3.3.1 Exchange

Question 1

Where does exchange always occur?

Answer 1

Across cell plasma membranes between two environments

Question 2

What is tissue fluid?

Answer 2

The environment around the cells of multicellular organisms

Question 3

Give 4 examples of things that need to be exchanged between an organism and it’s environment.

Answer 3

Respiratory gasses
Nutrients
Excretory products
Heat

Question 4

Give examples of active and passive exchange.

Answer 4

Active- active transport

Passive- osmosis and diffusion

Question 5

What is Fick’s law?

Answer 5

Diffusion ~ (surface area * difference in concentration) / length of diffusion pathway

Question 6

How does metabolic rate effect exchange?

Answer 6

High metabolic rate leads to exchange of more materials

Require larger SA:V ratio

Question 7

How do organisms evolve to make exchange more efficient?

Answer 7

A flattened shape so that no cell is ever far from the surface
Specialised exchange surfaces with large areas to increase the SA:V ratio

Question 8

What characterisers are shown by a surface specialised for exchange?

Answer 8

Large SA:V ratio
Thin to reduce diffusion distance
Selectively permeable to allow selected materials across
Movement of environmental medium to maintain diffusion gradient
Transport system to move internal medium to maintain diffusion gradient

Question 9

Why are specialised exchange surfaces often located inside an organism?

Answer 9

They are specialised to be thin and so would be easily damaged and dehydrated

Question 10

Describe gas exchange in a single-called organism.

Answer 10

Small= large SA:V ratio
Oxygen absorbed by diffusion across the body surface
Carbon dioxide from respiration diffuses out across their body surface
Cell wall has no effect on diffusion of gasses

Question 11

How have insects adapted for gas exchange?

Answer 11

Evolved an internal network of tubes called teaches
Trachea are supported by strengthened finds to prevent them from collapsing
Trachea extend into tracheoles
Tracheoles extent to body tissue
Air is brought directly to repairing tissue as there is a short diffusion pathway from a tracheole to any body cell

Question 12

In which three ways to respiratory gasses move in and out of the tracheal system in insects?

Answer 12

Along a diffusion gradient
Mass transport
The ends of the tracheoles are filled with water

Question 13

How to insects move respiratory gasses in and out of the tracheal system using diffusion?

Answer 13

Cells respire and use up oxygen so it’s concentration at the ends of tracheoles is low
Diffusion gradient is created so oxygen diffuses from the atmosphere along the tracheae and tracheoles to the cell
Removal of the carbon dioxide removed occurs the same way

Question 14

Why is diffusion the best method of gaseous exchange for insects?

Answer 14

Diffusion is air is much more rapid than in water

Question 15

How to insects move respiratory gasses in and out of the tracheal system using mass transport?

Answer 15

Contraction of muscles in the insect squeezes the trachea
Enables mass movements of air in and out
Speeds up exchange of respiratory gasses

Question 16

How to insects move respiratory gasses in and out of the tracheal system by having water in the ends of tracheoles?

Answer 16

During major activity, muscle cells around the tracheoles respire anaerobically
Lactate is produced which is soluble and lowers water potential of the muscle cell
Water moves into the muscles cells from the tracheoles by osmosis
The water in the tracheoles reduces in volume and so draws air in

Question 17

What is the result of anaerobic respiration in insects which involved the water filled tracheoles?

Answer 17

Fast rate as the final diffusion is in gas not liquid
Increased rate that air is moved in
But this leads to more water evaporation

Question 18

What are spiracles?

Answer 18

Tiny pores through which gasses enter and leave trachaea

Can be opened or closed by a valve

Question 19

Why are the valves to the spiracles of tracheae not constantly open?

Answer 19

Gasses exchange when they are open but water also evaporated

Closing then prevents water loss

Question 20

Why have fish evolved to have gills?

Answer 20

They are relatively large so have small SA:V ratio

So their body surface is not adequately to supply and remove their respiratory gasses

Question 21

What makes fish gas-tight?

Answer 21

They have a waterproof outer covering

Question 22

Describe the structure of the gills.

Answer 22

Located in the fishes body
Stacked full filaments
Gill lamellae are at right angles to the filaments

Question 23

What is the purpose of gill lamellae?

Answer 23

Increase surface area

Question 24

How does water enter and leave a fish?

Answer 24

Taken in through mouth
Forced over gills
Out through openings on each side of the body

Question 25

What is concurrent flow?

Answer 25

The flow of the water over the gill lamellae is opposite to the flow of the blood within them

Question 26

What is the purpose of concurrent flow?

Answer 26

Ensures maximum possible gas exchange

Maintain a diffusion gradient all the way across the gill lamellae

Question 27

How does concurrent flow increase gas exchange?

Answer 27

Blood well loaded with oxygen meets water with maximum oxygen concentration so diffusion from water to blood occurs
Blood with little oxygen meets water with most of its oxygen removes and diffusion from water to blood still takes place