Transport in Plants (Edexcel GCSE Combined Science: Biology): Flashcards
Exam code: 1SC0
1/340Still learning
Know0
Transpiration
Was this flashcard helpful?
Cards in this collection (34)
Transpiration
The loss of water vapour from the parts of a plant that are above ground (leaves, stem, flowers).
Transpiration stream
The continuous movement of water through the xylem vessels from the roots to the leaves to replace water lost by transpiration.
What is the pathway of water from the soil to the leaf?
root hair cell → root cortex cells → xylem → leaf mesophyll cells
How does water get from the soil into the root and across to the xylem?
By osmosis, passing into the root hair cells, through the root cortex and into the xylem vessels.
Where does water evaporate from during transpiration, and how does it leave the leaf?
It evaporates from the surfaces of the spongy mesophyll cells, then diffuses as water vapour out through the stomata.
What controls the diffusion of gases in and out of the leaf?
The stomata, specifically the guard cells.
Why do stomata open during the day?
To allow carbon dioxide to diffuse in and oxygen to diffuse out for photosynthesis (water vapour also diffuses out in transpiration).
Why do stomata close at night?
Photosynthesis cannot occur, so closing the stomata reduces the rate of transpiration and conserves water.
How does cohesion help water move up the xylem?
Water molecules are attracted to each other, forming a continuous unbroken column in which each molecule 'pulls' on the one below it.
Give three functions of transpiration in a plant.
Transporting mineral ions
Providing water to keep cells turgid (supporting the plant) and water for photosynthesis
Keeping the leaves cool as water evaporates
Transpiration is the loss of from the parts of the plant above ground.
water vapour
Water vapour leaves the leaf by diffusion through the .
stomata
Potometer
A piece of apparatus used to investigate the effect of environmental conditions on the rate of transpiration (water uptake).
Name four environmental factors that affect the rate of transpiration.
Air movement, humidity, light intensity and temperature.
How does increasing light intensity affect the rate of transpiration, and why?
It increases the rate, because more stomata open in bright light to maximise photosynthesis, so more water is lost by evaporation and diffusion.
What is the difference between a mass potometer and a bubble potometer?
A mass potometer measures the change in mass of a plant as water evaporates
A bubble potometer measures the uptake of water by a stem (the distance an air bubble moves)
Why is the shoot cut underwater when setting up a potometer?
To prevent air entering the xylem, which would break the water column or cause a blockage.
How is the rate of transpiration calculated with a bubble potometer?
By dividing the distance the bubble travelled by the time period; the further the bubble travels in the same time, the greater the rate.
How could you investigate the effect of air movement on transpiration?
Set up a fan or hairdryer to blow air over the plant (e.g. at different distances or fan speeds).
How could you investigate the effect of humidity on transpiration?
Spray water inside a plastic bag and enclose the plant within the bag.
Why should the leaves of the shoot be dried before starting the potometer investigation?
Wet leaves would affect (slow) the results.
The rate of transpiration can be investigated using a piece of apparatus called a .
potometer
As light intensity increases, more stomata open and the rate of transpiration .
increases
Translocation
The transport of sucrose and amino acids in the phloem, from regions of production (source) to regions of storage or use (sink).
What are the soluble products of photosynthesis that are translocated?
Sugars (mainly sucrose) and amino acids.
In which tissue does translocation occur, and what is it made of?
The phloem, which is made of living cells (as opposed to the dead cells of the xylem).
What is meant by 'source' and 'sink' in translocation?
Source – the region where the dissolved food is made
Sink – the region where the dissolved food is stored or used
Why is translocation described as an active process?
It requires energy.
In which directions can substances move in the phloem?
In many different directions, depending on the stage of development of the plant or the time of year.
After the plant has grown (e.g. in summer), which parts are the source and which are the sink?
The photosynthesising leaves are the source and the roots are the sinks, storing sucrose as starch until needed.
During winter, when many plants have no leaves, how does translocation help?
The phloem transports dissolved sucrose and amino acids from the storage organs to other parts of the plant so that respiration can continue.
What feature of phloem cells allows substances to flow easily between them?
The cells are joined end to end and have holes (sieve plates) in the end cell walls.
In translocation, dissolved food is always transported from to .
source / sink
Translocation takes place in the tubes, which are made of living cells.
phloem
Sign up to unlock flashcards
or