7b. MASS TRANSPORT IN PLANTS Flashcards
Name the two transport vessels in a plant
Xylem and Phloem
What is transported through the xylem, and in which direction?
Water and ions are transported up the plant
Describe the four structural features of a xylem vessel
Long tubes with no end walls
No organelles
Lignin
Bordered pits
Why are xylem long tubes with no end walls?
To allow a continuous stream of water to flow
Why do Xylem have no organelles?
So as not to obstruct the flow of water
Why are Xylem are surrounded by lignin?
To waterproof them
Why do Xylem have bordered pits?
To allow lateral movement of water
Name the theory by which water move up the xylem of a plant
Cohesion-tension theory
What is transpiration is driven by?
Evaporation from the stomata, which is driven by energy from the sun
As water evaporates from the stomata, describe the effect on the water potential of the mesophyll tissue
It reduces it
Which force causes water to be drawn up the xylem in one continuous column?
Cohesion
Which force draws the walls of the xylem inwards?
Tension
The tension in the xylem is caused by evaporation from the stomata, and which two forces acting together?
Cohesion and adhesion
Describe the pressure inside the xylem
It is more negative than the atmospheric pressure
Describe the relationship between the rate of evaporation from the leaf, and the amount of tension inside the xylem
As rate of evaporation increases, tension increases
Describe the relationship between the rate of evaporation and the pressure inside the xylem
As rate of evaporation increases, pressure becomes more negative
Name the five factors that affect the rate of transpiration
Temperature, humidity, light intensity, wind speed, number of stomata per area
Why does increasing temperature increase the rate of transpiration?
It would increase the KE of the particles
Why does increasing light intensity increase the rate of transpiration?
It would cause more stomata to open
Why does increasing humidity decrease the rate of transpiration?
It would decrease the water potential gradient between the inside and outside of the leaf
Why does increasing wind speed increase the rate of transpiration?
It would increase the water potential gradient between the inside and outside of the leaf
Describe the structure of the phloem
Sieve tube elements with sieve plates at either end. Attached to companion cells.
Describe the two adaptations of the phloem
No organelles, and thick walls.
Explain why the phloem has no organelles
To allow easier flow of dissolved sugars.
Explain why the phloem has thick walls
To withstand pressure.
How are the companion cells adapted to carry out their function?
They contain mitochodria to release energy for the active process of phloem loading.
What is translocation?
The movement of dissolved sugars from sources to sinks.
Why is sucrose translocated instead of glucose?
To prevent glucose being used in metabolic processes during translocation.
Define what a source is
Where glucose is produced or stored.
Give examples of a source
Leaves, tubers, tap roots
Define what a sink is
Where glucose is used or stored.
Give examples of a sink
Meristems, seeds, tubers, tap roots.
Explain how something can be a source and also a sink
When dissolved sugars are translocated to the organ for storage it is acting as a sink. But when glucose is removed for use, it is acting as a source.
How do sugars travel from the sources to the companion cells?
Diffusion
How do sugars move from the companion cells to the phloem?
Active transport
How does the introduction of sugars into the phloem affect the water potential inside the phloem?
It reduces it / makes it more negative
What is the effect of the reduction of the water potential inside the phloem?
It causes water to move by osmosis from the xylem to the phloem down a water potential gradient
How is the hydrostatic pressure inside the phloem increased?
More water is introduced into the phloem
What is the effect of the increasing hydrostatic pressure inside the phloem?
It causes the dissolved sugars to move through the phloem by mass flow
Which three gradients do dissolved sugars travel down in the phloem?
A hydrostatic pressure gradient, a concentration gradient, a pressure gradient
What two things can the sugars be used for at sinks?
Respiration and storage
Name the entire process by which dissolved sugars move from sources to sinks
Mass flow
How can a potometer be used to measure the rate of water uptake?
As water is taken up into the plant, the bubble in the capillary tube moves. We can measure the distance travelled by the bubble in a time.
Potometers can be used to measure the effect of variables on the rate of water uptake. Name these factors.
Light intensity, temperature, humidity.
If the IV was light intensity, name the CVs.
Temperature, humidity, same plant.
If the IV was temperature, name the CVs.
Light intensity, humidity, same plant.
If the IV was humidity, name the CVs.
Temperature, light intensity, same plant.
Why does using the same plant help make the results reliable?
Because the leaves will have the same surface area.
Why might the rate of water uptake into a plant not be the same as the rate of transpiration?
Because water can be used for turgidity, in photosynthesis, and produced in respiration
Which is faster - the speed of water movement through the capillary tube, or the speed of water movement through the plant roots?
Through the plant roots is faster
Why is the speed of the water movement through plant roots faster in the roots of the plant compared to the potometer?
Because the roots have a smaller diamater
Name five precautionary measures taken when setting up the potometer
Cut the shoots and insert the plant into the potometer underwater, dry the leaf, seal the joints with vaseline, and shut the tap
Why should you cut the shoots and insert the plant into the potometer underwater?
To prevent bubbles entering the xylem
Why should you dry the leaves?
Excess water on the leaves would lower the rate of transpiration
Why should you seal the joints with vaseline?
To prevent bubbles entering the capillary tube
Why should you shut the tap?
To ensure water isn’t introduced into the capillary tube from the reservoir
How would you return the bubble to zero to carry out repeats?
By opening the tap to introduce water from the reservoir
How would you calculate the distance the bubble travelled during the allocated time?
Final length - Initial length
How would you calculate the volume of water taken up?
πr2h
How would you calculate rate of water uptake?
volume of water uptake ÷ time
How would you calculate the surface area of a leaf?
Draw around the leaf onto graph paper. Count the whole and half squares. X2 for both sides.
How would you calculate rate of water uptake per surface area?
Rate of water uptake ÷ surface area
What is a xerophyte?
A species of plant that has adaptations tosurvive in an environment with little liquid water, e.g. cactus.
Describe five adaptations of xerophytes
Sunken stomata
Hairy leaves / hairy stomata
Thick waxy cuticle
Curled leaves
Spines instead of leaves
Explain how sunken stomata reduces water loss
Water vapour is trapped around the stomata, reducing the water potential gradient
Explain how hairy leaves / hairy stomata reduce water loss
The hairs trap water vapour around the leaves / stomata, reducing the water potential gradient
Explain how a thick waxy cuticle reduces water loss
It reduces evaporation
Explain how curled leaves reduces water loss
It traps water vapour around the leaf, which reduces the water potential gradient
Explain how having spines instead of leaves reduces the water loss
They reduce the surface area to volume ratio
