3 Exchange: SA to volume ratio

Question 1

When does the need for specialised gas exchange surfaces arise?

Answer 1

• sa:v decreases
• organism gets bigger

Question 2

How is the gas exchange of single celled organisms?

Answer 2

• easily enter cells
• distance needs to travel is shorter

Question 3

Examples of adaptations to increase SA

Answer 3

• root hair cell
• folds of mitochondria membranes

Question 4

What is surface area?

Answer 4

• total area of the organism that is exposed to the external environment

Question 5

What is volume?

Answer 5

• total internal volume of the organism ( total amount of space inside organism)

Question 6

As size increases, what happens to the SA:V ratio and why?

Answer 6

• decreases
• volume increases much more rapidly than surface are increases

Question 7

How do you work out SA:V ratio?

Answer 7

• surface area / volume

Question 8

How is gas exchanged throughout single celled organisms like flatworms?

Answer 8

• single celled = small size
• large SA:V ratio
• gas exchange can happen across external surface alone by simple diffusion
• no specialised gas exchange organs required as any cell not too far away from external gas exchange surface

Question 9

How is gas exchanged throughout large organisms like elephants?

Answer 9

• large size
• small SA:V ratio
• gas exchange can’t happen across external surfaces by simple diffusion
• specialised gas exchange surfaces needed as many cells too far away from external surface

Question 10

What is metabolic rate?

Answer 10

• total energy expenditure of an organism over a given time , including all energy spent on activities ( e.g. movement, digestion, exercise , thermoregulation)

Question 11

What is metabolic demand?

Answer 11

• how much oxygen and nutrients an organism needs to take in daily to respire enough to maintain the metabolic rate

Question 12

Relationship between mass of organism and its metabolic rate and why?

Answer 12

• greater mass = higher metabolic rate
• organisms with high metabolic rates require more efficient delivery of oxygen to cells as more respiration is needed

Question 13

Why have multicellular organisms developed more complex mass transport and exchange systems?

Answer 13

• efficient delivery of oxygen

Question 14

What does BMR stand for?

Answer 14

• basal metabolic rate

Question 15

What is the purpose of the BMR?

Answer 15

• represents min amount of energy required to maintain essential physiological processes e.g breathing, maintaining temp

Question 16

Why is heat lost more quickly in smaller animals?

Answer 16

• there is a larger surface area available for heat exchange

Question 17

What is used to counteract heat loss caused by smaller animals high SA:V ratio?

Answer 17

• have a higher basal metabolic rate per g of tissue

Question 18

What factors effect heat exchange?

Answer 18

• size
• shape

Question 19

What is the rate of heat loss dependent on?

Answer 19

• surface area

Question 20

Why do larger organisms lose heat slower?

Answer 20

• larger size = smaller surface area
• smaller surface area for heat exchange to happen
• heat loss is harder

Question 21

What features would animals living in cold environments have?

Answer 21

• mammals thermoregulate so maintain constant body temp
• size = cold habitats, often larger so lose less heat
• shape = short legs, small ears, streamlined compact body shape so gives smaller SA:V

Question 22

What features would animals living in a hot environment have?

Answer 22

-size = larger so lose more heat
- shape = long legs, large ears

Question 23

What are the four features of gas exchange surfaces?

Answer 23

• large surface area
• thin walls
• good ventilation with air
• good blood supply

Question 24

Why is a large surface area good for efficient gas exchange?

Answer 24

• to allow faster diffusion of gases across the surface

Question 25

Why are thin walls good for efficient gas exchange?

Answer 25

- ensure diffusion distance remains short

Question 26

Why is good ventilation with air good for efficient gas exchange?

Answer 26

- so diffusion gradients can be maintained

Question 27

Why is good blood supply good for efficient gas exchange?

Answer 27

- maintain high conc gradient so diffusion occurs faster

Question 28

What are mammals specialised organs?

Answer 28

- lungs - blood circulatory system

Question 29

What are the lungs specialised for?

Answer 29

- ventilation = to draw in oxygen from atmosphere and expel CO2 - gas exchange = e.g many small alveoli increases SA:V ratio

Question 30

What is the blood circulatory system specialised for?

Answer 30

- transport oxygen away from lungs to respiring cells - transport CO2 from respiring cells to lungs

Question 31

How to calculate rate of diffusion

Answer 31

- rate of diffusion is proportional to = surface area x difference in conc / membrane thickness

Question 32

How do you increase rate of diffusion?

Answer 32

- increase surface area - increase size of concentration gradient

Question 33

How do you decrease the rate of diffusion?

Answer 33

- increasing membrane thickness

Question 34

What law summarises rate of diffusion?

Answer 34

- Ficks law

Question 35

What are the adaptations of the small intestine?

Answer 35

- internal surface= covered in millions of folds called villi

Question 36

What do the villi in the small intestine do?

Answer 36

-increases SA - maintains conc gradient as villi have good blood supply - membranes of villi are very thin to allow short diffusion distance

Question 37

What are the adaptations of the lungs?

Answer 37

- lungs contain millions of tiny air sacs called alveoli

Question 38

What do the alveoli in the lungs do?

Answer 38

- alveoli increase SA - alveoli have very good blood supply which maintains the conc gradient - alveoli have thin membranes to allow for s short diffusion distance