3.1.3 transport in plants

Question 1

what does autotrophic mean
3.1.3(a)

Answer 1

they produce their own food
eg-they use photosynthesis to make glucose

Question 2

how do plants transport water and mineral ions
3.1.3(a)

Answer 2

they transport water and mineral ions from roots to all other parts of the plant for tugidity

Question 3

how to plants transport assimilates
3.1.3(a)

Answer 3

they transport assimilates from sources to sinks

Question 4

why don’t plants need to transport oxygen and carbon dioxide
3.1.3(a)

Answer 4

as they hvae a lower metabolic rate than animals (but still high)
so dont need to rapidly transport oxygen and carbon dioxide
it simply diffuses from the air to the inside of the leaf
-need transport systems to meet the high metabolic rate

Question 5

why do plants need transport systems
3.1.3(a)

Answer 5

they have a small SA:V ratio
large diffusion distance
need to transport water and mineral ions from roots to all parts of the plant

Question 6

what is the cambium
3.1.3(b)

Answer 6

thin layer between xylem and phloem
not always shown in diagrams

Question 7

where does the xylem point in leaves
3.1.3(b)

Answer 7

in leaves, the xylem in each vascular bundle points to the upper surface of the leaf

TIP-L for layer + leaf so upper surface of the ;eave

Question 8

where does the xylem point in stems
3.1.3(b)

Answer 8

in stems, the xylem in each vascular bundle points inward to the middle of the stem.

Question 9

what does the xylem form in roots
3.1.3(b)

Answer 9

in roots, the xylem forms an X shape in the middle of the vascular bundle.

“oo” middle

Question 10

what 4 cell types does xylem tissue consist of and are they dead or living
3.1.3(b)

Answer 10

xylem vessles (dead)
xylem tracheids (dead)
xylem fibres (dead)
xylem parenchyma (living)

Question 11

what is the function of xylem vesslels
3.1.3(b)

Answer 11

-dead
-carry water and mineral ions from roots to all parts of the plant

Question 12

what is the function of xylem tracheids
3.1.3(b)

Answer 12

-dead
-which also carry water and mineral ions but are slightly narrower than vessels

Question 13

what is the function of xylem fibres
3.1.3(b)

Answer 13

-dead
-which provide support, elasticity and tensile strength to the plant

Question 14

what is the function of xylem parenchyma
3.1.3(b)

Answer 14

-living
-which act as “packing” tissue to support the vessels

Question 15

how does the xylem vessels being dead help support its function
3.1.3(b)

Answer 15

-Xylem vessels are dead and do not contain any cytoplasm. This minimises their resistance to the flow of water

Question 16

what waterproof organic polymer do xylem vessels contain
3.1.3(b)

Answer 16

lignin

Question 17

what is the function of lignin
3.1.3(b)

Answer 17

Lignin prevents water loss and also prevents the vessel from collapsing.

Question 18

how does lignin allow flexibility
3.1.3(b)

Answer 18

lignin is deposited in spirals to allow flexibility

Question 19

what are the small pores in the lignin layer called
3.1.3(b)

Answer 19

bordered pits

Question 20

what is the function of bordered pits
3.1.3(b)

Answer 20

These allow water to move laterally in and out of the xylem vessel

Question 21

which walls doesn’t xylem vessels contain
3.1.3(b)

Answer 21

no end walls between xylem vessles

Question 22

as there are no end walls what function does this help support
3.1.3(b)

Answer 22

There are no end cell walls between xylem vessels, so xylem can transport a continuous column of water

Question 23

what is the function of phloem
3.1.3(b)

Answer 23

-transports assimilates (product of photosynthesis) from sources to sinks

Question 24

since plants don’t transport glucose what do they do instead
3.1.3(b)

Answer 24

Plants do not transport glucose, however. Glucose is a reducing sugar, so it’s too reactive to transport in the phloem. Instead, it is combined with fructose in a condensation reaction to form sucrose.

Sucrose is more soluble so can be transported in the sap
Sucrose is metabolically inactive so removed during transport

Question 25

what forms the phloem sap 3.1.3(b)

Answer 25

Sucrose, along with other organic molecules to be transported (e.g. amino acids) dissolves in water in the phloem to form phloem sap.

Question 26

what two cells does phloem tissue contain 3.1.3(b)

Answer 26

· Sieve tube elements, which stack end-to-end to form sieve tubes · Companion cells

Question 27

as sieve tube elements have no nucleus and very little cytoplasm what does this leave space for 3.1.3(b)

Answer 27

· No nucleus and very little cytoplasm, leaving space for sap to flow and reducing resistance

Question 28

what are the holes in the end wall of sieve tube elements called 3.1.3(b)

Answer 28

sieve plates

Question 29

what is the function of sieve plates 3.1.3(b)

Answer 29

allow the sap to move from one sieve tube element to the next

Question 30

why do companion cells contain many mitochondria 3.1.3(b)

Answer 30

Many mitochondria to produce ATP by aerobic respiration. ATP is needed for loading the phloem with sucrose, which involves active transport

Question 31

how are sieve tube elements directly linked to companion cells 3.1.3(b)

Answer 31

by plasmodesmata

Question 32

what is plasmodesmata 3.1.3(b)

Answer 32

Plasmodesmata are gaps in cell walls through which cytoplasm is continuous.

Question 33

what is transpiration 3.1.2(c)

Answer 33

Transpiration is the diffusion of water vapour out of the plant through the stomata in the leaves

Question 34

why does the stomata open 3.1.2(c)

Answer 34

open to allow gas exchange for photosynthesis.

Question 35

what is transpiration 3.1.2(c)

Answer 35

Transpiration therefore is a consequence of plants’ need to exchange gases, especially carbon dioxide, for photosynthesis.

Question 36

how does transpiration occur 3.1.2(c)

Answer 36

1. Water enters a leaf from the xylem, and moves by osmosis into the cells of the spongy mesophyll. 2. Water evaporates from the cell walls of the spongy mesophyll, into the air spaces. 3. Water vapour diffuses from the spongy mesophyll air spaces, through stomata, and out of the plant.

Question 37

how does water move when it leaves the plant 3.1.2(c)

Answer 37

Because the water is a gas at the point it leaves the plant, it moves by diffusion, NOT OSMOSIS. This means that the water vapour is moving down a water vapour concentration gradient, and NOT a Ψ gradient.

Question 38

how does light intensity affect transpiration rate 3.1.2(c)

Answer 38

When light shines on a plant, its stomata open to allow carbon dioxide to diffuse in for photosynthesis. Higher light intensity = more stomata open = greater rate of transpiration

Question 39

how does water availability affect transpiration rate 3.1.2(c)

Answer 39

If not much water is available, plants produce a hormone called ABA which causes the guard cells to close the stomata. The rate of transpiration would decrease.

Question 40

how does temperature affect transpiration rate 3.1.2(c)

Answer 40

A higher temperature will cause water to evaporate more easily and also cause water vapour to diffuse more quickly, so the rate of transpiration will increase.

Question 41

how does humidity affect transpiration rate 3.1.2(c)

Answer 41

High humidity means the air has a high concentration of water vapour. This will reduce the water vapour concentration gradient between the air spaces in the leaf and the outside. The rate of transpiration will therefore decrease

Question 42

how does wind affect transpiration rate 3.1.2(c)

Answer 42

Air movement outside the leaf will carry away water vapour that has just diffused out of the leaf. This maintains a high water vapour concentration gradient and so maintains a high rate of transpiration.

Question 43

what does a potometer do 3.1.2(c)

Answer 43

A potometer is a piece of equipment that is used to measure the rate of water uptake by a plant.

Question 44

what is the main assumption when using a potometer 3.1.2(c)

Answer 44

All the water taken up by the plant is transpired and none of it moves into cells or is used for photosynthesis

Question 45

how is each capillary tube filled 3.1.3(c)

Answer 45

The capillary tube is filled with water with a small air bubble inside. The distance moved by the air bubble is measured.

Question 46

once you measure the distance moved by the air bubble what can you do next 3.1.3(c)

Answer 46

measure volume of cylinder (pi x r^2) this allows you to calculate volume of water taken up

Question 47

how do you calculate rate of water uptake 3.1.3(c)

Answer 47

Rate of water uptake = volume of water taken up (mm3) ÷ time taken (min) = mm3 min-1

Question 48

how do you calculate rate of water uptake per 1mm of leaf area 3.1.3(c)

Answer 48

Rate of water uptake per 1mm of leaf area = rate (mm3min-1) ÷ leaf area in mm2 = mm3min-1mm-2

Question 49

how do you calculate leaf area 3.1.3(c)

Answer 49

draw leaf on graph paper then double it for the total surface area of the leaf -ensure you flatten the leaf

Question 50

why is it useful to calculate water uptake per 1mm of leaf area 3.1.3(c)

Answer 50

It’s useful to calculate rate per mm2 of leaf area because you can then make comparisons between different species with different leaf areas

Question 51

what are some practical precautions you have to take when setting up a potometer 3.1.3(c)

Answer 51

Set up underwater and cut stem underwater to avoid air entry, dry the leaves so water vapour can diffuse out of the stomata, cut stem at an angle to give high surface area for water uptake

Question 52

why do you have to keep control over variables 3.1.3(c)

Answer 52

Keep all relevant variables controlled so that the investigation is valid

Question 53

how do you calculate volume of water take up 3.1.3(c)

Answer 53

use volume of a cylinder (pi x r^2 x l)

Question 54

what is the transpiration stream 3.1.3(d)

Answer 54

The transpiration stream is the movement of water from the soil, into the roots, then up the stem, then out of the plant through the stomata in the leaves. -continous flow of water out the stomata

Question 55

what do the long hair extensions in the root hair cell increase 3.1.3(d)

Answer 55

-the SA of the root hair cell The root hair cells actively transport mineral ions into the cell from the soil, creating a more negative Ψ inside the cell. Water then enters the root hair cells by osmosis down the Ψ gradient

Question 56

what are the two ways water moves towards the xylem 3.1.3(d)

Answer 56

-the apoplast pathway -the symplast pathway

Question 57

what is the apoplast pathway 3.1.3(d)

Answer 57

where water molecules diffuse within and between the cell walls, without entering cells -forces water to pass through plasma/ cell surface membrane

Question 58

what is the symplast pathway 3.1.3(d)

Answer 58

where water molecules diffuse from one cell to the next through the cytoplasm and plasmodesmata

Question 59

what is the vascular bundle protected by 3.1.3(d)

Answer 59

The vascular bundle is protected by a layer of cells called the endodermis

Question 60

what do the endodermis cell walls contain and what does this form 3.1.3(d)

Answer 60

The endodermis cell walls contain a band of waterproof suberin (similar to lignin), which forms a structure called the Casparian strip

Question 61

what is the function of the casparian strip 3.1.3(d)

Answer 61

The waterproof Casparian strip in the endodermis stops the water molecules from being able to continue through the apoplast pathway, and they are forced into the symplast pathway before they enter the xylem

Question 62

what are the three processes that help water move up the stem 3.1.3(d)

Answer 62

-root pressure -transpiration pull -capillary action

Question 63

how does root pressure help pull water up the stem 3.1.3(d)

Answer 63

Water moves into xylem in roots increasing hydrostatic pressure, pushing water a few metres up the stem

Question 64

what is the cohesion-tension theory 3.1.3(d)

Answer 64

Water molecules H bond to each other which is cohesion, and as water molecules diffuse out of stomata they create tension that pulls a continuous column of water up the xylem

Question 65

what happens if the water column was broken by an air bubble 3.1.3(d)

Answer 65

If the water column becomes broken by an air bubble, then cohesion is broken and tension can no longer pull the column up the plant. In this case, water would move through the bordered pits into a xylem vessel where the water column was unbroken.

Question 66

how does capillary action move water up the stem 3.1.3(d)

Answer 66

Water molecules H bond to lignin, helping them to climb up the xylem vessel

Question 67

how does water move out of leaves 3.1.3(d)

Answer 67

· Water molecules move out of xylem and into spongy mesophyll cells by osmosis · Water molecules then move out of spongy mesophyll cells by osmosis into the cell wall o This makes the Ψ in the spongy mesophyll cell more negative, which ensures that water continues to enter spongy mesophyll cells by osmosis from the xylem · Water molecules evaporate from the spongy mesophyll cell walls into the air spaces · Water vapour molecules diffuse from the air spaces out through the stomata into the outside air

Question 68

what are xerophytes 3.1.3(e)

Answer 68

plant that have adapted through natural selection to live in conditions with low water availability

Question 69

how is marram grass adapted (5) 3.1.3(e)

Answer 69

· Rolled leaves so that air is trapped inside; this reduces the water vapour concentration gradient · Thick waxy cuticle on outer side of rolled leaf to reduce evaporation · Stomata are only on the inner surface · Stomata are in hairy pits in the lower epidermis, which allows water vapour to build up in the pits and reduces the water vapour concentration gradient · Dense spongy mesophyll with few air spaces so water doesn’t evaporate as easily

Question 70

how are cacti adapted 3.1.3

Answer 70

· Cacti are succulents – they store water in their stems which become fleshy and swollen · Leaves are reduced to spines reducing the surface area and number of stomata for transpiration · Stem is green to allow photosynthesis even without proper leaves · Roots are wide-spread and shallow to maximise uptake of any rain that does fall · Also have a large tap root that extends deep underground, to maximise water uptake from groundwater

Question 71

what are the other adaptations of xerophytes 3.1.3(e)

Answer 71

· Accumulate ions inside the spongy mesophyll cells, so that water tends to move into spongy mesophyll cells by osmosis instead of out into the air spaces · Leaf surfaces covered in silvery hairs to reflect light, which reduces leaf temperature and so lowers the rate of transpiration

Question 72

what are hydrophytes 3.1.3(e)

Answer 72

plants that live in water

Question 73

what are the adaptations hydrophytes 3.1.3(e)

Answer 73

· Many large air spaces in the leaves, which help to keep the leaf afloat · Air spaces in the stem (aerenchyma) which allows oxygen to diffuse quickly to the roots for aerobic respiration · Stomata are located on the upper epidermis so that gas exchange with the air is still possible

Question 74

What is translocation 3.1.3(f)

Answer 74

transport of assimilates from sources to sinks

Question 75

what is a source 3.1.3(f)

Answer 75

A part of the plant that loads assimilates into the phloem sieve tubes is called a source eg-the leaves

Question 76

what is a sink 3.1.3(f)

Answer 76

A part of the plant that removes assimilates from the phloem sieve tubes is called a sink eg-roots, or a flower.

Question 77

what are the three steps involved in translocation 3.1.3(f)

Answer 77

· Active loading of sucrose into the companion cells from source cells · The creation of hydrostatic pressure gradients in the sieve tubes · Unloading of sucrose into sink cells

Question 78

two steps to actively transport sucrose into companion cells 3.1.3(f)

Answer 78

1. H+ is actively transported out of the companion cells, creating an H+ concentration gradient 2. H+ and sucrose are co-transported from source cells into companion cells, using the H+ concentration gradient.

Question 79

hydrostatic pressure gradients in sieve tubes 3.1.3(f)

Answer 79

3. Sucrose diffuses from companion cells into sieve tube elements through plasmodesmata. 4. The Ψ in the sieve tube element becomes more negative. 5. Water moves from a nearby xylem vessel into the sieve tube elements, increasing the hydrostatic pressure in the sieve tube near the source. 6. Phloem sap flows towards sinks, down a hydrostatic pressure gradient

Question 80

unloading at sink cells 3.1.3(f)

Answer 80

7. Sucrose diffuses from sieve tube elements into sink cells through plasmodesmata 8. The Ψ in the sieve tube element becomes less negative 9. Water moves from the sieve tube element into a nearby xylem vessel, reducing the hydrostatic pressure in the sieve tube near the sink. 10. Inside sink cells, sucrose is immediately converted back to glucose and used for respiration or stored as starch, maintaining the sucrose concentration gradient

Question 81

explain the role of osmosis in plant support

Answer 81

-water enters the vacuole -pressure against cell wall (turgor pressure) -turgid cells support plant