Osmosis Research Paper

1. Osmosis, Active transport, and Facilitated diffusion

Osmosis:

Osmosis is the facilitated diffusion of water across the cell membrane of a cell. The inside layer of the cell membrane is hydrophilic, meaning water cannot easily pass through the membrane. The cell membrane has to have aquaporins, which are water channel proteins, that move the water across the membrane. If there is a water and salt solution outside the cell, the salt can enter the cell by diffusion, but the cell membrane is not permeable to the water. Because there is more solute solution inside the cell, there is less water. The aquaporins move the water across the membrane until equilibrium is reached.

When a red blood cell is placed in water, the process of osmosis moves

the water into the cell. This can cause the cell to burst, since it only has a weak cell membrane. If the red blood cell is placed in a high concentration of solute, the red blood cell will shrink as the water leaves the cell.

Active transport:
Active transport is when the cell moves something across the membrane against the concentration gradient. It needs ATP (energy). The cell uses transport proteins to push small ions and molecules through the cell membrane. Larger molecules are moved across the membrane with protein pumps. For the largest materials needed by cells, endocytosis and exocytosis are used to move molecules in and transport them out.
Example

Facilitated Diffusion:
It seems as though it would make sense for only small molecules to be able to enter the cell easily, but larger molecules such as glucose, can easily enter as well. The reason for this is facilitated diffusion. Facilitated diffusion is when a cell uses a transport protein as a carrier or channel for the molecule to pass through. These proteins make it easy for specific larger molecules to pass through the cell membrane, letting the cell use the molecules without needing ATP to get it into the cell.
In red blood cells, the sugar glucose is needed. They have protein carriers that allow glucose to move both in and out the cell without ATP, which gives the cell the material it needs, without using energy it uses for other things.

2. Plants, Animals
Plant cells have both a cell wall and a cell membrane for extra support and because they are often in water, and if they bring in water, they might burst if it were not for this extra layer of support. Animal cells have only a cell membrane. Plant cells have chloroplasts, which is a pigment they use for photosynthesis. Animal cells do not have this because they do not need to do photosynthesis. Animal cells have centrioles, which help with cell division, but plant cells do not have them, as they use a different system for cell division.
Both animal and plant cells have a nucleus, which holds the DNA (genetic information) of a cell. They also both have mitochondria, which make energy for the cell, and cytoplasm, which is the fluid in a cell consisting mostly of water and salt.
Animal and plant cells are both eukaryotic. They are multi-cellular organisms that have nucleuses and specialized organelles. Because they evolved more recently, many of their characteristics are the same. The more time passed, the more both animal and plant cells evolved to do their separate functions.

3. Prokaryotes and Eukaryotes
Prokaryotes and Eukaryotes have many differences. Prokaryotes have no nucleus, but Eukaryotes do. Eukaryotes have a mitochondria to give the cell energy, but Prokaryotes obtain energy from other forms, such as inorganic molecules like hydrogen sulfide. In Prokaryotic cells, chromosomes are found in the cytoplasm, and there are not many. Eukaryotic cells keep their chromosomes in the nucleus, and there are many more.
Endosymbiosis is the theory that Eukaryotic cells evolved from small Prokaryotic bacteria living in larger prokaryotic cells, and eventually evolving to form a single cell. Scientists are unsure how the smaller cell got inside the host, it may have been eaten but never digested, and then began to live inside it. This was helpful to both the cells. The host cell was provided with chemical energy from the smaller one, and the smaller cell had a protective layer surrounding it. After the bacterium was engulfed, the host cell would reproduce, and copies of the bacteria would be present in the resulting cells. The cycle would continue, making many replicas of this cell. Eventually, the team of two cells evolved to one cell. The bacteria became the mitochondria of the cell. Evidence for endosymbiosis is found in the membrane of the mitochondria, the DNA in the mitochondria, and reproduction. The mitochondria of Eukaryotic cells have their own cell membrane, as prokaryotic cells have. The DNA in the mitochondria have similar circular structure to the DNA in Prokaryotic cells. The reproduction process of mitochondria is the same to that of Prokaryotes: they pinch in half and must have a parent cell to be reproduced from, the cell cannot build it from nothing.
(http://evolution.berkeley.edu/evolibrary/article/endosymbiosis_01)

5. Differentiated Animal Cells
Pigment Cells:
Melanocytes produce melanin, is a pigment found in skin, hair, and eyes. Melanogenesis is the process which produces melanin, it is stimulated by UV light. When skin is senses UV radiation, it will produce proopiomelanocortin which starts the process of melanogenesis to produce melanin. Melanin is used to absorb UV radiation. Melanin found in the skin absorbs 99.9% of UV radiation, and removes it from the skin so it doesn’t harm it. It can also remove toxic metal ions that could also harm the cell. Melanin is responsible for skin color as well. Eumelanin is found in darker skin, and pheomelanin is found in lighter skin. Neuromelanin is found in brain cells, and in the nervous system, but does not absorb UV radiation.
Melanocyte cells are branched, the dendrites on the end of the branches are used to transfer pigment to other pigment cells near them. They also have a specialized organelle called a melanosome, which stores melanin.
If a melanocyte failed to undergo mitosis, the resulting cells would not all have DNA. In mitosis, the DNA replicates so the daughter cells will have the right amount of DNA to reproduce, and respond to the environment as needed. The resulting cells of this no-mitosis split will not have DNA, or not enough, so it will not be able to reproduce. If the cell cannot reproduce, it will eventually die out. If this continues to happen, there eventually will be no melanocytes, and UV radiation will damage the skin.

Muscle Cells:
Muscle cells expand and contract to allow motion.

The three types of muscle cells are cardiac, skeletal, and smooth. Cardiac muscles are only found in and near the heart. They push blood through the heart, and are involuntary (not controlled by the nervous system). Skeletal muscles are attached to the tendons and bones. They stabilize joints, help with posture, and power voluntary movement. Smooth muscles are found in organs. They work together to move substance like food through the body, and are involuntary. Muscles use proteins called actin and myosin to move. Calcium ions bond actin and pull it apart, which opens a place for myosin will bond. Actin and myosin push and pull against each other, which causes the expanding and contracting.

Striated muscles cells are long, and have long cylinders that have proteins called myofibrils. Skeletal muscles have a special muscle tissue called Epimysium, which is found along the entire muscle tendon. It protects the muscle from friction against other muscles or

bones.
If muscle cells didn’t undergo mitosis, but still did cytokinesis, there would be trouble. The resulting cells would not have enough DNA to replicate, and couldn’t evolve with their environment. This would mean less muscles cells could be produced, and the body would run out of muscle cells. This could cause the heart to stop working, limbs to stop moving, and organs to stop processing food or other substances. During the cell’s life, if the cell was put in an environment with less oxygen, the cell would be unable to adapt. This would cause the cell to die, and since it could not reproduce, cells would continue to die without reproducing.

Red Blood Cells
Red blood cells transport oxygen around the body.

They have no nuclei or mitochondria in human cells, which means their small size can fit through very small capillaries. They are produced in the bone marrow (since they cannot reproduce as they have no DNA from mitochondria and nucleus). They contain hemoglobin, an iron-rich protein, which attracts oxygen. This makes it easy for red blood cells to obtain oxygen, and then transport it to the tissue in the body through the bloodstream. They also pull out carbon dioxide from the blood stream, and transport it to the lungs to be breathed out.

Hemoglobin is an important feature in red blood cells, it attracts oxygen so the cell can perform its job. Because the cell has no DNA or RNA, it cannot be targeted but viruses.

Mature red blood cells do not have a nucleus, so they cannot do mitosis. Instead, they act as a carrier, and then die after about 120 days. The immature red blood cells found in bone marrow do have nuclei, and they divide to produce more immature red blood cells. If the immature red blood cells did not do mitosis before dividing, the resulting cells would not have DNA. This would mean that the resulting cells could not perform mitosis either, and therefore there would be a shortage of red blood cells. If there was a shortage of red blood cells, the tissues in the body would not receive the oxygen they needed, and might not be able to perform their jobs. The body would not be able to function properly if immature red

blood cells did not perform mitosis.