3 Plant Stems

Question 1

function of stem (4)

Answer 1

• flexible support, as plants are blown by wind etc.
• holding the leaves in the best position for obtaining sunlight for photosynthesis
• support the flowers to maximize pollination
• movement of materials around plant (provide route along which products of photosynthesis are carried, water moves through stem carrying mineral ions)

Question 2

epidermis (2)

Answer 2

• outer layer of stem

- does not provide support but protects the cells beneath it

Question 3

parenchyma (3)

Answer 3

• unspecialized
• can be modified to become suitable for storage and photosynthesis
• packing tissue

Question 4

collenchyma (5)

Answer 4

• modified parenchyma
• support
• living tissue
• thick secondary structure (thick cellulose primary cell walls)
• usually undo the epidermis

Question 5

sclerenchyma (5)

Answer 5

• modified parenchyma
• strong secondary cell wall
• gives strength
• supports the increasing weight of the upper part of plant as it grows
• builds in lignin in wall and becomes impermeable to water, which will make cell die

Question 6

compare and contrast sclerenchyma with xylem (3)

Answer 6

• both are dead cells
• both have thick secondary cell wall
• the xylem is for the transport of water with mineral ions, while the sclerenchyma just gives support

Question 7

sclereids

Answer 7

sclerenchyma cells that are completely impregnated with lignin

Question 8

xylem (6)

Answer 8

• transport tissue
• hollow
• can only transport water and minerals from roots to leaves in that direction (always upwards)
• give support
• most xylem cells are dead
• found together with phloem in vascular bundles

Question 9

phloem (5)

Answer 9

• transport tissue
• living tissue
• transports the dissolved product of photosynthesis from the leaves to where it is needed
• the flow through the phloem can go both up and down the plant
• found together with xylem in vascular bundles

Question 10

vascular bundles (3)

Answer 10

• transportation
• phloem on the outside and xylem on the inside
• often with strengthening sclerenchyma

Question 11

cambium

Answer 11

layer of unspecialized cells which divide and give rise to more specialized cells that then form both the xylem and the phloem

Question 12

draw and label vascular bundle (4) each one right gives one point up

Answer 12

see book

Question 13

draw and label ‘ditribution of different tissues in the stem’ (7)

Answer 13

see book

Question 14

what is true about both sclerenchyma and xylem fibres? (4)

Answer 14

• provide support
• neither transport glucose
• neither transport hormones
• sclerenchyma does not transport mineral ions

Question 15

Why does the cell wall form greater percentages of the total mass of the sclerenchyma fibre than of the phloem sieve tube?

Answer 15

because sclerenchyma fibres have thickened, lignified cell walls

Question 16

describe differences between structure of xylem and phloem (4)

Answer 16

• xylem cell walls contain lignin, but phloem cell walls contain no lignin
• xylem is hollow but phloem has cell contents
• xylem is dead, but phloem has companion cells
• xylem has pits but phloem does not

Question 17

Describe the positions in the stem of those tissues that contain lignin (2)

Answer 17

• sclerenchyma on the outer side of the vascular bundle

- xylem on the inner side of the vascular bundle

Question 18

explain how water is transported in the xylem to the leaves (3)

Answer 18

• water is evaporated from the leaves
• therefore leaf cells have a low water potential, water potential gradient is created
• adhesion of water molecules to xylem walls