# OCR AS BIOLOGY - F211 - Module 1 - Cells

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• Created on: 18-01-13 11:31

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AS UNIT F211: CELLS, EXCHANGE AND TRANSPORT
MODULE 1: CELLS
(a) State the resolution and magnification that can be achieved by a light microscope, a
transmission electron microscope and a scanning electron microscope
Light microscope ­
Resolution ­ 200nm
Magnification ­ x1500
Transmission electron microscope
Resolution ­ 0.1nm
Magnification ­ x500,000
Scanning electron microscope produces 3D image
Resolution ­ 0.1nm
Magnification ­ x100,000
(b) Explain the difference between magnification and resolution
Magnification is the degree to which the size of an image is larger than the actual size of the
object itself.
Resolution is the degree to which it is possible to distinguish between two objects that are close
together. So the higher the resolution, the greater the detail that can be seen).
(c) Explain the need for staining samples for use in light microscopy and electron microscopy
A lot of biological material is not coloured, so details cannot be seen when looking through
microscopes meaning it will be difficult to distinguish between different features.
For a light microscope, specimens can be stained using dye which would be taken up more by
denser parts that less dense, which would show a contrast.
For an electron microscope, objects are dipped in heavy metals such a led. Metal ions scatter
across the specimen which creates an image.
(d) Calculate the linear magnification of an image
Image size = actual size x magnification
Magnification = image size / actual size
Actual size = image size / magnification

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Describe and interpret drawings and photographs of eukaryotic cells as seen under an
electron microscope and be able to recognise the following structures:
(f) outline their functions
Nucleus:
Surrounded by nuclear envelope which contains pores
Inside is nucleolus and chromatin
Chromatin is made from DNA and controls cells activities
Pores allow substances to leave the nucleus e.g.…read more

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Small, round, membranebound organelle
Contains digestive enzymes which can be used to digest invading cells e.g in
phagocytosis.
Chloroplast:
Found in plant cells
Stacked up thylakiod membranes to form granum
Site of photosynthesis
Cell membrane:
Found on the surface of animal cells and inside the cell walls of plant cells.
Made mainly of lipids and proteins
Regulates movement of substances into and out of the cell
Has receptor molecules
Cilia:
Hairlike structures found on the surfaces of many cells.…read more

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To support the cells organelles by keeping them in place
To strengthen the cell and maintain its shape
Transporting materials eg movement of chromosomes during mitosis
Helps the cell to move ­ e.…read more

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Outline the roles of membranes within cells and at the surface of cells
Separating contents of the cell from its outside environment
Separating cell components from the cytoplasm
Cell signalling
Cell recognition
Regulating transport of materials into and out of the cell
Plasma membranes: on the surface control what leaves the cell
Membranes within organises: keep things in place such as enzymes for respiration in the
mitochondria
(b) State that plasma (cell surface) membranes are partially permeable barriers
All membranes are permeable to water molecules.…read more

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Allow small or charger particles to go across the membrane (molecules that are too large to
diffuse through, or hydrophilic molecules)
Carrier proteins:
Actively transport molecules across the membrane
Glycolipids and Glycoproteins:
Help to stabilise the membrane
Receptor sites for drugs, hormones and antibodies
Act as antigens
(e) Outline the effect of changing temperature on membrane structure and permeability
INCREASING THE TEMPERATURE GIVES MOLECULES MORE KINETIC ENGERGY.…read more

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An example of this is an insulin receptor.
Drugs can also bind to the receptor molecules on the cell's surface. Beta blockers are used to
prevent an increase in heart rate. These drugs are used for stressed.
Some drugs block the receptors and some drugs mimic a neurotransmitter.
(h) explain what is meant by passive transport (diffusion and facilitated diffusion including the
role of membrane proteins), active transport, endocytosis and exocytosis.…read more

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ACTIVE TRANSPORT
Moves a substance against their concentration gradient by using ATP.
Some carrier proteins can act as pumps...
They have a complementary shape to the shape of a specific molecule or ion
They carry the molecule ONE WAY across the plasma membrane
They use metabolic energy in the form of ATP which changes the shape of the protein,
ensuring a oneway flow
They are much faster than diffusion.
ENDOCYTOSIS USES ATP
The taking IN of substances.…read more

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Water potential: the tendency of water molecules to diffuse from a region of high water potential
to a region of low water potential.
When there are substances dissolved in the water, the water potential becomes more
negative, lowering it as there are not as many "free" water molecules.
(j) recognise and explain the effects that solutions of different water potentials can have upon
plant cells and animal cells
Solution of HIGH water potential
E.g. Distilled or pure water.…read more