Name the organelle that contains 70S ribosomes and small circular DNA in an animal cell.
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mitochondrion / mitochondria
Cells As The Basic Units Of Living Organisms
Describe the function of the rough endoplasmic reticulum and explain how its structure relates to its function.
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synthesises proteins / proteins for secretion; large surface area provided by stacked cisternae; ribosomes attached to the membrane translate mRNA; vesicles bud off to transport proteins to the Golgi body
Outline the role of the Golgi body in the secretion of a protein from a cell.
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receives vesicles containing protein from the RER; modifies the protein (e.g. adds carbohydrate to form glycoprotein); sorts and packages protein into secretory vesicles; vesicles move to and fuse with the cell surface membrane releasing protein by exocytosis
State two structural features visible on an electron micrograph that identify a chloroplast.
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double membrane / envelope; stacks of thylakoids / grana; presence of stroma; (any two)
Explain why the rough endoplasmic reticulum can be distinguished from the smooth endoplasmic reticulum on an electron micrograph.
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RER has ribosomes attached to its membrane appearing as dark dots; SER lacks these ribosomes giving a smoother appearance
State three organelles found in plant cells but not in animal cells.
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chloroplasts; cellulose cell wall; large permanent vacuole / tonoplast; plasmodesmata; (any three)
Suggest why plant cells generally do not need centrioles to divide successfully.
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spindle microtubules are organised by other microtubule-organising centres in plants; spindle still forms during mitosis without centrioles
State the molecule that supplies energy for active transport in cells.
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ATP / adenosine triphosphate
Name the process and the organelle that produce most of the ATP in eukaryotic cells.
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aerobic respiration; mitochondrion / mitochondria
State the polymer that forms the cell wall of a typical bacterium.
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peptidoglycan
Outline three features of a typical prokaryotic cell.
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unicellular; 1–5 µm in diameter; circular DNA / no true nucleus; 70S ribosomes; peptidoglycan cell wall; no membrane-bound organelles; (any three)
Compare and contrast the structure of a typical bacterial cell with that of a typical animal cell.
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both have a cell surface membrane / cytoplasm / ribosomes / DNA; bacterial cell is smaller (1–5 µm) than animal cell (10–100 µm); bacterial DNA is circular and free in cytoplasm whereas animal DNA is linear and inside a nucleus; bacteria have 70S ribosomes whereas animal cytoplasm has 80S ribosomes; bacteria lack membrane-bound organelles such as mitochondria and ER; bacteria have a peptidoglycan cell wall whereas animal cells have no cell wall; bacteria may possess plasmids; animal cells may have centrioles, lysosomes, cilia or microvilli (any six, must include similarities and differences)
Explain why the ribosomes in mitochondria are 70S rather than 80S.
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mitochondria are thought to have evolved from prokaryotic cells / endosymbiotic origin; they retain features of prokaryotes including 70S ribosomes and circular DNA
State the two components found in all viruses.
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nucleic acid (DNA or RNA) core; protein capsid
Explain why viruses are described as non-cellular.
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viruses lack a cell surface membrane / cytoplasm / ribosomes; cannot carry out metabolism / respiration independently; can only replicate inside a host cell
Some viruses possess an envelope. Describe the composition and origin of this envelope.
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made of phospholipids / phospholipid bilayer (often with glycoproteins); derived from the host cell’s surface membrane