Gas Exchange

Question 1

What are the characteristics of single-celled organisms and insects?

Answer 1

Small so therefore have a large surface area to volume ratio

Question 2

What is the internal system of insects?

Answer 2

Internal network of tubes called tracheae
Tracheae are supported by strengthened rings which prevent them from collapsing
Tracheae divide into smaller dead-end tubes called tracheoles
Tracheoles extend throughout the bodily tissues
This creates a short diffusion pathway

Question 3

How do respiratory gases move in/out of the trachea via the diffusion gradient?

Answer 3

When cells are respiring, oxygen is used up and the concentration at the ends of the tracheoles falls
The concentration gradient causes oxygen to diffuse from the air to the tracheae to cells
Carbon dioxide is produced by cells which creates an opposite concentration gradient
Carbon dioxide diffuse from the cell’s to the atmosphere
Diffusion in air is more rapid than in water so this is a quick method

Question 4

How do respiratory gases move in/out of the trachea via mass transport?

Answer 4

The contraction of muscles in insects can squeeze the tracheae enabling mass movements of air in and out
This spread up the exchange of respiratory gases

Question 5

How do respiratory gases move in and out of the trachea system via the ends of the tracheoles being filled with water?

Answer 5

During major activity, the muscle cells around the tracheoles respire anaerobically
This produces lactate which is soluble and lowers water potential
Water moves into the cells from the tracheoles by osmosis
The water decreases in volume and so draws air into them
The final diffusion pathway is in a gas rather than a liquid phase so is more rapid
This leads to greater water evaporation

Question 6

How do gases enter/leave the trachea?

Answer 6

Through tiny pores called spiracles on the body surface
Opened and closed by a valve
Mostly kept closed to reduce water loss

Question 7

How are spiracles opened

Answer 7

Via valves

Question 8

What are the problems associated with spiracles

Answer 8

When they are open, they cause water loss.

Question 9

Why are insects small?

Answer 9

The tracheal system relies mostly on diffusion. The diffusion pathway must be short which is why insects are small

Question 10

What is the outer coating of a fish

Answer 10

waterproof. Gas-tight outer coating

Question 11

Where are gills found

Answer 11

Fish, Under operculum

Question 12

What is the structure of a gill

Answer 12

Gills are made of gill filaments. Gill lamellea are at right angles to the gill filments which increase the surface area of the gill

Question 13

What is a countercurrent flow?

Answer 13

When water and blood flow in opposite directions.

Question 14

What os the water content of water

Answer 14

1%

Question 15

How does the countercurrent help the diffusion of oxygen?

Answer 15

There is alwasy a concentration gradient between the blood and water therfore diffusion happens across the entire gill and most of the oxygen gets diffused.

Question 16

How does photosynethesis and respiration benefit eachother?

Answer 16

The products of photosynthesis supplies the reactants of respiration and vice versa
Most CO2 is gained from external air

Question 17

How are leaves adapted for photosynethesis

Answer 17

Large surface area: rapid diffusion
Thin and flat leaves: short diffusion pathway
Stomata usually occur on the underside of the leaf: stops water loss
Numerous interconnecting air spaces: allow for gases to come in contact with mesophyll cells
Guard cells: open and close stoma to prevent water loss

Question 18

Describe how gases move in and out of the tracheal system?

Answer 18

Gas enters and leaves via spiracles,
Gas moves down a conc gradient,
O2 goes from high conc in water to low in blood,
C02 conc gradient is the other way,
Insects muscles contract when moving which squeezes the trachea so air moves in n out,

Question 19

Describe how gases move in and out the tracheaoles (water answer)?

Answer 19

Ends of tracheoles are filled with water,
Insects carry out anaerobic respiration when active, which produces lactate,
Lactate is soluble and lower the water potential in the respiring cells (muscle),
Water from traheoles moves into the muscle cells by osmosis,
This water volume from the tracheoles draws more volume of air into the tracheols,
The loss of water from the tracheoles leads to quicker diffusion of gases

Question 20

Land -dwelling insects lose water from their gas exchange surface. Use Ficks law to explain why they lose less when it is humid

Answer 20

Humdity reduces difference in conc between body and air,

Reduces the rate of diffusion from body to air

Question 21

Explain the advantage of countercurrent flow?

Answer 21

Diffusion gradient will be maintained all the way along the gill,
More oxygen will diffuse into the blood

Question 22

There is a one-way flow of water over the gills of a fish whereas there is a two-way flow of air in tje lungs of a mammal. Suggest one advantage to a fish of this one-way flow of water over its gills

Answer 22

Continous flow of water

Question 23

Explain what causes the oxygen conc in the trachea to fall when the spiracles are closed

Answer 23

Oxygen is used in respiration therfore diffuses (from tracheae) to tissue.
Oxygen unavle to enter organism

Question 24

Explain how the ventilation mechanism of a fish and the structure of its gills result in the efficint uptake of oxygen from water

Answer 24

Many lamellae on many filaments therfore large surface area
Large number of capillaries to remove oxygen to maintain gradient
Thin eputhelium therfore short diffusion pathway
Pressure changes to bring in more water
Countercurrent flow therfore diffusion along whole length

Question 25

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf

Answer 25

Carbon dioxide enters via stomata
Guard cells open stomata
Diffueses through air space
Down diffusion gradient

Question 26

water containing dissolved oxygen flows over the gill in the opposite direction to blood flow inside. Explain why this arrangment is important is important for effecient oxygen uptake

Answer 26

Maintains diffusion for whole length of the gill