Transport In Plants Flashcards
Why do Plants require a transport system ?
To ensure all cells receive a strong supply of the 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 between vessels
. Lignifed cell walls, providing mechanical support
. Parenchyma Tissue, lines the xylem, contains tannin a bitter chemical to defend against herbavours
Relate the structure of the phloem to its function
. Sieve tube elements transport sugars around the plant
. Companion cells designed for active transport of sugars into tubes
. Plasmodesmata allows flow of substances between cytoplasm of different cells
Describe the structure and functions of the vascular systems in the roots
Consists of the xylem and phloem. Xylem arranged in an X shape to provide resistance against force. Surrounded by endodermis, a water supply.
Describe the structure and function of the vascular system in the stem
Consists of the xylem and phloem. Xylem on the inside of the bundle to provide support and flexibility, phloem on the outside. Layer of meristem cells that provide new xylem and phloem tissues when required
Describe the Structure and function of the vascular systems in the leaves
Consists of xylem and phloem, forms the midrib and veins, Therefore spread from the center of the leaf in paralel line, xylem tissues found on the upper side of vascular bundles. involved in transport and support
Define Transpiration
Transpiration is the evaporation of water from the leaves of a plant through the stomata
It is a consequence of gaseous exchange; occurs when the plant opens the stomata to exchange oxygen and CO2
What factors affect the rate of transpiration
Increased light, increases transpiration
Increased temperature, increases transpiration
Increased humidity, decreases transpiration
Increased air movement, increases transpiration
Waxy cuticle prevents transpiration
How can we measure the transpiration rate ?
Potometer. The plant is cut and 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 = The tendency of water to move by osmosis, from a high water potential to a low. Pure distilled water has the highest 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 the root hair cells, where water moves through the cell walls and intercellular spaces. This pathway can only be used until water reaches the Casaparian strip
Explain what is meant by the symplastic pathway
A method of osmosis through the root hair cells, where water moves through the cytoplasm via. To begin this pathway, water must be actively into transported.
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 adaptations of xerophytes that allow them to live in dry conditions
> Smaller leaves – reduces surface area
Rolling leaves – reduces exposure of lower epidermis to the atmosphere
Densely packed mesophyll – prevents water loss via evaporation
Thick, waxy cuticles
Close stomata – in response to low water availability
Hair and pits – reduces water vapour potential gradient by trapping moist air
Deep roots or wide-spreading shallow roots
Give adaptation of hydrophones that allow them to live in wet conditions
> Thin or absent waxy cuticle – no need for conserving water supplies
Lots of stomata open constantly – maximises gas exchange by being placed on the upper surfaces
Flat and wide leaves – gives larger surface area to increase light absorption
Air sacs (found in some) – making it buoyant
