section 1: exchange & transport - topic 4: gas exchange in fish & insects Flashcards
there’s a … concentration of oxygen in water than in air?
lower.
in a fish, what is the gas exchange surface?
the gills.
what is the structure of the gills?
each gill is made of lots of thin plates called gill filaments (or primary lamellae) - give a big surface area for exchange of gases, thus increase the rate of diffusion.
the gill filaments are covered in lots of tiny structures called gill plates (or secondary lamellae) - increase the surface area even more.
each gill is supported by a gill arch.
the gill plates have lots of blood capillaries and a thin surface layer of cells to speed up diffusion between the water and blood.
what is the counter-current system?
in the gills of a fish, blood flows through the gill plates in one direction and water flows over in the opposite direction.
what does the counter-current system mean?
that the water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen.
why is the counter-current system good?
because it means that a steep concentration gradient is maintained between the water and the blood - so as much oxygen as possible diffuses from the water into the blood.
how are the gills ventilated in bony fish?
the fish opens its mouth, which lowers the floor of the buccal cavity (the space inside the mouth).
the volume of the buccal cavity increases, decreasing the pressure inside the cavity.
water is then sucked into the cavity.
when the fish closes its mouth, the floor of the buccal cavity is raised again.
the volume inside the cavity decreases, so the pressure increases, and water is forced out of the cavity across the gill filaments.
each gill is covered by a bony flap called the operculum (which protects the gill).
the increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills.
what do insects use for gas exchange?
tracheae - microscopic air-filled pipes.
what is the process of gas exchange in insects?
air moves into the tracheae through pores on the surface called spiracles.
oxygen down the concentration gradient towards the cells.
carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.
the tracheae branch off smaller tracheoles, which have thin, permeable walls, and go to individual cells.
what happens in the tracheoles?
they contain fluid which oxygen dissolves in.
the oxygen then diffuses from this fluid into body cells.
carbon dioxide diffuses in the opposite direction.
how do insects change the volume of their bodies?
by using rhythmic abdominal movements.
what does the tracheae and tracheoles give?
a large surface area.
how do tracheoles minimise diffusion distance?
because they’re lined with a single layer of cells.
