TRANSPORT IN PLANTS mod 3 Flashcards
(27 cards)
What does the xylem tissue transport?
What does the phloem tissue transport?
xylem - Water and mineral ions (up from root to leaves)
phloem - sugars (up and down)
What is the xylem’s other function?
Support. In a root, xylem is near the centre surrounded by phloem as support for the root when it pushes through the soil.
Stem - xylem and phloem are near the outside to prevent bending.
Leaf- Xylem and phloem make up a network of veins to support thin leaves.
Where is the xylem found in the tansverse cross sections?
At the top
How is the xylem vessel adapted for transporting water and minerals?
Long tube, no end walls making it uninterrupted and allowing water to pass through easily.
The cells contain no cytoplasm.
Walls are thickened with lignin to support and prevent collapse.
Water and ions move in and out laterally through pits in the walls when there is no lignin.
How is the phloem tissue adapted for transporting solutes? (sugars like sucrose mainly)
made up of SEIVE TUBE ELEMENTS, which are living cells that form the tube for transporting solutes through the plant. They are joined from end to end, the end walls have holes to allow solutes to pass through.
they have COMPANION CELLS to carry out living functions (providing energy for active transport)
How do you dissect a plant stem?
use a scalpel or a razor blade to cut a cross section of a stem (transverse or longitudinal) as thin as possible.
Use tweezers to put the sections in water temporarily (to stop them from drying out)
Transfer each section to a dish containing a stain, and leave for one minute.
Rine off the sections and mount them onto a slide.
how is water drawn into the plant?
enters via root hair cells,then passes through the root cortex, including the endodermis to reach the xylem.
(WATER IS DRAWN IN TO THE ROOTS VIA OSMOSIS)
How does water move during osmosis?
from and area of high wp to low wp down a wp gradient.
By what 2 pathways does water travel through roots (via root cortex) into the xylem?
*Symplast pathway * (through living parts of cells - the cytoplasm. Cytoplasms of neighbouring cells connect via plasmodesmata, water moves through osmosis)
Apoplast pathway (through non-living parts of the cell - cell walls. The walls are absorbent so water can diffuse through them. The water can carry solutes and move from areas of high hydrostatic pressure to low hydrostatic pressure, this is an example of mass flow)
What happens when water in the apoplast pathway gets to the endodermis cells in the root?
It is blocked by a waxy strip in the cell walls called the casparian strip. Now it has to take the symplast pathway.
(water now has to go through partially permeable cell membrane. once past the barrier water moves into the xylem)
At the leaves, how does water leave the xylem?
Water leaves the xylem and moves into the cells mainly by apoplast pathway.
Water evaporates from the cell walls into the spaces between the cells in the leaf
What happens when the stomata is open?
water diffuses out of the leaf down the WP gradient into the surrounding air.
The loss of water from the plant surface is called transpiration.
What mechanisms move water in the xylem?
cohesion, tension, adhesion
What happens regarding cohesion and tension when water evaporates from the leaves? (transpiration)
The evaporation of water creates tension (suction) which pulls more water into the leaf.
Water molecules are cohesive (stick together) so when some are pulled into the leaf, others follow.
Water enters the stem through the root cortex cells.
How is adhesion partly responsible for the movement of water?
water molecules are attracted to the walls of the xylem. This helps the water to rise up through the xylem vessels.
Why does a plant need to open its stomata?
To let in carbon dioxide so that it can produce glucose (photosynthesis)
This process lets water out — there is a higher concentration of water inside the leaves than in the air outside, so water moves out via diffusion.
What are the 4 main factors affecting transpiration rate? (water leaving the plant surface)
Light - The lighter, the faster the transpiration rate. (stomata open during day)
Temperature - Higher temperature, faster transpiration rate (water molecules have energy to evaporate faster)
Humidity - Lower humidity, faster transpiration rate. (if air around plant is dry, WP gradient between leaf and air is increased)
Wind - Higher wind speed, faster transpiration (wind blows away water from stomata increasing the WP gradient)
How would you use a potometer to estimate transpiration rate?
- Cut shoot underwater (prevent air entering xylem)
- Assemble potometer and insert shoot underwater
- remove apparatus from water but keep end of capillary tube submerged and check apparatus is water and air tight
- Dry leaves and give plant time to acclimate
- remove and of capillary tube from water beaker until bubble has formed then put the end of the tube back in the water.
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Record starting position of air bubble
start stopwatch and record distance moved by bubble per unit of time. Rate of air bubble movement is an estimate of transpiration rate. Change only ONE variable (temp)
How are xerophytic plants adapted to reduce water loss?
- Marram grass has stomata that are sunk in pits so they are sheltered from the wind slowing transpiration.
- In hot or windy conditions marram grass roll leaves to trap moist air slowing transpiration.
-Cacti and marram grass have thick waxy layer on epidermis
Cacti have spines to reduce SA for water loss:
How are hydrophillic plants adapted to survive in water?
Air spaces in tissues help the plant to float and act as store of oxygen for respiration. (Float on surface to increase amount of light received)
stomata only present on upper epidermis to maximise gas exchange
flexable leaves to prevent damage
What is translocation?
The movement of dissolved substances (assimilates) from source to sink.
What is an example of a source for sucrose?
The leaves, (and the sinks are usually meristems in the roots stems and leaves)
Give an example of both a sink and a source
Roots and leaves. Sucrose can be stored in the roots but transported to the leaves during growing season. (sucrose is usually made in the leaves)
What are the steps to mass flow of sap in the xylem?
- Sucrose is actively loaded into seive tube elements by companion cell and reduces WP.
- Water flows into phloem from xylem by osmosis and increases hydrostatic pressure in the seive tube elements
- Water moves down seive tube from higher hydrostatic pressure at source, lower at sink.
4.Sucrose is removed from seive tube elements by surrounding cells and increases WP in seive tube. - Water moves out of seive tube and reduces hydrostatic pressure
