IBDP Biology (2025+): Cells SL only

Centriole

a small cylindrical organelle which occur in pairs; located near the nucleus in animal cells; involved in the production of spindle fibres during cell division.

Centrosome

organelle situated near the nucleus in animal cells, involved in the formation of the spindle prior to nuclear division.

Chloroplast

organelle that is the site of photosynthesis and contains chlorophyll.

Contractile vacuole

a small vesicle in the cytoplasm of many freshwater protists that expels excess water.

Cytoplasm

fluid that fills each cell and is enclosed by the plasma membrane.

Cytoskeleton

a microscopic network of protein filaments and tubules in the cytoplasm that give cells shape and which are for internal organization.

Differentiation

process by which cells become specialized, when some genes and not others are expressed in a cell's genome.

Electron microscope (EM)

microscope in which a beam of electrons replaces light so the powers of magnification and resolution are correspondingly much greater.

Endoplasmic reticulum

system of branching membranes in the cytoplasm of eukaryotic cells, existing as rough ER (with ribosomes) or as smooth ER (without ribosomes).

Eukaryote

group of organisms that have a nuclear membrane surrounding their genetic material, i.e., they have a true nucleus.

Extracellular matrix (ECM)

a large network of proteins and other molecules that surround, support and give structure to cells and tissues in the body.

Egg/ovum (plural, ova)

a female gamete.

Embryo

an organism in the earliest stages of growth, when its basic structures are being formed.

Embryonic stem cell

undifferentiated cell in early-stage embryo, capable of continual cell division and of developing into all the cell types of an adult organism.

Flagellum (plural, flagella)

a long, thin structure occurring singly or in groups on some cells and tissues; used to propel unicellular organisms and to move liquids past anchored cells (flagella of prokaryotes and eukaryotes have a different internal structure).

Freeze etching

preparation of specimens for electron microscope examination by freezing, fracturing along natural structural lines and preparing a replica.

Gamete

a haploid male or female sex cell that is able to unite with another of the other sex to form a zygote.

Golgi apparatus

a stack of flattened membranes in the cytoplasm, involved in the processing, modifying and packaging of molecules.

Lysosome

membrane-bound vesicles, common in the cytoplasm, containing digestive enzymes.

Magnification

how many more times larger an object appears.

Microfilament

the thinnest class of the cytoskeletal fibres, made of solid rods of globular protein called actin.

Micro-organism

a living organism that cannot be seen by the naked eye, such as bacteria, protists and single-celled fungi.

Microtubule

tiny, hollow protein tube in cytoplasm (e.g. a component of the spindle).

Mitochondrion (pl. mitochondria)

organelle in eukaryotic cells, site of Krebs cycle and the electron-transport pathway.

Motile

capable of locomotion (whole organism movement).

Multicellular

consisting of many cells (e.g. animals, plants and most fungi).

Multinucleate

a cell that has two or more nuclei.

Multipotent

can create, maintain and repair the cells of one particular organ or tissue.

Nuclear envelope

a lipid bilayer surrounding the genetic material of the cell, containing nuclear pores that control the movement of molecules between the inside of the nucleus and the cytoplasm.

Nuclear pore

organized gaps in the nuclear membrane; exit points for mRNA.

Nucleolus

compact region of nucleus where ribosomes are synthesized.

Nucleus

largest organelle of eukaryotic cells; controls and directs the activity of the cell.

Organ

a part of an organism, consisting of a collection of tissues, having a definite form and structure, and performing one or more specialized functions.

Organelle

a unit of cell substructure.

Plasma membrane

the membrane of lipid and protein that forms the surface of cells; constructed as a fluid mosaic membrane.

Plastid

an organelle containing pigments (e.g. chloroplast).

Pluripotent

able to develop into many different types of cells or tissues in the body, except for becoming placental cells or totipotent stem cells.

Post-transcriptional modification

changes that occur to a newly transcribed mRNA, after transcription has occurred and prior to its translation into a protein.

Prokaryote

unicellular organism without a true nucleus; they have a loop of naked DNA.

Proliferation

increase in the number of cells as a result of cell growth and cell division.

Protists

eukaryotes consisting of single-celled organisms.

Resolution

the amount of detail that can be seen.

Sperm (spermatozoa)

motile male gametes of animals.

Spindle

structure formed from microtubules, associated with the movements of chromosomes in mitosis and meiosis.

Stem cell

undifferentiated cell in embryo or adult that can undergo unlimited division and can give rise to one of many different cell types.

Stem cell niche

specific microenvironments in the body that either maintain the stem cells or promote their proliferation and differentiation.

Striated

muscle tissue that is marked by alternating dark and light bands.

Tissue

collection of cells of similar structure and function.

Tonoplast

membrane around the plant cell vacuole.

Totipotent

capable of giving rise to any cell type in an organism, including making more totipotent stem cells and making the cells that become the placenta.

Ultrastructure

fine structure of cells, determined by electron microscopy.

Unicellular

consisting of a single cell (e.g. prokaryotes, protists and some fungi).

Vacuole

fluid-filled space in the cytoplasm, especially large and permanent in plant cells.

Vesicle

membrane-bound sac.

Transcription

the synthesis of messenger RNA using a DNA template.

Translation

the information of mRNA is decoded into protein (amino acid sequence).