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Cells, Exchange and Transport
(a) state the resolution and magnification that can be achieved by a light microscope, a transmission electron
microscope and a scanning electron microscope;
Microscope Resolution Magnification

Light 200nm X1400

Transmission 0.5nm X300000

Scanning 0.5nm X300000

SEM gives a 3d picture and cell surface structures can be…

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(f) outline the functions of the structures listed in (e);
Contains genetic information in DNA of chromosomes.
DNA is organised in genes which code for the production of proteins which control the activities of
the cell.
Makes ribosomes
Within the nucleus
Nuclear envelope,
A double membrane with nuclear…

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Helps draw water into cell by osmosis to keep it turgid
Cell wall (plant);
Mechanical support and protection
Prevents osmotic bursting
Chloroplasts (plant);
Contain chlorophyll
Absorb sunlight during photosynthesis to make glucose
Starch grains (plant);
Made up of many glucose molecules bonded together
Storage carbohydrate
(f) outline the interrelationship between…

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· Some have Flagella

Cell Membranes
(a) outline the roles of membranes
at the surface of cells;
o Separate cell contents from the outside environment
o Control entry and exit of molecules
o Permit movement of substances by exocytosis and endocytosis
o Cell recognition via cell surface antigens
o Provide…

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Stabilises the phospholipid bilayer by binding to polar heads and non-polar tails of phospholipids
Controls fluidity by preventing phospholipids solidifying at low temperatures and become too fluid at high
Reduces permeability and makes the barrier more complete, preventing molecules like water and ions from
passing through the membrane.…

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o eg. cytokines
o Insulin and glucagon do not cross cell membranes as they are large and polar. Glycoprotein receptor
molecules on the cell surface detect insulin
o Steroid are fat-soluble, so they cross the phospholipid bilayer and interact with receptors inside cells.

(g) explain the role of membrane-bound receptors…

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movement of sucrose out of sieve tube at sink
Membrane folds in, engulfing molecules
Triggered by binding of molecule to receptor site
Fuses with itself and pinches off
Formation of vesicle
Vesicle moves through cytoplasm via network of microtubules
Requires ATP
Substance packaged by Golgi apparatus are delivered…


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