Topic 3 Flashcards
(11 cards)
1
Q
What do potometers measure?
A
The amount of water uptake by a plant during a period of time
2
Q
Why is the plant cut under water?
A
Prevent air entering the xylem due to cohesion tension theory and breaking the continuous column of water. Only water is drawn into the xylem.
3
Q
How is rate calculated?
A
Volume of water / time taken for water to travel
4
Q
What are sieve tubes?
A
- Living cells
- No nucleus
- Contains few organelles
5
Q
What are companion cells?
A
Provide ATP for active transport of organic substances
6
Q
Describe translocation
A
- At the source sucrose is actively transported into the sieve tubes from companion cells
- Water potential decreases in the sieve tube
- Water potential enters sieve tube from the xylem and companion cells by osmosis
- This increases hydrostatic pressure in the sieve tubes
- At the sink sucrose is actively transported out of sieve tubes
- Water potential of sieve tubes increase at the sink
- Water leaves phloem by osmosis decreases hydrostatic pressure at the sink
- Creates a pressure gradient
7
Q
What do ringing experiments show?
A
- Stem bulges with fluid containing more sugar above sections where a ring of bark has been removed
- Shows removal of phloem prevents downwards flow of sugars
8
Q
What do radioactive tracers show?
A
- Radioactive isotopes of carbon in the form of CO2 that is supplied to the leaf is incorporated into organic substances and can be traced around the plant
- This shows that organic substances move from the source to the sink
9
Q
What do aphids show?
A
- Sap fed on by aphids flows out of stems more quickly at the top of the stem
- Shows pressure gradient in phloem
10
Q
What to metabolic inhibitors show?
A
- Translocation stops when inhibitors that prevent ATP synthesis are added to the phloem
- Shows translocation requires energy
11
Q
A
