Eduqas Biology for A Level Year 1 & AS: Study and Rev Guide

Organelle : a specialised structure found within eukaryotic cells that carries out a specific function for the cell. Eukaryotic cells (eukaryotes): contain DNA in chromosomes in a nucleus, and possess membrane- bound organelles, e.g. plants and animals. Resolving power: the minimum distance by which two points must be separated in order for them to be seen as two distinct points rather than a single focused image. Key Terms Pointer 1m = 1000mm 1mm = 1000μm 1 μ m = 1000nm 1.2 Cell structure and organisation Cell structure When studying cells it is important to have a concept of size, and what we use to measure structures within cells. The standard unit of measurement of length is the metre, m. This would not be appropriate to measure a cell as a typical cell would measure 0.003m. Instead we use a series of smaller measurements. Generalised structure of an animal cell Under the light microscope, only a few structures are easily visible within the cytoplasm. Using the electron microscope, many more structures called organelles are visible in eukaryotic cells. This is because the electron microscope uses electrons (rather than light), which have a much shorter wavelength and so the microscope has a greater magnification and higher resolving power . Organelles have specific roles within the cell, and are surrounded by a membrane. The membranes provide a large surface area for the transport of molecules and attachment of enzymes. Measurement Symbol How many there are in 1 metre 1 of these in metres is What it is used to measure Example metre m 1 1 larger organisms average human is 1.75m tall millimetre mm 1000 10 –3 tissues and organs skin varies between 0.5 and 4mm thick micrometre m m 1,000,000 10 –6 cells and organelles typical animal cell is 30 m m wide nanometre nm 1,000,000,000 10 –9 molecules DNA helix is 2.4nm wide 22 A Level Year 1/AS Biology: Study and Revision Guide

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