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external image 11kjwxy.png HW Post #1: Cell Division Results In Genetically Identical Daughter Cells

Cell's endowment of DNA, its genetic information, is called its genome. A prokaryotic genome is usually one long DNA molecule but a eukaryotic genome contains a number of DNA molecules. Human areeukaryoticand a normal human cell consists about 2 meters of DNA, which is about 250,000 times greater than the diameter of a cell. Nevertheless, this DNA should be copied and separated, before the cell divides to form a genetically similar daughter cell, so that the daughter cell will have a complete genome. Chromosomes control the reproduction and distribution of DNA. Each eukaryotic has a specific number of chromosomes. For example, human cells contain two set of 23 chromosomes, one set received from each parent, which is 46 chromosomes in total. This is an exception to productive cells, or gametes-sperms and eggs- and they only have one set of 23 chromosomes.

A mass of chromosomes is called a chromatin, which is a complex of DNA and protein molecules. Each one the eukaryote chromosomes, has a very long DNA that contains thousands of genes. Eukaryote cells replicate all of their chromosomes. The DNA molecules of each chromosome will be copied and new protein molecules will stick to the DNA. In this way, each chromosome will contain two similar copies that are called sister chromatics and have identical genes. Picture-1 shows a human chromosome that has replicated. Two chromatids are attached together at an area called centromere. Picture-2 shows a diagram that shows the separation of sister chromatids of a duplicated chromosome. Each chromatid is called a chromosome after it is separated from its sister chromatic. Now each chromosome would go to one of the daughter cells. In this way, each daughter cell will receive a full and identical series of chromosomes.

  • Campbell, Neil A. et. al. . (2008). Biology . San Francisco : Benjamin Cummings.
  • Pooyan, Mostafa. et. al. (2008). Biology Campbell. Tehran:

HW Post #2: Apoptosis

Apoptosis or programmed cell death is a controlled and managed form of cell death and is kind of a cellular suicide. This is a normal and constant process in body which happens for the regeneration of new cells. This process is very significant and important during normal development it is involved in aging and diseases, like AIDS, cancer, and Alzheimer. The deficient of the process of apoptosis will lead to the development of both benign and malignant tumors. Human embryo have more cells than human adults. as human grow, some cells are selected for execution so that normal development takes place. If the apoptosis doesn't happen in a embryo, it could lead to deformity in the growing embryo.


Individual Post #1: Honey Badger

"As tough as a Honey Badger." - South African saying
The honey badger is known as the most fearless and meanest animal on earth. They are almost invincible. they are considered to be impervious to bee stings, however, some badgers have been stung to death by honeybees. They are also immune to venomous snake because of their thick skin. Because of this, they almost have no enemies.

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Honey badgers almost eat anything and any kind of food is acceptable to them. They eat fruits, honey, insects and all sort of vertebratie prey and carrion. they live up to 26 years in captivity but in the wild they are likely to live 7 to 8 years.

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Honey badgers has a kind of mutualism and partnership with a kind of bird, called honey guides. First, the honey guide bird gets the attraction of the honey badger and then it leads the honey badger to the objective, food. For example, bees' nests. The honey badger, that knows his favorite food is in the nest, then attacks the bees' nest and eats some honey. But because the honey badger doesn't need all the food, it leaves the rest for the honey guide bird.


Individual Post #2: Why Can't We Tickle Ourselves?

We all have a spot in our body that we feel ticklish when it is touched by another person. It is usually not that hard to find this spot. For some of us it is above our knees, behind the neck, our waists. However, we don’t feel
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the same way when the same spot is touched by our own hands.

Scientists have discovered that this panic reaction of our body when we are tickled is simply because our body is trying to let us know that something is crawling on you. This

is a natural defense of our body to little creepy crawlers, such as spiders and bugs. The same panic feeling will lead to an uncontrollable laughter when another person tickles us.

So, if someone else can tickle us, why can’t we tickle ourselves? Scientific research has shown that our brain trained to know what to feel when a person moves or performs any function. When we touch our own body, the brain can prepare itself for it by taking away the feeling of unease and panic and not responding the same as it would when someone else tickles us.


Individual Post #3: Dolphins Sleep With One Eye Open!!
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As we know, dolphins are considered to be very intelligent animals. They have a brain to body mass equal to humans.

Dolphins let only one half of their brain to sleep at a time with one eye open. But why do they do that?

Dolphins have to always stay somewhat conscious because they need to periodicaly come up for air and keep an eye out for the potential predators. They cannot go completely unconscious and sleep like we do.


Individual Post #4: How do we see different colors?

How do we see different colors? Photoreceptors, located on the retina at the back of the eye, are what help us see different colors. There are two different types of photoreceptors: rods and cones.

Rods are used when there’s not much light. They can’t detect color well but they allow us to see in the dark. external image images?q=tbn:ANd9GcTeHsoOc0RwpiPwvzPKN5edWjtYHBtuwhFE5VoxjoiZRxNyRJf30A

What actually help us detect different colors are cones. Cones contain three different types of pigments that respond to certain colors. There are green, blue, and red cones that respond to those colors and combinations of them. In order to detect different colors, we need all three types of the cones.

Color blindness is a result of certain cones misinterpreting the wavelengths that correspond to their respective colors. Different colors have different wavelengths. Between red blue, and green, Red wavelengths are longest, green colors generate medium wavelengths, and blue colors have shorter wavelengths. For example, if green cones

respond to longer wavelengths, the brain would see the color green as red. Most color-blind people can't tell the difference between red and green.

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Individual Post #5: Sea wasp
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Sea wasp, also known as box jellyfish, is considered to be the most venomous organism on earth. Sea wasps have a box-shaped that reaches about 15 inches. Unlike most jellyfishes, Sea wasps use four eyes to see. The tentacles of a box jellyfish are armed with up to 5,000 nematocysts, or stinging cells. Just like how we avoid box jellyfishes, they avoid humans too. The stings usually occur when people bump into them. An interesting fact is that turtles are not affected by their sting and eat them. Box jellyfishes are transparent and pale blue in color, which makes them pretty much invisible in the water. A human being who is stung by these barbs would experience extreme pain and may die in minutes.


Individual Post #6: What Are Freckles?
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Freckles are small spots on the skin that contain more melanin that other skin cells. Freckles are genetic and are usually found on children who are under the age of puberty however it could be found on adults too. People with fair skin and light hair, usually blonde or red, usually have less melanin. Melanin is a pigment that protects the skin against sun’s rays. When the body gets exposed to the sun, freckles could get darker and appear more on the skin because the body produces more melanin as a protection against sun’s rays. If there is the same amount of melanin throughout the skin, it causes the freckles to fade. Freckles are mostly found on the nose and cheeks but some people also have them on the areas that are most exposed to the sun, like shoulders and arms.


Individual Post #7:Dreams
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Dreams are actually experiences of mental activities that occur during sleep. Everybody dreams. There could not be a night that we don’t dream because we have to dream. On average, we have five dreams per night. What matters in dreams is whether we do or do not remember them after we wake up. Children tend to remember their dreams better because they are naturally in touch with their subconscious thoughts and desires , but as they grow older, this ability tends to disappear. On average, a person will forget more than half of our dream a few minutes after he wakes up.


Individual Post #8:Fever
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Many people think that fever is an illness. But fever is actually a defence mechanism of the body to fight infections and slow down the growth of them. Fever is also a way that the body lets us know that there is something wrong. Fever is the raise of the temperature of the body above the normal range of 36.5–37.5 °C (98–100 °F). Fever is not considered medically significant until body temperature is above 38 oC. Fever is one of the body's natural defenses against bacteria and viruses. It simply slows down the growth of microorganisms in our body. Also, the body's defense mechanisms seem to work more efficiently at a higher temperature.


Individual Post #9:Why Do Bees Die After They Sting?

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Bees are a group of insects. There are three types of bees: Queen, Worker and Drone. Between these three types, only Queen and worker bumblebees can sting. However, worker bees can only sting only once in their lives and they die after they sting. Bee’s stinger is made of two shafts, lined with barbs like fishhooks. When a bee stings, barbs hold her onto the flesh and the stinger pulls out of her body and it can’t pull the barbed stinger back out. As the bee forces her stinger in, a poison is released and this poison continues to irritate the person stung, even after the bee is dead. Beside the stinger, it also leaves a part of its digestive tract, plus muscles and nerves. The bee dies because of massive abdominal rupture. Queen bees are not like workers and can sting several times in their lives. Drone bees cannot sting.


Individual Post #10: Cracking knuckles!

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I am one those guys that love cracking their knuckles. But always wanted to know where this sound is coming from! There are three types of joints: pivot joint, Sliding joint, and Hinge joint. Pivot joints are what stop your hand from bending more than usual. Hinge joints are joints that let our arms and legs swing like a door and sliding joints in the backbone are what make our body flexible. A protective fluid cushions most of the joints in our bodies with gases, such as oxygen, nitrogen and carbon dioxide, floating inside the fluid. When you bend your fingers, the joint capsule stretches. Gases release out of the fluid in order to make more room for the stretch. Scientists say that as the gas bubbles out of the fluid, your knuckles make a pop sound. Before your knuckle can crack again, the fluid must reabsorb the gas.