Transport in plants. Flashcards
(13 cards)
(a) What is the need for transport systems in multicellular
plants?
Plants need transport systems because:
They are multicellular with a low surface area to volume ratio.
Diffusion is too slow to meet their metabolic needs.
Substances must be moved over long distances.
(b) (i) What is the structure and function of the vascular
system in the roots, stems and leaves of
herbaceous dicotyledonous plants? (xylem)
Xylem tissue transports water and mineral ions around plants. It also provides structural support. It is mostly made up of xylem vessels.
Adaptations of xylem vessels:
1- They are elongated, hollow tubes without end walls.
2 -They lack organelles.
3 -Their walls are thickened with lignin for support.
4 -They have non-lignified pits that allow movement of water and ions into and out of vessels.
(b) (i) What is the structure and function of the vascular
system in the roots, stems and leaves of
herbaceous dicotyledonous plants? (phloem)
Phloem tissue transports sugars and amino acids (assimilates) around plants. It is mostly made up of sieve tube elements and companion cells.
Adaptations of sieve tube elements:
1 -They are connected end-to-end to form sieve tubes.
2 -They have sieve plates with pores at their ends to allow flow of sugars and amino acids.
3 -They lack nuclei and most organelles.
4 -They have only a thin layer of cytoplasm.
What are the adaptaion of the companion cell?
Adaptations of companion cells:
They are connected to sieve tube elements through pores (plasmodesmata).
The cytoplasm contains a large nucleus, many mitochondria to release energy for the active transport of substances through the sieve tube elements, and many ribosomes for protein synthesis.
(c) (i) What is the process of transpiration and
Water then moves through a plant as follows:
1 - Water enters a plant’s root hair cells via osmosis.
2 - It moves through the cell cytoplasm or cell walls towards the xylem.
3 - The xylem transports water from the roots up to the leaves.
4 - Water is used for photosynthesis.
5 - Some water evaporates from leaf cells by transpiration and diffuses out of the plant.
(c) (i) what is the environmental factors that affect
transpiration rate
Factors affect the transpiration rate as follows:
1 - Light intensity - At high light intensities, stomata open for maximum CO2 absorption for photosynthesis, increasing the transpiration rate.
2 - Temperature - At high temperatures, evaporation of water molecules is faster due to higher kinetic energy, increasing the transpiration rate.
3 - Humidity - Low humidity increases the water vapour gradient between the leaf and atmosphere, increasing the transpiration rate.
4 - Wind speed - High wind speeds increase the water vapour gradient between the leaf and atmosphere, increasing the transpiration rate.
How is the photometer partical caried out?
Steps in using a potometer:
1- Cut the shoot underwater at slant to increase the surface area for water uptake.
2 - Assemble the potometer with the shoot submerged in water.
3 - Keep the capillary tube end of the potometer submerged throughout the experiment.
4 - Check that the apparatus is airtight.
5 - Dry the leaves, and give the shoot time to acclimatise.
6 - Shut the tap, form an air bubble and record its position.
7 - Measure the distance the air bubble moves and the time taken.
8 - Change one variable at a time and keep everything else constant.
(d) What is the transport of water into the plant, through the
plant and to the air surrounding the leaves?
The apoplast pathway:
Water moves through spaces in the cell walls and between cells.
This occurs due to the cohesive and adhesive properties of water.
The symplast pathway:
Water moves from cell to cell through the cytoplasm and plasmodesmata.
This occurs due to water potential gradients.
(d) What is the mecghanism of the traport of water?
(cohesion tension theory and transpiration pull.)
The cohesion-tension theory explains how water moves upwards through the xylem against gravity.
Cohesion - Hydrogen bonding causes water molecules to stick together and move as one continuous column.
Adhesion - Hydrogen bonding between polar water molecules and non-polar cellulose in xylem vessel walls pulls water upwards through the xylem.
Transpiration pull - Evaporation of water at leaves creates the transpiration pull, and this tension is transmitted down the whole water column due to cohesion.
How does transpiration relates to gas exchange?
Transpiration is the evaporation of water from aerial parts of plants, especially leaves.
Why transpiration occurs:
1 - Water evaporates (changes from liquid water into gaseous water vapour) from the moist surfaces of mesophyll cells.
2 - Stomata open so they can absorb carbon dioxide for photosynthesis.
3 - This provides a pathway for water vapour loss through the open stomata.
4 - Water vapour moves down a water potential gradient from the air spaces in the leaf into the atmosphere.
(e) What are the adaptations of plants to the availability of water
in their environment?
Xerophytes
Xerophytes are plants adapted to living in dry environments with limited water availability. Without adaptations they would become desiccated (dry out) and die.
Key adaptations of xerophytes to reduce water loss:
1 - Thick waxy cuticle - This reduces water loss through evaporation.
2 - Rolling or folding of leaves - This encloses the stomata on the lower surface to reduce air flow and the evaporation of water.
3 - Hairs on leaves - These trap moist air against the leaf surface to reduce the diffusion gradient of water vapour.
4 - Sunken stomata in pits - These reduce air flow and the evaporation of water.
5 - Small, needle-like leaves - These reduce the surface area across which water can be lost.
6 - Water storage organs - These conserve water for when it is in low supply.
(f) What is the mechanism of translocation?
1 - At the source, solutes like sucrose are actively loaded into sieve tube elements from companion cells.
2 - This decreases the water potential in sieve tube elements.
3 - Water enters the sieve tube elements from the xylem and companion cells by osmosis.
4 - This increases hydrostatic pressure in the sieve tube elements at the source.
5 - At the sink, solutes are actively removed from the sieve tube elements.
6 - This increases the water potential in sieve tube elements at the sink.
7 - Water leaves the phloem by osmosis, decreasing the hydrostatic pressure at the sink.
8 - This creates a pressure gradient, pushing solutes from the source to areas of lower pressure at the sink.
How is sucrose brought into the companion cell?
1 - The proton pump, pumps out H+ ion to the surrounding. This is done by ATP.
2 - Because there is high conc of H+ outside the companion cell the H+ ion moves in through the co - transporter.
3 - However, H+ ion can’t just move by itself through the co transporter. Therefore it moves in with sucrose.
