3.3.1 Surface area to volume ratio

Question 1

The name given to the environment surrounding a cell

Answer 1

tissue fluid

Question 2

Single celled organisms can match their metabolic demands by

Answer 2

simple diffusion

Question 3

Exchange of materials in living organisms occurs at ..

Answer 3

exchange surfaces e.g. lungs, intestine

Question 4

How much material that needs to be exchanged in an organism depends on

Answer 4

its size and its metabolic rate

Question 5

Substances a cell exchanges with its environment include

Answer 5

oxygen, carbon dioxide, nutrients (glucose)

Question 6

Exchange of materials in living organisms takes place via (4 types of transport)..

Answer 6

simple diffusion
facilitated diffusion
osmosis
active transport

Question 7

As an organism gets larger what happens to its surface area to volume ratio?

Answer 7

its gets smaller - less efficient exchange.

Special exchange surfaces therefore required i.e. lungs

Question 8

How do larger organisms cope with their increasing size?

Answer 8

They have specialised exchange surfaces - which have large surface area:volume ratio!

OR

they are flat and thin therefore no cell is too far away from the surface

Question 9

What is ficks law?

Answer 9

diffusion rate is directly proportional to surface area x difference in concentration divided by length of the diffusion pahway

Question 10

How are specialised exchange surfaces adapted?

Answer 10

1. Large surface area to volume ratio
2. Thin - short diffusion pathway
3. Selectively permeable
4. Extensive blood supply to maintain concentration gradient

Question 11

single celled organisms SA: volume ratio is described as

Answer 11

large surface area to volume ratio

Question 12

single celled organisms obtain their nutrients via..

Answer 12

simple diffusion

Question 13

Why are insects usually small

Answer 13

their tracheal system relies on diffusion, for this to be efficient the diffusion path needs to be short and this is only achieved if the insects are small

Question 14

Maths Skills:

If a cube had a side length of 1cm, what would it’s SA be?

Answer 14

6 cm2

Question 15

Maths Skills:

If a cube had a side length of 1cm, what would it’s volume be?

Answer 15

1 cm3

Question 16

Maths Skills:

What is the SA:V ratio of a cube with a side of 1cm

Answer 16

6:1

Question 17

Maths Skills:

How do you calculate the volume of a sphere?

Answer 17

4/3 x 3.14 x r3

3.14 = pi, r = radius

Question 18

Maths skills:

How do you calculate the surface area of a sphere?

Answer 18

4 x 3.14 x r2

3.14 = pi, r = radius

Question 19

List 4 features of specialised exchange surfaces

Answer 19

1. Large SA - increases rate of exchange
2. Thin - short diffusion distance
3. Selectively permeable - allows selected materials to cross
4. Diffusion gradient maintained - eg by movement of medium - blood, air

Question 20

Remember substances not only have to move into cells, they have to move into organelles too.
What would move into mitochondria and why?

Answer 20

Oxygen and glucose for (aerobic) respiration

Question 21

explain the relationship between size and surface area to volume ratio in organisms

Answer 21

as size increases, SA:volume ratio decreases

Question 22

explain why oxygen uptake is a measure of metabolic rate in organisms

Answer 22

oxygen used in respiration which is chemical process

Question 23

describe and explain how the countercurrent system leads to efficient gas exchange across the gills of fish?

Answer 23

• blood and water will always flow in opposite directions
• diffusion gradient maintained across whole length of gill
• will always be a higher concentration of oxygen in blood than water

Question 24

amoebic gill disease (AGD) is caused by a parasite that lives on the gills of some species of fish. the disease causes the lamellae to become thicker and to fuse together.

AGD reduces the efficiency of gas exchange in fish, give 2 reasons why?

Answer 24

• thicker SO longer diffusion distance

- because fused, surface area reduced

Question 25

the volume of water passing over the gills increases if the temperature of the water increases. suggest why?

Answer 25

• more oxygen as less dissolved in water

- due to increased respiration

Question 26

how would you go about calculating the volume of water that would have to pass over the gills each hour to supply the oxygen required by the fish?

Answer 26

oxygen required by fish/ volume of oxygen absorbed by
gills

                                  X mass of fish

Question 27

many different substances enter and leave a cell by crossing its cell surface membrane. describe how substances can cross a cell surface membrane?

Answer 27

• simple diffusion from high to low concentration
• small, lipid-soluble substances pass via phospholipid bilayer
• large, polar molecules go through proteins
• water molecules move by osmosis
• active transport is movement from low to high concentration against concentration gradient
• involves carrier proteins and using ATP

Question 28

describe and explain how lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them?

Answer 28

• many capillaries provide large surface area SO faster diffusion
• alveoli lining thin SO short diffusion distance SO faster diffusion
• ventilation maintains concentration gradient SO fster diffusion