Movement Of Substances Into And Out Of The Cells

Question 1

Describe an example of where diffusion of gasses is important in multicellular organisms. [3]

Answer 1

Gas exchange in the lungs (of animals) for respiration OR gas exchange in the leaves for respiration OR gas exchange in the gills for respiration; [1 mark]
Oxygen moves from alveoli into the blood (animals) OR in from the air (spaces) into the spongy mesophyll cells (plants) OR from water in into the blood (fish); [1 mark]
Carbon dioxide moves from the blood into the alveoli (animals) OR out from the spongy mesophyll cells into the air spaces (plants) OR from the blood to the water (fish); [1 mark]
OR

Gas exchange in the leaves for photosynthesis; [1 mark]
Oxygen moves out from the spongy mesophyll/palisade cells into the air (spaces); [1 mark]
Carbon dioxide moves in from the air (spaces) into the palisade/spongy mesophyll cells; [1 mark]

Question 2

Identify one feature of a gas exchange surface which maximises the rate of diffusion.

Answer 2

Thin/short diffusion distance; [1 mark]
Steep concentration gradient; [1 mark]
Large surface area (to volume ratio) for gas exchange; [1 mark]

Question 3

Glucose is an example of a nutrient that is transported by active transport through the epithelial cell.
Explain what is happening along the folded membrane of the epithelial cell during the process of active transport of glucose. [3]

Answer 3

Any three of the following:

Glucose enters the carrier protein (from area of low glucose concentration); [1 mark]
(The carrier protein uses) energy/ATP; [1 mark]
Carrier protein changes shape; [1 mark]
The glucose is released on the other side of the membrane (area of high glucose concentration); [1 mark]

Question 4

Compare and contrast active transport and osmosis.

Answer 4

Minimum of one of the following:

Both involve transporting substances; [1 mark]
Both take place across a membrane; [1 mark]
Differences

Minimum of two of the following:

Active transport is from low to high concentration/against a concentration gradient whereas osmosis is from high to low water potential; [1 mark]
Active transport involves a carrier protein whereas osmosis does not; [1 mark]
Osmosis is the transport of water only whereas active transport involves the transport of many other things; [1 mark]

Question 5

Substances can move into and out of cells by a variety of mechanisms.
Explain the factors that affect the rate of movement of substances into and out of cells. [5]

Answer 5

Any five of the following:

Temperature increases (kinetic) energy / particle movement / more collisions; [1 mark]
A (bigger) difference in concentration / concentration gradient increases the rate of movement; [1 mark]
A short(er) distance increases diffusion / a short diffusion distance increases the rate of movement; [1 mark]
Larger surface area to (volume ratio) increases diffusion; [1 mark]
Lower mass / if the size of the particle is smaller particles move faster; [1 mark]
Larger particles / charged particles cannot pass through the cell membrane; [1 mark]
(Increased) oxygen / ATP / respiration / energy for active transport; [1 mark]

Question 6

One of the sugars absorbed by active transport is glucose.
Xylose is a sugar that is the same size as glucose, but it is not absorbed by active transport.
Suggest a reason why. [1]

Answer 6

Any one of the following:

Active transport is selective; [1 mark]
Transport/carrier proteins in the cell membrane can distinguish between glucose and xylose; [1 mark]
There is no transporter protein specific for xylose; [1 mark]