Unit 3 - Exchanging 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.
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
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;
Insects - Describe & explain how the structure of the insect gas exchange system:
* provides cells with sufficient oxygen
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;
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 well 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’
2. Reduces diffusion distance/pathway;
3. Permeable;
4. Allows diffusion of oxygen/carbon dioxide;
5. moist
6. 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 – How are proteins digested? (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);
- 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. (5)
- 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 emulsification 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;
