Exchange systems Flashcards
Surface area to volume ratios
Influence how substances and heat energy are transferred around multicellular organisms
Surface area alone can’t influence the rate of exchange
As volume increases more materials are needed for metabolism
The bigger the organism, the smaller the Sa:V ratio as a lot of cells are in contact with each other because of the increase in volume
What is mass transport?
The process of carrying substances to and from individual cells
In mammals this usually refers to the circulatory system which uses the blood
The blood also carries antibodies, waste and hromones
Mass transport in plants involves water and solutes in the xylem and phloem
How does surface area to volume ration affect heat exchange
If an organism has a large volume and its surface area is relatively small, it’s harder to loose heat from its body
Animals with a compact shape have a small surface area relative to their volume which minimises heat loss
What behavioural and physiological adaptations do organisms have to aid exchange
Animals with a high Sa:V ratio tend to loose more water through evaporation
To support metabolic rates, small mammals living in cold climates must eat large amounts of high energy foods
Thicker layers of fur
Hibernation
Larger organisms in hot climates find it harder to keep cool as their heat loss is relatively slow
Hippos spend much of the day in water - a behavioural adaptation
Elephant’s large ears increase their surface area
What are the 2 major adaptations of gas exchange surfaces?
Large surface area
Thin (often only one layer of epithelial cells) which provides a short diffusion pathway
A steep concentration gradient of gases across the exchange surface will be maintained
How do single celled organisms exchange gas
They absorb and release gases by diffusion through their outer surface
They have a relatively large surface area, a thin surface and a short diffusion pathway
No need for gas exchange system
Adaptations of fish gas exchange
Water enters through the mouth and passes through the gills
Each gill is made of gill filaments which provide a large surface area for gas exchange
The gill filaments are covered in lamellae which further increase surface area so increases diffusion rate
The lamellae have lots of blood capillaries and a thin surface epithelium to increase the rate of diffusion
Countercurrent system
Circulation replaces blood with saturated oxygen
Ventilation replaces water as oxygen is removed
Fish counter-current system
Blood flows over the lamellae in one direction and water in the other
This maintains a large concentration gradient between the water and the blood
The concentration of oxygen in water is always higher than that in the blood so as much oxygen as possible diffuses from the water into the blood
Diffusion gradient maintained along the whole length of the lamellae
How do insects exchange gas
Tracheae are used for gas exchange in insects
Air moves into the tracheae through pores on the surface called spiracles
Oxygen travels down a concentration gradient towards cells
The tracheae branch off into tracheoles which have thin, permeable walls and enter individual cells
This means oxygen diffuses directly into respiring cells and an insect’s circulatory system doesn’t transport oxygen
CO2 from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere
Insects use rhythmic abdominal movements to move air in and out of the spiracles
Dicotyledonous plants gas exchange
The main gas exchange surface is on the surface of the mesophyll cells which have a large surface area
The mesophyll cells are inside the lead
Gases move in and out of the leaf through the stomata in the epidermis
Guard cells control the opening and closing of the stomata
How do insects and plants control water loss
Insects can close their spiracles using muscles
They also have a waterproof waxy cuticle over their body and hairs surrounding their spiracles both of which reduce evaporation
When water enters the guard cells it makes them turgid which opens the stomatal pore. If a plant begins to get dehydrated the guard cells loose water and become flaccid which closes the pore
Xerophytic adaptations
Plants that live in warm, dry or windy habitats
Sunken stomata trap most air and reduce the concentration gradient of water between the leaf and air
A layer of hairs on the epidermis traps moist air around stomata
Curled leaves with stomata inside protect them from the wind which can increase the rate of diffusion and evaporation
A reduced number of stomata
Waxy, waterproof cuticles on leaves and stems reduce evaporation
How are the alveoli adapted for gas exchange
A thin exchange surface - the alveolar epithelium is only one cell thick so there’s a short diffusion pathway
A large surface area for gas exchange
A steep concentration gradient of O and CO2 is maintained between the alveoli and capillaries which increases the rate of diffusion. This is maintained by the flow of blood and ventilation
Ventilation/breathing process - inspiration
The external intercostal and diaphragm muscles contract
This causes the ribcage to move upwards and outwards and the diaphragm to flatten
As the volume of the thoracic cavity increases the lung pressure decreases to below atmospheric pressure
Air will always flow from an area of higher pressure to an area of lower pressure (so down the trachea into the lungs)
Inspiration is an active process so requires energy
Expiration
The external intercostal muscles and diaphragm muscles relax
The ribcage moves downwards and inwards and the diaphragm curves
As the volume of the thoracic cavity decreases, the air pressure increases to above atmospheric pressure
Air is forced down the pressure gradient and out of the lungs
Expiration is a passive process, though it can be forced e.g. blowing out candles
