Biology by Bradford
B3.1.6Lung volumes
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A trace like this comes from a : the line rises as air is breathed in.
B3.1 Gas exchange: revision map
The subtopic in the middle and twelve tasks round it: label six diagrams, complete a table, put a process in order and fill 58 gaps. Every standard level statement has a box; the two boxes for higher level only are dashed and badged HL, and drop off for an SL class. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
Gas exchange
Organisms · Form and functionHover over a box to see it. Untick it to leave it off this sheet and its printout.
NameB3.1.7, B3.1.8A leaf in section
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CO₂ diffuses in through the and spreads through the to the cells that photosynthesise. The upper is transparent, letting light through.
B3.1.10Counting stomata
Stomatal density is the number of stomata per unit . Paint clear nail varnish on the lower surface, peel off the , and count the stomata in the field of view at high power: 30 in a field of 0.15 mm² is per mm². Counts vary from field to field, so take counts and use the .
B3.1 examA transverse section of a dicotyledonous leaf
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B3.1.3Steep gradients
Diffusion stays fast only while the concentration gradient is steep. A dense network of and continuous carry absorbed O₂ away and keep bringing more CO₂. brings in fresh medium all the time: air to the lungs, over the gills.
B3.1.4Into the lungs
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A film of lines each tiny sac, lowering surface tension so its walls do not stick together and it does not when you breathe out. Hundreds of millions of sacs give the lungs a huge .
B3.1Gas exchange
B3.1.5Breathing in
Number the steps in order.
- Air flows in down the trachea and bronchi until the pressures are equal.
- The volume of the thorax increases.
- The pressure inside the lungs falls below atmospheric pressure.
- The diaphragm and the external intercostal muscles contract.
- The diaphragm flattens and moves down; the ribs move up and out.
Breathing out at rest is mostly passive, as these muscles relax. A forced breath out also uses the and the .
B3.1.9Transpiration rate
| If this rises | Transpiration rate | Because |
|---|---|---|
| Temperature | water evaporates and diffuses faster | |
| Humidity | the water vapour gradient from leaf to air is less steep | |
| Wind speed | humid air next to the leaf is blown away | |
| Light intensity | more open |
Transpiration is the loss of water vapour from leaves: the unavoidable cost of opening pores to take in for photosynthesis.
B3.1.1, B3.1.2Bigger is harder
As an organism grows, its volume rises faster than its surface area, so its surface area-to-volume ratio : the 1 cm cube has a ratio of 6:1, the 3 cm cube only . Its centre also lies farther from the surface. So a large organism needs a gas-exchange surface that is permeable and large in area, so that gases can dissolve, and so that the diffusion distance is short.
B3.1.11, B3.1.12, B3.1.13Dissociation curvesHL
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Each curve is because oxygen binding is : once one O₂ binds, the protein changes shape and the next binds more easily.
B3.1.11, B3.1.12Haemoglobin at workHL
Each haemoglobin molecule has four groups, each carrying one O₂. CO₂ binds at other, sites, changing the protein's shape so it holds O₂ less tightly. Actively respiring tissue makes more CO₂, so haemoglobin unloads more O₂ just where it is needed: the . Foetal haemoglobin has a affinity for O₂ than adult haemoglobin, so it takes O₂ from the mother's blood in the .
B3.1 examPart of an alveolus and an adjacent capillary
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Word bank 2:1200abdominal musclesadult haemoglobinair spacesallostericalveolusareablood flowBohr shiftbronchiolecapillariescapillarycastCO₂collapsecooperativedecreasesepidermisexpiratory reserve volumefallsfoetal haemoglobinguard cellhaemhigh CO₂higherincreasesinspiratory reserve volumeinternal intercostal musclesmeanmoistpalisade mesophyllplacentared blood cellrepeatS-shapedspirometerspongy mesophyllstomatasurface areasurfactantthintidal volumetype I pneumocytetype II pneumocyteveinVentilationvital capacitywaterwaxy cuticlexylem
Answer key
Every box on the sheet with its gaps filled in, as the subtopic reads in full.
GapsBigger is harder
As an organism grows, its volume rises faster than its surface area, so its surface area-to-volume ratio falls: the 1 cm cube has a ratio of 6:1, the 3 cm cube only 2:1. Its centre also lies farther from the surface. So a large organism needs a gas-exchange surface that is permeable and large in area, moist so that gases can dissolve, and thin so that the diffusion distance is short.
GapsSteep gradients
Diffusion stays fast only while the concentration gradient is steep. A dense network of capillaries and continuous blood flow carry absorbed O₂ away and keep bringing more CO₂. Ventilation brings in fresh medium all the time: air to the lungs, water over the gills.
LabelInto the lungs
- bronchiole
- alveolus
- capillary
A film of surfactant lines each tiny sac, lowering surface tension so its walls do not stick together and it does not collapse when you breathe out. Hundreds of millions of sacs give the lungs a huge surface area.
OrderBreathing in
- The diaphragm and the external intercostal muscles contract.
- The diaphragm flattens and moves down; the ribs move up and out.
- The volume of the thorax increases.
- The pressure inside the lungs falls below atmospheric pressure.
- Air flows in down the trachea and bronchi until the pressures are equal.
Breathing out at rest is mostly passive, as these muscles relax. A forced breath out also uses the internal intercostal muscles and the abdominal muscles.
LabelLung volumes
- tidal volume
- inspiratory reserve volume
- expiratory reserve volume
- vital capacity
A trace like this comes from a spirometer: the line rises as air is breathed in.
LabelA leaf in section
- waxy cuticle
- palisade mesophyll
- spongy mesophyll
- guard cell
- vein
CO₂ diffuses in through the stomata and spreads through the air spaces to the cells that photosynthesise. The upper epidermis is transparent, letting light through.
TableTranspiration rate
If this rises Transpiration rate Because Temperature increases water evaporates and diffuses faster Humidity decreases the water vapour gradient from leaf to air is less steep Wind speed increases humid air next to the leaf is blown away Light intensity increases more stomata open Transpiration is the loss of water vapour from leaves: the unavoidable cost of opening pores to take in CO₂ for photosynthesis.
GapsCounting stomata
Stomatal density is the number of stomata per unit area. Paint clear nail varnish on the lower surface, peel off the cast, and count the stomata in the field of view at high power: 30 in a field of 0.15 mm² is 200 per mm². Counts vary from field to field, so take repeat counts and use the mean.
LabelDissociation curves HL
- foetal haemoglobin
- adult haemoglobin
- high CO₂
Each curve is S-shaped because oxygen binding is cooperative: once one O₂ binds, the protein changes shape and the next binds more easily.
GapsHaemoglobin at work HL
Each haemoglobin molecule has four haem groups, each carrying one O₂. CO₂ binds at other, allosteric sites, changing the protein's shape so it holds O₂ less tightly. Actively respiring tissue makes more CO₂, so haemoglobin unloads more O₂ just where it is needed: the Bohr shift. Foetal haemoglobin has a higher affinity for O₂ than adult haemoglobin, so it takes O₂ from the mother's blood in the placenta.
Exam diagramPart of an alveolus and an adjacent capillary
- type I pneumocyte
- type II pneumocyte
- capillary
- red blood cell
Exam diagramA transverse section of a dicotyledonous leaf
- palisade mesophyll
- spongy mesophyll
- xylem
- guard cell