unit 3 mark scheme flashcards
(60 cards)
1
Q
describe the relationship between surface area to volume ratio and metabolic rate for a smaller organism
A
smaller so larger surface area to volume ratio, more heat loss per gram, faster rate of respiration and so releases more heat
2
Q
explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake
A
larger organisms have a smaller surface area to volume ratio OR smaller organisms have a larger surface area to volume ratio, so overcomes long diffusion pathway OR faster diffusion
3
Q
plants- explain why stomata open due to increase in light intensity
A
allowing carbon dioxide to enter for photosynthesis OR for gas exchange allowing photosynthesis
4
Q
plants- describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf
A
carbon dioxide enters via stomata, stomata opened by guard cells, diffuses through air spaces, down diffusion gradient
5
Q
plants-describe & explain an advantage and disadvantage to having a higher stomatal density
A
advantage- more carbon dioxide uptake, more photosynthesis so more/faster growth disadvantage- more water lost by transpiration, less photosynthesis so slower/less growth
6
Q
plants- adaptations to desert plants
A
- Hairs so ‘trap’ water vapour and water potential
gradient decreased; - Stomata in pits/grooves so ‘trap’ water vapour and
water potential gradient decreased; - Thick (cuticle/waxy) layer so increases diffusion
distance; - Waxy layer/cuticle so reduces
evaporation/transpiration; - Rolled/folded/curled leaves so ‘trap’ water vapour and
water potential gradient decreased; - Spikes/needles so reduces surface area to volume ratio
7
Q
fish - counter-current
mechanism
A
- Water and blood flow in opposite directions;
- Blood always passing water with a higher oxygen
concentration; - Diffusion/concentration gradient (maintained) along
(length of) lamella/filament;
8
Q
fish- explain 2 ways in which the structure of fish gills is adapted for efficient gas exchange
A
- Many lamellae / filaments so large surface area;
- Thin (surface) so short diffusion pathway
9
Q
insects - Describe &
explain how the
structure of the
insect gas exchange
system:
* provides cells
with sufficient oxygen
A
- Spiracles (lead) to tracheae (that lead) to
tracheoles; - Open spiracles allow diffusion of oxygen from air
OR
Oxygen diffusion through tracheae/tracheoles; - Tracheoles are highly branched so large surface
area (for exchange); - 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; - Tracheole walls are permeable to oxygen;
10
Q
Insects - Describe &
explain how the
structure of the
insect gas exchange
system:
limits water loss.(2)
A
- Cuticle/chitin in tracheae impermeable so reduce
water loss; - Spiracles close (e.g. during inactivity) preventing
water loss;
11
Q
Insects - Abdominal
Pumping (3)
A
- Abdominal pumping/pressure in tubes linked to
carbon dioxide release; - (Abdominal) pumping raises pressure in body;
- Air/carbon dioxide pushed out of body /air/carbon
dioxide moves down pressure gradient (to atmosphere)
12
Q
Insects -
Explain three ways
in which an insect’s
tracheal system is
adapted for efficient
gas exchange.
A
- Tracheoles have thin walls so short diffusion
distance to cells; - Highly branched / large number of
tracheoles so short diffusion distance to cells; - Highly branched / large number of
tracheoles so large surface area (for gas exchange); - Tracheae provide tubes full of air so fast diffusion
(into insect tissues); - 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); - Body can be moved (by muscles) to move
air so maintains diffusion / concentration gradient for
oxygen / carbon dioxide;
13
Q
Lungs - Describe and
explain one feature
of the alveolar
epithelium that
makes the epithelium well adapted as a
surface for gas
exchange.
A
- Flattened cells
OR
Single layer of cells; - Reduces diffusion distance/pathway;
- Permeable;
- Allows diffusion of oxygen/carbon dioxide;
- moist
- Increase rate of diffusion
14
Q
Lungs – describe and
explain inhaling (4)
A
- Diaphragm (muscle) contracts and external
intercostal muscles contract;
Ignore ribs move up and out - (Causes volume increase and) pressure decrease;
- Air moves down a pressure gradient
Ignore along
OR
Air enters from higher atmospheric pressure
15
Q
Lungs - Describe the
pathway taken by an
oxygen molecule
from an alveolus to the blood
A
- (Across) alveolar epithelium;
- Endothelium of capillary;
16
Q
Lungs - Explain
how one feature of
an alveolus allows
efficient gas
exchange to occur
A
- (The alveolar epithelium) is one cell thick;
Reject thin membrane - Creating a short diffusion pathway / reduces the
diffusion distance;
17
Q
Lungs – Describe how
we breathe in and
out.(4)
A
- Breathing in – diaphragm
contracts and external intercostal muscles contract; - (Causes) volume increase and pressure decrease
in thoracic cavity (to below atmospheric, resulting in air
moving in);
For thoracic cavity accept ‘lungs’ or ‘thorax’.
Reference to ‘thoracic cavity’ only required once. - Breathing out - Diaphragm
relaxes and internal intercostal muscles contract;
Accept diaphragm relaxes and (external) intercostal
muscles relax and lung tissue elastic (so recoils). - (Causes) volume decrease and pressure increase
in thoracic cavity (to above atmospheric, resulting in air
moving out);
18
Q
digestion – Proteins involved in
(4)
A
- Hydrolysis of peptide bonds;
- Endopeptidases break polypeptides into smaller
peptide chains; - Exopeptidases remove terminal amino acids;
- Dipeptidases hydrolyse/break down dipeptides into
amino acids
19
Q
compare endopeptidases and exopeptidases
A
- Endopeptidases hydrolyse internal (peptide bonds) 2. Exopeptidases remove amino acids/hydrolyse
(bonds) at end(s); - More ends or increase in surface area (for
exopeptidases);
20
Q
Digestion - Describe
the action of
membrane-bound
dipeptidases and
explain their
importance.(2)
A
- Hydrolyse (peptide bonds) to release amino acids;
- Amino acids can cross (cell) membrane by facilitated
diffusion;
OR
Maintain concentration gradient of amino acids for
absorption
21
Q
Digestion – Describe
the complete
digestion of starch
by a mammal.
A
- Hydrolysis;
- (Of) glycosidic bonds;
- (Starch) to maltose by amylase;
- (Maltose) to glucose by disaccharidase/maltase;
- Disaccharidase/maltase membrane-bound;
22
Q
Digestion - Function of
bile salts and micelles
(3)
A
- (Bile salts emulsify lipids forming) droplets which
increase surface areas (for lipase / enzyme action); - (So) faster hydrolysis / digestion (of triglycerides /
lipids); - Micelles carry fatty acids and glycerol /
monoglycerides to / through membrane / to (intestinal
epithelial) cell;
23
Q
Digestion – describe
lipid digestion (3)
A
- lipase hydrolyses triglycerides
- ester bonds
- Form monoglycerides and fatty acids
24
Q
Digestion – Explain
the advantages of
emulsification and
micelle formation.
(2)
A
- Droplets increase surface areas (for lipase /
enzyme action); - (So) faster hydrolysis / digestion (of triglycerides /
lipids); - Micelles carry fatty acids and glycerol /
monoglycerides to / through membrane / to (intestinal
epithelial) cell;
25
Absorption -
Describe and
explain two features
you would expect to
find in a cell
specialised for
absorption. (4)
1. Folded membrane/microvilli so large surface area
(for absorption);
Reject references to ‘villi’.
Accept ‘brush border’ for ‘microvilli’.
2. Large number of co-transport/carrier/channel
proteins so fast rate (of absorption)
OR
Large number of co-transport/carrier proteins for active
transport
OR
Large number of co-transport/carrier/channel
proteins for facilitated diffusion;
3. Large number of mitochondria so make (more)
ATP (by respiration)
OR
Large number of mitochondria for aerobic respiration
OR
Large number of mitochondria to release energy for
active transport;
4. Membrane-bound (digestive)
enzymes so maintains concentration gradient (for fast
absorption);
26
Absorption - Describe
the processes
involved in the
absorption and
transport of digested
lipid molecules from
the ileum into lymph
vessels. (4)
1. Micelles contain bile salts and fatty
acids/monoglycerides;
2. Make fatty acids/monoglycerides (more) soluble (in
water)
OR
Bring/release/carry fatty acids/monoglycerides to cell/lining
(of the iluem)
OR
Maintain high(er) concentration of fatty
acids/monoglycerides to cell/lining (of the ileum);
3. Fatty acids/monoglycerides absorbed by simple
diffusion;
4. Triglycerides (re)formed (in cells);
Accept chylomicrons form
5. Vesicles move to cell membrane;
27
Absorption - Describe
the role of micelles
in the absorption of
fats into the cells
lining the ileum (2)
1. Micelles include bile salts and fatty acids;
Ignore other correct components of micelles.
2. Make the fatty acids (more) soluble in water;
For 'fatty acids' accept fats / lipids.
3. Bring/release/carry fatty acids to cell/lining (of the
ileum);
For ‘fatty acids’ accept fats/lipids.
4. Maintain high(er) concentration of fatty acids to
cell/lining (of the ileum);
5. Fatty acids (absorbed) by diffusion;
28
Absorption - how is
the golgi apparatus
involved in the
absorption of
lipids.(3)
1. Modifies / processes triglycerides;
2. Combines triglycerides with proteins;
3. Packaged for release / exocytosis
OR
Forms vesicles;
29
Absorption – Explain
how
monosaccharides
and amino acids are
absorbed into the
blood (5)
1. Some by facilitated diffusion (when higher
concentration in lumen)
2. Sodium ions actively transported from ileum cell to blood;
3. Maintains / forms diffusion / concentration gradient for
sodium to enter cells from gut (and with it, glucose);
4. sodium ions enter cell by facilitated diffusion and bring
with it a molecule of glucose by co-transport;
5. Facilitated diffusion of glucose into blood/capillary;
30
Haemoglobin -
Binding of one
molecule of oxygen
to haemoglobin
makes it easier for a
second oxygen
molecule to bind. Explain why. (2)
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;
31
Haemoglobin -
Explain how
changes in the
shape of
haemoglobin result
in the S-shaped
(sigmoid)
oxyhaemoglobin
dissociation curve
(2)
1. First oxygen binds (to Hb) causing change in shape;
2. (Shape change of Hb) allows more O2 to bind (easily)
/ greater saturation with O2
OR
Cooperative binding
32
Haemoglobin -
Haemoglobin is a
protein with a
quaternary structure.
Explain the meaning
of quaternary
structure (1).
(Molecule contains) more than one polypeptide (chain)
33
Haemoglobin -
Describe the
advantage of the
Bohr effect during
intense exercise. (2)
1. Increases dissociation of oxygen;
Accept unloading/ release/reduced affinity for
dissociation
2. For aerobic respiration at the tissues/muscles/cells
OR
Anaerobic respiration delayed at the
tissues/muscles/cells
OR
Less lactate at the tissues/muscles/cells
34
Haemoglobin -
Describe and
explain the effect of
increasing carbon
dioxide
concentration on the
dissociation of
oxyhaemoglobin. (2)
1. Increases/more oxygen dissociation/unloading
OR
Deceases haemoglobin’s affinity for O2;
Accept more readily
Accept releases more O2
2. (By) decreasing (blood) pH/increasing acidity;
35
Haemoglobin – why
curve shifts left when
diving (2)
1. High(er) affinity for O2 (than haemoglobin)
OR
Dissociates oxygen less readily
OR
Associates more readily;
Accept holds O2 at lower ppO2
2. Allows (aerobic) respiration when diving/at low(er)
pO2
OR
Provides oxygen when haemoglobin unloaded
OR
Delays anaerobic respiration/lactate production
36
Haemoglobin –
Animals living at high altitudes shift to
left (3)
1. high altitudes have a low partial pressure of O2; 2. high saturation/affinity of Hb with O2 (at low partial
pressure O2);
3. sufficient/enough O2 supplied to respiring cells /
tissues;
37
Haemoglobin – why
small animals have
curved to the right (2)
1. Mouse haemoglobin/Hb has a lower affinity for
oxygen
OR
For the same pO2 the mouse haemoglobin/Hb is less
saturated
OR
At oxygen concentrations found in tissue
mouse haemoglobin/Hb is less saturated;
For ‘Hb is less saturated’ accept ‘less oxygen will be
bound to Hb’.
2. More oxygen can be
dissociated/released/unloaded (for metabolic
reactions/respiration);
Accept ‘oxygen
dissociated/released/unloaded more readily/easily/quickly
38
Haemoglobin – why
curve to the right for
more active animals
(2)
1. Curve to the right so lower affinity / % saturation
(of haemoglobin);
2. Haemoglobin unloads / dissociates more readily;
3. More oxygen to cells / tissues / muscles;
4. For greater / more / faster respiration
39
Heart & circulation –
dissection -
three control
measures the
student must use to
reduce the risks
associated with
carrying and using a
scalpel
1. Carry with blade protected / in tray
2. Cut away from body;
3. Cut onto hard surface;
4. Use sharp blade;
5. Dispose of used scalpel (blade) as instructed
40
Heart & circulation –
dissection. Control
measures when
packing away (2)
1. Carry/wash sharp instruments by holding handle
OR
Carry/wash sharp instruments by pointing away (from
body)/down;
Accept for ‘instruments’, a suitable named example, eg.
scalpel
2. Disinfect instruments/surfaces;
Accept for ‘instruments’, a suitable named example, eg.
scalpel
Accept for ‘disinfect’, sanitise OR use antiseptic
3. Disinfect hands
OR
Wash hands with soap (and water);
Accept for ‘disinfect’, sanitise OR use antiseptic
4. Put organ/gloves/paper towels in a (separate)
bag/bin/tray to dispose;
41
Heart & circulation -
Give the pathway a
red blood cell takes
when travelling in
the human
circulatory system
from a kidney to the
lungs. (3)
1. Renal vein;
2. Vena cava to right atrium;
3. Right ventricle to pulmonary artery;
42
Heart & circulation -
Name the blood
vessels that carry
blood to the
heart muscle. (1)
Coronary arteries
43
Heart & circulation -
Calculate Cardiac
Output (1)
Cardiac Output = Stroke Volume x Heart Rate
44
Heart & circulation –
what causes the semi-lunar valve to close (1)
Because pressure in aorta higher than in ventricle;
45
Heart & circulation –
explain how the
atrioventricular valve
is closed (2)
1. ventricle contracts and volume decreases
2. pressure (ventricle) increases so higher than pressure
of left atrium;
46
Heart & circulation -
Explain how an
arteriole can reduce
the blood flow into
capillaries. (2)
1. Muscle contracts;
2. Constricts/narrows arteriole/lumen;
47
Heart & circulation -
Artery – Structure and
Function (5)
1. Elastic tissue to allow stretching/recoil/ smooths out
flow of blood/maintains pressure;
2. (Elastic tissue) stretches when ventricles contract OR
Recoils when ventricle relaxes;
3. Muscle for contraction/vasoconstriction;
4. Thick wall withstands pressure OR stop bursting;
5. Smooth endothelium reduces friction;
48
Heart & circulation -
Explain four ways in
which the structure
of the aorta is
related to its
function.
1. Elastic tissue to allow stretching / recoil /
smoothes out flow of blood / maintains pressure;
2. (Elastic tissue) stretches when ventricles contract
OR
Recoils when ventricle relaxes;
3. Muscle for contraction / vasoconstriction;
4. Thick wall withstands pressure OR stop bursting;
5. Smooth endothelium reduces friction;
6. Aortic valve / semi-lunar valve prevents backflow
49
Heart & circulation
Fish – describe type of
circulation in fish (1)
1. Single circulatory system
2 chambers/1 ventricle1 atrium
3. One vein carrying blood towards the heart/ One artery
carrying blood away
50
Tissue fluid - Explain
how water from
tissue fluid is returned to the circulatory system.
(4)
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;
51
Tissue fluid - Explain
the role of the heart
in the formation of
tissue fluid. (2)
1. Contraction of ventricle(s) produces high blood /
hydrostatic pressure;
2. (This) forces water (and some dissolved
substances) out (of blood capillaries)
52
Tissue fluid - High
absorption of salt
from the diet can
result in a higher
than normal
concentration of salt
in the blood plasma
entering capillaries.
This can lead to a
build-up of tissue
fluid.
Explain how. (4)
1. (Higher salt) results in lower water potential of
tissue fluid;
2. (So) less water returns to capillary by osmosis (at
venule end);
OR
3. (Higher salt) results in higher blood pressure /
volume;
4. (So) more fluid pushed / forced out (at arteriole
end) of capillary;
53
Tissue fluid - High
blood pressure
leads to an
accumulation of
tissue fluid. Explain
how. (2)
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.
54
Tissue fluid -
Formation and
reabsorption (8)
1. At arteriole end high hydrostatic pressure/blood
pressure;
2. Hydrostatic pressure higher than effect of osmosis;
3. Small molecules/named example eg glucose; water
4. Forces out;
5. Proteins remain in blood/ not removed as they are too
large to leave capillary;
6. Increasing/giving higher concentration of blood
proteins so proteins lower water potential of blood;
7. Water/fluid moves back into blood;
8. Water moves by osmosis
55
Water - Describe the
cohesion-tension
theory of water
transport in the
xylem. (5)
1. Water lost from leaf because of transpiration /
evaporation of water (molecules) / diffusion from
mesophyll / leaf cells;
OR
Transpiration / evaporation / diffusion of water
(molecules) through stomata / from leaves;
2. Lowers water potential of mesophyll / leaf cells;
3. Water pulled up xylem (creating tension);
4. Water molecules cohere / ‘stick’ together by
hydrogen bonds;
5. (forming continuous) water column;
6. Adhesion of water (molecules) to walls of xylem;
56
Water - A
potometer measures
the rate of water
uptake rather than
the rate of
transpiration.
Give two reasons
why the potometer
does not truly
measure the rate of
transpiration.
(2)
1. Water used for support / turgidity;
Accept: water used in (the cell’s) hydrolysis or
condensation (reactions) for one mark. Allow a named
example of these reactions
2. Water used in photosynthesis;
3. Water produced in respiration;
4. Apparatus not sealed / ‘leaks’;
57
Water -
Give two precaution
s the students
should have taken
when setting up the
potometer to obtain
reliable
measurements of
water uptake by the
plant shoot. (2)
1. Seal joints / ensure airtight / ensure watertight;
Answer must refer to precautions when setting up the
apparatus
Ignore: references to keeping other factors constant
2. Cut shoot under water;
3. Cut shoot at a slant;
4. Dry off leaves;
5. Insert into apparatus under water;
6. Ensure no air bubbles are present;
7. Shut tap;
8. Note where bubble is at start / move bubble to the
start position;
58
Sucrose - Describe
the transport of
carbohydrate in
plants. (5)
1. (At source) sucrose is transported into the
phloem/sieve element/tube;
2. By active transport
OR
By co-transport with H+
;
Accept co-transport with hydrogen/H ions
3. By companion/transfer cells;
4. Lowers water potential in phloem and water enters
by osmosis;
Accept pressure gradient?
For ‘phloem’ accept ‘sieve element/tube’.
5. (Produces) high (hydrostatic) pressure;
6. Mass flow;
7. Transport from site of photosynthesis to respiring
cells
OR
Transport from site of photosynthesis to storage organ
OR
Transport from storage organ to respiring cells;
59
Sucrose - Use your
understanding of the
mass flow
hypothesis to
explain how
pressure is generated inside this phloem tube. (3)
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);
60
Sucrose - Phloem
pressure is reduced
during the hottest
part of the day. Use
your understanding
of transpiration and
mass flow to explain
why.(3)
1. High (rate of) transpiration/evaporation;
2. Water lost through stomata
OR
(High) tension in xylem;
3. (Causes) less water movement from xylem to
phloem
OR
Insufficient water potential in phloem to draw water from
xylem
