3.1.3 transport in plant

Question 1

what is a dicotyledenous plant?

Answer 1

they have 2 seed leaves when they germinate

Question 2

how do gases diffuse in and out of leaves? (simple diffusion)

Answer 2

via stomata
- since leaves are thin, flat so have high SA

and root hair cells
- large SA

all allows for simple diffusion

Question 3

how are leaves adapted to give a small diffusion distance?

Answer 3

thin and flat with a big SA

Question 4

why do plants need specialised transport systems?

Answer 4

• to deliver water, mineral ions and organic solutes to cells + tissues
• small sa:vol ratio so larger diffusion distance
• high metabolic rate so more oxygen demand
• large size and need to move substances up and down from roots to leaves

Question 5

define transpiration stream

Answer 5

evaporation of water vapour from stomata

Question 6

define transpiration

Answer 6

movement of water up the plant

Question 7

give summary of how water moves from root hair, up stem, into leaf, and out of stomata.

Answer 7

• water moves along water potential gradient through the plant
• from area of high to low water potential
  -starts from root hair cells, and leaves as vapour from stomata into air

Question 8

describe water movement across the root

Answer 8

1. mineral ions move into root hair cells via facilitated diffusion and active transport
2. lowers ψ inside root cell, creating a ψ gradient
3. so water moves in from soil to root hair cell, by osmosis
4. water moves through cells across the cortex of the root, by osmosis, towards xylem
5. 2 ways water can travel through cortex:
   - apoplast pathway: through cell wall
   - symplast : through cytoplasm via channels called plasmodesmata
6. water reaches endodermis, where the cells have a strip of waxy waterproof material (suberin) in walls, forming casparian strip, which water cannot pass through
7. water crosses through symplastic pathway as apoplast is blocked
8. slowing down flow of water, so there is control ober mineral ions passing through

Question 9

apoplast pathway

Answer 9

water travels through cellulose cell wall , as cellulose is fully permeable to water. quick transport route

Question 10

symplastic pathway

Answer 10

water travels through cytoplasm via channels called plasmodesmata

Question 11

describe water movement up stem

Answer 11

1. water moves from xylem in roots to xylem in stems
2. these are non-living/ no cell contents
3. water movement up stems is MASS FLOW (moves as whole column) not osmosis
4. transpiration from leaves causes ψ gradient to keep water moving upwards
5. 3 forces move water
   - root pressure from below, mineral ions enter RHCs, lowering ψ, so water moves in as well creating hydrostatic pressure
   - cohesion tension theory: water molecules are polar, so attract one another forming H-bonds, so as water molecules move up xylem they attract further water molecules and pull them up against gravity
   - adhesion: water molecules attracted to lignin lining on xylem walls so crawl up sides of vessels + xylem vessels are narrow, so water is in more contact with walls causing capillary effect

Question 12

features of xylem vessels that make them adapted to carry water up

Answer 12

1. xylem tissue made up of many xylem vessel elements stacked end to end, forming xylem vessels
2. start as living cells, but as they differentiate, tey lose all cell contents and end walls to become continuous hollow tubes that are non-living
3. narrow —> increases adhesion forces and helps maintain pressure
4. cellulose cell wall remains and lignin lines the walls. lignin is strong —> vessels won’t burst due to pressure + waterproof (water won’t leak out)
5. tiny holes called pits in walls that allow water to move sideways into neighbouring vessels if there are any blockages/ air locks

Question 13

is water transport passive or active, why?

Answer 13

passive. evaporation of water VAPOUR from stomata of leaves drives movement of water. no ATP needed.

Question 14

describe water transport across leaf

Answer 14

1. water from xylem vessels in leaf enter mesophyll cells by osmosis
2. water evaporates into air spaces of spongy mesophyll cells, so the spaces are SATURATED with water vapour
3. air spaces are close to stomata, so water vapour evaporates out, into air by DIFFUSIOn down a ψ gradient (high to low).
4. this is called transpiration
5. as water evaporates out of leaf a ψ gradient is maintained, so more water molecules move out into leaf
6. which pulls more water up xylem by cohesion and adhesion

Question 15

what adaptations do plants have to minimise water vapour loss by transpiration?

Answer 15

1. waxy cuticle = reduces water loss through epidermis
2. stoma on undersurface of leaves = less evaporation due to direct heating from sun
3. stoma closed at night = no light for photosynthesis
4. some plants lose leaves, when ground is frozen

Question 16

why is important plants don’t lose too much water by transpiration?

Answer 16

• plants need water to remain turgid, so cells can push up against each other to hold stem, branches upright
• all reactions take place in aq solution
• plant loses too much water = wilt + die

Question 17

how does light intensity affect rate of transpiration?

Answer 17

• higher LI, faster ROT as light is needed for photosynthesis, so it keep stoma open.
• higher LI = more open stoma = increases rate of water vapour diffusing out
• in dark, stoma close as no light

Question 18

how does humidity affect rate of transpiration?

Answer 18

-humidity is the measure of water vapour in air
- high = low rate of transp, due to a smaller water potential gradient between inside and outside
- dry air = high ROT

Question 19

how does temperature effect the ROT?

Answer 19

• high temp = more kinetic energy of water molecules = more evaporation from spongy mesophyll cells into air spaces of leaves
• high temp = higher conc of water vapor that external air can hold before it becomes saturated so it increases humidity and water potential

Question 20

how does air movement affect ROT?

Answer 20

• hairs on surface of leaf trap air
• lower air movement = water vapour accumulates so water potential increases around stomata, reducing diffusion gradient, so ROT increases

Question 21

how does soil water availability affect ROT?

Answer 21

amount of H2O available in soil affects ROT.
- dry soil = plant under H2O stress, lowers ROT

Question 22

translocation

Answer 22

transport of organic solutes around a plant

Question 23

what is an assimilate?

Answer 23

molecules made my plant itself

Question 24

examples of assimilates

Answer 24

1. sugars
2. a.a
3. proteins
4. plant hormones

Question 25

what is phloem tissue made up of?

Answer 25

• sieve tube elects joined together to make continuous column
• companion cells which help them function

Question 26

what are sieve tube elements?

Answer 26

• narrow and living cells, & lack of usual organelles
• no vacuole, nucleus, ribosomes
• little cytoplasm

Question 27

what is a sieve plate?

Answer 27

• where 2 sieve elements meet
• made from walls of both cells
• lots of large pores
• where end walls used to be

Question 28

what are companion cells?

Answer 28

• typical plant cells
• larger number of mitochondria and ribosomes
• smaller vacuoles

Question 29

what is the plasmodesmata?

Answer 29

channels connecting neighboring plant cells, allows substances to move from one cell to other cell. where substances loaded into sieve tubes

Question 30

why do companion cells have lots of mitochondria?

Answer 30

they have a high respiration rate, lots of ATP used to loads substances into sieve tubes

Question 31

sieve pores

Answer 31

the allow flow of solutes through sieve tubes with little restriction

Question 32

contents of sieve tubes

Answer 32

sap flows inside

Question 33

how does process of translocation work?

Answer 33

movement of sap involves mass flow and it is an active process

Question 34

what is the source?

Answer 34

part of plant that loads organic solutes into phloem

Question 35

sink

Answer 35

part of plant that takes organic solutes out of phloem

Question 36

what is the direction of transport in the phloem?

Answer 36

up OR down

Question 37

mechanism for mass flow of phloem sap

Answer 37

1. sucrose is actively loaded into sieve tube element at source, reducing water potential
2. water enters by osmosis from xylem increasing hydrostatic pressure in sieve tube element
3. water moves down sieve tube from higher HP at source to lower at sink
   (pressure gradient that makes sap move)
4. sucrose is removed from sieve tube at sink and diffuses into surroundings cells with a lower sucrose conc, increasing water potential in sieve tube and decreasing it those cells
5. so water moves out by osmosis and reduces HP in sieve tube

Question 38

describe how each of these features adapts xylem vessels for their function of transporting water from roots to leaves

a. no cell contents
b. no end walls in xylem elements
c. diameter between 0.01mm and 0.2mm
d. lignified walls
e. pits

Answer 38

a. creates a continuous hollow tube so there is no restriction of water flow, making water flow faster

b. no barrier in the way that is restricting water flow through vessel, making water flow faster

c. narrow walls allowed for greater capillary action as there is more contact between water and walls, increasing the attraction

d. provides strength so the vessels don’t burst due to water pressure. waterproof so stops water from leaking out

e. allow water so move sideways into neighboring vessels if there are any blockages or air locks so allows air locks to be avoided