3.3.4.2 Mass Transport in plants Flashcards
Describe one piece of evidence that supports the root pressure theory and explain how it supports the theory
- sap discharged from a cut stem
- only upward force could make this happen
The diameter of a tree is less during the day than it is at night.
Explain how this supports cohesion tension theory?
- evaporation of water through leaves mainly during daytime
- so tension in xylem creates an inward pull
- so xylem vessels become narrower due to the adhesion of water molecules to walls of xylem vessels
The diameter of a tree is less during the day than it is at night.
Explain how this does NOT support root pressure theory
- root pressure gives OUTWARD force pushing on walls of xylem
- so trees would become wider not narrower as xylem should = wider
Using the cohesion tension theory explain the changes in the circumference of a tree throughout the day?
- inc of light, at the start of the day, causes stomata to open
- so water evaporates out of stomata causing water to move across the leaf by OSMOSIS
- evaporation exerts force causing tension in water columns
- cohesion holds water column together
- adhesion between walls of xylem and water mol results in pulling force which causes water columns to decrease in volume
- hence xylem vessels and tree trunk both = narrower
Which part of the cortex forms the apoplast pathway?
The cell walls
use your knowledge of transpiration to explain changes in rate of flow in xylem?
- stomata open
- transpiration highest around midday as middle of day warmer
- increased tension
explain why values for pressure in xylem are negative?
- inside xylem lower than atmospheric pressure
- water under tension
describe how high pressure is produced in leaves?
- wp becomes lower
- water enters phloem by osmosis
- increase volume of water increases pressure
explain one way in which sieve cells are adapted for mass transport?
- few organelles
- so easier flow
explain one way in which companion cells are adapted for mass transport?
- many mitochondria
- to release ATP
- for active transport
in an investigation where a translocation inhibitor is used, why is it important that the rate of photosynthesis is kept constant?
- rate of photosynthesis related to rate of sucrose production
- rate of translocation higher when sucrose concentration higher
a student investigated the rate of transpiration from a leafy shoot.
she used a potometer to measure the rate of water uptake by the shoot.
suggest one environmental factor the student should keep constant during the investigation?
temperature
a student investigated the rate of transpiration from a leafy shoot.
she used a potometer to measure the rate of water uptake by the shoot.
the student cut the shoot and put it into the potometer under water. explain why?
prevent air entering
a student investigated the rate of transpiration from a leafy shoot.
she used a potometer to measure the rate of water uptake by the shoot.
the student wanted to calculate the rate of water uptake by the shoot in cm3 per minute.
what measurements did she need to make?
- distance and time
- diameter of capillary tube
a student investigated the rate of transpiration from a leafy shoot.
she used a potometer to measure the rate of water uptake by the shoot.
the student assumed that water uptake was equivalent to rate of transpiration.
give 2 reasons why this might NOT be valid assumption?
- used in photosynthesis
- used to provide turgidity
