Exchange Flashcards
(41 cards)
Features of specialised exchange surfaces
- Large SA:V - increases the rate of exchange
- Thin - short diffusion path - materials cross surface rapidly.
- Selectively permeable - selected substances can cross.
- Movement of environmental medium (e.g. air) maintains diffusion gradient.
- Transport system so that internal medium moves - maintains diffusion gradient.
How does gas exchange across the body surface of a single-celled organism occur?
by diffusion.
diffusion across the CSM of a single-celled organism (3)
- Small and have large SA:V.
- Oxygen is absorbed by diffusion across their body surface - through CSM.
- CO2 from respiration diffuses out across CSM.
describe the process of gas exchange in insects
– Air moves into the tracheae through the open spiracles - O2moves down concentration gradient from the air to the cells - CO2 moves down concentration gradient from the cells to the spiracles and then out into the atmosphere -The tracheae branch off into tracheoles which have permeable walls
Purpose of abdominal pumping in insects
to move air in and out of the spiracles at a faster rate - increase in pressure in tracheae forces air out down a pressure gradient. air with a higher oxygen concentration is then drawn in.
Mechanisms used by insects to conserve water
- small SA:V
- waterproof coverings
spiracles can be closed to reduce water loss.
structure of the specialised gas exchange surface in fish
gills - formed of gill filaments with gill lamellae at right angles - to increase the surface area if the gills for exchange.
what does counter current flow in the gills mean?
the flow of water over the gills and blood through the gills occur in opposite directions.
importance of counter current exchange in the gills.
vs. parallel flow
- Blood and water flow over the gill lamellae in opposite directions.
The maximum possible gas exchange occurs as a diffusion gradient for oxygen uptake is maintained across the entire width of the gill lamellae.
This means a higher percentage of oxygen from the water can be absorbed into the fish’s blood.
Parallel flow would mean a diffusion gradient was only maintained across part of the length of the fish lamellae. Only 50% of available oxygen would be absorbed into the blood.
what do plants require gases for?
- CO2 for photosynthesis
- O2 for respiration
Adaptations of plants to dry environments (xerophytes)
- stomata sunken in pits which trap moist air, reducing the concentration gradient between the leaf and the air
- hairs on epidermis - also trap moist air.
- curled leaves with stomata on the inside - moist air trapped, stomata protected from wind.
- thick, waxy cuticle, especially on the upper stomata - reduced evaporation (LDP)
gas exchange in plants
gases from the air diffuse into air spaces within the leaf via the stomata. Gases then diffuse into mesophyll cells in the leaf which have a large surface area.
what controls the opening and closing of the stomata?
guard cells
why is it important to control the opening and closing of the stomata?
- open to allow for gas exchange.
- close to prevent water loss
gross structure of the human gas-exchange system
- Lungs - mammalian organ where gas exchange occurs.
- Trachea - flexible airway supported by rings of cartilage
- Bronchi - 2 divisions of the trachea, each leads to 1 lung.
- Bronchioles - branching divisions of the bronchi.
- Alveoli - minute air sacs, epithelial lining is the gas exchange surface.
Adaptations of the alveolar epithelium for efficient gas exchange
1) Large number of alveoli provide a large SA for gas exchange.
2) Alveoli are surrounded by a network of capillaries which also have a large surface area.
3) Thin exchange surface as the alveolar epithelium and capillary endothelium are each only 1 cell thick - so short diffusion pathway.
4) Steep concentration gradient of oxygen and carbon dioxide between the alveoli and capillaries, which is maintained by circulation of blood and ventilation in the lungs
How do gases from the air enter the blood in mammals?
Travel into the lungs through trachea, bronchi, bronchioles, alveoli. Travel across alveoli epithelium and capillary endothelium down diffusion gradient.
Why does air constantly need to be moved in and out of the lungs?
to maintain a diffusion gradient of gases in the alveoli
Describe what happens in inhalation
- The external intercostal and diaphragm muscles contract.
- This causes the ribcage to move upwards and outwards and the diaphragm to flatten, so the volume of the thorax cavity increases.
- As volume increases, air pressure in the lungs decreases.
- Air is forced into the lungs down a pressure gradient (higher atmospheric pressure to lower air pressure in lungs)
Describe the stages of normal exhalation
1) The external ICM and diaphragm muscles relax.
2) The ribcage moves downwards and inwards and the diaphragm domes upwards.
3) The volume of the thoracic cavity decreases, causing air pressure to increase.
4) Air is forced out of the lungs down a pressure gradient.
Describe what happens in forced exhalation
the external ICM relax and the internal ICM contract, pulling the ribcage further down and inwards. The interaction of the 2 sets of ICM is antagonistic here.
which parts of breathing are active and which are passive?
inhalation - active
exhalation - passive
forced exhalation - active
where in the lungs does gas exchange occur?
the alveoli
pulmonary ventilation rate equation and explanation
Pulmonary ventilation rate = tidal volume x breathing rate
Pulmonary ventilation rate - dm3 min-1, the total volume of air moved into the lungs during 1 minute.
Tidal volume - dm3, the volume of air normally taken in in each breath when the body is at rest.
Breathing (ventilation) rate - min-1, the number of breaths taken in 1 minute.
