Adaptations for transport: Plants C3

Question 1

write the word equation for photosynthesis

Answer 1

carbon dioxide + water to glucose + oxygen

Question 2

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

Answer 2

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

Question 3

how is water and mineral ion transported in plants?

Answer 3

photosynthetic cells in leaf need water and mineral ions which are available only in soil

so transport of water and mineral ions from roots to leaves is essential

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

Question 4

how are photosynthates transported?

Answer 4

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)

Question 5

where is the vascular tissue in the leaf?

Answer 5

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

Question 6

where is the vascular tissue found in the stem?

Answer 6

vascular bundles arranged around the periphery of the stem

Question 7

where is the vascular tissue found in the root?

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

why do waterlogged soils struggle to uptake ions to roots?

Answer 10

they lack oxygen

Question 11

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

Answer 11

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

Question 12

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

Answer 12

symplast
apoplast
vacuolar

Question 13

define the apoplast pathway

Answer 13

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

Question 14

define the symplast pathway

Answer 14

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

Question 15

define the vacuolar pathway

Answer 15

water can move via the cytoplasm and vacuoles

Question 16

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

Answer 16

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

Question 17

why is the Casparian strip beneficial to the plant?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

cyanide is a respiratory inhibitor

Casparian strip stops apoplast pathway

movement of ions into the xylem requires active transport

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

Question 20

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

Answer 20

some mineral ions are toxic

Question 21

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

Answer 21

Casparian strip forces ions to cross membrane into symplast pathway by active transport

Casparian strip is very impermeable

there are no transport proteins in membrane

Question 22

why do plants need to absorb nitrates from the soil?

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

large SA for absorption of water and mineral ions

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

Question 25

define transpiration

Answer 25

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

Question 26

describe the transpiration stream

Answer 26

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

Question 27

define cohesion

Answer 27

water molecules attracted to each other by hydrogen bonds

Question 28

define adhesion

Answer 28

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

Question 29

how does water travel up the xylem to the leaves of the plant using cohesion tension theory? (transpiration pull) (give 4 points)

Answer 29

as water vapour diffuses out of stomata by transpiration, water molecules are drawn up from behind to replace those lost water molecules are drawn across leaf and up xylem this is possible because of cohesion between water molecules due to hydrogen bonds and adhesion between water molecules and xylem vessel walls this upward movement of water creates tension on xylem vessel walls

Question 30

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

Answer 30

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

Question 31

why is capillarity not useful in large trees?

Answer 31

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

Question 32

what increases the rate of respiration in a plant?

Answer 32

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

Question 33

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

Answer 33

temperature wind speed humidity light intensity

Question 34

explain each of the 4 factors that increase rate of transpiration

Answer 34

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

Question 35

what is a potometer?

Answer 35

measures rate of uptake of water by shoot which indicates rate of transpiration

Question 36

give the labels for the set up of the potometer

Answer 36

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

Question 37

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

Answer 37

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

Question 38

give six steps on how to set up the potometer

Answer 38

cut leafy shoot underwater to prevent entry of air bubbles into xylem vessels as these would break hydrogen bonds affecting cohesion completely fill apparatus with water to avoid introducing air bubbles into glassware fit leafy shoot and seal all joints with Vaseline so apparatus is airtight pat leaves dry otherwise water potential gradient will be reduced and could affect results introduce one air bubble into capillary tube (open the tap) measure distance air bubble moves along scale in a specific time

Question 39

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

Answer 39

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

Question 40

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

Answer 40

repeat 3x to allow calculation of a mean

Question 41

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

Answer 41

standard deviation

Question 42

what is standard deviation?

Answer 42

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

Question 43

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

Answer 43

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

Question 44

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

Answer 44

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

Question 45

how do you calculate standard deviation? give 6 steps

Answer 45

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

Question 46

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

Answer 46

vessels tracheids fibres xylem parenchyma

Question 47

what is the role of vessels in the xylem tissue?

Answer 47

the main cells that conduct water

Question 48

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

Answer 48

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

Question 49

what is the function of tracheids in xylem tissue?

Answer 49

they also conduct water but are less efficient than vessels

Question 50

what are tracheids made of in the xylem tissue?

Answer 50

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

Question 51

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

Answer 51

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

Question 52

what is the role of fibres in the xylem tissue?

Answer 52

no role in transport and is only there for support only

Question 53

what is the role of xylem parenchyma in xylem tissue?

Answer 53

they are living cells and are packing tissue

Question 54

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

Answer 54

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

Question 55

why is lignin being hydrophilic important to xylem function?

Answer 55

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

Question 56

what does phloem transport?

Answer 56

amino acids and sucrose

Question 57

what 4 types of cell is phloem tissue made of?

Answer 57

sieve tubes companion cells phloem fibres phloem parenchyma

Question 58

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

Answer 58

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

Question 59

what are sieve tubes made of in the phloem tissue?

Answer 59

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

Question 60

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

Answer 60

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

Question 61

what is the role of phloem fibres in phloem tissue?

Answer 61

for support

Question 62

what is the role of phloem parenchyma in phloem tissue?

Answer 62

they are living tissue

Question 63

what runs through the sieve plates in phloem tissue?

Answer 63

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

Question 64

define translocation

Answer 64

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

Question 65

what is the liquid inside the phloem called?

Answer 65

sap

Question 66

what is the movement of molecules called in phloem?

Answer 66

bi-directional

Question 67

what is the source in a plant?

Answer 67

the region where the products of photosynthesis is produced and exported

Question 68

what is the sink in a plant?

Answer 68

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

Question 69

give an example of a source

Answer 69

leaf

Question 70

give examples of sinks

Answer 70

root, shoot tips, flowers, fruit, seeds

Question 71

describe the 'ringing experiment' in three points used to provide evidence for translocation in phloem

Answer 71

remove a ring of outer bark tissue from woody stem to remove phloem analysis of phloem contents above and below ring shows organic compounds can't be transported past removed bark region buldging due to accumulated phloem sap that can't move down further

Question 72

what 2 things does the 'ringing experiment' show?

Answer 72

phloem is around on outside just under bark transport of organic compounds can be downwards

Question 73

describe the aphid experiment to provide evidence for translocation in the phloem in 4 points and explain why it's more accurate than a human using a syringe

Answer 73

aphids can be used to collect contents of individual phloem sieve tube cells have specialised mouthparts called stylets which are used to penetrate sieve tubes to feed on sugary sap inside if anaesthetised with co2, stylet can be cut off and left in stem which means pure phloem sap collected through stylet for analysis more accurate than human with a syringe as aphid's enzymes ensure that stylet doesn't get blocked

Question 74

describe radioisotope labelling used to provide evidence for translocation in phloem in 4 points

Answer 74

one leaf of a plant is supplied with radioactive 14co2 after 20 minutes, plant placed on photographic film and dark areas on film show areas containing radioactivity results show that radioactive carbon is fixed into sugar at source and then translocated to sink parts of plant (shown as dark regions) shows sugar is transported bidirectionally since radioactivity seen in aerial parts of plant as well as roots

Question 75

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

Answer 75

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

Question 76

what is the mass flow hypothesis?

Answer 76

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

Question 77

how does the mass flow theory work?

Answer 77

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

Question 78

what does the mass flow theory not explain?

Answer 78

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

Question 79

what are the arguments against the mass flow theory?

Answer 79

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

Question 80

what are some alternative theories to the mass flow theory?

Answer 80

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

Question 81

what are mesophytes?

Answer 81

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

Question 82

what do mesophytes grow best in?

Answer 82

well-drained soils and moderately dry air

Question 83

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

Answer 83

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

Question 84

what are hydrophytes?

Answer 84

water plants that live submerged/partially submerged in water

Question 85

give 5 features of a hydrophyte and their explanations

Answer 85

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

Question 86

what are xerophytes?

Answer 86

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

Question 87

what is an example of a xerophyte?

Answer 87

marram grass

Question 88

give 5 features of marram grass and their explanations

Answer 88

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

Question 89

describe the xerophytic adaptations of cacti

Answer 89

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

Question 90

why do pine trees have needle-like leaves?

Answer 90

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

Question 91

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

Answer 91

to conserve water

Question 92

label the different structures present in a root

Answer 92

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

Question 93

label the different structures present in a stem

Answer 93

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

Question 94

label the different structures present in a leaf

Answer 94

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