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Bio Ms Thomson > T3 Exchange of substances > Flashcards

T3 Exchange of substances Flashcards

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Biology 101 flashcards
1
Q

The action of endopeptidases and exopeptidases can increase the rate of protein digestion.
Describe how. 2 marks

A
  1. Exopeptidases hydrolyse peptide bonds at the ends of a
    polypeptide/protein AND endopeptidases hydrolyse internal peptide
    bonds within a polypeptide/protein;
    Reference to ‘hydrolyse’ required at least once
  2. More ‘ends’
    OR
    More surface area;
    Accept even if via action of incorrect enzyme
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2
Q

As humans age, there is a decrease in body protein.
Give the name of one body protein that could have resulted in:
1. reduced muscle power
2. reduced immunity
2 marks

A
  1. Actin/myosin/tropomyosin;
    Accept troponin
    Accept ATP synthase/hydrolase
  2. Antibodies;
    Accept immunoglobulins
    Accept lysozyme
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3
Q

Describe the role of enzymes in the digestion of proteins in a mammal.
4 marks

A

1.   (Reference to) hydrolysis of peptide bonds;
2.   Endopeptidase act in the middle of protein/polypeptide
OR
Endopeptidase produces short(er) polypeptides/ increase number of ends;
3.   Exopeptidases act at end of protein/polypeptide
OR
Exopeptidase produces dipeptides/amino acids;
4.   Dipeptidase acts on dipeptide/between two amino acids
OR
Dipeptidase produces (single) amino acids;
Accept chain/chain of amino acids/peptide for polypeptide
Accept digest/breakdown/ break for ‘act’
Mark points 2, 3 and 4 reject answers where substrate or product is
incorrect eg ‘Endopeptidase produces dipeptides’
Ignore references to source and location of enzymes

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4
Q

The food eaten by a rabbit is digested mainly by microorganisms in its caecum. The
caecum is a section of intestine attached between the ileum and the large intestine. The
resulting semi-digested material leaves the anus of a rabbit as soft, caecal droppings. The
rabbit then eats these caecal droppings.
Use this information to suggest how eating its own caecal droppings helps a
rabbit’s digestion and absorption of dietary protein. 3 marks

A

1.   More/remaining/undigested (protein) broken down;
Accept all (protein) broken down
2.   (So more) amino acids absorbed;
3.   (Because) protein/food passes again through stomach/ileum;

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5
Q

Suggest and explain why the combined actions of endopeptidases and exopeptidases are
more efficient than exopeptidases on their own.
2 marks

A
  1. Endopeptidases hydrolyse internal (peptide bonds)
    OR
    Exopeptidases remove amino acids/hydrolyse (bonds) at end(s);
    Accept: break for hydrolyse.
    Accept: endopeptidases break (proteins) into shorter chains.
  2. More ends or increase in surface area (for exopeptidases);
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6
Q

The addition of a respiratory inhibitor stops the absorption of amino acids.
Use the diagram to expain why. 3 marks

A

) 1. No/less ATP produced
OR
No active transport;
2. Sodium (ions) not moved (into/out of cell);
Accept: sodium (ions) increase in cell.
Accept: sodium (ions) cannot diffuse into cell.
3. No diffusion gradient for sodium (to move into cell with amino
acid)
OR
No concentration gradient for sodium (to move into cell with amino acid);
Accept: converse for all three points.
Note: no active transport of sodium (ions) equals 2 marks.

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7
Q

Describe the role of the enzymes of the digestive system in the complete breakdown of starch. 5 marks

A
  1. Amylase;
  2. (Starch) to maltose:
  3. Maltase;
    Maltose to glucose;
  4. Hydrolysis;
  5. (Of) glycosidic bond;
    Q Do not penalise incorrect site for digestion or incorrect site of
    enzyme production.
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8
Q

Describe the processes involved in the absorption of the products of starch digestion. 5 marks

A
  1. Glucose moves in with sodium (into epithelial cell);
  2. Via (carrier / channel) protein / symport;
  3. Sodium removed (from epithelial cell) by active transport / sodium- potassium pump;
    Into blood;
  4. Maintaining low concentration of sodium (in epithelial cell) / maintaining sodium
    concentration gradient (between lumen and epithelial cell);
  5. Glucose moves into blood;
    By (facilitated) diffusion;
    Q Only allow diffusion mark in context of movement of glucose into
    the blood.
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9
Q

From save my exams so probs not a definite question.

Explain how the lining of the trachea, bronchus and bronchioles provide protection against pathogens.

A

Cilia beat to move mucus away from the lungs and up towards the mouth. Mucus is produced by goblet cells and acts as a barrier to pathogens from entering the ciliated epithelium. The mucus also traps bacteria and microorganisms, while blood vessels bring macrophages to engulf any pathogens in phagocytosis.

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10
Q

Describe and explain one feature of the alveolar epithelium that makes the epithelium well
adapted as a surface for gas exchange. Do not refer to surface area or moisture in your
answer.
2 marks

A

Mark in pairs: 1 and 2 OR 3 and 4
1. Flattened cells
OR
Single layer of cells;
Reject thin cell wall/membrane
Accept thin cells
Accept ‘one cell thick’
2. Reduces diffusion distance/pathway;
3. Permeable;
4. Allows diffusion of oxygen/carbon dioxide;
Ignore gas exchange

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11
Q

Tidal volume is the volume of air inhaled and exhaled during a single breath when a person
is resting. The tidal volume in a person with emphysema is reduced compared with the tidal
volume in a healthy person.
Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide
between the blood and the alveoli. 3 marks

A
  1. Less carbon dioxide exhaled/moves out (of lung)
    OR
    More carbon dioxide remains (in lung);
  2. (So) reduced diffusion/concentration gradient (between blood and alveoli);
  3. Less/slower movement of carbon dioxide out of blood
    OR
    More carbon dioxide stays in blood;
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12
Q

Explain the advantage for larger animals of having a specialised system that facilitates
oxygen uptake 2 marks

A
  1. Large(r) organisms have a small(er) surface area:volume (ratio);
    OR
    Small(er) organisms have a large(r) surface area:volume (ratio);
  2. Overcomes long diffusion pathway
    OR
    Faster diffusion;
    Accept short diffusion pathway
    Accept for ‘faster’, more
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13
Q

Describe and explain the mechanism that causes lungs to fill with air.
3 marks

A

  1. Diaphragm (muscle) contracts and external intercostal muscles contract;
Ignore ribs move up and out
2. (Causes volume increase and) pressure decrease;
3. Air moves down a pressure gradient
Ignore along
OR
Air enters from higher atmospheric pressure;

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14
Q

Describe and explain the advantage of the counter-current principle in gas exchange
across a fish gill. 3 marks

A

1.   Water and blood flow in opposite directions;
2.   Maintains diffusion/concentration gradient of oxygen
Accept: converse for carbon dioxide
Accept: equilibrium not reached
OR
Oxygen concentration always higher (in water);
3.   (Diffusion) along length of lamellae/filament/gill/capillary;
Accept: all/whole of lamellae/filament//gill/capillary

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15
Q

Describe the pathway taken by an oxygen molecule from an alveolus to the blood. 2 marks

A
  1. (Across) alveolar epithelium;
  2. Endothelium / epithelium of capillary;
    Incorrect sequence = maximum of 1 mark
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16
Q

Explain how one feature of an alveolus allows efficient gas exchange to occur. 2 marks

A
  1. (The alveolar epithelium) is one cell thick;
    Reject thin membrane
  2. Creating a short diffusion pathway / reduces the diffusion distance;
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17
Q

Describe and explain the mechanism that causes forced expiration. 4 marks

A
  1. Contraction of internal intercostal muscles;
  2. Relaxation of diaphragm muscles / of external intercostal muscles;
  3. Causes decrease in volume of chest / thoracic cavity;
  4. Air pushed down pressure gradient.
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18
Q

The people in group B were recovering from an asthma attack.
Explain how an asthma attack caused the drop in the mean FEV. 4 marks

A
  1. Muscle walls of bronchi / bronchioles contract;
  2. Walls of bronchi / bronchioles secrete more mucus;
  3. Diameter of airways reduced;
  4. (Therefore) flow of air reduced.
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19
Q

Explain three ways in which an insect’s tracheal system is adapted for efficient gas
exchange. 3 marks

A
  1. Tracheoles have thin walls so short diffusion distance to cells;
  2. Highly branched / large number of tracheoles so short diffusion distance to
    cells;
  3. Highly branched / large number of tracheoles so large surface area (for gas
    exchange);
  4. Tracheae provide tubes full of air so fast diffusion (into insect tissues);
  5. Fluid in the end of the tracheoles that moves out (into tissues) during exercise
    so faster diffusion through the air to the gas exchange surface;
    OR
    Fluid in the end of the tracheoles that moves out (into tissues) during exercise
    so larger surface area (for gas exchange);
  6. Body can be moved (by muscles) to move air so maintains diffusion /
    concentration gradient for oxygen / carbon dioxide;
  7. Do not accept unqualified references to thin membranes.
    Max 2 if any reference to blood
    Ignore references to spiracles
  8. Accept ‘water’ for fluid.
    Accept ‘cells’ and ‘tissues’ as interchangeable words.
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20
Q

The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from
water.
Some other species of insect have larvae that are a similar size and shape to damselfly
larvae and also live in water. These larvae do not actively hunt prey and do not have gills.
Explain how the presence of gills adapts the damselfly to its way of life. 2 marks

A
  1. Damselfly larvae has high(er) metabolic / respiratory (rate);
  2. (So) uses more oxygen (per unit time / per unit mass);
    Idea of ‘more / high’ is needed for both mark points.
  3. Accept ‘needs’ for ‘uses’
  4. Ignore references to absorbing / obtaining / uptake of more
    oxygen
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21
Q

Name the structure through which gases enter and leave the body of an insect. 1 mark

A

Spiracles

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22
Q

Name the small tubes that carry gases directly to and from the cells of an insect. 1 mark

A

Tracheoles

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23
Q

Explain the movement of oxygen into the gas exchange system of an insect when it is at
rest. 3 marks

A
  1. Oxygen used in (aerobic) respiration;
  2. (so) oxygen (concentration) gradient (established);
    Accept description of gradient
    Ignore: ‘along gradient idea’ unless direction is made clear
    Ignore: movement through gas/water
    Reject: gradient in wrong direction
  3. (so) oxygen diffuses in; 2 and 3.
    Accept: oxygen moves down a diffusion gradient for 2 marks
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24
Q

  Describe how the structure of the insect gas exchange system:
*   provides cells with sufficient oxygen
*   limits water loss.
Explain your answers. 5 marks

A
  1. Spiracles (lead) to tracheae (that lead) to tracheoles;
  2. Open spiracles allow diffusion of oxygen from air
    OR
    Oxygen diffusion through tracheae/tracheoles;
  3. Tracheoles are highly branched so large surface area (for exchange);
  4. Tracheole (walls) thin so short diffusion distance (to cells)
    OR
    Highly branched tracheoles so short diffusion distance (to cells)
    OR
    Tracheoles push into cells so short diffusion distance;
  5. Tracheole walls are permeable to oxygen;
  6. Cuticle/chitin in tracheae impermeable so reduce water loss;
  7. Spiracles close (eg.during inactivity) preventing water loss;
    Accept 8. (Tiny) hairs around spiracles reduce evaporation
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25
Q

Describe how humans breathe in and out. 5 marks

A

Breathing in
1. Diaphragm (muscles) contract and diaphragm flattens;
Accept lungs or thorax for ‘thoracic cavity’
2. External intercostal muscles contract and ribcage pulled up/out;
3. (Causes) volume increase and pressure decrease in thoracic cavity (to below
atmospheric pressure);
Breathing out
4. Diaphragm (muscles) relaxes and internal intercostal muscles contract;
5. (Causes) volume decrease and pressure increase in thoracic cavity (to above
atmospheric pressure);
Accept labelled structures in correct position on a diagram

26
Q

Describe and explain how the countercurrent system leads to efficient gas exchange
across the gills of a fish. 3 marks

A
  1. Water and blood flow in opposite directions;
    Accept: diagram if clearly annotated
  2. Maintains concentration / diffusion gradient / equilibrium not reached / water
    always next to blood with a lower concentration of oxygen;
    Must have the idea of ‘maintaining’ or ‘always’ in reference to
    concentration / diffusion gradient
    Accept: constant concentration / diffusion gradient
  3. Along whole / length of gill / lamellae;
    Accept: gill plate / gill filament
27
Q

Amoebic gill disease (AGD) is caused by a parasite that lives on the gills of some species
of fish. The disease causes the lamellae to become thicker and to fuse together.
AGD reduces the efficiency of gas exchange in fish. Give two reasons why. 2 marks

A
  1. (Thicker lamellae so) greater / longer diffusion distance / pathway;
    Q Neutral: ‘thicker’ diffusion pathway
  2. (Lamellae fuse so) reduced surface area;
    Accept: reduced SA:VOL
28
Q

Explain two ways in which the structure of fish gills is adapted for efficient gas exchange.
2 marks

A
  1. Many lamellae / filaments so large surface area;
  2. Thin (surface) so short diffusion pathway;
    1 & 2 must each have a feature and a consequence
29
Q

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted
for efficient gas exchange. 6 marks

A
  1. Large surface area provided by lamellae / filaments increases diffusion / makes
    diffusion efficient;;
    Q Candidates are required to refer to lamellae or filaments. Do not
    penalise for confusion between two
  2. Thin epithelium / distance between water and blood;
  3. Water and blood flow in opposite directions / countercurrent;
  4. (Point 4) maintains concentration gradient (along gill) / equilibrium not reached /
    as water always next to blood with lower concentration of oxygen;
  5. Circulation replaces blood saturated with oxygen;
  6. Ventilation replaces water (as oxygen removed);
30
Q

Mackerel live in the surface waters of the sea. Toadfish live on the seabed in deep water.
The concentration of oxygen is higher in the surface waters than it is in water close to the
seabed. Suggest why. 2 marks

A

Mixing of air and water (at surface);
Air has higher concentration of oxygen than water;
Diffusion into water;
Plants / seaweeds near surface / in light;
Produce oxygen by photosynthesis;

31
Q

Describe and explain the effect of increasing carbon dioxide concentration on the
dissociation of oxyhaemoglobin. 2 marks

A

  Increases/more oxygen dissociation/unloading
OR
Deceases haemoglobin’s affinity for O 2;
Accept more readily
Accept releases more O2
2. (By) decreasing (blood) pH/increasing acidity;
Reject if reference made to active site

32
Q

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen
molecule to bind.
Explain why. 2 marks

A
  1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin;
    Ignore ref. to ‘positive cooperativity’ unqualified
    Ignore ref. to named bonds
    Accept conformational shift caused
  2. Creates / leads to / uncovers second / another binding site
    OR
    Uncovers another iron / Fe / haem group to bind to;
    Reject ref. to active site
33
Q

At birth 98% of the haemoglobin is HbF. By the age of 6 months, the HbF has usually
completely disappeared from the baby’s blood and been replaced by HbA.
Use the graph above to explain why this change is an advantage for the baby. 2 marks

A
  1. (HbA has) lower affinity for O2 at low partial pressures;
    OR
    (HbA has) lower affinity for oxygen at pp found in tissues;
  2. Easier unloading of O2 for (aerobic) respiration;
34
Q

Formula for Percentage saturation of haemoglobin with oxygen

A

(Oxygenated haemoglobin/maximum saturation) X100

35
Q

Describe the role of haemoglobin in supplying oxygen to the tissues of the body 2 marks

A

Oxyhaemoglobin formed/ haemoglobin is loaded/
uptakes/associates/binds with oxygen in area of higher ppO2 /
in gas exchange surface/lungs/gills;
Reference to “react with” = max 1
Accept: reversible interaction with oxygen
Ignore: haemoglobin is carried / contained in red blood cells
2. (oxygen) unloaded/dissociates from/relea

36
Q

In humans, substances move out of the capillaries to form tissue fluid. Describe how this
tissue fluid is returned to the circulatory system. 3 marks

A
  1. (Hydrostatic) pressure lower in capillary / blood / higher in tissues / tissue fluid;
  2. Water (returns);
  3. By osmosis;
  4. Water potential lower / more negative in blood / capillary / higher / less negative
    water potential in tissues / via water potential gradient;
  5. Due to protein (in blood);
  6. (Returns) via lymph (system / vessels);
    First marking point must be in context of between blood and tissue
    fluid.
    Neutral: References to hydrostatic pressure and water potential at
    arteriole end of capillary
37
Q

The haemoglobin in one organism may have a different chemical structure from the
haemoglobin in another organism. Describe how. 1 mark

A

Different primary structure / amino acids / different number of polypeptide chains;
Question is about haemoglobin so do not credit differences in DNA

38
Q

The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the
capillary. Explain why. 1 mark

A

Loss of water / loss of fluid / friction (against capillary lining).

39
Q

High blood pressure leads to an accumulation of tissue fluid. Explain how. 3 marks

A
  1. High blood pressure = high hydrostatic pressure;
  2. Increases outward pressure from (arterial) end of capillary / reduces inward
    pressure at (venule) end of capillary;
  3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.
    Allow lymph system not able to drain tissues fast enough
40
Q

The water potential of the blood plasma is more negative at the venule end of the capillary
than at the arteriole end of the capillary. Explain why. 3 marks

A
  1. Water has left the capillary;
  2. Proteins (in blood) too large to leave capillary;
  3. Increasing / giving higher concentration of blood proteins (and thus wp).
41
Q

Explain the role of the heart in the formation of tissue fluid. 2 marks

A
  1. Contraction of ventricle(s) produces high blood / hydrostatic
    pressure;
  2. (This) forces water (and some dissolved substances) out (of
    blood capillaries);
  3. Do not accept contraction / pumping of the heart
  4. Reject blood / plasma / tissue fluid forced out
42
Q

Lymphoedema is a swelling in the legs which may be caused by a blockage in the
lymphatic system.
Suggest how a blockage in the lymphatic system could cause lymphoedema. 1 mark

A

Excess tissue fluid cannot be (re)absorbed / builds up;
The idea of excess is important
Accept ‘drained’ for absorbed

43
Q

Give one way in which blood plasma is different from tissue fluid. 1 mark

A

More / larger proteins / less urea / carbon dioxide / more glucose / amino acids / fatty
acids / oxygen / high(hydrostatic) pressure;
Q Reference to blood cells / water potential = neutral
Q No Protein should not be credited

44
Q

The blood pressure is high at the start of the capillary. Explain how the left ventricle
causes the blood to be at high pressure. 1 mark

A
  1. Contracts;
    Q Do not accept pumping of heart / heart beating
45
Q

The blood pressure decreases along the length of the capillary. What causes this
decrease in pressure? 1 mark

A

Loss of fluid / volume;
Friction / resistance (of capillary wall);
Q Reference to a narrow lumen is not sufficient to gain a mark
unless friction or resistance is mentioned.

46
Q

In children, some diets may result in a low concentration of protein in blood plasma. This can cause the accumulation of tissue fluid. Explain the link between a low concentration of protein in blood plasma and the accumulation of tissue fluid. 3 marks

A

Water potential (in capillary) not as low / is higher / less negative / water potential
gradient is reduced;
More tissue fluid formed (at arteriole end);
Less / no water absorbed (into blood capillary) by osmosis; (into blood capillary);
Q The last two marking points must be in context of movement into
the blood capillary

47
Q

The hydrostatic pressure of the blood at the arteriole end of the capillary helps to form tissue fluid. Explain how. 2 marks

A

Hydrostatic pressure higher than osmotic “effect”;
Forces / squeezes / pushes out / water / small molecules / ions / examples;

48
Q

Describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue. 4 marks

A
  1. permeable capillary wall / membrane;
  2. single cell thick / thin walls, reduces diffusion distance;
  3. flattened (endothelial) cells, reduces diffusion distance;
  4. fenestrations, allows large molecules through;
  5. small diameter / narrow, gives a large surface area to volume / short diffusion
    distance;
  6. narrow lumen, reduces flow rate giving more time for diffusion;
  7. red blood cells in contact with wall / pass singly, gives short diffusion distance /
    more time for diffusion;
    (allow 1 mark for 2 features with no explanation)
49
Q

Explain how tissue fluid is formed and how it may be returned to the circulatory system. 6 marks

A
  1. (hydrostatic) pressure of blood high at arterial end;
  2. fluid / water / soluble molecules pass out (reject plasma);
  3. proteins / large molecules remain;
  4. this lowers the water potential / water potential becomes more negative;
  5. water moves back into venous end of capillary (reject tissue fluid) by osmosis /
    diffusion;
  6. lymph system collects any excess tissue fluid which returns to blood /
    circulatory system / link with vena cava / returns tissue fluid to vein;
50
Q

Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs.
Do not include descriptions of pressure changes in the heart or the role of heart valves in your answer. 3 marks

A
  1. Renal vein;
  2. Vena cava to right atrium;
  3. Right ventricle to pulmonary artery;
51
Q

Tissue fluid is formed from blood at the arteriole end of a capillary bed.
Explain how water from tissue fluid is returned to the circulatory system. 4 marks

A
  1. (Plasma) proteins remain;
    Accept albumin/globulins/fibrinogen for (plasma) protein
  2. (Creates) water potential gradient
    OR
    Reduces water potential (of blood);
  3. Water moves (to blood) by osmosis;
  4. Returns (to blood) by lymphatic system;
52
Q

Explain how an arteriole can reduce the blood flow into capillaries. 2 marks

A
  1. Muscle contracts;
  2. Constricts/narrows arteriole/lumen;
    Accept decreases for constricts/narrows
    Accept vasoconstriction for 1 mark
53
Q

Tick (✓) one box next to th: blood vessel carrying blood at the lowest blood pressure:
Capillary
Pulmonary vein
Renal vein
Vena cava

A

Vena Cava

54
Q

Give two safety precautions that should be followed when dissecting a heart. 1 mark

A

Accept any two suitable safety precautions for 1 mark, eg;
Use a sharp scalpel/scissors
Wash hands/wear gloves
Disinfect bench/equipment
Cover any cuts
Cut away from self/others/on a hard surface
Safe disposal
Ignore take care with scalpel/scissors or keep away from fingers
Ignore goggles

55
Q

The mass flow hypothesis is used to explain the movement of substances through phloem.
Use your understanding of the mass flow hypothesis to explain how pressure is generated inside this phloem tube. 3 marks

A
  1. Sucrose actively transported (into phloem);
  2. Lowering/reducing water potential
    OR
    More negative water potential;
  3. Water moves (into phloem) by osmosis (from xylem);
56
Q

Figure 2 shows a slice of leaf stalk with coloured water inside groups of xylem vessels.
Figure 2
Explain why coloured water moved up the stalks. 3 marks.

A

1.   Water evaporates/is transpired (from leaves/ stalk/celery/plant);
2.   Water potential gradient/lower water potential creates
tension/pulls up water
OR
Osmosis creates tension/pulls up water;
Accept negative pressure for tension
3.   Hydrogen bonds/cohesion/adhesion maintains column;

57
Q

The student used a sharp scalpel to cut the celery. Describe how she should ensure she handled the scalpel safely during this procedure. 2 marks

A

1.   Cut away from body;
Accept description of cutting technique to avoid cutting fingers
2.   Against hard/non-slip/flat surface;
Accept named hard surface eg tile/board

58
Q

Aquaporins are channel proteins that allow the diffusion of water across membranes. One type of aquaporin, called PIP1, can also transport carbon dioxide molecules across membranes.
Figure 2 shows the structure of a water molecule and of a carbon dioxide molecule. They are drawn to the same scale.
Suggest two reasons why water molecules and carbon dioxide molecules can both pass
through PIP1.

Figure 2 is just a diagram of a H20 and CO2 molecule

A
  1. Both small / similar size (so fit channel);
  2. Have a similar shape (so bind to / fit channel);
  3. Accept same height and width
    Ignore refs to polar / non-polar
  4. Accept Aquaporin complementary to oxygen(s)
59
Q

The scientists first produced transgenic poplar trees. These trees all had a length of foreign DNA inserted into them. This DNA led to the production of single-stranded RNA that specifically inhibited expression of the gene for PIP1.
The scientists then measured the difference in the amount of PIP1 in leaves of transgenic poplars and in leaves of wild type poplars without the foreign DNA. The amount of PIP1 in the transgenic poplars was approximately 15% of that in the wild type poplars.
Using this information, what can you conclude about the effect of the foreign DNA in the transgenic poplar trees? 3 marks

The transgenic poplars still produced some PIP1.
Suggest why. 1 mark

A
  1. Single-stranded RNA (has base sequence) complementary to PIP1 mRNA;
  2. Binds to mRNA (of PIP1) / leads to destruction of mRNA;
  3. Prevents / reduces translation (of PIP1);
  4. Reduces photosynthesis/named process that uses water;
  5. Less made is insufficient

Not all of mRNA bound to single-stranded RNA / there is more mRNA than interfering
RNA
OR
Not all mRNA destroyed / disabled;
Accept mutations in transgene,
Accept not all cells with transgenes

60
Q

Describe the mass flow hypothesis for the mechanism of translocation in plants. 4 marks

A
  1. In source / leaf sugars actively transported into phloem;
  2. By companion cells;
  3. Lowers water potential of sieve cell / tube and water enters by osmosis;
  4. Increase in pressure causes mass movement (towards sink / root);
  5. Sugars used / converted in root for respiration for storage.
    Accept starch

Bio Ms Thomson (8 decks)

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