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Lab 5: Cells - Biology

Lab 5: Cells - Biology


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Introduction:

The cell theory states that all living things are composed of cells, which are the basic units of life, and that all cells arise from existing cells. In this course, we closely study both types of cells: prokaryotic and eukaryotic. Prokaryotes lack a nucleus and true organelles, and are typically significantly smaller than eukaryotic cells. Prokaryotic organisms are found within the domains Bacteria and Archaea. Eukaryotic cells contain nuclei as well as other organelles that work together to support the homeostasis of the whole cell. Though eukaryotes are larger than prokaryotes, we must use a microscope to view all cells, which are typically too small to see with the naked eye.

There are vast differences between cell types, but a few features are common to all cells: plasma membrane, cytoplasm, ribosomes, and cytoskeleton. All cells also use DNA for their genetic material. In eukaryotes, this is within the nucleus while in prokaryotes, it is found in the nucleoid region of the cytoplasm. Prokaryotes generally have a cell wall made of peptidoglycan and some have flagella or fimbriae, which are used for movement or attachment. Eukaryotes have several more organelles and are further differentiated into 2 categories: plant cells and animal cells.

Some organelles common to eukaryotes include mitochondria, peroxisomes, vesicles, lysosomes, smooth and rough endoplasmic reticula, and Golgi bodies. Animal cells tend to lack cell walls and chloroplasts, while plant cells do contain chloroplasts and have cellulose cell walls.

In this lab, bacterial, animal, and plant cells will be observed using the microscope. Students will draw what was visualized to record their observations.

Part 1: Bacterial Cells

View a prepared slide of common bacterial cell types; prepare a wet mount of cyanobacteria and observe under the microscope.

Materials:

  • Compound microscope
  • Methylene blue
  • Microscope slide
  • Cover slip
  • Transfer pipette
  • Culture of Oscillatoria

Procedure:

A. Fixed Slide of Bacterial Types

  1. Examine the demonstration slide of mixed bacteria. There are 3 common shapes: round (coccus), rod (bacillus), and spiral (spirillum). The slide should have several of each type of bacteria.
  2. Draw each of the bacterial shapes in the spaces at right.

B. Wet Mount of Oscillatora

  1. Using the transfer pipette, transfer a drop of liquid culture onto a microscope slide.
  2. Place coverslip onto the slide.
  3. Use the SCANNING (4x) objective to focus. You are looking for very faint green thin filaments.
  4. Switch to low power (10x). You may be able to see lines going across the filaments, but the image will likely just look like green floss.
  5. Once you have centered and focused the image, switch to high power (40x) and refocus. The individual cells should be visible at this magnification; each filament is composed of cells stacked on top of each other. Remember, do NOT use the coarse adjustment knob at this point!
  6. Sketch the bacteria at low and high power. Label the cytoplasm and cell wall of a single cell. Draw your cells to scale.

Questions:

1. Why are nuclei not visible within the cells viewed?

2. The common name for species like Oscillatoria is blue-green algae. This group of bacteria is capable of photosynthesizing. Do they contain chloroplasts? Explain.

Part 2: Animal Cells

Prepare a wet mount of a human cheek cell and observe under the microscope.

Materials:

  • Compound microscope
  • Methylene blue
  • Microscope slide
  • Cover slip
  • Toothpick

Procedure:

  1. Put a drop of methylene blue on the slide.
  2. Gently scrape the inside of your cheek with the flat side of a toothpick. Scrape lightly!
  3. Stir the end of the toothpick in the stain and throw the toothpick away.
  4. Place a coverslip onto the slide.
  5. Use the SCANNING (4x) objective to focus. You probably will not see the cells at this power.
  6. Switch to low power (10x). Cells should be visible, but they will be small and look like nearly clear purplish blobs. If you are looking at something very dark purple, it is probably not a cell.
  7. Once you think you have located a cell, switch to high power (40x) and refocus. Remember, do NOT use the coarse adjustment knob at this point!
  8. Sketch the cell at low and high power. Label the nucleus, cytoplasm, and cell membrane of a single cell. Draw your cells to scale.

Questions:

1. Why is methylene blue added?

2. The light microscope used in the lab is not powerful enough to view other organelles in the cheek cell.

a. What parts of the cell were visible?

b. List 2 organelles that were NOT visible but should have been in the cheek cell.

3. Is the cheek cell a eukaryote or prokaryote? How do you know?

4. Keeping in mind that the mouth is the first site of chemical digestion in a human. Your saliva starts the process of breaking down the food you eat. Keeping this in mind, what organelle do you think would be numerous inside the cells of your mouth?

Part 3: Plant Cells

Prepare wet mounts of an onion cell and an Elodea leaf cell and observe both under the microscope.

Materials:

  • Compound microscope
  • Microscope slide
  • Cover slip
  • Dropper bottle with dH2O
  • Forceps
  • Pre-cut onion bulb
  • Culture of Elodea
  • Dissecting needle

Procedure:

A. Wet Mount of an Onion Cell

  1. Put a drop of water onto the microscope slide.
  2. Using the forceps, gently peel off a small piece of the “membrane” of the onion (epidermis). It should be very thin and may curl up on itself.
  3. Place the onion sample into the drop of water on your slide. Try to unroll/straighten out the sample to view a single layer of cells. You may need to use the dissecting needle to do this.
  4. Place a coverslip onto the slide.
  5. Use the SCANNING (4x) objective to focus. Cells walls should be visible: they will look like semi-clear grid lines.
  6. Once you think you have located a cell, switch to high power (40x) and refocus.
  7. Sketch the cell at low and high power. Label the nucleus, cytoplasm, and cell wall of a single cell. Draw your cells to scale.

B. Wet Mount of an Elodea Leaf Cell

  1. Put a drop of water onto the microscope slide.
  2. Using the forceps, gently tear off a small piece of a leaf from Elodea.
  3. Place the Elodea leaf into the drop of water on your slide.
  4. Place a coverslip onto the slide.
  5. Use the SCANNING (4x) objective to focus. Cells walls should be visible: they will look like dark grid lines.
  6. Once you think you have located a cell, switch to high power (40x) and refocus.
  7. Sketch the cell at low and high power. Label the chloroplasts, cytoplasm, and cell wall of a single cell. The nucleus may be visible as well—it will be a large, clear figure. Draw your cells to scale.

Questions:

1. Describe the shape and the location of chloroplasts.

2. Were chloroplasts observed in the onion cells? Why or why not?

3. “Animal cells have mitochondria; plant cells have chloroplasts.” Is this statement true or false? Explain.

4. Fill out the Venn diagram below to show the differences and similarities between the onion cells and the Elodea cells.


Lab 5 Ap Sample 3

Introduction
Cellular respiration is a series of enzyme-mediated reactions that release the energy from carbohydrates. It begins in the cytosol with glycolysis and is completed within the mitochondria. Cellular Respiration can be summarized with the following equation:

C6H12O6 + 6O2 → 6CO2 + 6H2O + 686 kilocalories of energy/mole of glucose oxidized

Cellular respiration could be measured in several different ways, but in this experiment oxygen consumption is used. To do this, it uses a number of the physical laws of gases including the equation, PV = nRT, where P stands for pressure, V for volume, n for the number of molecules, R for the gas constant, and T for temperature. This law shows the many relationships between these factors and how they affect each other.

This experiment compares respiration rates in germinating and non-germinating peas. Germination is the growth processes of a seed. It requires a lot of energy to break the seed coat and as it continues to grow this energy need increases. Respiration is required to access this energy so as the seed germinates its respiration rates increase. Non-germinating seeds, however, are dormant and use very little respiration. Some respiration must occur in order for the seed to live.

Hypothesis
The rate of cellular respiration will be greater in germinating peas than in dry peas, and temperature will have a direct effect on this rate.

Materials
This lab required a room temperature bath and a 10°C bath, ice, a 100-mL graduated cylinder, 50 germinating peas, paper towels, 150 mL of water, dry peas, beads, six vials with attached stoppers and pipettes, absorbent cotton, 5-mL pipette, 15% KOH, non-absorbent cotton, masking tape, and a timer.

Methods
A room temperature bath and a 10°C bath were prepared. A 100-mL graduated cylinder was filled with 50 mL of water. Then, 25 germinating peas were added and the amount of displaced water was determined and recorded. The peas were then removed and placed on a paper towel until needed for Respirometer 1. The graduated cylinder was then refilled with 50 mL of water. 25 dry peas were added and beads were added until the volume equaled that of the germinating peas. The peas and beads were removed and placed on a paper towel for use in Respirometer 2. After refilling the graduated cylinder with 50 mL of water, beads were added until the volume again equaled that of the germinating peas. They were removed and placed in a paper towel for use in Respirometer 3.
The above procedures were repeated to prepare a second set of germinating peas, dry peas and beads, and beads for use in Respirometers 4, 5, and 6. The respirometers were prepared next by first placing a small wad of absorbent cotton in the bottom of each respirometer and saturating it with 15% KOH, being careful not to get any on the sides of the vial. Next, a piece of non-absorbent cotton was placed on top of the KOH-soaked cotton. The first set of germinating peas, peas and beads, and beads were added to Respirometers 1, 2, and 3. Then the second set was added to Respirometers 4, 5, and 6.
A masking tape sling was created for each of the water baths to hold the respirometers out of the water during equilibration. Respirometers 1, 2, and 3 were placed in the room-temperature bath, and Respirometers 4,5,and 6 were placed in the 10°C water bath. The respirometers were allowed to equilibrate for 10 minutes and then were immersed entirely in the water bath. They were checked for leaks and an initial reading was taken. Then additional readings were taken every 5 minutes for 20 minutes.


Watch the video: Stat115 Lab5 (July 2022).


Comments:

  1. Lothair

    really strange

  2. Madoc

    This can and should be discussed :) endlessly

  3. Ata

    Excellent, very useful information



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