Science · Grades 6–10
Cells and cell structures · quick reference
Do not assume every cell has every organelle. Bacterial cells have ribosomes but no membrane-bound nucleus.
Key terms at a glance
Cell membrane
The selectively permeable boundary around a cell.
Cytoplasm
The cell contents inside the membrane, excluding the nucleus in a eukaryotic cell.
Nucleus
The membrane-bound structure that contains most DNA in a eukaryotic cell.
Ribosome
The cellular structure where proteins are assembled.
Mitochondrion
An organelle where much aerobic cellular respiration occurs in eukaryotes.
Chloroplast
An organelle that carries out photosynthesis in plants and algae.
Cell wall
A relatively rigid layer outside the cell membrane in plants, fungi and many microbes.
Vacuole
A membrane-bound compartment used for storage and other functions in cells.
DNA
The molecule that stores hereditary information in cells.
Gene
A DNA sequence that contributes to a functional product such as an RNA or protein.
Chromosome
An organized DNA-containing structure carrying genetic information.
Prokaryote
An organism whose cells lack a membrane-bound nucleus.
Eukaryote
An organism whose cells contain a membrane-bound nucleus.
Diffusion
The net spread of particles from higher to lower concentration due to random motion.
Osmosis
The net movement of water across a selectively permeable membrane toward lower water potential.
Active transport
Membrane transport that requires energy to move substances against an electrochemical gradient.
Tissue
A group of cells working together in a particular function.
Organ
A body structure containing different tissues that work together.
Organ system
A group of organs cooperating in major body functions.
Homeostasis
Regulation that keeps internal conditions within a workable range.
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Learning preview · teacher review required. Grade bands are approximate, not official curriculum alignment.