Chapter 7 - Mass Flow Flashcards
What organelle do companion cells have more of?
Mitochondria
What is the role of companion cells?
Support sieve tube cells
Provide ATP
How can we use radioactive labels as evidence for mass flow?
Grow plant in normal atmosphere
Introduce artificial atmosphere with C14
Measure presence of C14 as it moves down stem
How can we use ringing as evidence for mass flow in the phloem?
Remove the bark (contains the phloem)
Solutes cannot move up/ down
Bulge forms
Fluid above ring has more solute than fluid below it
Are the cells in the phloem living or dead?
Living
What is transported in the phloem?
Assimilates
What direction do assimilates move in the phloem?
Up and down
Describe the sieve tube cells
Living, little cytoplasm, few organelles
Describe sieve plates
Thin pores between sieve tube cells
Describe the serial dilution method (briefly)
- cylinders of plant tissue, slice up
- weigh mass at start
- submerge in solute for 1 hour
- weigh again
- calculate percentage difference
How do you calculate the percentage difference
Percentage difference = (difference (g) / start mass (g)) x 100
Make 30cm^3 of 0.75 mol dm-3 of a stock solution of 1.8 moles dm3
(30/ 1.8) x 0.75 = 12.5
What happens at the source?
1 - AT pumps sucrose into STE from low to high conc
2- lowering the water potential
3- water moves in by osmosis from CC
4 - creating high hydrostatic pressure
What happens at the sink?
1- uses assimilates creating low conc (eg - sucrose to starch in potatoes)
2- increases WP so water moves out by osmosis
3 - decreasing pressure in the phloem
What is diffusion?
The net movement of molecules from a high to low concentration
Passive (no ATP)
How does concentration affect diffusion
Example
The steeper the conc grad the faster the rate of diffusion
Ventilation/ circulation in lungs and counter current in fish maintain con grad
How does diffusion distance affect the rate of diffusion?
Example?
The shorter the diffusion distance the faster the rate of diffusion
Eg) thin epithelium in capillaries
How does surface area affect the rate of diffusion?
Example?
The larger the surface area the faster the rate of diffusion
Eg) folded membrane of alveoli in lungs
What is facilitated diffusion?
The passive movement of molecules across the membrane from an area of high conc to low conc via a specific transmembrane protein
What do protein channels transport?
Small polar molecules
What do carrier proteins transport?
Large molecules eg) glucose
describe the observation made when ringing a plant (removing the outer layer)
because the phloem vessels are located on the outside, swelling would occur due to accumulation of sugar, the tissue below this would die
what affect would high wind speed have on water uptake?
increase uptake
cohesion tension would pull up more as it is lost to the surroundings
describe the differences between arteries and veins
ARTERIES - thick muscle, thick elastic, thick wall, no valves
VEINS - thin muscle, thin elastic, thin walls, valves present
