High School

We appreciate your visit to a i What is the purpose of the scientific method ii Explain what is meant by a control group as used in scientific experimentation b. This page offers clear insights and highlights the essential aspects of the topic. Our goal is to provide a helpful and engaging learning experience. Explore the content and find the answers you need!

(a) (i) What is the purpose of the scientific method?

(ii) Explain what is meant by a control group, as used in scientific experimentation.

(b) Answer the following in relation to investigations you carried out.

(i) When preparing a sample of cells on a microscope slide, suggest two advantages of using a coverslip.
1.
2.

(ii) Name the molecules whose presence in a specimen of food can be tested for by:
1. Using either Sudan III or brown paper.
2. Using iodine.

(iii) When isolating DNA from a plant tissue, state one reason for each of the following:
1. Chopping the tissue.
2. Heating the mixture to 60°C for exactly 15 minutes.
3. The above step must only last 15 minutes.
4. If ethanol at room temperature is added after the mixture is filtered, no DNA appears in the solution.

Answer :

(a) (i) The purpose of the scientific method is to systematically investigate and understand natural phenomena. It provides a structured approach to research, allowing scientists to make observations, form hypotheses, conduct experiments, analyze data, and draw conclusions. This process helps ensure that findings are reliable, repeatable, and objective.

(ii) A control group in scientific experimentation is a group that does not receive the treatment or experimental intervention being tested. It is used as a baseline to compare against the results from the experimental group, ensuring that the effects observed are due to the treatment and not other variables.

(b) (i) When preparing a sample of cells on a microscope slide, two advantages of using a coverslip are:

  1. It helps flatten the specimen, ensuring a uniform thickness, which improves the focus and clarity of the microscopic image.
  2. It protects the specimen from drying out and prevents the objective lens from touching the sample, which could damage it.

(ii) Molecules that can be tested for in a food specimen include:

  1. Using either Sudan III or brown paper: These are methods to test for lipids (fats). Sudan III stains lipids red, and brown paper will turn translucent if fats are present.
  2. Using iodine: This test is used to detect the presence of starch. Iodine reacts with starch, turning it a blue-black color.

(iii) When isolating DNA from plant tissue, reasons for certain steps include:

  1. Chopping the tissue: This increases the surface area, allowing enzymes and chemicals used in the extraction process to more effectively break down cell walls and release cellular contents, including DNA.
  2. Heating the mixture to 60°C for exactly 15 minutes: This helps denature proteins and inactivate enzymes that could degrade DNA, while also softening and breaking open cell walls and membranes.
  3. The above step must only last 15 minutes: Longer heating could degrade the DNA, reducing the yield and quality of the extracted DNA.
  4. If ethanol at room temperature is added after filtering, no DNA appears in the solution, because ethanol must be cold (usually chilled) to precipitate DNA effectively, allowing it to be separated from the solution.

Thanks for taking the time to read a i What is the purpose of the scientific method ii Explain what is meant by a control group as used in scientific experimentation b. We hope the insights shared have been valuable and enhanced your understanding of the topic. Don�t hesitate to browse our website for more informative and engaging content!

Rewritten by : Barada