B8 (Transport in plants) Flashcards
What are the two different tissues plants use to transport substances?
xylem
phloem
What does the xylem tissue consist of
hollow tubes
What is the xylem’s function?
-transporting water and dissolved mineral ions from the roots, through the stem and to the leaves
-providing support for the plant and helping to keep it upright
What does the phloem tissue consist of?
living cells
What are the phloems functions
-transporting sucrose
-transporting amino acids
Where are the xylem and phloem located?
In vascular bundles in different positions depending on the part of the plant.
Describe how the xylem and phloem are positioned in the leaf of the plant
Xylem is on top, and phloem is below in the vascular bundle within the vein.
Describe how the xylem and phloem are positioned in the stem of the plant
Xylem is on the inside, and phloem is on the outside in vascular bundles around the stem.
Describe how the xylem and phloem are positioned in the root of the plant
Xylem is central in an X-shape, with phloem surrounding it.
Differences between xylem and phloem
Xylem:
-consists of mainly dead elements
-conducts water and minerals from the root to the aerial part of the plant
Phloem:
-Consists of living tissues
-Conducts prepared sucrose from the leaves to storage and growing plants of the plant
Similarities between xylem and phloem
Both are vascular tissues in plants.
Both transport substances (xylem → water, phloem → sugars).
What does the positioning of the xylem and phloem in the stem do?
gives protections against bending sideways due to wind
What are root hair cells?
specialised cells found in roots of plants that are adapted to absorb water and minerals from soil
What do root hair cells have?
long, hair-like structures which are extensions or outgrowths of epidermal cells
How are root hair cells specialised?
Large surface area → Maximizes water and mineral absorption.
Thin cell wall → Shortens diffusion distance.
Many mitochondria → Provide energy for active transport.
No chloroplasts → Underground, so no photosynthesis needed.
How does water travel through the plant?
the roots (root hair cell-> root cortex)- stem (xylem) - leaves- evaporates into air
What enters through osmosis? What enters through active transport?
Osmosis: Water enters the root hair cells.
Active Transport: Mineral ions (e.g., nitrates) enter against the concentration gradient.
How does the water travel up the xylem?
Water evaporation from mesophyll cell surfaces into air spaces and out through the stomata.
Lower water potential in leaves, creating a suction effect.
What is transpiration?
Transpiration is the loss of water vapour from leaves through the stomata. Water forms a thin layer on mesophyll cell surfaces and evaporates into air spaces in the spongy mesophyll. This creates a higher water vapor concentration inside the leaf than outside, causing water to diffuse out through the stomata. As water evaporates, it creates suction, pulling more water up the xylem from the roots.
What is the transpiration pull?
-the force that draws water molecules up through the plant from the roots to the leaves, caused by water evaporation through stomata. This creates a water potential gradient, pulling water through the xylem.
What factors affect transpiration rate?
- Temperature
- Wind speed
- Humidity
Why and how does temperature affect transpiration rate?
Transpiration rate increases
The kinetic energy of water molecules increases so they evaporate and diffuse faster from the mesophyll cells
Why and how does wind speed affect transpiration rate?
transpiration rate increases
The wind removes the water vapour surrounding the leaf faster
Why and how does humidity affect transpiration rate?
Humidity decreases transpiration rate
If the air surrounding the leaf has more water vapour, there will be a weaker concentration gradient for diffusion
What purpose does water serve in the plant other than photosynthesis
Keeps the plant turgid and helps support it
When does wilting happen?
If the amount of water the plant loses from its leaves is GREATER
than the amount of water that is available in the soil to travel into the plant through its roots
What happens to the plant when it wilts
It will become soft and droop because the cell walls become flaccid and cannot support the plant
What is translocation?
The movement of sucrose and amino acids in the phloem from sources to sinks.
What are sources?
The parts of the plants that release sucrose or amino acids
What are sinks?
Parts of the plant that use or store sucrose or amino acids
How does the potometer work?
Setup: A plant shoot is cut underwater to avoid air entering the xylem. The shoot is then connected to the potometer, which is filled with water.
Transpiration: As the plant loses water through transpiration, the water is pulled up through the xylem from the potometer.
Measurement: The decrease in water level in the potometer’s tube can be measured. This is an indicator of how much water the plant has transpired. The faster the water level drops, the higher the rate of transpiration.
How do you investigate the effects of varying the temperature on the rate of transpiration?
Cut a small shoot off a plant. A tree such as willow is suitable.
Set up a potometer with the cut shoot as shown in Figure 1.
Place the apparatus in a cool room.
Record the temperature of the room.
Measure the time taken for the bubble in the capillary tube to move a given distance.
Repeat steps 4 and 5 in a warm room, then in a hot room.
