Mrs H bio 7 Mass Transport in Plants Flashcards
give the 4 main properties of water
1.metabolite in many metabolic reactions (e.g. condensation and hyrolysis
2.important solvent in which metabolic reactions occur as it has a relatively high heath capacity, buffering temp changes
3.relatively large latent heat of vaporisation, providing a cooling effect with little water loss through evaporation
4.strong cohesion due to H bonds which supports columns of water in tube like transport cells of plants and produces surface tension where water meets air
why is water good as a solvent?
they are charged with O2 atoms being slightly - and H atoms being slightly +, these opposite charges attract forming H bonds. Because it is charged, it is a very good solvent
charged or polar molecules like salts, sugars, amino acids dissolve readily in water and are called hydrophilic
uncharged or nonpolar molecules like lipids dont dissolve well in water and are called hydrophobic
why are H bonds in water useful?
H bonds are weak meaning htey can break and form spontaneously at the temps found in living cells without needing enzymes
how can water resist temp changes?
H bonds between water molecules can absorb a lot of energy meaning it has a high specific heat capacity
what does a high specific heat capacity mean?
takes a lot of energy to heat up
why is water’s high specific heat capacity useful?
-does not change temp easily
-constant temp useful for living organisms because doesnt experience rapid temp changes
-good habitat as temp underwater is likely to be more stable then temp on land
-water inside organisms fairly stable allowing it to maintain internal body temp
what is cohesion?
tendency of molecules within a substance to “stick together”
why is water cohesive?
water molecules are very cohesive as they are polar H bonds
why is water’s cohesion useful?
helps water to flow which is useful for transporting substances like in the xylem
also gives water high surface tension allowing small organisms like pond skaters to “walk” on pond surfaces
what is transpiration?
water is obtained by the plant from the soil via their roots and passes through the roots to the stem where the xylem transports it to the leaves. water then leaves through stomatal plants by diffusion
list all 8 properties of water
polar, solvent, reactive, metabolite, high latent heat of vaporisation, high specific heat capacity, cohesive and adhesive
how does water move through a plant?
- minerals move into the roots via active transport against the conc gradient
2.this lowers the water potential of the roots so water enters the roots via osmosis down the water potential gradient
3.water moves through the cortex
4.water evaporates from the spongy mesophyll into air spaces due to the heat from the sun and out the stomata via transpiration - this pulls the water up the xylem in a continuous column due to tension as water moves from the narrow xylem to the spongy mesophyll cells via osmosis
6.also though cohesion, water molecules stick to each other and adhesion causes them to stick to the walls of the xylem
give 3 adaptations of the xylem
- long cells/ hollow tubes with no end walls and 2contain lignin which waterproofs them and they have thick walls to withstand water pressure
- no cytoplasm so no obstruction and easy flow
what 4 factors increase the rate of transpiration?
- light
2.temp
3.humidity
4.air movement
how does light intensity affect transpiration?
stomata open in the light and close in the dark, rate of transpiration in higher in the light
how does temp affect transpiration?
^ in temp means ^ in rate of transpiration as temp increasing causes diffusion to occur quicker due to increased kinetic energy
how does humidity affect transpiration?
air spaces in leaf are saturated with water vapour + the air outside the leaf contains much less so the higher conc gradient between inside and out the higher the rate of diffusion as water leaves down the conc grad
how does air movement affect transpiration?
air movement over a leaf moves water vapour away from the stomatal pores which increases water potential gradient between inside and outside increasing the rate of transpiration
how are Xerophyte plants adapted to reduce water loss?
- reduced no. of stomata
2.stomata in pits
3.hairs to trap water
4.rolled leaves
5.leaves reduced to spines
6.thick waxy cuticles
what is translocation?
movement of sugars and ions through the phloem
give an adaptation of the phloem
seive cells
what are seive cells always accompanied by and why?
companion cells that contain lots of mitochondria and ribosomes to provide proteins and ATP that seive cells cannot
where does the mass flow theory of translocation say that substances move from and to?
source to the sink
describe the steps of the mass flow hypothesis for translocation in plants
- at source cells, sucrose is actively transported into the phloem by companion cells which lowers the water potential in the seive tubes of the phloem causing water to move from a high WP to a low WP by osmosis
2.movement of water into phloem creates a high pressure near the source and therefore a lower pressure in the phloem next to the sinks therefore, moving down the pressure gradient, sucrose and water are transported down the phloem - at sink cells sucrose is transported into them via AT using carrier proteins to be used for respiration or stored as starch
4.removal of sucrose from phloem means higher WP in seive tube and there is a higher WP in phloem than in xylem so water moves into the xylem via osmosis
