Cell structure, microscopy and the origin of cells

Learning objectives

State the cell theory and the functions of life carried out by a unicellular organism, and explain how atypical cells such as striated muscle fibres, aseptate fungal hyphae, mature red blood cells and phloem sieve tube elements challenge the theory

Compare prokaryotic and eukaryotic cell structure, identifying the cell wall, plasma membrane, cytoplasm, ribosomes and nucleoid of a prokaryote and the nucleus and membrane-bound organelles of a eukaryote

Distinguish light and electron microscopy in terms of magnification and resolution, calculate magnification and actual size from a scale bar or from measurements, and outline the use of freeze fracture, cryogenic electron microscopy and fluorescent stains to reveal cell structure

Explain why the surface area to volume ratio limits cell size, and relate it to the rates of exchange of materials and of heat with the surroundings

(HL) Outline the evidence for the spontaneous origin of organic molecules on the early Earth, including the Miller–Urey experiment and conditions at hydrothermal vents, and explain why a self-replicating RNA molecule and the formation of vesicles are regarded as key steps

(HL) Describe the last universal common ancestor as the organism from which all current life descends, and explain the endosymbiotic theory for the origin of mitochondria and chloroplasts using their double membranes, 70S ribosomes and circular DNA as evidence