Gas Exchange

Question 1

Describe and explain example of how the human breathing system is adapted to achieve sufficient gas exchange despite humans’ low SA:V

Answer 1

• Lungs provide a large internal surface area OR many alveoli provide a short diffusion distance as they are one cell thick

• Constant blood supply to the lungs, maintaining a concentration gradient

Question 2

Why would a molecule of oxygen diffuse into a SINGLE-celled prokaryotic cell quicker than it would diffuse into a SINGLE, eukaryotic cell

Answer 2

• Eukaryotic cells are larger, so longer diffusion distance THEREFORE takes longer time to reach the centre

(Single-celled so shorter diffusion distance)

Question 3

A mouses resting heart fate can be 5x faster than a human’s at a similar body temperature because

Answer 3

• A mouse has a HIGHER SA:V ratio SO loses heat MORE quickly
• So faster respiration replaces heat

Question 4

Why do Insects have Specialised Gas Exchange Systems?

Answer 4

multicellular organism so has a small surface area to volume ratio, large diffusion distance, high demand & body surface made of exoskeleton (impermeable barrier to reduce water loss)
therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they require a specialised gas exchange system called Tracheal system

Question 5

Describe how oxygen in the tracheoles reaches the muscle cells of the insect

Answer 5

• Air diffuses along the trachea and tracheoles
• Oxygen is then dissolved in the water at the end of the tracheoles
• where it diffuses into the muscle cells

Question 6

Some insects are very active. after a period of time the flying muscles respire anaerobically and the products of of ANAEROBIC respiration accumulate in the cells. Suggest how this affects the supply of oxygen to the flying muscle cells

Answer 6

• Anaerobic respiration produces lactic acid

• which lowers the water potential in the muscle cells (anything that isn’t water makes water less pure, so lowering water potential)

• So water from the tracheoles moves into the muscle cells by osmosis

• Allowing oxygen in the tracheoles to diffuse directly into the cells, so shorter diffusion pathway

Question 7

Not beneficial for stomata to be on the top surface because

Answer 7

• Stomata could become blocked by drops of rain which would reduce the rate of gaseous exchange
• Stomata would be in direct sunlight which will increase water loss by evaporation

Question 8

Way of counting stomata

Answer 8

• Measure stomatal density
• units- number of stomata/mm2

Question 9

Long time intervals between spiracle opening could be an advantage to insects because

Answer 9

Conserves water by reducing water loss by evaporation

Question 10

When counting, cells that touch top or left lines are counted but not cells that tough right or bottom lines are not counted

Answer 10

• to avoid counting same cells twice
• to get comparable results

Question 11

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

Answer 11

• Many lamella/ filaments which provide a large surface area
• Thin surface so short diffusion pathway

Question 12

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

Answer 12

Water and blood flow in opposite directions;

Allow diagram showing counter-flow

2. Blood always passing water with a higher oxygen concentration;
3. Diffusion gradient maintained throughout length (of gill)

OR

Question 13

Explain 3 ways in which an insects tracheal system is adapted for efficient gas exchange

Answer 13

• Tracheoles have thin walls which provides a short diffusion distance to cells
• highly branched/ large number of tracheoles - large surface area
• body moved by muscles to move air so maintains diffusion/ concentration gradient
• Fluid at the end of tracheoles, which move out into tissues to increase surface area

Question 14

How are leaves of xerophytes in dry environments adapted to survive

Answer 14

• Smaller surface area- so LESS evaporation/LESS heat absorbed
• Thicker leaves- increased diffusion distance(increased distance= longer time for water to diffuse out)
• fewer stomata- LESS diffusion
• Smaller SA:V ratio- so leas evaporation

Question 15

Describe the relationship between size and surface area to volume ratio

Answer 15

• As size increases, surface area to volume ratio decreases

Question 16

If an organism is active- they have a higher metabolic rate so respire more so they require more oxygen+ATP

Answer 16

Link these to the question

less CO2 so removed less oxygen present, less aerobic respiration

Less CO2 and water present, less photosynthesis reaction less growth

Question 17

Explain why oxygen uptake is a measure of metabolic rate in organisms

Answer 17

oxygen is used in respiration which is a metabolic process

Question 18

The volume of water passing over the gills increases if the temperature of the water increases. Explain why.

Answer 18

Increased respiration
Increase temp increased activity of enzymes

Question 19

Explain the movement of oxygen into the gas exchange system of an insect when it is at rest.

Answer 19

1. Oxygen used in (aerobic) respiration;
2. (so) oxygen (concentration) gradient
   (established);
3. (so) oxygen diffuses in

Question 20

Explain 3 ways in which an insects tracheal system is adapted for efficient gas exchange (3)

Answer 20

• thin walls - small area to diffuse across
• highly branched - large surface area
• trachea have tubes full of air so that diffusion is fast

Question 21

standard deviation

Answer 21

Spread of data around the mean

Question 22

Disadvantage of a large mean/amount of stomata

Answer 22

More water loss by evaporation, so less photosynthetic reactions, reduces metabolic rate

Question 23

Describe the gross structure of the human gas exchange system and how we breathe in and out.

Answer 23

1. Named structures - trachea, bronchi, bronchioles, alveoli
2. Above structures named in correct order
3. Breathing in - diaphragm contracts and external intercostal muscles contract
4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in)
5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract
6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out)

Question 24

Compare and contrast the structure and properties of triglycerides and phospholipids

Answer 24

1. Both contain ester bonds between glycerol and fatty acid;
2. Both contain glycerol;
3. Fatty acids on both may be saturated or unsaturated;
4. Both are insoluble in water;
5. Both contain C, H and O but phospholipids also contain P;
6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;
8. Phospholipids form monolayer/micelle/bilayer in water but triglycerides don’t

Question 25

Describe the pathway taken by an oxygen molecule from an alveolus to the blood

Answer 25

1. (Across) alveolar epithelium;
2. Endothelium / epithelium of capillary;

Question 26

Explain how one feature of an alveolus allows efficient gas exchange to occur

Answer 26

The alveolar epithelium is one cell thick. This creates a short diffusion pathway.

Question 27

Describe how the student could use an eyepiece graticule to determine the mean diameter of stomata

Answer 27

1. Measure (each stoma) using eyepiece graticule;
2. Calibrate eyepiece graticule against stage micrometer / ruler / graph paper;
3. Take a number of measurements (to calculate mean

Question 28

Explain how the cuticle reduces water loss. (1)

Answer 28

(waxy so) impermeable to water / waterproof / stops water passing through

Question 29

Slow growth of a plant can be due to

Answer 29

Small number of stomata , less uptake of CO2, so less photosyntheis- less growth of the plant

Question 30

Name the process by which oxygen passes from an alveolus in the lungs into the blood

Answer 30

• Simple diffusion

Question 31

2 adaptations of the structure of alveoli for efficient gas exchange

Answer 31

• thin walls, so decreased diffusion distance
• total surface area is large

Question 32

Fire-breather cannot breathe out properly. explain why

Answer 32

• Loss in elastic tissue
• less recoil

Question 33

The stomata close when the light is turned off.
Explain the advantage of this to the plant.

Answer 33

1. (Because) water is lost through stomata;
2. (Closure) prevents / reduces water loss;
3. Maintain water content of cells.

Question 34

Suggest and explain one advantage and one disadvantage of increased stomatal density

Answer 34

Advantage
• more CO2 uptake so more photosynthesis/faster growth

Disadvantage
• more water loss so less photosynthesis less growth

Question 35

Suggest two ways the student could improve the quality of her scientific drawing of this gill

Answer 35

1. Don’t use shading;
2. Only use single lines/don’t use sketching (lines)/ensure lines are continuous/connected;
3. Add further labels/annotations;
4. Don’t cross label lines;
5. Add magnification/scale (bar);

Question 36

Explain how the gills of a fish are adapted for efficient gas exchange

Answer 36

Large surface area provided by many lamellae
Thin epithelium so short diffusion distance
Water and blood flow in opposite directions
Water always next to blood with a lower conc of oxygen
Circulation replaces blood saturated with oxygen
Ventilation replaces water as oxygen removed

Question 37

Pumping raises pressure in the body
Which pushes air our of body
As moves down a pressure gradient to atmosphere

Question 38

Use your knowledge of gas exchange in leaves to explain why plants grown w little water grow slowly

Answer 38

Stomata close
Less uptake of CO2 less photosynthesis

Question 39

Describe how CO2 in the air outside a leaf reaches mesophyll cells inside the leaf

Answer 39

Co2 via stomata
Stomata opened by guard cells
Diffuses through air spaces
Down a diffusion gradient