Lyrapettigrew
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Hello, I have been revising how use use microscopes practically etc. and found some questions which I thought may be of help. However, despite having answered them, this is not my strongest area and therefore I was wondering if someone may take a look to offer advice or improvements.

Question 1:
A light microscope has an eyepiece lens of 12x and an objective lens of 50x

i. Calculate its total magnification:
So since total magnification = eyepiece magnification * objective magnification

Total magnification = 12 * 50 = 600x

ii. The image of a structure produced by the microscope has a diameter of 15mm, find the real life of the structure in micrometers.

Right, in this part I thought that I should use the formula:

length of object = length of image/magnification
length of object = 15*1000/600
length of object = 25 micrometers

iii. Why is the microscope unable to see structures only 2 nm across, even when using a more powerful lens?
Though magnification, the extent which an object has been enlarged by a microscope, is important there is another factor which may even have a greater effect on the quality of the image. The resolution, being the ability to distinguish between two individual points that are very close together as opposed to one merged, fuzzy point, permits one to scrutinise the image in greater detail and depends upon the resolution or resolving power of the microscope. The resolution of a light microscope is around 0.2 μm, or 200 nm. This means that it cannot distinguish two points closer than 200 nm. Consequently, the resolving power of the light microscope is greater than the structures with a 2nm diameter, so even by increasing the magnification they would still appear as merged blobs instead of individual structures.

Question 2:
Below you will find an electron micrograph. I have attached it with the post.

i. What are the two organelles found in the photomicrograph?
I really am not sure to me they look a bit like circular chloroplasts accounting to the lines which appear like cristae or matrix. I have not answered ii and iii until I am adamant on this section because otherwise my answers would be pointless 😂 I am really struggling identifying these organelles and have been staring and countless pictures of every possible organelle but cannot form a sound conclusion.
ii. State two structure visible in the photomicrograph that are characteristics of this organelle.
iii. State the main function of this organelle.
iv. The scale at the bottom is labelled 50nm. Estimate the diameter of the left-hand organelle in micrometers.

So using a ruler I measured the diameter to be 4.5 cm = 45 mm. Then I measured the scale bar representing 50 nm which was approximately 5mm.
Converting these measurements to micrometers:
45 mm = 45000
5 mm = 5000
50 nm = 0.05
So would the actual length be 45000/5000 * 0.05 = 0.45 micrometers ?

Or would I not convert and use:
45/5 * 50 = 450

I am confused about how to solve this.
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niaphonic
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I think your answer to Question 1 is great, very detailed explanation.

As for Question 2, I think the fact that the organelle is round, is making you doubt yourself!
You recognised the cristae and matrix - which would make them mitochondria.
If you google "transmission electron microscope chloroplast", you can see that in the TEM image, the internal structure of the organelle would look quite different - with the lamellae and thylakoids.
So, if I saw that image in an exam I would go with mitochondria.

for Q2 part iv, you started off doing exactly as I would do: measure the diameter of the organelle in mm, measure the length of the scale bar in mm, see how many times the scale bar would fit into the diameter (45/5 = 9).
So, now that you know that the 50nm scale bar would fit into the diameter of the organelle 9 times (50nm x 9 = 450nm), you can convert your answer into micrometres (450nm/1000 = 0.45um)

Your first answer is correct - but if it helps you to think it through step by step like I did above, it saves you a bit of effort with all of those unit conversions (and reduces the chance that you'll make a mistake with converting units when you don't have to, or when writing out all of those zeroes when you're nervous in the exam!)
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Lyrapettigrew
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(Original post by niaphonic)
I think your answer to Question 1 is great, very detailed explanation.

As for Question 2, I think the fact that the organelle is round, is making you doubt yourself!
You recognised the cristae and matrix - which would make them mitochondria.
If you google "transmission electron microscope chloroplast", you can see that in the TEM image, the internal structure of the organelle would look quite different - with the lamellae and thylakoids.
So, if I saw that image in an exam I would go with mitochondria.

for Q2 part iv, you started off doing exactly as I would do: measure the diameter of the organelle in mm, measure the length of the scale bar in mm, see how many times the scale bar would fit into the diameter (45/5 = 9).
So, now that you know that the 50nm scale bar would fit into the diameter of the organelle 9 times (50nm x 9 = 450nm), you can convert your answer into micrometres (450nm/1000 = 0.45um)

Your first answer is correct - but if it helps you to think it through step by step like I did above, it saves you a bit of effort with all of those unit conversions (and reduces the chance that you'll make a mistake with converting units when you don't have to, or when writing out all of those zeroes when you're nervous in the exam!)
Hello, thank you very much for your reply and great help.

Question 2:

i. I am so sorry I have no idea why I wrote chloroplast, I 100% meant mitochondria (maybe chloroplasts where on my mind 😂)
ii. So the two structures visible in the photomicrograph that are characteristics of this organelle are the cristae and matrix?
iii. The most important function of mitochondria is arguably to produce energy. Moreover, smaller and more simplistic molecules of nutrition are sent to the mitochondria to be processed and to produce charged molecules which combine with oxygen to produce ATP.
This is a process known as oxidative phosphorylation.
Mitochondria additionally assist cells to maintain the proper concentration of calcium ions within the cell. Furthermore, these organelles aid in building certain parts of blood and hormones like testosterone and estrogen.

Should I improve upon my answer to explain the function of mitochondria, specifically how they produce energy?

iv. Thank you very much for producing a clearer solution.
So, as mentioned measuring the diameter to be 4.5 cm = 45 mm. Then measuring the scale bar representing 50 nm which was approximately 5mm.
45/5 = 9
9*50=450 nm

450nm = 0.045 um

Are my answers correct now? Thank you very much again 😁
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niaphonic
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(Original post by Lyrapettigrew)
Hello, thank you very much for your reply and great help.

Question 2:

i. I am so sorry I have no idea why I wrote chloroplast, I 100% meant mitochondria (maybe chloroplasts where on my mind 😂)
ii. So the two structures visible in the photomicrograph that are characteristics of this organelle are the cristae and matrix?
iii. The most important function of mitochondria is arguably to produce energy. Moreover, smaller and more simplistic molecules of nutrition are sent to the mitochondria to be processed and to produce charged molecules which combine with oxygen to produce ATP.
This is a process known as oxidative phosphorylation.
Mitochondria additionally assist cells to maintain the proper concentration of calcium ions within the cell. Furthermore, these organelles aid in building certain parts of blood and hormones like testosterone and estrogen.

Should I improve upon my answer to explain the function of mitochondria, specifically how they produce energy?

iv. Thank you very much for producing a clearer solution.
So, as mentioned measuring the diameter to be 4.5 cm = 45 mm. Then measuring the scale bar representing 50 nm which was approximately 5mm.
45/5 = 9
9*50=450 nm

450nm = 0.045 um

Are my answers correct now? Thank you very much again 😁
i) and ii): yes, I would name cristae and mitochondrial matrix as the two structures that are characteristic of this organelle.

iii) "State the main function of this organelle"
Any question that asks you to "state" something, doesn't require a detailed answer - it should be focused and specific, so in this case I would write something like: "The mitochondrion is the site of aerobic respiration, where energy/ATP is released from glucose and supplied to the cell."


I would avoid the terms "make" or "produce" energy/ATP, as the energy is "released" from organic molecules (such as glucose) during respiration (be careful, as some revision sites might use the incorrect terminology).
It's tempting to write everything you know in response to an answer, but my tip would be - try to keep your answers focused on what the question is asking you. You will only receive credit in the exam for what the question asks, so anything extra is likely to be wasted effort on your part.

On the other hand, if the question asked: "explain how ATP is released through aerobic respiration", then you would provide an in-depth explanation of the different stages of aerobic respiration.

Identifying the command words (explain, suggest, state..) is key to answering the questions in the right way
Keep doing practice questions and mark your answers using the mark scheme, to get a better idea of how the command words link up with the marking points.

Good luck!
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