M3: ch 9 - transport in plants

Question 1

what are the need for transport systems

Answer 1

• metabolic demands: many internal and underground parts do not photosynthesise so do not make their own glucose or oxygen. They need these transporting to them and also to remove waste products.
• Size: Some small or primitive plants, such as mosses, absorb all the nutrients they need directly from their
  environment. Larger plants do not have a large enough surface area to take in what they need
• Surface area : Volume- although leaves have a relatively
  large surface are to
  volume ratio, when the stems and
  roots are taken into
  account, they have a small SA:V
  ratio. This means that they cannot rely on diffusion alone to supply their cells with what they need.

Question 2

what are the plant processes

Answer 2

• Photosynthesis – plants producing
  glucose, through sunlight
• Respiration – plants supplying energy
• Active Transport – energy required to
  move and transport substances

Question 3

what are the two transport systems in plants

Answer 3

Transpiration System:
- The movement of water molecules and dissolved minerals ions
- Xylem vessels
- Passive process
Translocation System:
- The movement of sugars (Sucrose) & amino acids
- Phloem vessel – sieve & companion cells
- Active process

Question 4

what is the vascular bundle

Answer 4

• Vascular tissue is distributed throughout the plant
• Vascular tissue is made up of xylem and phloem tissue
• As well as the transport of substances the vascular bundle has structural support
  purposes

Question 5

vascular bundle in the roots + draw it

Answer 5

• provides a ‘drill’ like structure
• This enables the plant to push down into the root
• Xylem tissues is the strongest so is in the centre – X structure
• Phloem in four separate sections

Question 6

vascular bundle in the leaf + draw it

Answer 6

• Xylem is located on top of the phloem
• This only applies to dicotyledonous plants, other plants types have a different structure

Question 7

vascular bundle in the stem + draw it

Answer 7

• Xylem is located on the inside – in non-wooded plants
• This provides additional support to the stem
• The cambium layer contains meristem cells

Question 8

what is the structure of the xylem vessel

Answer 8

• thick lignified cell wall
• non lignified pit
• hollow tube - no cytoplasm
• xylem parenchyma
• spirals of lignin running around the lumen of the xylem
• broken end wall - continuous tube for water to run through

Question 9

why are the spiral bands of lignin in the xylem vessel important

Answer 9

• strengthens + thickens the xylem wall - to prevent collapse of xylem
• reinforces the xylem vessels so that they do not collapse under the transpiration pull
• makes the wall waterproof - water is at low pressure
• improves adhesion of water molecules - reduces lateral loss of water through wall
• spiral pattern allows flexibility, movement + stretching - increases capillarity
• prevents stem breaking

Question 10

what is the structure of the phloem vessel

Answer 10

• thin layer of cytoplasm in sieve tube element
• dense cytoplasm of companion cell
• large nucleus
• mitochondria
• plasmodesmata linking cytoplasm of companion cell (with nucleus) and sieve tube element
• sieve plate - with large pores that allow sap to move through the sieve tube elements

Question 11

what happens if the water potential inside the cell is low (high salt conc)

Answer 11

water moves into cell by osmosis (down the conc gradient)

Question 12

what happens if the water potential inside the cell is high (low salt conc)

Answer 12

water moves out the cell by osmosis (down the conc gradient)

Question 13

low external water potential

Answer 13

• water moves out of the cell by osmosis (down the conc gradient)
• Plants can survive this or short periods, as they can shrink the cell membrane away from the cell water
• The cell is said to be plasmolysed

Question 14

root hair cells

Answer 14

• These are specialised exchange surfaces for the uptake of water and mineral ions
• Root hair cells are about 200 – 250μm, this makes them visible to the naked eye
• With thousands on each root, they maximise surface area in contact with the soil

Question 15

absorbing water

Answer 15

• Water and mineral ions are contained within small air spaces in soil
• When the roots make contact with the soil water moves into the roots via osmosis
• The osmosis occurs because there is a
  higher concentration of solutes in the plant than inside the soil

Question 16

what are the water movement pathways

Answer 16

• symplast
• vacuolar
• apoplast

Question 17

what is the symplast pathway

Answer 17

• the movement of water through the living spaces of the cell – cytoplasm
• Changing cells through the plasmodesmata
• Each cell further away from the roots
  has a lower water potential so water is
  drawn up the plant

Question 18

what are the stages of the symplast pathway

Answer 18

1. water enters the cytoplasm across the partially permeable plasma membrane
2. water can move into the sap in the vacuole, through the tonoplast
3. water may move from cell to cell through the plasmodesmata
4. water may move from cell to cell through adjacent plasma membranes and cell walls

Question 19

what is the vacuolar pathway

Answer 19

• Vacuolar pathway is the same as the
  symplast pathway when the water
  moves through the cells vacuoles in
  addition to the cytoplasm
• This is the slowest route

Question 20

what is the apoplast pathway

Answer 20

• This is the movement of water
  though the cell wall and intracellular spaces
• Cohesive and tension forces acting on the cell walls pulls the water up the plant
• This is the fastest movement of water

Question 21

what are the stages of the apoplast pathway