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Flashcards in 13. Exchange And Transport Deck (69):

List some examples of things which need to be interchanged between an organism and it's environment.

Respiratory gases (oxygen and carbon dioxide)
Nutrients (glucose, fatty acids, amino acids, vitamins and minerals)
Excretory products (urea and carbon dioxide)


Exchange can take place in two ways:

Passively by diffusion and osmosis
Actively by active transport


In what conditions do effective exchange rates occur?

The organism must have a large surface area to volume ratio.


What have organisms evolved to overcome the problem of increased volume?

A flattened shape so that no cell is ever far from the surface e.g flatworm

Specialised exchange surfaces with large areas to increase the surface area to volume ratio e.g lungs in mammals, gills in fish.


Which characteristics do efficient exchange surfaces show?

A large surface area to volume ratio to increase the rate of exchange
Very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly.
Partially permeable to allow selected materials to cross without obstruction.
Movement of the environmental medium e.g air, to maintain a diffusion gradient
Movement of the internal medium e.g blood to maintain a diffusion gradient.


Single-felled organisms have...

A large surface area to volume ratio.


Most insects live on land aka

They are terrestrial


What is a problem for terrestrial organisms?

Water easily evaporates from the surface of their bodies and they can become dehydrated. They therefore need to conserve water.


Which features of an insect conflict with the need to conserve water?

Their efficient gas exchange surfaces with thin, permeable surface and large surface area.


Which two features do terrestrial organisms usually exhibit which reduce water loss?

Waterproof coverings over their body surfaces (exoskeleton for insects)
Small surface area to volume ratio to minimise the area over which water is lost.


How do insects diffuse respiratory gases?

They have developed an internal network of tubes called tracheae.


What are tracheae supported by?

Strengthened rings to prevent them from collapsing.


The tracheae divide...

Into smaller tubes called tracheoles. These extend throughout the body tissues of the insect. The oxygen is therefore brought directly to the respiring tissues.


Give the two ways that the respiratory gases move in and out of the tracheal system

Along a diffusion gradient


Where do gases enter and leave tracheae?

Through tiny pores called spiracles on the body surface. The spiracles may be opened and closed by a valve. When the spiracles are open water can evaporate from the insect.


How often are spiracles opened?

Periodically to allow gas exchange. However they are usually closed to prevent water loss


What are the limitations of the tracheal system of gas exchange?

Relies mostly on diffusion
For diffusion to be effective the diffusion pathway needs to be short
This limits the size that insects can attain


What are gills made up of?

Gill filaments.


What is at right angles to the gill filaments?

Gill lamellae


What do gill lamellae do?

Increase the surface area of the gills.


How does oxygen get to the gill filaments a fish?

Water is taken in through the mouth and forced over the gills and out through an opening on each side of the body.


The flow of water and the flow of blood over the gill lamellae is in........... .............
This is called............. .........

Opposite directions.
This is called countercurrent flow.


What does countercurrent flow enable?

It enables the maximum possible gas exchange to take place. There is a fairly constant rate of diffusion across the entire length of the gill lamellae. 80% of the oxygen available is absorbed into the blood of the fish.


If blood flowed in the same direction as the water over the gill lamellae what would happen?

Far less gas exchange would take place. The diffusion gradient would only be maintained across part of the length of the gill lamellae and only 50% of the available oxygen would be absorbed.


Explain the features of countercurrent flow.

Blood that is already well loaded with oxygen meets water, which has it's maximum concentration of oxygen. Therefore diffusion of oxygen from the water to the blood takes place.

Blood with little or no oxygen meets water which has had most of its oxygen removed. The diffusion of oxygen from water to blood takes place.


What is the difference shown be plants from animals?

They photosynthesise!


How is the need for gas exchange with the external air reduced for plants?

At times the gases produced in one process e.g respiration, can be used for the other e.g photosynthesis (and visa versa).


When photosynthesis is taking place, where is carbon dioxide obtained from?

Although some carbon dioxide comes from respiration of cells, most of it has to be obtained from the external air.


When respiration takes place where is oxygen obtained from?

Some oxygen is obtained from photosynthesis but most of it diffuses out of the plant.


When photosynthesis is not occurring, where is oxygen obtained from?

When photosynthesis is not occurring i.e in the dark, oxygen constantly diffuses into the leaf, from the air, as it is constantly being used by cells during respiration. Carbon dioxide produced, diffuses out.


How are the diffusion gradients in a leaf maintained?

By mitochondria carrying out respiration and chloroplasts carrying out photosynthesis.


How does gas exchange work in a plant?

- No living cell is far from the external air, and therefore a source of oxygen and carbon dioxide.
- Diffusion takes place in the gas phase (air) which makes it more rapid than if it were in water.


Why is no specialised transport system needed for plants?

- There is a short, fast diffusion pathway.
- A plant leaf has a very large surface area compared with volume of living tissue.


In plants gases move...

Into and through the plant be diffusion.


What adaptions does a leaf have that makes gas diffusion rapid?

- A thin, flat shape that provides a large surface area
- Many stomata (mostly in lower epidermis)
- Numerous interconnecting air-spaces that occur throughout the mesophyll


What are stomata?

Stomata are minute pores which occur mainly on leaves, especially the underside.


How do stomata contribute to gas exchange?

- Each stoma, is surrounded by a pair of guard cells that can open and close the stomatal pore.
- They control the rate of gaseous exchange.
-This is important because terrestrial organisms lose water by evaporation.


Plants have to balance the conflicting needs of gas exchange and control of water loss. How do they do this?

By completely or partly closing stomata at times when water loss would be excessive.


Why do large organisms need a transport system?

- The surface area to volume ratio decreases to a point where the needs of the organism can not be met by the body surface alone.

- As organisms have evolved into larger and more complex structures their tissues and organs become more specialised and dependant on each other.


Which factors do the need of a specialised transport system and circulatory pump depend on?

- The surface area to volume ratio.
- how active the organism is.


Name some of the features of transport systems...

- A suitable medium in which to carry materials e.g blood (usually a liquid based on water as it readily dissolves substances and can be moved around easily).

- A form of mass transport in which the transport medium is moved around in bulk over large distances.

- A closed system of tubular vessels that contains the transport medium and forms a branching network to distribute to all parts of the organism.

- A mechanism for moving the transport medium within vessels. This requires a pressure difference between one part of the medium and the other.

-A mechanism to maintain the mass flow movement in one direction e.g valves.

- A means of controlling the flow of the transport medium to suit the changing needs of different parts of the organism.


A mechanism for moving the transport medium within vessels is necessary for a transport system. This requires a pressure difference between one part of the medium and the other.

Give the two ways this pressure difference is achieved...

1. Animals use muscular contraction either of the body muscles or of a specialised pumping organ, such as the heart.

2. Plants do not possess muscles and so often rely on passive neutral physical processes such as the evaporation of water.


Why is it necessary for substances to be delivered to the rest of the body quickly in the human circulatory system?

Mammals have a high body temperature and hence a high rate of metabolism.


Mammals have which type of circulatory system?

A double one.


Why do they have this?

Because there is a pressure drop at the lungs. Blood needs to come back to the heart to be pumped to the rest of the body with a high enough pressure.


Name three types of vessel in the circulatory system of a mammal.

Arteries, veins, capillaries, arterioles.


By what method do substances move into cells in the final part of the transport system in mammals?

By diffusion.


Why is the diffusion that takes place in the final stage of the transport system rapid?

-large surface area
-short diffusion pathway
-steep diffusion gradient


Describe arteries

They carry blood away from the heart into the arterioles.


Describe arterioles.

Arterioles are smaller arteries that control blood flow from arteries to capillaries.


What are capillaries?

Capillaries are tiny vessels that link arterioles to veins.


What are veins?

Veins carry blood from capillaries back to the heart.


What is the layered structure of all blood vessels (except capillaries)?

-tough outer layer that resists pressure changes

-muscle layer that can contract and so control blood flow

-elastic layer that helps to maintain blood pressure by stretching and springing back

- thin inner lining (endothelium) that is smooth to prevent friction and thin to allow diffusion

-lumen (the central cavity of the blood vessel which blood flows through


How is the structure of an artery adapted to its function to transport blood rapidly under high pressure from the heart to the tissues?

- the muscle layer is thick compared to veins. They can be constricted and dilated in order to control the volume of blood passing through them.

-the elastic layer is relatively thick compared with veins because it is important that blood pressure in arteries is kept high to reach the extremities of the body. The stretching and recoil action helps to maintain high pressure and smooth pressure surges created. The beating of the heart.

- the overall thickness of the wall is large (resists the vessel bursting under pressure)

- there are no valves (except in the arteries leaving the heart) because blood is under constant high pressure.


Arterioles are adapted to their function. How?

- The muscle layer is relatively thicker than in the arteries - the contraction of this muscle layer allows constriction of the lumen of the arteriole which restricts the blood flow and so controls it's movement into the capillaries that supply the tissues with blood.

- The elastic layer is relatively thinner than in the arteries because blood pressure is lower.


How are veins adapted to their function of transporting blood slowly under low pressure from the tissues back to the heart?

- the muscle layer is relatively thin compared to arteries because veins cannot control flow of blood to the tissues as it carries blood away from the tissues.

- the elastic layer is relatively thin compared to arteries because the low pressure of blood within the veins will not cause them to burst and there is no recoil action.

- the overall thickness of the wall is small because pressure is too low to create any risk of bursting. It also allows them to be flattened easily, aiding the flow of blood within them.

- there are valves throughout to ensure that blood does not flow backwards. When body muscle contract veins are compressed pressurising the blood within them. It is directed in one direction only.


The function of capillaries is to exchange metabolic materials such as oxygen carbon dioxide, and glucose between the blood and the cells of the body. How is it adapted to do this?

- their walls constrict only in the lining layer - diffusion pathway is short.

- they are numerous and highly branched providing a large surface area for diffusion.

- they have a narrow diameter, so permeate tissues, which means that no cell is far from a capillary.

- narrow lumen so red blood cells are squeezed flat up against it. This brings them even closer to the cells to which they supply oxygen. This again reduces the diffusion distance.

- there are spaces between the lining (endothelial) cells that allow white blood cells to escape in order to deal with infections within tissues.


What is tissue fluid?

A watery liquid that contains glucose, amino acids, fatty acids, salts and oxygen. Tissue fluid supplies all of these substances to the tissues. It receives carbon dioxide and other waste materials from these tissues.


Tissue fluid is...

The immediate environment of cell- the cells are bathed in tissue fluid.


What kind of environment does tissue fluid provide for the cells it surrounds?

A mostly constant environment.


When blood is pumped through the capillaries pressure is created at the arterial end of the capillaries. What is the pressure called?

Hydrostatic pressure.


What does the hydrostatic pressure at the arterial end of the capillaries force the tissue fluid to do?

The pressure forces the tissue fluid out of the blood plasma .


The outward pressure to move the tissue fluid out of the blood plasma is opposed by two other forces. Name them.

- the hydrostatic pressure of the tissue fluid outside the capillaries which prevents outward movement of liquid.
- the lower water potential of the blood, due to plasma proteins that pulls water back into the blood within the capillaries.


What is the resultant force of the combined forces on the tissue fluid at the arterial end of the capillary?

It creates an overall pressure that pushes tissue fluid out of the capillaries . The pressure is only enough to force small molecules out of the capillaries leaving cells and protein in the blood.


What is the filtration under the pressure called in the formation of tissue fluid?



Describe how tissue fluid returns to the capillaries after it has exchanged metabolic materials with the cells it baths.

-the loss of tissue fluid from the capillaries reduces the hydrostatic pressure inside them.

- as a result, by the time the blood has reached the venous end of the capillary it's hydrostatic pressure is less than that of the tissue fluid outside it.

- therefore, tissue fluid is forced back into the capillaries by the higher hydrostatic pressure outside them.

- in addition, the osmotic forces resulting from the proteins in the blood plasma pull water back into the capillaries.


Not all of the tissue fluid is returned to the capillaries immediately. How is this eventually returned?

Via the lymphatic system. The system of vessels begin in the tissues . They form a network throughout the whole body.


How does the lymphatic system drain it's contents back into the bloodstream?

Via two ducts that join veins close to the heart.


How is the contents of the lymphatic system moved?

- hydrostatic pressure of the tissue fluid that has left the capillaries
- contraction of body muscles that squeeze the lymph vessels - valves in lymph vessels ensure no back-flow.