Question bank IMSO Science 2017

EXPERIMENT: Frog muscle twitch

INTRODUCTION
During the 1780s, biologist Luigi Galvani observed an interesting phenomenon while he was conducting experiments involving frogs. While cutting a frog’s leg, his steel scalpel touched a brass hook holding the leg in place. The leg of the dead frog twitched!

Galvani performed more experiments and was convinced that a life force within the muscles of the frog was the source of “animal electricity”. His colleague, Alessandro Volta could replicate Galvani’s experiment but was sceptical of his hypothesis.

What conditions present in the dead frog’s muscle during Galvani’s accidental discovery were responsible for his observations? Could it be the presence of two different metals? Or substances present in the muscle? Or substances found only in animals?

You will be conducting a simplified version of Galvani’s experiment with instrument G instead of frog muscle.

AIM OF EXPERIMENT
The aim of this experiment is to investigate the conditions that are necessary for the dead frog’s muscle to twitch. You will use instrument G instead of frog legs.

WHAT YOU WILL NEED
A. Circuit consisting of a 9V battery, two copper rods E1 and E2, a switch and instrument G. The parts of the circuit are drawn and labelled in Figure 2 below.
B. Three liquids (S1, S2, and S3) in separate containers.
C. Lemon wedge in container labelled S4.
D. Paper towel.

WHAT YOU WILL DO
1. Set up the circuit as shown in Figure 3 and ensure the switch on the battery holder is set to “OFF” position. NOTE: Open the lid of container with liquid S1 carefully to avoid spilling the liquid.
2. Orientate instrument G such that the white compass needle points to “50” as shown in Figure 4.
3. Flip the switch on the battery holder to “ON” position.
4. Observe and record in Table 1, the reading on instrument G when the needle stops moving.
5. Observe and record in Table 2, what happened in the container and to the copper rods.
6. Wipe the copper rods dry with the paper towel provided.
7. Repeat steps 1 to 4 with S2 and wipe the copper rods dry.
8. Repeat steps 1 to 4 with S3 and wipe the copper rods dry.
9. Set up the circuit with the wedge of lemon as shown in Figure 5 and ensure the switch on the battery holder is set to “OFF” position.
10. Repeat steps 2 to 4 with the wedge of lemon.

SECTION 1: RESULTS
Based on your observations, record the required readings on instrument G in Table 1.

| Material | S1: Salt solution | S2: Sugar solution | S3: Lemon juice | S4: Lemon wedge |
| --- | --- | --- | --- | --- |
| Reading on instrument G with switch in “ON” position / unit | ____ | ____ | ____ | ____ |

[4 marks]

Table 2

| Observations of solution S1 | Observations of copper rods |
| --- | --- |
| ____ | ____ |

[2 marks]

SECTION 2: CONCLUSION
The aim of the experiment is to investigate the conditions that are necessary for the dead frog’s muscle to twitch. You used instrument G instead of frog legs.
Based on your observations, what conditions were necessary for the dead frog’s muscle to twitch? [2 marks]

SECTION 3: QUESTIONS
1. Student A replaced solution S1 in Figure 3 with a paper clip. He noticed that the white needle deflected by a greater degree as compared to solution S1. Based on this observation, comment on the property of the paper clip. [1 mark]



Editorial conceptual diagram; colours and positions are schematic, not observed results.

SECTION 3, QUESTION 2
Why is it necessary to wipe the copper rod dry in step 5? [1 mark]

Editorial source note: the question says step 5; the wiping instruction actually appears in step 6.



Editorial conceptual diagram; colours and positions are schematic, not observed results.

SECTION 3, QUESTION 3
S3 is extracted from the same lemon that the wedge is cut from. Suggest a reason for the difference in your observation with the lemon juice and lemon wedge. [1 mark]

SECTION 3, QUESTION 4
If you are given distilled water and a fully saturated salt solution (containing 360 g of salt per litre of water), and materials provided in the above experiment, how would you determine the amount of salt in solution S1? List all the steps you will carry out. [4 marks]

SECTION 3, QUESTION 5
Student B used the same steps in the experiment and obtained readings for three salt solutions. They are tabulated below:

| Concentration of salt solution (g/l) | G reading: 1st (units) | 2nd | 3rd |
| --- | --- | --- | --- |
| 40 | 16 | 18 | 16 |
| 180 | 79 | 82 | 80 |
| 250 | 111 | 112 | 113 |

In the grid on the next page, plot a graph to show how the reading on instrument G changes with the concentration of the salt solution. Show on the graph, how you would estimate the concentration of salt solution, S1. [6 marks]

Estimated concentration of S1: __________ g/l

SECTION 3, QUESTION 6
Would you use the same graph to estimate the concentration of salt in S3? Why? [1 mark]

The figure below shows the longitudinal section of a flower. Identify the parts that are the anther and stigma.

Forensic scientists were tasked to collect samples from a crime scene to identify the culprit. Which type of cells should the scientists extract from the samples in order to obtain all 23 pairs of chromosomes?

A population consists of all the organisms ____________________.

Food chains usually contain no more than four trophic levels because _____________________.

The figure below shows how primates can be classified. Which of the following conclusions can be made from the figure?

Which of the statements below on respiration is false?

The figure below shows how some land near a lake is used. Which of the following actions will most likely cause the lake to flood?

The figure below shows an area being developed for industry and agriculture. Which of the following is most likely to cause an initial increase in plant life in the lake?

John wanted to find out the conditions needed for a metal paper clip to rust. His experimental set-ups and findings are shown below. Which two set-ups can be used to show that water is needed for iron to rust?

The fruit of Plant P is shown below. Which of the following maps correctly shows how Plant P is dispersed?

Warfarin is a poison used to control rat populations. It is an anticoagulant that prevents blood clotting. However, some rats are resistant to warfarin and are not affected by the poison. The figure below shows changes in the percentage of rats resistant to warfarin in a particular rat population over a period of about four years. High levels of warfarin were used on this population during Year 2. Which of the following can be inferred from the graph?

A. The use of warfarin results in healthier rats in year 3 and 4.

B. Rats developed resistance to warfarin at the beginning of Year 2.

C. As with rats, the use of warfarin will result in high levels in human beings.

D. If even higher levels of warfarin were used at the beginning of Year 2, 100% of the rat population could become resistant to it at the beginning of Year 3.

The human body requires blood to supply enough oxygen to all parts of the body. A person involved in a car accident lost a large amount of blood and went into shock. How would his/her typical pulse rate and respiratory rate immediately change?