Brainscape's Knowledge GenomeTM

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


See full index

biology paper 1 > 3.3.4 mass transport > Flashcards

3.3.4 mass transport Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards
1
Q

loading, transport and unloading of oxygen

A

at gas exchange surface carbon dioxide is constantly being removed

pH is slightly raised due to the low concentration of carbon dioxide

higher pH changes shape of haemoglobin into one that can load oxygen readily
shape also increases affinity for oxygen so its not released when being transported around the blood to the tissues

carbon dioxide is produced by respiring cells
carbion dioxide is acidic in solution = pH of blood within tissue is lowered

lower pH changes the shape of haemoglobin into one with a lower affinity

haemoglobin releases its oxygen into respiring tissues

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

effects of carbon dioxide concentration

A

greater the concentration of carbon dioxide, the more readily the haemoglobin releases its oxygen
dissolved carbon dioxide is acidic and low pH causes haemoglobin to change shape

gas exchange surface (lungs) = concentration of carbon dioxide is low because it diffuses across the exchange surface and is excreted from organism
reduced carbon dioxide concentration has shifted the oxygen dissocation curve to the left

rapidly respiring tissues = concentration of carbon dioxide is high
affinity of haemoglobin is reduced meaning oxygen is readily unloaded from haemoglobin into muscles
increased carbon dioxide concentration has shifted the oxygen dissocation curve to the right

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

oxygen dissociation curves

A

important facts:
1. further to the left of the curve, the greater afffinity of haemoglobin for oxygen (loads oxygen readily but unloads it less easily

  1. further to the right of the curve, lower affinity of haemoglobin for oxygen (loads oxygen less readily but unloads it more easily
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

oxygen dissociation curves

A

graph of relationship between saturation of haemoglobin with oxygen and the partial pressure is know as the oxygen dissocation curve

explanation:

  • shape of haemoglobin molecule makes it difficult for first oxygen to bind to the four sites because they are closely united
    therefore at low oxygen concentrations, low oxygen binds to the haemoglobin
    shallow curve initially
  • binding of first oxygen changes quaternary structure causing it to change shape. change in shape makes it easier for other oxygens to bind
    binding of first molecule induces other subunits to bind to the oxygen molecule
  • smaller increase in partial pressure to bind the second oxygen than to bind the first one = positive cooperativity
    gradient of curve steepens

-harder for fourth oxygen molecule to bind due to probability due to most sites being taken.
less of a chance to find an empty site to bind to
gradient of curve reduces and graph flatterns off

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

oxygen transport

A

in respiration, pO2 is low

at low pO2 oxygen dissociates from oxyhaemoglobin and can diffuse to respiring cells

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

transport of oxygen by haemoglobin

A

amount of oxygen in the tissue is reffered to as its partial pressure for oxygen (pO2) or as oxygen tension

oxygen transport is measured in kPa

ventilation allows lung tissue to have a high pO2
where pO2 is high, more oxygen is able to disassociate with haemoglobin molecules to be transported

% of highest haemoglobin saturation is here

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

oxyhaemoglobin and respiring tissue

A

in respiring tissue, oxygen disassociates (releases) from oxyhaemoglobin - caused by CO2 which causes the haemoglobin to bind more loosely to the oxygen

oxygen can then diffuse out of the erythrocytes and to respiring cells

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

oxyhaemoglobin

A

oxyhaemoglobin = haemoglobin oxygenated

as oxygen is added it causes the molecule to undergo a conformational change (changes shape X4)

once one binds it causes a change which causes the proteins around the next Haem group to open up a little

this makes it easier for the following oxygens to bind

as it takes it up oxygen it then becomes easier to take in more (happens opposite way as well)

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

process of oxygen

A

in the lungs, oxygen diffuses into blood plasma

then passes down a concentration gradient and into erythrocytes

oxygen binds to haemoglobin to maintain concentration gradient

oxygen binds to haem group Fe2+ group of the haemoglobin

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

erythrocytes = red blood cells

A

adaptations:

  1. biconcave shape maximises surface area for gas exchange
  2. small and flexible to pass through narrow capillaries
  3. no nucleus = more room to carry respiratory gases
  4. packed with haemoglobin (Hb)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

different haemoglobins and different affinities

A

from the shape of the haemoglobin molecule

each haemoglobin has a slightly different amino acid sequence, therefore has a slightly different tertiary sequence and quaternary structure and different oxygen binding properties

dependant on its structure the affinity ranges from high to low

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

role of haemoglobin

A

to transport oxygen

to be efficient oxygen must:

  • readily associate with oxygen at the surface where gas exchange takes place
  • readily disassociate from oxygen at the tissues requiring it

achieves this but changing affinities under different conditions

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

loading and unloading oxygen

A

loading/association = haemoglobin binds with oxygen (takes place in lungs)

unloading/diassociation = haemoglobin releases oxygen (takes place in tissues)

haemoglobins with a high affinity for oxygen take up oxygen more easily, but release it less easily

haemoglobins with a low affinity for oxygen take up oxygen less easily, but release it more easily

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

describe haemoglobin molecule structure

A
  1. primary structure = sequence of amino acids in the four polypeptide chains
  2. secondary structure = each polypeptide chain is coiled into a helix
  3. tertiary structure = polypeptide chain is folded into a precise shape
  4. quaternary structure = all four polypeptide chains are linked to form a spherical molecule
    each has a haem group conatins Fe2+ ion which can combine with a single oxygen molecule making a total of 4 that can be carried by a single haemoglobin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

single circulation=fish

A

single system (fish):
heart > gills > body > heart

low activity and do not need to maintain temperature so less energy is needed

blood at low pressure and flow is slow

diagram on notes

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

open system = insects

A

insects = 1nm to 13cm

blood not always held in vessels

blood circulates through body cavity

lymph and blood not distinguished (haemolymph)

dorsal muscular pumping organ

insects have a seperate tracheal system to transport oxygen and carbon dioxide

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

advantages of double circulation

A
  1. blood flows quickly due to blood pressure created by heart
  2. heart can increase pressure of blood flowing to body tissues without increasing pressure of blood to delicate lungs
  3. blood stays in blood vessels
    in all vertebrates eg fish, birds and mammals
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

double circulation

A

double systems = mammals

left heart > body > right heart > lungs > left heart

aorta > vena cava > pulmonary artery > pulmonary vein

two seperate circuits:
1. pulmonary = carries deoxygenated blood to lungs to pick up oxygen
2. systematic = carries oxygenated blood to body tissues

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

mammals circulatory system broken down

A
  1. arterties
  2. veins
  3. capillaries
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

why is the blood passed through twice?

A

mammals have a double closed circulatory system in which blood is confined to vessels and passes through the heart twice for each complete circuit of the body

when blood is passed through the lungs = low pressure so passes through twice to increase pressure so circulatory is not slow

passes through twice = high rate of metabolism

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

features of transport systems

A
  • suitable medium in which to carry materials eg blood
    normally a liquid but can be a gas
  • a form of mass transport in which the transport medium is moved in bulk over large distances = more rapid diffusion
  • closed system of tubular vessels that contain the transport medium and forms a branching network to distrubute all over the organism
  • mechanism for moving the transport medium within vessles
    requires a pressure difference
    eg animals = muscle contraction
    eg plants = passive processes - evapouration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Pulmonary Circuit

A
  1. Deoxygenated blood begins in the right atrium. Before blood can be pumped around the body, it needs to be pumped to the lungs to get oxygenated.
  2. The deoxygenated blood in the right atrium is pumped into the right ventricle. From here is is pumped into the pulmonary circuit through the pulmonary artery.
  3. The lungs oxygenate the blood. The pulmonary circuit carries the blood to the lungs where it is oxygenated (via gas exchange).
  4. The oxygenated blood returns to the left atrium. Then the oxygenated blood is carried back to the heart via the pulmonary vein.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Systemic Circuit

A
  1. The oxygenated blood is ready to be pumped around the body. The oxygenated blood returns from the pulmonary circuit, and passes into the left atrium, then into the left ventricle. The oxygenated blood can now be pumped around the body in the systemic circuit.
  2. The oxygenated blood is pumped out of the left ventricle. From the left ventricle it is pumped out into the aorta, and is carried around the body.
  3. The blood gives oxygen to body cells. The blood unloads oxygen and gives it to the body’s cells. The blood becomes deoxygenated as oxygen is used up.

4.The deoxygenated blood returns to the right atrium. The vena cava (veins) carry the blood (now deoxygenated) back to the heart, and the cycle starts again.

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

cardiac muscle

A

thick muscular layer

myogenic = can contract and relax without nervous or hormonal stimulation

never tires aslong as it has a supply of oxygen and glucose

diagram on notes

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

supplying heart with oxygen

A

heart does not use this oxygen to supply its own respiratory needs

instead heart is supplied by coronary arteries which branch off the aorta shortly after it leaves the heart

blockage of these arteries lead to myocardial infection or heart attacks
muscle cells are unable to respire aerobically so die

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

draw the internal structure+ external structure

A

diagram on notes

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

blood flow through the heart

A

blood comes into the heart from the body

then passes to the lungs to collect oxygen = double circulatory system

often returns to the heart so it can leave to be transported to the body again

body > vena cava > deoxygenated blood > atrium > tricupsid valve > right ventricle > pulmonary artery > lungs

pulmonary vein > oxygenated blood > atrium > bicupsid valve > left ventricle > aorta >

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

structure of the heart

A

atrium = thin walled, elastic and stretches as it collects blood

ventricle = thick muscular wall as it has to contract strongly to pump blood a distance (either to lungs or rest of body)

right ventricle = pumps blood only to lungs and has a thinner muscular wall than the left ventricle

left ventricle = thick muscular wall, enabling it to contract to create enough pressure to pump blood to the rest of the body

both pumps pump in time and pump same volume of blood but are two seperate pumps

aorta = connected to left ventricle and carries oxygenated blood to all parts of the body except the lungs

vena cava = connected to right atrium and brings back deoxygenated blood from tissues of the body (except lungs)

pulmonary artery = connected to right ventricle and carries deoxygenated blood to the lungs where oxygen is replenished and carbon dioxide is removed

pulmonary vein = connected to the left atrium and brings oxygenated blood back from the lungs

diagram on notes

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

where is the heart found?

A

found between the two lungs

lies in the thoracic cavity behind the sternum (breastbone)

enclosed by the pericardium = prevents damage

pericardial fluid is secreted between them to aid movement and protect the heart
also prevents blood from overflowing

walls of the heart = made of cardiac muscle (myocardium) rammed with mitochondria, only found in heart

never tires but cannot respire anaerobically and cannot tolerate a lack of O2

30
Q

describe the process of the relaxation of the heart (diastole)

A

Blood returns to the atria of the heart through the pulmonary vein (from the lungs) and vena cava.

As the atria, fill, the pressure in them rises, causing the atrioventricular valves to open, allowing the blood to pass into the ventricles

The relaxation of the ventricles causes them to recall and reduces the pressure within the ventricle. This causes the pressure to be lower than that in the aorta and pulmonary artery

Semi-lunar valves close causing the dub heart beat sound

31
Q

describe the contraction of the atria (atrial systole)

A

The contraction of the atrial walls, along with the recoil of the relaxed ventricle walls forces, the remaining blood into the ventricles from the atria

The muscle of the ventricle walls remains relaxed

32
Q

describe the contraction of the ventricles (ventricular systole)

A

Walls contract simultaneously, increasing the blood pressure within them, forcing shut the atrioventricular valves and preventing backflow of blood into the atria

Causes the characteristic of the lub sound of the heartbeat

When the AV valves close, the pressure in the ventricles rises further, forcing the blood from the ventricles into the blood vessels

Ventricles have thick, muscular walls, which means a contract forcefully, creating high-pressure are necessary to pump blood around the body

Differences in the thickness of the lining of the wall, compared to the left ventricle to the right shows the extremities of the need to pump blood around the body

33
Q

how do valves control blood flow?

A

AV valves = these are between the left atrium and ventricle, and the right atrium and ventricle, and these prevent backflow of blood. When contraction of the ventricles means ventricular pressure exceeds atrial pressure closure of these valves, ensures that when the ventricles contract blood within the move to the aorta and pulmonary artery rather than back to the atria.

Semi-lunar valves = these prevent backflow of blood into the ventricles, when the pressure in these vessels exceeds that in the ventricles, this arises when the elastic walls of the vessels recoil increasing pressure

pocket valves = occur throughout the whole venous system, and are found in veins, they ensure that when the veins are squeezed blood flows back towards the heart, rather than away from it.

34
Q

what is cardiac output?

A

Is the volume of the blood pumped by one ventricle of the heart in one minute

Usually measured in DM3 minutes -1, and depends upon two factors

  1. The heart rate
  2. The stroke volume
35
Q

what is the cardiac output equation?

A

cardiac output = heart rate x stroke volume

36
Q

what is the difference between arteries, veins and capillaries?

A

different relative proportions of each layer

see notes/powerpoint

37
Q
A
38
Q

what is the capillaries structure and functions?

A

walls consist of mostly linining layer = extremely thin walls so diffusion pathways are short
allows for rapid diffusion of materials between blood and cells

numerous and highly branched = large SA for exchange

lumen is narrow = RBC are squeezed against side of capillary which reduces diffusion pathways

spaces between endothelial cells = allow white blood cells to escape in order to deal with infections within tissues

39
Q

what is the veins structure and functions?

A

muscle layer is relatively thin compared to artieries = veins cannot carry blood away from tissues and therefore their constriction and dilation cannot control the flow of blood to tissues

elastic layer is relatively thin compared to arteries = low pressure of blood within the veins will not cause them to burst and pressure is too low to create a recoil action

overall thickness of wall is small = no need for thick wall as the pressure within the veins is low,, it wont burst
allows them to be flatterned easily = aiding blood flow

valves at intervals throughout = prevents backflow of blood
valves ensure pressure directs blood in one direction only which is towards the heart

40
Q

what are the arteriole structure and functions?

A

muscle layer is relatively thicker than in arteries = allows constriction of the lumen which restricts blood flow and so controls movement into capillaries that supply the tissues with blood

elastic layer is relatively thinner than in arteries = blood pressure is lower

41
Q

what are the artery’s structure and functions?

A

muscle layer is thick compared to veins = smaller arteries can be constricted and dilated in order to control the volume of blood passing through

elastic layer is relatively thick compared to veins = to keep high blood pressure. elastic wall is stretched and this stretching and recoil action helps to maintain high pressure and smooth pressure surges created by the beating of the heart

overall thickness of the heart = resists vessel bursting under pressure

42
Q

describe the structure of blood vessels

A

arteries = carry blood away from heart and into arterioles

arterioles = smaller artieries that control blood flow artieries to capillaries

capillaries = tiny vessels that link arterioles to veins

veins = carry blood from capillaries to the heart

all have the same structure:
1. tough fibrous structure that resists pressure changes from both within and outside
2. elastic layer that helps maintain blood pressure by stretching and sprinking back
3. muscle layer that can contract and control the flow of blood
4. thin inner lining (endothellium) that is smooth to reduce friction and thin to allow diffusion
5. lumen that is not a layer but a central cavity of the blood vessel

43
Q

what is tissue fluid?

A

tissue fluid = liquid that bathes cells and metabolic materials are made in the liquid

watery liquid that contains glucose, amino acids, fatty acids, oxygen, ions in solution and supplies all these substances to tissues

in return it recieves carbon dioxide and other waste materials

formed from blood plasma and is controlled by various homeostatis systems

44
Q

how is blood plasma formed as well as hydrostatic pressure?

A

hydrostatic pressure = created by the pumping of the heart and blood pushing against the container its within

outward pressure is opposed by:
1. hydrostatic pressure of the tissue fluid outside the capillaries, which resists outward movement of liquid
2. lower water potential of blood, due to plasma proteins, that causes the water to move back into the blood within the capillaries

filtration under pressure = ultrafiltration

pushed out by hydrostatic pressure: diagram on notes

45
Q

describe how tissue fluid gets returned back to the circulatory system

A

loss of tissue fluid from capillaries reduces the hydrostatic pressure inside them

by the time the blood has reached the venous end of the capillary network its hydrostatic pressure is usually lower than that of the tissue fluid outside of it

therefore tissue fluid is forced back into capillaries by the higher hydrostatic pressure outside them

in addition, plasma has lost water and still contains proteins. therefore has a lower water potential than the tissue fluid

water leaves the tissues by osmosis down a water potential gradient

46
Q

what is the lymphatic system?

A

system of vessels that begin in the cells

drain contents back into bloodstream via two ducts that join veins close to the heart

contents are moved by:
1. hydrostatic pressure of the tissue fluid that has left the capillaries
2. contraction of body muscles that squeeze the lymph vessels
these valves in the lymph vessels ensure fluid inside them move away from the direction of the heart

47
Q

what is oncotic pressure?

A

oncontic pressure = pressure created by the osmotic effects of the solutes in a solution

measured in Kpa, the highest oncotic pressure is 0kPa

if water moves out of an area, the oncontic pressure of that area will decrease and that value will become more negative

any substaces which remain in a solution like the blood, such as plasma proteins, will have an osmotic effect and therefore lower the oncotic pressure

48
Q

what is the role of hydrostatic pressure in the formation of tissue fluid?

A

hydrostatic pressure pushes out while oncotic pressure pulls in

in the capillaries, hydrostatic pressure increases filtration by pushing fluid and solute out of the capillaries, while capillaries oncotic pressure pulls fluid into the capillaries and preventing fluid from leaving

hydrostatic pressure is based on the pressure excerted by the blood pushinf against the walls of the capillaries
whilst oncontic pressure exsists because of the proteins that do not leave the capillary and draw water

49
Q

what is oedema?

A

condition where there is an accumulation of tissue fluid in the cavities or tissues of the body

50
Q

describe the net movementof tissue fluid

A

eg arteriole end

  1. net hydrostatic pressure moves out of the capillary
  2. net oncotic pressure moves fluid into the capillary
  3. net movement is outwards at the arteriole end of the capillary
51
Q

what are the two types of mass transport in plants?

A

xylem = transports water and dissolved minerals from the roots, up through the plant and eventually out through the leaf stomata in one direction

phloem = transports the dissolved products of photosynthesis in various directions around the plant

52
Q

how does water move out of the stomata?

A

humidity of atmosphere is usually less than that of air spaces next to the stomata

as a result there is a water potential gradient from the air spaces through the stomata to the air

when stomata is open = water vapour molecules diffuse out of air spaces and into surrounding air

water lost by diffusion from air spaces is replaced by water evapourating from the cells walls of surrounding mesophyll cells

by changing the size of the stomatal pores, plants can control their rate of transpiration

53
Q

what is a potometer?

A

potometer= device used to estimate transpiration rates

experimental method = distance moved by an air bubble can be recored every minute and can be used to indicate the rate of water uptake by the plant

diagram on notes

54
Q

why do plants need transport systems?

A
  • multi cellular = higher demand for resources
  • SA:V ratio = as organisms get bigger SA:V ratio gets smaller
    diffusion alone is insufficient to supply resources

diagram on notes

55
Q

how does water travel into and through a plant/

A
  1. water moves from the soil into the root hair cells by osmosis and moves across the root to the vascular bundle in the middle
  2. vascular bundle contains vessels called xylem that carry water around the plant
  3. water moves into the xylem vessels in the root
  4. xylem are long hollow tubes that run from the roots and leaves and carry water up to the leaves

diagrams on notes

56
Q

describe the movement of water across the cells of a leaf

A

water is lost from mesophyll cells by evapouration from their cell walls to the air spaces in the leafs
replaced by water reaching the mesophyll cells from the xylem via cell walls or via the cytoplasm

cytoplasmic route:

  1. mesophyll cells lose water to the air spaces by evapouration due to the heat supplied by the sun
  2. these cells now have a lower water potential and so water enters by osmosis from neighbouring cells
  3. the loss of water from these neighbouring cells lowers their water potential
  4. they in turn take in water from their neighbours by osmosis

water potential gradient is created that pulls water from xylem, across leaf mesophyll and finally out into atmosphere

57
Q

describe the movement of water up the stem in the xylem

A

cohesion tension = responsible for the movement of water up the xylem > from roots to leaves

process:
1. water evapourates from mesophyll cells due to heat from the sun leading to transpiration

  1. water molecules form hydrogen bonds between one another and hence stick together = cohesion
  2. water forms a continous unbroken column across the mesophyll cells and down the xylem
  3. as water evapourates from the mesophyll cells in the leaf into the air spaces beneath the stomata, more molecules are drawn up behind as a result of this cohesion
  4. column of water is therefore pulled up the xylem as a result of transpiration = called transpiration pull
  5. transpiration pull puts the xylem under tension (negative pressure) = cohesion tension theory
58
Q

what is the role of cohesion?

A

water molecules have a special property that makes them stick together in long chains so they travel up though the xylem in long continuous chains or columns

cohesion = water attracts each other due to H+ bonds

water molecules are pulled up the xylem following the water potential

water evapourates from the leaves creating tension (transpiration) and the cohesive nature moves the whole column of water up the xylem

59
Q

what evidence is there that supports cohesion theory?

A

change in diameter of tree trunks according to the rate of transpiration
during the day = transpiration is at its greatest and theres more tension (more negative pressure)
pulls walls inwards
at night = transpiration is at its lowest and theres less tension
diameter of trunk increases

broken xylem vessels and air entering = water cannot be drawn up
the continous column of water is broken and can no longer stick together
water cannot leak out and air is sucked in

60
Q

what are xylem vessels?

A

xylem vessels are involved in the movement of water and minerals through a plant from its roots to leaves

transported through the xylem vessels up the stem to the leaves

evapourates from leaves = transpiration

xylem cells = dead, doesnt have cytoplasm or organelles leaving
large space for water to flow through

61
Q

describe some xylem adaptations

A

lignin in cell walls = strengths the cell wall so vessels do not collapse
also waterproof so vessels do not leak

no end walls = forms a long continous tube, with nothing to get in the way of water flowing through them

doesnt need energy = uses energy from sun from evapouration of water on leaves

62
Q

what are the steps of transpiration?

A
  1. water is constantly lost from the leaves, this occurs due to evapouration due to heat + water loss from the stomata
    FOLLOWS WATER POTENTIAL
  2. water molecule leaves the cell it pulls the others its attached to along behind it pulling a column of water molecules across the leaf and up through the xylem
    PULLING FORCE IS CALLED TENSION + COHESION AND PRODUCES A CONCENTRATION GRADIENT
  3. adhesion (sticking to walls) occurs as a result of attraction between the molecules and the walls of the vessel
    ADHESION HOLDS THE COLUMN OF WATER IN PLACE

diagram on notes

63
Q

describe the phloem

A

individual seive tube elements that make up the phoem are alive
they have no nucleus, very few organelles and only a few strands of cytoplams

cell walls do not disappear but form structures called seive plates through these strands of cytoplasm can pass through

hypothesis = mass flow hypothesis

diagram on notes

64
Q

describe the transportation process in the phloem

A

transport of soluable organic substances within a plant = translocation

solutes are transported in sieve tube elements

plant transports them from sites of production = sources

places where they will be used directly or stored for using future use = sinks

molecules transported = sucrose, amino acids, inorganic ions such as potassium, chloride, phosphate and magnesium ions

65
Q

describe the mechanism of translocation (mass flow theory)

A
  1. transfer of sucrose into sieve elements from photosynthesising tissue
    - sucrose is manufactured from the products of photosynthesis in cells with chloroplasts
    - sucrose diffuses down a concentration gradient into sieve elements
    - hydrogen ions are actively transported from companion cells into the spaces in cell walls using ADP
    - hydrogen ions diffuse down a concentration gradient through carrier proteins into sieve elements
    - sucrose + H+ = co transport and facilitated diffusion into companion cells
  2. mass flow of sucrose through sieve tube elements
    mass flow is the bulk movement of a substance through a given channel or area
    - sucrose produced by photosynthesising cells is actively transported into sieve channels (like above)
    - causes sieve tubes to have a lower water potential
    - water moves from xylem into the sieve tubes by osmosis, creating a high hydrostatic pressure
    - at the sink, sugars leave the phloem to be used up by respiration or converted into starch via active transport, lowering hydrostatic pressure, so water leaves via osmosis to these respiring cells lowering hydrostatic pressure
    - result = pressure gradient from source to sink, pushing out sugars/water
66
Q

what evidence is available that supports the fact that translocation of organic molecules occurs in phloem

A
  1. phloem is cut, a solution of organic molecules flown out
  2. plants provided with radioactive carbon dioxide can be shown to have radioactive labelled carbon in phloem after a short period of time
  3. aphids are a type of insect that feed on plants that penetrate the phloem through needle like moths. they extract contents from sieve tubes
  4. removal of a ring of phloem from around the whole circumference of stem leads to the accumulation of sugars below it
67
Q

describe the use of tracer experiments

A

radioactice isotype are useful for tracing the movement of substance in plants

if a plant is then grown in an atmosphere containing CO2 the CO isotype will be incorparated into the sugars produced during photosynthesis

radioactive sugars can be traced as they move within the plant using autoradiography
INVOLVES TAKING THIN CROSS SECTIONS OF THE PLANT STEM AND PLACING THEM ON A PIECE OF XRAY FILM
FILM BECOMES BLACKENED WHERE IT HAS BEEN EXPOSED TO RADIATION PROCED BY 14C IN SUGARS

blackened regions corrospond to where phloem tissue is in the stem, other tissues do not blacken the film showing that phloem is responsible for translocation

68
Q

what were the ringer experiment conclusions?

A
  1. phloem = tissue responsible for translocating sugars in the plants
  2. ring of tissue has not extented into the xylem, continuity has not been broken
69
Q

what were the ringer experiment findings?

A
  1. sugars of the phloem accumulating above the ring, leading to swelling in this region
  2. interruption of flow of sugars to the region below the ring and death of tissues in this region
70
Q

describe the use of ringer experiments

A
  1. section of the outer layers (protective layer and phloem) is removed around the complete circumference of a woody stem while it is still attached to the rest of the plant
  2. after a period of time, the region of the stem immediately above the missing ring of tissue is seen to swell
  3. samples of the liquid that has been accumulated in this swollen region are found to be rich in sugars and other dissolved substances and other dissolved organic substances
  4. some non-photosynthetic tissues in the region below the ring (towards the ring) are found to wither and die, while those above the ring continue to grow

diagram in textbook

biology paper 1 (23 decks)

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