3 Organisms exchange substances: 6 Exchange Flashcards
What is the relationship between the size of an organism and its surface area to volume ratio?
As size increases, surface area to volume ratio decreases.
What substances do organisms need to exchange with the environment?
Respiratory gases
Nutrients (e.g. glucose, ions…)
Waste products (e.g. urea…)
Heat
How does the shape of an organism affect its substance exchange?
Animals with a compact shape have a small SA:V ratio which minimises heat loss.
Animals with a less compact shape have a larger SA:V ratio which increases heat loss.
What are the adaptations for gas exchange in a single-celled organism?
They have a very large SA: V so diffusion is sufficient for gas exchange.
For some, their surface consists only of a plasma membrane but for those with a cell wall, it doesn’t provide an additional barrier to diffusion.
What are the adaptations for gas exchange in insects?
Insects have spiracles on their body surface.
The gases that enter the spiracles move into the tracheae (a network of internal tubes held open by strengthened rings).
The tracheae then divide into smaller dead end tracheoles, which spread throughout the body, allowing O2 to be brought directly to respiring tissues.
How do respiratory gases move into and out of the tracheal system in insects? What are the different ways?
Diffusion gradient:
- cell respiration means the concentration of O2 falls towards the ends of the tracheoles
- this creates a diffusion gradient that causes O2 to diffuse from the atmosphere along the tracheal system to the cells
- CO2 is produced during respiration
- this creates a diffusion gradient which cause CO2 to diffuse along the tracheal system from the cells to the atmosphere
- diffusion in air is much faster than in water
Mass transport:
- the contraction of muscles can squeeze the trachea, enabling mass movements of air in and out
Water-filled ends of the tracheoles:
- during major activity, the muscle cells around the tracheoles respire anaerobically
- this produces lactate, which is soluble and lowers the water potential of the muscle cells
- water moves into the cells from the tracheoles via osmosis
- the water in the tracheoles decreases so air is drawn further in
- the final diffusion pathway is in air instead of water so it’s more rapid
- but there’s greater water evaporation
What are the adaptations for gas exchange in fish?
Counter-current flow:
- blood and water flow in opposite directions.
- high O2 conc water will always meet low O2 conc blood so a concentration gradient is always maintained.
- O2 diffuses into the blood along the entire length of the gill.
Gill lamellae/ filaments increase surface area.
Thin surface so short diffusion pathway.
What are the adaptations for gas exchange in leaves?
- no living cell is very far from external air, or from a stoma
- diffusion occurs in the gas phase
- short, fast diffusion pathway
- air spaces provide a large SA:V
- mesophyll cells have a large surface area
What are the adaptations to reduce water loss in insects?
- small SA:V to minimise the area over which water is lost
- waterproof coverings
- spiracles that can be closed to reduce water loss
What are the adaptations to reduce water loss in xerophytes?
- a thick cuticle
- less water can escape
- rolling up of leaves
- traps water vapour to reduce water potential gradient
- hairy leaves
- traps water vapour to reduce water potential gradient
- sunken stomata
- traps water vapour to reduce water potential gradient
- reduced SA:V
- needle-like leaves reduce the rate of water loss
Why are mammalian lungs located inside the body?
- air isn’t dense enough to support and protect the lungs
- the body would otherwise lose too much water
What is the structure of the human gas exchange system?
- trachea
- a flexible airway that is supported by rings of cartilage
- bronchi
- two divisions of the trachea, each leading to one lung
- bronchioles
- a series of branching subdivisions of the bronchi
- alveoli
- minute air-sacs at the end of the bronchioles
- between the alveoli are collagen and elastic fibres which allow the alveoli to stretch and spring back to expel CO2 rich air
- lined with alveolar epithelium
What happens in inspiration?
An active process.
- external intercostal muscles contract, internal intercostal muscles relax
- ribs are pulled upwards and outwards
- diaphragm muscles contract
- this increases the thorax volume, decreasing the pressure in the lungs
- atmospheric pressure is greater than pulmonary pressure so air is forced into the lungs
What happens in expiration?
A passive process.
- internal intercostal muscles contract, external intercostal muscles relax
- ribs move downwards and inwards
- diaphragm muscles relax (pushed up by the contents of the abdomen which were compressed)
- this decreases the thorax volume, increasing the pressure in the lungs
- pulmonary pressure is greater than atmospheric pressure so air is forced out of the lungs.
What are the essential features of the alveolar epithelium that allow for rapid diffusion?
Rapid diffusion is achieved by:
- slowing red blood cells as they pass through the pulmonary capillaries, which gives more time for diffusion.
- red blood cells are flattened against the capillary walls which reduces diffusion distance.
- alveolar and capillary walls are very thin so a short diffusion pathway.
- large surface area
- lungs are continually ventilated and the heart constantly circulates blood, maintaining steep concentration gradients.
