Levels of Organisms and Cell Structure Vocabulary

Vocabulary definitions for IGCSE Biology Unit 2 covering cellular organization, organelles, specialised animal and plant cells, stem cell types, and therapeutic cloning.

Organelle

A subcellular component within a cell that carries out a specific task or process.

Cell

The basic functional and structural unit in a living organism.

Tissue

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

Organ

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

Organ System

A group of organs with related functions working together to perform body functions within an organism.

Unicellular Organism

An organism that is made up of only a single cell.

Multicellular Organism

An organism made up of collections of many cells.

Cell Membrane

A subcellular structure that encloses the cell and controls what enters and leaves.

Cytoplasm

A jelly-like structure inside the cell membrane where chemical reactions occur.

Nucleus

An organelle in eukaryotic cells that contains genetic material.

Mitochondria

Organelles within the cytoplasm that serve as the site of aerobic respiration.

Ribosomes

Very small organelles where protein synthesis takes place.

Cell Wall

An outer layer made of cellulose present in plant cells that gives the cell shape and protection.

Chloroplast

A plant organelle that contains chlorophyll and is the site of photosynthesis.

Permanent Vacuole

A large organelle in plant cells filled with cell sap that expands to push cytoplasm against the cell wall, maintaining turgidity.

Vesicle

An organelle used to transport substances within the cell.

Turgidity

The firm, swollen state of a plant cell created when the vacuole pushes against the cell wall, enabling a high surface area to volume ratio for sunlight absorption.

Cell Differentiation

The process by which an unspecialised cell develops specific structural characteristics and subcellular composition to perform a specific function.

Stem Cell

An undifferentiated or unspecialised cell capable of dividing infinitely and giving rise to differentiated specialised cell types.

Totipotent Stem Cell

A fully undifferentiated stem cell capable of differentiating into all cell types, including extraembryonic structures such as the placenta and umbilical cord.

Pluripotent Stem Cell

An embryonic stem cell that can differentiate into all body cell types except extraembryonic tissues like the placenta and umbilical cord.

Multipotent Stem Cell

An adult stem cell with limited differentiation ability that can give rise to two or more specific types of cells.

Unipotent Stem Cell

A stem cell that has the ability to differentiate into only one specific cell type.

Ciliated Epithelial Cell

A specialised animal cell with hair-like extensions (cilia) that beat to sweep mucus and trapped particles up to the throat.

Acrosome

A cap-like organelle located in the head of a sperm cell containing digestive enzymes to penetrate the egg cell wall.

Myelin Sheath

A fatty covering on the axon of a nerve cell (made from Schwann cells) that insulates the cell and speeds up nerve impulse transmission.

Root Hair Cell

A specialised plant root epidermal cell with a extended surface area and thin walls for absorbing water and mineral ions from the soil.

Xylem Vessel

A hollow plant tissue made of dead cells with lignin-thickened walls, specialized for conducting water continuously and supporting the plant.

Lignin

A tough substance that thickens the walls of xylem vessels, providing structural support to the plant and preventing water leakage.

Palisade Mesophyll Cell

A column-shaped leaf cell packed with chloroplasts and positioned under the upper epidermis to maximize sunlight absorption for photosynthesis.

Meristem Cells

Unspecialised totipotent cells located in the growing tips of plant roots and shoots that can divide to generate an entire new plant.

Therapeutic Cloning

A process where an embryo is created using the patient's own genetic material to produce matching stem cells that will not be rejected by the immune system.