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biolala > Adaptations for transport: Plants > Flashcards

Adaptations for transport: Plants Flashcards

1
Q

write the word equation for photosynthesis

A

carbon dioxide + water to glucose + oxygen

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2
Q

what is different about plants’ transport systems compared to animals?

A

they have two separate transport systems instead of transporting water mineral ions and organic molecules together

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3
Q

how is water and mineral ion transported in plants?

A

photosynthetic cells in the leaf need water and mineral ions which are available only in the soil so the transport of water and mineral ions from the roots to the leaves is essential

these molecules are transported upwards in hollow tubes formed by dead cells called xylem tissue

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4
Q

how are photosynthates transported?

A

glucose produced during photosynthesis is used to make sucrose and amino acids
these molecules must be moved from the leaves to other organs of the plant
photosynthates are transported upwards and downwards in phloem tissue (bi-directional movement)

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5
Q

where is the vascular tissue in the leaf?

A

vascular bundle (xylem and phloem) arranged as a vein or midrib

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6
Q

where is the vascular tissue found in the stem?

A

vascular bundles arranged around the periphery of the stem

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7
Q

where is the vascular tissue found in the root?

A

arranged in the centre of the root and together with the endodermis and pericycle is called the stele. there are no vascular bundles in the root

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8
Q

how are mineral ions like NO3- and water transported to the root?

A

they are actively transported from the soil to the root which lowers the water potential inside the root hair cell so water also enters by osmosis

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9
Q

where is the energy for active transport coming from to aid the transport of mineral ions?

A

oxygen enters the roots from the soil to be used in aerobic respiration, providing ATP for active transport

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10
Q

why do waterlogged soils struggle to uptake ions to roots?

A

they lack oxygen

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11
Q

how does the uptake of water and mineral ions happen across the root?

A

they travel through the root cells of the cortex to the endodermis down a water potential gradient

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12
Q

what are three routes of the transport of water across the root?

A

symplast
apoplast
vacuolar

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13
Q

define the apoplast pathway

A

water is taken up by the root hair cell and moves across the cortex by cohesion via the cell walls

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14
Q

define the symplast pathway

A

water moves from the cytoplasm of one cell to the next by osmosis via plasmodesmata

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15
Q

define the vacuolar pathway

A

water can move via the cytoplasm and vacuoles

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16
Q

describe the route of water and mineral ions into the xylem. there are 6 points

A

the cell walls of all endodermal cells contain a Casparian strip made of a waxy substance called suberin that is impermeable to water molecules and mineral ions, meaning the apoplast pathway is blocked at this point

water and mineral ions from the apoplast pathway are forced across the cell membrane into the symplast pathway

active transport is needed to move ions into the cytoplasm of the endodermal cells

mineral ions then diffuse in the pericycle and then into the xylem

therefore the only way that water and mineral ions can pass through the endodermis to the pericycle and into the xylem is by the symplast pathway

water follows by osmosis down a water potential gradient

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17
Q

why is the Casparian strip beneficial to the plant?

A

it gives the plant greater control over which ions can enter the xylem and are transported to the rest of the plant

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18
Q

how is hydrostatic pressure generated in the root and what effect does it have on water?

A

when water moves from the endodermal cells of the root and into the xylem by osmosis, this generates hydrostatic pressure and forces water a small distance up the xylem

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19
Q

how would cyanide result in a reduction in root pressure? reference the Casparian strip

A

Casparian strip stops apoplast pathway

cyanide is a respiratory inhibitor

movement of ions into the xylem requires active transport

water potential in the xylem is not reduced so there is less root pressure

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20
Q

why does the plant need to control the entry of mineral ions into the xylem?

A

some mineral ions are toxic

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21
Q

how does the plant ensure toxic ions can’t enter the cells?

A

Casparian strip forces ions to cross the membrane into the symplast pathway by active transport and the Casparian strip is very impermeable
also there are no transport proteins in the membrane

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22
Q

why do plants need to absorb nitrates from the soil?

A

required for synthesis of amino acids and nucleotides(DNA, RNA, ATP)
nitrogenous base and proteins

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23
Q

name some other mineral ions absorbed by plants and state their uses

A

potassium ions for opening stomata
magnesium ions for constituent of chlorophyll
PO4 3- or phosphate ions for synthesis of phospholipids and constituent of nucleotides
calcium is a structural component in plant cell walls

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24
Q

give 2 features of root hair cells that are adaptations for uptake and mineral ions

A

large surface area for absorption of water and mineral ions

large numbers of mitochondria to generate ATP for active transport of ions

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25
Q

define transpiration

A

the evaporation of water from inside the leaves through the stomata and into the atmosphere

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26
Q

describe the transpiration stream

A

water is absorbed by the root hair cells by osmosis

water moves through the root tissue into the xylem and is transported up the xylem in the plant stem to the leaf by cohesion

water is transported by osmosis from the xylem in the leaf to the cells of the spongy mesophyll where it evaporates from the surface of the cells into the air spaces

water vapour then diffuses from the air spaces out of the leaf through the stomata down a water potential gradient

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27
Q

define cohesion

A

water molecules are attracted to each other by hydrogen bonds

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28
Q

define adhesion

A

water molecules are attracted to the hydrophilic lining of the lignified xylem vessel walls

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29
Q

how does water travel up the xylem to the leaves of the plant using cohesion tension theory? (transpiration pull)

A

as water vapour diffuses out of the stomata of the leaf by transpiration, water molecules are drawn up from behind to replace those lost

water molecules are drawn across the leaf and up the xylem and this is possible because of cohesion between water molecules due to hydrogen bonds and adhesion between water molecules and the xylem vessel walls
this upward movement of water creates tension on the xylem vessel walls

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30
Q

what are two other processes that help water move up the xylem a small amount?

A

capillarity - the forces of adhesion and cohesion allow water molecules to rise up the narrow tubes for a short distance which is useful in small plants

root pressure

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31
Q

why is capillarity not useful in large trees?

A

it’s useful for small plants and not in larger plants because after a short distance capillary action is opposed by gravity

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32
Q

what increases the rate of respiration?

A

any factor that increases the water potential gradient between the water vapour in the leaf and surrounding atmosphere

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33
Q

what are four factors the rate of transpiration is increased by?

A

temperature
wind speed
humidity
light intensity

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34
Q

explain each of the 4 factors that increase rate of transpiration

A

temperature -
rise in temperature increases the kinetic energy of the water molecules and increases the rate of evaporation and diffusion of the water vapour into the atmosphere
water potential is also lower in high temperatures which increases the water potential gradient

wind speed -
still air results in a layer of water vapour around the stomata of a leaf
this reduces the water potential gradient between the outside and inside of the leaf
air movement blows away the diffusion shell and increases the rate of transpiration from the leaf

humidity -
water potential gradient inside and out of the leaf decreases when there is more water vapour in the atmosphere
usually, there is a steep water potential gradient between the inside of the leaf and the atmosphere as the leaf is saturated with water vapour

light intensity -
light causes stomata to open to allow gas exchange for photosynthesis

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35
Q

what is a potometer?

A

this apparatus measures the rate of uptake of water by the shoot which indicates the rate of transpiration

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36
Q

give the labels for the set up of the potometer

A

beaker with water
air bubble in capillary tube
graduated scale in mm along the capillary tube
tap
reservoir of water
bung
plant cutting/leafy shoot

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37
Q

why is the rate of uptake only an estimate of the transpiration rate?

A

some water is used by the plant as a reactant in photosynthesis

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38
Q

give six steps on how to set up the potometer

A

cut a leafy shoot underwater to prevent the entry of air bubbles into the xylem vessels as these would break hydrogen bonds affecting cohesion

completely fill the apparatus with water to avoid introducing air bubbles into the glassware

fit leafy shoot and seal all joints with Vaseline so apparatus is airtight

pat the leaves dry otherwise the water potential gradient will be reduced and this could affect the results

introduce one air bubble into the capillary tube (open the tap)

measure the distance the air bubble moves along the scale in a specific time

39
Q

how can you calculate the volume of water taken up from the capillary tube per minute?

A

pi x radius ^2 x height
h = distance moved by bubble
r^2 = internal radius of capillary tube

40
Q

how could you improve the reliability of the data collected in the potometer experiment?

A

repeat 3x to allow calculation of a mean

41
Q

what can you calculate from potometer data after working out the mean?

A

standard deviation

42
Q

what is standard deviation?

A

a measure of the spread of a set of data
it is an indication of the amount of variation or dispersion in the data set

43
Q

what does a low standard deviation indicate and what does a high standard deviation indicate?

A

low -
the values are close to the mean so therefore are more consistent and more reliable
‘thin’ curve
high -
data values are further from the mean so spread out over a wider range, meaning they are less consistent and less reliable
‘fat’ curve

44
Q

what is the formula of standard deviation? what does each symbol mean?

A

https://www.savemyexams.com/a-level/biology/ocr/17/revision-notes/4-biodiversity-evolution–disease/4-3-classification–evolution/4-3-8-standard-deviation/

45
Q

how do you calculate standard deviation? give 6 steps

A

1 - calculate mean for the data set
2 - subtract the mean from each value
3 - square each answer
4 - add up all the squares
5 - divide this total by the number of pieces of data minus 1
6 - find the square root of that value

46
Q

what are the 4 different types of cell that a xylem is composed of?

A

vessels
tracheids
fibres
xylem parenchyma

47
Q

what is the role of vessels in the xylem tissue?

A

the main cells that conduct water

48
Q

what are the vessels in the xylem tissue made up of?

A

continuous column of dead cells arranged end to end with completely dissolved cross/end-walls to form long, hollow tubes that transport water from roots to leaves

their walls are thickened with lignin which is impermeable to water and strengthens and supports the plants so the vessel doesn’t collapse under pressure

49
Q

what is the function of tracheids in xylem tissue?

A

they also conduct water but are less efficient than vessels

50
Q

what are tracheids made of in the xylem tissue?

A

they are similar to vessels but are more elongated with tapering ends
cell walls are also thickened and impregnated with lignin

51
Q

how are the pits efficient in tracheids and vessels in xylem tissue?

A

they both have pits in their side walls
in vessels they allow movement of water between adjacent vessels
in tracheids they are involved in movement of water to nearby living tissue

52
Q

what is the role of fibres in the xylem tissue?

A

no role in transport and is only there for support only

53
Q

what is the role of xylem parenchyma in xylem tissue?

A

they are living cells and are packing tissue

54
Q

why is it important that vessel walls are impermeable to water and solutes?

A

so that xylem is not leaky and water keeps moving upwards to the leaves in one unbroken column

55
Q

why is lignin being hydrophilic important to xylem function?

A

water molecules are attracted to the walls of the xylem vessels supporting adhesion
it also strengthens and supports the plant

56
Q

what does phloem transport?

A

amino acids and sucrose

57
Q

what 4 types of cell is phloem tissue made of?

A

sieve tubes
companion cells
phloem fibres
phloem parenchyma

58
Q

what is the function of sieve tubes in the phloem tissue?

A

transport sucrose and amino acids up/down plant stem
they have few organelles, creating more space for transport of solutes

59
Q

what are sieve tubes made of in the phloem tissue?

A

they are formed from cells called sieve elements placed end to end
the thin cellulose wall at the ends of these cells is perforated to form sieve plates that allow the cytoplasm from one cell to run into an adjacent cell and allow passage of dissolved solutes

60
Q

what is the role of companion cells in the phloem tissue? why are they important?

A

they are connected to sieve tubes via plasmodesmata
they don’t transport organic compounds but they have a nucleus and provide ATP for the active transport of sugars into/out of the sieve tubes
this is important since sieve tubes cells lose their nucleus and other organelles as they mature

61
Q

what is the role of phloem fibres in phloem tissue?

A

for support

62
Q

what is the role of phloem parenchyma in phloem tissue?

A

they are living tissue

63
Q

what runs through the sieve plates in phloem tissue?

A

phloem protein or filaments in the cytoplasm run through the sieve plates
smaller strands of cytoplasm run through the side walls of sieve tube cells into adjacent companion cells through the plasmodesmata

64
Q

define translocation

A

the transport of soluble organic materials produced by photosynthesis in the phloem

65
Q

what is the liquid inside the phloem called?

A

sap

66
Q

what is the movement of molecules called in phloem?

A

bi-directional

67
Q

what is the source in a plant?

A

the region where the products of photosynthesis is produced and exported

68
Q

what is the sink in a plant?

A

the region where products of photosynthesis are stored or used for growth

69
Q

give an example of a source

A

leaf

70
Q

give examples of sinks

A

root, shoot tips, flowers, fruit, seeds

71
Q

describe the ‘ringing experiment’ used to provide evidence for translocation in phloem

A

you remove a ring of outer bark tissue from a woody stem to remove the phloem

analysis of the phloem contents just above and below the ring shows that organic compounds cannot be transported past the region where the bark has been removed

a bulge can be seen due to accumulated phloem sap that can’t move down any further

72
Q

what does the ‘ringing experiment’ show?

A

phloem is around on the outside just under the bark

transport of organic compounds can be downwards

73
Q

describe the aphid experiment to provide evidence for translocation in the phloem and explain why it’s more accurate than a human using a syringe

A

aphids are small insects that can be used to collect the contents of individual phloem sieve tube cells

aphids have specialised mouthparts called stylets which are used to penetrate sieve tubes to feed on the sugary sap inside

if aphids are anaesthetised with co2 the stylet can be cut off and left in the stem which means the pure phloem sap can be collected through the stylet for analysis

this technique is more accurate than a human with a syringe/needle as the aphid’s enzymes ensure that the stylet doesn’t get blocked

74
Q

describe radioisotope labelling used to provide evidence for translocation in phloem

A

a plant is supplied with radioactive 14co2

the radioactive 14co2 will be supplied to one leaf of the plant

after 20 minutes the whole plant is placed on photographic film and dark areas on the film show areas containing radioactivity

the result of this experiment shows that radioactive carbon is fixed into the sugar at the source and then translocated to sink parts of the plant (shown as dark regions) and shows that sugar is transported bidirectionally since the radioactivity is seen in the aerial parts of the plant as well as the roots

75
Q

which parts of the plant contain the most radioactivity and explain your answer using source and sink?

A

leaf A which is the source, roots, shoot tips, young leaves

sucrose is produced at the source and is transported to sink regions that cannot photosynthesis or are actively growing

76
Q

what is the mass flow hypothesis?

A

it is the main theory to explain translocation

sugars flow passively from areas of high concentration in the leaf (source) to areas of low concentration (sinks like growing tissue) down a pressure gradient

77
Q

how does the mass flow theory work?

A

sucrose made in photosynthesis is loaded by active transport into the sieve tubes, using ATP

water enters the sieve tubes along a water potential gradient by osmosis

the pressure in the sieve tubes increases and the sucrose moved down a pressure gradient through the phloem towards the sinks

sucrose is unloaded by active transport into the cells at the sinks

water moves by osmosis out of the phloem as the sucrose is removed and the pressure in the phloem tissue becomes lower at the sink

78
Q

what does the mass flow theory not explain?

A

the observations that sucrose is transported in sieve tubes at a rate of 25 - 100 cm per hour even though diffusion alone would give a transport rate of 0.2mm per day

79
Q

what are the arguments against the mass flow theory?

A

no explanation of sieve plates which seem to act as barriers to flow

sucrose and amino acids have been observed moving a different rates and in different directions

sieve tubes have a high rate of ATP consumption, and translocation is slowed or stopped if respiratory inhibitors such as cyanide are added

the companion cells are found all along the sieve tubes not just in the sources and sinks and contain numerous mitochondria for the production of ATP so if companion cells purely load and unload photosynthates from the sieve tubes they would not be needed anywhere but the sources and sinks

therefore there must be an active process within the sieve tubes that maybe involved

80
Q

what are some alternative theories to the mass flow theory?

A

streaming in the cytoplasm of sieve tubes could be responsible for bi-directional movements

protein filaments have been observed passing through the sieve pores suggesting different solutes are transported by different filaments

81
Q

what are mesophytes?

A

most of the plants in temperate regions and most crop plants are mesophytes

82
Q

what do mesophytes grow best in?

A

well-drained soils and moderately dry air

83
Q

what are three plant behaviours that allow mesophytes to survive at unfavourable times of the year?

A

deciduous trees shed leaves in autumn to survive unfavourable conditions in winter and new leaves grow in spring

bulbs and corms, which are storage organs, are produced by non-woody plants to survive underground over winter

annual plants produce seeds and die in the same year as seeds survive winter frost and germinate the next spring when conditions are more favourable

84
Q

what are hydrophytes?

A

water plants that live submerged/partially submerged in water

85
Q

give 5 features of a hydrophyte and their explanations

A

stomata on the upper epidermis -
to allow gas exchange with the air above

large air spaces -
to provide buoyancy for the leaves and act as a reservoir of oxygen and co2

thin waxy cuticle -
no need to reduce water loss as they live on/in water

xylem tissues poorly developed -
no need to transport large quantities of water as plant is aquatic

little lignin in plant tissue -
water is a supportive medium and so little lignin is required to support the xylem tissue

86
Q

what are xerophytes?

A

these plants are adapted to conditions of low water availability and live in hot desert conditions/cold regions where soil is frozen/exposed windy locations

87
Q

what is an example of a xerophyte?

A

marram grass

88
Q

give 5 features of marram grass and their explanations

A

sunken stomata in pits -
water vapour trapped in the pits decreases the water potential gradient between the inside and outside of the leaf so less water is lost by transpiration

hairs on leaf surface -
water vapour trapped between the hairs decreases the water potential gradient between inside and outside of the leaf so less water is lost by transpiration

thick waxy cuticle -
reduces water loss from the epidermis

rolled leaves -
stomata less exposed to the atmosphere
water vapour trapped decreases the water potential gradient between inside and outside of the leaf so less water is lost by transpiration

reduced leaf size/spines -
reduces the surface area from which transpiration can occur

89
Q

describe the xerophytic adaptations of cacti

A

store water in succulent stems

leaves are reduced to spines to reduce surface area for transpiration

thick waxy cuticle

shallow spreading roots/long deep roots to maximise water absorption from soil

90
Q

why do pine trees have needle-like leaves?

A

to greatly reduce surface area of leaf available for water loss by transpiration

91
Q

why do many xerophytes open stomata at night and close them during the day?

A

to conserve water

92
Q

label the different structures present in a root

A

stele, phloem, xylem, endodermis, pericycle, cortex, epidermic, root hair

93
Q

label the different structures present in a stem

A

phloem, xylem, vascular cambium which is the border between the xylem and phloem, pith, cortex

94
Q

label the different structures present in a leaf

A

waxy cuticle
upper epidermis
palisade mesophyll
spongy mesophyll
vein-like vascular bundle containing xylem and phloem
lower epidermis
stomata and guard cells

biolala (17 decks)

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