Transport In Plants Flashcards
What is a potometer?
• apparatus that measures rate of uptake of water by the shoot which indicates rate of transpiration
Setting equipment
- cut shoot underwater and fill apparatus underwater to avoid introducing air bubbles
- seal all joints with glassware e.g Vaseline which makes it air tight
- open tap, resets bubble back to zero
- observe the distance moved by the bubble in mm in a given time period
- repeat 3x for reliability
- dry off leaves as the stomata will be blocked by water and you wouldn’t get a potiential gradient
Once water/mineral ions reach endodermis they must travel via the symplast pathway, why?
- because the walls of the cells of the endodermis is impregnated with a waxy substance called Suberin ie castparian strip
- Suberin -= im permable to water /mineral ions and castparian strip prevents use of apoplexy pathway so the only way they can pss through endodermis to pericycle is via symplast pathway
The castparian strip ensures control over water going into the xylem
How do mineral ions/ water enter xylem from endodermis?
• actively transported from the outside of the endodermal cells into cytoplasm,pericycle and then into xylem. Water flows by osmosis down a water potiential gradient
Define transpiration?
• is the evaporation of water from inside the leaves through the stomata to the atmosphere
What is capillarity?
• forces adhesion and cohesion which allow water molecules to travel up narrow tubes for a short distance and useful in small plants
- it’s not useful in larger tress because after a while it’s opposed by gravity
• root pressure is another force that helps water move up the xylem. This pressure is caused by osmosis as water moves down a potential gradient following mineral uptake in the root tissues
What is the cohesion tension theory?
- movement of water up larger trees can be explained by this. As water molecules evaporate from the leaves the water column is pulled up the xylem in one unbroken stream
- water evaporates from the leaves faster than it can enter the roots and therefore the water column is put under tension
How are sieve tube elements adapted to their function?
- few organelles ( no nucleus / mitochondria )
- have companion cells to provide ATP and other metabolic activities
- end walls are perforated by sieve plates to allow transport
- elongated shape to form tubes
- phloem protein for translocation
What is translocation?
• transport of the soluble organic materials produced by photosynthesis
Arguments against mass flow theory?
- does not explain the existence sieve plates so may stop the flow of sugars
- companion cells have mitochondria which provides ATP which suggests that process is not just passive diffusion
- sucrose and amino acids have been observed to flow at different rates in different directions in the phloem
- cynaide slows down translocation, suggests respiration is involved
Alternative theories?
- an active process may be involved
- cytoplasmic steaming may be responsible for bidirectional translocation
- phloem protein fibres may be involved in translocation
What are mesophytes, hydrophytes and xerophytes?
• Mesophytes are plants living in conditions of adequate water supplies. They grow best in well drained soils/moderately dry air. They have behaviours that help them survive at unfavourable times of year
- trees shed leaves and grow new ones in spring
- annual plants they produce seeds that are dominant and germinate next spring
- bulbs and corns are produced by some flowering plants to survive winter
• Hydrophytes : are water plants that live submerged or partially submerged in water e.g water lily
- little lignin in plant issues : bc water is a supportive medium
- xylem tissue poorly developed : don’t need to transport water bc they live in water
- stomata at upper surface of leaf : for gas exchange with air in atmosphere
- leaves have thin cuticle : no need to cut down water loss
- stems/leaves have a large air space : CO2/O2 for gas exchange + buoyancy
• Xerophytes : adapted to conditions of low water availability. They live in hot dry desert conditions or cold regions where soil is dry for much of the year e.g Marram grass
- rolled leaf : reduces S.A for transpiration to conserve water
- suken stomata : reduces WPG between leaf and atomosphere. Decreases water loss by transpiration
- thick cuticle : reduces water loss from upper epidermis
- hairs on leaf surface of leaf : trap water vapour and reduces WPG between inside/outside the leaf
Function of the xylem tissue?
• transports mineral ions and water from roots to leaves so photosynthesis can occur
Function of the phloem?
• transports sucrose and amino acids in a bi-directional movement from the leaves to other organs of the plant e.g flower and roots
Function of roots?
• to absorb mineral ions ( Mg2+, phosphorus, nitrates ) and water from soil
What does the stem contain?
• vascular tissue ( xylem and phloem ) for transport and provides structural support
