Section B Mandatory Experiment Questions (7– 9)
• Each question carries 30 marks.
• If time allows you can attempt to answer all three questions here and you will be marked out of your best three.
• All answers should be written clearly on the exam paper.
Divided into part (a) and part (b)
Part (a) is based on the theory linked to the mandatory experiment
Part (b) is based on the details, method, results and control used in the experiment
• It is essential you cover all of the mandatory experiments in detail.
• In recent years we have seen questions in this section that contain key parts from a mixture of experiments.
• You will need a clear understanding of the scientific method focusing on:
● What a control is
● What the variable in each experiment is
● What the constant factors in each experiment are.
Key exam techniques for Section B
• Write the topic next to each question
• Part (a) is theory so definitions and keywords are required here
• Part (b) is the details of the experiment:
● Read each part carefully and highlight the keywords
● If the method is asked for use bullet points and keep answers as concise as possible
● Only include a diagram if asked, your diagrams should contain a minimum of three correct labels to ensure full marks
● Results should include both the experiment results and the control results.
• You will be given a certain amount of space to answer each part of the question. If your answer is shorter than the amount of lines provided don’t panic, trust your knowledge. Don’t feel the need to expand as you may make a mistake that could lead to a cancellation.
SAMPLE ANSWERS FOR SECTION B EXAM QUESTIONS
Each question has the key terms to look out for in the exam underlined.
2012 Question 7
(a) In relation to the scientific method, explain each of the
following:
(i) Data: Observations or results obtained (3)
(ii) Replicates: Repeats of an experiment (3)
(b) Answer the following by reference to some of the investigations that you carried out in the course of your studies
(i) How did you expose the semi-lunar valves when dissecting the sheep’s or ox’s heart?
Cut open the aorta/pulmonary artery (3)
(ii) How did you show that alcohol was present when investigating the production of alcohol by yeast? Iodoform test/add potassium iodide and sodium hypochlorite and warm (3)
(iii) What type of agar plates did you use when investigating the digestive activity of seeds? Starch (3)
(iv) How did you demonstrate that digestive activity had taken place in the investigation referred to in part (iii) The sections of the agar plate where digestive activity had taken place did not turn blue/black when iodine was added (3)
(v) How did you demonstrate the requirement for oxygen when investigating the factors necessary for seed germination?
Add boiled water to remove oxygen and cover with a layer of oil to stop oxygen from entering (3)
(vi) What did you use as a selectively permeable membrane in your investigation of osmosis?
Visking tubing (3)
(vii) What growth regulator did you use when investigating plant growth?
Indole acetic acid (IAA) (3)
(viii) A microscope has an eyepiece lens marked x10 and an objective lens marked x20. What is the total magnification of the image?
200 * (3)
2010 Question 9
(a)
(i) What is a tropism? Growth of a plant in response to a
stimulus (3)
(ii) What is a plant growth regulator? Controls the growth of
a plant (3) (b) Answer the following in relation to an investigation that you carried out into the effect of the growth regulator IAA on plant tissue.
(i) What plant tissue did you use? Cress seeds (3)
(ii) Describe how you carried out the investigation.
• Made a stock solution of IAA
• Carried out a serial dilution of IAA so that the IAA concentration is decreasing in each of the seven petri dishes • Line the cress seeds along graph paper in the lid of each dish and cover each with a different IAA concentration
• Seal and incubate plates on their side for 2-3 days
(4x3) i.e. 3 marks for 4 correct points (iii) Describe the control that you used Water or no IAA in a petri dish (3) (iv) Compare the results you obtained in the experiment and the control Control: Some growth is seen due to IAA being present naturally in the cress seeds
Experiment: Some dishes show root or shoot growth or no growth depending on the concentration. IAA may cause cell elongation or inhibition in roots or shoots. (2x3)
2011 Question 9
(a) (i) How are the two strands of the DNA molecule joined together? Hydrogen bonds (3) (ii) What is ‘junk’ DNA? Non-coding DNA/DNA that has not got a known function (3)
(b) Answer the following questions by referring to the procedures that you used to isolate DNA from a plant tissue.
(i) Having obtained a plant tissue, e.g. onion,
1. What was the first procedure that you followed? Cut the onion with a knife/scalpel (3)
2. What was the reason for that procedure? To increase the surface area of the onion (3)
(ii) Washing-up liquid is then used in the isolation. Give a reason for its use. To break down the cell membranes and release the DNA (3)
(iii) Salt (sodium chloride) is also used in the isolation. Give a reason for its use. To clump the DNA together (3)
(iv)
1. What is protease? An enzyme that breaks down protein (3) 2. Why is a protease necessary when isolating DNA? DNA is combined with proteins so they must be broken down so the DNA can be isolated (3)
(v) The final stage of the isolation involves the use of freezer-cold ethanol.
1. Describe how it is used. Poured slowly down the side of the test-tube (3)
2. For what purpose is it used? To remove water from the DNA so it can float and be isolated (3)