Lab Practices/ Microscopes + Scientific Method

controlled experiment

experiment in which only one variable is changed

pH paper (universal indicator)

paper saturated with a chemical to show whether a substance is acidic or basic

According to the data, this enzyme would probably work best at what pH values?

1) 7 and 8

An experimental setup is shown in the diagram below. Which hypothesis would most likely be tested using this setup?

1) Green water plants release a gas in the presence of light

Which laboratory equipment should be used to observe the surface details of structures A, B, and C of the earthworm?

1) Stereoscope

When viewed with a compound light microscope, which letter would best illustrate the way in which the microscope inverts and reverses the image?

3) F

Hypothesis

An educated guess

Identify the structure indicated by arrow B.

B is indicating a nucleus

Celsius scale

The temperature scale on which water freezes at 0 degrees and boils at 100 degrees

Scientists breed mice to be as genetically alike as possible to use in experiments. Explain why scientists would want mice that are genetically alike. In your answer be sure to explain: - The advantage of using genetically alike mice - Why cloned mice would be even better

If the mice are nearly genetically alike, differences in the mice are not likely to affect the result of the experiment. Cloned mice are even better since they are genetically identical

total magnification

objective lens x ocular lens

Biuret Reagent

solution that turns lavender to violet (purple) in the presence of proteins

control group

the group that does not receive the experimental treatment

active transport

the movement of materials through a cell membrane using energy

independent variable

variable that is manipulated

The steps of the Scientific Method are...

1. Question 2. Research 3. Hypothesis 4. Experiment 5. Collect Data 6. Analyze Data 7. Conclusion

medium objective

10x

A student studied the upper layer of cells of a tissue sample on a slide, using the high-power objective of the compound microscope shown. Which part of the microscope should the student adjust to observe the lower layer of the sample?

2) B - Fine adjustment knob

The photograph shows onion-root tip tissue viewed under the high-power objective of a compound light microscope. The photograph illustrates stages in the process of...

2) Mitotic cell division in plants

After examining the graphs, the scientist could reasonably assume that at a low temperature the frogs would...

2) Produce less carbon dioxide

A student performed an experiment involving two strains of microorganisms, strain A and strain B, cultured in various temperatures for 24 hours. The results of this experiment are shown in the data table below. Based on the results of the experiment, the student inferred that strain A was more resistant to higher temperatures than strain B was. What, if anything, must the student do for this inference to be considered a reasonable conclusion?

2) Repeat this experiment several times and obtain similar results

A student performing an experiment noticed that the beaker containing the water being heated had a small crack. It was not leaking. What should the student do?

2) Stop heating the beaker and report the crack to the teacher

An unsafe procedure for heating a nutrient solution in a flask would be to...

2) Stopper the flask tightly to prevent evaporation of the solution

A student tossed a coin five times and observed results of four tails and one head. He concluded that when a coin is tossed, there is an 80% chance of getting a tail and a 20% chance of getting a head. The conclusion would be more valid if...

3) A greater number of tosses had been used

A student conducted an original, well-designed experiment, carefully following proper scientific procedure. In order for the conclusions to become generally accepted, the experiment must...

3) Be repeated to verify the reliability of the data

A drug company tested a new medication before putting it on the commercial market. Pills without medication were given to 500 test subjects in group A, and pills with medication were given to 500 subjects in group B. In this experiment, the individuals in group A served as the...

3) Control

As part of a laboratory experiment, a thin slice of peeled raw potato weighing 10 grams is placed in an oven at 80 degrees celsius. After 5 hours, the potato sample is removed from the oven and weighed again. The purpose of this experiment might be to...

3) Determine the water content of potato tissue

In order to find the percentage of organic matter in soil from several different locations, a student collected the samples, weighed them immediately, roasted them for several minutes in a flame to burn off organic matter, and and weighed them again. The student concluded that the difference between the first and second weights represented the weight of the organic matter in the soil. The most serious mistake that the student made in this experiment was in...

3) Failing to dry the samples before first weighing them

A new drug for the treatment of asthma is tested on 100 people. The people are evenly divided into two groups. One group is given the drug, and the other group is given a glucose pill. The group that is given the glucose pill serves as the...

3) Limiting factor

If a student spills nitric acid on her arm, she should first...

3) Rinse her arm with water

To test for the presence of glucose, a student added the same amount of Benedict's solution to each of four test tubes. (Benedict's is a glucose indicator that is a royal blue color when no glucose is present. To determine if glucose is present, Benedict's must be mixed in the unknown solution and heated for several minutes.) Two of the test tubes contained unknown solutions. The other two test tubes contained known solutions. The chart below shows the color results obtained after the solutions were heated in the four test tubes in a hot water bath. The student could correctly conclude that...

3) Tube 1 did not contain glucose, but tube 2 did

Pieces of pH paper were used to test the contents of three test tubes. The results are shown in the diagram below. Which statement about the tubes is correct?

3) Tube B contains an acid

When they are not being used during a laboratory investigation, electrical devices should be...

3) Unplugged

Structure A has a diameter of 3 millimeters. What is the approximate diameter of the blood vessel indicated by C?

4) 0.5 mm

Chlorophyll can be removed from leaves by boiling them in alcohol, a flammable solvent. In addition to wearing safety goggles, which is the safest procedure to follow?

4) A beaker of leaves and alcohol should be placed into a larger beaker of water and heated on a hot plate

When heavy rains occur while apple orchards are in bloom, the apple crop the following fall is much smaller than normal. This information can best be described as...

4) An observation

A student viewing a specimen under the low-power objective of a compound light microscope switched to high power and noticed that the field of view darkened considerably. Which microscope part identified on this microscope would the student adjust to brighten the field of view?

4) D - Diaphragm

Which of the steps listed below would be first in a scientific investigation?

4) Define the problem to be investigated

After watching the behavior of earthworms in soil, a biology student suggested that the penetration of air into the soil promotes the root development of plants. The student then set up the following experiment. The important data to be recorded in this experiment will come from the observation of the increase in...

4) Number of roots

The graph below represents the results of an investigation of the growth of three identical bacterial cultures incubated at different temperatures. Which inference can be made from the graph?

4) Refrigeration will most likely slow the growth of these bacteria

The independent variable in this experiment was...

4) Temperature of the environment

Which safety procedure should a student follow during a dissection?

4) The student should direct the cutting motion away from her body

While focusing a microscope on high power, a student crushed the coverslip. The student probably...

4) Used the coarse adjustment

high objective

40x

low objective

4x

Benedict's solution

A chemical indicator that, when added to a solution and heated, changes from blue to light green to red in the presence of increasing concentrations of sugar.

Describe the function of a control group in an experiment.

A control group provides a basis for comparison. It is an established reference point where you know what should happen. You compare what happens to the control group to what happens with the experimental group

Variable

A factor that can change in an experiment

Identify the structure indicated by arrow A.

A is indicating the chromosomes of a dividing nucleus

BTB - Bromothymol Blue

A liquid indicator that turns YELLOW in an ACID does not change in a base.

Describe one modification you would make in the design of this experiment to make the results more reliable.

A modification to make the experiment more reliable would be to use more plants. OR The experiment could be repeated several times

Scientific Method

A series of steps followed to solve problems including collecting data, formulating a hypothesis, testing the hypothesis, and stating conclusions.

Lugol's solution

A yellow-brown indicator that turns blue-black when it comes into contact with starch.

Osmosis

Diffusion of water through a selectively permeable membrane

Diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

State one way this experiment could be improved to make the results more reliable.

One way the reliability of the conclusions could be increased is to do the same experiment over several times, or to use more than just two plants for the experiment. If the conclusion applies to different kinds of plants, the experiment would have to use many kinds of plants, too

A student placed five geranium plants of equal size in five environmental chambers. Growing conditions were the same for each plant except that each chamber was illuminated by a different color of light of the same intensity. At the end of 20 days, plant growth was measured. State the possible hypothesis for this experiment.

Plants grown in different colors of light will grow different amounts. OR If plants are grown in normal light, they will grow larger than plants grown in different colors of light

State the purpose of using stains in a wet-mount slide preparation.

Stains are used to make certain cell organelles more visible

What technique could be used to make the organelle indicated by letter X more visible?

Stains are used to make certain cell organelles more visible

State the hypothesis being tested in this experiment.

The amount of air available will affect the growth of roots on plants

field of view

The area visible through the microscope eyepiece

A student observed a one-celled organism in the field of view of a compound light microscope as shown in the adjacent diagram. On the diagram, draw an arrow to indicate the direction the organism would seem to move if the student moved the slide on the stage to the left and down.

The arrow drawn should point to the right and upward

What control should be used in this experiment?

The control should be plants grown in white (normal) light. (The control should not be grown in sunlight since the intensity would be so much greater.)

In attempting to demonstrate the effectiveness of a new vaccine, a scientists performed these experimental procedures: - One hundred genetically similar rats were divided into two groups of 50 rats each (group A and group B). - Each rat in group A was given an injection of the vaccine in a glucose-and-water solution. - Each rat in group B was given an injection of the glucose-and-water solution containing no vaccine. - After several weeks, all rats in both groups were exposed to the disease for which the vaccine was developed. Identify the dependent variable that was studied in this experiment.

The dependent variable is the effectiveness of the vaccine: how many rats get sick or do not get sick

Describe one adjustment that could be made to the microscope to make the field of view brighter.

The disk diaphragm could be adjusted to let more light pass through the specimen

The eyepiece of a compound light microscope has a magnification of 10X and the low-power objective and high-power objective lenses have magnifications of 10X and 30X, respectively. If the diameter of the low-power field measures 1500 micrometers, the diameter of the high-power field will measure either 4500 micrometers or 500 micrometers. Select the correct diameter. Support your answer.

The high-power field always has a smaller diameter and covers less area than the low-power field. Therefore, the high-power field would be smaller---500 micrometers in this case

A group of 24 frogs was separated into two equal groups. Group A was placed in an environment in which the temperature was a constant 35 degrees fahrenheit. Group B was placed in a similar environment, except the temperature was a constant 65 degrees fahrenheit. Equal amounts of food were given to each group at the start of the experiment and again every 24 hours. Immediately before each daily feeding, the excess food from the prior feeding was removed and measured. This allowed the scientist to determine the daily amount of food each group of frogs consumed. Each day, the heart rate and breathing rate of the frogs were checked. At the end of the experiment, the following bar graphs were prepared: Using one or more complete sentences, state the hypothesis the scientist was most likely investigating in this experiment.

The hypothesis the scientist was most likely investigating was: Temperature affects the activity level of frogs

In an investigation to determine the effects of environmental pH on the germination of dandelion seeds, 25 dandelion seeds were added to each of five petri dishes. Each dish contained a solution that differed from the others only in its pH, as shown below. All other environmental conditions were the same. The dishes were covered and observed for 10 days. The data table the student designed is shown below. State the independent variable in this investigation.

The independent variable in this investigation is the pH of the solution

A student was working on an investigation to measure the relative activity of an enzyme at various pH values. He collected the following data: pH 2, enzyme activity 10; pH 8, enzyme activity 50; pH 12, enzyme activity 10; pH 4, enzyme activity 20; pH 6, enzyme activity 40; pH 10, enzyme activity 40 Identify the independent variable in this experiment.

The independent variable is pH

passive transport

The movement of materials through a cell membrane without using energy

The image is a representation of an animal cell as it would appear when viewed with a compound light microscope. Identify the organelle indicated by letter X.

The nucleus

dependent variable

The outcome factor; the variable that may change in response to manipulations of the independent variable.

A student prepared the following list of steps for performing a laboratory investigation. She omitted one important step for completing the investigation. State the procedure that is missing from the chart.

The step that is missing is one stating that it is important to draw a conclusion

The diagram below shows a student heating some test tubes with chemicals in them during a laboratory activity. Describe one error in the laboratory procedure shown in the diagram.

The student should be wearing goggles. OR The test tubes should be pointed away from all students in the area

The diagram below shows a student conducting a laboratory experiment. Describe a safety procedure the student should be following that is not represented in the diagram.

The student should wear goggles. OR The test tube should not be aimed at the student's face. OR The student should tie back her hair

A student wants to shorten the ripening time for tomatoes. He predicts that the more water the seedlings receive, the faster the tomatoes will ripen. To test this prediction, he grows 20 tomato plants in a garden in full sunlight that has dry soil and 20 in a garden in a shadier location where there is a greater moisture content in the soil. He then records the time it takes for fruit to develop and ripen on the plants in each garden location. State a serious error the student made with the design of this experiment.

The student varied both the amount of light and the amount of moisture, so the reason for any differences in ripening time between the two groups cannot be determined

Using the information in the data table, construct a line graph on the grid provided, following the directions below: - Provide an appropriate title for the graph. - Make and label an appropriate scale, without any breaks, on each axis. - Plot the data on the grid. Surround each data point with a small circle and connect the points.

Title: Effect of pH on Enzyme Activity Independent variable (x-axis): pH level Dependent variable (y-axis): Enzyme Activity (2, 10) (4, 20) (6, 40) (8, 50) (10, 40) (12, 10)

Organize the data by filling in the data table provided. Follow these directions when completing your data table. - Provide an appropriate title for the data table. - Fill in the first box in each column with an appropriate heading. - Arrange the data so that pH values are in increasing order.

Title: Effect of pH on Enzyme Activity Independent variable: pH level Dependent variable: Enzyme Activity pH 2, enzyme activity 10 pH 4, enzyme activity 20 pH 6, enzyme activity 40 pH 8, enzyme activity 50 pH 10, enzyme activity 40 pH 12, enzyme activity 10

experiment

a set of controlled observations that test the hypothesis

compound light microscope

microscope that allows light to pass through a specimen and uses two lenses to form an image