transport in plants

Question 1

why do plants need a specialised transport system?

Answer 1

• multicellular plants are large/have a small surface area:volume ratio
• so cannot rely on diffusion alone

Question 2

why do cells in the root tissue have a high metabolic rate?

Answer 2

• cells in root tissue absorb mineral ions by active transport
• ## so require high levels of ATP produce through respiration)

sugars must be transported to these tissues due to their high metabolic rate

Question 3

what is transpiration?

Answer 3

evapouration of water from a plants surface

Question 4

explain the process of transpiraton

hint: 4 points

Answer 4

1) water enters the plant through the roots
2) water travels up the xylem
3) water evapourates from the moist cell walls and accumulates in the spaces between cells in the leaf
4) when the stomato open, it moves out the leaf down the concentration gradient

Question 5

what is the transpiration stream?

Answer 5

movement of water up through the xylem from roots to the leaves

Question 5

what are xerophytes?

Answer 5

plants adapted to dry enviroments

Question 6

list some adapations of xerophytes for WATER LOSS

Answer 6

• smaller leaves to REDUCE surface area for water loss
• packed mesophyll + thick waxy cuticle to prevent water loss through evaporation
• stomatos can close to prevent water loss
• contains hairs + pits which trap moist air- reduces water vapour potential gradient
• rolled leaves - reduces exposure of lower epidermis to atmosphere - traps moist air

Question 7

what is translocation?

Answer 7

the process by which organic materials are transported around a plant

Question 8

is translocation an energy recquiring process?

Answer 8

yes
- because it involves active transport

Question 9

what are sources vs what are sinks?

Answer 9

sources= where the assimilates are produced e.g. photosynthesising leaves

sinks= regions where assimilates are required e.g. roots which carry out active transport, growing regions

Question 10

what are assimilates?

Answer 10

molecules made as a result of photosynthesis, that are transported through the plant by translocation

Question 11

outline the basics of cohesion tension theory

Answer 11

1) water lost from leaf due to transpiration
2) lowers water potential of mesophyll/leaf cells
3) so water pulled up xylem, creating tension
4) water molecules bonded together by hydrogen bonds (cohesion)
5) so water moves up in single continous column

Question 12

what usually happens after cohesion- tension of a plant

hint: has something to do with replacing water lost

Answer 12

diffusion in the roots:
- water pulled upwards so water potentail at bottom of plant decreases
- so water diffuses into roots by osmosis down water potential gradient

Question 13

list 5 ways in which water may be used by a plant (NOT transpiration)

Answer 13

1) light dependant reaction in photosynthesis
- electrons from water enable ATP production/H+ ions used to reduce NADP

2) hydrolysis reactions within the plant

3) to create turgor –> pressure exerted by water in a plant cell

4) as a solvent for transport of substances

5) as a component of cytoplasm

Question 14

list + describe how the xylem cells are adapted for their functions

Answer 14

1) lignin in cell walls
- provide structural support to withstand tension
2) xylem cells have no end walls + are stacked
- provides/makes a continous column of water
3) have pores/pits
- enables sideways flow of water
4) narrow tubes
- increases surface area for adhesion

Question 15

what is the key idea of translocation?

Answer 15

assimilates are moved from sources to sinks

Question 16

what are sources?

Answer 16

where assimilates are produced
e.g. photosynthesising leaves

Question 17

what are sinks?

Answer 17

regions where assimilates are aquired
e.g. roots that carry out active transport

Question 18

explain the mass flow hypothesis

Answer 18

1) in source/leaf, sugars are actively transported into phloem by companion cells
2) this lowers water potential in sieve tubes, so water moves in by osmosis
3) increase in pressure from water moving in, causes mass transport of sugars from soruce to sink
4) sugars are used in root for respiration/storage

Question 19

explain how water enters a plant root from soil + travels through epidermis (5 marks)

Answer 19

1) water enters root hair cells by osmosis
2) actie transport of mineral ions creates water potential gradient
3) so water moves through cortex down water potential gradient
4) through cell vacuoles + cytoplasm (symplastic pathway)
5) + then through apoplastic pathway (cell walls)

Question 20

what is the symplastic pathway?

Answer 20

• route water and solutes take to move through plant tissues
• involving cytoplasm + vacuoles
• connected by plasmodesmata

Question 21

what is the apoplastic pathway?

Answer 21

• route water + dissolved substances take to move through plant tissues
• travelling through cell walls + intercellular spaces

Question 22

explain how ringing is used to investigate transport in plants

Answer 22

ringing - proves sucrose must be transported in the phloem

1) phloem vessels are located outside xylem vessels
2) ring is cut outside of stem –> halts transport in phloem NOT xylem
3) tissue above ring swells (due to accumulated sucrose) + growth stops (because sucrose can no longer be transported)

Question 23

explain how tracing is used to investigate transport in plants

Answer 23

• sucrose produced during photosynthesis can be traced by exposing leaves to carbon dioxide containing radioactive carbon

1) plant frozen very quickly in liquid nitrogen
2) placed on photographic film
3) pathway travelled by radioactive sucrose down phloem can be traced

Question 24

explain the importance of the xylem being kept open in a continous tube (3 marks)

Answer 24

- allows for unbroken column of water - so water molecules cohere by hydrogen bonding - so water is drawn up from xylem into cells by tension