unit 3 Exchange Of Substances Flashcards
The relationship between surface
area to volume ratio and metabolic
rate for a smaller organism
- (Smaller so) larger surface area to volume ratio;
- More heat loss (per gram)
- Faster rate of respiration, releases more heat
Explain the advantage for larger
animals of having a specialised system
that facilitates oxygen uptake
- Large(r) organisms have a small(er) surface area:volume (ratio);
OR
Small(er) organisms have a large(r) surface area:volume (ratio); - Overcomes long diffusion pathway
OR
Faster diffusion
Plants – explain why stomata open due to
increase in light intensity (1)
allowing carbon dioxide to enter for photosynthesis;
Or
for gas exchange allowing photosynthesis
Plants -Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf (4)
- (Carbon dioxide enters) via stomata; Reject stroma
- (Stomata opened by) guard cells;
- Diffuses through air spaces;
- Down diffusion gradient;
Plants – describe & explain an advantage
and disadvantage to having a higher stomatal density
Advantage
1. More carbon dioxide uptake;
2. More photosynthesis so faster/more growth;
Disadvantage
3. More water loss/transpiration
Accept plant wilts for ‘more water loss’
4. Less photosynthesis so slower/less growth;
Plants - Adaptations to desert plants (6)
- 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; - Spines/needles so reduces surface area to volume ratio;
fish - counter-current mechanism (3)
- 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;
Fish -Explain two ways in which the structure of fish gills is adapted for efficient gas exchange.(2)
- Many lamellae / filaments so large surface area;
- Thin (surface) so short diffusion pathway;
Insects - Describe & explain how the
structure of the insect gas exchange
system:
• provides cells with sufficient oxygen
- 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;
Insects - Describe & explain how the
structure of the insect gas exchange
system:
• limits water loss.(2)
- Cuticle/chitin in tracheae impermeable so reduce water loss;
- Spiracles close (eg.during inactivity) preventing water loss;
Insects - Abdominal Pumping (3)
- 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)
Insects -Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.
- 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;
Lungs - Describe and explain one feature
of the alveolar epithelium that makes the
epithelium wall adapted as a surface for gas exchange.
Mark in pairs
1. Flattened cells
OR
Single layer of cells;
Reject thin cell wall/membrane
Accept thin cells
Accept ‘one cell thick’
- Reduces diffusion distance/pathway;
- Permeable;
- Allows diffusion of oxygen/carbon dioxide;
- moist
- Increase rate of diffusion
Lungs – describe and explain inhaling (4)
- 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;
Lungs - Describe the pathway taken by an
oxygen molecule from an alveolus to
the blood. (2)
- (Across) alveolar epithelium;
- Endothelium of capillary;
Lungs - Explain how one feature of
an alveolus allows efficient gas exchange to occur.
- (The alveolar epithelium) is one cell thick;
Reject thin membrane - Creating a short diffusion pathway / reduces the diffusion distance;
Lungs - Describe the gross structure of
the human gas exchange system (1)
- Named structures – trachea, bronchi, bronchioles, alveoli;
Lungs – Describe how we breathe in and
out. (4)
- 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);
Digestion – Proteins (4)
- Hydrolysis of peptide bonds;
- Endopeptidases break polypeptides into smaller peptide chains;
- Exopeptidases remove terminal amino acids;
- Dipeptidases hydrolyse/break down dipeptides into amino acids;
Digestion – Compare endopeptidase and
exopeptidase (3)
- Endopeptidases hydrolyse internal (peptide bonds); endopeptidase and
exopeptidase - Exopeptidases remove amino acids/hydrolyse (bonds) at end(s);
- More ends or increase in surface area (for exopeptidases);
Digestion - Describe the action of
membrane-bound dipeptidases and
explain their importance.(2)
- 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;
Digestion – Describe the complete
digestion of starch by a mammal.
- Hydrolysis;
- (Of) glycosidic bonds;
- (Starch) to maltose by amylase;
- (Maltose) to glucose by disaccharidase/maltase
- Disaccharidase/maltase membrane-bound;
Digestion - Function of bile salts and micelles (3)
- (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;
Digestion – describe lipid digestion (3)
- lipase hydrolyses triglycerides
- ester bonds
- Form monoglycerides and fatty acids
Digestion – Explain the advantages of
emmulsification and micelle formation.
(2)
- 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;
Digestion – Explain the advantages of
emmulsification and micelle formation.
(2)
. 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;
Absorption -Describe and explain two features you would expect to find in a cell
specialised for absorption. (4)
- Folded membrane/microvilli so large surface area (for absorption);
Reject references to ‘villi’.
Accept ‘brush border’ for ‘microvilli’. - 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; - 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; - Membrane-bound (digestive)
enzymes so maintains concentration gradient (for fast absorption);
Absorption - Describe the processes
involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. (4)
- Micelles contain bile salts and fatty
acids/monoglycerides; - 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); - Fatty acids/monoglycerides absorbed by simple diffusion;
- Triglycerides (re)formed (in cells);
Accept chylomicrons form - Vesicles move to cell membrane;
Absorption - Describe the role of micelles
in the absorption of fats into the cells
lining the ileum (2)
- Micelles include bile salts and fatty acids;
Ignore other correct components of micelles. - Make the fatty acids (more) soluble in water;
For ‘fatty acids’ accept fats / lipids. - Bring/release/carry fatty acids to cell/lining (of the ileum);
For ‘fatty acids’ accept fats/lipids. - Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
- Fatty acids (absorbed) by diffusion;
Absorption - how is the golgi apparatus
involved in the absorption of lipids.(3)
- Modifies / processes triglycerides;
- Combines triglycerides with proteins;
- Packaged for release / exocytosis
OR
Forms vesicles;
Absorption – Explain how monosaccharides and amino acids are
absorbed into the blood (5)
- Some by facilitated diffusion (when higher concentration in lumen)
- Sodium ions actively transported from ileum cell to blood;
- Maintains / forms diffusion / concentration gradient for sodium to enter cells from gut (and with it, glucose);
- sodium ions enter cell by facilitated diffusion and bring with it a molecule of glucose by co-transport;
- Facilitated diffusion of glucose into blood/capillary;
Haemoglobin - Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.
Explain why. (2)
- 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 - Creates / leads to / uncovers second / another binding site
OR
Uncovers another iron / Fe / haem group to bind to
Haemoglobin -Explain how changes in the
shape of haemoglobin result in the S-shaped (sigmoid) oxyhaemoglobin
dissociation curve (2)
- First oxygen binds (to Hb) causing change in shape;
- (Shape change of Hb) allows more O2 to bind (easily) / greater saturation with O2
OR
Cooperative binding;
Haemoglobin -Haemoglobin is a
protein with a quaternary structure.
Explain the meaning of quaternary
structure (1).
(Molecule contains) more than one polypeptide (chain)
Haemoglobin -Describe the
advantage of the Bohr effect during
intense exercise. (2)
- Increases dissociation of oxygen;
Accept unloading/ release/reduced affinity for dissociation - 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;
Haemoglobin -Describe and explain the effect of increasing carbon dioxide
concentration on the dissociation of
oxyhaemoglobin. (2)
- Increases/more oxygen dissociation/unloading
OR
Deceases haemoglobin’s affinity for O2;
Accept more readily
Accept releases more O2 - (By) decreasing (blood) pH/increasing acidity;
Haemoglobin – why curve shifts left when
diving (2)
- High(er) affinity for O2 (than haemoglobin)
OR
Dissociates oxygen less readily
OR
Associates more readily;
Accept holds O2 at lower ppO2 - Allows (aerobic) respiration when diving/at low(er) pO2
OR
Provides oxygen when haemoglobin unloaded
OR
Delays anaerobic respiration/lactate production;
Haemoglobin –Animals living at high altitudes shift to left (3)
- high altitudes have a low partial pressure of O2;
- high saturation/affinity of Hb with O2 (at low partial pressure O2);
- sufficient/enough O2 supplied to respiring cells / tissues;
Haemoglobin – why small animals have
curved to the right (2)
- Curve to the right so lower affinity / % saturation (of haemoglobin);
- Haemoglobin unloads / dissociates more readily;
- More oxygen to cells / tissues / muscles;
- For greater / more / faster respiration;
Haemoglobin – why curve to the right for
more active animals (2)
- Curve to the right so lower affinity / % saturation (of haemoglobin);
- Haemoglobin unloads / dissociates more readily;
- More oxygen to cells / tissues / muscles;
- For greater / more / faster respiration;
Heart & circulation –dissection -three control measures the student must use to
reduce the risks associated with carrying and using a scalpel.
- Carry with blade protected / in tray
- Cut away from body;
- Cut onto hard surface;
- Use sharp blade;
- Dispose of used scalpel (blade) as instructed;
Heart & circulation –dissection. Control
measures when packing away (2)
- 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 - Disinfect instruments/surfaces;
Accept for ‘instruments’, a suitable named example, eg. scalpel
Accept for ‘disinfect’, sanitise OR use antiseptic - Disinfect hands
OR
Wash hands with soap (and water);
Accept for ‘disinfect’, sanitise OR use antiseptic - Put organ/gloves/paper towels in a (separate) bag/bin/tray to dispose;
Heart & circulation -Give the pathway a
red blood cell takes when travelling in
the human circulatory system from a kidney to the lungs. (3)
- Renal vein;
- Vena cava to right atrium;
- Right ventricle to pulmonary artery;
Heart & circulation - Name the blood
vessels that carry blood to the heart muscle. (1)
Coronary arteries;
Heart & circulation -Calculate Cardiac
Output (1)
Cardiac Output = Stroke Volume x Heart Rate
Heart & circulation – what causes the semilunar valve to close (1)
Because pressure in aorta higher than in ventricle;
Heart & circulation –explain how the
atrioventricular valve is closed (2)
- ventricle contracts and volume decreases
- pressure (ventricle) increases so higher than pressure of left atrium;
Heart & circulation - Explain how an
arteriole can reduce the blood flow into
capillaries. (2)
- Muscle contracts;
- Constricts/narrows arteriole/lumen;
Heart & circulation -Artery – Structure and
Function (5)
- Elastic tissue to allow stretching/recoil/ smooths out flow of blood/maintains pressure;
- (Elastic tissue) stretches when ventricles contract
OR
Recoils when ventricle relaxes; - Muscle for contraction/vasoconstriction;
- Thick wall withstands pressure OR stop bursting;
- Smooth endothelium reduces friction;
Heart & circulation - Explain four ways in
which the structure of the aorta is related to its function.
- Elastic tissue to allow stretching / recoil / smoothes out flow of blood / maintains pressure;
- (Elastic tissue) stretches when ventricles contract
OR
Recoils when ventricle relaxes; - Muscle for contraction / vasoconstriction;
- Thick wall withstands pressure OR stop bursting;
- Smooth endothelium reduces friction;
- Aortic valve / semi-lunar valve prevents backflow.
Heart & circulation Fish – describe type of
circulation in fish (1)
- Single circulatory system
2 chambers/1 ventricle1 atrium - One vein carrying blood towards the heart/ One artery carrying blood away
Tissue fluid - Explain how water from
tissue fluid is returned to the circulatory system. (4)
- (Plasma) proteins remain;
Accept albumin/globulins/fibrinogen for (plasma) protein - (Creates) water potential gradient
OR
Reduces water potential (of blood); - Water moves (to blood) by osmosis;
- Returns (to blood) by lymphatic system;
Tissue fluid - Explain the role of the heart
in the formation of tissue fluid. (2)
- Contraction of ventricle(s) produces high blood / hydrostatic pressure;
- (This) forces water (and some dissolved
substances) out (of blood capillaries);
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)
- (Higher salt) results in lower water potential of tissue fluid;
- (So) less water returns to capillary by osmosis (at venule end);
OR - (Higher salt) results in higher blood pressure / volume;
- (So) more fluid pushed / forced out (at arteriole end) of capillary;
Tissue fluid - High blood pressure
leads to an accumulation of tissue fluid. Explain how. (2)
- High blood pressure = high hydrostatic pressure;
- Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary;
- (So) more tissue fluid formed / less tissue fluid is reabsorbed.
Tissue fluid -Formation and reabsorption (8)
- At arteriole end high hydrostatic pressure/blood pressure;
- Hydrostatic pressure higher than effect of osmosis;
- Small molecules/named example eg glucose; water
- Forces out;
- Proteins remain in blood/ not removed as they are too large to leave capillary;
- Increasing/giving higher concentration of blood proteins so proteins lower water potential of blood;
- Water/fluid moves back into blood;
- Water moves by osmosis
Water - Describe the cohesion-tension
theory of water transport in the xylem. (5)
- 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; - Lowers water potential of mesophyll / leaf cells;
- Water pulled up xylem (creating tension);
- Water molecules cohere / ‘stick’ together by hydrogen bonds;
- (forming continuous) water column;
- Adhesion of water (molecules) to walls of xylem
Water - T 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)
- 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 - Water used in photosynthesis;
- Water produced in respiration;
- Apparatus not sealed / ‘leaks’;
Water - Give two precautions the students
should have taken when setting up the
potometer to obtain reliable measurements of water uptake by the
plant shoot. (2)
- Seal joints / ensure airtight / ensure watertight;
Answer must refer to precautions when setting up the apparatus
Ignore: references to keeping other factors constant - Cut shoot under water;
- Cut shoot at a slant;
- Dry off leaves;
- Insert into apparatus under water;
- Ensure no air bubbles are present;
- Shut tap;
- Note where bubble is at start / move bubble to the start position;
Sucrose - Describe the transport of
carbohydrate in plants. (5)
- (At source) sucrose is transported into the phloem/sieve element/tube;
- By active transport
OR
By co-transport with H+;
Accept co-transport with hydrogen/H ions - By companion/transfer cells;
- Lowers water potential in phloem and water enters by osmosis;
Accept pressure gradient
For ‘phloem’ accept ‘sieve element/tube’. - (Produces) high (hydrostatic) pressure;
- Mass flow;
- 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;
Sucrose - Use your understanding of the
mass flow hypothesis to explain how
pressure is generated inside this phloem tube. (3)
- Sucrose actively transported (into phloem);
- Lowering/reducing water potential
OR
More negative water potential; - Water moves (into phloem) by osmosis (from xylem);
Sucrose - Phloem pressure is reduced
during the hottest part of the day. Use
your understanding of transpiration and
mass flow to explain why. (3)
- High (rate of) transpiration/evaporation;
- Water lost through stomata
OR
(High) tension in xylem; - (Causes) less water movement from xylem to phloem
OR
Insufficient water potential in phloem to draw water from xylem;
