Digestive System

 The digestive system is an important part of our bodies also. It gives us the energy, and nutrients we requrie to survive. It also gets rid of unwanted waste in our bodies, as well as others, too.
 Each of the digestive systems is similar in these ways:

• they all have mouths
• they all have "guts"
• they all have an anus

-All of these things probably evolved in similar ways. As creatures first began to evolve, they needed a way for food to get in and get out, using their mouths, and anuses. They also needed a way to digest their food, which is why they physically needed guts.

The rat, and human digestive systems are similar.

picture from enchantedlearning.com

-There are two types of digestion: mechanical, and chemical.
-Chemical digestion is when pepsin splits the complex molecules into smaller chains of amino acids.
-Mechanical digestion is when things are broken into chunks of food, rather than a whole.
-The human digestive system, and some mammals too, produce saliva. This saliva is more than just water. It softens and lubricates food, and it helps our food stay together.
-I'm sure we first started out as eating things that are whole, such as nuts, which is why human jaws were bigger back then. As we began to eat less strained things, mechanical digestion came into play, so that we don't choke.

-Our stomach uses chemicals called gastric juices to try and make food tinier. This takes about 3 or 4 hours.
-Unlike the frog, our liver is not bulit to withhold our weight in jumping. It is though, built to hold glycogen, and break down toxic substances.
-The nutrients in the complex digestive system are absorbed in the small intestine. Humans have a lot of surface area, which is helpful when it comes to absorbing more nutrients.
-The pancreas is in charge of breaking down carbohydrates, and the gallbladder is in charge of breaking down fats.
-The large intestine is used to absorb water, which is possible thanks to osmosis.
-And like almost all other things, the waste we produde is removed through the anus.

A frog's digestive system.

Liver & stomach(left), Stomach lining(right)

-The frog's liver takes up a big portion of its entire body. Making it the largest organ in its digestive system.
-The reason its so big is because it needs to make bile. Bile assists the digestion in the small intestine. It rids waste. The liver also stores vitamins, and processes toxins for its kidneys. This is similar in the humans.
-The gallbladder stores the bile produced by the liver.
-The elastic esophagus, and stomach help the frog eat a large amount of food. This is an advantage because the more you eat, the more energy you'll recieve.
-The frog's pancreas is built to have insulin. This insulin is used for homeostasis, which proves as an advantage.
-When food enters the frog, it goes to the stomach, into the small intestine. From there, the food moves to the large intestine, then the cloaca (frog bladder), and lastly out the anus.
-One disadvantage to having a small and large intestine is that if you loose one, you die, and homeostasis is needed to keep it running.
-Nutrients are absorbed in the capillary walls. Note the difference. Humans absorb their nutrients from the small intestine. This means the frog digestive system came first, because its simple, and doesn't need to absorb their food the way we do.

The crayfish's digestive system.
-The food the crayfish eats enters to the esophogus, then to the stomach. It enters the intestine, and digestive gland, and like the human, leaves through the anus.
-In the crayfish, nutrients are absorbed in the intestine, and digestive glands, just as a humans.
-The crayfish has two stomachs. This has it's advantages and it's disadvantages. For one, it can eat more, and it can eat things that take long to digest, like grass.
-The digestive glands are packed with enzymes, with allow it to digest faster, and can recieve it's energy faster.

The earthworm's digestive system.

-Earthworms eat soil, and the nutrients they recieve are absorbed from the typhlosole, or an infolding of the intsestinal wall.
-The food in the earthworm moves from mouth, to muscular pharynx, to esophagus, to crop, then to gizzard, and finally out the anus. Just like the human, frog, and crayfish.
-The purpose of a worm's crop is to temporarily store soil, which is all a worm can eat.
-The purpose of the gizzard is to grind the soil, and realease
and break up organic matter. The worm does this by using pebbles, or mechanical digestion.
-Also, a worm doesn't need homeostasis or enzymes to perform any actions, unlike us.
-The nutrients from the soil are absorbed by the blood.
-The purpose of the typhlosole is to increase the surface area for digestion and absorption.
-And, alike the others, the undigested waste exits through the anus.

Muscular System

 The muscular system is important in many ways. It contains tissues, controls movement, provides mass, and gives us strength. Without it, other functions would not work.

The earthworm's muscular system is special. It has two kinds: longitutinal, and circular. 

-Circular and longitutinal muscles help the worm move itself. It does this by squeezing all of its muscles forward. 

-As mentioned before, it also uses bristles (satae) to move. 

-Compared to other organisms, a worm has less muscles. We, for example, have muscles in our arms, and legs, while worms do not.
-A worm has an advantage when it comes to muscles because as the circular muscles move, the diameter of the worm's body is reduced, making its body thinner. A human, for example, cannot do this. When the worm does this, it becomes smaller, which is good to fit into smaller places, and to not be seen. 

The crayfish has muscles everywhere. 

-The telson or urapod help the crayfish swim backwards. This is advantageful because without this muscle, the crayfish wouldn't be able to look at its predator, behind it. Also, it can escape quickly. 

-Unlike the worm, the crayfish has muscles everywhere; in its legs, tail, and body. This helps with locomotion. 

-Muscles fill up the entire abdomen of the crayfish. The extensor is what makes the tail straight, and the flexor is what curls it up.

-Having lots of muscle in its legs is an advantage. This is because it can walk, or crawl, faster. This is helpful when running from prey. This is similar in swimming. With more muscles in the tail, it can swim away faster.
-An advantage to having a lot of muscles is that it can be damaged easily. They can be used for defense, but can be damaged while trying to fight. 

The frog is next. 

frog's abdominal muscles

-Like humans, the frog's muscles are attached to its bones. This makes a full range of motion, controlled by our skeleton.

-In order to move, the muscles must contract, shorten, and relax.

-The strongest muscles in the frog's body are in its legs, and abdomen, just like a crayfish. The legs have a lot of muscle because they are needed to jump long distances.

-The abdomen has strong muscles because when a frog jumps, it lands on its abdomen. If it wasn't strong, bones would break as it lands. This was probably different before. Before, the frog probably had a weaker abdomen, and as time passed, frogs evolved stronger abdomens because of
its use.
-One disadvantage to the frog's muscles is that the lower back legs aren't meant to bend the way a human's is. This means it can't walk, or run, or skip. That's right: you can't play hop scotch with it. Anyways, this is bad because it can't get very far in a short amount of time. This makes it easier to get caught.

The rat's muscles are simple. 

-The rat's muscles work in groups. Some move in and some move out.

-The rat is flexible. This means less injury. This is an advantage. The less injury you have, the less risk of dying you'll have.

-The rat has a group of muscles that are on its shoulder. Unlike the human, who has one.

-The rat's muscles are similar to ours and the frog's because they need oxygen to contract, and move. The rat's thigh muscle (biceps femoris) is similar to ours. They both form knee flexion. 

Finally, the human.

taken from the Holt, Rinehart, and Winston biology textbook

-The human obviously has some differences compared to the other organisms. 

-Us humans have a gluteus maximus. This is not only your butt, but a strong, hip extening muscle. This is essential in running, and walking. 

-We also have arms to move, unlike the worm. This is all thanks to the deltoid muscle. The deltoid is our shoulder muscle, which control the movement in our shoulder, and also lets our arms move in rotation. 

-Lastly, we have a muscle called vastus lateralis. This muscle is just above our knee. It allows us to move our knee. Most animals *cough cough worm cough* don't have knees. An advantage to having them would be running. Running can help you escape from prey, and get you places faster. A disadvantage is that like other muscles, it can get injured easily. 

Skeletal System

 The skeletal system is important. It allows movement, protection, support, mineral storage, and blood cell formation.

The earthworm's skeletal system is different. It has no bones. It has a hydrostatic skeleton, which means instead of bones, it has a fluid-filled cavity surrounded by muscles. We'll go into detail about muscles later. 

-This means the worm has no ribs, no arms, or no legs. But that's obvious. This also means the worm has no calcium nor requires its intake. This differs from all of the other organisms.

-A disadvantage to not having muscles is that it has no strength. You don't see a worm doing push-ups. But, that means its weak, and can't really defend itself. 

-The worm also has this thing called a coelom. If this coelom gets injured, the worm dies. One mistake, and boom, you're dead.

-An advantage, however, to not having a skeleton is that movement is easier. Shocking, right? Actually, a worm is more flexible, and can move with more ease. This is helpful in many ways. It can get out of trouble in a matter of minutes, which comes in handy when you don't have muscles to fight.

-Another advantage is that the healing process regenerates quickly. The worm doesn't have to wait too long for some of its body to come back. This is helpful because, it can get back to normal quicker.

The crayfish's skeletal system is next. 

crayfish's exoskeleton

-The crayfish has a antennae, which is used for senses. This is an advantage because it can sense danger early, and can run away.

-Like the worm, the crayfish is segmented, but in a different way. Its tail is segmented. This allows flexibility, which is helpful when it comes to swimming.

-The crayfish has an exoskeleton, which is made out of chittin, protein, and lipids. This exoskeleton has its goods and its bads. One good thing is that it can protect the creature. On other creatures, an injury will come in first contact with our skin, but on an exoskeleton, the injury hits the bones first.

-The crayfish has a cheliped. This is its claws.These work as hands, as well as scissors, which is an advantage because it can be used as defense.

-Since the crayfish has bones, it has calcium. This calcium can be used to make muscles contract, have blood clot, and allow nerves to send and recieve messages, kind of like ours.

-More about exoskeletons: The exoskeleton limits the size of the organism, which is a bad thing. If you need to be big, to scare other organisms, and not be eaten, this is a disadvantage.

-Also, this exsoskeleton weighs. The more heavy it is, the more weight the organism has to carry.

-But, on the bright side, the exoskeleton provides homeostasis for the organism. It keeps it warm or cold, and that's definitley an advantage.

Next is the grass frog. 

-The grass frog has an endoskeleton. This means the skeleton is underneath the skin.

-The frog has a hollow, flat skull bone. This makes it easier to hide, and provides a better eyesight.

-The frog's skeleton differs from the human's because it doesn't have a neck. That means it cannot turn to look behind it.

-The frog has no fibula. Instead, it has a tibiofibula. This is an advantage because they can jump farther. If it can jump farther, it can run away, and avoid danger.
-A disadvantage to being a frog is that it can only jump. It cannot run in use of danger, making its 'getaway' slower than normal.

-The frog also has a square pelivs. Ours is circular. This allows more movement because it slides up, and down the spine, making jumping easier. 

Next is the white rat. 

-The rat has an endoskeleton. This is helpful in many ways. First, the mandible or maxialla are used in many ways. They are the bones that form the jaw. This allows chewing, which allows defense, eating, and comes in handy when you need to cut things. This is also used to chew threw things that are really hard.

-The rat has a caudal vertabrae, which make up the tail. This tail is used for balance, and homeostasis. A disadvantage about having a tail is that it can get caught in places, and it can be easier to get caught by prey. Also, its another bone that can be broken. Don't want that happening.

-Along with a tail, the rat uses its low pelvis for balance. This is an advantage because it needs to walk, and run.

-The rat has five vertabrae:

• cervical- makes up the neck of the rat. 
• thoratic-  holds the cervical and lumbar vertabrae together.
• lumbar- hold the thoratic and sacral vertabrae together.
• caudal- this is the part where the rest of the skeleton is connected to the tail.
• sacral- holds lumbar, and caudal vertabrae together.

Final is the human skeleton. 

-The human skeleton contains calcium. This calcium is present so that our bones stay big and strong. It also makes sure that muscles contract, blood cells clot, and nerves send messages.

-We have a bone called a patella. The patella allows movement. If it weren't there, our leg would be a straight, long, stick, and we wouldn't be able to move very comfortably. It is also an advantage because it allows us to run, jump, and skip. This comes in handy in many ways. Like performing a daily task, or a complicated one. This is a disadvantage because it can break, like any other bone. The worm has no patella, which means it has one less bone to break, or none at all.

-We also have phlanges. The phlanges in our hands let us grab things, which was only recently evolved. The phlanges in our feet are used for balance. Without them, we would not be able to walk. This an advantage because we need our fingers for everything: eating, climbing, etc. Without them, it would be harder to maintain things, and capture prey.

-Compared to the frog, the human hand is a lot less thin, and the frog has less bones. The frog also can't grab things, which is why you can see humans are more recently developed than frogs. 

Integumentary System

 The integumetary system is the largest organ in our bodies. It is the outside of us. Our skin, our fur, our armor. This system proctects as well as helps our bodies. It protects us from disease, or bacteria, and the sun's UV rays. It also maintains homeostasis (hot or cold) and removes waste from the subaceous glands, and sweat glands.



First, I looked at the integumentary system of a grass frog.

-The grass frog's skin produces mucus. This allows its skin to stay moist. This is a disadvantage because if it isn't moist, it could suffocate.
-The frog's skin is meant for camoflauge produced by melanin. This is advantageful because it can hide from prey, and survive.
-Its skin is permable for both water and gas. This allows it to swim undearneath the water for a long time, which can be used to run away from prey, and even get food.
-The frog also uses its skin for respiration, and protection. It protects its skeleton, and organs from getting damaged. It can breathe under the water, which makes the water a great place to be if you're a frog.
-A frog is ectothermic, which means it gets its energy from the sun. Being ectothermic allows less food intake, which makes a less risk for dying.

Second, I looked at the integumentary system of a rat.

-The rat has fur, which is an advantage because it can keep warm in cold temperatures.
-The rat has whiskers, which are used for sensory. It helps it determine if it fits in a hole, or something.
-The rat has fingernails, which are advantageful because it can use it to hurt a prey, or catch food, and can dig holes, and rip cords or sutff.
-A rat is endothermic, which means its warm blooded. This means a rat has to get food from eating things, such as cheese, to get energy. This has a disadvantage because you have to go and search for food. While doing this, something bad could happen, which allows you to loose your life.


Then, I looked at the crayfish's integumentary system.

-The crayfish has an armor, which is by all means an advantage. This allows it to survive, and less likely to be eaten.
-The crayfish's armor is not permable, which means it uses it mouth to eat, like the worm.
-The crayfish has claws, which act kind of like scissors. This allows it to defend itself from things like humans.
-The crayfish also has an exoskeleton, which is used for protection.
-The crayfish is ectothermic, which makes it virtually useless in the dark. The crayfish depends on the sun for energy, and without energy, it can't do much.

Next, I looked at the integumentary system of an earthworm.

-The worm has mucous glands, which allow it to slither. This is useful because it can manuever through dirt easily.
-The worm has neither lungs nor gills, and exchanges gas through its skin. This is not useful when it comes to water. If it has to run into water, it will die.
-The skin is thin, which means it can perform diffusion. Diffusion is when something moves from a higher concentration to a lower one, or spreading something more widely. This is helpful because it can get food, and gas from here.
-The worm's skin has satae or bristles. This makes movement easier, and that means the worm can move with better ease.

Next, I looked at the integumentary system of a human.

taken from the Holt, Rinehart, and Winston Biology textbook

-The human skin is made up of three layers: Epidermis, Dermis, and Subcutaenos Tissue. This is useful because it protects, it has senses, it keeps you warm, and it contains blood, muscle, and sweat.
-The skin is used as a barrier. It keeps the inside stuff protected, and the outside stuff, such as disease, and UV, out.
-The skin maintains homeostasis by having hair, and nerves, and, releasing sweat. Sweat cools you down, while hair can keep you warm. Nerves are used for sensory.

-The skin also removes waste, like sweat, oil, dirt, and dead skin. Without the release of oil, our skin would be really dry, and would crack easily, almost like a mask. Dead skin comes off of our bodies all the time, and if it were to remain on us, our skin wouldn't be so healthy.
-The human skin is endothermic, which means we gets energy from the things we eat. The only disadvange this gives us is that we spend a lot of money, and we need a lot of it to get more and more energy.