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Slide 1

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Biology (B3) Revision…read more

Slide 2

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Exchange of materials…read more

Slide 3

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· Osmosis ­ movement of water
· Like diffusion, movement of water molecules
is random and require no energy from cell
· Osmosis diffusion of water across partially permeable
· Water moves from area of high concentration
(dilute solution) to area of low concentration
(more concentrated solution)
· Cell membrane = partially permeable…read more

Slide 4

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Active transport
· Cells may need to absorb substances which are in
short supply, i.e. against concentration
· Cells use active transport to absorb substances across
partially permeable membrane against concentration
· Active transport requires use of energy released in
· Cells able to absorb ions from dilute solution, e.g. root
hair cells absorb mineral ions from dilute solution in
soil by active transport
· Glucose can be reabsorbed in kidney tubules by active
transport…read more

Slide 5

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The sports drink dilemma
· When you exercise, muscles respire to release energy, glucose ( a sugar) used in
· After a while, body gets hot and sweat more to cool down ­ swear contains water
and mineral ions ­ if you sweat a lot body cells may become dehydrated
· If exercise for a long time may be necessary to replace sugar, mineral ions and
water been used or lost
· Sport drinks = solutions of sugar and mineral ions
· Water un drinks helps to rehydrate body cells
· Drinks designed to help balance concentration of body fluids and concentrations
inside cells ­ if drink concentration match body fluids solution is called isotonic
· Evidence for benefits of sports drinks = varied. Some sports experts think just as
good to drink water for short periods for exercise ­ drinks may hep athletes who
need replace mineral ions and sugar as well as water…read more

Slide 6

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Exchanging materials ­ the lungs
· Large = complex organisms have special exchange surfaces to
obtain all food and oxygen needed ­ soluble materials (solutes)
absorbed by intestine. Oxygen is absorbed by lungs and carbon
dioxide removed from them
· Efficient exchange surfaces have large surface are, thin walls or
short diffusion path and efficient transport system ­ blood supply in
· Lungs contain gaseous exchange surface ­ surface area of lungs is
increased by alveoli (air sacs)
· Alveoli have thin walls, large surface areas and good blood supply
· Lungs are ventilated to maintain a steep diffusion gradient
· Oxygen diffuses into many capillaries surrounding alveoli and carbon
dioxide diffuses back out into lungs to be breathed out…read more

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