Transport In Plants

Question 1

What direction does xylem tissue transport water and mineral ions?

Answer 1

Up

Roots to leaves

Question 2

What direction does phloem tissue transport organic substances?

Answer 2

Up and DOWN

Question 3

Describe xylem vessels

Answer 3

Long, tube like structures formed from dead cells joined end to end.
No end walls…uninterrupted

Question 4

Cohesion tension in xylem

Answer 4

Helps move water up the plants

• water evaporates from leaves
• creating tension, pulling more water into leaf
• water is cohesive so when some are pulled the others follow
• the whole column of water moves in xylem, upwards
• water enters stem through roots

Question 5

What is transpiration

Answer 5

Evaporation of water from plants surface

When stomata open it moves out of the leaf down the concentration gradient

Question 6

4 factors affecting transpiration rate

Answer 6

Light
Temperature
Humidity
Wind

Question 7

What can you use to measure transpiration rate

Answer 7

Photometer
Cut a shoot underwater at a slant. Assemble to photometer underwater, so no air enters. Remove apparatus from water keeping end of capillary tube submerged. Must be water and airtight.
Remove the end of the capillary tube from the water beaker and let one air bubble form and put back underwater. Record starting position. Start stopwatch and record distance moved by the bubble.
Change a variable at a time e.g. Temp,wind,humidity,light and keep others constant.

Question 8

Sieve tube elements and companion cells in phloem

Answer 8

Sieve tube elements are living cellls that form the tube for transporting solutes, they have no nucleus and few organelles.
There is a companion cell for each sieve tube element. They carry out living functions for sieve cells(provide energy)

Question 9

Translocation in the phloem

Answer 9

The movement of solutes (assimilates) to where they’re needed in a plant.
It requires energy.
It moves solutes from source(where the solute is made(high concentration)) to sink(where the solute is used up(lower concentration)).
Enzymes maintain the concentration gradient from source to sink by changing the solutes at the sink. Making a lower concentration at the sink than source.

Question 10

An example of a sink and source

Answer 10

Sink-other parts of the plant e.g. Food storage organs e.g. Tuber cells in potatoes
Source-usually the leaves

Question 11

Mass flow hypothesis

For phloem transport

Answer 11

1)active transport loads the solutes from companion cells into sieve tubes at the source.
Lowers the water potential in sieve tubes(water enters tubes by osmosis from xylem and companion cells)
High pressure in sieve tubes at source end.
2)at sink, solutes are removed from phloem.
Increasing water potential in sieve tubes, water leaves tubes by osmosis.
Lowers pressure in sieve tubes.
3)pressure gradient from source to sink end, which pushes solutes along the sieve tubes towards the sink.
When they reach the sink the solutes are used (respiration) or stored(starch).

Question 12

Evidence for mass flow

Answer 12

For:
-if a ring of bark is removed from a woody stem, a bulge forms above the ring. Bulge has higher concentration of sugars than below the ring, evidence for downward flow.
-radioactive tracer can track movement of organic substances.
-investigation with aphids. Sap flows out nearer leaves, evidence for pressure gradient.
-metabolic inhibitor in phloem stops translocation, evidence for active transport.
Against:
-sugar travels to many sinks, not just one with higher water potential.
-sieve plates create a barrier to mass flow. Lots of pressure needed for solutes to get through at a reasonable rate.

Question 13

How can translocation be demonstrated experimentally?

Answer 13

Using radioactive tracers.