2_LabReport-+Movement+in+and+out+of+Cells

Lab Report: Movement in and out of cells
__Exploration 4A__ Results Discussion Questions 1. What was the control in this activity? The controls were: the type of plant (Beetroot, or //Beta vulgaris//) the volume of beetroot in each test tube the volume of liquid in each test tube
 * Tube || Content || Intensity of light ||
 * A || 4ml of water || 94.88 ||
 * B || 4ml of 25% alcohol || 86.22 ||
 * C || 4ml of 50% alcohol || 35.06 ||
 * D || 4ml of hot water || 94.94 ||
 * E || 4ml of water || 90.98 ||

2. How do you analyze the results of this experiment one variable at a time? I would compare test tubes in which share one common variable. For example, while finding out how the surface area of the beet root affects diffusion, I would compare test tubes A and E, and while finding out the effect of temperature, I would compare Tube A and D.

3. Why was it necessary to wash the beetroot slices throughly before using them in this exploration? So that the coloration of the liquid in the test tubes would only be due to diffusion during the 15 minutes, and not anything else.

4. The main source of error in any biological experiment is usually the natural variation of living things. What did you do to ensure that this variation was minimized? The pieces used in this experiment were all sliced from the same beetroot. However, I could have repeated the experiment, or compared my data with the rest of the class'.

5. Does alcohol have an effect on beetroot cell membranes? Was the concentration of alcohol a factor too? Suggest an explanation for your observations. Yes. Alcohol is an organic solvent, and will dissolve the phospholipids in the membranes, damaging it. As seen from the results, the higher the concentration, the more colored the solution is. This show that the higher the concentration, the more damaged the cell membrane, as more pigment would be able to seep out.

6. Suggest an explanation for the observations of tube D & E too. Tube E: The solution in tube E, in which the slices were further cut up into 3 places, was more pigmented than the one in tube A, in which the slices were not further cut up. This shows that the greater surface area of the beetroot, the more diffusion takes place. This is because there is more contact with the external environment, and hence more space for diffusion to occur. Tube D: The solution in tube D, in which the slices were placed in hot water, was slightly less pigmented than the one in tube A, in which the slices were placed in water of room temperature. The was only a percentage change of roughly 0.06%, however, so the difference is negligible. One might expect the high temperature (90-100`C) to results in the molecules gaining kinetic energy and hence diffusing faster, or violent collisions that damage the cell membrane, both of which result in the water getting more pigmented. However, this was not what happened in our experiment. This might be because by the time we had chopped up everything and placed the beetroots in the water, it had already cooled significantly.

7. What are the factors you can think of that would affect the leaking of the pigment out of the beetroot cells? the permeability of the cell membrane which is in turn affected by: -the physical environment (temperature, solution placed in/solvent） -physical stress (eg. cutting) -the composition of the cell membrane

//Note: (you may skip this part:) ) from http://www.uvm.edu/~bio1and2/lab/Lab%20manuals%20Fall%202005/Lab%202%20Membranes.doc, http://www.scienceteacherprogram.org/biology/:// //Certain treatments can stress and damage the cell’s membranes. High temperatures cause violent molecular collisions that can physically destroy a membrane, whereas freezing causes water to crystallize as ice and expand because of hydrogen bond alignment, often rupturing membranes. Application of physical stress, such as cutting, or organic solvents to cells can also rupture membranes. Organic solvents dissolve a membrane’s lipids, in effect reducing the membrane to tatters.// **//Spec·tro·pho·tom·e·ter n//**//: An instrument used to measure the relative intensities of wavelengths in a spectrum.// //Spectrophotometry is based on the principle that some substances absorb light of a particular wavelength better than of another wavelength. Each substance has an “absorption signature,” where it absorbs a certain amount of one wavelength of light, a different amount of a different wavelength of light, and so on. A spectrophotometer projects a beam of light of a particular wavelength through a solution contained in a glass cuvette, a test tube made of optically clear glass. The pigment will absorb some of the light, and the amount absorbed is proportional to the quantity of pigment present in the cuvette. This proportionality is called the Beer-Lambert Law:// //A = Elc// //The Beer-Lambert Law states the absorbance (A) of light is proportional to the light path (l) times the concentration (c) of the substance. The molar extinction coefficient (E, epsilon) is also included. Different substances absorb different amounts of light and therefore have different E values. Note that there is a linear relationship between absorbance and concentration.//

__Exploration 4B__ Results

agar cubes ||= Length (cm) ||= Surface area (cm2) ||= Volume (cm3) ||= Surface area to volume ratio ||= Rate of conductivity change || Discussion Questions 1. What precautions did you take in this experiment? - made sure that all the agar pieces were in cubes (ie roughly 90` angles), even though the blocks they came in were not. - changed the water after every experiment - stirred continuously and gently at roughly the same speed
 * = No or pieces of
 * 1 || 2 || 24 || 8 || 3:1 || 0.38 ||
 * 8 || 1 || 48 || 8 || 6:1 || 0.96 ||
 * 64 || 0.5 || 96 || 8 || 12:1 || 1.46 ||

2. What can you infer from the results above? The greater the surface area, the greater the rate of conductivity change.

3. What do the graphs reveal to you about the rate of diffusion and the surface area of the agar? The greater the surface area, the greater the rate of diffusion.

5. Compare this experiment with the one that you did in Lower Secondary where coloured agars were soaked in acid. Which do you think is more accurate? I think this one is more accurate, as we are able to obtain quantitative data, which is more accurate, as compared to qualitative data by just observing and describing the color.

6. How do you relate this to the shape of simple to complex living organisms? The bigger and organism is, the smaller it's surface area to volume ratio, making it more difficult for it to exchange things with its surroundings/diffusion to occur. As a cell has to constantly have materials moving in and out of its cell membrane, it cannot be too large, as this would hinder the process. Also, larger animals would loose body heat more slowly, as compared to smaller animals. This means that smaller animals would have to have higher metabolism rates or more insulation in order to make up for it.

7. Once a cell grows to a certain size it becomes too large for the complete diffusion of needed substances throughout its cytoplasm. As a cell grows, is the surface area of the cell membrane as efficient relative to the volume of the cell? No, it would not be. If the ratio of surface area of the cell membrane to the volume of the cell is too small, then diffusion would not be able to happen quickly and efficiently enough, and the cell would have insufficient materials required to support life. (In cell division, cells split into 2 daughter cells, once again increasing the ration of the surface area of the cell membrane to the volume of the cell)

8. Examine the agar cells below and work out the surface area to volume ratio of each cell. Which is the most efficient and which is least? The most efficient ones would be the ones with the greatest surface area to volume ratio (the one with lengths of 0.5cm).

//(Note: I checked the Internet for some questions in which I wasn't that sure of the answers. However, I merely glanced through it, and then later re-wrote it from memory. I could have quoted them, but I forgot to take down the websites I used, so..)//