GAMSAT Practice Questions- Section III
Answers and explanations
Do you need an MCQ strategy for difficult questions? Do you need to develop an approach to equation of motion questions? Want to learn a simple strategy for thinking about stereoisomers? Or did you run out of time? Get Newton to Medicine- our Section III GAMSAT Study Manual. This manual includes HUNDREDS of GAMSAT Practice questions for section III; The best way to improve your section III mark is to LEARN by DOING as many GAMSAT-style questions as you can. USE multiple choice technique. USE simple approaches such as “Calculation” and “Comparison” (We show you Two Methods for Approaching Section III Questions). Learn ACTIVELY. Learn from your mistakes. Learn a way of thinking that will take you beyond scientific knowledge to scientific understanding.
4. The answer is B
If you are just starting out with this type of question, try this simple study prop to give yourself a feel for how to look at the images.
Use a piece of blu-tac rolled into a ball as the central carbon atom.
Use 4 different coloured drawing pins pushed into the blu-tac at the 4 points of a pyramid to represent the 4 different groups attached to the carbon.
Now assign a group to each coloured pin and note which is which.
Using this simple prop it is easy to rotate the molecule and compare whether molecules are mirror images/ superimposable.
Unfortunately props like this are NOT allowed in the GAMSAT
However, once you have become familiar with these concepts, it becomes easier to imagine the chemical structures and rotate them in your head.
To be able to be superimposed on each other, the structures must be able to be rotated so that the constituents groups superimpose over each other. The best way to answer this question is to leave one molecule as it is (let’s say molecule I for example) and try to rotate the others in space to superimpose over I. This is where a modification of the R-S naming technique comes in handy.
Take structure I. The green pin (actual if you are using the ball-pin model or virtual if you are imagining it in your head) is facing away from us. We then read the other substituents in a clockwise direction starting with red: Red, Blue, Yellow.
Any structure that is superimposable should also have this property.
So examine structure II. Rotate it in your head so that green is pointed away from you and in clockwise order we read Red, Yellow, Blue. (This can be difficult initially. Practice using the ball and pins- make the structure and leave it sitting on the desk as it is on paper. Now move your head so that you view the structure with green pointed away and read the substituents clockwise starting with red. With practice you will be able to imagine this from the two dimensional image on paper) i.e. Structure I and II are NOT superimposable.
Now looking at structure III we get Red, Blue, Yellow and finally structure IV Red, Blue, Yellow (make sure green is pointed away from you- i.e. you are viewing from UNDERNEATH the structure in a clockwise direction).
Hence Structures I, III and IV are superimposable (all Red, Blue, Yellow) whilst structure II is not (Red, Yellow, Blue).
The answer is B.
5. The answer is D
First it is vital that you know the definitions of each of the above options. Read the question carefully- we are looking for which statement is FALSE. An approach to these questions is to test the “trueness” of each statement.
(A) A diastereomer is a pair of stereoisomers that are NOT mirror images
Hence, option A asks if I and III are a pair of stereoisomers that are not mirror images. By rotating the images in your head you see that they are NOT mirror images. However, the images can actually be superimposed on one another and hence these are identical molecules- so A is true- I and III are actually identical molecules NOT diasteromers.
(B) From question 1 we know that I and II are not superimposable (This is an important way to save time in the GAMSAT- use what you have already worked out in previous questions!) Hence B is also true
(C) Chiral enantiomers are non superimposable mirror images. From Question 1 and B we know that I and II are not superimposable. Thus it just remains to determine if they are mirror images, which they are on rotation. Hence C is also true.
(D) Are III and IV mirror images? On comparison they are NOT. Hence D is false
So the answer is D.
6. The answer is A
To answer this question, you do not need to know anything about growth hormone production specifically. You just need to be able to follow the consequences of positive and negative feedback.
INCREASED somatostatin will mean INCREASED inhibition of the anterior pituitary and so LESS GH.
LESS GH, means LESS IGF-1 (D is incorrect). The consequences of this will include LESS muscle growth (Hence A is correct) and less bone growth (B in incorrect). Somatostatin is not linked (and hence is not shown by the diagram to influence) to Ghrelin (C is incorrect).
The answer is A.
7. The answer is C
Recall that negative feedback is when something acts to eliminate or reduce the stimulus.
Let’s use the technique of COMPARISON (More on this in MediRed's Newton to Medicine GAMSAT Section III Study Manual):
A) Liver- secretes IGF-1 which provides its closest negative feedback one organ up to the anterior pituitary.
B) Muscle is not shown to provide any feedback in this diagram
C) the anterior pituitary secretes GH which then provides direct negative feedback to the secreting organ, the anterior pituitary- hence this is the most direct example of negative feedback shown.
D) Adipose tissue releases free fatty acids which provide negative feedback 3 organs up at the hypothalamus.
The answer is C.
8. The answer is A
In this question we are given a consequence and asked to determine which upstream action could cause this.
The COMPARISON technique is again useful: Which of the options listed will lead to reduced lipolysis?
A) Poor sleep- we are told in the text at the start of this question that sleep is a stimulator of GH secretion. Hence POOR sleep will lead to LOW GH levels which will lead to LOW IGF-1 levels and reduced lipolysis effect on adipose. This is the correct answer.
B) High GHRH will lead to HIGH GH levels will lead to HIGH IGF-1 levels and INCREASED lipolysis by adipose tissue.
C) HIGH ghrelin levels will also lead to HIGH GH levels will lead to HIGH IGF-1 levels and INCREASED lipolysis by adipose tissue.
D) LOW somatostatin levels will lead to LOW inhibition of the anterior pituitary and hence HIGH GH levels will lead to HIGH IGF-1 levels and INCREASED lipolysis by adipose tissue.
The answer is A.
Practice is key in GAMSAT Preparation! We have over 220 Section III practice questions like this in our Section III GAMSAT Study Manual- Newton to Medicine. Check it out here!