organisms exchange substances with their environment Flashcards
state 4 examples of things that organisms need to exchange with their environment (exchange)
- respiration gases (oxygen, carbon dioxide)
- glucose/nutrients
- heat
- waste (e.g. urea)
how do the surface area to volume ratios of small & large organisms affect them? (exchange)
- small organisms have a large surface area to volume ratio, therefore can rely only on diffusion for substance exchange
- large organisms have a small surface area to volume ratio, therefore must rely on mass transport systems & other processes (diffusion, osmosis, active transport) for substance exchange
what have organisms evolved to have relative to their SA:V ratio? (exchange)
- a flattened shape so that no cell is ever far from the surface (e.g. leaf)
- specialised a change surfaces with large areas to increase the SA:V ratio (e.g. lungs in mammals)
state 5 features of specialised exchange surfaces (exchange)
- a large surface area relative to the volume of the organism, which increases the rate of exchange
- very thin so that the diffusion distance is short & therefore materials cross the exchange surface rapidly
- selectively permeable to allow selected materials to cross
- movement of the environmental medium (e.g. air) to maintain a diffusion gradient
- a transport system to ensure the movement of the internal medium (e.g. blood) to maintain a diffusion gradient
what is diffusion proportional to? (exchange)
- diffusion ∝ (surface area X difference in concentration) ÷ length of diffusion path
what makes up the respiratory ventilation centre & where are they located? (exchange)
- made up of an inspiratory centre & expiratory centre
- found in the medulla
outline the process of inspiration/inhalation (exchange)
- external intercostal muscles contract & internal intercostal muscles relax (ribs move up & out)
- diaphragm contracts & moves down (forms a flattened disc)
- thorax volume increases, which causes pressure in the thorax to decrease
- air is drawn up into the lungs as atmospheric pressure in grater than pulmonary pressure
outline the process of expiration/exhalation (exchange)
- internal intercostal muscles contract & external intercostal muscles relax (ribs move in)
- diaphragm relaxes & moves upwards (bends back into a disc)
- thorax volume decreases, so pressure in the thorax increases
- air is forced out of the lungs as pulmonary pressure is greater than that of the atmosphere
are inspiration & expiration active or passive processes? (exchange)
- inspiration (breathing in) is an active process, therefore requires energy
- exhalation (breathing out) is a mostly passive process, so doesn’t require much energy
why are mammalian lungs located inside the body? (exchange)
- air is not dense enough to support & protect them as they are delicate
- the body as a whole would otherwise lose large amounts of water & dry out
why is the volume of oxygen absorbed & carbon dioxide expelled large in mammals? (exchange)
- they are large organisms with a large volume of living cells
- they maintain a higher body temperature, which is related to them having high metabolic & respiratory rates
outline 8 components of the respiratory system (exchange)
- trachea
- bronchi
- bronchiole
- alveoli
- diaphragm
- ribcage
- intercostal muscle
- lung
where is the site of gas exchange in mammals? (exchange)
- the epithelium of the alveoli
what must there be to n sure a constant supply of oxygen to the body? (exchange)
- a diffusion gradient must be maintained at the alveolar surface
why do organisms with internal exchange surfaces have a means of moving the external medium over the surface? (exchange)
- because diffusion alone is not fast enough to maintain adequate transfer of oxygen & carbon dioxide over the trachea, bronchi & bronchioles
what lines/surrounds each alveolus? (exchange)
- lined with epithelial cells (0.05µm - 0.3µm thick)
- surrounded by a network of pulmonary capillaries (7µm - 10µm thick)
- these capillaries have walls that are only a single layer of cells thick (0.04µm - 0.2 μm)
why is diffusion of gases between the alveoli & the blood very quick? (6) (exchange)
- red blood cells are slowed as they pass through pulmonary capillaries, which allows more time for diffusion
- the distance between the alveolar air & RBCs is reduced as they pass through RBCs are flattened against the capillary walls
- the walls of both alveoli & capillaries are very thin & therefore the distance over which diffusion takes place is very short
- alveoli & pulmonary capillaries have a very large total surface area
- breathing movements constantly ventilate the lungs, & action around the heart constantly circulates blood around the alveoli. Together they ensure that a step concentration gradient of the gases to be exchanged is maintained
- blood flow through the pulmonary capillaries maintains a concentration gradient of
outline the descriptions & symptoms of the following lung diseases & explain their effect on lung function: tuberculosis, fibrosis, asthma, emphysema (exchange)
tuberculosis:
- caused by bacteria
- causes an immune response building a wall around the lungs. Hard lumps are formed
- SYMPTOMS = persistent cough, fatigue
- affects lung function as it decreases tidal volume, can lead to fibrosis which also decreases tidal volume
fibrosis:
- scar tissue in the lungs due to infection/chemical exposure
- SYMPTOMS = shortness of breath, dry cough
- affects lung function as they become thick & less elastic so can’t explanations as much. This decreases forced vital capacity & tidal volume
asthma:
- airways become inflames (can be allergy due to dust/pollen)
- SYMPTOMS = wheezing, tight chest
- affects lung function as muscle in the bronchioles contracts & lots of mucus is produced. This constricts the airways & causes decreased air flow & there decreased FEV1
emphysema:
- caused by smoking/pollution(long term)
- SYMPTOMS: inflammation for the alveoli by foreign particles (attracts phagocytes)
- affects lung function as phagocytes break down elastin which means the alveoli can’t stretch & recoil as well. This damages the alveoli walls, which decreases surface area, which decreased the rate of exchange. This decreases FEV1
outline the structure of fish gills & how they work (exchange)
- located behind the fish head
- are made up of gill filaments that are stacked up in a pile
- gill lamellae are at right angles to the gill filaments. They increase the surface area of the gills
- lots of capillaries maintains a concentration gradient
- water is taken in through the mouth & is forced over the gills & out through an opening on each side of the body
- the flow of blood & water occur in the opposite direction
why is the countercurrent flow system important? (exchange)
- for ensuring that the maximum possible gas exchange is achieved
- if the water & blood flowed in the same direction far less gas exchange would be achieved
what is the countercurrent system?
- blood & water flow over the gills lamellae in opposite directions
what does the arrangement of the countercurrent flow system mean for blood? (exchange)
- blood that is already well loaded with oxygen meets water, which has its maximum concentration of oxygen
- therefore diffusion of oxygen from the water to the blood takes place
- blood with little oxygen in it meets water that has had most (but not all of) its oxygen removed
- this means that diffusion of oxygen from the water to the blood takes place
what does the countercurrent flow system mean for oxygen uptake? (exchange)
- a diffusion gradient for oxygen uptake is maintained across the entire width of the gill lamellae
- this means that 80% of the oxygen available in the water is absorbed into the blood of the fish
outline & explain the process of gas exchange in single celled organisms (4)(exchange)
- are small & therefore have a large SA:V ratio
- oxygen is absorbed by diffusion across their body surface (this is covered by only a cell-surface membrane
- carbon dioxide from respiration diffuses across their body surface in the same way
- when a living cell is surrounded by a cell wall, there is no additional barrier to the diffusion of gases
what are the characteristics of an insect? (4) (exchange)
- 3 body segments (head, thorax, abdomen)
- 3 pairs of jointed legs
- normally have antennae
- wings (1 or 2 pairs)
what have insects evolved to have to aid gas exchange? (2) (exchange)
- tracheae (internal network of tubes) that are supported by strengthened rings to stop them from collapsing
- these are further divided into smaller dead-end tubes (trachaeoles) that extend throughout the body tissues of the insect
outline the route taken by oxygen into an insect (exchange)
- spiracles —> trachea —> trachaeoles —> oxygen diffuses directly into relieving cells (no oxygen is transported around the body)
explain 3 ways in which respiratory gases can move in & out of the tracheal system (exchange)
along a diffusion gradient:
- when cells are respiring, O2 is used up so its concentration towards the end off the trachaeoles falls
- this creates a diffusion gradient that causes O2 to diffuse from the atmosphere along the tracheae & trachaeoles
- CO2 produced during respiration creates a diffusion gradient in the opposite direction they causes CO2 to diffuse along the trachaeoles & trachea to the atmosphere
mass transport:
- the contraction of muscles in insects can squeeze the trachea, enabling mass movements of air in & out
- this further speeds up the exchange of respiratory gases
the ends of trachaeoles are filled with water:
- during periods of major activity, the muscle cells around the trachaeoles respire & carrot out some anaerobic respiration
- this produces lactate, which is soluble & lowers the water potential of the muscle cells, therefore water moves into the cells via osmosis
- the water in the end of the trachaeoles decreases in volume & in doing so draws air further into them
- this means the final diffusion pathway is in a gas rather than liquid phase & therefore diffusion is more rapid
- this increases the rate at which air is moved in the trachaeoles, but leads to greater water evaporation
explain what spiracles are & how they work (exchange)
- holes on the body surface that gases enter & leave the tracheae from
- when they are open water vapour can evaporate from the insect
- most of the time they are closed to prevent water loss
- they are periodically opened to allow for gas exchange
why must insects be small? (exchange)
- to maintain a short diffusion distance
what is abdominal pumping in insects & why is it effective? (4) (exchange)
- occurs during vigorous exercise
- insects flex their abdomen repeatedly
- this increases abdominal pressure & ‘squeezes’ the tracheae/trachaeoles
- the creation of a pressure gradient helps to force out CO2
what happens to oxygen & carbon dioxide when photosynthesis is taking/not taking place? (4) (exchange)
taking place:
- although some carbon dioxide comes from respiration of cells, most if it is obtained from the external air
- in the same way, come oxygen from photosynthesis is used in respiration but most of it diffuses out of the plant
not taking place:
- oxygen diffuses into the leaf because it is constantly being used by cells during respiration
- in the same way, carbon dioxide produced during respiration diffuses out of
how is gas exchange in plants similar to that of insects? (2) (exchange)
- no living cell is far from the external air, & therefore a source of oxygen & carbon dioxide
- diffusion takes place in the gas phase (air), which makes it more rapid than if it were in water
what is the diffusion pathway like in plants & why? (3) (exchange)
- short & fast
- no living cell is far from a source of oxygen/carbon dioxide
- diffusion takes place in air, which if faster than if it were in water
where does most of the gas exchange in plants occur? (exchange)
- the leaves
outline 3 leaf adaptations that allow for rapid diffusion (exchange)
- lots of stomata (small pores) so no cell is far from one, & therefore the diffusion pathway is short
- numerous interconnecting air-spaces that occur throughout the mesophyll so that bases can readily come in contact with the mesophyll cells
- large surface area of mesophyll calls for rapid diffusion
where are stomata mostly found? (exchange)
- the underside of leaves
what surrounds each stoma & why are the important? (2) (exchange)
- each stoma is surrounded by a pair of guard cells that c open & close the stomata pore, so that they can control the rate of gas exchange
- this is important because terrestrial organisms lose water by evaporation
how do plants control the rate of water lost? (2) (exchange)
- by closing the stomata at times where water loss would be excessive
- this balances the conflicting needs of gas exchange & the control of water loss
how do insects limit water loss (3) (exchange)
- they have a small SA:V ratio to minimise the area over which water is lost
- they have waterproof coverings over their body surfaces. Insects have a rigid outer skeleton of chitin that is covered with a waterproof cuticle
- spiracles are the openings of the tracheae at the body surfaces that can be closed to reduce water loss. This conflicts with he need for exogenous & so occurs largely when the insect is at rest
why can’t plants have a small SA:V ratio? (2) (exchange)
- because they photosynthesise
- this requires a large leaf surface area for the capture of light & for the exchange of gases
what are xerophytes? (exchange)
- plants that are adapted for life in warm, dry or windy habitats
- they are all adapted to prevent water loss
- e.g. cacti & marram grass
outline 5 plant adaptations of xerophytes that prevent water loss (exchange)
- a thick cuticle —> although the waxy cuticle of leaves forms a waterproof barrier, up to 10% of water loss can still occur by this route. The thicker the cuticle, the less water can escape by this means (e.g. holly)
- rolling up of leaves —> most leaves have their stomata largely (or entirely) confined to the lower epidermis. The rolling f the leaves in a way that protects the lower epidermis from the outside helps to trap a region of still air within the rolled leaf. This region becomes saturated with water vapour & so has a very high water potential. There is no water potential gradient between the inside & outside of the leaf & therefore no water loss (e.g. marram grass)
- hairy leaves —> a thick layer of hairs on laves (especially on the lower epidermis) traps still, moist air next to the leaf surface. The water potential gradient between the inside & the outside of the leaves is reduced & therefore less water is lost by evaporation (e.g. heather plants)
- stomata in pits or grooves —> trap still, moist air next to the leaf & reduce the water potential gradient (e.g. pine trees)
- a reduced SA:V ratio of the leaves —> by having leaves that are small & roughly circular in cross section (e.g. like in pine needles) rather than leaves that are broad & flat, the rate of water loss can be reduced. This reduction in SA is balanced against the need for a sufficient area for photosynthesis to meet the requirements of the plant
what should adaptations of xerophytes always be related to? (exchange)
- reducing water potential gradient & therefore slower diffusion, less water loss from air spaces & hence reduced evaporation of water
