In 1928, Sir Alexander Fleming was studying Staphylococcus bacteria growing in culture dishes. He noticed that a mold called Penicillium was also growing in some of the dishes. As shown in the illustration below, Petri dish A represents a dish containing only Staphylococcus bacteria. In dishes containing thePenicillium mold, represented by Petri dish B below, Fleming noticed that a clear area existed around the mold because all the bacteria in this area had died. In the culture dishes without the mold, no clear areas were present. Fleming suggested that the mold was producing a chemical that killed the bacteria. He decided to isolate this substance and test it to see if it would kill bacteria. Fleming grew some Penicillium mold in a nutrient broth. After the mold grew in the broth, he removed all the mold from the broth and added the broth to a culture of bacteria. All the bacteria died.Which of the following statements is a reasonable expression of Fleming's hypothesis?

Penicillium mold produces a substance that kills Staphylococcus.

There are clear areas around the Penicillium mold where Staphylococcus doesn't grow.

Without mold in the culture dish, there were no clear areas in the bacteria.

Using the information from the previous question: Fleming grew Penicillium in broth, removed the Penicillium, and poured the broth into culture dishes containing bacteria to see if the broth would kill the bacteria. What step in the scientific method does this represent?

Testing a hypothesis by experiment

Rejecting the old hypothesis and making a new one

Why do scientists sometimes discard theories?

Contradictory observations are found.

The steps in the scientific method were not followed in order.

Public opinion disagrees with the theory.

The theory is opposed by the church.

Gary noticed that two plants of the same type were different in size after three weeks, even though they were initially the same size when his mother planted them on the same day. Since the larger plant was in the full sun all day and the smaller plant was in the shade of a tree for most of the day, Gary believed that the sunshine was responsible for the difference in plant size. In order to test this, Gary bought ten small plants of the same size and type. He also made sure they have the same amount and type of soil. Gary then built a frame to hold a canvas roof over five of the plants, while the other five were nearby but out in the sun. Gary was careful to make sure that each plant received exactly the same amount of water and plant food every day.Which of the following is a reasonable statement of Gary's hypothesis?

Plants that get more sunshine grow larger than plants that get less sunshine.

Different plants have different characteristics

Plants that grow in the shade grow larger

Plants that don't receive water will die.

Plants that receive the same amount of water and plant food will grow the same amount.

What scientific reason might Gary have for insisting that the container size for the all plants be the same?

Gary wanted to make sure the size of the container did not affect differential plant growth in his experiment.

Gary wanted to determine if the size of the container would affect the plant growth.

Gary wanted to control how much plant food his plants received.

Gary wanted his garden to look organized.

There is no possible scientific reason for having the same-sized containers.

What scientific reason might Gary have for insisting that all plants receive the same amount of water every day?

Gary wanted to test the effect of shade on plant growth, and therefore he wanted to have no variables other than the amount of sunshine on the plants.

Gary wanted to test the effect of the amount of water on plant growth.

Gary's hypothesis was that water quality was affecting plant growth.

There is no possible scientific reason for having the same amount of water for each plant every day.

Which of the following factors did Gary not control in his experimental setup that may be varying?

All of the above are possible factors that Gary did not control

Soil temperature due to the different colors of the containers

Water loss due to evaporation from the soil

The effect of insects, which may attack one set of plants but not the other

When a mosquito sucks blood from its host, it penetrates the skin with its sharp beak and injects an anti-coagulant so that the blood will not clot. It then sucks some blood and removes its beak. If the mosquito carries disease-causing microorganisms, it injects these into its host along with the anti-coagulant. It was assumed for a long time that the typhus virus was injected by the louse (singular for lice) when sucking blood in a manner similar to the mosquito. This turned out not to be true. The infection is not in the saliva of the louse but in the feces. The disease is thought to be spread when louse feces come in contact with scratches or bite wounds on the host's skin. A test of this was carried out in 1922 when two workers fed infected lice on a monkey, taking great care that no louse feces came into contact with the monkey. After two weeks, the monkey had not become ill with typhus. The workers then injected the monkey with typhus, and the monkey became ill within a few days. Why did the workers inject the monkey with typhus near the end of the experiment?

To prove that the monkey was not immune to typhus

To prove that the lice carried the typhus virus

To prove the monkey was similar to man

To prove that mosquitoes were not carriers of typhus

To demonstrate that the workers were mean

During Pasteur's time, anthrax was a widespread and disastrous disease for livestock. Many people whose livelihood was raising livestock lost large portions of their herds to this disease. Around 1876, a horse doctor in eastern France named Louvrier claimed to have invented a cure for anthrax. The influential men of the community supported Louvrier's claim of having cured hundreds of cows of anthrax. Pasteur went to Louvrier's hometown to evaluate the cure. The cure was explained to Pasteur as a multi-step process during which: 1) the cow was rubbed vigorously to make her as hot as possible; 2) long gashes were cut into the cows skin; 3) turpentine was poured into the cuts; 4) an inch-thick coating of cow manure mixed with hot vinegar was plastered onto the cow; and 5) the cow was completely wrapped in a cloth. Since some cows recover from anthrax with no treatment, performing the cure on a single cow would not be conclusive, so Pasteur proposed an experiment to test Louvrier's cure. Four healthy cows were to be injected with anthrax microbes. After the cows became ill, Louvrier would pick two of the cows (A and B) and perform his cure on them, while the other two cows (C and D) would be left untreated. The experiment was performed, and after a few days, one of the untreated cows died and the other got better. Of the cows treated by Louvrier's cure, one cow died and the other got better. In this experiment, what was the purpose of infecting cows C and D?

To serve as experimental controls (a comparison of treated to untreated cows)

To give Louvrier more than two cows to choose from

To make sure the injection actually contained anthrax

To kill as many cows as possible

a tentative explanation for a phenomenon.

a description of a consistent pattern in observations.

an observation that remains constant.

a description of a consistent pattern in observations.

an observation that remains constant.

a tentative explanation for a phenomenon.

A number of people became ill after eating oysters in a restaurant. Which of the following statements is a hypothesis about this occurrence?

Bacteria in the oysters may have caused the illness.

Everyone who ate oysters got sick.

People got sick whether the oysters they ate were raw or cooked.

Symptoms included nausea and dizziness.

The cook felt really bad about it.

Which statement best describes the reason for using experimental controls?

Experimental controls allow comparison between groups that are different in only one variable.

Experimental controls eliminate the need for large sample sizes.

Experimental controls eliminate the need for statistical tests.

Experimental controls reduce the number of measurements needed.

A student decides to set up an experiment to determine the relationship between the growth rate of plants and the presence of detergent in the soil. He sets up ten seed pots. In five of the seed pots, he mixes a precise amount of detergent with the soil. The other five seed pots have no detergent in the soil. The five seed pots with detergent are placed in the sun, and the five seed pots with no detergent are placed in the shade. All ten seed pots receive the same amount of water as well as the same number and type of seeds. He grows the plants for two months and charts the growth every two days. What is wrong with his experiment?

The student has two variables different between the groups.

The student did not add detergent to all ten pots.

The student has no experimental control on the soil.

If you have a control group for your experiment, which of the following is true?

The control group must be identical to the test group except for one variable.

There can be more than one difference between the control group and the test group but no more than three differences, or else the experiment is invalid.

The control group and the test group may have many differences between them.

If the hypothesis is rejected by the experiment, then:

the experiment may have been a success.

the experiment must be poorly designed.

the experiment didn't follow the scientific method.

Chemistry Chapter 1 Homework 1-2

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Chemistry Chapter 1 Homework 1-2

Using the information from the previous question: Fleming grew Penicillium in broth, removed the Penicillium, and poured the broth into culture dishes containing bacteria to see if the broth would kill the bacteria. What step in the scientific method does this represent?

A scientific investigation is not valid unless every step in the scientific method is present and carried out in the exact order listed in this chapter.

Which of the following is closest in meaning to the word “hypothesis”?

Why do scientists sometimes discard theories?

What scientific reason might Gary have for insisting that the container size for the all plants be the same?

What scientific reason might Gary have for insisting that all plants receive the same amount of water every day?

What was the variable being tested in Gary's experiment?

Which of the following factors did Gary not control in his experimental setup that may be varying?

When a theory has been known for a long time, it becomes a law.

A hypothesis is:

A scientific law is:

A number of people became ill after eating oysters in a restaurant. Which of the following statements is a hypothesis about this occurrence?

Which statement best describes the reason for using experimental controls?

A scientist plants two rows of corn for experimentation. She puts fertilizer on row 1 but does not put fertilizer on row 2. Both rows receive the same amount of sun and water. She checks the growth of the corn over the course of five months. What is acting as the control in this experiment?

If you have a control group for your experiment, which of the following is true?

If the hypothesis is rejected by the experiment, then:

A well-substantiated explanation of an aspect of the natural world is a: