Gas exchange Flashcards
Describe and explain how the structure of the mammalian breathing system enables efficient uptake of oxygen into the blood.(6)
- Alveoli provide a large surface area;
- Walls of alveoli thin to provide a short diffusion pathway;
- Walls of capillary thin/close to alveoli provides
a short diffusion pathway; - Walls (of capillaries/alveoli) have flattened cells;
- Cell membrane permeable to gases;
- Many blood capillaries provide a large surface area;
- Intercostal/chest muscles/diaphragm muscles / to ventilate lungs / maintain a diffusion/concentration gradient;
- Wide trachea / branching of bronchi/bronchioles for efficient flow of air;
- Cartilage rings keep airways open;
Describe how muscles in the thorax (chest) cause air to enter the lungs during breathing.
Diaphragm/intercostal muscles contract;
Increases volume of thorax/chest/lungs;
Negative/lower pressure in lungs;
In normal breathing, describe the part played by the intercostal muscles
Contract;
ribs move upwards/out;
increasing volume/decreasing pressure in chest/thorax/lungs
Describe the difference in the composition of gases in inhaled and exhaled air. Explain how these differences are caused.
1 inhaled air contains more oxygen than exhaled air;
2 inhaled air contains less carbon dioxide than exhaled air;
3 inhaled air contains less water (vapour);
4 relative amount/percentage of nitrogen also changes;
5 respiration results in lower blood oxygen / higher blood carbon dioxide;
6 oxygen enters blood / carbon dioxide leaves blood in alveoli;
7 by diffusion;
8 water vapour diffuses from moist surface;
Describe how the structure of the lungs and the red blood cells enable efficient diffusion and transport of oxygen.
1 Large surface area produced by many alveoli;
2 Single layer of epithelial cells / very thin epithelium / squamous / pavement;
3 Capillary walls one cell thick;
4 Giving short diffusion pathway;
5 RBC thin / flattened / disc-shaped so large surface area;
6 No nucleus / mitochondria;
7 Haemoglobin for transport of oxygen;
8 Red cell close to capillary wall;
Pulmonary tuberculosis is a disease of the lungs. Describe the transmission and course of infection of pulmonary tuberculosis.
1 (Bacteria transmitted in) droplets / aerosol;
2 (Bacteria) engulfed / ingested by phagocytes / macrophages;
3 (Bacteria) encased in named structure e.g. wall /
tubercle / granuloma / nodule;
4 (Bacteria) are dormant / not active / not replicating;
5 If immunosuppressed, bacteria activate / replicate / released;
6 Bacteria destroy alveoli / capillary / epithelial cells;
7 (Leads to) fibrosis / scar tissue / cavities /calcification;
8 (Damage) leads to less diffusion /less surface area / increases diffusion distance;
9 (Activation / damage allows bacteria) to enter blood / spreads (to other organs);
Emphysema is another disease of the lungs. People with emphysema may feel weak and tired. Explain why.
1 Alveoli break down / collapse / rupture / walls thicken;
2 Less surface area / increases diffusion distance / less diffusion;
3 Loss of elastin / elastic tissue / elastase involved;
4 (Alveoli / lungs) cannot recoil / spring back / have reduced elasticity / more difficult to expel air;
5 Reduced diffusion gradient / air not replenished / less air leaves lungs;
6 Less oxygen enters blood / tissues;
7 Less respiration / less energy released / less ATP produced;
Pulmonary fibrosis
when scars form on the epithelia that are damaged, increasing the diffusion pathway, loss of elasticity in lung tissue, which reduces the concentration gradient, narrowing of vessels, reducing air flow and concentration gradient. Results in shortness of breath, dry cough, tiredness (insufficient oxygen for respiration)
Asthma
caused by physical factors called allergens in the environment. These allergens include pollen, dust mites faeces and fur.
These allergens trigger an inflammatory response by the immune system.
White blood cells called mast cells release histamines, which cause the smooth circular muscles of the bronchioles to contract, narrowing the airways (bronchoconstriction).
The epithelial cells also secrete more mucus, which further blocks the airways.
The constricted bronchioles stimulate wheezing and coughing as the lungs try to loosen the mucus. The constrictions reduce the tidal volume, so alveolar air is only replaced slowly. The oxygen concentration gradient across the alveolar epithelium is reduced, so the rate of diffusion in the alveoli is reduced by Fick’s law. Less oxygen diffuses into the blood, so less oxygen is available for cellular respiration throughout the body.
A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.
1 Large surface area provided by lamellae/filaments;
2 Increases diffusion/makes diffusion efficient;
3 Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions/countercurrent;
5 maintains concentration gradient (along gill)/equilibrium
not reached;
5 Not enough to say gives steep concentration gradient
6 As water always next to blood with lower concentration of oxygen;
7 Circulation replaces blood saturated with oxygen;
8 Ventilation replaces water (as oxygen removed);
Describe and explain how fish maintain a flow of water over their gills.
- mouth opens, operculum/opercular valve shuts;
- floor of mouth lowered;
- water enters due to decreased pressure / increased volume;
- mouth closes, operculum/opercular valve opens;
- floor raised results in increased pressure / decreased volume;
- high/increased pressure forces/pushes water over gills;
Explain how the countercurrent principle helps fish to extract oxygen from water.
Water flows in opposite direction to blood;
across (gill) lamellae;
so difference in concentration maintained;
diffusion gradient maintained / diffusion over full length.
Insect have more than 1.5 million tracheoles. The distance between the ends of the tracheoles in the muscle is approximately 4 µm. Explain how these features allow efficient oxygen supply.
Large number gives large (total) surface area;
For diffusion;
Short distance between tracheoles gives short pathway;
Movement/diffusion through muscle is slow;
An insect lives in air. Describe how the insect is able to obtain oxygen and limit water loss.
1 Air enters through (open) spiracles;
2 Through tracheae;
3 Diffusion gradient in trachea
4 Tracheae associated with all cells/closely associated with cells;
5 Oxygen diffuses into cells;
6 Ventilation replacing air in tracheae;
7 Body covered with (waterproof) waxy layer/cuticle;
8 Spiracles are able to close open in response to carbon dioxide at a critical level;
Fluid filled tracheoles allow some control over gas exchange. When the insect is at rest the fluid is in the tracheoles. This slows down the diffusion of oxygen to the muscles, this slows down respiration and thus the production of CO2. It means CO2 levels will rise slowly and limit the number of times the spiracles open, thus reducing water loss. When the insect starts to move, the muscles produce lactic acid, this lowers the water potential of the muscles, which draws the fluid out of the tracheoles (by osmosis) and now diffusion of oxygen will be faster through the air filled tracheoles.
Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf.
- (Carbon dioxide enters) via stomata;
- (Stomata opened by) guard cells;
- Diffuses through air spaces;
- Down diffusion gradient;
