3.3.4.2 Mass Transport In Plants

Question 1

How is xylem adapted

Answer 1

No end walls, long continuous tube-water flows as a continuous column

No cytoplasm - no obstructions/easier water flow

Thick cell walls with lignin-provides support to withstand tension and preventing water loss

Question 2

Cohesion theory in plants

Answer 2

-Water is lost from leaf by transpiration-water evaporates through stomata.
Reducing water potential
-So water is drawn out of xylem down water potential gradient
-creates tension in xylem
-hydrogen bond result in cohesion between h20 molecules, so it’s pulled up as a continuous column
-water also adheres to xylem
-water enters roots via osmosis

Question 3

How to set up a photometer

Answer 3

1) cut a shoot underwater at a slant (no air)
2) capillary end submerged in water
3) insert shoot underwater
4) insure it’s watertight/airtight
5)dry leaves allows time for shoot to acclimatise
6) shut tap to reservoir
7) formation of air bubble

Question 4

How to measure rate of transpiration

Answer 4

Record position of air bubble

Record distance it moves in a certain time (60 seconds)

Calculate volume of air bubble (pi x r^2)- times volume by distance

Calculate rate of water uptake- divide volume by time taken

Question 5

Limitation of photometer

Answer 5

Water uptake might not be rate of transpiration:
-water used for support and water used in respiration/photosynthesis

Question 6

How is the phloem adapted

Answer 6

Sieve tube elements - no nucleus/ few organelles, this maximises space for organic substances

Companion cells - lots of mitochondria for atp to active transport of solutes

Question 7

What is translocation

Answer 7

Movement of assimilated (solutes such as sucrose )

From source cells (leaves ) to sink cells ( storage - roots) by mass flow

Question 8

Mass flow hypothesis/transloctiom

Answer 8

At source - sucrose is actively transported into phloem by sieve cells by companion cells

This lowers the water potential in sieve tubes so water enters from xylem by osmosis

This increases hydrostatic pressure in sieve tubes and creates a hydrostatic pressure gradients

Mass flow occurs - from source to sink

At sink - sucrose is removed by active transport, ready for use by respiring cells or stored

Question 9

Use of traces experiments to investigate transport in plants

Answer 9

Leaf supplies with radioactive tracer ( CO2 containing isotope c14)

It’s incorporated into organic substances during photosynthesis

These move via translocation

Movement is tracked via Geiger counter