Transport in cells

Question 1

Explain how substances may move into and out of cells across the cell membranes via diffusion

Answer 1

Diffusion is the process through passive transport whereby particles move along the concentration gradient from a high concentration to a low concentration.
For example, diffusion occurs in villi where there is a lower concentration of, for example, glucose outside the cell than there is inside. The glucose particles travel through the semi-permeable cell membrane and into the cell. The opposite occurs when there is a higher concentration inside the cell than outside, and hence particles will move out the cell through the cell membrane.

Question 2

Describe diffusion

Answer 2

Diffusion is the process through passive transport whereby particles move down the concentration gradient from a high concentration to a low concentration.

Question 3

Recall that some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney

Answer 3

Waste products have a higher concentration in cells than in the nearby blood vessels, so those waste products travel down the concentration gradient and into the bloodstream.

Question 4

Describe factors the affect the rate of diffusion

Answer 4

• The permeability/ lack of surface diffusion is occurring over
• Concentration gradient (difference in concentration)
• The density of the particles

Question 5

Recall that a single-celled organism has a relatively large surface area to volume ratio to allow sufficient transport of molecules into and out of the cell

Answer 5

This is so that they can maximize the transportation of oxygen/water/minerals in and out of the cell.

Question 6

Explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials

Answer 6

In instances where diffusion is key, cells, organs and tissues are adapted to increase their rate of diffusion:

• Increased surface area (like the projections of villi in the small intestine)
• Lots of mitochondria, to release lots of energy for active transport
• Highly permeable cell membrane
• High blood supply to transport diffused particles away quickly to keep the concentration low, and the concentration gradient high

Question 7

List factors that increase the effectiveness of an exchange surface

Answer 7

• High surface area: volume ratio
• Large blood supply
• Thin membrane
• Increasing the difference in concentration, therefore a steeper concentration gradient

Question 8

Describe osmosis and understand the osmosis required practical

Answer 8

Osmosis is essentially diffusion, except with the concentration of water in solutions. Osmosis occurs along the concentration gradient (passive transport).
Osmosis ends when the concentration gradient between two solutions is balanced: when the concentration of water between two solutions separated by a membrane is isotonic.

Question 9

HYPERTONIC

Answer 9

Higher concentration of solutes outside the cell. Water will move out of the cell via osmosis

Question 10

HYPOTONIC

Answer 10

Lower concentration of solutes outside the cell. Water will move into the cell via osmosis

Question 11

ISOTONIC

Answer 11

Equal concentration of water between two solutions