3.1 Surface area to volume

Question 1

When calculating surface area to volume ratio remember:

Answer 1

convert all the numbers to the same units

Question 2

conversion of nm to um:

Answer 2

/ 1000

Question 3

Greater volume results in…

Answer 3

londer diffusion distance to the cells and tissues of the organisms

Question 4

Exam Tip

Answer 4

Students often only focus on the transport of nutrients and gases when writing about the adaptations for facilitating exchange. Make sure you don’t forget about the importance of removing toxic waste products from tissues and cells. If toxic waste products build-up (e.g. urea and carbon dioxide) within cells or tissues they can cause damage/death.

Question 5

Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse. (3)

Answer 5

mouse
* smaller so larger SA:V ratio
* more heat lost per gram of tissue
* faster rate of respiration to release heat

Question 6

Suggest why the student concluded that they couldn’t make a conclusion based on the table of relationship between the stage of development and metabolic rate.

Answer 6

• no information about the egg
• so cannot compare all stages
• no standard deviations given for comparison

Question 7

Suggest how the environmental conditions have resulted in development of systems for oxygen uptake outside the body. (2)

Answer 7

• water has a low oxygen concentration
• having a system outside the body gives large surface area in contact w/ water to maximise diffusion of oxygen into the body

Question 8

Describe the changes that occur in the body when air is inspired? (6)

Answer 8

• external intercostal muscles: contract
• internal intercostal muscles: relax
• diaphragm: contracts (flattens)
• air pressure in lungs: air moves in -> pressure increases
• lung volume: increases (to decrease pressure)
• movement of air: from atm pressure into lower lung pressure

Question 9

Describe the changes that occur in the body when air is expired? (6)

Answer 9

• external intercostal muscles: relax
• internal intercostal muscles: contracts
• diaphragm: relaxes
• air pressure in lungs: drops as air moves out
• lung volume: decreases
• movement of air: from high pressure in lungs to low atm pressure

Question 10

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air and the alveoli and blood in the capillaries around them. (5)

Answer 10

• many alveoli walls folded provide large SA
• many capillaries provide a large SA
• so fast diffusion
  ..
• alveoli epithelium is thin -> short distance betw/ alveoli and blood
• squamous epithelium
• so short diffusion distance
• so fast diffusion
  …
• ventilation
• maintains a diffusion gradient
• so fast diffusion

Question 11

Equation for pulmonary ventilation.

Answer 11

Pulmonary ventilation = tidal volume x ventilation rate.

Question 12

One student concluded that the data shows more cigarettes smoked per day will increase deaths. Do you agree? (3)

Answer 12

• There is a positive correlation between lung cancer deaths and cigarette smoke.
• The data overlaps
• correlation does not prove causation.
• Other factors such as genetics or pollution could cause the deaths
• No correlation coefficient statistic to know if the correlation is significant.