3.3 Transport in Plants Flashcards
Why do plants require a transport system ?
To ensure all cells receive a strong supply of nutrient
Important as they get their nutrients against gravity
Relate the structure of the xylem to its function.
Used to transport water
Long continuous columns made of dead tissue
Contain pits allowing water to move sideways between vessels
Thickened with lignin to withstand pressure and provide support
Relate the structure of phloem to its function.
Sieve tube elements transport sugars around the plant
Companion cells allow for active transport of sugars into tubes
Plasmodesmata allow flow of substances between cytoplasm of different cells
Describe the structure and function of the vascular system in the roots.
Consists of xylem and phloem
Xylem on the inside of the bundle to provide support and flexibility, phloem on the outside
Layer of meristem cells that produce new xylem and phloem tissue when required
Describe the structure and function of the vascular system in the leaves
Consists of xylem and phloem, forms the midrib and veins
Involved in transport and support.
Define transpiration.
The evaporation of water from the leaves of a plant
Consequence of gaseous exchange: occurs when the plant opens the stomata to exchange oxygen and CO2.
Name factors that affect the rate of transpiration.
Increased light - increased rate
Increased temp - increased rate
Increased humidity - reduced rate
Increased air movement - increased rate
Waxy cuticle in upper eperdermis prevents transpiration
How can we measure transpiration rate ?
Potometer
Plant cutting is placed in a water filled tube that contains an air bubble
Rate of transpiration is calculated by measuring the movement of the air bubble over time
Define water potential as a mechanism of movement in plants.
Water potential is the tendency of water to move by osmosis, from high water potential to low
This is the basis of how water moves to areas it is needed in plants
Explain what is meant by the apoplastic pathway .
A method of osmosis through the root hair cells
Water moves through the cell walls and intercellular spaces
This pathway can only be used until water reaches the Casparian strip.
Explain what is meant by the symplastic pathway
A method of osmosis through the root hair cells
Water moves through the cytoplasm via plasmodesmata
To begin this pathway, water must be actively transported into cells.
Explain the cohesion tension theory.
Water molecules form hydrogen bonds with each other, causing them to stick together (cohesion)
The surface tension of the water also creates the sticking effect
Therefore as water is lost through transpiration, more can be drawn up the stem from the roots.
Give adaptations of xerophytes that allows them to live in dry conditions.
•Small / rolled leaves
•Thick waxy cuticle
•Stomata often closed
•Hairs to trap moist air
Give adaptations of hydrophytes that allow them to live in wet conditions.
•Thin or absent waxy cuticle
•Stomata often open
•Wide, flat leaves
•Air spaces for buoyancy
Summarise the mechanism of translocation.
Sucrose produced in leaves loaded into sieve tubes via active transport
This lowers water potential of leaves, causing water to move in from the xylem
Assimilates move along the sieve tube towards areas of lower hydrostatic pressure (sink
Sucrose diffuses into surrounding cells where it is needed.
