Chapter 7- Gas Exchange In Fish And Insects Flashcards
What system do fish use for gas exchange?
The counter-current system
What is the counter current system?
1) water containing oxygen, enters the fish through its mouth and passes out the gills.
2) blood flows through the gill plates in one direction and water flows over in the opposite direction.
3) this maintains a large concentration gradient between the water and blood. Oxygen always higher is water so as much oxygen as possible diffuses from water into blood.
How are the gills adapted for gas exchange?
1) each gill is covered in primary lamellae which increase surface area for exchange of gases. Primary lamella are covered in secondary lamellae, which increase surface area even more.
2) the gill plates have lots of blood capillaries very close to the lamellae allowing for a short diffusion distance and they have good blood supply.
3) gill filaments have thin walls which reduce diffusion distance.
How are fish gills ventilated?
1) the fish opens its mouth, which lowers the floor of the buccal cavity. The volume of the buccal cavity increases, decreasing the pressure inside the cavity. Water is then sucked into the cavity.
2) when the fish closes its mouth, the floor of the buccal cavity is raised again. The volume of the cavity decreases and pressure increases, so water is forced out the cavity across the gill filaments.
3) each gill is covered by a bony flap called the operculum. The increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills.
How do you dissect fish gills?
1) make sure to wear labcoat and gloves since fish dissection is messy.
2) place the chosen fish in a dissection tray or cutting board.
3) push back the operculum and use scissors to carefully remove the gills. Cut each arch through the bone at the top and bottom.
4) if you look closely you’ll be able to see the gill filaments. Finish off by drawing the gill and labelling it.
How do insects undergo gas exchange?
1) air enters the insects body and into the trachea, by pores on the insects surface called spiracles
2) the trachea branch off into smaller tracheoles which have thin permeable walls and go to individual cells. The tracheoles also have fluid that oxygen dissolves in (tracheal fluid).
3) oxygen then diffuses down the concentration gradient from this fluid into body cells. Carbon dioxide difssues in the opposite direction, towards the spirackes to be released into the atmosphere.
How do insects remain ventilated?
1) insects use rhythmic abdominal movements to change the volume of their bodies to move air in and out of the spiracles.
2) when larger insects are flying, they use their wing movements to pump their thoraxes.
3) insects also open and close their spiracles, depending on oxygen demand.
How do you dissect insects?
1) first fix the insect to a dissecting board. You can put dissecting pins through its legs to hold it in place.
2) to examine the trachea, you’ll need to carefully cut and remove a piece of exoskeleton from along the length of the insects abdomen.
3) use a syringe to fill the abdomen with saline solution. You should be able to see a network of very thin, silvery grey tubes and these are the trachea. They look silver as they are filled with air.
3) you should also be able to see rings of chitin in the walls of the trachea, as they are there for support to prevent them from collapsing.
