Transport In Plants Flashcards
Why do plants require a transport system
To ensure all cells receive a strong supply of nutrients they require.
Especially important as a plant must be able to transport substances up their stem (against gravity)
Relate the structure of xylem to its function
Long continuous columns made of dead tissue, allowing transportation of water
Contain pits, allowing water to move sideways
Thickened with a tough surface, provided structural support
Relate the structure of phloem to its function
Sieve tube elements transport sugars around the plant
Companion cells designed 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 arranged in an X shape to provide resistane against force. Surrounded by endodermis, a water supply
Describe the structure and function of the vascular system in the stem
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 gas exchange; occurs when the plant opens the stomata to exchange oxygen and CO2
Name factors that affect the rate of transpiration
Increased light intensity increases transpiration
Increased temperature increases transpiration
Increased humidity decreases transpiration
Increased air movement increases transpiration
Waxy cuticle 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
Water potential = the tendency of water to move by osmosis, from high water potential to low. Pure distilled water has the highest water potential of 0
This is the basis by which water moves to the areas it is needed within plants
Explain what is meant by the apoplastic pathway
A method of osmosis through root hair cells, where water moves through the cell walls and intercellular spaces. This pathway can only be used until the water reaches the Casparian strippl
Explain what is meant by the symplastic pathway
A method of osmosis through the root hair cells, where 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 this sticking effect. Therefore as water is lost through transpiration, more can be drawn up the stem from the roots
Give adaptions of xerophytes that allow them to live in dry conditions
Small rolled leaves
Densely packed mesophyll
Thick waxy cuticle
Stomata often closed
Hairs to trap moist air
Give adaptions 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
