Transport In Plants Module 3 Flashcards
Why do multicellular plants require transport systems? [3]
- Size
- Metabolic rate
- Surface area to volume ration
What are the transport vessels in plants?
Xylem and phloem
What is the cambium?
The growing layer of the plant
What is an assimilate?
Product of photosynthesis
How are vascular bundles organised in the stem of a plant? Draw a diagram
Vascular bundles surround the stem to give support
Xylem faces in and phloem outwards
How are vascular bundles organised in the leaf of a plant? Draw a diagram
In the main vain of the leaf the vascular bundles are located with xylem on top and phloem below
How are vascular bundles organised in the roots of a plant? Draw a diagram
Vascular bundles are located in the centre of the root, the xylem in an X shape surrounded by phloem
Located in the middle to help the plant withstand strains from the weather
What is transpiration?
Loss of water through stomata during gas exchange?
What is transpiration a consequence of?
GAS EXCHANGE
How does light affect transpiration?
Increasing light intensity will increase transpiration rate as more gas exchange is required for more photosynthesis subsequently letting out water vapour from stomata
How does humidity affect transpiration rate?
Lower air humidity will increase rate of transpiration in an attempt to maintain water potential gradient with inside and outside environments
How does temperature affect transpiration rate?
As kinetic energy is raised the rate of evaporation will also increase thus resulting in an increase in transpiration
How does air movement affect transpiration rate?
If wind speed is higher, as water in the air moves away from plant more water will transpire to maintain gradient
What are the 4 factors affecting transpiration?
- Light
- Humidity
- Temperature
- Air movement
How is gas exchange controlled in plants?
Opening and closing of stomata, via the guard cells
How do guard cells work?
Guard cells have cellulose rings inside them which can lengthen and increased at optimal conditions by pumping in solutes
How does the transpiration stream work? [4]
- Water enters root by osmosis
- Water is transported up xylem until it reaches the leaves
- Water moves by osmosis into a poplar pathway into intercellular spaces
- Water moves out of leaves via stomata down concentration gradient
Benefits of transpiration [2]
- Delivers water to cells that need it
- Cools down leaves and prevents heat damage
Limitations of transpiration [2]
- Limits water availability
- During high rates of photosynthesis, stomata are continuously open meaning a lot of water is lost and supply cannot meet the demand
What is the theory for movement in the transpiration stream?
Cohesion tension theory
What evidence is there for the cohesion tension theory? [2]
- Changes in tree diameter between day and night when water is needed
- Breaking of xylem means water can no longer be drawn up
What is a limitation of using a potometer?
It assumes that uptake and loss of water are the same
Why do we cut the stem at an angle when using a potometer?
To ensure a large SA
Why don’t we want any air bubbles when using a potometer?
Will cause blockage in xylem
Why do we need to ensure leaves on shoot are dry when using a potometer?
To maintain diffusion gradient
Why should we assemble potometer underwater?
To ensure there are no air bubbles
What are the 5 roles of water in a plant?
- Turgor pressure
- Evaporation to keep plant cool
- Transport mineral ions and assimilates
- Raw minerals
- Cell expansion, allows plant roots to forces their way through ground surface
How does water enter plants?
Through ROOT HAIR CELL
What are 3 adaptions of root hair cells?
- Microscopic so can easily penetrate soil
- Large SA:V ratio
- Thin surface layer to ensure fast diffusion and osmosis
Why does water move into the root hair cell by osmosis?
Soil has a low concentration of minerals and a high water potential whereas cell cytoplasm has lots of minerals and a lower water potential so water will move into the root hair cell by osmosis due to the water potential gradient
What are the 2 pathways water can take across the root?
Symplast and apoplast
What is the symplast pathway?
Water moves through cytoplasm and plasmodesmata
This works as RHC has higher water potential than adjacent cell so water will move by osmosis until it reaches xylem
What is the apoplast pathway?
Movement of water through cell walls and intercellular spaces, with no resistance
Once reaching endodermis the pathway is stopped by the casparian strip - waterproof strip - so water is forced into symplast pathway
What is the casparian strip made of?
Suebrin - a waterproof material
What 3 steps happen when water reaches endodermis?
- Crosses selectively permeable membrane to remove toxins
- Minerals moves into xylem by active transport
- Water moves into xylem by osmosis
Why is glucose converted to sucrose during translocation?
Sucrose is more stable and less likely to react with other molecules than glucose is
Where are assimilate transported from and to?
From a source to a sink
Sources are where assimilates are made e.g photosynthesising leaves and storages
Sink is where assimilates are needed such as in the roots and shoots
Describe how sucrose is loaded into the phloem?
- ATP is used to pump hydrogen ions into cell wall of companion cell via active transport
- This creates a concentration gradient of Hydrogen ions
- As hydrogen ions move back in they bring sucrose with them
- Sucrose can move through plasmodesmata into sieve tube element
How does mass flow occur in the sieve tube element?
As sucrose moves into sieve tube element, the water potential is lowered meaning water will move in by osmosis from xylem
This water increased the hydrostatic pressure in the sieve tube element allowing for the hydrostatic movement of phloem sap to the sink from the source
Why is translocation regarded an active process?
If mitochondria is poisoned or disabled the process doesn’t work meaning that energy from ATP is required for the process to occur
What type of plant is a cacti and what adaptations do they have?
Cacti are xerophytes
- Sunken stomata
- Only open stomata at night
- Spines to reduce SA and trap moist air
- Shallow roots
- Thick waxy cuticle
What type of plant is marram grass and what adaptations do they have?
Marram grass is a xerophytes
- Sunken stomata
- Curled leaves to trap moisture air
- Long roots
- Thick waxy cuticle
What type of plant is a water lily and what adaptations do they have?
A water lily is a hydrophyte
- Always open stomata
- Thin waxy cuticle or none
- Wide flat surface to make the most of light for photosynthesis
What is the function of the xylem?
To transport water and minerals through the plant in one direction from root to shoot
Explain the structure of the xylem vessel [3]
- Non living hollow tube of cells
- Has pits (gaps in lignin) to allow water and substances to move across xylem vessels
- Has rings of lignin to maintain structure of vessel
Explain the structure of the phloem vessel [4]
- Consists of 2 elements the sieve tube element and companion cell
- Has pores on sieve tube plate to allow assimilates to pass through
- Plasmodesmata between sieve tube element and coompanion cells
- Companion cell has lots of mitochondria
What is the function of the phloem?
Transport assimilates from sources to sinks in both directions around the plant
What is cohesion in regard to water molecules?
The ability of water molecules to form hydrogen bonds between each other
What is adhesion in regard to water molecules?
The ability of water molecules to form hydrogen bonds with molecules in the wall of the xylem
What is capillary action?
The ability of water to move upwards, against gravity, in thin tubes
What is transpiration pull?
When capillary action occurs and water drags more water molecules into the vessel to keep the movement of water constant
