Transport In Plants Flashcards
(23 cards)
Organic compounds synthesised in the leaves of a plant can b transported to the plants roots. This transport is called translocation and occurs in the phloem tissue of the plant.
One theory of translocation states that organic substances are pushed from a high pressure in the leaves to a lower pressure in the roots.
Describe how a high pressure is produced in the leaves. (3)
- wp becomes lower
- water enters phloem by osmosis
- increased vol of water causes increased pressure
PCMBS is a substance that inhibits the uptake of sucrose by plant cells.
Scientists investigated the effect of PCMBS on the rate of translocation in sugar beet. Figure 9 shows their results ( rate of translocation is constant then PCMBS is added and the lines curves downwards steeply declining)
During thirty experiment the scientists ensured that the rate of photosynthesis of their plants remained constant.
Explain why this was important. (2)
- rate of photosynthesis relates to the rate of sucrose production
- rate of translocation is higher when sucrose conc is higher
PCMBS is a substance that inhibits the uptake of sucrose by plant cells.
Scientists investigated the effect of PCMBS on the rate of translocation in sugar beet. Figure 9 shows their results ( rate of translocation is constant then PCMBS is added and the lines curves downwards steeply declining)
The scientists concluded that some translocation must occur in the spaces in the cell.
Explain how the information in figure 9 supports this conclusion. (2)
- rate of translocation doesn’t fall to 0
- But sucrose no longer able to enter cytoplasm of phloem cells
A student investigated the distribution of stomata on leaves from 2 species of plant. She removed small pieces from the lower surface of the leaves of each plant species. She mounted these pieces on separate microscope slides. She then counted the number of stomata in several parts of the epidermis on each piece of leaf tissue using an optical microscope.
Suggest appropriate units the student should use to compare the distribution of stomata on leaves. (1)
Number of stomata per mm^2
A student investigated the distribution of stomata on leaves from 2 species of plant. She removed small pieces from the lower surface of the leaves of each plant species. She mounted these pieces on separate microscope slides. She then counted the number of stomata in several parts of the epidermis on each piece of leaf tissue using an optical microscope.
The pieces of leaf tissue examined were very thin.
Explain why this was important. (2)
- single layer of cells
- so the light could pass through tissue
A student investigated the distribution of stomata on leaves from 2 species of plant. She removed small pieces from the lower surface of the leaves of each plant species. She mounted these pieces on separate microscope slides. She then counted the number of stomata in several parts of the epidermis on each piece of leaf tissue using an optical microscope.
Give two reasons why it was important that the student controlled the number of stomata in several parts of each piece of leaf tissue. (2)
- distribution may not be uniform
- to obtain a reliable mean
A student investigated the distribution of stomata on leaves from 2 species of plant. She removed small pieces from the lower surface of the leaves of each plant species. She mounted these pieces on separate microscope slides. She then counted the number of stomata in several parts of the epidermis on each piece of leaf tissue using an optical microscope.
One of the two plant species used by the student in this investigation was a xerophyte.
Other than the distribution of stomata, suggest and explain two xerophytic features the leaves of this plant might have. (2)
- hairs on the lower epidermis of the leaf traps water vapour and wp gradient decreases
- leaf is rolled up so traps water vapour and reduces wp gradient decreases
A student investigated the distribution of stomata on leaves from 2 species of plant. She removed small pieces from the lower surface of the leaves of each plant species. She mounted these pieces on separate microscope slides. She then counted the number of stomata in several parts of the epidermis on each piece of leaf tissue using an optical microscope.
One of the two plant species used by the student in this investigation was a xerophyte.
The student then compared the rate of transpiration (evaporation of water) from the two species of plant. She did this by measuring the rate of water uptake by each plant species.
Suggest two reasons why the rate of water uptake by a plant may not be the same rate as transpiration. (2)
- used for photosynthesis
- water used for hydrolysis/ turgidity/ produced in respiration
Describe the processes involved in the transport of sugars in plant stems. (5)
- active transport is used to pump sucrose from mesophyll cells to companions cells then into sieve tube
- water enters by osmosis from xylem and companion cells into sieve tube as increased conc of sucrose lowers wp
- this produces a high hydrostatic pressure
- mass flow towards sink
- at sink sugars are removed
Stomata are found mainly on the underside of the leaves of dicotyledonous plants. A student painted a layer of nail varnish on the lower epidermis of the leaf. She peeled off the dry layer of nail varnish and placed it on a microscope slide. The student was able to see the impressions of the stomata on the nail varnish using an optical microscope.
She then determined the mean diameter of the stomata.
Describe how the student could use an eyepiece graticule to determine the mean diameter of the stomata. (3)
- measure each stoma using eyepiece graticule
- calibrate eyepiece graticule against stage micrometer/ ruler
- take no of measurements to calculate a mean diameter
(Graph shows ABA reduces the mea stomata diameter compared with control a lot)
ABA is a substance that some plant species produce when little water is available.
Explain why producing ABA may help these species survive in dry conditions. (2)
- reduces evaporation
- so less water needed from the dry soil
(Graph shows Lam13 reduces the mea stomata diameter compared with control a lot)
Many species of plants can be infected by powdery mildew which is spread by microscopic spores in the air.
Suggest how treatment with Lam13 might protect plants against powdery mildew infection. (1)
Closes stomata so fewer spores enter leaf
Describe the cohesion-tension theory of water transport in the xylem. (5)
- evaporation of water from leaves pulls up more water from xylem creating tension
- this lowers the wp of mesophyll cells
- water molecules are polar so (cohesion) many weak hydrogen bonds stick them together
- cohesion maintains continuous columns of water
- adhesion of water molecules to walls of xylem
Read Q6 in as booklet.
Treatment D is a control. Explain how the measurement obtained from this control is used by the scientist. (2)
- used to compare with effects of other treatments
- shows effect of substance X naturally
Read Q6 in as booklet.
Using figure 4 and table 3, what can you conclude from treatments D and E about root growth? (3)
- root growth has doubled from D-E when substance X is added
- D shows substance isn’t required for root growth
- substance X moves through plant
Read Q6 in as booklet.
The mass flow hypothesis is used to explain the movement of substances through the phloem.
Evaluate whether the information from this investigation supports this hypothesis.
Do not consider statistical analysis in the answer. (4)
FOR:
- F shows phloem is involved
- G shows active transport is involved because 4’c reduces movement
- roots are the sink
- agar block is the source of
AGAINST:
- no bulge above ringing in F
- no role for osmosis
- movement could be due to gravity
- roots still grow without functioning phloem
- no leaves/sugars to act as a source
A student used the apparatus shown in figure 5 and a digital balance to determine the rate of water movement in a celery stalk in grams per hour per group of xylem vessels.
The student measured the time taken for water movement.
Give two other measurements he made to calculate the rate of water movement. (2)
- initial and final mass of beaker and all contents
- no of groups of xylem vessels
A different student used coloured water to investigate the movement of water in leaf stalks of celery.
During the procedure she:
- cut equal lengths of stalk from each plant
- put the cut end if each stalk into water
- left these stalks to take up the coloured water for 20 minutes
- used a sharp scalpel to cut slices from the stalks at 1mm intervals until she reached a slice with no coloured water
Explain why the water moved up the stalks. (3)
- evaporation from leaves lowers wp and creates tension which pulls water up
- many weak hydrogen bonds form cohesion which maintains column of water
The student used a sharp scalpel to cut the celery. Describe how she should ensure she handled the scalpel safely during this procedure. (2)
- cut away from her body
- cut against a hard surface
The mass flow hypothesis is used to explain the movement of substances through the phloem.
Use your understanding of the mass flow hypothesis to explain how pressure is generated inside this phloem tube. (3)
- sucrose is actively transported into phloem
- lowing wp
- water moves into phloem by osmosis from xylem
Phloem pressure is reduced during the hottest part of the day (graph also shows rate of water movement is increased). Use information from figure 6 along with your understanding of transpiration and mass flow to explain why. (3)
- high rate of transpiration
- water lost through stomata
- less water movement from xylem to phloem as insufficient wp in phloem
Read information of Q9.2 in as booklet.
Using information in table 4, what can you conclude about the effect of different factors on the mean shelf life of cut flowers? Explain your conclusions. (4)
- SD’s dont overlap for mean shelf life
- shelf life significantly longer in April
- no significant difference in mean no of stomata so not linked to shelf life
- significant difference in mean transpiration rate so linked to shelf life significantly
Read information for Q9.2 in as booklet.
Other than a change in temperature, give one change the scientist could make to environmental conditions to increase the cut flowers shelf life.
Explain your answer (3)
- reduce light intensity
- stomata close
- decreased rate of transpiration
