Xylem

Question 1

What does xylem tissue transport?

Answer 1

Water and mineral ions in a solution

Move up the plant from roots to leaves

Question 2

What does phloem tissue transport?

Answer 2

Organic substances like sugars (also in solution) both up and down the plant

Question 3

What are both xylem and phloem are?

Answer 3

Mass transport system - move substances over large distances

Question 4

What are xylem vessels a part of?

Answer 4

Xylem tissue

Question 5

What do xylem vessels transport?

Answer 5

Water and ions

Question 6

Properties of xylem vessels

Answer 6

• Long, tube-like strcture formed by dead cells (vessel elements) joined end to end
• No end walls on these cells - making interrupted tube allowing water to pass through the middle easily

Question 7

What does cohesion and tension help to do?

Answer 7

• Helps the water move up plants from roots to leaves against the force of gravity

Question 8

Explain cohesion tension theory of water transport

Answer 8

1. Water evaporates from leaves at the ‘top’ of xylem (transpiration)
2. Creates tension (suction) which pulls more water into leaf
3. Water molecules are cohesive so when pulled into the leaf others follow, the whole column of water in xylem from leaves down to roots move upwards
4. Water enters the stem through roots

Question 9

What does it mean that water is cohesive?

Answer 9

They stick together

Question 10

What is transpiration?

Answer 10

Evaporation of water from pant’s surface especially the leaves

Question 11

Steps of transpiration:

Answer 11

1. Water evaporates from the moist cell walls and accumulates in the cells between cells in the leaf
2. Whe stomata open it moves out of the leaf down the concentration gradient (more water inside the leaf than in the air outside)

Question 12

Why is transpiration a side effect of photsynthesis?

Answer 12

Plant needs to open up its stomata to let C02 that it can produce glucose

but this lets water out

Question 13

What are four main factors affect transpiration rate?

Answer 13

1. Light
2. Temperature
3. Humidity
4. Wind

Question 14

How does light affect transpiration?

Answer 14

1. The lighter it is the faster the transpiration rate - pos correlation betwen light intensity and transpiration rate
2. Stomata open when light to let in C02 for photosynthesis
3. When dark , stomata close so little transpiration

Question 15

How is temperature affect transpiration?

Answer 15

• The higher the temperature , the faster the transpiration rate
• Warmer water molecules have more energy so they evaporate from cells inside the leaf faster
• Increasing concentration gradient between the inside and outside of leaf , making water diffuse out of the leaf faster

Question 16

How is humidity affecting transpiration rates?

Answer 16

• Lower humidity , faster the rate of transpiration (neg correlation)
• If the air around the plant is dry , the concentration gradient between leaf and air is increased , increases transpiration

Question 17

How does wind affect transpiration?

Answer 17

• The winder it is , faster rate of transpiration
• Lots of air movement blows away water molecules away from stomata
• Increases concentration gradient , increases rate of transpiration

Question 18

What is a potometer?

Answer 18

Special piece of apparatus used to estimate transpiration rate

Measure water uptake by plant

Assumed water uptake is directly related to water loss in leaves

(estimate how different factors affect transpiration rate)

Question 19

Instructions:

Potometer used to estimate transpiration rates

Answer 19

• Cut a choot underwater to prevent air entering xylem, cut in slant to increase SA for water uptake
• Assemble potometer in water and insert shoot underwater - no air enter
• Remove apparatus from water but keep end of capillary tube submerged in beaker of water
• Check appratus is waterlight and airlight
• Dry leaves and allow time for shoot to accilmatlse and shut tap
• Remove end of capillary tube from beaker until one air bubble formed and put back in water
• Record startling position of air bubble
• Start stopwatch and record distance moved by bubble per unit time (-rate of transpiration)

Question 20

What is air bubble sometimes called?

Answer 20

Air-water meniscus

Question 21

What to make sure of the potmeter experiment?

Answer 21

Only change one variable at a time(e.g temperature)

all other variables (humidity , light) must be constant

Question 22

Instructions of dissecting plants

Answer 22

1. Use scapel to cut a cross-section of stem, cut sections as thinly as possible for better viewing under a microscoope
2. Use tweezers to gently place the cut section in water until you come to use them. Stops to drying them out
3. Transfer each section to a dish containing a stain e.g toluidine blue and leave in one minute. It will stain the lignin in walls of xylem-vessel blue-green allowing position of xylem vessels and examine structure
4. Rinse off sections in water and mount onto slide