7. TRANSPORT IN PLANTS

Question 1

Why is light required for photosynthesis

Answer 1

it is a source of energy

Question 2

How have leaves evolved for photosynthesis

Answer 2

have large surface area:volume ratio

- for efficient capture of carbon dioxide and light

Question 3

How do plants obtain mineral salts and water for nutrition

Answer 3

through extensive root systems below ground

Question 4

Why do plants need magnesium ions

Answer 4

ions part of the chlorophyll molecule which is required for photosynthesis

Question 5

Why are transport systems needed

Answer 5

• to move substances from where they are absorbed to where they are needed
• to move substances from where they are produced to where they are needed for metabolism
• to move substances to a different part of the plant for storage

Question 6

Functions of the xylem

Answer 6

• long distance transport of water and mineral salts

- mechanical support and strength

Question 7

What are the caps outside vascular bundles made of

Answer 7

• sclerenchyma fibres

- provide extra support for the stem

Question 8

What are sclerenchyma fibres

Answer 8

• long, dead, empty cells with lignified cell walls

- only provide extra support for the stem

Question 9

Features of xylem

Answer 9

• dead cells: no protoplasm to get in the way of transport
• no end walls
• lignified cell walls: prevent xylem collapsing due to pressure differences

narrow diameter: helps to prevent air locks
pits in wall: allow water to bypass air locks. allow water to move out of xylem to living cells

Question 10

Support of stems and roots

Answer 10

STEMS
need to be supported in air
ROOTS
subject to pulling strain from above ground

Question 11

What is wood

Answer 11

in the stems and roots of trees and shrubs, extra xylem is made, forming wood

Question 12

What are the strengthening tissues

Answer 12

xylem and sclerenchyma

Question 13

What is hydrostatic pressure

Answer 13

• pressure exerted by a liquid
• pressure at top becomes lesser than pressure at bottom of xylem vessel as water is removed from the leaves due to transpiration
• pressure difference causes water to move up the xylem vessels in continuous columns

Question 14

What is mass flow

Answer 14

• movement of water in xylem

- all the water molecules and any dissolved solutes move together as a body of liquid

Question 15

Cohesion and adhesion

Answer 15

COHESION: water molecules are attracted to each other by hydrogen bonds
ADHESION: water molecules are attracted to the cellulose and lignin in the cell walls of xylem

help to move water by mass flow in a continuous column in xylem

Question 16

Position of vascular bundles in stems

Answer 16

• arranged in rods around the centre
• xylem inside and phloem outside separated by cambium
• sclerenchyma caps at the ends for support
• strong rods help to support the stem

Question 17

Process of movement of water through the xylem

Answer 17

largely passive from high water potential to lower water potential

Question 18

What is root pressure

Answer 18

• cells surrounding xylem vessel elements actively pump solutes such as mineral ions into water in xylem
• decreasing water potential of the solution in the xylem
• drawing water from the surrounding root cells
• this influx of water increases the hydrostatic pressure at the base of the xylem vessel

Question 19

What are assimilates

Answer 19

substances which the plant itself has made for example sugars, which are made by photosynthesis in leaves

Question 20

What are the functions of Casparian strips

Answer 20

• allow control of substances entering xylem

- help with the generation of root pressure