3.1.1 Exchange Surfaces

compilation of exam questions and answers from question packs and relative markschemes found online. applicable for AS and A Level OCR A A level Biology students, spec 2016 onwards :) i have included the maximum number of marks awarded for each question however, in the answers i have recorded every point recorded in the markscheme to widen and deepen understanding. each point is marked at the end with a semi-colon [;] good luck revising!! - 09/05/2026

Explain how smoking causes a smoker's cough and how the cough itself can lead to further problems in the lungs over a period of time. [6 marks]

causes

• causes tar;

• cigarette smoke stimulates goblet cells to secrete more mucus;

• mucus in the airways build up & it can not be removed;

• more pathogens/bacteria/viruses/microbes are trapped in the mucus;

• the cough is an attempt to increase airflow;

effects

• frequent coughing damages alveoli/elastic fibres;

• formation of scar tissue;

• the bronchi walls thicken;

• lumen of bronchi narrows;

• air flow restricted;

• damage to alveoli causes reduced surface area for gaseous exchange;

Alveoli (air sacks) contain many elastic fibres

Explain the role of these elastic fibres during ventilation. [2 marks]

to prevent bursting; they recoil; to return air sac to original size/shape;

to help expel air;

A steep diffusion gradient can be maintained by ventilating the lungs. This refreshes the air in the air sacs.

Explain how refreshing the air in the air sacs helps to maintain a steep diffusion gradient. [2 marks]

increases partial pressure/ concentration of O₂ in air sac; concentration of O₂ in air sac is higher than in the blood;

OR

decreases partial pressure/concentration of CO₂ in air sac; so concentration of CO₂ in air sac is lower than in the blood;

Describe and explain one other way in which a steep diffusion gradient is maintained in the lungs. [2 marks]

either

continuous blood flow in the capillaries; to bring in more CO₂/ take away more O₂;

or

oxygen combines with haemoglobin; to keep concentration in blood / plasma low;

Using the mammalian gaseous exchange system as an example, explain how the different cells and tissues enable the effective exchange of gases. [4 marks]

• thin squamous epithelium in alveoli and the thin endothelium of capillary; provide short diffusion distance;

• surfactant from epithelial cells, reducing tension/ preventing alveoli from collapsing; ! THIS IS NOT MENTIONED IN SPEC FROM 2016 ONWARDS! surfactant is a complex mixture of phospholipids and proteins produced from type II alveolar epithelial cell, it forms a thin layer inside the alveoli. main functions include reducing surface tension in water molecules at the surface of alveolar fluid, this prevents the alveoli from collapsing, makes it easier for lungs to inflated, reduces water loss and the fluid in the alveoli from increasing which can hinder gas exchange. this question was taken from OCR June 2011 question pack

• red blood cells/ erythrocytes; transport O₂ & CO₂ to and from alveoli;

• diaphragm and intercostals muscles; maintain concentration/diffusion gradient;

• ciliated epithelium & goblet cells; removal of dust/bacteria/pollen/spores;

• cartilage; hold airway open;

• smooth muscle; constrict airway & control diameter of blood vessels;

• elastic fibres/tissue; recoil/ aid in ventilation;

• macrophage/ neutrophil; engulf/ destroy pathogens; or protect from infection;

Describe how spirometer would be used to measure tidal volume. [3 marks]

no breathing through the nose; subject breathes evenly/regularly/normally; measure the height/ amplitude of waves from the trace; measure at least 3 waves and calculate mean;

detail of how spirometer works;

• breathe in, lid goes up, as breathe out l

Describe how you could use a spirometer trace to measure the rate of oxygen uptake. [3 marks]

measure volume of oxygen used/ decrease in volume in chamber; find difference in height from one peak/ trough to another or draw line along tips of peaks/troughs to measure volume change; measure time taken to use this oxygen; divide volume by the time taken;

Suggest two factors that should be considered when carrying out a risk assessment for an experiment using a spirometer. [2 marks]

check health of volunteer; oxygen used; new//sterilised/disinfected mouthpiece for each volunteer; soda lime needs to be working; sufficient oxygen in chamber; water levels not too high / water must not enter tubes; ensure valves are working correctly;

State two features of alveoli that enable sufficient gaseous exchange. [2 marks]

large surface area; alveolar walls have epithelium one cell thick; it is made up of squamous cells / epithelium; very close to capillaries/ good blood supply/ many capillaries; surfactant !NOT IN THIS SPEC!

As part of an allergic response, certain cells in the lungs release histamine.

Histamine is a cell signalling molecule that stimulates smooth muscle in the wall of bronchioles to contract.

Suggest how histamine stimulates smooth muscle contraction. [2 marks]

histamine attaches/ binds to receptors/ glycoprotein; on the plasma/ cell surface membrane of smooth muscle cell; complementary shape; triggers response/ causes effect inside cells; e.g. opening of sodium channels in cell surface membrane

Another action of histamine is to make capillary walls more permeable.

Suggest two effects this increased permeability may have on the surrounding tissues. [2 marks]

more tissue fluid formed; increases pressure in tissue; leads to selling/inflammation/oedema; more white blood cells pass into tissues; larger molecules pass into tissue fluid;