Drafts

When plants form leafy branches, the branch grows from the base of an axillary bud. This bud contains an axillary meristem that drives cellular division at the base of the branch and grows it outwards. This is an iterative process that repeats hundreds of times and allows plants to have multiple sets of the same organs. Because every branch happens near the axillary bud on the stem of the plant, the location of branches is very predictable. In roots, branching occurs very differently. Roots only have the apical meristem at the end of the root and do not contain axillary meristems to grow branches. Instead, in roots the branches grow out from the stem of the root from the pericycle tissue in the vasuclarture of the root. This causes branching patterns in root to be highly unpredicatable as they do not reply on a specific stem cell organ to cause the branching. Also, root hairs are created from single cells that grow out in organized directional growth to increase the surface area of the root, increasing with it the ability to uptake water and nutrients. 

Group think is a type of thinking that occurs when people place more importance on maintaining group cohesiveness than on assessing the facts of the problem with which the group is concerned. This involves different types of group behaviors under this umbrella. For example, group polarization is the strengthening of shared beliefs. People who discuss shared views will come to believe in them more strongly-this can be positive or negative (ex. if the beliefs involve violence)
Groups tend to do things that individuals wouldn't usually do. Other types of group behavior include deindividualization or a lack of individual responsibility that comes from being in a crowd. This is sometimes referred to as Mob Mentality.

Compliance is the changing of ones behavior as a result of other people directing or asking for the change. There are ways to gain compliance like the “in the door technique.” This is the act of asking for a small commitment and, after gaining compliance, asking for a bigger commitment. People are more likely to say yes to something bigger if you say yes to something small first.

When standing, because of gravity, blood pools at the feet due to the generation of hydrostatic pressure. Thus, blood does not return to the heart as quickly. End diastolic volume decreases (EDV). If this decreases, then cardiac output decreases because Q = HR * SV (EDV-ESV). Blood pressure also drops because (BP = Q * TPR). This leads to less flow because flow is proportional to a change in pressure / resistance - decreased flow to brain. As a result the pressure is higher in the heart. All these events decrease O2 (oxygen) delivery to brain. This is why we pass out because of lack of oxygen in the brain. We c prevent fainting by using our skeletal muscle pump (by wiggling toes, bending knees slightly, etc.). This skeletal muscle pump will generate more pressure and restore our end diastolic volume and reverse the effects.

During human embryonic development, the brain forms from the walls of the neural tube. The human proto-brain is divided into four sections: the forebrain, the midbrain, the hindbrain, and the spinal cord. The forebrain is the largest section and forms two distinct structures, the telencephalon and the diencephalon. The telencephalon is the largest of the two and goes on to form the cortex that wraps around the diencephalon and midbrain sections in the fully developed brain. The diencephalon goes on to form the group of structures commonly known as the brain stem, composed of the thalamus, the hypothalamus, and the basal telencephalon. In addition to these grey matter structures, the developing brain forms the inner capsule. The inner capsule is a group of white matter - myelinated axon bundles - continuous with the cortical white matter that connects the thalamus to the cortex. Another important white matter structure is a commissure known as the corpus callosum that is an important link between the two hemispheres of the brain. The midbrain is made of the tectum and the tegmentum, which are responsible for a lot of auditory and visual reflexes. Through it runs the cerebrospinal aqueduct that transports cerebrospinal fluid (CSF) between the brain and spinal cord. As for the forebrain, the hindbrain can be split into two sections. The rostral-most section contains the cerebellum, our motor control centre, and the pons, which serves as a relay centre between the forebrain and the cerebellum. The caudal-most section contains the medulla, which switches signals between the body and the brain from ipsilateral to contralateral. Lastly, the spinal cord is composed of the dorsal horn, the intermediate zone, and the ventral horn. These grey matter structures are all involved in the relay of signals between the body and the brain. The dorsal horn is involved in signal reception, the intermediate zone is largely composed of interneurons and serves as a relay point, and the ventral horn is the location of efferent neurons that carry information to effector organs in the body such as muscles.

There are three types of point mutations. There are missence mutations, nonsense mutations, and silent mutations. Missence mutations happen when there is a change of a single base pair. This tiny change causes te substitution of a different amino acid in the protein. This small letter change may have no effect, if the individual is lucky, but it may render the protein malfunctional. An example of this would be sickle cell anemia. Second type of point mutation is nonsense mutation. This leads to an early stop codon. Unfortunately, when there is an early stop codon, the protein as a whole cannot be fully developed. This would be very bad if this protein is necessary to the individual. Lastly, silent mutation. This one is very interesting as it actually is not bad for the individual. This kind of mutation changes a base pair, but the amino acid stays the same, as some amino acids have different base pair letterings, but pair for the same protein.

Among different species, there is some varioation in chromomsome numbers that are tolerated by the species.  For example, plants are quiet tolerant and can survive with varying chromosome number.  In nature, three mechanisms which chromosome numbers can chamge is through meiotic nondisjunciton, mitotic abnormalities, and interspecies crossing.  Meoitic nondisjuction is when the chromosomes do not seperate properly during gamete production.  This can happen in both meiosis 1 and meiosis 2.  In meosis 1, gametes are monosomic and trisomic.  In meosis 2, half the gametes formed will be normal while the other half are abnormal.  In a very rare case, there is complete nondisjuction when all the chromosomes go to a single cell.  For example, a dipoloid species would form a tetraploid species.  The condition is called autopolyploidy.  In interspecies crosses, the recult is allopoidy.  The first generation with the cross will likely survive but when the chromosomes line up  in meosis there might be some issues.  It is possible but not likely.  

There are key behavioral traits that humans had in their environment of evolutionary adaptiveness that creates the eating patterns we experience now.  One key difference is the risk and energy early humans put into getting the food.   With the advent of cars and grocery stores, humans expend less energy to get more food than would be available in their environment of evolutionary adaptiveness.  As a result, the calorie intake exponentially exceeds the calorie expenditure used to get food.  The human body also evolved to hold large energy reserves for times when food is scarce.  In our novel environment, this means our body is designed to hold onto the food we eat.  If we exceed the amount of food we should intake, we are designed to retain the energy as fat which increases our vulnerability to obesity.  In our environment of evolutionary adaptiveness, our central nervous system has evolved to crave “palatable, energy-dense food”.  Because our novel environment put these types of food in easy access, there is nothing stopping us from over-indulging.  All these eating patterns humans evolved to have were designed to capitalize on high energy food and maximization of energy storage.  With the availability of food in the novel environment, it is important to recognize these behavioral patterns and make choices to fight these behaviors.

Development of a human embryo and its brain comes about in three stages: blastulation, gastrulation, and neurulation. First, the egg and sperm fuse into a zygote which has an internal plasma membrane and an external zona pellucida. The zygote cleaves internally, maintaining the same volume inside the zona pellucida but multiplying the number of cells inside it, at which point it is called a morula. The cells inside the zona pellucida go through compaction and differentiation starts to occur. A sphere of trophoblasts develops just under the zona pellucida and around the mass of embryoblasts inside the embryo. The embryoblasts then accumulate at the top half of the embryo, leaving a space called a blastocoel under them. This whole process is known as blastulation and the resulting structure is a blastocyst. Gastrulation follows blastulation first by the loss of the zona pellucida. Then, the mass of embryoblasts forms an inner cavity called the amniotic cavity. The cells under the amniotic cavity become epiblasts and the cells under the epiblasts become hypoblasts. These two cell layers are collectively known as the bilaminar disc. The primitive streak forms along the middle of the bilaminar disc, on the epiblast layer. This primitive streak is composed of epiblast cells migrating down and forming a middle layer of cells between the two original layers of the bilaminar disc. This forms a trilaminar disc with three layers known as germ layers. The topmost layer is the ectoderm, the middle layer is the mesoderm, and the bottom layer is the endoderm. The ectoderm will form the nervous system and the skin. The mesoderm will make the muscles and bones. The endoderm will make the viscera. The formation of these layers is known as gastrulation.

For species who do not reproduce asexually, mechanimss of sex determination are essential to the survival of species.  In humans, the sex of an individual is determined by the presence of a Y chromosome.  It is important to note that sex and gender are two different concepts.  Sex is determined by biology while gender is a social construct.  In other species, sex is determined through other mechanisms.  The sex of fruit flies is determined by the ratio of sex chromosomes and autosomal chromosomes.  Some species have their sex determined through temporal influences.  

Pressure, temperature and volume interact with one another as shown by the equation: PV = nRT. Pressure and volume are inversely related while pressure and temperature are directly proportional. This can be seen through an example using a fire syringe. A fire syringe is a simple glass cylinder with a piston that pushes down inside. When a small piece of gun powder cotton is placed inside and the piston is pushed down quickly, the cotton ignites and a spark can be seen. The science behind it lies in the aforementioned equation. When the piston is moving down, the volume is decreasing. With this drop, the pressure starts building up. The pressure causes the temperature to start increasing. This makes the gun cotton powder to ignite, causing a spark.