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!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Frogs can do lots of things but I am only going to list a few of the things they can do like jump one hundred times their body length, absorb water and oxygen trough their skin and some can even change color.
Frogs are amphibians so they can go in and out of water. Frogs are
cold-blooded, meaning that their body temperatures change with the temperature
of their surroundings. When temperatures drop, some frogs dig burrows
underground or in the mud at the bottom of ponds. They hibernate in these
burrows until spring, perfectly still and scarcely breathing.
Frogs are cold blooded which means that they're body temperature changes with what the temperature is outside.
Frogs can be found in most freshwater places.
Frogs have been around for approximately 190 million years.
frog jumpingIchthyostega,
prehistoric predecessor to the modern frog, lived 370 million years
ago during the Devonian Period. Sometimes referred to as "the
first four-legged fish," skeletal remains of this earliest-known
amphibian were first discovered in East Greenland. many frogs can leap up to twenty times their body
length. (That would be about a 100-foot jump for you or me!) The longest
frog jump on record was made by a frog named Santjie at a frog derby
held in South Africa. Santjie bested the competition with a jump of
33 feet 5.5 inches.It takes less than a second for a frog's
tongue to roll out, adhere to prey, and roll back into the frog's mouth.
This week was a nice change from previous weeks in that it was not nearly so rushed because we only had one dissection. Also, this week the animal was large enough that we could really identify the organs without the magnifying glasses, so that was nice!!
We looked at perch, which have bilateral symmetry like all other vertebrates (I think). They have eight fins total, which we could all see: two on their backs (dorsal), two pectoral, two pelvic, one caudal, and one anal. Perch have nostrils that are of course not for breathing but for smelling things in the water like prey, predators, and pollution. They don't have eyelids, we assume because they don't need them.
They have a complete digestive system, which is pretty similar to ours; food goes in the mouth and then through the esophagus (which was so short we couldn't really see it), then to the stomach. The liver, gall bladder, and pancreas all help with the digestive process, and there is a large intestine and finally the anus. We discussed the functions of the pancreas a bit, one of which is to respond to increased blood sugar by releasing insulin. Insulin allows the sugar to leave the blood and go into the muscles and tissues. When the pancreas is not able to regulate blood sugar, the result is diabetes. Type 1 diabetes is when the immune system attacks the insulin-producing cells, and type 2 diabetes is when the pancreas doesn't make enough insulin or the body doesn't respond to insulin but the insulin-producing cells have not been destroyed.
We saw the gills and also these things called gill rakers, which keep large food particles from getting into the gills. They looked pretty much like this:
The opercula are the hard things that cover the gills and protect them. The circulatory system is the first closed circulatory system we've seen. There is a small two chambered heart that pumps blood first to the gills to get oxygen and then to brain and rest of the body to give the cells and tissues the oxygen they need. Then, the blood comes back to the heart. It is a low pressure, single circuit system that has both veins and arteries. The crayfish had a heart and some arteries, but then the blood flowed freely through the animal's body, so it was an open circulatory system.
One special thing about the perch is that it has something called a lateral line on each side. It really looks like a little line on each side of the fish's body and it has hair cells for detecting vibrations in the water. When we say "hair cell" we don't mean hairs, but little cells that have a part sticking out of them that looks like a hair. When the hair-like part is moved, it sends information to the fish's brain about the vibration it detected. This is something cool about fish that we don't have, although our ears use similar methods for detecting sounds and keeping us balanced.
The pictures in our dissection guides mentioned two brain parts, the cerebrum and the cerebellum. We forgot to go through the details of the perch nervous system, so we'll talk about that next time. Three things I thought were cool about the dissection:
The swim bladders were HUGE!
The liver was easy to identify and looked like other animals' livers.
The heart was really close to the head and mouth, but we could take it out and examine it.
Lastly, we discussed current scientific research on perch. Since several students focused their blog posts on the topic of eating perch, I chose this article, which looked at food contamination issues. Basically, the researchers bought various fish from markets in Saudi Arabia and put them on ice for 0, 24, or 48 hours, and then fried some of the fish. They measured the levels of chemicals called "biogenic amines" in all the different types of samples and compared them. These chemicals are made by bacteria that live in the fish and are the major cause of food poisoning from fish. Symptoms include hypertension (high blood pressure), headaches, diarrhea, rash, and can result in death on rare occasions. They found that the levels of these chemicals increased the longer the fish were stored, and frying the fish increased the levels further. So be careful of your fish fry! Here is some fried perch -->
Perch are awesome because they are fish and all fish are awesome. I mean, perch are the best because they are really tasty when fried and they're really fun to catch. There are some kinds of perch that are yellow and some are black. However the best thing about them is that they are very easy to catch, and did I mention, that they are very tasty!!!!
I personally have fished for perch and filleted them and they are really tasty so i am excited to dissect one so i will have dissected one, ate one, and filleted one.
I wonder how big the orgins will be.
I wonder if we will be able to tell whether is a boy or girl.
in the class about grasshoppers and crayfish i learned that both grasshoppers and crayfish are arthropods and have hearts but no blood vessels. i liked that we got to dissect both of them because they where both very interesting. i could not figure out the sex of my crayfish but other students could so i just went with it. a lot of students had eaten crayfish an said they where tasty. I'm vegetarian so i wouldn't know. but they look tasty.
in the class about grasshoppers and crayfish i learned that both grasshoppers and crayfish are arthropods and have hearts but no blood vessels. i liked that we got to dissect both of them because they where both very interesting. i could not figure out the sex of my crayfish but other students could so i just went with it.
a lot of students had eaten crayfish an said they where tasty. I'm vegetarian so i wouldn't know. but they look tasty.