Unit 3 Reflection

In unit 3, we learned about the cell and all its processes and many intricacies. We learned about the complexity of organelles and how our energy is collected. Although a wide variety of topics were covered, they all shared a common theme: the cell. I think that most of the unit was quite easy, because some of it was just a review of 7th grade biology. I even knew a little in depth information about photosynthesis and cellular respiration before learning this unit. But if one thing is the hardest to grasp in this unit, it would be cellular respiration. I think this is because it has 3 sort of overlapping parts rather than photosynthesis' 2 distinct parts. Even after watching the vodcast, I was still not completely sure about where reactants went in and products came out.

One thing that definitely helped is drawing a diagram. By illustrating the 3 pieces of CR separately and with clean sketches, I was able to understand where and why certain reactants entered CR. This taught me the important skill of drawing diagrams. A diagram is not something that would help only in biology; it could also be applied to chemistry, physics, and a variety of other topics. I do think that I'm a better student now than at the start of this unit. I have learned important studying skills as well as gained a better understanding of the way a cell works. I want to learn more about photosynthesis and cellular respiration. How exactly does ATP synthase work? What are the "in between" steps of the reactions that weren't taught in class? To study for this test, I will probably not make flash cards because I feel like I have already mastered the concept of organelles. However, I will definitely draw out the reactions of photosynthesis and 3 parts of cellular respiration. This process will help me tackle the exact processes and give me a deeper understanding on the topic.

Egg Diffusion Lab Conclusion & Analysis

In the egg diffusion lab, we took 2 eggs and placed them in 2 liquids for a few days: deionized water and corn syrup. We hypothesized that the egg in the deionized water would expand and that the egg in the corn syrup would shrink.

When the concentration of sugar (solute) in the external solution was high, water (solvent) left the egg to maintain the proportion of water to sugar. This caused the mass and circumference to decrease. This is proved by the fact that most of the groups' eggs in corn syrup decreased in mass by around 45%, which is a large difference. The change in circumference also hovered around -21%.

A cells internal environment changes depending on its external environment through a process known as "diffusion". Diffusion always moves molecules from areas of high concentration to low concentration. For example, if a large amount of water is outside of the cell, the water will enter the cell until both sides of the membrane have around the same water concentration. However, if a solute like the sugar in corn syrup is unable to pass through the membrane, then water diffuses out of the cell until the ratio of water to sugar is the same on both sides of the cell membrane.

This lab demonstrates the biological principle of diffusion. Diffusion is extremely important to cells and allows for water and nutrients to move in and out of the cell without the use of energy. By putting an egg, essentially a cell, in a hypertonic solution we investigated the effects solute concentration had on a cell.

Fresh vegetables may be sprinkled with water to counteract the natural process of water leaving the plant cells due to diffusion. If water is sprinkled on the vegetables, the concentration gradient would be less steep which would decrease the rate at which water escapes vegetable cells. This helps prevent the vegetables from wilting or becoming squishy. Salting definitely has a detrimental effect on roadside plants. When salt approaches the roots of a plant, it creates a gradient that forces water out of the root cells. This causes the plant to wilt and may eventually result in its death.

After understanding the results of this experiment, I would like to test what would happen if I removed some of the egg white from another egg and injected it with a hypertonic sugar fluid. This egg would then be placed in a beaker of deionized water. I hypothesize that this egg would absorb water until it bursts. If this hypothesis is correct, it would prove that the membrane is semipermeable from both sides.

Egg Cell Macromolecules Conclusion & Analysis

What macromolecules are present in the cell and where are they?

     The membrane contains polysaccharides. When we put the membrane in an iodine solution to test for polysaccharides, it turned black. The membrane contains this because it uses polysaccharides to communicate with other cells. The egg white had proteins floating around in it. We know this because when the separated egg white was dropped in copper sulfate, a chemical that tests for peptide bonds, the solution turned purplish. The egg white may contain proteins for helping the developing chicken embryo grow. The proteins would provide nourishment and vital ingredients for life.The egg yolk was composed of lipids. This was learned when the broken down yolk was put in a solution of Sudan IV. Soon, it turned a shade of orange. The yolk probably contains lipids because it is actually a cell. Cells have phospholipid membranes, so this is the most likely reason for a positive lipid test.

     One possible error is that a sample was contaminated. If one sample was accidentally mixed with the one being tested, it may show positive results when in reality the macromolecule is only present in the contaminant. If this happened, then the macromolecules that the evidence proved may not normally be present. Another mistake that could have occurred is if an inadequate amount of testing substance was used. In the procedure, it only said how many drops should be added. This is not a very accurate measurement and people may have also miscounted the amount of drops of a chemical they added. This may cause no results to be displayed even when a part of the cell contains a certain macromolecule. These inaccuracies can be remedied in the future by assigning each table a certain part of the egg rather than having each group test every single part of the egg. This new procedure would reduce the chance of contamination. The amount of testing chemical should also be changed from "drops" to "milliliters". This is a more standard and widely accepted measurement unit and would help prevent not using enough testing solution.

     The purpose of this lab was to learn about the function and location of macromolecules in the cell. This relates to an activity I did in seventh grade where we made a chart of the macromolecules and wrote facts about what they did and where in the cell they are found. What I learned in this lab can be applied to situations where I may need to retrieve a certain macromolecule from the cell. With this information, it will be easier to know where the molecule is and how to isolate it.


Monosaccharide Test tubes- From the left: water, membrane, white, yolk