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BIOLOGY UNIT 3!!…read more

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Active Transport
· It allows cells to move substances from an area of LOW
concentration to HIGH concentration, so it moves against
the gradient.
· As a result the cell can absorb ions from very dilute
· It takes energy for active transport to take place. The active
transport system carries a molecule across the membrane
and then returns it to its original position. This energy comes
from cellular respiration.
· If a cell is making lots of energy it can carry out lots of active
· These cells include: root hair cells, and gut lining cells, these
cells normally have lots of MITOCHONDRIA.
Importance of Active Transport:
· Its used widely in cells, by using active transport, plants can
absorb mineral ion, even though its against concentration
· Some marine bird and reptiles take in lots of salt from the
water, their kidneys can't get rid of it all, they have special
salt glands, the sodium ions have to be moved against
concentration by active transport.…read more

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Exchange of gases in the lungs
The breathing system:
· Body needs constant supply of oxygen for cellular respiration.
· Lungs are found in the upper part of the body (thorax), protected by ribs. Lungs are
separated from the digestive organs by the diaphragm.
· Your ribs move up and out, diaphragm flattens when you breathe, this pulls air into your
lungs. When breathing out your ribs move down and in and the diaphragm returns to the
dome shape.
Exchange of gas in the lungs:
· Lungs are adapted to do gas exchange, they are made of clusters of alveoli. These tiny air
sacs have large surface areas, rich blood supply and moist surface, as this makes for the
most affective diffusion of gases.
· The rich blood supply maintains a concentration gradient in both directions, oxygen
constantly removed into the blood and carbon dioxide constantly removed into the lungs.
Atmospheric gas Air breathed in Air breathed out
Nitrogen 79% 79%
Oxygen 21% 16%
Carbon dioxide 0.04% 4%…read more

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Exchange in the gut
Absorption in the small intestines:
· Food molecules need to be available to your body cells, they provide fuel for respiration and
the building blocks of all tissues in your body, for this to happen they must move from your
small intestine into your bloodstream, this happens by DIFFUSION and ACTIVE TRANSPORT.
· This is why its important food is broken down into soluble form, only when molecules are
dissolved in water can diffusion take place.
· Digested food molecules are small enough to pass freely through the walls of the small
intestines into blood vessels, they move in this direction because of the concentration
· The lining of the small intestine has thousands of VILLI, these increase the uptake of digested
food by diffusion because the villi increase the surface area of the small intestine.
· The lining of the small intestines has an excellent blood supply, which carries away the
digested food molecules, so a steep concentration is maintained all the time, this makes
diffusion more rapid.
· Glucose and other dissolved food molecules are moved from the small intestine into the
blood by active transport, against the concentration gradient, this ensures that none of the
digested food is wasted and lost in faeces.…read more

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Exchange of materials in other organisms
Gas exchange in fish:
· Fish can't get oxygen directly from the water because they are covered in scales, but fish have gills.
· They are made up of many thin layers of tissue with rich blood supply, the gills are so thin so there's
only a short distance for diffusion to happen, the surfaces are always moist as they are in water!
· Bony fish gills are contained in a gill cavity, water is pumped over them constantly to maintain the
concentration gradient, some types of shark have to constantly swim so water is moving over their
· Gills don't work in air, they suffocate without water on them as the gill stacks all stick together as
there isn't a big enough surface area available for fish to get oxygen in the air.
Tadpoles and frogs:
· Frogs are amphibians, their eggs hatch in water into tadpoles which spend all their time in water.
They have external frilly gills with a large surface area and rich blood supply.
· When tadpoles turn into frogs the external gills are reabsorbed into the body of the frog
(METAMOPHOSIS). An adult has moist skin and rich blood supply and gas exchange takes place
through the skin.
· The mouth = very large, thin skinned is important for gas exchange, it has very simple lungs for when
its on land.…read more

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Exchange of materials in other organisms
The respiratory system in insects:
· Insects muscles need a lot of oxygen, no gaseous exchange can take place
through their tough outer covering, to supply their needs they have an
internal respiratory system.
· They have SPIRACLES which open and close depending on the oxygen they
need, they also prevent water loss.
· Spiracles lead into a system of tubes that run to the cells, most of the gas
exchange takes place in the TRACHEOLES, these tiny tubes are freely
permeable to gases, and are moist.
· Insects have no blood supply, the tracheoles have very large surface areas
and come into close contact with individual cells so they are very effective
at gas exchange.…read more

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really helpful. well detailed and structured, but to the point. thank you!!



This is really good. Thank you.

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