Plant Funtions Tracker mini test

Question 1

Describe how to dissect a stem, longitudinally and transversely, to demonstrate the position and structure of xylem. (5)

Answer 1

Cut the stem into very thin sections
Longitudinally = length ways
Transversely = across the stem
Place on a microscope slide
Add a drop of water
Add two drops of stain (toluidine blue O)
View the xylem under the microscope

Question 2

Describe how to draw stained sections of plant tissue to show the distribution of xylem and phloem. (5)

Answer 2

Sharp pencil
One continuous line
Diagram fills at least half the page
Magnification stated
Xylem and phloem labelled
Label lines drawn with a ruler

Question 3

Structure and function of xylem vessels

Answer 3

Structure: 2 of each- Long, tube like structures
No end walls
No cytoplasm or organelles
Cell walls thickened with lignin
Lignin has holes called pits

Function: One of each- To transport water and mineral ions

Question 4

Structure and function of Sieve Tube Elements

Answer 4

Structure: 2 of each-Joined end to end to form sieve tubes
Have sieve plates
Very thin cytoplasm
Few organelles

Function: One of each- To transport assimilates, for example sucrose

Question 5

Structure and function of Companion cells

Answer 5

Structure: 2 of each-Joined to the sieve tube elements
Contain all organelles
Lots of mitochondria

Function: One of each- To aid the loading of sucrose into the phloem

Question 6

. Explain the need for transport systems in multicellular plants. (3)

Answer 6

Large organisms, so some cells too deep for rate of diffusion to be sufficient
Small surface area to volume ratio
High metabolic rate (but much lower than animals)

Question 7

1. Define the term translocation. (3)

Answer 7

Energy-requiring process
Transports assimilates, for example sucrose
From the source to the sink

Question 8

. Describe active loading of sucrose into the phloem at the source. (5)

Answer 8

Companion cell actively pump hydrogen ions out by active transport
This sets up a diffusion gradient of hydrogen ions
Hydrogen ions diffuse back into the companion cell
Through a co transporter protein
Sucrose travels at the same time
Sucrose diffuses through the plasmodesmata into the sieve tube elements

Question 9

3. Describe how sucrose solution moves through the phloem. (6)

Answer 9

Sucrose enters the sieve tube element at the source
This lowers the water potential
Water moves into the sieve tube element by osmosis
This increases the hydrostatic pressure
Sucrose leaves the phloem at the sink
Water follows by osmosis
This reduces the hydrostatic pressure at the sink
Therefore, sucrose solution moves via mass flow.