8)Transport in plants Flashcards
(19 cards)
Xylem vessels
Function: transport water and minerals and provide support
Adaptation:
* Continuous hollow tube with no cell organelles, to allow water to flow freely with minimum resistance
* No end walls to allow water to flow freely with minimum resistance in a continuous water column
* lignin in walls that is water proof to prevent leakage in water
* Thick lignified walls for support
* Pits to allow lateral movement of water to nearby cells
Function of phloem
Translocation of sucrose and amino acids from source to sink in a bidirectional movement
Explain how water from the soil reaches the xylem in root
1.Root hair cells absorb water from soil by osmosis from high to low water potential through a partially permeable membrane
2.Water moves down water potential gradient to the cortex by osmosis
3.water enters the xylem through pits
Define transpiration
- Water in air spaces of spongy mesophyll cells evaporate
- Water vapour diffuses out the leaf
- Through the stomata
How water from soil reaches the leaf
How water moves up against gravity
How transpiration helps in movement of water up the plant
1.Root hair cells absorb water from soil by osmosis
- Water surrounding air spaces of spongy mesophyll evaporate, and they diffuse out of the leaf through the stomata by the process transpiration
- so decrease in water potential in mesophyll cells of the leaf
- so more water will be absorbed from xylem vessels by osmosis
- water potential gradient between leaf and root, creates a negative pressure in xylem vessels
- creating a transpiration pull causing tension on walls of xylem vessels
- so water moves up in a continuous water column maintained by
*Cohesion between water molecules
* Adhesion between water molecules and xylem vessels
External environmental factors affecting rate of respiration(4)
- Temperature
- Light intensity
- Wind speed
- Humidity
How does temperature affect rate of transpiration
Increase in temperature
* increases evaporation
* increasing the water potential gradient
* Kinetic energy of molecules increase
* Rate of diffusion of water vapour out of leaf through stomata increases
* causing increase in rate of transpiration
(above optimum temp stomata will close reducing water loss by transpiration)
How does light intensity affect rate of transpiration
Increase in light intensity
* Affects the opening of stomata
* where the higher the light intensity the stomata will open wider
* to allow more co2 to diffuse into the leaf
* so more water vapour will diffuse out of leaf through stomata
* so increase in rate of transpiration
How does wind speed affect rate of transpiration m
Increase in wind speed
* wind moves water vapour away from stomata
* thus maintaining a steep diffusion gradient
* so more water vapour diffuses out of the leaf through the stomata
* so increase rate of transpiration
How does humidity affect rate of transpiration
Humid air
* more water particles suspended in air surrounding leaf
* so less steep diffusion gradient
* so decrease in rate of diffusion of water vapour out of the leaf
* so decrease in rate of transpiration
Explain how the internal structure of the leaf results in loss of large amount of water in transpiration
- spongy mesophyll:
* surrounded by a layer of water that evaporates in the air spaces - Guard cells open the stomata :
* To allow water vapour to diffuse out of the leaf down diffusion gradient - Xylem vessels
* transport water and supply the mesophyll cells in leaf with water by osmosis to replace the lost water
Effect of increasing in the number of leaves on the water uptake
More leaves
1. Increase in number of stomata
2. increase in surface area exposed to external environmental factors
*so increase rate of evaporation so increase rate of transpiration through stomata
*so higher transpiration pull
*so higher water uptake
What causes plant to wilt
- Increase in rate of transpiration
* Increase in temp
* increase in light intensity
* increase in wind speed
* decrease in humidity - so amount of water lost is more than the amount of water absorbed
Or
plant is in a salted solution so water will move by osmosis down water potential gradient so cells become flaccid so loss of turgor pressure
Why plant needs water
- Keeps cells turgid
- Raw material for photosynthesis
- Solvent: dissolves miners and nutrients to be transported
Describe how leaf acts as a source at one time of the year and a sink at another time
Leaf as a source:
1. No limiting factors (e.g. by having high light intensity and high co2 conc)
2. More photosynthesis in leaves, producing more glucose
3. Glucose condensed into sucrose
4. sucrose is translocated through phloem in bidirectional movement
5. From source which is leaves to sink which is the root
6. where glucose can be stored as starch or used in respiration
Leaf as a sink:
1. More limiting factors (e.g. low light intensity & low co2 conc. )
2. Less photosynthesis in leaves
3. Starch in root is broken into glucose
4. sucrose is translocated upwards from the source which is root now and the sink which is leaf
5. Leaf used glucose for respiration or making cellulose in cell wall
Plant defence mechanism in case of shortage of water
- Wilting
* leaves collapse and stomata closes
* reducing surface area exposed to environmental factors (e.g. high temp, high light intensity) reducing heat absorption, evaporation, thus reducing water loss - Leaf fall
* In severe conditions (e.g. high wind speed
* plant allows leaves to fall
* so no water loss can occur
* plant removes chlorophyll from leaves and storing them before leaves fall
*but there is no photosynthesis
* plants use food stored in root for respiration
Adaptations of hydrophytes floating on surface of water
- Leaves with large surface area:
* to absorb more light energy - Large air spaces
* to float on water (low density) / for buoyancy
* to absorb more light energy
3.Stomata on upper surface of leaf:
* to allow gas exchange with air which is faster than through water
* no stomata on lower surface to prevent entry of water - Roots not attached to sea bed:
* so not to be cut by water current - Thin cuticle:
doesnt need to reduce water loss
Adaptations of hydrophytes found in deep water
No stomata as they under go gas exchange water
Adaptations of xerophytes
- Leaves
* needle like structure:
to reduce the surface area that’s exposed to high temperature
* Fewer number of stomata:
to reduce water loss by transpiration
* Thin waxy cuticle:
to reduce water loss
* sunken stomata:
to avoid exposure to dry air so to reduce water loss by transpiration
reduce exposure to air current
* hairs:
to trap a layer of humid air reducing diffusion gradient to reduce water loss so reduce transpiration - Roots
* Close to the surface, shallow laterally branching roots to be able to absorb tiniest rainfall before evaporation
OR
* Deep penetrating roots to be able to reach lower water table
- more root hair cells for larger surface area for maximum absorption of water by osmosis
- Stem
* Green to absorb light and carry photosynthesis
*Upright shape, to reduce surface area to environmental factors
* Succulent for storage of water
