Module 3.1 Gas exchange in fish and insects Flashcards
Why can’t fish rely on diffusion for gas exchange? What is their specialised exchange system called?
They are waterproof and have a small SA:V ratio, meaning they require a specialised exchange system for gas exchange.
List the structure of the tracheal system in order:
From the environment, air enters the insect via spiracles and into the air tubules ( trachea and tracheoles ). These tracheoles deliver oxygen straight to individual cells, down the oxygen concentration gradient.
Why is the tracheal system always saturated? How do the spiracles help with this?
The oxygen delivered will dissolve into the fluid and then diffuses into the body cells, CO2 will do this in the opposite direction. As of this, spiracles can control when they open and close to regulate water loss and prevent dehydrating, which would inevitably kill the insect if they were to dehydrate.
What does the tracheal fluid do when an insect is active?
When tissues are active, the tracheal fluid can be withdrawn into the body fluid in order to increase the surface ara of the tracheole wall exposed to air. This will mean there is then more oxygen available to absorb.
What is the limitations of the tracheal system? How can this be resolved?
The system relies on passive movement of air into the trachea, meaning diffusion can place limits on the body. However, larger insects are able to mechanically pump air into the body to increase their O2 delivery.
How do larger insects mechanically pump air into the body? 2 ways:
Volume of thorax: wing movement changes the volume of the thorax forcing air into the tracheal tubes due to pressure dropping. if pressure drops, air is pushed in, and if pressure gains, the air is pushed out.
Volume of abdomen: By increasing the volume of their abdomen by breathing movements, the spiracles at the front of the body open and air enters the system. As it contracts, the front spiracles close and the back spiracles open, forcing air out.
Do fish have a more or less efficient gas exchange system? why?
Theirs is more efficient as they have to extract oxygen from the water they intake, which is at a much lower concentration.
Describe the movement of the mouth and buccal cavity, in terms of water movement.
As the mouth opens, the buccal cavity floor lowers and the operculum closes, meaning water moves into the buccal cavity. As the mouth closes, the buccal cavity rises and the operculum opens, meaning water moves across the gills and out of the opercular cavity.
What is the primary and secondary lamellae? what is the purpose for the secondary lamellae?
The primary lamellae are 4 gill filaments in which are attached to a bony arch. The secondary lamellae is the folded surface of the primary lamellae. They mean that the gills have an even larger surface area for gas exchange.
What is the counter-current exchange system? Why does it flow this way?
If blood flowed the same direction as water, a concentration gradient would reach an equilibrium with the blood, which is very insufficient. To tackle tis, fish have a counter-current exchange system in which blood flows the other way, meaning there is a constant steep concentration gradient the whole length of the gill. Water is always next to blood with a lower oxygen concentration.
What features of the fish gas exchange system makes it more efficient?
Many lamellae folds: means it has a larger surface area.
Thin lamellae: means there is a short diffusion pathway.
Good blood supply: Constant concentration gradient so oxygen delivery is more efficient.
