3 Plant Stems more in depth

Question 1

how is the xylem built up?

Answer 1

• the first xylem the plant makes is called protoxylem
• vertically angled cellulose microfibrils increase strength
• increasing amounts of lignin are added to cell walls, so cell becomes impermeable to water (this lignified tissue is called= metaxylem)
• xylem forms hollow tubes because the end walls between the cells break down
• water then moves out of xylem into surrounding cells through pits

Question 2

protoxylem (2)

Answer 2

• first xylem plant makes

- can stretch and grow because the walls are not fully lignified

Question 3

metaxylem

Answer 3

• lignified xylem vessels

Question 4

transpiration stream

Answer 4

the movement of water up from the soil through the root hair cells, across the root of the xylem, across the leaf until evaporated and diffuses out of the stomata down a concentration gradient

Question 5

Phloem(7)

Answer 5

• living tissue that transports food in the form of organic solutes around the plant
• these molecules move from leaves to the tissues where they are needed
• translocation occurs
• phloem cells do not become lignified, so the contents remain living
• walls between the cells form sieve plates
• mature phloem cells have no nucleus
• mature phloem cells survive because of companion cells

Question 6

translocation

Answer 6

the active movement of substances around a plant in the phloem

Question 7

sieve plates (2)

Answer 7

• the perforated walls between phloem cells that allow the phloem sap to flow
• transport

Question 8

companion cells (4)

Answer 8

• very active cells closely associated with the sieve tube that supplies the phloem vessels with everything they need and load sucrose into the phloem
• linked to sieve tube by many plasmodesmata
• infoldings that increase the surface area over which they can transport sucrose
• have many mitochondria to supply ATP

Question 9

draw arrangement of xylem, phloem, sclerenchyma (7)

Answer 9

see book