Size and surface area

Question 1

Surface area : volume ratio

SIze and surface area

Answer 1

Smaller organisms have higher surface area : volume ratios than larger organisms

Question 2

Transport systems in single-celled organisms

SIze and surface area

Answer 2

Substances can diffuse directy into or out of the cell across the cell-surface membrane
The diffusion rate is quick because of small distances the substances have to travel

Question 3

Transport systems in multicellular organisms

SIze and surface area

Answer 3

Diffusion across membrances is too slow:
1. Some cells are deep within body - big distance to travel
2. Larger animals have a low SA:V ratio - difficult to exchange enough substances to supply a large volume of aniamal through relatively small outer surface
So they need specialised exchange organs - like the lungs
Need effienct system to carry substances to and from their individual cells - mass transport

Question 4

Mass transport

SIze and surface area

Answer 4

Mass transport in mammals usually refers to circulatory system, which uses blood to carry glucose and oxygen around the body
Also carries hormones, antibodies and waste (CO2)
Mass transport in plants involves transport of water and solutes in xylem and phloem

Question 5

How does body size effect heat exchange?

SIze and surface area

Answer 5

Rate of heat loss depends on an organisms surface area
An animal with a large vol has a relatively small SA - harder for it to lose heat from its body
If an organism is small, its relative surface area is large so heat is lost more easily
Means smaller organisms need a relatively high metabolic rate, in order to generate enough heat to stay warm

Question 6

How does body shape affect heat exchange?

SIze and surface area

Answer 6

Animals (of any size) with a compact shape have a small SA relative to their vol - minimising heat loss from their surface
Animals with a less compact shape have a larger SA relative to their vol - increases heat loss from their surface

Question 7

Behavioural and phsyiological adpatations to aid exchange

SIze and surface area

Answer 7

1. Animals with high SA:V tend to lose more water as it evaporates from surface
   Problem for animals living in hot regions where water evaporates quickly
   Some small desert mammals have kidney structure adaptations so that they produce less urine
2. To support high metabolic rates, small mammals living in cold regions need to eat large amounts of high energy foods such as seeds and nuts
3. Smaller mammals may have thick layers of fur or hibernate when the weather gets really cold
4. Larger organisms living in hot regions find it hard to keep cool as their heat loss is relatively slow
   Elephants have developed large flat ears to increase SA, allowing them to lose more heat
   Hippos spend much of the day in water - behavioural adaptation