell

A specialized plant cell with a long extension to increase surface area for the absorption of water and mineral ions from the soil.

Palisade Cell

A specialized plant cell that is the main site of photosynthesis, containing many chloroplasts for trapping light.

Xylem Cell

A specialized plant cell that transports water and minerals; it is a dead, hollow cell with no end walls to ensure no obstruction to flow.

Red Blood Cell

A specialized animal cell that lacks a nucleus and contains haemoglobin to transport oxygen to all body cells.

Motor Nerve Cell

A specialized animal cell with a long axon insulated by a myelin sheath to transmit electrical impulses to effectors.

Chloroplast

A membrane-bound organelle containing chlorophyll found in plant cells, used as the site for photosynthesis.

Vacuole

A membrane-bound organelle used for storage; plant cells typically have one large permanent vacuole, while animal cells may have small temporary vacuoles.