3. Surface Area to Volume Ratio

Question 1

Do multicellular organisms have a large or small SA:V ratio?

Answer 1

Small

Question 2

Do unicellular organisms have a large or small SA:V ratio?

Answer 2

Large

Question 3

What do cells need to do to survive (in terms of importing/exporting products)?

Answer 3

Import molecules and expel waste products through its plasma membrane

Question 4

If a cell’s surface area is too small compared to its volume…

Answer 4

not enough of the necessary molecules can get in, and not enough waste (including heat) can get out

Question 5

Why is a large SA:V ratio beneficial?

Answer 5

1. Shorter diffusion pathways: takes less time (& energy if active transport) for molecules to move in/out of cells
2. Easier to generate concentration gradients: makes diffusion more efficient

Question 6

Why would a large SA:V ratio not be beneficial?

Answer 6

1. Small, warm-blooded mammals lose heat very quickly: need to eat almost constantly
2. Desert plants would lose water quickly with flat leaves, so they minimise their SA:V ratio to conserve water

Question 7

Unicellular organisms exchange materials by _____ with their environment

Answer 7

diffusion

Question 8

A large SA:V ratio gives a ______ for diffusion

Answer 8

short distance

Question 9

Most large, multicellular organisms have specialised…

Answer 9

exchange systems

Question 10

Adaptations of polar bear (there are 4)

Answer 10

1. Round structure: reduces SA to prevent heat loss
2. Tiny ears - prevents heat loss
3. Black skin
4. Hollow fur - traps air as an insulating layer

Question 11

What does cell division allow for?

Answer 11

Cell differentiation
Specialised functions
More complex multicellular life

Question 12

Cells compartmentalise - what does this mean?

Answer 12

They use membranes to carry out metabolic processes. In eukaryotes, these are called organelles.

Question 13

What are organelles made of?

Answer 13

Membranes. This maximises the SA for reactions.

Question 14

What do some organs (eg. intestines) do?

Answer 14

Fold up to maximise SA:V ratio, making absorption of food molecules more efficient

Question 15

Adaptations of roots

Answer 15

They are long and branched, with root hairs on the cells to maximise the SA for water uptake

Question 16

What else do multicellular organisms need to exchange apart from nutrients and gases, and why is this important?

Answer 16

Heat!

This helps to maintain bodies at a constant temperature at a certain range, regardless of external temperature.

Question 17

2 factors that influence heat exchange

Answer 17

Size and shape

Question 18

Rate of heat loss is dependent on the ______ of the organism

Answer 18

surface area

Question 19

Effect of size on heat exchange

Answer 19

Large organism = large volume = smaller SA relative to its size, so heat loss is harder.
Small organism = small volume = high SA. Since there is a high SA where heat exchange can happen, these organisms need to have a HIGHER METABOLIC RATE to generate more heat for it to stay warm

Question 20

Effect of shape on heat exchange

Answer 20

More compact shape = small SA = no need for high metabolic rate to minimise heat loss from the body
Less compact shape = high SA = high metabolic rate to produce more heat to maintain body temp

Question 21

Small desert mammals

Answer 21

High SA:V ratio: fast loss of water. To control this, they develop smaller kidneys to produce less urine.

Question 22

Elephant

Answer 22

Low SA:V ratio: hard to cool down during hot months. Large ears to increase SA.