3.3.4.2 mass transport in plants

Question 1

Adaptation of a root hair cell

Answer 1

Large surface area to volume ratio
Absorb of water from the soil to plant

Osmosis from high water potential to lower the potential area

High density of mitochondria and carrier protein : ATP need for active transport

Question 2

Use of water (how is this related to assumption of potometer experiment)

Answer 2

Fill up vacuole , leaf cell turgidity
Photosynthesis
Medium to transfer mineral ions
Hydrolysis to put down small molecules

It’s not valid to assume that water uptake what is equivalent to the rate of transpiration?

Question 3

Definition of transpiration

Answer 3

Evaporation of water from the leaves of plants via stomata

Question 4

How water potential allow absorption in the route to continue?

Answer 4

water potential of soil is higher than the water move into the cell and cell water potential increase so is higher than the next cell so process continue.

Question 5

Factor that affects evaporation rate

Answer 5

Humidity
Higher humidity, shallow water potential gradient, less net movement of water from leave to air , lower evaporation rate

Wind : higher windspeed, maintain water, potential gradient due to constantly remove water on, leave surface and water vapour/ moisture air, higher evaporation rate

Temperature : higher temperature, more kinetic energy, move faster water, molecules move, diffuser move further apart from each other, change from liquid to gas increase, evaporation rate

Light intensity: increase in light intensity, more stomata open, so increase in flow rate due to cohesion of water molecules

Question 6

what causes water to move up the xylem?

Describe the cohesion tension theory of water transport in the xylem

Answer 6

1. Transpiration stream(pulling force) /evaporation/diffusion of water through stomata/from leaves
2. Lower water potential of Mesophyll/ leaf cell
3. Water pulled up xylem creating tension –Create negative pulling pressure
4. Water molecules cohere together by hydrogen bonds (cohesion) –Water is dipolar with negative oxygen and and positive hydrogen and attract each other
5. Adhesion of water to walls of xylem–Attraction with wall of xylem
6. Forming continuously water column (capillary action)– Narrower tube , surface area to volume ratio increased, more adhesive force, more pulling force

additional : Root pressure (pushing force) from leaves cell to xylem

Question 7

Structure of xylem related to the function

Answer 7

Long, continuous, hollow tube: continuous column of water pull up, maintain transpiration stream, quick easy, water flow
No end wall/ no organelle : easy and more waterflow, no obstruction
Lignin wall : withstand cohesion tension ,provide support and strength, prevent collapse
Pits in wall : allow lateral movement / get round block vessel

Question 8

Use of potometer

Answer 8

Measuring the rate of transpiration

Question 9

How to measure the rate of transpiration (cm3 per min)

Answer 9

Measure the distance of water move
Measure the time

Measure the radius of capillary tooth
Distance divided by time

Question 10

Precaution of the experiment, using potometer

Answer 10

Seal the bug tight and put Vaseline on plants
No air is allowed in , prevent water backflow to the reservoir by gravity, air bubble going back

Cut the stem in water
No air bubble lock , allow continuous water column with cohesion, prevent air bubble not moving

Dry leaves
No water blocks stomata to affect the rate of evaporation

No water bubble in apparatus
Accurate, volume calculation

Question 11

How do you create different factor for transpiration experiment in Lab?

Answer 11

Wind, fan
Temperature , radiator
Humidity , plastic bag environment

Question 12

Use of resourvoir in the experiment of potometer

Answer 12

Reset/ return the bubble back to the starting point
allow repeat
Increase reliability / anomalous, result, can be, identify

Question 13

Definition of translocation

Answer 13

Transport of organic molecule from source (production) to sink (used/stored) via phloem

Question 14

Structure and function of phloem

Answer 14

Rough, endoplasmic reticulum: produce carrier protein for active transport
Mitochondria : ATP for active transport against a concentration gradient

Plasmodesmata : allow cell to cell, transport and communication
Organelles pushed to the side/ at edge (no nucleus) (live) / few organelles/ more room : easier and more flow
Thick wall : resist pressure

Sieve element + companion cell

Question 15

Explain to experiment of mass flow theory

Answer 15

Ringing experiment
Ring of protective bark layer of phloem removed around whole conference of woody stem
After Time region, immediately above the ring start to swell
Sample taken from swollen region are rich in sugar, and other substances
Non photosynthetic tissue below the ring die, while those above continue to grow

Tracer experiment
Radioactive isotope can be used to treat the movement of substances in the plant
Plants grow in an atmosphere of CO2 14 in cooperate C 14 into sugar a produced during photosynthesis
Radioactive isotope can then be traced using autoradiography
Thin cross-section of the plant stem can be taken place on a piece of x-ray film
The film appears black where it has been exposed to the radiation produced by c14 in sugar

Question 16

Why the diameter of the trunk decrease during midday

Answer 16

Adhesion of water molecule to wall of xylem
Result, in tention as water pull up stem
Pulling in the wall

Midday = warmers / brightest
Stomata open in light , more, water lost
Water evaporate more when warm / more heat energy for water evaporation
Hydrogen bond /cohesion between water molecules
Adhesion between water, molecules and wall of xylem
Pulled inward by fast flow of water by tension

Question 17

How to measure the rate of water loss per millimetre square of surface area of the leaves of the shoot

Answer 17

Draw round each leave on graph paper, and count the square
of both sides of the leave
Divide the rate of water loss by total surface area

Question 18

Why the rate of water movement through a shoot in potometer may not be the same as the rate of water movement throughout the shoot of a whole plant

Answer 18

Plant has root (stem cut)
Xylem cell, very narrow (tube )

Question 19

Why water molecules and carbon dioxide can pass through same channel protein

Answer 19

Small similar in size to fit through the channel
similar shape bind with channel

Question 20

The use of control in an experiment

Answer 20

Used to compare effects of other treatment/ as baseline
Show measure the effect of dependent variable

Question 21

Describe the transport of carbonhydrates inplants (mass transport)

Answer 21

1. Sucrose actively transported into phloem (cell); OR Sucrose is co-transported/moved with H+ into phloem (cell);
2. (By) companion/transfer cells;
3. Lowers water potential in seive cell (in phloem)
   4.water enters (from xylem) by osmosis;
4. ((Produces) high(er) (hydrostatic) pressure; OR (Produces hydrostatic) pressure gradient
   6.Due to increased volume of water
5. Mass flow to respiring cells OR Mass flow to storage tissue/organ;
6. Unloaded/removed (from phloem) by active transport;

Question 22

During their experiment measureing rate of translocation, the scientists ensured that the rate of photosynthesis of
their plants remained constant.
Explain why this was important.

Answer 22

1. Rate of photosynthesis related to rate of sucrose production;
2. Rate of translocation higher when sucrose concentration is higher.

Question 23

What other information is required in order to calculate the mean rate of movement
of the carbon down the trunk apart from amount of carbon and time?

Answer 23

length of trunk