AQA biology Unit 2 Gas exchange and oxygen dissociation
More model answers you should know for the unit 2 exam
- Created by: Katie
- Created on: 16-04-12 14:29
What is the relationship between an organisms size
The larger the organism, the smaller the ratio therefore the slower the rate of diffusion across the gas exchange surface
Features of specialized gas exchange surfaces
large S.A to volume ratio
Thin (short diffusion pathway)
Partially permiable
movement of external medium to maintain concentration gradient
movement of internal medium to maintain concentration gradient
How have large organisms adapted to be efficient a
Flattened shape so no cell is ever far away from the surface
Specialized exchange surfaces with large S.A to increase the surface area to volume ratio(e.g lungs or gills)
Gas exchange in insects
Air enters through open spiracles and passes through the tracheae.
There is a diffusion gradient in the tracheae causing oxygen to diffuse into cells. Ventilation replaces air in tracheae maintaining concentration gradient.
Spiracles are able to close
How do respiratory gases move in and out of trache
Down a concentration gradient (air moving in has a high oxygen content, at the tissues the oxygen concentration is low as it is used in respiration)
Ventilation by movement of muscles in the abdomen creates mass air movement
NOTE: Spiracles closing also conserves water and that it is the buildup of CO2 that causes the spiracles to open.
Insects have no blood system so oxygen diffuses to the tracheae straight to the tissues
How insects are adapted to conserve water
Small S.A to volume ratio
Waterproof coverings on body surfaces
ability to close spiracles
How insects are adapted to be efficient at gas exc
Numerous spiracles to increase S.A
Short diffusion pathway as their is no blood
Many traceoles to increase S.A
Concentration gradient maintained by ventilation and the removal of oxygen by respiring tissues
Gas exchange in fish
Water enters through the mouth and s forced across the gill filaments.
The water flow in the opposite direction to the blood in the lamellae. This is known as countercurrent flow which produces a concentration gradient to promote the diffusion of oxygen from the water along the whole length of the gill.
Water finally passes out through the operculum
Why are fish gills efficient at gas exchange
Numerous gill filaments with numerous lamellae-increased S.A
Thin squamous epithelium cells on gill and capillaries - Short diffusion pathway
Gills are well supplied with numerous small capillaries - increased S.A
Countercurrent flow - maintains steep concentration gradient
Constant ventilation and circulation of blood maintains concentration gradient
Gas exchange in plants
During respiration oxygen diffuses into the plant when the stomata are open
Carbon dioxide diffuses out of the plant
During photosynthesis the opposite happens
In the mesophyll layer the plant has numerous air spaces to aid gaseous diffusion
GAses do not have to be dissolved in water for diffusion through the stomata
Stomata close to conserve water. When this happens no gas exchange can occur through the stomata
How plants are adapted to increase gas exchange
Numerous stomata (increase S.A)
Diffusion takes place in gas phase
Long flat leaves ensure no living cell is far from external air
Air spaces in spongy mesophyll (short diffusion pathway as it doesn't have to pass through cells)
Photosynthesis and respiration maintains concentration gradient
Structure of haemoglobin
Primary structure consists of 4 polypeptide chains built of amino acids
Secondary structure consists of these chains coiled into alpha-helices connected with hydrogen bonds
Tertiary structure provides a globular shape with futher bonding
Quaternary structure of 4 chains linked together to form a spherical molecule.
Each polypeptide is associated with a haem group containing Iron (II) ions
Role of haemoglobin
Readily associates with oxygen at gas exchange surfaces as it has a high affinity there
Readily dissociates from oxygen at respiring tissues as it has a lower affinity here
Oxygen dissociation curves
Further to the left greater affinity for oxygen (takes it up readily but releases it less readily)
Further to the right lower affinity for oxygen (takes it up less readily but releases it more easily
Effects of carbon dioxide concentration
Greater concentration of CO2 the more readily haemoglobin releases its oxygen (Bohr effect) Oxygen dissociation curve shifts right
Loading, Transporting and unloading of oxygen
Carbon Dioxide is constantly removed at gas exchange surfaces
pH is higher due tolow levels of CO2
Haemoglobin loads oxygen more readily
Haemoglobin has a high affinity in this state so does not release oxygen during transport
Carbon Dioxide is produced in respiring cells and is acidic so the pH is lower
Shape of haemoglobin changes into one with a lower affinity for oxygen
haemoglobin releases its oxygen to the respiring cells
Why does haemoglobin unloads oxygen
Carbon dioxide levels increase Ph becomes more acidic
haemoglobin changes shape (ionic bonds are changed)
More oxygen is dissociated
Explain the advantage of the curve being on the le
High percentage saturation at low partial pressures of oxygen
LOw oxygen environments include High altitudes, Underwater, burrows, in the uterus
Explain the advantage of the curve being further l
Haemoglobin has a lower affinity for oxygen so release oxygen more readily to respiring cells.
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