Wow! We dissected snakes! Most were pretty long, around 2-3.5 feet or so. There was one that was very small, and my guess was that we ordered so many they didn't have enough large ones so they took a younger, smaller one. We were disappointed about not being able to see any animals inside the stomachs of our snakes. I guess they didn't feed them before sacrificing them. But we did learn a lot!
The snake is in class Reptilia, which is a group of animals well adapted to live on land. We noticed the differences between the scales on the bottom of the snake compared to those on top, and saw that the eyes are covered with scale, not a thin membrane like the frog's eyes. We thought it was cool that each scute, which is a scale on the ventral side of the snake, corresponds to a rib in the snake!
It took us a while to find the tongue of the snake, it is tiny and black and forked. It is a sense organ for smell, and it tastes things in the air, then puts them on the roof of its mouth where Jacobson's organ sends information about the molecules to the brain. The snake does not have ears, but detects vibrations in the ground through ossicles, which are ear bones.
Snakes have two nares (basically like nostrils) on their snouts, and two inside their mouth, and that's how they breathe. It turns out they generally have one big long lung going along their bodies, and also a second very small one that doesn't function. Of course all the organs of the snake need to be long and thin to fit in their bodies, so the hear, liver, and kidneys are also like that. There is a lot of fatty tissue in the snake, we figured to keep their bodies warm when it gets cold.
Like the frog, the snake's heart has three chambers and the blood mixes in the ventricle. This is different from how our heart works. We'll see with the next dissection how a mammalian heart is organized.
Research article: This week's research article was about how snake venom does what it does. We discussed that snake venom is not a poison because eating it is not dangerous. But when it gets in an animal's bloodstream, it does several things. For one thing, it has specific proteins in the venom that prevent the blood from clotting, so that the other proteins in the venom can attack the entire animal. The other proteins often do things like block the signal from the nerves to the muscles, but they can also attack and kill red blood cells. The article I discussed was "The collagen-binding integrin a2b1 is a novel interaction partner of the T. flavoviridis venom protein flavocetin-A". They found that a specific venom protein called flavocetin-A sticks very tightly to a protein called integrin a2b1 as a way of blocking blood clotting, and this could be a helpful piece of information for developing new drug treatments for medical purposes.
Review from last week: We didn't have time to discuss frog research last week, so I shared this article about tadpoles and how they respond to parasites and predators. I also mentioned this article which explored how tadpoles start to get bulgy and fat after coming in contact with predatory salamanders. Weird! This image shows a regular tadpole on the left, and the bulgy morph on the right.
We finally got to dissect frogs, the stereotype of all dissections. I had never dissected one before though!
Q & A about frogs:
1. What is the significance of frogs (why were they a part of the evolutionary diversity animal dissection kit)? They represent the transition from an aquatic lifestyle to a terrestrial one -- the shift from water life forms to life on land.
2. What is a tetrapod? An animal with four limbs, typically two forelimbs with upper arms, forearms, and hands, as well as two hindlimbs with thighs, lower legs, and feet.
3. Do frogs have nostrils? Yes, we found two nostrils, right where you'd expect them.
4. How do frogs hear? They don't have external ears, but they have tympani, which are disc-like structures used for sound reception, and they have an inner ear.
5. Do frogs have eyelids? Well, they don't have moveable eyelids, but they have a nictitating membrane that moistens and protects the eye.
6. What is the glottis? The glottis is a slit-like opening at the back of the throat that leads to the lungs. It is next to the opening to the esophagus, which leads to the stomach.
7. How many sets of teeth do frogs have? They have two sets of teeth, an outer set of maxillary teeth and also vomerine teeth. We had a hard time finding these teeth, because they don't look like our teeth. They look more like little bumps of cartilage.
8. What are Eustachian tubes? Frogs have them on the sides of the roofs of their mouths, and they lead the ears. Their function is to equalize pressure inside the frog.
9. What internal organs did we look for? We saw the stomach, small intestine, large instestine, liver, gallbladder, and pancreas. We also saw the heart and lungs, and eventually found the kidneys, bladder, and reproductive organs (testes in males and ovaries in females).
10. How many chambers did the hearts have? They had three chambers: two atria and one ventricle.
11. Could we tell the males and females apart? Yes, it was very cool. The females had long squiggly oviducts that ran all the way up the sides of the frogs, which sortof looked like small intestine. I guessed that perhaps they needed really long oviducts because they need to squirt out a huge number of eggs at one time. The males didn't have this, and instead had testes, which looked like small white kidneys and were located right near the kidneys (which were dark red).
12. What do kidneys do? Kidneys filter the blood and put the waste products into the urine to be peed out. We clarified that the reason urine doesn't look like blood is because the hemoglobin bound to oxygen, which gives blood its red color, isn't a waste product, and that waste products are colorless or yellow, for the most part.
We also spent time in class going over how to put videos into blog posts. Hopefully we will all have amazing blogs in our lives, and we vow to share them with each other. This video is an animation about a frog done by kids in France ages 9-10 with their teacher.
Sunday, December 2, 2012
I am glad i am not a crybaby frog!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
