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Topics in Plant Bio Notes - Cell Expansion and Walls III

Submitted by samihaalam on Thu, 11/23/2017 - 13:43

As well as having a great eccet on waer intake in the cell, turgor pressure can also mediate rapid movements in the cell. For example, there is one plant where if it is touched, all of the leaves very rapidly close up and shrink back. This is caused by changes in turgor pressure. When the leaf is normal wih nothing touching it, the flexor cells and the extensor cells are both extended and turgid. But, after the plant has been touched, the flexor cells become stretched and the extensor ccells become flaccid. In the turgid state, the cell is completely filled with water. But as the cell is touched and begins to shrink, H+ ions enter the cell, while Cl-, K+, and some water leave the cell. This leaves the cell in its flaccid state, where there is still some water, but it is in pockets, and the overall size of the cell is smaller, as previously described. There is low turgor pressure in this state. Then, after a while, the cells begin to sweel to their turgid state, and H2-, K+, and Cl- enter the cell, while H+ leaves the cell. This allows the cell to completely filll up with water so that there is high turgor pressure in the cell.

Turgor pressure is also very important in sunflower movement. Sunflowers move in response to the sunn and follow it though the day. At night, the sunflowers still move to face the east even though there is no sunlight, so that they can be in the optimal position when the sun rises. This is due to their intrinsic circadian rhythms. However, this movemen of following the sun is due to changes in turgor pressure in the cells at the base of the moving organ in the sunflower.

The primary cell wall contains cellulose microfibrils that are a part of a polysaccharide matrix. The matrix has pectins, which are polysaccharides that can create a hydrated gel phase, and hemicellulose, which are flexible polysaccharides that like cellulose. The primary cell wall is about 25% cellulose, 25% hemicellulose, 35% pectin, and 1-8% structural proteins, but these numbers can be highly variable depending on the tested structure. These are the parts in the priamry cell wall that are involved in expanding the cell. 

Neurobio Paper 3 Draft 2

Submitted by samihaalam on Wed, 11/22/2017 - 23:45

4. What methodological approach has been used?

The researchers inserted electrodes into the thalamus. They tapped on and around a pateint' s stump and, using the electrode, recorded which neurons were activated in response to the tapping. This was teh receptive field. Then, again using the electrode, the researchers inserted the electrode into the thalamus at different depths corresponding to the depths in which the neurons in the receptive field were. They then added current to the electrode to electrically stimulate that particular depth. The patient was fully awak for this, and thus the patient responded where they felt pain or a sensation after being electrically stimulated in certain parts of their receptive field. This was called the projective field.

5. What were the results of their experiments?

One would normally expect that the receptive field and the projective field to line up perectly, since if a neuron or brain region is stimulated by a certain body part, then that neuron should then map back to that body part and stimulate the same body part. However, the researchers found different results. In general, some of the neurons or depths that were stimulated by the stump in the receptive field projected to a projective field in the phantom limb. In some cases, some depths did not have a receptive field, but when stimulated, they led to pain or unpleasant sensation in the phantom limb, indicating that the thalamus still has a representation of the limb even though it is no longer there. One would normally expect the brain to re-wire itself, so that there would be no representation of something that wasn’t there, but that does not seem to be the case.

6. What are the strengths of this study?

One strength of this study was that it was a good use of an opportunistic study. Another strength was that it was a good simple, straightforward study. There was also good, clear concise writing and diagrams. They were also able to clearly map ou precisely both the receptive and projective field. 

Neurobio Paper 3 Draft 1 - Phantom Limb Stuff

Submitted by samihaalam on Wed, 11/22/2017 - 06:04

1. What is the objective/hypothesis/question of this study?

The objective of this study was to explore the causes of phantom limbs. It was already known that there was a representation in the thalamus of the missing limb, but this was done to see if there was any sort of connection between this representation and phantom sensatoins/pain.

2. What is the rationale/relevance of this question?

As stated before, it was previously estabished that even though a limb had been amputated, there was still a representation of that limb in the thalamus. It is important to study the causes of this sensation to understan and come up with new therapeuic studies to help people suffering from phantom sensations. 55-85% of amputees experience phantom pains or phantom sensations, so it is a widespread issue that affects a majority of people who have had limbs amputated. This study was done on the preface of performing a new therapy - the experimenters inserted something ino the brains of these patients at the site in the thalamus where the pain from the missing limb is coming from. If there is any phantom pain or stub pain, the pateitn could then stimulate the thing in their brain, which would stimulate the area in a way to alleviate the pain sensation. Along the way, the researchers mapped out patients' receptive and projective fields for around the stump.

This is a last ditch effort, opprotunistic kind of study. This is because these surgeries were performed on people who normal drugs and therapies didn't work on. In one case, a patient had been experiencing phantom pains for years before this study came along. Therefore, the researchers had to wait for patients to volunteer for this study in a way, and thus the rationale for this study was really to help people who had tried every other option, and were still not getting the results they wanted in their pain management.

3. What system are the authors using to answer this question? Why?

The authors are using human patients in this study. This is because this is a problem that affects humans, and they'd designed a study in which it was possible and feasible to test their theories on humans, so it would make the most sense to do this on humans. Another reason they used humans was because it would have been difficult to use mice or rats for this study due to the nature of this study. The researchers could have easily identified the rats recceptive field, but it would have been a challenge to map out the projective field. This is becuse the projective field was determined by researchers stimulating certain neurons in the brain, and then having the patients describe where they feel pain or tingling sensations. Mice or rats would not be able to commnicate clearly where they wer feeling pain or anything. On the other han, it would be easy to determine the receptive fields on rodents because that was easily determined by tapping different areas around or near the stump, and then recording which neurons or which part of the brain was active in response to the tapping. It also would have been difficult for researchers to determine if the rodents were feelign phantom sensations at all in the irst place. 

Neurobio Notes L11

Submitted by samihaalam on Tue, 11/21/2017 - 22:34

The nervous system is useful to sense the environment around us and thus move in accordance to the environment. The spinal cord plays a huge part in movement; information is passed between the brain and the muscles via the spinal cord. However, the spinal cord also has a certain amount of autonomy from the brain.

One very well known example of the spinal cord having autonomy from the brain is in the case of Lloyd Olsen and his headless chicken, Mike. Mike was born in April 1945, and on September 10, 1945, Lloyd chopped Mike's head off. Mike continued to walk around after this happened, as well as preening, pecking for food, and attempting to crow. He then took Mike and went around for two years showing off his headless chicken. This isn't a perfect example of spinal cord autonomy as one ear and most of the brain stem was still intact on Mike, but it is still a remarkable example of how the spinal cord can mostly function, even without being connected to a brain. It also is probably where the phrase "running around like a chicken without its head" come from. The town in Colorado where Lloyd and Mike come from still celebrate them today.

There are two types of muscle: smooth and striated mucles. Of the striated muscle, there is also two types of that: cardiac and skeletal. In the somatic motor system, muscles pull, and never push against each other. Motor neurons are in the ventral horns of the spinal cord, while sensory information enters through the dorsal horns of the spinal cord. To control the force of a muscle contraction, either the number of active motor units can be changed or the rate of motor unit firing can be changed. Amyotrophic Lateral Scelrosis (ALS) is a very serious degenarative disease in which a person's alpha motor units start degenerating. It is not very well understood why only the alpha motor units degenerate in this disease. 

Topics in Plant Bio Notes - Cell Expansion and Walls II

Submitted by samihaalam on Tue, 11/21/2017 - 01:51

The cell wal is a very important feature in plant cells. It determines the mechanical strength of the cell, ascts as an exoskeletion controlling shape and allowing high turgot pressure to develop, and acts as a barrier by limiting the size of molecules that can reach the plasma membrane. Additionally, the cell wall can expand and change shape, whic controls the overrall shape of the cell. Plant cells walls are the most abundant source of organic carbon in nature. 

There are two cell walls in plants. The primary cell wall is forme by growing cells and is relatively unspecialized. It is the outermost cell wall layer. The primary cell wall includes the Zone of Cell Elongation and the Zone of Cell Division. 

The secondary cell wall is formed after cell growh has stopped and id highly specialized - both in structure and composition. This is determined by how the cell has differentiated. This is the next inner cell wall layer. This includes the Zone of Cell Differentiation and the mature cells layer. Plant cells also have a plasma membrane, on the inside of the secondary cell wall. 

It is very important for cells to keep ions, sugars, and metabolite levels controlled in their cells. The plasma membrane plays an important role in this. It is permeable to water, oxygen, and carbon dioxied, but other compounds need to actively transported  into the cells via protein channels. H+ is an exmple of an ion that needs to be actively transported across the membrane. A difference in H+ concentrations inside and outside the cell causes a pH gradient across the membrane. Proton gradients and electrical gradients are be harnessed to actively transport other molecules. 

Osmosis can help to change the size of the cell because the plasma membrane is permeable to water, but not solutes or ions dissolved in the water. This means that if there is a high concentration of ios inside the cell, osmosis will drive the water inside of the cell as well, to balance out the high amount of solutes. Thus, the cell will swell, as there will be a lot of water entering it. This movement of water causes turgor pressure. 

This turgor pressure happens due to the cell wall in plant cells. When the cell swells with water inside of the plasma membrane, the plasma membrane will eventually reach a point where it is fully stretched out and is pressed up against the secondary cell wall in the plants. The cell wall will push back against the cell, and won't allow more water to enter the cell. The plasma membrane and the cell wall pushing against each other causes a pressure called turgor pressure inside the cell. 

Water can enter the cell through simple diffusion, or it could enter the cell through aquaporins- portein channels that are selective for water specifically. If there is high turgor pressure in the cell, enzymes in the cell wall will work to loosen the cell wall sugars so that the cell wall itself is loosened, and thus the cell wall expands. There will be less pressure with an expanded cell wall because the plasma membrane will no longer be pressing up right against it. This will then allow for more water to enter the cell, as the turgor pressure has been reduceed due to the expanded cell wall. Thus, an uptake of water will cause plant cells to grow, due to turgor pressure. 

Topics in Plant Bio Notes - Cell Expansion and Walls

Submitted by samihaalam on Sat, 11/18/2017 - 16:16

Animals usually do not form multiple identical organs and usually can not grow back whole organs once they have been lost. Plants, however, usually can do this; they can produce thousands of leaves and roots and hundreds of stems in a lifetime. This process in plants is known as iterative development. It is important for plants to be able to do this becaue they have a transitory existence - their leaves and flowers fall off every year, their roots die and regrow, etc. This is a major difference between plants and animals. 

In plants, new organs form at the meristems. This region of the plant contains undifferentiated cells called meristematic cells.They are regions where cell division occurs in the plant. An apical meristem is a meristem that occurs at the tips of the plant, and cause primary growth by lengthening the plant. Lateral meristems cause secondary growth by widening the plant. 

A developing root or shoot tip normally contains four regions. The bottom-most layer is where the mature cells are - tisues in this region are usually fixed unless there is injury to the area. The next layer in the Zone of Cell Differentiation. In this region, mature cells start forming. The layer on top of that layer is the Zone of Cell Elongation. Here, cells elongate, with little division. The outer-most layer is the Zone of Cell Division - new organs begin to form in this layer. 

After a cataclysmic injury, formerly fixed tissue can begin to regenerate and produce new shoots. This is due to plant cells' totipotent nature - they can de-differentiate, begin to divide, and re-differentiate into any other cell type at any point. This means that an entire plant could potentially be regenerated from a single plant cell.

Wheat Varieties

Submitted by samihaalam on Sat, 11/18/2017 - 15:26

Wheat originated around 10,000 BP in Southwestern Asia. One species of wheat is Triticum monococcum, or Einkorn. Today, it is harvested mainly in the Middle East and Southern Europe. It contains glumes that fit tightly around its seeds. The domesticated version of this species differs from the wild version only in its shattering abilities; the seeds don't fall off in the domesticated species as easily as they do in the wild species, which makes it easier to harvest them. Another species of wheat is Triticum turgidum. Two common subspecies of this are Triticum turgidum ssp. dicocooides (emmer) and  Triticum turgidum ssp. durum (durum). Their seeds do not have glumes around them. A third species of wheat is Triticum aestivum, or bread wheat. There also appears to be no glume around its seeds. Interestinglty, although these are all species of wheat, each of these species has a diffferent number of chromosomes.  

Topics in Plant Bio Notes - Polyploidy Part II

Submitted by samihaalam on Sat, 11/18/2017 - 14:33

The number of somatic cells in an organism is referred to as the diploid number, or 2n. The number of gametes is the haploid number, or 1n. The ancestral haploid number is 1x, which is the base number. For example, and individual with three sets of homologous chromosomes would be 3x, or triploid. The diploidy number is when an individual has two sets of homologous chromosomes. The haploidy number is when an individual has half the normal set of homologous chromosomes. Aneuploidy occrus when one or more chromosomes of the normal set are absent or present in excess. Polyploidy occurs when an individual has more than two complete sets of homologous  chromosomes. 80% of flowering plants are polyploids, as well as some fish, amphibians, and lizards. A subset of polyploidy is called allopolyploidy, which is when there is a doubling of the haploids of two different ancestral species into one hybrid. This is opposed to autopolyploidy, which is when there is nondisjunction in meiosis or mitosis, causing all the chromosomes to not separate from each other, leading to diploid gametes. This is derived from a single species or closely related species. An example of a common autopolyploidy species is the potato. Bananas are triploid, which leads to them being larger and have a lot less seeds. In general, polyploidy leads to an increased nucles and cell size, which leads to larger plants, larger fruits, and more seeds. It also leads to a slower growth rate and later maturity, increased heterozygosity, releaxed natural selection due to redundant gene copies, and overall exra copies, leading to greater variation and greater adaptability.

Topics in Plant Bio Notes - Polyploidy

Submitted by samihaalam on Sat, 11/18/2017 - 01:06

Wheat originated around 10,000 BP in Southwestern Asia. One species is Triticum monococcum, or Einkorn. TOady, it is haarvested mainly in the Middle East and Southern Europe. The domesticated version of this species differes from its wild version by its shattering abilities - its seeds don't fall off as easily in the wild version, which makes it easier to harvest them. They're glumes that fit tightly around the seeds. THere is also only one seed per spikelet. Another species of wheat is Triticum turgidum. A subspecies of this is Triticum turgidum ssp. dicocooides, or emmer. a second subspeices of this is Triticum turgidum ssp. durum, or durum. It is harveter mainlty in Italy, Spain, and the US. Its seeds do not have glumes around them. A third what species is Triticum aestivum, or bread wheat. There are several different subspecies of this. There also appears to be no glume around its seeds. Interestinglty, although these are all species of wheat, each of teh three species has a diffferent number of overall chromosomes from one antoher.  

Topics in Plant Bio Notes - Genetically Modified Crops Part II

Submitted by samihaalam on Wed, 11/15/2017 - 23:55

An example of a GMO is chymosin. Adding some extract from the lining of a calf's fourth stomach to milk can turn the milk into cheese. This is because it contains chymosin, a protein that can curdle milk. Certain bacteria also possess a gene for chymosin, and produce an indistinguishable enzyme. Today, more than 90% of all cheese is produced using this enzyme from the bacteria - the "recombinant" enzyme. 

Genetically Modified Organisms (or GMOs) are organisms which have inserted DNA that originated in a different species. 

Genetic Modification is the process in which a single gene is inserted into a new genome. It is also called recombinanat DNA and can be faster than just breeding the two species together. For example, in a previous class we discussed a technique in which two different plants - one that was an "elite tomato" and one that was a "poor," but disease resistant tomato. To get an elite, disease resistant tomato, these two plants would need to be crossed, which would result in some of the F1 offspring inherting the disease resistant gene, and some which did not. The ones that inherited the disease resistant gene would then have to be cross again with the original elite tomato. Some of the F2 generation offspring will thus still have the disease-resistant gene as well as less of the "poor" tomato genes and mroe of the "elite" tomato genes. These specific individuals in the F2 generation would then have to be crossed again to the eilte tomato, and so on until the "poor" tomato genes have disappeared except for the disease-resistant gene. Thus, an elite tomato that is also disease-resistant will have been formed. DNA markers help in this process by identifying the disease resistant gene, but this is still a tedious process that takes many generations and a lot of luck. Thus, GM would greatly speed this process up, as the disease-resistant gene could definitely be inherited in one generation. 


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