2.2 - Adaptations for gas exchange Flashcards
All living organisms exchange gases with their environment. Gases are exchanged across respiratory surfaces. A respiratory surface must be:
Thin (short diffusion pathway)
Permeable to gases
Have a large surface area
Have a mechanism to produce steep diffusion gradient across respiratory surface
Gases are always exchanged by _______. Single celled organisms such as the Amoeba have a large _______ ____ to ______ ratio and a ____ cell membrane so diffusion into the cell is rapid. Also Amoeba is a single cell is thin so diffusion distances inside the cell are short.
diffusion
surface area
volume
thin
Larger organisms (multicellular) have a lower surface area to volume ratio than smaller organisms, so they must have a ventilation mechanism. Why can flatworms carry out gas exchange more efficiently than an spherical organism?
They have a larger surface area to vol ratio than spherical organisms of same vol, hence, no part of the body is far from the surface and so diffusion paths are short
The earthworm is cylindrical and so its ______ ____ to _______ ratio is smaller than a flatworms. Its skin is the __________ surface, which it keeps moist by secreting _____. It has a low oxygen requirement because it is slow moving and has a low _______ rate. Enough oxygen diffuses across the skin surface to reach the blood ________ beneath. Haemoglobin present in the blood capillaries carries oxygen around the body in blood _____. This maintains a steep conc gradient at the respiratory surface. _______ diffuses out across the skin, _____ a conc gradient.
Surface area to volume
respiratory
mucus
metabolic
capillaries
vessels
Carbon dioxide
down
Many multicellular animals, have special features not seen in unicellular organisms:
Higher _______ rate.
Increase in size = tissues and organs become more __________
Maintain steep _______ gradient across the respiratory surfaces
Respiratory surfaces must be ___ = fragile, so need to be protected
metabolic
interdependent
concentration
thin
For efficient gas exchange, what do the more advanced multicellular organisms need?
A ventilation mechanism
An internal transport system, the circulation system, to move gases between the respiratory surface and respiring cells
A respiratory pigment in the blood to increase its oxygen carrying capacity (haemoglobin).
Where does gas exchange take place when an amphibian is active or inactive?
Inactive - uses its moist, permeable skin with well-developed capillary system below surface.
Active - uses its lungs (surface is highly folded = high S.A)
Where does gas exchange take place in reptiles?
Reptiles have more efficient lungs than amphibians. Gaseous exchange occurs exclusively in the lungs (sac-like) and has more complex folding. Reptiles have ribs, but no diaphragm. Ventilation is aided by the movement of ribs by the intercostal muscle.
Birds have a high respiratory rate. Where does gas exchange take place in birds?
In the small and compact lungs, composed of numerous branching air tubes called bronchi. Parabronchi (smallest air tubes) have an extensive blood capillary network, it’s here that gaseous exchange takes place. Birds ribs and flight muscles also help ventilate.
Fish are active and need a good oxygen supply. Gas exchange takes place across a special respiratory surface, the gill. Gills have:
A one-way current of water, kept flowing by specialised ventilation mechanism.
Many folds, providing large S.A over which water can flow, and over which gases can be exchanged
Large surface area maintained by density of water flowing through
Why is the ventilation system less efficient in cartilaginous fish?
They don’t have a special mechanism to force water over the gills, and must keep swimming for ventilation to happen
Water and blood flow in the same direction (parallel flow)
Blood’s oxygen conc is limited to 50% of its possible maximum value (as max saturation of water is 100%)
Gas exchange doesn’t occur continuously across whole gill lamella.
See NC 1
What is parallel flow?
Blood and water flow in the same direction at the gill lamellae, maintaining the conc gradient for oxygen to diffuse into the blood only up to the point where its conc in the blood and water is equal
How does the ventilation work in bony fish?
It’s achieved by pressure changes in the buccal (mouth) and opercular (gill) cavities. The water pressure in the mouth cavity is higher than in the opercular cavity. The operculum acts as both a valve, letting water out, and as a pump, moving water past the gill filaments.
How does the ventilation mechanism work in bony fish when it takes in water?
a) mouth opens
b) operculum closes
c) floor of mouth is lowered
d) volume inside mouth cavity increases
e) Pressure inside mouth decreases
f) Water flows in as the external pressure is higher than the pressure inside the mouth
See NC 2
How does the ventilation mechanism work in bony fish when water is forced?
a) The mouth closes
b) The operculum opens
c) The floor of the mouth is raised
d) The volume inside the mouth cavity decreases
e) The pressure inside the mouth cavity increases
f) water flows out over the gills because the pressure in the mouth cavity is higher than in the opercular cavity and outside
See NC 2
