Transpiration

Question 1

How does water enter roots

Answer 1

Root hair cells

Question 2

Define transpiration

Answer 2

Water constantly evaporating from surface of leaves

Question 3

Describe process of the transpiration stream

Answer 3

• starts with evaporation of water from cells inside the leaf
• water vapour diffuses through air spaces in spongy mesophyll and out of leaf through stomata
• water passes from xylem into leaf to replace water that’s been lost
• water drawn into root hair cells and up xylem vessels to the leaf

Question 4

Importance of transpiration

Answer 4

Brings water to the leaf which is required for photosynthesis
Transports dissolved minerals which play important roles in the plant
Evaporation of water from leaf cools the leaf down

Question 5

Factors that affect rate of transpiration

Answer 5

• higher transpiration at higher temp
  = evaporation faster at higher temps
• faster transpiration at dry conditions
• transpiration increases in windy conditions
  = wind removed any water vapour
  = allow more water to evaporate
• transpiration increases when light intensity increases
  = increases rate of photosynthesis
  = stomata open to let co2 enter

Question 6

How do stomata work

Answer 6

• surrounded by 2 guard cells
• when high light intensity
  = guard cells swell and change shape
  = causes stomata to open
  = co2 can diffuse into leaf
• in hot conditions stomata close
  = reduce water loss by transpiration
  = can’t photosynthesise

Question 7

How does water moves from roots to leaves

Answer 7

Transpiration stream in xylem

Question 8

Adv of few stomata

Answer 8

Less water lost
= won’t wilt

Question 9

Importance of active transport in root hair cells

Answer 9

Movement of mineral ions again concentration gradient

Question 10

Why does a plant contain both glucose and starch in the leaf

Answer 10

Glucose needed for photosynthesis
= excess glucose converted to starch

Question 11

Why does a leaf in no light contain glucose but not starch

Answer 11

Starch has been converted to glucose
= glucose used for respiration
= there’s no light to make new glucose by photosynthesis

Question 12

Define transpiration stream (3 marks)

Answer 12

Movement of water from roots up stem
Via xylem to the leaves
Water evaporates via stomata

Question 13

Importance of transpiration

Answer 13

Brings in water to leaf for photosynthesis
Transports dissolved minerals like magnesium ions
Evaporation of water from leaf cools down the leaf