gas exchange

Question 1

what happens to the surface area to volume ratio as an organism gets larger

Answer 1

decreases

Question 2

larger organisms have……

Answer 2

smaller surface area to volume ratio

Question 3

smaller organisms have….

Answer 3

larger surface area to volume ratio

Question 4

why can small organisms meet their gas exchange needs by diffusion across their cell membrane

Answer 4

because they have a large enough surface area to volume ratio

Question 5

why do larger organisms not rely on diffusion (alone) to meet O2 demands to all of their cells

Answer 5

because they have a relatively small surface area to volume ratio

Question 6

why have larger organisms developed specialised gas exchange surfaces and adaptations to ensure the rapid diffusion of gases

Answer 6

because they have a relatively small surface area to volume ratio

Question 7

what makes a good exchange surface

Answer 7

large surface area
large concentration gradient
thin exchange surface

Question 8

what is the most effective surface for gas exchange in an insect

Answer 8

large, thin and permeable area

Question 9

what do insects have to limit water loss

Answer 9

1. Shiny waterproof covering over their body surfaces. This is usually a rigid outer skeleton (exoskeleton) covered with a waterproof cuticle.
2. Relatively small surface area to volume ratio to minimise the area over which water is lost.

Question 10

describe the movement of oxygen through out insects

Answer 10

1. Oxygen enters the insect through spiracles and into the tracheae.
2. Spiracles close;
3. Oxygen diffuses through the tracheae into the tracheoles (down a conc. Gradient);
4. Oxygen is delivered directly to the respiring tissues

Question 11

what is the function of the spiracles

Answer 11

• pores open and close to control water loss
• maintains the concentration gradient
• open when CO2 levels increase

Question 12

what is the role of the exoskeleton and why can’t gas exchange occur on its surface

Answer 12

• role is to protect the organs
• tough and thick so cant have gas exchange taking place

Question 13

what is the function of chitin

Answer 13

strengthens the trachea and keeps it open for gas exchange

Question 14

what is the trachea

Answer 14

network of tubes supported by chitin

Question 15

what are tracheoles

Answer 15

• small tubes with thin walls (short diffusion path) which extend throughout the body
• highly branched with large surface area

Question 16

how does oxygen diffusion occur in insects

Answer 16

1) Tissues respire using oxygen, which reduces the concentration of oxygen at the tissue.

2) Oxygen moves from an area of higher concentration to lower concentration so moves from the tracheae to the tissue.

3) This lowers the oxygen concentration in the tracheae so oxygen moves into the tracheae from outside the insect via the spiracles.

Question 17

how does carbon dioxide diffusion occur in insects

Answer 17

1) Respiration produces CO2, increasing the concentration at the tissue

2) CO2 moves from an area of high concentration at the tissue to the low concentration in the tracheae.

3) CO2 then moves from high concentration in tracheae to low concentration outside the insect via the spiracles.

Question 18

what is abdominal pumping

Answer 18

Movement of the insects muscles creates a mass movement of air in and out the trachea thus increasing the rate of gaseous exchange

Question 19

how does lactate become lactic acid

Answer 19

dissolves in water

Question 20

how does an insect get additional oxygen during flight

Answer 20

1. flight
2. anaerobic respiration occurs and produces lactic acid
3. this lowers the water potential
4. so water moves into muscle cells (from tracheoles) through osmosis
5. this reduces diffusion distance for oxygen

Question 21

what happens at rest in the tracheoles

Answer 21

fills with water at the narrow ends

Question 22

what is the gas exchange organ in the fish

Answer 22

gills ( large surface area )

Question 23

describe the structure of the fish gills

Answer 23

• each fish has 4 gills
• they have projections called gill filaments
• each filament has MANY lamellae at 90 degrees to increase SA

Question 24

describe the pathway of water in a fish

Answer 24

in through the mouth
passes through the lamellae (where most O2 is removed)
and (oxygen poor) water leaves through gill opening

Question 25

what does the lamellae have

Answer 25

contains capillaries and a thin membrane

Question 26

Explain two ways in which the structure of fish gills is adapted for efficient gas exchange (2)

Answer 26

1. Many filaments/lamellae so there’s a large surface area;
2. Lamellae are thin for a short diffusion pathway

Question 27

describe the countercurrent flow

Answer 27

water and blood flow in opposite directions to maintain a favourable concentration gradient along the whole length of the gill

Question 28

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange. (6)

Answer 28

1 Large surface area provided by many lamellae/filaments so that Increases diffusion/makes diffusion efficient;

2 Thin epithelium of lamellae/distance between water and blood so that there is short diffusion distance;

3 Water and blood flow in opposite directions/counter current so that a concentration gradient (along gill) is maintained /equilibrium not reached;

4 As water always next to blood with lower concentration of oxygen;

5 Circulation replaces blood saturated with oxygen;

6 Ventilation replaces water (as oxygen removed);

Question 29

Explain how the counter current mechanism in fish gills ensures the maximum amount of oxygen passes into the blood flowing through the gills (3)

Answer 29

1. Water and blood flow in opposite directions;
2. Blood always passing water with a higher oxygen concentration (in water);
3. Oxygen diffusion / concentration gradient maintained across the full length of the gill lamellae/filaments;

Question 30

give the adaptations of leaf for gaseous exchange

Answer 30

1. Flat – gives larger surface area to volume ratio
2. Many Stomata – pores to allow air to move in and out of leaf.
3. Air spaces in leaf so short distance between mesophyll cells and air

Question 31

describe the diffusion of CO2 for photosynthesis

Answer 31

1. Mesophyll cells photosynthesise and this reduces the concentration of CO2 in the cells.
2. CO2 diffuses from the air spaces into the cells.
3. This in turn reduces the CO2 concentration in the air spaces causing CO2 to move into the air spaces from the air outside the leaf, through the stomata.

Question 32

describe the diffusion of O2 in plants

Answer 32

1. Mesophyll cells produce O2 as a result of photosynthesis.
2. O2 diffuses into the air spaces from the cells
3. This increases the concentration of O2 in the air spaces, causing O2 to move from the air spaces to outside the leaf via the stomata.

Question 33

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf. (4

Answer 33

1. (Carbon dioxide enters) via stomata;
2. (Stomata opened by) guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient;

Question 34

give adaptations to reduce water loss in plants

Answer 34

At night, the guard cells close the stomata to prevent water loss.

Question 35

explain how do guard cells close the stomata

Answer 35

in photosynthesis, sugars are produced
which lower the water potential (in chloroplasts)
so water moves in the guard cell and causes it to swell so stomata closes

Question 36

how do you calculate stomatal density

Answer 36

• find how big the area is
• how many (organelles) in that area

Question 37

where are xerophytic plants found

Answer 37

These live in dry/arid environments

Question 38

give the leaf adaptations xerophytic plants have that reduce water loss

(HINT fick’s law)

Answer 38

1. Reduced number of stomata SO Less Surface Area for water loss
2. Stomata in pits SO Reduced concentration gradient
3. Hairs to trap water vapour SO Reduced concentration gradient
4. Rolled leaves SO Reduced concentration gradient
5. Leaves reduced to spines SO Less surface area for water loss
6. Thick waxy cuticles SO Increased diffusion distance