5 (Living Things Maintain a Dynamic Equilibrium Which Sustains Life)

LESSON I: INTRODUCTION TO RESPIRATION

To Address NYS Standard: 5 (Living things maintain a dynamic equilibrium which sustains life)

Behavioural Objective: The students will be able to understand the basic structures and functions that an organism must have and perform in order to do respiration.

Explanation of Lesson Plan: This lesson will give students the basic vocabulary necessary to properly discuss the respiratory system. Students will learn the importance of surface area, proper blood flow, and how many animals exchange gasses.

Hook: (3 minutes) “We know that it is important for all cells to have oxygen, and to get rid of their wastes. We know they need nutrients, and we have discovered how they get those. But how do cells deep within an organism’s body get the gasses that they need? How do they dump off their wastes? Recall our demonstration of capillaries from before. A smaller diameter and a slower speed made the system more efficient. We can’t really slow down air, so we must use larger surface area to compensate!”

Test of Prior Learning: (5 minutes) 1. Why is it important to have a lot of surface area? 2. What about your respiratory system can you change? What about it can’t you change?

New Learning: (30 minutes) 1. All organisms, in some form or another, need to exchange gasses. This is the purpose of the respiratory system, to exchange gasses. 2. Of course, we have to do so in the right directions, and at the right places. 3. The atmosphere is the respiratory medium, or the source of oxygen for many organisms. We are bathed in about 21% oxygen, while water is a very small percentage of oxygen. 4. The thing that gets this dissolved oxygen from the medium into the organism is called the respiratory surface. This should be LARGE! 5. If you’re an amoeba, you can use your entire surface, which is nice. 6. Or, if you’re a hydra, all your cells are close enough to water for diffusion to work its magic. 7. However, if you’re a marmoset, tiger, or lemur, your entire body surface doesn’t have access to the outside, and the outside might not be wet…indeed, it’s probably dry. So you have to have an internal respiratory surface which you keep wet. 8. You also have to have a means to ventilate this structure, that is, move air or water past it. 9. Let’s start with fish. They have gills. These don’t have to be kept wet, as they are in the water. 10. There are many species with gills. Fish, crustaceans, mollusks, sea stars, many sea worms, and others. 11. These can simply wave their gills about in the water, or, like fish, they can push a stream of water past them. 12. They do so in a very specific way, called countercurrent exchange. You might not understand this, but I think you’ll like it.

[Explanation of countercurrent exchange]

13. So this can make gills very good at extracting what little oxygen there is in water out of it. 14. In insects, there is a system of tracheae (tracheal system). These are small tubes which open to the world through spiracles. 15. The ends of the trachea can actually enter individual body cells, and one often sees mitochondria clustered around the ends. Wild! 16. This is a problem, though, because the system must be kept moist, and much water can be lost. Things that use their skin as a respiratory surface, like some amphibians, earthworms, etc., must be kept moist. 17. So the system is usually folded inside the animal. 18. Insects can expand and contract their body cavity to ventilate their tracheae. 19. They can also do something called tracheal fluttering, to keep water in. They don’t open the spiracles a whole lot this way! 20. Lungs are the next step. Spiders, terrestrial snails, and vertebrates have lungs. 21. Amphibians use their skin to aid their lungs. Turtles’ shells restrict their breathing, so they have to use moist mucous membranes in their mouth and anus to help out. 22. Lungs have a huge surface area in humans, about 100 square meters.

Test of New Learning: (5 minutes) 1. Why is surface area so important? 2. Gasses diffuse slower in water, so why do we keep mucous membranes wet?

Assignment: