Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Contents
1 Exchange of Materials 3
2 Transporting Substances Around the Body 9
3 Microbiology 16
End of Unit Questions 22
Copyright © 2009 Daniel Holloway
Significant contribution Nelson Thornes AQA Science [GCSE Biology]
2…read more

Page 3

Preview of page 3

Here's a taster:

Active Transport
Two of the main ways in which diffused substances are transported across cells are osmosis
and diffusion. Diffusion is the movement of a fluid across a concentration gradient useful to
the cells; osmosis is the movement of water across a semi-permeable membrane. However,
sometimes substances need to be transported against a concentration gradient or
membrane, which is when active transport takes place.
By active transport, cells are able to move substances from an area of low concentration to
an area of high concentration.…read more

Page 4

Preview of page 4

Here's a taster:

Active transport is an important process in plants. The uptake of mineral ions through the
soil requires active transport because the ions are found in very dilute solutions, whereas
the solution inside the plant cells is a lot stronger. This means the ions have to be taken in
against the gradient (from dilute to concentrated). Glucose is moved out of the gut and
kidney into your blood, even though that is against a gradient.…read more

Page 5

Preview of page 5

Here's a taster:

The diagram here shows an alveolus (singular of alveoli). It has been adapted to make
gaseous exchange as efficient as possible in the following ways:
spherical shape gives large surface area
moist surface makes diffusion easy as gases can dissolve
thin walls make diffusion easy
good bloody supply (explained before)
The following table shows the effectiveness of the gas exchange in the lungs:
Air Breathed In Air Breathed Out
Nitrogen, N Approx 80% Approx 80%
Oxygen, O 20% 16%
Carbon Dioxide, CO2 0.…read more

Page 6

Preview of page 6

Here's a taster:

The lining of the small intestine is folded into thousands of tiny villi (above). These greatly
increase the uptake of digested food by diffusion. This is because only a certain amount of
digested food molecules can diffuse over a certain surface area at a given time ­ so the villi
increase the surface area dramatically.…read more

Page 7

Preview of page 7

Here's a taster:

This also prevents water loss, much
like plant stomata. Spiracles lead to a tube system which delivers the oxygen straight to the
tissues where it is needed. Most of the gas exchange takes place in the tracheoles, tiny
tubes which are freely permeable to gases. They are moist and constantly have air pumped
in and out of them by the insect to maintain a steady concentration gradient.
Material Exchange in Plants
All plants require carbon dioxide and water for photosynthesis.…read more

Page 8

Preview of page 8

Here's a taster:

Transpiration
The loss of water vapour through the surface of
the leaves is called transpiration. As water is lost
through the opening in stomata, more water is
pulled up through the xylem to take its place. This
constant movement of water around the plant is
known as the transpiration stream. Because it is
all caused by evaporation, anything affecting
evaporation on a plant will also affect
transpiration. Factors which increase evaporation
will also increase transpiration.…read more

Page 9

Preview of page 9

Here's a taster:

The Circulatory System
The blood circulation system we have is made up of three main
components: blood vessels, the heart and the blood. It is made up
of two different blood systems ­ a double circulation. The diagram
shows that one transports blood from the heart to the lungs and
back again, the other takes blood around the rest of the body.…read more

Page 10

Preview of page 10

Here's a taster:

The veins carry blood towards the heart, usually low in oxygen and hence are deep purple-
red in colour. No pulse in veins, but they do contain valves usually which prevent the
backflow of blood.
The capillaries are found in junctions between the arteries and veins. These are found in
huge networks. The walls are a single cell thick so that substances which need to get out of
the blood and into body cells can easily via diffusion.…read more

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »