How to find experimental design in biology
Help Questions
ACT Science › How to find experimental design in biology
The chart above shows the height growth of three different plant species after a period of 2 weeks. Each plant species was grown in 4 different soil mediums. All the plants were grown in the same environment with equal amounts of light, water, and oxygen.
What factor would weaken the design of this experiment?
Plant 1 requires more light than Plant 2 and Plant 3 in order to reach maximum growth.
All four mediums contain different soil nutrients.
All three plants require equal amounts of oxygen and water.
Plant height growth was measured by a computer program.
The water used by the plants had mineral levels tested through out the experiment.
Explanation
Since the experiment design leaves light constant for all three plant species, a factor such as a different light preference for one plant species would weaken the control environment for the experiment.
The chart above shows the height growth of three different plant species after a period of 2 weeks. Each plant species was grown in 4 different soil mediums. All the plants were grown in the same environment with equal amounts of light, water, and oxygen.
Based on the chart, soil Medium C has what effect on plant growth?
Soil Medium C is beneficial for Plant 1, but has negative effects on Plant 2 and Plant 3.
Soil Medium C is beneficial for all three plant types.
Soil Medium C is beneficial for Plant 2, but detrimental for Plant 1 and Plant 3.
Soil Medium C does not seem to have a noticable effect on Plant 1, but has a beneficial effect on Plant 2 and Plant 3.
Soil Medium C has a negative effect on the height growth of all three plants.
Explanation
Plant 1 is the only plant that had an increased height growth in Medium C. Plant 2 and Plant 3 had decreased height when in Medium C.
Mitochondria make 90% of the energy needed by the body to sustain life. The Mitochondrial Free Radical Theory of Aging (MFRTA) theorizes that individuals who live longest produce fewer mitochondrial oxygen reactive species than individuals that have a shorter life span. Therefore, lifespan will increase if fewer mtROS are produced, and lifespan will decrease if more mtROS are produced. An experiment was done to test this theory, and the results are shown in the chart below. Four test groups of flies were involved, two groups consisted of females, and two groups consisted of males.
| | Test group 1 | Test group 2 | Test group 3 | Test group 4 | | | ------------------- | ---------------- | ---------------- | ---------------- | ------- | | # of mtROS | 3.9 | 2.5 | 3.2 | 2.7 | | Lifespan | 110 days | 120 days | 95 days | 89 days |
What information would weaken the experiment's results?
An experiment suggesting there is a high-percent error in measuring mitochondrial oxygen reactive species.
An experiment consisting of a control group of both males and females.
A separate experiment done with a different test species that had similar results.
An experiment suggesting mitochondria make more than ninety percent of the body's energy.
An experiment testing the lifespan of flies in an oxygen-deprived environment.
Explanation
An experiment casting doubt on the accuracy of mtROS measurement, which is the independent variable, would drastically weaken the experiment's results.
Mitochondria make 90% of the energy needed by the body to sustain life. The Mitochondrial Free Radical Theory of Aging (MFRTA) theorizes that individuals who live longest produce fewer mitochondrial oxygen reactive species than individuals that have a shorter life span. Therefore, lifespan will increase if fewer mtROS are produced, and lifespan will decrease if more mtROS are produced. An experiment was done to test this theory, and the results are shown in the chart below. Four test groups of flies were involved, two groups consisted of females, and two groups consisted of males.
| | Test group 1 | Test group 2 | Test group 3 | Test group 4 | | | ------------------- | ---------------- | ---------------- | ---------------- | ------- | | # of mtROS | 3.9 | 2.5 | 3.2 | 2.7 | | Lifespan | 110 days | 120 days | 95 days | 89 days |
Does this data support or dispute the MFRTA theory?
The data does not support the MFRTA theory because it was not able to show an inverse relationship between the number of mtROS and the lifespan of the organisms.
The data supports the theory because some test groups had low numbers of mtROSs and also had long lifespans.
The data does not support the theory because it shows an inverse relationship between the mtROS amount and the length of lifespan.
The data does not support the theory because the experiment does not test the information needed to address the MFRTA theory.
The data supports the theory because it shows an inverse relationship, a high mtROS amount correlates to a high lifespan.
Explanation
According to the theory, test group 1 had the greatest number of mtROS, therefore it should have the shortest lifespan. However, it has a lifestpan of 110 days, the second longest life span in the experiment.
There is a certain species of rabbit that is known to reproduce quickly. 250 of these rabbits were introduced into a new environment, and their population was measured in ten year intervals.
What assumption did the scientists make in this experiment?
There will be no external variables that may affect the population of the rabbits
This species of rabbit will evolve to adapt to the new environment
All brown rabbits reproduce at a faster rate than white rabbits
This species of rabbit will reproduce at the same rate, regardless of environment
Explanation
The scientists are attempting to isolate the rabbits and measure their population growth to discover some sort of rate of population increase. They are assuming that there will be no external forces acting upon the rabbits that might create fluctuations in population (disease, famine, predators, etc.)
The problem does not mention color, so that assumption is incorrect. The problem also does not compare reproductive rates in environments, so that assumption is incorrect. Finally, there is no mention of evolution or new traits, so that assumption is incorrect.
There is a certain species of rabbit that is known to reproduce quickly. 250 of these rabbits were introduced into a new environment, and their population was measured in ten year intervals.
Which of the following statements, if true, might prevent the scientists from being able to generalize their findings to this species of rabbit as a whole?
There was a genetic disorder found in this population of rabbits that caused them to have shorter life spans than the average rabbit of this species
250 rabbits is an ideal starting population from which to draw a reasonable conclusion
No external or unforeseen variables acted upon the experiment
This species of rabbits has a natural fear of humans
Explanation
The experiment measures two things: time passed and population. If these rabbits have a disease that kills them faster than normal, this would affect population and population growth rate. The rate observed in the experiment would be lower than the rate of the general population.
Whether or not the species of rabbits has a natural fear of humans is irrelevant to the population/time passing equation. The other two answer choices, if true, would both support the findings.
Mitochondria make 90% of the energy needed by the body to sustain life. The Mitochondrial Free Radical Theory of Aging (MFRTA) theorizes that individuals who live longest produce fewer mitochondrial oxygen reactive species than individuals that have a shorter life span. Therefore, lifespan will increase if fewer mtROS are produced, and lifespan will decrease if more mtROS are produced. An experiment was done to test this theory, and the results are shown in the chart below. Four test groups of flies were involved, two groups consisted of females, and two groups consisted of males.
| | Test group 1 | Test group 2 | Test group 3 | Test group 4 | | | ------------------- | ---------------- | ---------------- | ---------------- | ------- | | # of mtROS | 3.9 | 2.5 | 3.2 | 2.7 | | Lifespan | 110 days | 120 days | 95 days | 89 days |
What, if added, would strengthen the results of the experiment?
Two test groups consisting of a mixed male and female population that showed an overall decrease in lifespan with higher mtROS amounts.
Two test groups consisting of a mixed male and female population that had a mtROS amount of 5 and a lifespan of 150 days.
Two test groups, one male and one female, having a genetic mitochondrial disease but a significantly long lifespan.
A test group living in an isolated environment that showed a lifespan of 100 days and a mtROS amount of three.
All of the answers listed.
Explanation
The experiment's results would be strengthened if the influence of sex was addressed. Two test groups with mixed sex populations would eliminate the sex variable from the results. Showing the inverse relationship with males and females in a mixed group would add another layer to the experiment.
An experiment was done to test the antibiotic resistance of the bacteria Pseudomonas flourescens and Escherichia coli by using the antibiotic disk sensitivity method_._ Four different antibiotics were tested on each bacterium. Media were prepared with each type of bacterium and a drop of each antibiotic was added to each corner of the plates, a different antibiotic in each corner. The cultures were observed for eighteen hours. After this period of time, the zones of inhibition (where the bacteria was not able to grow due to the antibiotic) were measured. The table below shows the results of the four antibiotics on the two bacteria, Pseudomonas flourescens and Escherichia coli.
| | Antibiotic 1 | Antibiotic 2 | Antibiotic 3 | Antibiotic 4 | | | ------------------------- | ---------------- | ---------------- | ---------------- | ---- | | Pseudomonas flourescens | 11mm | 2mm | 5mm | 20mm | | Escherichia coli | 10mm | 8mm | 3mm | 10mm |
Which change to the experimental design would strengthen the results?
Testing the four antibiotics on separate plates
Focusing on only two antibiotics instead of four
Observing the cultures after two hours instead of eighteen hours
Focusing on only one bacteria strain and using more than four antibiotics
All of the choices listed would strengthen the experiment
Explanation
Testing the antibiotics on different plates would eliminate any possible combination reactions. All of the other answer choices would weaken the results instead of strengthen.
A group of scientists wanted to test the effects of Nitra-Grow, a chemical additive that can be given to plants to help them grow. 3 test groups of plants were given all the same time of sunlight, the same type of soil, and the same amount of water. Plant A was given no extra chemicals. Plant B was given 5g of Nitra-Grow. Plant C was given 5g of Ammonia to see if Nitra-Grow worked any better than a basic nitrogen-based household product. The plants are then measured on 5 consecutive days to find their average height (in cm).
| DAY | Height Plant A (cm) | Height Plant B (cm) | Height Plant C (cm) |
|---|---|---|---|
| 1 | 1.2 | 1.2 | 1.2 |
| 2 | 1.4 | 1.4 | 1.2 |
| 3 | 1.6 | 1.8 | 1.3 |
| 4 | 1.8 | 2.4 | 1.3 |
| 5 | 2.0 | 2.6 | 1.4 |
What is the dependent variable?
Height of the plant
Day of measurement
Type of soil
Type of chemical added
Explanation
Answer, is the height of the plant. The Height of the plant DEPENDS on what type of chemical was being added to the plant. (The type of chemical added is the independent variable, because the scientist controlled what chemical went in each plant).
A biologist wanted to do an experiment involving two species of large cat (species A and species B) around a potential new food source.
He isolated the populations of each cat in a location that closely approximated their natural environment, except this potential new food source was the only food source available to them.
Experiment 1:
When species A was left alone with the new food source, their numbers decreased rapidly until none were left.
Experiment 2:
When species B was left alone with the new food source, their numbers increased and the species flourished.
Experiment 3:
When an equal number of species A and B were placed with the new food source, both species maintained relatively constant numbers.
Why is it important that each species was in a location that closely approximated their natural environment?
This is the only way to isolate their response to the new food source
It is irrelevant data
This is the safest way to keep them away from predators
This will make the cats more comfortable, and thus more agreeable to the experiment
Explanation
For this experiment, the goal is to isolate the response of the cats to the food source. Everything else must be controlled; there can only be one indirect variable: the food source. Any variation aside from the variable being tested could result in unwanted additional changes in the cats' behaviors. By keeping their environments constant, any changes can be assumed to be the result of the altered food source.