Cell Structures
Description and Function
Cell wall: An outer layer of cellulose or chitin; not found in all eukaryotes. Provide rigidity, tensile strength and structure.
Cell membrane: A phospholipid bilayer containing proteins and other molecules. A partially permeable barrier.
Nucleus: Enclosed by an envelope. Composed of two membranes perforated by pores. Contains chromosomes of DNA.
Nucleolus: A dense body within the nucleus. Assembles ribosomes.
Centrioles: Hollow cylinders made up of a ring of nine protein microtubules. The proteins are arranged in a helix to form a hollow tube. Form spindle fibres in mitosis.
Cytoplasm: Mainly water that also contains enzymes, salts, organelles and various organic molecules. Chemical reactions occur here, substances can be moved around easily.
Smooth endoplasmic reticulum: A system of interconnected membrane-bound flattened sacs. Formation of lipids and steroids.
Rough endoplasmic reticulum: A system of interconnected membrane-bound flattened sacs. Ribosomes attached to the outer surface. Formation of proteins.
Golgi apparatus: Stacks of flattened membrane-bound sacs formed by fusion vesicles from the ER. Packages proteins into vesicles.
Lysome: Vesicles containing digestive enzymes. Break down cell debris.
Mitochondria: Have a double membrane. Inner membrane folds into a structure called cristae. Fluid inside the membrane is called the matrix. Aerobic respiration.
Ribosomes: Made of RNA and protein. These small organelles are found free in the cytoplasm or attached to endoplasmic reticulum. Protein synthesis.
Chloroplasts: A structure found in eukaryotic plant cells that contain chlorophyll for photosynthesis.

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Notes for Biology Topic 3 voice of the genome. Edexcel - SNAB