Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biology A level > 3.4 Gas exchange and mass transport in plants > Flashcards

3.4 Gas exchange and mass transport in plants Flashcards

1
Q

What tissues make up a leaf?

A

epidermal tissue
spongy mesophyll tissue
xylem and phloem tissues
palisade mesophyll tissue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What adaptions do leaves have to maximise photosynthesis?

A

epidermal tissue covers the whole leaf - prevents water leaving
upper epidermis is transparent for light
the palisade layer is near the top of the leaf to get the most light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the purpose of the vascular bundle in the leaf?

A

provides suppport for the leaf

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does the xylem do?

A

transports water and other nutrients from the roots to the leaves - transpiration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does the phloem do?

A

transports the sucrose made during photosynthesis away from the leaves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the purpose of the air spaces in the spongy mesophyll?

A

increases the diffusion of gases through the leaf

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What happens to O2 in the leaf when it is dark?

A

it diffuses into the leaf because it is used for resp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the purpose of the upper epidermis?

A

transparent to allow light to pass through and protects against mechanical damage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the purpose of the lower epidermis?

A

protects leaf tissue from mechanical damage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the purpose of the waxy cuticle?

A

waterproof (impermeable to water) - prevents water leaving by evapouration, reducing water loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the purpose of the palisade mesophyll?

A

main site of photosynthesis - has the highest density of chloroplasts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the purpose of the spongy mesophyll layer?

A

site of gas exchange - contains vascular bundle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the purpose of the guard cells?

A

they open and close the stomata

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the purpose of the stomata?

A

allows entry and exit of gases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Is CO2 moving into or out of the plant?

A

into the plant for photosynthesis, it is exchanged with the environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why is there a net movement of O2 out of the plant?

A

the rate of photosynthesis is greater than the rate of resp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are xerophytes?

A

plants that are adapted to environments where water supply is short

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the two examples of xerophytes?

A

marram grass and cacti

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How are cacti adapted to their environment?

A

spines - reduces SA for stomata = fewer stomata —> lower rate of transpiration
thick - storing water, suuculent stem
folded - allows it to expand and contract = maximises storage of water
small SA:VOL = round
long and shallow root system - close to the surface, catches precipitation of rain after it falls = increases uptake of water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How is tension created in the plant?

A

by transpiration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is cohesion?

A

bonding (attraction) between the same molecules - water bonds to itself

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is adhesion?

A

attraction/bonding between different molecules = water and lignin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Why are the water molecules adhesive to the lignin plant wall?

A

there is a hydrophyllic lining on the walls

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is transpiration?

A

the loss of water vapour from the stomata by evapouration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What factors affect transpiration?

A

light intensity
temp
humidity
wind

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the cohesion-tension theory?

A

how water moves against gravity up the plant, a combination of cohesion and adhesion of water molecules and root pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How are water molecules cohesive?

A

water is dipolar - H bonds can form between water molecules so they stick together and travel up the xylem

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

How is root pressue created in the plant?

A

as water moves into the roots by osmosis it increases the volume of liquid inside the root = pressure inside the root increases
forces water above it upwards

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

How is water moved up the xylem (method)?

A
  1. water evapourates out the stomata on leaves. This loss in water volume creates a lower pressure
  2. water is lost by transpiration, more water is pulled up the xylem to replace it and it and moves due to negative pressure
  3. due to H bonds between water molecules, they are cohesive - creates a transpiration stream
  4. water molecules also adhere to the walls of the xylem - helps pull the continuous column of water up
  5. as this collumn of water is pulled up the xylem it creates tension, pulling the xylem in to become narrower
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is the purpose of packing cells?

A

to fill space so that all cells touch each other for diffusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What does desicating mean?

A

drying out

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What are features of a TS stem?

A

epidermis
cortex
phloem
vascular cambium
xylem
pith

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What are features of a root?

A

phloem
epidermis
exodermis
pericycle
endodermis
xylem
vascular cambium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Which features of a stem and root are parenchyma cells?

A

cortex
pith

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What are parenchyma cells?

A

packing cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Why is the vascular bundle in the middle of the root?

A

for support as it is subject to the pull of gravity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What is the structure and function of the xylem vessel element?

A

Structure:
lignified = lignin patterns in young xylem
non-living
stacked end to end
end walls desintgrate to form hollow tubes

function - transports water and mineral ions

38
Q

What is the structure and function of the xylem tracheid?

A

structure:
lignified
non-living
has vessel elements but has tappered end wall

function - transport water and mineral ions

39
Q

What is the structure and function of xylem fibres?

A

lignified
non-living

function - mechanical support for tissue

40
Q

What is the structure and function of parenchyma cells in the xylem?

A

not lignified - cellulose in cell wall
living

function - packing cells

41
Q

How does light intensity affect transpiration rate?

A

increased light intensity –> increased rate of transpiration
it stiumulates stomatal opening
more stomata open = more water diffuses out as there is a higher SA for diffusion

42
Q

How does temperature affect rate of transpiration?

A

increased temp = increased transpiration rate
increased temp increases evapouration of water out of mesophyll cells into air spaces
air spaces are saturated with water = steeper diff grad

43
Q

How does humidity affect the rate of transpiration?

A

increased humidity = decreased transpiration rate
as water vapour leaves the plant, the leaves are still saturated from the air so reduces the diff grad

44
Q

How does air movement affect transpiration rate?

A

increased air movement = increased transpiration rate
removes humid air from the leaf’s surface - increases diffusion grad

45
Q

What is capillary action of water moving up the stem?

A

the ability of liquid to move through a narrow space against gravity
occurs due to intermolecular forces between h2o molecules and external forces
can move 1m max up the xylem

46
Q

What is the root pressure theory for movement of water up the stem?

A

ions pumped into root tissue - water potential grad formed between root and soil
more water moves into the roots = increase in hydrostatic pressure
max root pressure - 0.5KPa = not enough for big trees

47
Q

What ions are taken up by a plant and why?

A

Mg 2+ = main component of chlorophyll
K+ = synthesise proteins
PO4 3- = for membranes

48
Q

What is evidence for active transport in plants?

A

ion conc in root tissue is greater than in the soil - against the conc grad
resp inhibited added to root reduces uptake - reduces ATP

49
Q

What is the cytoplasmic route of water evapouration ?

A

water is lost from the mesophyll cells by evap. from their cell walls to the air spaces of the leaf. This is replaced by water from the xylem via the cells walls and cytoplasm

50
Q

How does the cytoplasmic route of water evapouration occurs?

A

mesophyll cells lost water to the air spaces by evpouration due to heat from the sun
cells have a lower water potential - water enters by osmosis from neighbouring cells
neighbouring cells have a lower water potential
take in turns of water by osmosis

51
Q

what environments do xerophytes live in?

A

high rain fall but high temps so rain is quickly evapourated
or coastal areas = salty soil has lower water potential of the soil solution reducing the water potential between the soil and the root hair cells - slows osmosis

52
Q

What are all the xerophytic adaptions?

A

thick waxy cuticle
leaf curling
hairs on leaves
sunken stomata
reduced leaves
fewer stomata

53
Q

How does a thick waxy cuticle prevent transpiration?

A

forms a waterproof barrier - impermeable to water

54
Q

How does leaf curling prevent transpiration?

A

protects the lower epidermis from the outside
helps to trap a region of air so the leaf can become saturated with water vapour - reducing the water potential between leaf and air

55
Q

How does hairs on the leaf prevent transpiration?

A

traps moist air next to the leaf’s surface, reduces the water potential between air and leaf- keeps air around stomata humid

56
Q

How does sunken stomata prevent transpiration?

A

sheltered from the air movements and traps moist air next to the leaf , reduced water potential grad between leaf and air

57
Q

What are the features of a xylem tissue? (TS)

A

tracheid
parenchyma cells
fibre
lignified wall

58
Q

What are features of xylem tissue? (LS)

A

lignin rings
remains of end wall
perforated end walls

59
Q

What is a tracheid?

A

a long and tapered lignified cell in the xylem

60
Q

What is the role of the phloem?

A

transports the products of photosynthesis - sucrose and amino acids, from source to sink

61
Q

What are examples of storage organs of plants?

A

bulbs and tubers

62
Q

Describe the phloem structure.

A

living tissue - no lignin
stacked end to end

63
Q

what does it mean that translocation is bidirectional?

A

the movement of sucrose and amino acids can be upwards or downwards depending where the source and sink are located

64
Q

Why do tubers become sources in winter?

A

flowers and leaves have dropped off
they have all the sucrose stored for growth

65
Q

What are the 3 mecahnisms for translocation?

A

diffusion
cytoplasmic streaming
Munch’s mass flow hypothesis

66
Q

Why isn’t translocation done simply by diffusion alone?

A

diffusion alone is too slow for the rates of translocation found

67
Q

What is cytoplasmic streaming?

A

directed flow of the liquid component of the cytoplasm

68
Q

What is a summary of Munch’s mass flow hypothesis?

A

passive flow of sucrose - sap moves down a hydrostatic press grad

69
Q

What is hydrostatic pressure?

A

liquid pushing against its container

70
Q

Why will there always be a constant flow of sucrose?

A

photosynthesis and resp - no equilibrium is reached

71
Q

What are the criticisms of Munch’s mass flow hypothesis?

A

sucrose and amino acids transported at different rates in the same tissue
sucrose and amino acids translocate in different directions at the same time in the same tissue
it is not passive - companion cells have lots of mitochondira = supports sieve tube with ATP , high O2 consumption in phloem - high rate of resp
resp inhibitor added = rate of translocation decreased

72
Q

What is the process of munch’s mass flow hypothesis?

A
  1. sucrose is actively transported into the phloem from the companion cells
  2. water moves into the phloem by osmosis from the xylem
    build up of hydrostatic pressure in the phloem
  3. mass flow of sap down a hydrostatic pressure grad
  4. sucrose is actively unloaded into the sink cells where it is used up
  5. water is taken up by osmosis in the root hair cells and mineral ions are taken up by ACT. in the xylem = lowers water potential in xylem
  6. water moves back into xylem from the phloem by osmosis
  7. water moves up the xylem by cohesion-tension theory
73
Q

What is the process of sucrose entering the phloem?

A
  1. H+ ions are actively pumped out of the companion cell into the source tissue
    accumulation of H+ ions outside of the companion cell - grad of H+ ions to passively move back into the companion cell
  2. passive diff of H+ into companion cell also takes sucrose into companion cell by a symport co-transport protein
    indirect active transport of sucrose going down H+ grad
  3. build up of sucrose in companion cell higher than the seive tube element
  4. passive movement of sucrose by facili. diff into the seive tube element

The whole process is active because of the ATP used initally in step 1

74
Q

Describe the sieve tube element structure.

A

living cells
no nucleus
contains few organelles
end walls are perferated for continuous mass flow of sap
forms a hollow tube for max mass flow

75
Q

What is the role of companion cells?

A

provides ATP required for ACT of organic substances

76
Q

what is a source?

A

where the organic substances are produced

77
Q

What is a sink?

A

where the organic substances are used up

78
Q

How are tracers used to investigate translocation?

A

uses radioactive CO2 which is visible on x-ray
photosyn –> glucose –> sucrose which is transported
you are able to see where the sucrose is transported due to the radioactive C
measure rate of translocation

79
Q

What is the method of using tracers for investigating translocation?

A
  1. expose 1 leaf to radioactive CO2 (14CO2)
  2. 14CO2 is taken up by photosyn
  3. after varying exposing times, put the plant in liquid nitrogen so it dies and all the reactions stop so the molecules are fixed in place
  4. x-ray plant to produce autoradiograph which shows the location of any compounds containing 14C
80
Q

How is ringing used to investigate translocation?

A

remove a ring of stem/stalk which removes the phloem but the xylem remains
bulging above removed section = shows sap moves downwards as phloem is removed
underneath doesnt bulge = growth has not occured as there was no resp, no sap for resp

81
Q

How are aphids used to investigate translocation?

A

they feed on sap by their stylets
place aphids on different parts of the stem
stylet is cut off and left in phloem
gather the sap from stylet and test for sucrose conc
collect sap from different points of the stem

82
Q

What is the aphids stylet?

A

specialised mouth part to pierce stem to access the phloem to drink sap

83
Q

Why can’t you insert a needle in the phloem to get sap sample?

A

the sap would get stuck - aphids have enzymes that prevent this in their stylet

84
Q

What are the features of phloem tissue? (TS)

A

companion cell
cell wall
cell membrane
cytoplasm
vacuole
nucleus
sieve tube cell

85
Q

What are sieve tube cells?

A

elongated cells stacked to form a series of tubes

86
Q

Why are sieve plates perferated?

A

allows cytoplasmic connections = connects one cell to another

87
Q

describe the structure of a companion cell

A

adjacent to sieve tube elements
large nucleus
lots of organelles
permeable - has plasmadesmata

88
Q

How do you calculate the rate of water uptake?

A

rate of watee uptake (mm3S-1)=
speed of air bubble movement (mms-1) x cross-sec area of capillary tube (mm2)

89
Q

How does the potometer expt work to estimate transpiration rate?

A

as water is transpired, the shoot absorbs water from the potometer, the air bubble moves along the capillary tube

90
Q

How is the equipment of the potometer set up?

A

shoot is cut from plant underwater
do not want any air in the system so everything is done underwater however the leaves need to be dry - water can block pores preventing transpiration

91
Q

Why is petrolium jelly used in the potometer expt?

A

blocks joints in apparatus - makes them air tight

92
Q

What 3 measurements are taken in the potometer expt?

A

distance travelled by air bubble (mm)
time it takes bubble to travel (secs)
diameter of capillary tube (mm)

Biology A level (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions