U3T6 – Mass Transport in Plants

Mass Transport in Plants

1 / 25

Xylem or Phloem ? - This type of cell is living, but with few organelles.

Xylem

Phloem

2 / 25

Xylem or Phloem ? - This type of cell is carries dissolved organic substances both up and down the plant

Xylem

Phloem

3 / 25

Xylem or Phloem ? - No end plates on these cells

Xylem

Phloem

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What is transpiration the movement of?

Water, with dissolved organic substances.

Pure water.

Water with dissolved mineral ions.

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Through which part does the water evaporate out of the leaf?

Guard Cells

Stomata

Lower Epidermis Cells

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The evaporation of water molecules out of the leaf, 'pulls' the water molecules behind up. What is this 'pull' called ?

Cohesion

Tension

Mass Flow

7 / 25

Water molecules stick together due to what type of bond?

Oxide Bonds

Hydroxide Bonds

Hydrogen Bonds

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What term is used to describe the 'sticking' together of water molecules?

Cohesion

Tension

Mass Flow

9 / 25

Which of the following would decrease the rate of transpiration?

High Humidity

High Light Intensity

High Temperature

10 / 25

How does an increase in wind speed, increase the rate of transpiration?

Increases or maintains the water potential gradient between the air inside the leaf, and the air outside.

Increase in wind is detected by small hairs on the leaves, which open the stomata.

Decreases the water potential gradient between the air inside the leaf, and the air outside.

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What piece of equipment is used to measure transpiration ?

Transpirometer

Potometer

Respirometer

12 / 25

Which direction will the bubble move?

Towards the beaker

Towards the plant

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What is the tap and water reservoir above it for?

Getting the bubble into the tube

Measuring the volume of water

Resetting the bubble to the start position

14 / 25

How do you calculate the rate of water transpired by the plant?

Measure the drop in water from the beaker then divide by time.

Measure the drop in water from the reservoir above the tap.

Measure the radius of the capillary tube, then using the cross section area, multiply by the distance moved by the bubble and divide by time.

15 / 25

Which would not increase the volume of water transpired by the plant?

Low light Intensity

Low Humidity

High wind speed

16 / 25

What is translocation the movement of?

Water, with mineral ions.

Pure sucrose.

Organic substances dissolved in water.

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In terms of translocation, what is an 'assimilate'?

An estimation of the mass of glucose your plant will use.

Any organic substance that becomes part of the plant's cells. E.g Amino Acids, Glucose etc.

The mass of amino acids produced by converting glucose.

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Which of the following is an example of a 'source' ?

A photosynthesising leaf.

A Respiring meristem.

A storage tuber in the root.

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Which of the following is an example of a 'sink' ?

A photosynthesising leaf.

A Respiring meristem.

A root hair cell absorbing nitrate ions.

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The Mass Flow Hypothesis, is the best explanation for translocation in plants. What does it suggest happens at 'sources'?

Substances move by diffusion from a high concentration where they are made, to a lower concentration in the phloem.

Substances are actively transported out of the source cell into the phloem, reducing the water potential in the phloem.

Substances are stored, reducing the concentration in the source, creating a concentration gradient.

21 / 25

In the mass flow hypothesis, the water potential is reduced in the phloem near the sources. What will happen to water movement?

Water will move into the source cells via osmosis, from the phloem. Reducing the pressure in the phloem.

The same amount of water will move in as move out as it is now isotonic.

Water will move into the phloem via osmosis, increasing the pressure.

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What happens to the solutes at the sink?

They are pumped back up phloem going the other way.

They are more dense so sink down, and gather in cells on the lower surface.

Enzymes break them down or join them together as insoluble storage.

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At the sink, solutes are removed from the phloem, what effect does this have on water movement?

The water potential is increased, so water moves out of the phloem reducing pressure.

The water potential is decreased, so water moves into the phloem increasing pressure.

The water potential remains isotonic, as other solutes are pumped in to replace those lost.

24 / 25

Which of the following is evidence against the mass flow hypothesis?

Removal of xylem on a tree trunk ( ringing) causes a bulge above it, which has more sucrose.

Sieve plates cause a barrier to the pressure gradient in mass flow and would slow the flow.

Radioactive CO2 shows movement from leaf to the roots.

25 / 25

If a small tube is inserted into the phloem through the bark of a tree, sap containing sucrose leaks out. Where on the tree will the most sap leak from due to the highest hydrostatic pressure?

Top of the branch, nearest the leaves.

Middle of the tree, near the top of the trunk.

Bottom of the trunk.

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