C2: Movement of substances

Question 1

what is diffusion

Answer 1

Diffusion is the net movement of particles (atoms,
or ions) from a region where they are of higher
oncentration to a region where they are of lower
concentration; that is, down a concentration gradient
(until equilibrium is reached).

Question 2

whats a concentraion gradient

Answer 2

Concentration gradient is the difference in concentration between two regions.

molecules diffuse down a concentration gradient

Question 3

Which net direction do you think the salt
molecules would move towards? Explain.

salt solution b has a higher concentration than a

Answer 3

There is a higher concentration of salt in solution B than solution A.
There will be a net movement of salt molecules from solution B to solution A
by diffusion until equilibrium is reached.

Question 4

the steeper the concentration gradient, the _______

Answer 4

the faster the rate of diffusion

Question 5

does equilibrium have movement

Answer 5

yes but no net movement, net movement will stop

Question 6

factors that affect rate of diffusion

Answer 6

• Temperature
  − The higher the temperature, the faster the rate of diffusion as the particles have
  more kinetic energy and they move faster
• Concentration gradient
  − The steeper the concentration gradient, the faster the rate of diffusion
• Diffusion distance
  – The shorter the diffusion distance, the faster the rate of diffusion
• Surface area-to-volume ratio
  – The larger the surface area-to-volume ratio, the faster the rate of diffusion

Question 7

explain diffusion distance and state an example of how diffusion distance is kept short in living organisms

Answer 7

• the shorter diffusion distance, the less time needed for the substance to travel, hence the rate of diffusion is higher
• In living organisms, diffusion distance is kept short by having a
  one-cell thick area for exchange of substances. For example:
  – gaseous exchange in the lungs
  – gaseous exchange in plants
  – absorption of nutrients in small intestine

Question 8

lungs have ? for faster diffusion

Answer 8

one-cell thick capillary walls

Question 9

why do cells need a large surface area to volume ratio

Answer 9

• The rate of food and
  oxygen intake is slower
  as the cell grows larger.
• Hence, it is not
  beneficial for the cell to
  grow too big.

Question 10

what is osmosis

Answer 10

Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

Question 10

what is water potential

Answer 10

Water potential is a measure of the tendency of water to move from one place to another.
* A dilute solution has a higher water potential.
* A concentrated solution has a lower water potential.

Question 11

osmosis is affected by factors:

Answer 11

temperature
sa to vol ratio
diffusion distance
water potential gradient

Question 12

What happens to a plant cell in a solution with higher water potential?

Answer 12

1. Cell sap has lower
   water potential than surrounding solution.
2. Water enters by osmosis.
3. Cell expands and turgid.
4. Cell wall prevents cell from bursting.

Question 13

What happens to an animal cell in a solution with higher water potential?

Answer 13

cytoplasm has lower WP than outside solution, water molecules enter by osmosis, cell expamds and bursts

Question 14

What happens to a plant cell in a solution with lower water potential?

Answer 14

1. Cell sap has higher water potential than surrounding solution.
2. Water leaves by osmosis from the vacuole and cytoplasm through the partially permeable cell membrane
3. Cell becomes flaccid.
4. Cytoplasm shrinks away from cell wall and cell becomes plasmolysed.

Question 15

What happens to an animal cell in a solution with lower water potential?

Answer 15

cytoplasm has hugher WP than outside solution, water molecules leave by osmosis, cell shrinks in size (crenated) spikes appear

Question 16

Why Is Turgor Important in Plants?

Answer 16

• Turgor plays an important role in maintaining the shape of soft tissues in plants.
• It keeps herbaceous (non-woody) plants firm and upright.
• Loss of turgidity (bc of high rate of water loss) causes the plant to wilt.
• Plasmolysis causes tissues to become limp or flaccid.
• When cells of a plant become flaccid, the plant wilts.
• Water may be added to the soil to dilute the soil solution. This causes water molecules to enter the plant cells and keeps the plant firm and upright.

Question 17

too much fertiliser =

Answer 17

soil solution will be very concentrated and water molecules move out of cell by osmosis, inability of roots to absorb water and evaporation of water from leaves will cause it to wilt. unless water is added to dilute the soil solution

Question 18

what is active transport

Answer 18

Active transport is the process in which
* cellular energy is used to move the particles of a substance across a membrane
* against its concentration gradient, ie, from a region where the particles are of lower concentration to a region where they are of higher concentration.

Question 19

Differences between diffusion and active transport

Answer 19

Diffusion
* Down a concentration gradient
active transport
* Against a concentration gradient
diffusion
* Energy from respiration not required
active transport
* Energy from respiration required
diffusion
* Cell membrane not required
active transport
* Cell membrane required