3.1.3 transport in plants NOT ON MOCK

Question 1

why do plants require a transport system

Answer 1

To ensure all cells receive a strong supply of the nutrients they require. Especially important as a plant must be able to transport substances up their stem against gravity

mclaird: Many parts of a plan of either internal or underground, because there is no photosynthesis, a transport system is needed. Also some plants are relatively big so have a small surface area to volume ratio and they are also relatively metabolically active

Question 2

Relate the structure of xylem to its function

Answer 2

mclaird: The xylem makes up part of the vascular bundle. It moves the water and soluble mineral irons in transpiration. Walls are impregnated with lignin which strengthens the cells and what makes it waterproof. The border pits allow water to move sideways within the xylem and these are created when there are incomplete rings of lignin

Question 3

Relate the structure of phloem to its function

Answer 3

sieve tube elements transports sugars around the plant. companion cells designed for active transport of sugars into tubes. Plasmodesmata to allow flow of substances between cytoplasm of different cells

Question 4

describe the structure and function of the vascular system in the roots

Answer 4

consists of xylem and phloem. Xylem arranged in an X shape to provide resistance against force and surrounded by endodermis, water supply

mclaird: Around the vascular bundle is a layer of cells called endodermis. Just inside the endodermis is a layer of meristem cells which are cells are able to divide called the pericycle

Question 5

Describe the structure and function of the vascular system in the stem

Answer 5

The vascular bundles are found near the outer edge of the stem. The xylem is found towards the inside of each vascular bundle and the phloem towards the outside. In between is a layer of cambium which are meristems that divide to produce new xylem and phloem. In trees the vascular bundle forms a continuous ring

Question 6

Describe the structure and function of the vascular system in the leaves

Answer 6

consists of xylem and phloem, forms the mid-rib and veins. Involved in transport and support

Within each vein, the xylem is located on top of the phloem

Question 7

Define transpiration

Answer 7

Transpiration is the loss of water from a plant by evaporation and most of it occurs via the leaves and via the stomata

Question 8

Name factors that affect the rate of transpiration

Answer 8

increased light increases transpiration
increased temperature increases transpiration
increased humidity decreases transpiration
increased air movement increases transpiration
Waxy cuticle prevents transpiration

Question 9

How can leaf structure affect transpiration

Answer 9

Leaf surface area, thickness of epidermis and cuticle, stomatal frequency, size and position and stomatal density

Question 10

How can we measure transpiration rate

Answer 10

potometer. Plant cutting is placed in a Watertight tube that contains an air bubble. Rate of transpiration is calculated by measuring the movement of the air bubble over time

Question 11

What precautions much you take when using a potometer

Answer 11

all apparatus needs to be underwater to ensure no air bubbles and you have to cut the stem diagonally underwater for larger surface area

Joints sealed with Vaseline to prevent water loss

The leaves need to be dried and plant needs to be healthy and a climatisation period to be given

Question 13

what is the limitations of a potometer

Answer 13

Measures water uptake, Cutting plant shoot may damage plants and plant has no roots so no resistance to water being pulled up

Question 14

Define water potential as a mechanism of movement in plants

Answer 14

Water potential: the tendency of water to move by osmosis, from high water potential to low. This is the basis by which water moved to the area is it is needed within plants

Question 15

What are the problems with transpiration

Answer 15

It is hard to distinguish between water vapour and water evaporated from the leaf. It is an estimate as water can be used by the plant for photosynthesis so not all of it evaporates out

Question 16

What does transpiration provide plants with water for

Answer 16

The water is required for photosynthesis, it transports mineral ions from the soil into the plant and maintains turgidity. It keeps a plant cool on a hot day and provide support for stems and leaves through turgour pressure

Question 17

Explain what is meant by the apoplastic pathway

Answer 17

A method of osmosis through the root hair cells, where water moves through the cell walls and intercellular spaces. This pathway can only be used until water reaches the casparian strip

Question 18

explain what is meant by the symplastic pathway

Answer 18

a method of osmosis through the root hair cells, where water moves through the cytoplasm via plasmodesmata. To begin this pathway, water must be actively transported into cells

Question 19

explain what is meant by vacuolar pathway

Answer 19

This is where water is not confined to just the cytoplasm but goes through the vacuole too

Question 20

Explain what is meant by casparian strip

Answer 20

prevents harmful substances entering the xylem. The endodermis is home to the casparian strip . The Kasparian strip is an impermeable layer of suberin (waxy material) . As a result of water in the apoplast pathway is forced into symplast pathway

Question 21

Describe the steps of the movement of water into the xylem into root hair cells

Answer 21

1. water is found in air spaces in the soil (minerals and h2o)
2. minerals are absorbed into the root hair cells by active transport
3. this lowers the water potential and water moves into the root hair cells by osmosis
4. water then moves across the cortex down the water potential gradient
5. it travels through the cells via the 3 pathways
6. when water reaches the endodermis, the apoplast pathway is blocked by the casparian strip so water is diverted into the symplast pathway.
7. water and mineral ions are diverted into the symplast pathway. this insures all the mineral ions are in the cytoplasm
8. plasma membrane transporters actively pump mineral ions from the cortex into the medulla and xylem
9. Water then passes/moves via osmosis down the water potential gradient into the xylem and medulla and it can’t come out once it is gone

Question 22

If the water potential inside the cell is low will the water move in or out by osmosis

Answer 22

in

Question 23

Describe root pressure

Answer 23

Water is pushed up the xylem by hydrostatic pressure. Mineral ions are pumped into the xylem vessels in the route by the endodermal cells which lowers the water potential in the xylem. Water moves in from the surrounding cells by osmosis which raises the hydrostatic pressure so pushes water up the xylem

Question 24

describe capillarity

Answer 24

Water rises up narrow tubes due to the adhesive forces between the water molecules and the wall of the tube

Question 25

Explain the cohesion tension theory

Answer 25

water molecules form hydrogen bonds with each other, causing them to stick together (cohesion) . The surface tension of the water also create this sticking affect, therefore as water is lost through transpiration, more can be drawn up by the stem from the roots

Question 26

What would happen if the roots were deprived of oxygen

Answer 26

The pumping of the ions would stop as it requires ATP produced in aerobic respiration. Oxygen required for aerobic respiration

Question 27

Give to limitations of root pressure hypothesis

Answer 27

The pressure measured is not enough to get water to the top of the trees

Relies on the use of the plants energy atp for active transport

Question 28

give adaptations of xerophytes That allow them to live in dry conditions

Answer 28

small/rolled leaves

densely packed mesophyll

thick waxy cuticle

stomata often closed

Hairs to trap moist air

Question 29

Give adaptations of hydrophyte that allow them to live in wet conditions

Answer 29

thin or absent waxy cuticle,

stomata often open,

wide, flat leaves,

airspaces for buoyancy

Question 30

Summarise the mechanism of translocation

Answer 30

sucrose produced in leaves loaded into sieve tubes via active transport and requires energy

lowers water potential, causing water to move in from xylem

Assimilates move along the city tube towards areas of lower hydrostatic pressure(sink) . Sucrose defuses into surrounding cells where it is needed

Question 31

Define source in terms of translocation

Answer 31

any exporting region that produces photosynthetic above and beyond that of its own needs eg mature leaves

Question 32

Define sink in terms of translocation

Answer 32

Any non photosynthetic organ or an organ that does not produce enough photosynthate To meet its own needs e.g. storage organs or roots

Question 33

What is the mass flow model in terms of translocation

Answer 33

The flow moves from the source to the sink.

Source: sugars are actively loaded into the sieve element-companion so complex. Called phloem loading

sink: sugars are un loaded into the sink cells, called phloem unloading

In source tissue, active phloem loading leads to a buildup of sugars. Causes a steep drop in water potential, so water enters sieve elements from xylem via osmosis and this phloem turgour pressure increases

in sink tissue, phloem unloading leads to lower sugar concentration. Less solids so water potential increases and water leaves phloem And enters sink sieve elements and xylem. This phloem turgour pressure decreases

Question 34

How did the solutes move in translocation

Answer 34

The solution is moving in the same elements buy bulk flow. No membranes are crossed from one save tube to another and solutes are moving at the same rate as the water. Water movement is driven by pressure gradient and not water potential gradient. The water enters and exits the phloem by osmosis and the sucrose is loaded in and unloaded out of the phloem using energy

Question 35

describe phloem loading from the source cells

Answer 35

sucrose movement into the phloem is via two simultaneous methods.

Via apoplastic pathway from the cell wall through the cell membrane into the companion cell. It requires active transport against its chemical potential gradient. Involves a sucrose H+ co transporter

via symplast pathway. through open pores called plasmodesmata, A passive process which happens when there is enough solution gradient

Question 36

Describe how to measure volume and transpiration rate

Answer 36

measuring the volume of water taken up by the shoot involves calculating the volume of a cylinder e.g. the length of capillary tube. The volume of a cylinder is given by the formula V = pie r squared X height

R is the radius of the capillary tube and H is the length of capillary tube.

rate of transpiration = Volume divided by time taken

Question 37

ppq:The following statements refer to the movement of water from the cortex of the route into the xylem. Which of the following statements are true

most of the water moves across the root cortex by the apoplast pathway

at the endodermis water has to enter the symplast pathway

casparian Strips in the endodermis contain the chemical lignin

Answer 37

1 and 2 are true

Question 38

ppq: which mechanism is used at each point

into root cells
across root via symplast pathway
up the stem in the xylem
across leaf via apoplast pathway 
out of leaf via stomata

Answer 38

into root cells OSMOSIS

across root via symplast pathway OSMOSIS

up the stem in the xylem MASS FLOW

across leaf via apoplast pathway MASS FLOW

out of leaf via stomata DIFFUSION

Question 39

ppq:Define the process of adhesion

Answer 39

Attraction of water molecules to the impermeable walls of xylem tissue

Question 40

ppq: Describe how the student could ensure that a valid comparison could be made between the two leafy shoots

Answer 40

The student could look at both of the leaf surface area and ensure they are both the same sizes

also compare the transpiration rate per unit area

Question 41

ppq: The cohesion tension theory is often used to explain the mechanism by which water moves up the xylem from the roots to the leaves, use this theory to explain how water moves from the roots to the leaves

Answer 41

Evaporation at the top of the xylem, which creates the tension in xylem. Water molecules stick together to form a chain and the chain is pulled up by tension

Question 42

ppq: Soluble mineral ions are present in soil, explain why water molecules can form hydrogen bonds with nitrate ions

Answer 42

Water molecules are polar so that hydrogen bonds conform between the partially positive hydrogen atoms in the water and an oxygen atom of nitrate

Question 43

ppq: Name the pours through which most water vapour is lost from a leaf

Answer 43

stomata

Question 44

ppq:Describe how the guard cells around in the leaf pores are adapted to their role

Answer 44

They have an unevenly thick cell wall so able to change shape

Question 45

ppq: Name one other part (not stomata) from which water may be lost

Answer 45

Epidermis/cuticle

Question 46

ppq: Complete the following passage

when water is lost from the cells of the leaf it reduces the ___ in those cells. as a result, water enters the cells by ___. this process occurs across the plasma membrane which is ___. if all the water lost from the leaf cells is not replaced, they lose ____ And the leaf may wilt

Answer 46

when water is lost from the cells of the leaf it reduces the WATER POTENTIAL in those cells.

as a result, water enters the cells by OSMOSIS.

this process occurs across the plasma membrane which is PARTIALLY PERMEABLE

if all the water lost from the leaf cells is not replaced, they lose TURGIDITY And the leaf may wilt

Question 47

ppq: complete the following paragraph

At step a, charged particles are moved out of the companion cells by the process of ___. this creates a ___ Gradient between the companion cells and its surroundings. At step b, the charged particles and assimilates are co transported by ___into the companion cells. the assimilates build up in the companion cells and move by ___ into the sieve tube element at step c assimilates, such as sucrose and____ can be loaded in this way

Answer 47

At step a, charged particles are moved out of the companion cells by the process of ACTIVE TRANSPORT

this creates a CONCENTRATION Gradient between the companion cells and its surroundings.

At step b, the charged particles and assimilates are co transported by FACILIATED DIFFUSION into the companion cells.

the assimilates build up in the companion cells and move by DIFFUSION into the sieve tube element at step c

assimilates, such as sucrose and AMINO ACIDS can be loaded in this way

Question 48

ppq: Suggest what evidence a scientist might expect to see in companion cells using an electron microscope

Answer 48

Many mitochondria, plasma does matter between companion cells and save tubes and many ribosomes

Question 49

ppq: Distinguish between the term transpiration and the transformation stream

Answer 49

transpiration: loss of water vapour from parts of the plant e.g. leaves

transpiration stream: Movement of water up xylem vessels, from roots to leaves

Question 50

ppq: Explain why believes not all be in the same size in an investigation may affect the results and suggest how the student could improve this this

Answer 50

If the surface area of the leaves is different, there will be a different number of stomata so the student should choose shoots with similar sized leaves or a least a similar size surface area

Question 51

ppq: Explain why put in the potometer Underwater and then leaves getting wet will affect the results and suggest had a student could improve this

Answer 51

The water potential outside the leaf is too high so the student should assemble without watching the leaves or waiting until the leaves dry

Question 52

ppq: Describe how the lab warming up quickly will affect the results and suggest had a student could improve the investigation

Answer 52

increased temperature will increase evaporation and transpiration so therefore the students should control the temperature and carry out in a room with controlled temperature

Question 53

ppq: Name the sugar most commonly transported through the stem of a plant and the tissue that transports the sugar

Answer 53

Sucrose and phloem

Question 54

ppq: Sugar molecules are actively loaded into the transport issue. Describe how active loading takes place

Answer 54

Hydrogen ions are pumped out of companion cells. This creates gradient and the hydrogen ions re-enter the companion cells. Sucrose moves with hydrogen ions down concentration gradient by facilitated diffusion. Sucrose diffuses into sieve tube elements through plasmodesmata

Question 55

ppq: Describe how assimilates are loaded into the phloem

Answer 55

Active transport of hydrogen irons out of companion cells. This creates concentration gradient. Facilitated diffusion of hydrogen ions back into companion cells. Sucrose moves in with hydrogen ions by cotransport and sucrose diffuses through plasmodesmata into sieve tube element

Question 56

ppq: Suggest why a bunch of flowers might survive longer if the ends of the stems are removed immediately before the flowers are placed in water

Answer 56

because of air in the xylem

Question 57

ppq: Explain why water loss from the leaves of a plant is unavoidable

Answer 57

Stomata open to allow gassiest exchange for photosynthesis. Photosynthesis is essential for the plant to gain energy and some water is lost through the cuticle

Question 58

ppq: State what is meant by the term is source and sink

Answer 58

source: site where sucrose are loaded into phloem

Sync: site was sucrose is unloaded from phloem

Question 59

ppq: when the bar is removed from a tree, the phloem is also removed. If I complete ring of bark is removed, the tree trunk can be seen to swell above the cut.

Suggest two reasons why the trunk swells above the cut

Answer 59

Sugars cannot pass the cut, this decreases water potential and water moves into the cells. The damage triggers increased cell division to produce cells to store sugars and the cut causes infection