structure and function (transport in plants)

what does the phloem do

from where to where

transports sucrose and amino acids made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem

movement of substances in the phloem is

up and down, either way

in diagrams, phloem is always on the _____ and the xylem is always on the ______

phloem is always on the outside and xylem is always on the inside

what does the xylem do

transports water and minerals from the roots to the stem and leaves via transpiration

xylem and phloem are arranged throughout plant in _______

xylem and phloem are arranged throughout plant in vascular bundles

structural features of xylem (2)

• It is composed of dead cells which form hollow tubes

• Xylem cells are strengthened by lignin and so are adapted for the transport of water in the transpiration stream

labelled xylem diagram

xylem/phloem cross section of a STEM

xylem/phloem + root _____ cells cross section of root

root hair cells grow _____ soil particles and ______ water and ________ from the soil

grow between soil particles and absorb water and minerals from the soil

how is water //mineral ions absorbed by root hair cells

1. Roots hair cells take up mineral ions from the soil by active transport

2. The water concentration of the cell cytoplasm is reduced due to the presence of mineral ions - cell is hypertonic (more solutes) to hypotonic, hypo → hyper

3. Water moves into the root hair cell by osmosis

root hair cells have a large ________ ________

large surface area → extended hair, more space for transport

define transpiration

the loss of water vapour from the parts of the plant that are above ground. e.g. leaves/stems

what is transpiration caused by, and where (2)

through evaporation of water at the surfaces of the spongy mesophyll cells

and diffusion of water vapour through the stomata

what is the transpiration stream, and what does it ‘look’ like

as water evaporates/diffuses out, water is drawn up from the rest of the plant through xylem to fill the empty space. this means more water is drawn up from roots

• Due to cohesion, the water in the xylem creates a continuous unbroken column (each individual molecule ‘pulls’ on the one below it)

• Transpiration produces tension or ‘pulls’ on the water in the xylem vessels

uses of water in plants (4) - so basically why transpiration is important

Turgidity: Water is stored in plant cells’ vacuoles to make them turgid, providing structural support.

Photosynthesis: Only 5% of water taken up by plants is used for photosynthesis, which is essential for making their own food.

Transport: Water transports mineral ions throughout the plant.

Cooling: Evaporation of water cools the leaves

why does transpiration cool the plant

the conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspace requires heat energy. The use of heat to convert water into water vapour helps to cool the plant down

If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels _______

If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker

wind	high
humidity	high
light	high
temperature	high

piece of equipment used to measure transpiration

potometer

how does a mass potometer work

measures a change in mass of a plant as a measure of the amount of water that has evaporated from the leaves and stem

how does a bubble potometer work

A bubble potometer measures the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation consequently pulling water up through the stem to replace it

labelled bubble potometer diagram

rate of transpiration (for bubble potometer) =

distance moved by bubble (m) / time (minutes)

transpiration method, and why for some steps

• Cut a shoot underwater

  • To prevent air entering the xylem and place in tube

• Set up the apparatus as shown in the diagram

• make sure it is airtight, using Vaseline to seal any gaps

• Dry the leaves of the shoot

  • Wet leaves will affect the results

• 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

• Record the starting location of the air bubble

• Leave for 30 minutes

• Record the end location of the air bubble

• Change the light intensity

• Reset the bubble by opening the tap below the reservoir

• Repeat the experiment

• Calculate the rate of transpiration by dividing the distance the bubble travelled by the time period

  • The further the bubble travels in the same time period, the greater the rate of transpiration

transpiration increases when light intensity is _____. this is because…

transpiration increases when light intensity is HIGH. This is becaues more stomata tend to be open in bright light in order to maximise photosynthesis

(The more stomata that are open, the more water can be lost by evaporation and diffusion through the stomatal pores)

transpiration potometer cormss

• Change - change the intensity of the light

• Organisms - same plant species, size, age, number of leaves

• Repeat - repeat x3, take avgs

• Measurement 1 - measure the distance travelled by the bubble (m)

• Measurement 2 - ...in 30 minutes (to calculate the rate of transpiration)

• Same - control the temperature, wind speed and humidity of the environment