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Biology Unit 3




Leaves

Carbon dioxide diffuses into the air spaces within the leaf. It then diffuses into the cells for
photosynthesis. (6CO2 + 6H2O -> C6H12O6 + 6O2)

The underneath of the leaf is an exchange surface. It's covered with little holes called stomata which
the carbon dioxide diffuses…

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Biology Unit 3




The area inside the leaf forms another exchange surface which increases the area of the surface so
more carbon dioxide can get into the cells.

The water vapour escapes from the stomata by transpiration which is where the water vapour
escapes by diffusion because there is a…

Page 3

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Biology Unit 3




Transport of water into root hairs

1. As ions are absorbed into the root hairs by active transport, the water potential lowers
2. Water will then follow along a concentration gradient into the hairs by osmosis.
3. The water then enters the xylem which travels into the…

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Biology Unit 3




Respiratory System:

The breathing system gets oxygen from the air into the bloodstream for respiration. It also gets rid
of carbon dioxide from the bloodstream. The lungs are in the thorax (the area above the diaphragm).
The lungs are protected by the rib cage. The air first…

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Biology Unit 3




Alveoli

They are small sacks at the end of bronchioles. They cause a massive increase in surface area. The
diffusion distance is very small (1 cell thick). The endothelium (wall of the capillary) is flattened. The
epithelium (alveolar wall) is flattened. The lining of the alveoli is…

Page 6

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Biology Unit 3




Absorption in the digestive system

Inside the small intestines, duodenum and ileum, there are millions and millions of tiny projections
called villi. They have a central capillary and lacteal capillary so that absorption is fast and direct. Food
is absorbed either by diffusion or active transport. The…

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Biology Unit 3




Gas Exchange in Fish

Fish use gills for gas exchange. Gills have numerous folds
that give them a very large surface area. The rows of gill
filaments have many protrusions called gill lamellae. The
folds are kept supported and moist by the water that is
continually pumped…

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Biology Unit 3




every cell in the body. The veins then take the used, deoxygenated blood back to the heart at low
pressure. However, the pulmonary vein is an exception.




Single circulatory systems

Blood passes once through the heart for one trip around the body. Fish, amphibians and reptiles have…

Page 9

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Biology Unit 3




2. The use of Stents

Stents are narrow tubes capable of supplying a blood flow equivalent to an artery. Fatty deposits
building up on the inner surface of the arteries that supply blood to the heart muscles can cause
coronary heart disease. These fatty deposits restrict the…

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Biology Unit 3




Capillaries
Most exchange of nutrients and gases takes place here. Small diameter, large surface area for
diffusion
Lungs > carbon dioxide is exchanged for oxygen
Tissues > O2, CO2, nutrients and wastes are exchanged
Kidneys > wastes are released to be eliminated from body
Intestine > nutrients…

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