transport in plants

Question 1

Plants contain two types of transport vessels

Answer 1

Xylem vessels Phloem vessels

Question 2

state functions of transport vessels

Answer 2

Xylem vessels – which carry water and minerals (pronounced: zi-lem) Phloem vessels – which carry food materials (sucrose and amino acids) made by the plant (pronounced: flow-em)

Question 3

These are arranged throughout… in groups called ..

Answer 3

• the root, stem and leaves -vascular bundles

Question 4

Answer 4

Question 5

Answer 5

Question 6

Answer 6

Question 8

Remember that xylem is always on the … and phloem is always on the…

Answer 8

• inside
• outside.

Question 9

Root Hair Cells

Answer 9

Root hairs are single-celled extensions of epidermis cells in the root

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

Water enters the root hair cells by osmosis

This happens because soil water has a higher water potential than the cytoplasm of the root hair cell

Question 10

How the Large Surface Area of Root Hair Cells is Useful

Answer 10

The root hair increases the surface area of the cells significantly

This large surface area is important as it increases the rate of the absorption of water by osmosis and mineral ions by active transport

Question 11

Pathway of Water through Root to Leaf

Answer 11

Osmosis causes water to pass into the root hair cells, through the root cortex and into the xylem vessels:

Pathway of water into and across a root

Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells

So the pathway is:

root hair cell → root cortex cells → xylem → leaf mesophyll cells

Question 12

Answer 12

Question 13

investigate Pathway of Water through Root to Leaf

Answer 13

The pathway can be investigated by placing a plant (like celery) into a beaker of water that has had a stain added to it (food colouring will work well)

After a few hours, you can see the leaves of the celery turning the same colour as the dyed water, proving that water is being taken up by the celery

Investigating water movement in plants using a stain

If a cross section of the celery is cut, only certain areas of the stalk is stained with the dye, showing that the water is being carried in specific vessels through the stem – these are the xylem vessels

Cut section of celery stalk showing that only the xylem vessels are dyed with the stain

Question 14

What is Transpiration?

Answer 14

Water travels up xylem from the roots into the leaves of the plant to replace the water that has been lost due to transpiration

Transpiration is defined as the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

Xylem is adapted in many ways:

A substance called lignin is deposited in the cell walls which causes the xylem cells to die

These cells then become hollow (as they lose all their organelles and cytoplasm) and join end-to-end to form a continuous tube for water and mineral ions to travel through from the roots

Lignin strengthens the plant to help it withstand the pressure of the water movement

Movement in xylem only takes place in one direction – from roots to leaves (unlike phloem where movement takes place in different directions)

Question 15

traspiration is defined as

Answer 15

the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

Question 16

Transpiration has several functions in plants:

Answer 16

transporting mineral ions

providing water to keep cells turgid in order to support the structure of the plant

providing water to leaf cells for photosynthesis

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

Question 17

How does Transpiration Occur?

Answer 17

Evaporation takes place from the surfaces of spongy mesophyll cells

The many interconnecting air spaces between these cells and the stomata creates a large surface area

This means evaporation can happen rapidly when stomata are open

Question 18

How is the Transpiration Stream Created?

Answer 18

Water molecules are attracted to each other by cohesion – creating a continuous column of water up the plant

Water moves through the xylem vessels in a continuous transpiration stream from roots to leaves via the stem

Transpiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves

As water molecules are held together by cohesive forces (each individual molecule ‘pulls’ on the one below it), so water is pulled up through the plant

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

Question 19

Wilting

Answer 19

If more water evaporates from the leaves of a plant than is available in the soil to move into the root by osmosis, then wilting will occur

This is when all the cells of the plant are not full of water, so the strength of the cell walls cannot support the plant and it starts to collapse

Question 20

Factors Affecting Transpiration

Answer 20

Question 21

Investigating the role of environmental factors in
determining the rate of transpiration from a leafy shoot

Answer 21

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

Set up the apparatus as shown in the diagram below and 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 the environmental factor you are investigating

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

Record the starting location of the air bubble

Leave for a set period of time

Record the end location of air bubble

Change the light intensity or wind speed or level of humidity or temperature (only one – whichever factor is being investigated)

Reset the bubble by opening the tap below the reservoir

Repeat the experiment

The further the bubble travels in the same time period, the faster transpiration is occurring and vice versa

Investigating transpiration rates using a potometer

Environmental factors can be investigated in the following ways:

Temperature : Temperature of room (cold room and warm room)

Humidity : Spray water in plastic bag and wrap around plant

Question 22

Temperature & Humidity on Transpiration Rate

Answer 22

Question 23

Transport of Food

Answer 23

The soluble products of photosynthesis are sugars (mainly sucrose) and amino acids

These are transported around the plant in the phloem tubes which are made of living cells (as opposed to xylem vessels which are made of dead cells)

The cells are joined end to end and contain holes in the end cell walls (called sieve plates) which allow easy flow of substances from one cell to the next

The transport of sucrose and amino acids in phloem, from regions of production to regions of storage or use, is called translocation

Transport in the phloem goes in many different directions depending on the stage of development of the plant or the time of year; however dissolved food is always transported from source (where it’s made) to sink (where it’s stored or used):

During winter, when many plants have no leaves, the phloem tubes may transport dissolved sucrose and amino acids from the storage organs to other parts of the plant so that respiration can continue

During a growth period (eg during the spring), the storage organs (eg roots) would be the source and the many growing areas of the plant would be the sinks

After the plant has grown (usually during the summer), the leaves are photosynthesizing and producing large quantities of sugars; so they become the source and the roots become the sinks – storing sucrose as starch until it is needed again

Question 24

Comparision between xylem and phloem tissue

Answer 24