Biology Labs
Which labeled cellular structure on your cardiac muscle image separates and protects the cell from the environment?
cell membrane
Which structure in the cheek cells did you observe that separates and protects the cell from the environment?
cell membrane
Which cellular structures that you observed using the microscope are common to all eukaryotes and prokaryotes?
cell membrane, cytoplasm
What organelles or cellular structures were common to all the different organisms looked at with the microscope?
cell membrane, cytoplasm, nucleus
Which structure did you see in the eukaryotic cells that is absent in the prokaryotes?
nucleus
controlled experiment
one parameter is varied among test groups that are otherwise treated the same
narrow-spectrum antibiotic
only works on a limited range of organisms
multicellular organisms
they consist of more than one cell, usually with numerous different cell types dividing the labor of the organism
microscopic
to be visible only with the aid of a magnifying lens
You were asked to label the cytoplasm on your Spirogyra image. What is the function of the cytoplasm?
to contain all the substances needed to keep the cell alive
Most plant cells have the following structures that can be seen with a light microscope
- A cell wall for sturdier stature, usually made of cellulose and pectin - A central vacuole for storage and water balance - Chloroplasts for photosynthesis - Cytoplasm - A nucleus, which is a membrane-bound structure where a majority of the cell's hereditary information is found
All cells have
- A plasma membrane that acts as a barrier between the cell's inner components and its surroundings - Cytoplasm, which is the semifluid matrix that fills the cell and contains all the dissolved and suspended ions and other molecules needed to keep the cell alive - A central location for hereditary material - Ribosomes for protein synthesis
Which of the following states a characteristic of a scientific hypothesis?
- A scientific hypothesis is based on observation. - A scientific hypothesis predicts a testable result. - A scientific hypothesis is specific.
Common shape types
- Coccus (plural: cocci) - spherical-shaped - Bacillus (plural: bacilli) - rod-shaped - Spirillum (plural: spirilla) - spiral-shaped
Common arrangement types
- Diplo - a pair of cells connected - Clump - several cells connected like a bunch of grapes - Chain - a line of cells connected end-to-end - Tetrad - a group of four cells arranged in a square - Sarcina - a group of eight cells arranged in a cube
gram-negative bacteria
- cannot retain the principal stain applied to them because of the properties of their cell walls - have a thinner peptidoglycan cell wall and an outer membrane made of lipopolysaccharides
Differences between Prokaryotic and Eukaryotic Cells
- Eukaryotic cells have membrane-bound organelles, such as a nucleus or mitochondria. - Prokaryotic cells do not contain membrane-bound organelles. Prokaryotes do contain a nucleoid, which is a region where the circular chromosome of DNA is located. Prokaryotic cells that perform photosynthesis have structures called thylakoids, where the photosynthetic chlorophyll molecules are located.
Examples of quantitative data
- How many triangular scales a snake has - The increase of bone remodeling cells called osteoclasts, based on the rate of exercise - The number of eggs a bird lays per nesting period
With a light microscope, the following structures of animal cells can be seen
- Nucleus - Cell membrane - Cytoplasm - If present, a flagellum, which is a long, thin, tail-like structure used for locomotion
When present in a protist cell, the following structures can be seen with a light microscope
- Nucleus - Cytoplasm - Contractile vacuole that serves an excretory role - Food vacuole that aids in digestion - Cell membrane - Pseudopodia (pseudopods), which are fingerlike projections that aid in locomotion and the capture of food particles - Cilia, which are short, hair like projections that usually line the outer cell membrane to aid in locomotion - Oral groove, where food particles are ingested - Gullet, which is the oral cavity just past the oral groove where food vacuoles form - Chloroplasts - Flagellum
Gram's method of staining requires careful execution to obtain reliable results. The reason for this is that there is a large probability for error to occur. Some reasons why error may be introduced are as follows
- Poor Gram stain results may occur if smears are prepared on dirty slides. Oils and other grime on the slide can alter the effectiveness of the reagents. Slides should always be cleaned thoroughly before use. - Excessive heat during fixation can alter the cell morphology and make the cells more easily decolorized. - Excessive washing with water between steps can cause wash-out and, therefore, should not be done for more than 5 seconds. - Insufficient iodine exposure will generate less crystal violet-iodine complexes within the cell, and the cells in general will be easier to decolorize, thus causing erratic results. - Cells tend to decolorize too easily if crystal violet is prepared at a concentration that is too low, causing all cells to seem gram-negative. - Prolonged decolorization will eventually cause all of the bacterial cells to be decolored. - Excessive counterstaining can cause the safranin, which also can be a principal dye, to replace the crystal violet-iodine complex in gram-positive cells. - - Therefore, the counterstain should not be left on the slide for more than 30 seconds. - Faulty reagents might lead to erroneous Gram reactions. For example, Gram's iodine loses its effectiveness over time due to exposure to air and high temperatures.
Prokaryotic cells can generally be divided into categories based on three cell shapes
- Rod-like - Round - Spiral
The mechanisms for Gram staining are as follows
- The bacterial cells must be killed and adhered to the slide to allow staining to occur. This can be done by a method called heat-fixation, which involves a slide with a sample of bacteria on it being passed quickly through a flame. - Crystal violet is then applied as a principal stain. Both gram-positive and gram-negative bacteria become blue/purple in color during this step because crystal violet can enter both types of cells. Iodine is applied to the cells, which forms large chemical complexes with the crystal violet ions within the cell. - A decolorizer, ethanol, is introduced to serve as a solvent to rinse out the crystal violet-iodine complex. The success of the decolorizer depends on the thickness of the cell wall. In the case of the gram-negative bacteria, the crystal violet-iodine complexes are quickly and completely washed out owing to the relatively thin nature of the cell wall. The cells become colorless once again. In contrast, in the gram-positive bacteria, the crystal violet-iodine complexes become stuck in the thick peptidoglycan cell wall and the cells remain blue/purple in color. - Safranin can be used as a counterstain to give the decolorized gram-negative bacteria a red/pink color.
Examples of qualitative data
- The shape of a snake's scales - The pattern of remodeled bone in response to changes in physical activity - The nesting behaviors of mother birds
Gram stain
- a Danish bacteriologist, Hans Christian Gram, developed a special type of staining method - used to categorize all bacterial species into two different groups based on the composition of their cell walls
Gram-positive bacteria
- able to retain the principal stain applied to them because of the properties of their cell walls - have thick cell walls composed primarily of a carbohydrate known as peptidoglycan
Hypothesis
- describes a possible, testable outcome - said to be an educated guess because formulating the hypothesis typically requires research into ideas and existing outcomes related to the hypothesis - can be written in terms of independent and dependent variables
antibiotic disk diffusion test
- one way to determine which antibiotics can be used to treat a particular type of bacteria - involves growing the bacteria on a nutrient agar-filled plate onto which one or more round disks containing various antibiotics are arranged evenly. As the bacteria multiply, the antibiotics slowly diffuse out of the disks and into the surrounding nutrient agar gel. Diffusion occurs along a concentration gradient. The farther the antibiotic is from the disk, the lower its concentration.
Specialized cells
- shapes specific to their function - also contain certain types of organelles as well as relative numbers of those organelles needed to carry out their function
Which of the highlighted structures in the image below is the nucleus?
2
Of the four cell types that you observed in the lab, which was the largest? Remember the total magnification notes on your images.
Amoeba cell
dependent variable
Another parameter, measured during the course of the experiment
Based on your results, which antibiotics could be classified as narrow-spectrum?
Both could be classified as narrow-spectrum.
A student is performing a Gram stain of a mixed culture of both E. coli and S. aureus and he forgets to decolorize with ethanol. What should his slide look like?
Both the E. coli and S. aureus should appear blue/purple.
Independent variable
In controlled experiments, the parameter that is varied by the scientist
What was the purpose of adding iodine after the application of the principal stain?
Iodine forms a complex with crystal violet that is then too large to move out of the cell.
What is the function of the nucleus in the Euglena cells you observed?
It contains DNA and controls the cell.
What is the function of the cell wall in the onion cell you looked at?
It protects the cell and provides shape and support.
Refer to your observations of the shapes of the organisms that do and do not have cell walls. What effect does the cell wall have on the shape of the organism?
It restricts the cell shape. The Spirogyra cells are fairly uniform rectangles. Animal and Amoeba cells had more variable shapes.
Suppose a student hypothesized that mice would grow best if fed apple slices. She used four mice, all of which she incubated for seven days. She fed the first mouse apple slices, the second raw steak, the third fruit punch, and the fourth was not given any food. At the end of seven days, she found the following changes in mass for the four mice: the one fed apple slices gained 1.00 g, the one fed raw steak gained 0.61 g, the one given fruit punch gained 4.20 g, and the one given only water died by week's end. Did the results of her experiment support her hypothesis?
No. The mouse gained the most mass from the fruit punch, not the apple slices.
How many independent variables should an experiment have?
One
Suppose a scientist was observing a new species of butterfly. He observed a new color that had not been seen in butterflies before. Was the data he collected qualitative or quantitative? Please explain.
Qualitative; observing color is descriptive.
What pattern did you observe when comparing which antibiotics were effective against the two species of bacteria?
Some antibiotics had at least some effect for both species and some only worked against one of the species.
What was the purpose for heat-fixation of the bacterial slides?
The heat kills the bacteria and makes them adhere to the slide.
Why did you not see chloroplasts in the onion root cells?
The roots are underground and are not exposed to light. Therefore, they do not need chloroplasts
What is the scientific method?
The scientific method is a way of learning about the universe through observation and experimentation.
What is the function of the vacuoles you saw in the Paramecium?
They store fluids, nutrients, and waste.
Suppose a student gave two mice water alone and incubated one for one day and the second for six days. The first mouse maintained its mass, and the second mouse died on the sixth day. What is the most likely explanation?
Water, without nutrients from food, is not adequate for six days.
Do results need to be evaluated?
Yes to ensure that the experiments were conducted properly and that conclusions are valid
principal stain in Gram's method
a blue/purple ionic compound called crystal violet. The counterstain is a red/pink ionic compound called safranin
Cell Wall
a rigid layer outside the plasma membrane that gives the cell a structured shape and strengthens the cell by resisting osmotic pressure
Experiment
a test of the hypothesis you formulated. It provides results that either support or disprove the hypothesis
Cytoplasm
a thick, jellylike substance that is enclosed in the plasma membrane
The size of a skin cell
about 30 μm (30 × 10-6 or 0.000030 m)
Which antibiotic had the largest diffusion ring into the S. aureus growth?
ampicillin
Positive control groups
are expected to produce a positive result
What color and shape were the onion root cells?
blue and rectangular
Which cellular structure did you observe in the Spirogyra, but not in the other cells?
chloroplast
Where in the Spirogyra cell does photosynthesis, which creates the biological molecule used for fuel, occur?
chloroplasts
Which organelles' function is primarily locomotion?
cilia and flagella
Nucleus
contains most of the genetic material of the cell and the mitochondria supply most of the energy for eukaryotes
Qualitative data
descriptive
total magnification
eyepiece magnification × objective magnification
Suppose a student hypothesized that mice would grow best if fed raw pasta. He fed one mouse the raw pasta, another mouse was fed apple slices, and another mouse received no food. Both the raw pasta mouse and the control mouse had lost mass by the end of two days but the apple slice mouse gained mass. The student concludes that his hypothesis is not supported by his data. Which of the following is the next step?
generate a new hypothesis
Which bacteria is affected by the decolorizer, ethanol?
gram-negative bacteria with thin cell walls that allow the ethanol through to wash out the dye-iodine complexes
How did you classify the E. coli bacteria from the Gram staining experiment?
gram-negative, rod-shaped, dispersed individually and diplo
Suppose you are trying to identify an unknown bacterial species. You perform a Gram stain and the slide is a blue/purple color when you are finished. Are the bacteria gram-positive or gram-negative?
gram-positive
How did you classify the S. aureus bacteria from the Gram staining experiment?
gram-positive, spherical-shaped, arranged individually and in clumps
Quantitative data
include specific measurements of a particular parameter, such as time, temperature, mass, or volume
Observation
involves witnessing a natural phenomenon
Which choice describes the characteristics of the Amoeba you observed using the microscope?
irregular shape and pink color
Magnification
is achieved with two optical elements, the ocular lens (eyepiece) and the objective lenses (objective)
Flagella
long, hair-like extensions that extend from the cell and aid in locomotion
Macroscopic
means to be seen with the naked eye
Vacuoles
membrane-bound storage areas that store fluid and nutrients as well as wastes
Bacteria
mostly colorless and invisible to light microscopy
Eukaryotes
much more complex organisms. Eukaryotic cells are divided into organized, membranous compartments. This is important because metabolic processes that need different conditions can occur simultaneously within the cell without interfering with each other. Plants, animals, protists, and fungi are all types of eukaryotes. Eukaryotic cell size typically ranges from 20 - 80 µm long. This larger size allows for some of the eukaryotic cell structures to be seen with a light microscope.
Negative control groups
not receive treatment and are compared to experimental groups that do receive treatment
Which antibiotics were NOT effective at all against E. coli?
penicillin and erythromycin
What do all cells have?
plasma membrane (cell membrane) and cytoplasm
Two basic types of cells
prokaryotes and eukaryotes
Common Cellular Structures
several structures commonly found in cells, including the cell wall, vacuoles, flagella, and cilia
Cilia
shorter and more numerous than flagella. Rows of cilia move in waves to propel the cell or to move fluids around the cell and remove particles from those fluids.
What must you do in order to observe bacteria under the microscope
stain them
A common theme in biology
that function follows form
Cells
the building blocks of life
ocular lens
the lens at the top of the microscope through which you look to see the image
Prokaryotes
the oldest and most structurally simple organisms on Earth. The size of prokaryotes ranges from 2 - 8 µm long. Due to this small size, cell shape is the only characteristic of prokaryotes that can be seen with a light microscope
objective lens
the one closest to the slide and further magnifies the object on the slide
Compound light microscopes
typically have three or four objectives, which are the lenses that increase the size of the image of an object, with magnifications such as 4X, 10X, 40X, and 100X
Protists
typically larger cells and are very diverse in their structural components
Prokaryotes
which consist of the bacteria and archaea, are mostly unicellular organisms and are the smallest and the simplest form of living things
Eukaryotes
which consist of the protists, fungi, plants, and animals, can be found as both unicellular and multicellular organisms
broad-spectrum antibiotic
works on both types of bacteria