3.3.4.2 Mass transport in plants Flashcards
What is the function of xylem tissue?
Xylem tissue transports water and mineral ions in solution.
Give four factors that affect transpiration rate.
- Light
- Temperature
- Humidity
- Wind
Name a piece of apparatus used to measure transpiration rate.
A potometer
What is meant by the term transpiration?
[1 mark]
The evaporation of water from plant surfaces.
Describe how the cohesion-tension theory helps explain water movement in plants.
[3 marks]
- Transpiration from the leaves at the ‘top’ of the xylem creates tension, which pulls more water into the leaf.
- Water molecules are cohesive, so when some are pulled into the leaf others follow.
- This means the whole column of water in the xylem, from the leaves down to the roots, moves upwards, pulling water into the stem through the roots.
What is the function of phloem tissue?
Phloem tissue transports organic substances (in solution) both up and down the plant.
A scientist is investigating where the products of photosynthesis are translocated to in a plant. To do this several upper leaves of a plant were exposed to a radioactive tracer in the form of radioactively-labelled CO₂. The plant was then left for 24 hours before an autoradiograph of the whole plant was taken.
Explain how the leaves of the plant can act as a source of translocation.
[1 mark]
Leaves can act as a source because they are a part of a plant where solutes/products of photosynthesis are made.
A scientist is investigating where the products of photosynthesis are translocated to in a plant. To do this several upper leaves of a plant were exposed to a radioactive tracer in the form of radioactively-labelled CO₂. The plant was then left for 24 hours before an autoradiograph of the whole plant was taken.
The autoradiograph showed radioactivity in the roots and fruits. Explain why radioactivity was seen in the fruits.
[1 mark]
Radioactive solutes/products of photosynthesis have been translocated to the fruits because the fruits are acting as a sink.
According to the mass flow hypothesis, how is a pressure gradient set up in the phloem?
- The solutes are actively loaded into the sieve tubes of the phloem at the source.
- This lowers the water potential inside the sieve tubes, so water enters the tubes by osmosis.
- This creates a high pressure inside the sieve tubes at the source end of the phloem.
- At the sink end, solutes are removed from the phloem.
- This increases the water potential inside the sieve tubes, so water leaves the tubes by osmosis.
- This lowers the pressure inside the sieve tubes.
- The result is a pressure gradient from the source end to the sink end.
What is meant by the term translocation?
Translocation is the movement of solutes to where they’re needed in a plant.
Translocation moves solutes from ______ to _____.
Translocation moves solutes from ‘sources’ to ‘sinks’.
How are enzymes involved in the process of translocation?
- Enzymes maintain a concentration gradient from the source to the sink by changing the solutes at the sink.
- This makes sure there’s always a lower concentration at the sink than at the source.
Water leaves from the air spaces in a plant by a process called _________. This takes place mainly through pores called ______ in the epidermis of the leaf. Water evaporates into the air spaces from mesophyll cells. As a result, these cells have a ____ water potential and so draw water by ______ from neighbouring cells. In this way, a water potential gradient is set up that draws water from the xylem. Water is pulled up the xylem because water molecules stick together - a phenomenon called _______. During the night the diameter of a tree trunk _______.
Water leaves from the air spaces in a plant by a process called transpiration. This takes place mainly through pores called stomata in the epidermis of the leaf. Water evaporates into the air spaces from mesophyll cells. As a result, these cells have a lower water potential and so draw water by osmosis from neighbouring cells. In this way, a water potential gradient is set up that draws water from the xylem. Water is pulled up the xylem because water molecules stick together - a phenomenon called cohesion. During the night the diameter of a tree trunk increases.
