3.4 Movement Of Water And Solutes Through plant

Question 1

Water movement in stem.

Answer 1

The movement of water against gravity in narrow tubes such as xylem vessels.
Water can move up through very narrow xylem vessels by capillarity due to surface tension and adhesion.
Distance water travels is very small- contribution to water movement is probably insignificant.

Question 2

Water movement in stem - root pressure.

Answer 2

Build up of osmotic pressure in root system of plant which forces water upwards in xylem.

Question 3

Water movement in stem.

Transpiration - definition

Answer 3

Loss of water vapor from leaves and other plant surfaces.

Question 4

Water movement in stem.

Guttation

Answer 4

Occurs in some small herbaceous plants.
Water is forced by root pressure through the plant and out or leaves forming water droplets.

Some plants have hydathodes to facilitate guttation.

Question 5

Movement of water through root.

Casparian strip.

Answer 5

On reaching endodermis the movement of water by apoplastic pathway is blocked by the CASPARIAN STRIP.

CASPARIAN STRIP is impermeable layer around each endodermal cell.
It contains a waterproof wax called suberin.
Forces water to enter the endodermal cell by osmosis.
Water may have to pass through PASSAGE CELLS.
Regulates entry of minerals, possibly prevents entry if pathogens.

Question 6

Factors affecting rate if transpiration.

Soil water

Answer 6

If the amount of water a plant looses is not made up from up from the soil transpiration cannot continue successfully.
If absorption of water does not keep up with transpiration, loss turn or will occur and stomata will close.
Closure of stomata will result in reduced transpiration and photosynthesis.

Question 7

Factors affecting rate if transpiration.

Soil moisture, indirect.

Answer 7

Soil moisture can affect transpiration rates indirectly.

Stomata close in response to low soil moisture levels via plant growth regulator, abscisic acid.

Question 8

Active transport- examples

Answer 8

Uptake if mineral nutrients by cells.

Question 9

Active transport definition

Answer 9

Uptake if a substance across a membrane against a concentration gradient.

Question 10

Mass flow (Bulk flow) examples.

Answer 10

Water movement in xylem (transpirational pull).
Water movement in the phloem (mass flow)
Water movement between cells in apoplast.

Question 11

Active transport.

Answer 11

Uses carrier proteins embedded in the membrane to carry substances selectively across it.

Energy is required for this process.

Question 12

Mass flow (bulk flow) notes.

Answer 12

Rate if flow depends on:
Pressure difference at each end of system.
Radius of vessel.
Distance travelled.
Viscosity of liquid.
Pressure which causes water to move is called HYDRISTATIC PRESSURE.
values can be positive (pushing pressure) or negative (sucking pressure).
Rate of flow is fastest when gradient is steep, viscosity low, vessel is wide and distance short.

Question 13

Osmosis - description

Answer 13

Solutes are substances dissolved in water eg. Sugars or ions.
Selectively permeable membrane allows water to pass freely but excludes some solutes.

Rate of osmosis depends in concentration gradient of water across membrane.

Concentration gradient - the greater the difference in water concentration the faster the rate of osmosis.

Question 14

Osmosis - example.

Answer 14

Water passes into and out of cells across their cell membrane by osmosis and through adjacent cells via plasmodesmata (symplast pathway).

Question 15

Diffusion -definition

Answer 15

Transport of gases or solutes from a region of high concentration to a region of lower concentration of the transported substance.

Question 16

Diffusion - notes

Answer 16

Rate of diffusion:

Proportional to the concentration gradient, temperature, distance travelled.

Faster when gradient is steep, temp is high and distance is short.

Question 17

Example of diffusion.

Answer 17

Gasses eg, 02. + CO2 exchange in leaf.

Water vapor - transpiration.

Dissolved substances eg. Movement of minerals in the soil.

Question 18

Mass flow (bulk flow) definition

Answer 18

Movement of water in response to pressure gradient.

Question 19

Osmosis - definition.

Answer 19

Movement of water from a height water /solute concentration to a low water high solute concentration across a selectively permeable membrane.

Question 20

Factors affecting transpiration.

Wind speed

Answer 20

At high wind speed stomata close to prevent excessive water loss - transpiration stops.
Close to the surface of the leaf is boundary layer of still air.
Water vapor diffuses from the highest concentration within leaf to lower concentration in moving air beyond boundary layer.
Low wind speed- wide boundary layer - wide distance to travel. Low diffusion on still days.
High wind speed - narrow boundary layer short distance to travel. High rates of diffusion in breezy days.

Question 21

Factors affecting transpiration -temperature.

Answer 21

At high temperatures the stomata will close and transpiration will cease.
Increasing rate of diffusion of water vapor from leaf.
Stomata open more widely.

Question 22

Way to increase humidity around plants - transpiration.

Answer 22

Misting in propagation unit.

Damping down in a greenhouse - wetting floors/benches.

Question 23

Factors affecting the rate if transpiration - Humidity and water vapor concentration.

Answer 23

Water vapor concentration inside the leaf is always saturated (100% relative humidity).
Water concentration outside leaf is lower.
Water moves from leaf along water vapor concentration gradient.
If humidity around leaf is high, water gradient becomes less steep - transpiration slows.