Biology Unit 3 (B3) revision notes


HideShow resource information
  • Created by: umar ali
  • Created on: 26-12-11 17:48
Preview of Biology Unit 3 (B3) revision notes

First 325 words of the document:

Biology B3 Notes(Hope They Help Leave A Comment)
Unit 1: Exchange of Materials
Unit 2: Transporting Substances Around the Body
Unit 3: Microbiology
B3-1 : Exchange of Materials
Active Transport
Two of the main ways in which diffused substances are transported across cells
areosmosis 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 transportedagainst 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 and
area of high concentration. This is what is meant by moving against the gradient. Because the
substances are being transported against a gradient, energy is required for an active transport
system to carry a molecule across the membrane and then return to its original position (see
below diagram).
The energy required for active transport to take place coms from cellular respiration. The rate
of active transport and rate of respiration in cells are closely linked. The process of respiration
releases energy ­ so in other words, the more respiration happening, the more active transport
is taking place. This is why cells involved in active transport (e.g. root hair cells and gut lining
cells) usually have a lot of mitochondria to provide the energy needed from respiration.
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

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Active transport is also used in marine birds and
reptiles, because they consume large amounts of salt when they drink water, and as the kidneys
cannot get rid of it all, they have salt glands which use active transport. Without the ability for
the cells to do active transport, these marine animals would die, so active transport is essential
to their lives.
Gaseous Exchange
We require a constant supply of oxygen to allow for respiration.…read more

Page 3

Preview of page 3

Here's a taster:

The lungs have been adapted especially for making gas exchange more efficient. They are made
up of clusters of alveoli, which are tiny air sacs with large surface areas, and are kept moist.
They also have a rich blood supply, which maintains a concentration gradient in both directions.
Carbon dioxide constantly being removed from the blood and oxygen constantly entering the
lungs means that gas exchange happens at the highest concentration gradients to make it rapid
and effective.…read more

Page 4

Preview of page 4

Here's a taster:

They move along a very steep
concentration gradient.
The lining of the small intestine is folded into thousands of tiny villi. 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 5

Preview of page 5

Here's a taster:

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. The carbon dioxide is obtained
via diffusion through the leaves. The flattened shape of the leaves increases the surface area for
diffusion to take place across.…read more

Page 6

Preview of page 6

Here's a taster:

B3-2 : Transporting Substances Around the Body
The Circulatory System
The blood circulation system we have is made up of three main components: blood vessels,
the heart and theblood. It is made up of two different blood systems ­ adouble 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 7

Preview of page 7

Here's a taster:

Theveins 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
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

Page 8

Preview of page 8

Here's a taster:

Red blood cells are the most common cell type in the human body. There are around 5 million
per each square milimetre of blood. The function of red blood cells is to pick up oxygen from the
lungs and deliver it to cells and tissues where it is needed.…read more

Page 9

Preview of page 9

Here's a taster:

­ and this oxygen is carried
to the exercising muscles
Exercise is definitely very beneficial to us when done regularly. Regular exercise increases the
size of both the heart and the lungs, and they develop a bigger and more efficient blood supply ­
meaning they will begin to function as effectively as possible, whether you are exercising or not.…read more

Page 10

Preview of page 10

Here's a taster:

Urine contains waste urea along with excess mineral ions and water not needed by the body.
The quantaties vary depending on how much you have taken in and given out. For example, on a
hot day if you drink little and exercise a lot, you will produce very little urine, which will be
concentrated, a dark yellow. Whereas if you drink lots and do no exercise on a cold day, you will
produce a lot of dilute, pretty colourless urine.…read more


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »