Plant systems 4.2.3.2 pt2

how is root hair cells adapted for absorption

large surface area for maximum absorption, hair shape acts as an anchor in soil, has a partially permeable membrane so molecules can enter

describe process by which plant takes up water

by osmosis through the partially permeable membrane of the root hair cells. the water particles move from an area of high water concentration (the soil) to an area of low water concentration in the cell

how does a plant take up mineral ions

by active transport, from an area of lower mineral concentration the soil to an area of higher mineral concentration the cell using energy from respiration

what is transpiration

when excess water is evaporated from the stomata of the leaf

cohesion

intermolecular forces of attraction between water molecules, enabling them to move together up the xylem in one continuous column

adhesion

forces of attraction between the water molecules and xylem cell wall which prevents them from falling down due to gravity

transpiration stream movement throughout plant 8 steps

1. water enters the root hair cell via osmosis

2. moves through the root, down the water concentration gradient

3. into the xylem

4. the water moves upwards from suction force that are created from water loss from stomata

5. enabled by transpiration stream adhesion and cohesion

6. moves into mesophyll cells via osmosis

7. evaporates into air spaces

8. diffuses through stomata

functions of transpiration stream

1. water for photosynthesis

2. mineral transport

3. keeps cells turgid

4. cools the plant

factors affecting rate of transpiration

1. light intensity

2. temperature

3. air movement

4. humidity

light intensity and transpiration

increase in rate of transpiration as light intensity increases as stoma open for gas exchange during photosynthesis, which allows water to exit. this increases stops as all stoma are open/ another limiting factor

temp and transpiration

higher temp increases rate as rate of evaporation is increased

air mov and transpiration

increases rate of transpiration at high air mov as wind moves water vapor outside stomata faster, increasing water potential gradient

humidity and transpiration

less humid means more transpiration as increased water potential gradient

practical using potometer for transpiration

• Cut a shoot underwater to prevent air entering the xylem and place in tube

• Set up the apparatus as shown in the diagram and make sure it is airtight, using Vaseline to seal any gaps

• Dry the leaves of the shoot

• Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water

• Set up a lamp 10cm from the leaf

• Allow the plant to adapt to the new environment for 5 minutes

transpiration stream

water evaporates from mesophyll cells into the airspaces. this vapor diffuses out through the stomata down the water potential gradient. the loss of water from the mesophyll cells reduces the water potential of these cells so water moves by osmosis from surrounding cells down the water potential gradient. water from the xylem moves into the mesophyll cells down the water potential gradient. the loss of water from the xylem causes water to be pulled up the xylem (transpiration pull) in the stem and roots in a continuous flow known as the transpiration stream