Chapter 1: Cell structure
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The simplest cells are prokaryotic cells, which are thought to have evolved before, and given rise to, the much more complex and much larger eukaryotic cells. Prokaryotic cells lack a true nucleus and have smaller (70S) ribosomes than eukaryotic cells. They also lack membrane-bound organelles. Their DNA is circular and lies naked in the cytoplasm.
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All eukaryotic cells possess a nucleus containing one or more nucleoli and DNA. The DNA is linear and bound to proteins to form chromatin.
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The cytoplasm of eukaryotic cells contains many membrane-bound organelles providing separate compartments for specialised activities (division of labour). Organelles of eukaryotic cells include endoplasmic reticulum (ER), 80S ribosomes, mitochondria, Golgi apparatus and lysosomes. Animal cells also contain a centrosome and centrioles. Plant cells may contain chloroplasts, often have a large, permanent, central vacuole and have a cell wall containing cellulose.
End-of-chapter questions 1 Which one of the following cell structures can be seen with a light microscope? A mitochondrion B ribosome C rough ER D smooth ER
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2 The use of electrons as a source of radiation in the electron microscope allows high resolution to be achieved because electrons: A are negatively charged. B can be focused using electromagnets. C have a very short wavelength. D travel at the speed of light.
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3 Which one of the following structures is found in animal cells, but not in plant cells? A cell surface membrane B centriole C chloroplast D Golgi body
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4 Copy and complete the following table, which compares light microscopes with electron microscopes. Some boxes have been filled in for you. Feature source of radiation wavelength of radiation used maximum resolution lenses specimen stains image
Light microscope
Electron microscope about 0.005 nm 0.5 nm in practice
glass non-living or dead coloured dyes coloured
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