Topic 4

Question 1

The bigger an object

Answer 1

the smaller the SA:Volume ratio

Question 2

What does the SA:Volume ratio of an organism dictate?

Answer 2

The SA:Volume ratio of an organism dictates whether the organism needs a separate transport to carry substances around

Question 3

How does SA:volume ratio affect diffusion in larger organisms?

Answer 3

In larger organisms, animals have a smaller surface area to volume ratio meaning diffusion would not be sufficient.

This means that a transport system is required.
As animals became larger they develop more specialised gas exchange surfaces. This allows substances to be exchanged efficiently therefore allowing the organisms metabolic demands to be met.

Question 4

How does SA:volume ratio affect diffusion in unicellular organisms?

Answer 4

For unicellular organisms, such as amoeba, all gases and nutrients diffuse straight through to the cell membrane and also diffuse rapidly to all parts of the cell.

In single celled organisms diffusion alone is enough to transport substances. This is because they have a large surface area to volume ratio.

Question 5

Small organisms

Answer 5

Small organisms = large SA:Vol ratio = no need for a transport system

Question 6

Large organisms

Answer 6

c

Question 7

Mass flow

Answer 7

The movement of substances from high pressure to low pressure

Question 8

Factors affecting the rate of diffusion

Answer 8

The surface area

Difference in concentration gradient of the particles diffusing

The distance over which diffusion is taking place

Question 9

How does surface area affect the rate of diffusion?

Answer 9

The surface area - the bigger the surface area the more particles can be exchanged at the same time

Question 10

How does difference in concentration gradient affect the rate of diffusion?

Answer 10

The more particles there are on one side of a membrane compared with the other, the faster they move across.

Maintaining the gradient makes diffusion faster

Question 11

What is an exchange surface?

Answer 11

An exchange surface is the place that substances are moved across membranes in an organism, for example the lungs of birds or mammals and the gills of fish.

Question 12

Features of an efficient exchange surface

Answer 12

Large surface area - more particles can move across

Very thin surface (membrane) so that the diffusion distance is short, which increases the rate of exchange

Permeability of exchange surface to the particular substance - to let the substances through pores

Question 13

Features of an efficient gas exchange surface

Answer 13

Large surface area giving sufficient gaseous exchange to supply all the needs of the organism

Very thin surface (membrane) so that the diffusion distance is short, which increases the rate of exchange

In animals, a rich blood supply to the respiratory surfaces. The blood is involved in the transport of the respiratory gases to and from the site of gaseous exchange, helping to maintain a steep concentration gradient

Moist surfaces as diffusion takes place with the gases in solution

Permeable surfaces that will allow free passage of respiratory gases

Question 14

Epiglottis

Answer 14

Epiglottis - flap of tissue that closes over the glottis, in a reflex action when food is swallowed. This prevents food from entering the gas exchange system

Question 15

Incomplete rings of cartilage

Answer 15

Incomplete rings of cartilage - prevent the trachea and bronchi from collapsing but allow food to be swallowed and moved down the oesophagus

Question 16

Passive transport

Answer 16

Passive transport takes place as a result of concentration pressure of electrochemical gradients and involves no energy from the cell

Question 17

Passive transport

Answer 17

Passive transport is transport that takes place as a result of concentration pressure of electrochemical gradients and involves no energy from the cell

Question 18

Examples of passive transport mechanisms

Answer 18

Diffusion

Facilitated diffusion

Osmosis

Question 19

Examples of passive transport mechanisms

Answer 19

Diffusion

Facilitated diffusion

Osmosis

Question 20

Examples of active transport mechanisms

Answer 20

Active transport

Endocytosis

Exocytosis

Question 21

Diffusion

Answer 21

The movement of the particles in a liquid or gas down a concentration gradient from an area where they are at a relatively high concentration to an area where they are at a relatively low concentration

Question 22

Facilitated diffusion

Answer 22

The movement of particles down a concentration gradient through either a carrier protein or a channel protein.

For example, ions such as Na+ and molecules such as glucose are charged. These particles cannot move via diffusion since the cell membrane would repel them. Instead they travel through channel or carrier proteins.

Question 23

Osmosis

Answer 23

This is the movement of free water molecules from an area of high concentration to an area of low concentration.

This happens across a partially permeable membrane.