Reproduction: Is sex important?

        For a population of organisms to survive, they depend on either sexual or asexual reproduction. Both of these methods have their benefits and costs, and neither is perfect for the survival of the organisms. Sexual reproduction can help spread positive genetic traits and even the dissemination of disease or parasite resistance, as the genes from each parent are naturally selected to benefit the offspring. The nine-banded armadillo benefits from this genetic variety, which helps it become unique and resist disease. However, sexual reproduction takes more time and energy, and competition can be detrimental to the population. Furthermore, asexual reproduction is simple and does not require a mate, but it often results in swift extinction due to clones being genetically identical and vulnerable to the same threats. Philodina utilize asexual reproduction to propagate all over the planet, using anhydrobiosis to travel long distances. This helps overcome vulnerability as a mass, and takes advantage of the benefits of asexual reproduction. Furthermore, the Atta colombica ant travels with disease-free fungus, which helps protect the asexually reproducing fungus gardens against outbreaks of parasites. E. coli can cope with the problems of asexual reproduction by picking up loose DNA from the environment, viruses, animals and dead bacteria.
        After reading about these organisms and methods from the article ("Dr. Tatiana's Sex Advice to All Creation"), several questions still remain: how are eggs fertilized? How does asexual reproduction (e.g. binary fission) occur? And how exactly do these mutations occur during meiosis? I look forward to finding some answers in this unit.

Unit 3 Reflection

        In this unit, we explored cells and their processes of photosynthesis and cellular respiration. While prokaryotic, autotrophic cells were the original ones, after cyanobacteria evolved, there was enough oxygen for heterotrophs to prosper. According to the endocytotic theory, eukaryotes with different organelles evolved as a result of heterotrophs consuming smaller autotrophs and cyanobacteria through phagocytosis, and the consumed bacteria surviving and living in symbiosis, creating the organelles we see today. These organelles include many membrane-bound structures, including the nucleus, lysosomes, ribosomes, mitochondria, and chloroplasts. The cell membrane has also evolved to be semipermeable and to allow protein-facilitated transport. A similar method of transport--diffusion--plays an important role in the osmosis of water, which not only helps maintain equilibrium, but also makes processes such as photosynthesis and cellular respiration possible.

The organelles of a eukaryotic animal cell

        Photosynthesis uses carbon dioxide, water, and light in a series of light dependent reactions, diffusing the H+ ions from water across the thylakoid, and producing NADPH and ATP to be used in the Calvin cycle. The Calvin cycle produces sugar from carbon dioxide and the molecules formed in the light independent reactions. Cellular respiration does the opposite, breaking down glucose to form ATP for energy storage through glycolysis, the Krebs cycle, and the electron transport chain. This yields 36 ATP in total from 6 glucose and 6 oxygen molecules.
        In general, I found understanding the processes of photosynthesis and cellular respiration a big jump from the relatively simple concepts that we covered earlier. In addition, though I found diffusion natural, the complex tonicities of osmosis were confusing when I was first exposed to them. However, after completing several labs and going through the steps of the processes, I found all of these concepts much easier to grasp. The egg diffusion lab helped me understand the impact of hyper- or hypotonic solutions on the movement of water across a membrane, and the photosynthesis virtual lab helped me better correlate each factor of photosynthesis with its rate and output.

The egg diffusion lab showed the effects of tonicity with a semipermeable membrane

        I still feel that the cellular processes of energy are extremely complex with details, and I would like to explore the different steps, such as glycolysis and the Calvin cycle, more in depth. This would provide a better understanding of how exactly each molecule is formed and used throughout the process.

Egg Diffusion Lab

      In the egg diffusion lab, we tested how osmosis in different solutions of water would affect the cell. Using eggs to represent cells, we submerged them in corn syrup and deionized water, and recorded the circumference and mass of the eggs before and after the submersion. Overall, the eggs in the sugar water decreased in mass about 46.1%, and decreased in circumference about 22.1%. This was caused by the presence of a hypertonic solution, as the high concentration of solute (sugar) led to water diffusing out of the egg to decrease its mass and circumference.

Class data tables for deionized and sugar water

      A cell attempts to maintain equilibrium, and thus water diffuses in or out of the cell when the solute concentration changes due to the solute molecules being to large to diffuse through the cell membrane. For example, when the egg was in the vinegar bath, the tonicity was hypertonic, and thus water left the cell. When the egg was submerged in water, the tonicity was hypotonic, and so water entered the cell. Lastly, putting the egg in sugar water made the tonicity hypertonic again, causing water to diffuse out of the cell once more.
      This lab demonstrates the law of diffusion that occurs naturally: substances diffuse from areas of high concentration to low concentration. Also, when solutes are unable to diffuse through a membrane, water instead diffuses in the process of osmosis. The different solutions that the egg was exposed to showed the diffusion of water to maintain equilibrium, including solutions that were hypertonic or hypotonic.
      The sprinkling of water on vegetables prevents the diffusion of water out of the vegetables, and even leads to some water diffusing in due to the hypotonic nature. This preserves the "freshness" of the vegetables keeping them hydrated. In addition, the salting of roads to lower the melting point of ice can adversely affect plants nearby to put out water (and shrivel) due to the hypertonic solution of salt in the water.
      After this experiment, I would want to further explore the osmosis of water in cells by testing an extremely hypotonic solution. The opposite of the hypertonic solution, I would want to see if cells might swell and possibly pop due to having too low of solute concentration in the solution outside (like water in bloodstream).

Egg Macromolecules Lab

      In the egg macromolecules lab, we asked if monosacchardies are present in the cell nucleus, represented by the egg yolk. We found that they indeed were present in the egg yolk, as a chemical test involving benedicts solution produced a color change from blue to green (rated a 7/10 on our scale compared to the 0/10 of water). This indicated the presence of monosaccharides, in this case glucose, present in the cell nucleus to provide energy, and supports our claim by showing how they can be found in the egg yolk in our experiment.

Monosaccharide test results
(control, egg white, egg yolk, egg membrane from left to right)

      Furthermore, we also asked if proteins can be found in the egg white, representing the cytoplasm. Here, we found that they were present, and the CuSO4 compound we introduced produced a color change from dark blue to light purple. This was a 9/l0 on our scale, and was supported by the presence of enzymes and structural proteins throughout the cytoplasm. Thus, this supports the claim with proteins.

Protein test results
(control, egg white, egg yolk, egg membrane from left to right)

      In addition, we asked whether lipids are present in the egg membrane. We found that lipids are in the cell membrane, as the Sudan III test yielded positive results of a color change from red to brownish orange (7/10). This supports the claim and can be explained by the presence of lipids as phospholipids making up the cell membrane.

Some macromolecule data tables

      While our hypothesis was supported by our data, several errors may have occured and thus skewed the results. For example, we may not have added the correct amount of test substance for each macromolecule test. This potentially incorrect drop amount may have caused the color and scale rating to be lower than the actual amount, due to having less test substance to create a noticeable effect; more care on correct dropper measurement would prevent this. Furthermore, the amount of test sample could have changed our results as well, and made the data lower due to a more diluted exposure to the testing substance. Standardizing this in some way could improve and negate this error; for example, setting a specific measure for each part of the egg, such as a mass measure, could make it more even across tests. These errors may have affected several of the tests, as every group member used a different (estimated) amount of egg membrane, yolk, or white to test.

      Lastly, this lab was done in order to identify macromolecules in different parts of the cell. This taught me the concept of macromolecules being the building blocks behind many of the cell parts and organelles. I learned how glucose can be found in the cell nucleus, how lipids make up the cell membrane as phospholipids, and how structural proteins are found throughout the cell, including in organelles. All in all, based on my experience from this lab, I would also be able to identify the presence of various macromolecules in different types of cells, regardless of their type or origin, even without much knowledge of the cell itself.