Mass Transport In Plants Flashcards
(14 cards)
Explain how water is held together
The charge on the hydrogen atoms is slightly positive and that on the oxygen atom is slightly negative.
Attraction between the positively charged hydrogen atom of one water molecule and the negatively charged oxygen of another water molecule causes water molecules to group together, held by hydrogen bonds.
Explain the boiling point of water
Water has a high boiling point.
Although hydrogen bonds are weak individually, lots of them are strong together and require a lot of energy to break.
Give 6 properties of water, explaining how they are useful
1) it is a metabolite (reactant) in many metabolic reactions, including condensation and hydrolysis reactions.
2) it is a polar molecule so can act as a universal solvent in which metabolic reactions occur faster (e.g. in the cytoplasm of cells).
3) It has a relatively high heat capacity, so it can buffer changes in temperature - it takes a lot of energy to increase the temperature of water, and lots must be lost to decrease its temperature.
4) it has a relatively large latent heat of vaporisation (lots of energy is needed to convert it to a gas), providing a cooling effect with little loss of water through evaporation.
5) has strong cohesion between water molecules - this supports columns of water in the things like the xylem and produces surface tension when water meets air, allowing small organisms to survive on the surface.
6) strong adhesion -allows it to cling to sides of things such as the xylem
Give the biological functions of these inorganic ions:
Iron ions
Sodium ions
Phosphate ions
Hydrogen ions (3)
Magnesium ions
Calcium ions
Iron ions- are a component of haemoglobin and bind reversibly with oxygen
Sodium ions- are involved in the co-transport of glucose and amino acids in the small intestine
Phosphate ions- are components of ATP, phospholipids, DNA and RNA
Hydrogen ions:
-are involved in the co-transport of sucrose in the phloem companion cells,
- Lower the pH of the blood,
- Cause the Bohr shift- more oxygen is released at the same partial pressure of oxygen
Magnesium ions - fundamental component in chlorophyll
Calcium ions- fundamental component in bones, synapses etc.
What does the null hypothesis mean
There’s no correlation between the independent variable and dependent variable
What’s the correlation co-efficient
A statistical test completed to see if there’s a correlation between two variables
Outline the cohesion -tension theory of water transport
This occurs in the xylem
- water is lost from the leaf through transpiration (the evaporation of water molecules which then diffuse out of the spongy mesophyll, through the stomata and out of the leaf)
- this lowers the water potential of the mesophyll cells, drawing water out of the xylem by osmosis.
- water is then pulled up the xylem, creating tension, as the water molecules stick together due to cohesion by hydrogen bonding
- this forms a continuous column of water
- adhesion of water molecules to walls of the xylem prevents movement back down the xylem
Explain how root hair cells absorb water
- root hair cells actively transport nitrate ions into the xylem cells, lowering the water potential at the bottom of the xylem. This causes water to move into the xylem by osmosis
Outline how to use a potometer
1) a leafy shoot is cut underwater, maintaining the continuous column of water. make sure water doesn’t get on the leaves.
2) Assemble and Fill the potometer with water, making sure there are no water bubbles.
3) using a rubber tube, fit the leafy shoot to the potometer under water.
4) to ensure the joints are airtight, remove the potometer from underwater and seal all joints with vaseline
5) introduce an air bubble into the capillary tube to track the movement of water taken up by the shoot. As transpiration occurs, water moves through the capillary tube and the air bubble moves with it
6) measure the volume of water taken up
What’s dry mass
Samples that have been dried in an oven at 100°C at intervals until the mass doesn’t change
Outline the made flow hypothesis for the mechanism of translocation
- this occurs in the phloem, where organic substances are transported from the source to the sink
- sucrose is actively loaded into the companion cells, requiring ATP. It diffuses from the companion cells to the sieve tube cells.
- this lowers the water potential in the sieve tube, and water enters by osmosis from the xylem. This increases the volume, creating a high hydrostatic pressure.
- water moves down the hydrostatic pressure gradient, transporting sucrose towards the roots and other storage tissues (the sink)
- at the sink, sucrose is removed from the phloem and is used in respiration to produce ATP or stored
- water moves back to the xylem
Give 4 experiments that show transport in plants
1) ringing experiments
2) autoradiography using radioactive tracers
3) aphid experiment
4) metabolic inhibitors
Explain how ringing experiments work
-in the stem, the phloem vessels are exterior to the xylem vessels. A ring is cut on the outside of the stem, removing the phloem but not the xylem.
After a week, there’s a swelling above the ring and reduced growth under it. This proves that sugars are transported downwards in the phloem from the source to the sink
Explain how autoradiography using radioactive tracers works
- one leaf is exposed to carbon dioxide containing the radioactive isotope, Carbon 14. This will be taken up during photosynthesis and incorporated into glucose and then sucrose.
The plant is frozen in liquid nitrogen to kill it and fix it in place.
Thin horizontal sections of the plant tissue are taken, and the resulting autoradiograph shows the sucrose moving down the phloem
