B2.2 The challenges of size - Plant Transport Systems

Question 1

State the function of the xylem

Answer 1

Transports water and mineral ions from the roots to the stem, leaves and flowers

Question 2

State the function of the phloem

Answer 2

Transports dissolves sugars from photosynthesis, and other soluble food molecules from the leaves to all other areas of the plant

Question 3

Name the structure formed by xylem and phloem within the plant

Answer 3

Vascular bundle

Question 4

What tissue makes up the bulk of the plant in woody plants like trees

Answer 4

Xylem

Question 5

Describe an experiment that can be done to easily visualise the xylem in plant tissue

Answer 5

• Place celery in a jug of water containing food colouring
• Leave for 24 hours
• Cut slice of celery and veiw using magnifiying glass or light microscope.

Question 6

Describe the structure of xylem

Answer 6

• Made from dead cells
• No cell walls at the ends of cells
• Dead cells form tubes for water and mineral ions to flow
• Xylem cellulose cell wall is thickened and stiffened with lignin to provide support

Question 7

Destribe the structure of phloem.

Answer 7

• Made of living cells
• Cell walls connecting these cells do not completely breakdown creating sieve plates
• Sieve plates allow dissolved sugars to pass
• Connected cells form a tube allowing dissolved sugers to be transported

Question 8

State the direction of flow in the xylem

Answer 8

One-way - Roots to leaves

Question 9

State the direction of flow in the phloem

Answer 9

Two-way

Question 10

State which tissue in a plant would transport glucose

Answer 10

Phloem

Question 11

If a cross section was taken through the plant in the stem, where would you expect the vascular bundle to be found?

Answer 11

• Bundles organised spherically in the cortex
• Larger phloem at top of the bundle with smaller xylem tubes underneath.

Question 12

If a cross section was taken through the plant in the root, where would you expect the vascular bundle to be found?

Answer 12

• Bundle in the centre of the root
• Xylem in the centre of the bundle
• Phloem around the outside of the xylem
• Surrounded by ground tissue

Question 13

If a cross section was taken through the plant in the leaf, where would you expect the vascular bundle to be found?

Answer 13

• Bundles found in the spongy mesophyll layer
• Xylem closest to palisade mesophyll layer (towards top of the leaf).
• Phloem closest to the lower epidermis

Question 14

How do vascular bundles provide support?

Answer 14

• In the leaf they form a network that supports softer tissue
• In the stem they are loacted around the outer edge providing the stem with strength to resit bending
• In the root they are found in the centre to enable the root to act as an anchor

Question 15

What is transpiration?

Answer 15

The movement of water through the xylem.

Question 16

Explain the transpiration stream.

Answer 16

• The stream of water though the plants xylem caused by the loss of water through the plants stomata in the wind.
• Water evaporates through stomata
• Water potential gradient between leaves and stem - water moves into leaves by osmosis
• Water potential gradient between stem and roots - water moves into stem by osmosis
• Water potential gradient between roots and soil - water moves into root hair cells by osmosis

Question 17

Explain what makes water vapour diffuse from the inside of the a cell into the air?

Answer 17

• Water evaporates from inside the leaf into the leaf’s air spaces
• Concentration gradient between the air inside leaf and the air outside the leaf
• Water vapour diffuses from the area of high concrentration or the air inside the leaf, to the area of low concentration of the air outside the leaf

Question 18

Explain the structure of the stomata and how they open and close to control gaseous exchange.

Answer 18

• Stomata are made up of two guard cells,
• When there is plenty of light and water the guard cells take up water by osmosis and become turgid,
• The inner wall of the guard cell is thickened so the cell curves as it becomes turgid creating a gap between the two guard cells,
• This gap is known as the stomata,
• If conditions for photosynthesis are poor then the guard cells lose water and become flacid,
• When the cells are flacid the gap between them closes.

Question 19

Explain why the upper surface of many leaves is covered in a thick, waxy cuticle?

Answer 19

• To prevent uncontrolled water loss
• In hot environemnts this layer is very think and shiny

Question 20

How can the rate of transpiration be calculated?

Answer 20

• Calculate the rate of movement of an air bubble using a potometer
• rate of movement = distance (mm) ÷ time (s)

Question 21

Why does the plants need for CO₂ increase the rate of transpiration in a plant.

Answer 21

• Plants need glucose for respiration
• Glucose is product of photosynthesis
• Photosynthesis requires carbon dioxide and water
• Plant must open stomata to enable the diffusion of carbon dioxide into the leaf
• Open stomata allows water vapour to leave the leaf via diffusion
• Loss of water from leaf increases rate of transpiration

Question 22

State the factors affecting the rate of transpiration

Answer 22

• Light intensity = increase light, increase transpiration
• Temperature = increase temperature, increase transpiration
• Air movement = increase air movement, increase transpiration
• Humidity = increase humidty, decrease transpiration

Question 23

Explain what the ringing experiment shows.

Answer 23

• IA ring of bark is scraped away that also removes the phloem, exposing the xylem.
• Sugar then attempts to move down the stem but is stopped by the ring.
• This is demonstrated by a bulge of sugar forms above the ring.
• Suggesting that sugar moves down the stem in the phloem and sugar transported by the phloem.

Question 24

Expalin how the potometer experiment can be used to measure the rate of transpiration

Answer 24

• Set up potometer making sure the stem is cut under water to ensure no air bubble
• Release an air bubble into the capillary tube
• As the water evaporates form the leaves and moves into the stem the bubble moves towards the plant
• Measure how fast the air bubble travels
• Refil and repeat the experiment