Organelles

Key Knowledge:

The structure and specialisation of plant and animal cell organelles for distinct functions, including chloroplasts and mitochondria

Organelles are specialised sub-structures within a cell that serve a specific function (i.e. organelle = ‘little organ’)

Prokaryotic cells do not typically possess any membrane-bound organelles, whereas eukaryotic cells possess several

Universal Organelles (prokaryotes and eukaryotes)

	Ribosomes
	Structure: Two subunits made of RNA and protein; larger in eukaryotes (80S) than prokaryotes (70S) Function: Provides internal structure and mediates intracellular transport (less developed in prokaryotes)

	Cytoskeleton
	Structure: A filamentous scaffolding within the cytoplasm (fluid portion of the cytoplasm is the cytosol) Function: Provides internal structure and mediates intracellular transport (less developed in prokaryotes)

	Plasma Membrane
	Structure: Phospholipid bilayer embedded with proteins (not an organelle per se , but a vital structure) Function: Semi-permeable and selective barrier surrounding the cell

Eukaryotic Organelles (animal and plant cells)

	Nucleus
	Structure: Double membrane structure with pores; contains an inner region called a nucleolus Function: Stores genetic material (DNA) as chromatin; nucleolus is site of ribosome assembly

	Endoplasmic Reticulum
	Structure: A membrane network that may be bare (smooth ER) or studded with ribosomes (rough ER) Function: Transports materials between organelles (smooth ER = lipids ; rough ER = proteins)

	Golgi Apparatus
	Structure: An assembly of vesicles and folded membranes located near the cell membrane Function: Involved in the sorting, storing, modification and export of secretory products

	Mitochondrion
	Structure: Double membrane structure, inner membrane highly folded into internal cristae Function: Site of aerobic respiration (ATP production)

	Peroxisome
	Structure: Membranous sac containing a variety of catabolic enzymes Function: Catalyses breakdown of toxic substances (e.g. H2O2) and other metabolites

	Centrosome
	Structure: Microtubule organising centre (contains paired centrioles in animal cells but not plant cells) Function: Radiating microtubules form spindle fibres and contribute to cell division (mitosis / meiosis)

Plant Organelles (not found in animal cells)

	Chloroplast
	Structure: Double membrane structure with internal stacks of membranous discs (thylakoids) Function: Site of photosynthesis – manufactured organic molecules are stored in various plastids

	Cell Wall
	Structure: External outer covering made of cellulose (not an organelle per se , but a vital structure) Function: Provides support and mechanical strength; prevents excess water uptake

	Vacuole (large and central)
	Structure: Fluid-filled internal cavity surrounded by a membrane (tonoplast) Function: Maintains hydrostatic pressure (animal cells may have small, temporary vacuoles)

Animal Organelles (not found in plant cells – although this is debatable)

	Lysosome
	Structure: Membranous sacs filled with hydrolytic enzymes Function: Breakdown / hydrolysis of macromolecules (plant cells may have a comparable structure)

Brent Cornell