3.3.1 SURFACE AREA TO VOLUME RATIO

Question 1

As the surface area and volume of an organism increase, the SA: V ratio…

Answer 1

Decreases

Question 2

Single celled organisms have a…. SA: V ratio which allows for…

Answer 2

HIGH SA:V ratio, allows for the exchange of substances via simple diffusion

Question 3

Why does the SA: V ratio decrease as organisms increase in size?

Answer 3

• there is less surface area for the absorption of nutrients and gases and secretion of waste products
• the greater volume results in a longer diffusion distance to the cells and tissues of the organism

Question 4

What are the needs for a specialised system for gas exchange?

Answer 4

• Supply of oxygen- organisms require ATP in order to carry out biochemical processes required for survival . Majority of ATP is produced through aerobic respiration which requires oxygen
• removal of carbon dioxide. It is a waste products of aerobic respiration, if it accumulates in cells/ tissues it alters the pH

Question 5

What is the metabolic rate of an organism?

Answer 5

The amount of energy expended by that organism within a given period of time

Question 6

What is the basal metabolic rate of an organism?

Answer 6

• metabolic rate of an organism at rest
• BMR significantly lower than when an organism is actively moving

Question 7

Ways the basal metabolic rate can be measured:

Answer 7

• oxygen consumption
• carbon dioxide production
• heat production

Question 8

The greater the mass of an organism….

Answer 8

The higher the metabolic rate

Question 9

Is the BMR higher or lower in smaller animals?

Answer 9

• Higher in smaller animals
• smaller animals have a greater SA:V ration so they lose more heat, meaning they have to use up more energy to maintain their body temperature

Question 10

Explain why plants have, in general, a much lower Basal Metabolic Rate than animals. (2 marks)

Answer 10

• plants are immobile
• plants don’t have to maintain a high body temperature
• less energy is required so respiration is slower

Question 11

Why can a mouse’s resting heart rate be 5 times faster than a human’s at a similar body temperature of 37 DC? (2 marks)

Answer 11

• a mouse has a much higher SA:Vol ratio
• faster heart rate supplies cells with oxygen for respiration

Question 12

The size of an organism is…. proportional to its SA:Vol ratio…

Answer 12

Oppositely

Question 13

Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake (2 marks)

Answer 13

• smaller organisms have a larger SA:Vol ratio
• faster diffusion