Question

Scientific method

Read the following story carefully, then answer all the questions that appear at the end of it. [It is a hypothetical study, raised by the teacher, I present all the available information. Than you for your help]

Ana was looking for a project for her school's Science Fair. You read in a scientific journal about a study in which chickens were fed antibiotics. According to the study, chickens that were fed antibiotics grew faster than those that were not fed antibiotics.

Ana thought about this experiment for a long time. After reading more about the topic in the library, she decided to design an experiment using shrimp. She selected a species that grows to a maximum size of 10 centimeters and mature in approximately 6 to 8 weeks. The female produces 100 to 400 eggs that hatch in 2 to 3 weeks. Ana's teacher helped her order 144 shrimp and Ana obtained the antibiotic Aureomycin from her doctor.

Groups	Aureomycin (mg)
1	0
2	2.5
3	5.0
4	100
5	200
6	300

When the shrimp arrived, Ana divided them into 6 groups, each group had 12 males and 12 females. She placed each group in identical glass containers, gave everyone the same food, and changed the water every 7 days. The 6 groups were treated in the same way except that different doses of the antibiotic were added to 5 containers each time the water was changed, as indicated in the following table:

Weekly before changing the water, the average size for each group was noted. These data are presented in the following table.

Groups	AVERAGE SIZE OF THE GROUPS (cm)
	Week 1	Week 2	Week 3	Week 4	Week 5	Week 6
1	1.51	3.12	4.05	4.63	6.05	6.94
2	4.05	6.15	7.23	7.37	7.43	7.45
3	2.55	5.05	6.55	7.55	7.63	7.70
4	4.50	6.50	8.00	9.05	9.55	10.00
5	1.55	3.10	4.20	4.55	4.70	4.75
6	1.55	1.95	2.55	2.85	2.91	2.95

1. Define the problem
2. Express a possible hypothesis
3. Identify the variables: independent and dependent, and 5 variables under control
4. Is there a control group in this research? What function does it have?
5. Underline all the sentences that are part of the experimental design.
6. Analyze the data, what is the conclusion?

Answer 1

Define the problem

As any group of individuals, animals will grow naturally at different rates and different sized ,based on differences in their genetic makeup. Large number of chickens taken to minimize any random errors that might occur due to some chickens growing slightly faster or slightly slower than normal some chickens may respond to the antibiotic differently to other chickens, growing in unusual or unexpected ways. Taking the average length of many chickens will minimize any random errors that might occur due to such unusual phenomena.

Express a possible hypothesis

Anne’s hypothesis is that chickens   given an antibiotic (Aureomycin) will grow at a faster rate than those chickens   that are not given an antibiotic. Anne’s hypothesis may also relate to the amount of antibiotic used – chickens   given a larger amount of an antibiotic will grow at a faster rate than those chickens given a smaller amount of the same antibiotic. Presumably, the antibiotic will kill any infections that may harm the chickens   and slow their growth.

Identify the variable

Independent variable – antibiotic

Dependent variable – Size or length of chickens

Control group in this Research

The control was Group 1, which did not receive any of the antibiotic. In this experiment, chickens in the control group grow at their natural rate, unaffected by the antibiotic. By comparing the experimental groups to the control group allows Anne to determine the effect that the antibiotic has on the growth of the chickens – does it cause them to grow faster or slower than normal?

Anne used a large number of chickens . Ann ensured that each group of chickens contained 12 males and 12 females (because male and female chickens may grow at different rates and mature at different sizes). Anne treated all six groups of chickens in exactly the same way – except for the amount of antibiotic that each group received. This means Anne could be confident that any difference between the average sizes of the chickens was only due to the amount of antibiotic that they received and not, for example, due to differences in the amount of food they received.

Analyse the data

	Group 1	Group 2	Group 3	Group 4	Group 5	Group 6
Average length by which the chickens have grown / cm (length week 6 – length week 1)	5.43	3.4	5.15	5.5	3.2	1.4

(hint : to calculate Average length by which chickens have grown ( length week 6- length of week 1)

Conclusion

The results show that relatively small amounts of antibiotic slow down or inhibit the growth of the chickens. Group 2 (given 2.5 mg of antibiotic) increased in length by an average of 3.4 cm and Group 3 (given 5.0 mg of antibiotic) increased in length by 5.15 cm compared to the increase in length of the control group of 5.43 cm. Group 4, given 100 mg of antibiotic, grew at a slightly faster rate than the control group, increasing in length by an average of 5.5 cm compared to the control group’s average increase in length of 5.43 cm. Whether or not this difference is significant is debatable. Relatively large amounts of antibiotic also seem to slow down or inhibit the growth of the chickens. Group 5 (given 200 mg of antibiotic) increased in length by 3.2 cm and Group 6 (given 300 mg of antibiotic) increased in length by only 1.4 cm compared to the increase in length of the control group of 5.43 cm. Based upon these results, it appears that there is an optimum amount of antibiotic (100 mg) that should be given to the chickens in order to increase the rate at which they grow. More (200 mg) or less (.50 mg) than this amount of antibiotic slows or inhibits the growth of the chickens