Unit 3.3- Transport in plants Flashcards
Dicotyledonous plants definition:
Plants with two seed leaves and a branching pattern of veins in the leaf
Meristem definition:
A layer of dividing cells
Phloem definition:
Transports dissolved assimilates
Vascular tissue definition:
Consists of cells specialised for transporting fluids by mass flow
Xylem definition:
Transports water and minerals
Why can plants’ demand for oxygen be met by diffusion?
They are not very active so their respiration rate is low
What do plants have a high demand for?
Water and sugars
Why do plants need a transport system?
To move:
- Water and minerals from the roots up to the leaves
- Sugars from the leaves to the rest of the plant
Why are collenchyma and sclernchyma also found in vascular bundles as well as just xylem and phloem?
They provide strength and support the plant
What is the structure of xylem and phloem in the young root?
- Central core of xylem often in the shape of an X
- Phloem is found in between the arms of the X
- This provides strength
- The endodermis is a sheeth of cells around the vascualr bundle
- The medulla is the space in the rest of it (not actually space i think)
What is the translocation system?
- The movement of sucrose and amino acids through phloem vessels
- Active process
What is the structure of xylem and phloem in the stem?
- Vascular bundles are found near the outer edge of the stem
- The xylem is found in the inner most third
- The phloem is found in the middle third
- The sclerenchyma is found in the outer most third
- The medulla is the bit in the middle
- The cortex is between the bundles
- The collenchyma is a layer around the edge
- The cambium is a layer of meristem cells found between the xylem and phloem. It produces new xylem and phloem
What is the difference in the structure of xylem and phloem in the stem in woody and non-woody plants
- In non-woody plants the bundles are separate and discrete
- In woody plants, the bundles are separate in the young stem but become a continuous ring in older stems
- This provides strength and flexibility
Companion cells definition:
The cells that help to load the sucrose onto the sieve tubes
How are xylem vessels formed?
- Lignin impregnates the walls of the cells forming the xylem vessels
- This makes the walls waterproof which kills the cells
- This leaves a long column of dead cells with no contents
- The lignin strengthens the walls and prevents it from collapsing, keeping it open at all times
What does the lignin do in xylem vessels?
- Prevents it from collapsing
- Keeps the vessel open at all times, even when water is in short supply
- The lignin thickening forms patterns in the cell walls. they may be spiral. annular (rings) or reticulate (a network of broken rings). This prevents the vessel from being too rigid and allows some flexibility in the stem or branch
What are bordered pits?
- Gaps in the cell wall where lignification is not complete
- The bordered pits in two adjacent vessels are lined up so that water can pass from one vessel to the other
- They also allow water to leave the xylem and move to the living parts of the plant
What is phloem tissue made up of?
Sieve tube elements and companion cells
What is sap made up of?
Sucrose dissolved in water
What are companion cells?
- Found in between sieve tubes
- Large nucleus and dense cytoplasm
- Many mitochondria to produce the ATP needed for active processes
- Carry out the metabolic processes needed to load the assimilates actively into sieve tubes
Plasmodesmata definition:
Gaps in the cell wall containing cytoplasm that connects two cells
What is the apoplast pathway?
- Does not pass through any plasma membrane into cells
- Therefore the water moves by mass flow rather than osmosis
- Any dissolved mineral ions and salts can be carried by the water
What is the symplast pathway?
The water passes through the plasmodesmata from one cell to another
What is the vacular pathway?
Water passes through the plasmodesmata from one cell to another but can also pass through the vacuoles in the cells
Potometer definition:
A device that can measure the rate of water uptake as a leafy stem transpires
Transpiration definition:
The loss of water vapour from the arial parts of a plant, mostly through the stomata in the leaves
How does light intensity affect transpiration rate?
In light, the stomata open which increases transpiration
How does temperature affect transpiration rate?
Increases it by:
- Increasing the rate of evaporation from the surface
- Increases the rate of diffusion through the stomata because the water molecules have more kinetic energy
- Decreases the water vapour potential in the air, allowing a more rapid diffusion of water molecules out of the leaf
How does relative humidity affect transpiration rate?
Higher relative humidity in the air decreases the rate of transpiration
How does wind affect transpiration rate?
Air moving outside the leaf will carry more water vapour with it, maintaining a high water vapour potential gradient
How does water availability affect transpiration rate?
If there is little water in the soil, then the lost water cannot be replaced. If there is insufficient water in the soil then the stomata close and the leaves will wilt
What percentage of water uptake by plants is lost by transpiration?
More than 95%
This means that potometers are reasonably accurate because almost all the water taken by plants will be lost by transpiration
What precautions are taken to ensure results from a potometere are accurate?
- Set it up under water to ensure there are no air bubbles in the apparatus
- Ensure the shoot is healthy
- Cut the stem under water to prevent air from entering the xylem
- Cut the stem at an angle to provide a large surface area in contact with the water
- Dry the leaves
Adhesion definition:
The attraction between water molecules and the wall of the xylem vessel
Cohesion definition:
The attraction between water molecules caused by hydrogen bonds
The transpiration stream definition:
The movement of water from the soil, through the plant, to the air surrounding the leaves. The main driving force is the water potential gradient between the soil and the air in the leaf air spaces
Endodermis definition:
A layer of cells surrounding the medulla and xylem
Assimilates definition:
Substances that have become part of the plant
Sink definition:
A part of the plant where assimilates are removed from the transport system
Source definition:
A part of the plant that loads materials into the transport system
Translocation definition:
The transport of assimilates through a plant
Hydrophyte definition:
A plant adapted to living in water or where the ground is very wet
Xerophyte definition:
A plant adapted to living in dry conditions
