transport in plants 2.51, 2.52, 2.53, 2.54, 2.55B, 2.56B, 2.57B, 2.58B Flashcards
how is water absorbed by hair root cells?
plants take in water from soil through their root hairs
they are the main site of water absorption in a plant
root hair cells are thin-walled (short distance)
hair extensions (increasing surface area)
root hair cell absorbs water and minerals from the soil
mineral ions active transported
water osmosis
how is water absorbed from the root hair cell to the plant?
water moves down a concentration gradient that is constantly being maintained by water being brought up the xylem in the middle of the root
the water is carried in the xylem vessels
what is the definition of transpiration?
the evaporation of water from the surface of a plant
what is transpiration?
causes water to be pulled up the xylem in the stem and roots in the transpiration stream
the water vapour evaporates out of the stomata
whats the functions of the transpiration stream?
- carry mineral ions to the leaves to synthesise amino acids and chlorophyll
- to keep a high pressure in leaf cells holding leaves up
- evaporation cools leaves
- supplies water for photosynthesis
environmental conditions on transpiration
temperature:
on a hot day, the water will quickly evaporate from the leaves as eater molecules have more kinetic energy
as temperature increases transpiration increases
environmental conditions on transpiration
humidity:
very humid air contains lots of water vapour, therefore there is a smaller concentration gradient so transpiration slows down
if dry air the diffusion of water vapour from the leaf will increase and be rapid
if humidity increases transpiration decreases
environmental conditions on transpiration
wind speed:
in still air, the region around the stomata and leaf will become saturated with water vapour so transpiration will slow down
in windy/moving air, the water vapour will be blown away from the leaf as it diffuses out, speeding up transpiration
as wind speed increases transpiration increases
environmental conditions on transpiration
light intensity:
in daylight, stomata are open to supply carbon dioxide to the leaf for photosynthesis
this allows more water to diffuse out of the leaf
the greater the light intensity the greater the rate of transpiration
environmental conditions on transpiration
water supply:
if water supply is short, and the plant is losing water by transpiration faster than it is being taken in by the roots
the plant will start to wilt and the guard cells will become flaccid and the stomata will close therefore decreasing the rate of defusion
practical
measuring the rate of transpiration:
potometer measures the rate of water uptake from a leafy shoot as 90% of water is lost to transportation we use this as a measure of the rate of transpiration
how to set up:
- potometer must be set up underwater- preventing air bubbles from entering the system and blocking the xylem
- cut the stem of the shoot
- put the shoot stem in a bung, grease the joint with petroleum jelly - preventing water loss and the entry of air
- put the bung in the potometer
- make sure tap is closed and full of water with no air bubbles and then lift potometer out of water
- leave the end of the capillary tube out of the water until an air bubble forms and then put the end in water
- measure the rate of transportation by the distance moved by the air bubble in 5 minutes
- repeat the experiment and take a number of readings to find the mean
a potometer can be used to collect readings in normal air, windy conditions, increased temperature, increased humidity and so on.
remove leaves or cover in vaseline to show the importance of the stomatas
what’s the role of the xylem in transporting water, mineral ions from the root to other parts of plant?
- made up of thick-walled dead cells containing no cytoplasm, completely hollow
- cell wall contains lignin, waterproof
- end walls have broken down so they form a continuous transport system throughout plant
- transports water and mineral ions from roots to leaves
- nitrate ions needed to make amino acids and proteins
- magnesium ions needed to make chlorophyll
what’s the role of the phloem in transporting water, mineral ions from the root to other parts of plant?
- this consists of living cells
- tubes are formed by cells arranged end to end but have cell walls made of cellulose
- the sugar made in photosynthesis is converted to sucrose
- phloem transports sucrose and amino acids from the leaves to the growing points or storage area
- moving sucrose and amino acid around the plant requires energy, called translocation
