AS biology Ms Timms: January 2013

Thursday, 31 January 2013

Homework 31.1.13

Watch- Wonders of life

http://www.bbc.co.uk/iplayer/episode/b01qh3bb/hd/Wonders_of_Life_What_Is_Life/

downloaded video is in the shared area

Wednesday, 30 January 2013

tissue fluid formation

Tissue fluid formation:

1.Blood from the heart passes through arteries & arterioles &finally the capillaries.

2.Capillaries are much narrower & this creates pressure at the arterial end of the capillary = hydrostatic pressure

3.This pressure forces tissue fluid out of the blood plasma.

4.This pressure is opposed by two other forces

a)Hydrostatic pressure of the tissue fluid outside the capillaries

b)The lower water potential of the blood, due to the plasma protein- pulls water back into the blood

The overall effect of all these forces results in tissue fluid leaving the capillaries. The pressure is only enough to force small molecules out of the capillaries- leaves cells & proteins.

Tissue fluid return:

Exchange of metabolic materials in the tissue fluid- tissue fluid needs to be returned to the circulatory system.

1.The loss of tissue fluid from the capillaries at the arterial end reduces the hydrostatic pressure inside them.

2.Therefore at the venous end the hydrostatic pressure is less than the tissue fluid surrounding the capillaries.

3.Plasma proteins in the capillaries generate an osmotic pressure that draws water back into the capillaries.

4.Tissue fluid is forced back into the capillaries.

Tissue fluid images

Summary questions- vessels lesson

Transport system background info- vessels lesson

Why do large organisms need a transport system?

1.All organisms need to exchange materials between themselves and their environment.

2.In small organisms this exchange can occur over the surface of their body.

3.However, with increasing size, the surface area to volume ratio decreases to the point where the needs of the organism cannot be met by the body surface alone. Need specialist exchange surfaces.

4.In larger and more complex multicellular organisms, the tissues & organs have become more specialised & dependent on one another- this makes a transport system all the more essential.

Whether or not there is a specialised transport system, and whether or not it is circulated by a pump depends on 2 things:

1.The surface area to volume ratio

(the lower the surface area to volume ratio the greater the need for a specialised transport system)

2. The activity of the organism

(the more active the organism the greater the need for a specialised transport system)

Features of transport systems

1.A suitable medium to carry materials

(usually liquid & water based due to water readily dissolving substances)

2. A form of mass transport- bulk movement over large distances

A closed system of tubular vessels that contain the transport medium that form a branching network to reach all parts of the organism.

3. A mechanism for moving the transport medium within vessels. This requires a pressure difference between one part of the system and another- this is achieved in 2 ways:

a)Muscle contraction- body muscles or pumping organ.

b)Means to control the direction of flow of the medium- e.g. Valves