Author: Philip Colls
Document comments: Created by the \'abHTML to RTF .Net\'bb 5.8.2.9

Gas exchange Booklet revision questions      NAME:
Q1. (a)     Describe the pathway taken by an oxygen molecule from an alveolus to the blood.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________ (2)
(b)     Explain how one feature of an alveolus allows efficient gas exchange to occur.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________ (2)
Carbon monoxide is a poisonous gas that is present in cigarette smoke. This carbon monoxide can be absorbed into the blood where it binds with haemoglobin. Scientists investigated the concentration of carbon monoxide in cars in which people were smoking or not smoking. They measured the concentration with the car windows open and closed. The graph shows the scientists’ results as they presented them. A value of ± 2 standard deviations from the mean includes over 95% of the data.

(c)     In England, in October 2015, a law was introduced making it illegal to smoke in a car carrying someone who is under the age of 18. Following the introduction of the law, a politician stated:
‘It is dangerous to smoke when a child is in the car. Higher levels of deadly toxins can build up, even on short journeys, and children breathe faster than adults, meaning they inhale more of the deadly toxins.’
Use the information provided and the data in the graph to evaluate the politician’s statements.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
____________________________________________________ (4) (Total 8 marks)
Q2.
(a)     Explain two ways in which the structure of fish gills is adapted for efficient gas exchange.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
(2)

(b)     Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(Total 5 marks)
Q3.
Figure 1 shows the stages of development of an insect called a damselfly.

(a)     The adult damselfly uses a tracheal system for gas exchange. Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.
1. _________________________________________________________________
___________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
___________________________________________________________________
3. _________________________________________________________________
___________________________________________________________________
________________________________________________________________(3)
(b)     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)
(c)     A scientist measured the size of each gill lamella of the gills of 40 damselfly larvae.
His results are shown in the table.

Mean width / mm
(± uncertainty / mm)

1.61
(± 0.19)

Mean width / mm
(± uncertainty / mm)

6.12
(± 0.41)

Calculate the mean surface area of one side of one gill lamella. Assume that a gill lamella is rectangular and give your answer to an appropriate number of significant figures. Include the percentage error (uncertainty) of surface area in your answer. Show your working.

Mean surface area = ____________________
Percentage error (uncertainty) of surface area = ____________________
(3)
(d)     A student used an optical microscope to observe part of a damselfly larva gill.
Figure 2 shows the drawing the student produced.
 
Suggest two ways the student could improve the quality of her scientific drawing of this gill.
1. _________________________________________________________________
___________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
____________________________________________________(2) (Total 10 marks)
Q4. Breathing out as hard as you can is called forced expiration.
(a)     Describe and explain the mechanism that causes forced expiration.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________(4)
Two groups of people volunteered to take part in an experiment.
•        People in group A were healthy.
•        People in group B were recovering from an asthma attack.
Each person breathed in as deeply as they could. They then breathed out by forced expiration.
A scientist measured the volume of air breathed out during forced expiration by each person.
The graph below shows the results.
                         
Time breathing out / s
(b)     Forced expiration volume (FEV) is the volume of air a person can breathe out in1 second. Using data from the first second of forced expiration, calculate the percentage decrease in the FEV for group B compared with group A.

 							Answer = ____________________ %
(1)
(c)     The people in group B were recovering from an asthma attack.
Explain how an asthma attack caused the drop in the mean FEV shown in the figure above.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(4)
(Total 9 marks)
Q5.
(a)     Describe the gross structure of the human gas exchange system and how we breathe in and out.

(6)
(b)     Mucus produced by epithelial cells in the human gas exchange system contains triglycerides and phospholipids.
Compare and contrast the structure and properties of triglycerides and phospholipids.

(5)
(c)     Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached.
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.

(4)
(Total 15 marks)
Q6.
Scientists studied three species of plant.
They selected fully grown leaves from five different plants of each species.
For each leaf they measured:
•        leaf surface area
•        leaf thickness
•        the number of stomata per mm^2.
The scientists’ results are shown in the table below.

Plant species

Mean leaf surface area
/ mm^2

Mean leaf thickness
/ µm

Mean number of
stomata per mm^2

A | 218.0 | 191.5 | 380.0
B | 17.0 | 296.3 | 136.0
C | 2.2 | 354.8 | 419.0
(a)     How did the scientists ensure they could make a valid comparison between leaves from different species?
___________________________________________________________________
___________________________________________________________________
(1)
(b)     Describe a method you could use to find the surface area of a leaf.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
 (3)
(c)     (i)      Which species, A or B, would you predict grew in a drier environment?
Explain one feature that caused you to choose this species.
Species _______________________________________________________
Explanation ____________________________________________________
______________________________________________________________
____________________________________________________________(1)
(ii)     Other than the features of leaves in the table above, give two features of leaves of xerophytes.
For each feature explain how it reduces water loss.
Feature 1 ______________________________________________________
Explanation ____________________________________________________
______________________________________________________________
Feature 2 ______________________________________________________
Explanation ____________________________________________________
______________________________________________________________
(2)
(d)     Species C has a high number of stomata per mm^2. Despite this it loses a small amount of water.
Use the data to explain why.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(1)
(Total 8 marks)
Q7.
Scientists used fossil leaves from one species of pine tree to investigate whether changes in the concentration of carbon dioxide in the air over long periods of time had led to changes in the number of stomata in the leaves.
Their method is outlined below.
•        They selected sites of different ages.
•        They collected between 11 and 24 fossil leaves from each site.
•        They found the mean number of stomata per mm^2 on the leaves from each site.
•        They estimated the age of each sample by dating organic remains around the leaves at each site.
They compared results from the fossil leaves with leaves from the same species of pine tree growing today.
They knew the concentration of carbon dioxide in the air at different times in the past.

Their results are shown in the table.

Age of sample/years

Concentration of carbon dioxide in the air/%

Mean number of stomata per mm^2 
(± standard deviation)

present day | 0.0350 | 92 (±2)
5000 | 0.0270 | 87 (±4)
10 000 | 0.0250 | 95 (±2)
15 000 | 0.0205 | 108 (±6)
20 000 | 0.0195 | 115 (±4)
25 000 | 0.0188 | 118 (±6)
30 000 | 0.0190 | 130 (±6)
(a)     The concentration of carbon dioxide in the air has changed with time. Use the data to describe how.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(2)
(b)     The scientists calculated the mean number of stomata per mm^2 and the standard deviation.
What does the standard deviation show?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________(2)
(c)     The scientists found the age of the fossil leaves by dating the organic remains around them.
Would this have affected the accuracy of their data? Explain your answer.
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(1)
(d)     30 000 years ago the mean number of stomata per mm^2 on the lower epidermis of pine tree leaves was much higher than it is today. This would have enabled the plant to grow faster when the carbon dioxide concentration of the air was low.
Explain why.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(1)
(e)     A student who saw these results concluded that as the carbon dioxide concentration of the air had increased the number of stomata per mm^2 in leaves had decreased.
Do the results support this conclusion?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(Extra space)________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(f)      The leaves of plants that grow in dry areas usually have a low number of stomata per mm^2. Use your knowledge of leaf structure to suggest three other adaptations that the leaves might have that enable the plants to grow well in dry conditions.
1. _________________________________________________________________
2. _________________________________________________________________
3. _________________________________________________________________
(3)
(Total 12 marks)

Mark schemes
Q1.
(a)     1.      (Across) alveolar epithelium;
2.      Endothelium / epithelium of capillary;
Incorrect sequence = maximum of 1 mark
2
(b)     1.      (The alveolar epithelium) is one cell thick;
Reject thin membrane
2.      Creating a short diffusion pathway / reduces the diffusion distance;
2 max
(c)     For
1.      Significantly higher concentrations of CO (compared with no smoking) with closed window (as no overlap in 2 × SD);
Accept higher concentrations of CO with closed window are not due to chance
Idea of higher is required, not just difference
2.      Any increase in CO could be dangerous;
OR
CO causes less oxygen to be carried / provided (which could be deadly in children);
3.      (significantly) higher levels after (just) 5 minutes (with closed windows supporting short journey statement);
Idea of higher is required, not just difference
Against
4.      No idea if (roughly) 5ppm is ‘deadly’;
5.      No significant difference with open window (as 2 × SD overlaps);
Accept difference with open window could be due to chance
6.      No data on child breathing rates;
OR
Idea that children breathe faster but have smaller lung volume, so overall volume of CO inhaled could be similar;
4 max
[8]
Q2.
(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
2
(b)     1.      Water and blood flow in opposite directions;
Allow diagram showing counter-flow
2.      Blood always passing water with a higher oxygen concentration;
3.      Diffusion gradient maintained throughout length (of gill)
OR
Diffusion occurs throughout length of gill
OR
If water and blood flowed in same direction equilibrium would be reached;
3
[5]
Q3.
(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;
1.      Do not accept unqualified references to thin membranes.
Max 2 if any reference to blood
Ignore references to spiracles
5.      Accept ‘water’ for fluid.
Accept ‘cells’ and ‘tissues’ as interchangeable words.
3 max
(b)     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.
2.      Accept ‘needs’ for ‘uses’
2.      Ignore references to absorbing / obtaining / uptake of more oxygen
2
(c)     Mean SA = 9.85 mm ^2 / 9.9 mm ^2 ;
Percentage uncertainty of SA = 18.5 / 18.7 / 19;
If both answers incorrect 1 mark for
Percentage uncertainty of dimensions 11.8 / 12 and 6.70 / 6.7
Surface area correctly calculated with correct units but not rounded to appropriate sf (9.8532 mm ^2)
Surface area correct (with appropriate sf) but no / incorrect unit given
Both answers correct = 3 marks
1 answer correct only = 2
Both answers incorrect = max 1
3 max
(d)     1.      Don’t use shading;
2.      Only use single lines / don’t use sketching (lines) / ensure lines are continuous / connected;
3.      Add further labels / annotations;
4.      Don’t cross label lines;
5.      Add magnification / scale (bar);
Reject ‘colour in’.
Reject ‘use of electron microscopes’
Ignore ‘use a sharp pencil’
2 max
[10]
Q4.
(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.
4
(b)     19(%);
1
(c)     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.
4
[9]
Q5.
(a)     1.      Named structures – trachea, bronchi, bronchioles, alveoli;
Reject mp1 if structures from other physiological systems are named but award mp2 if the correct structures are in the correct order.
2.      Above structures named in correct order
OR
Above structures labelled in correct positions on a diagram;
Reject mp1 if structures from other physiological systems are named but award mp2 if the correct structures are in the correct order.
3.      Breathing in – diaphragm contracts and external intercostal muscles contract;
4.      (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.
5.      Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
Accept diaphragm relaxes and (external) intercostal muscles relax and lung tissue elastic (so recoils).
6.      (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);
For thoracic cavity accept ‘lungs’ or ‘thorax’.
Reference to ‘thoracic cavity’ only required once.
If idea of thoracic cavity is missing or incorrect, allow ECF for mark point 6.
6
(b)     1.      Both contain ester bonds (between glycerol and fatty acid);
All statements must be clearly comparative or linked by the candidate, not inferred from separate statements.
Accept mark points shown on adjacent annotated diagrams.
2.      Both contain glycerol;
3.      Fatty acids on both may be saturated or unsaturated;
4.      Both are insoluble in water;
5.      Both contain C, H and O but phospholipids also contain P;
Must relate to element.
6.      Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
7.      Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;
Accept ‘non-polar’ for hydrophobic and ‘polar’ for hydrophilic.
8.      Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;
5 max
(c)     1.      Glucose and galactose;
Ignore α or β for glucose
2.      Joined by condensation (reaction);
3.      Joined by glycosidic bond;
4.      Added to polypeptide in Golgi (apparatus);;
4
[15]
Q6.
(a)      (Scientists) used fully grown leaves / used five plants of each (species).
Ignore other references to methodology. Reward only information provided in the Resource.
Do not accept reference to number of leaves − different plants were used.
1
(b)     Either
1.      Draw around leaf on graph paper;
Mark as a trio − MP1, MP2 and MP3 OR MP4, MP5 and MP6. Do not mix and match.
Both aspects needed for mark − drawing and type of paper.
2.      Count squares (however described);
There is no reward for additional detail e.g. dealing with part squares.
3.      Multiply by 2 (for upper and lower leaf surface);
OR
4.      Draw around a leaf on paper of known mass (per unit area);
Both aspects needed for mark − drawing and mass of paper.
5.      Cut out and weigh;
6.      Multiply by 2 (for upper and lower leaf surface).
3
(c)     (i)      Species B (no mark)
1.      Smaller surface area
         so
         less evaporation / less heat absorbed;
Correctly selected feature and the explanation required for 1 mark.
In all marking points − ‘less water loss’ is insufficient as an explanation but accept transpiration for evaporation or diffusion.
2.      Thicker leaves
         so
         greater diffusion distance (for water);
Accept ‘thicker leaves so more water storage’.
3.      Fewer stomata / lower stomatal density
         so
         less diffusion / evaporation (of water);
4.      Smaller surface area to volume ratio
         so
         less evaporation.
1 max
(ii)     1.      Thick(er) cuticle
         so
          increase in diffusion
          distance / slower (rate of) diffusion;
Feature and explanation needed for each mark.
Reject other features not related to leaves.
Reject features related to water storage.
‘Cuticle’ alone is insufficient (all leaves have a cuticle). Reject suggestion of ‘less’ diffusion, for idea of ‘slower diffusion’, an idea of rate is required.
2.      Hairs on leaves
         so
         reduction in air movements / increase in humidity / decrease in water potential gradient;
3.      Curled leaves
         so
         reduction in air movements / increase in humidity / decrease in water potential gradient;
4.      Sunken stomata
         so
         reduction in air movements / increase in humidity / decrease in water potential gradient.
2 max
(d)     Small leaves / surface area so (total) number of stomata is low.
Both aspects needed for mark.
1
[8]
Q7.
(a)     1.      The more recent the sample the greater the concentration;
Accept converse
This could be expressed by reference to time e.g. ‘concentration has increased since 25 000 years ago
2.      Increases most in last 5000 years / more or less constant / slight increase between 30 000 and 15 000 years ago;
2
(b)     1.      Variation in data / spread of data;
Reject references to range e.g. ‘range of data’
2.      Around the mean;
Both marks are possible in the context of using the data
2
(c)     1.      Yes as pine leaves not in organic matter of the same age;
2.      No as organic matter would be the same age as the pine leaves;
Accept either approach
1 max
(d)     Can get more CO_2 for photosynthesis;
More CO_2 enters leaf is insufficient. 
Accept light-independent (reaction) as equivalent
1
(e)     Any three from:
1.      (Overall data show) negative correlation;
Do not allow description of correlation because in question stem
2.      Little change in number of stomata in last 10 000 years;
3.      Small sample size;
4.      Only one species studied;
5.      Other factors / named factor may have affected number of stomata;
6.      Evidence does not support the conclusion between 30 000 and 25 000 years ago / between 5000 years ago and present day;
Accept reference to either one of these age ranges
7.      Appropriate reference to standard deviations (in comparing means);
E.g. no overlap between 15 000 and 10 000 years ago
3 max
(f)     Any three from :
1.      Thick cuticle;
2.      Small leaves / low surface area;
Accept other ways of describing ‘small’, e.g. ‘needle-like’
3.      Hairy leaves;
4.      Sunken stomata;
5.      Rolled leaves;
3 max
[12]