100% satisfaction guarantee Immediately available after payment Both online and in PDF No strings attached
logo-home
Previously searched by you
Previously searched by you
logo
Summary Cell structure $3.97
Add to cart
Quickly navigate to
Preview
  2.  
  3. AQA
  4.  
  5. A Level Biology
  6.  
  7. Unit 2 - Cells

Summary

Summary Cell structure
 0 purchase
  • Course
  • Unit 2 - Cells
  • Institution
  • AQA

Summary notes for AQA A-level Biology cell structure. Includes clear information on Microscopy, cell fractionation, organelles, cell specialisation, prokaryotic cells and mitosis. Summarised from class notes and the official course textbook. From an A* student.

Preview 2 out of 10  pages

Document information

  • April 16, 2022
  • 10
  • 2021/2022
  • Summary

Subjects

  • microscopes
  • cell fractionation
  • organelles
  • cell specialisation
  • prokaryotic cells
  • mitosis

Written for

  • A/AS Level
  • AQA
  • A Level Biology
  • Unit 2 - Cells
All documents for this subject (290)

Seller

avatar-seller
amybowler

Content preview

Cells


Methods of studying cells
Microscopes
They magnify an image. Optical microscopes rely on a
beam of light passing through a thin object. The material
on the slide = object and the appearance through the
microscope = image.

Total magnification of a microscope is the magnification
of each of the lenses multiplied.



Magnification
Magnification = image size / actual size




Cell fractionation
The process where cells are broken open to access organelles.

1. The tissue is placed in a cold, isotonic buffer solution
• Cold: to reduce activity of hydrolytic enzymes that may digest organelles after
lysosomes are broken
• Isotonic: The water potential is the same as the organelles so there is no osmosis
and no osmotic damage (shrinking or bursting)
• Buffer: pH can be controlled so it doesn’t denature enzymes

2. The tissue is homogenised
Breaks open the cells and releases organelles. The fluid is filtered to remove unbroken
cells and large debris

3. Ultracentrifugation
• Tube of filtrate is placed in a centrifuge and spun at slow speed
• The heaviest organelles forced to the bottom where they form a pellet
• The fluid at the top, supernatant, is removed and placed into a fresh tube and spun
faster than before
• The next heaviest organelles are forced to the bottom to form a pellet etc

You then study the pellet of organelles.

Organelles in size order:
• Nuclei
• Mitochondria
• Lysosomes
• Ribosomes

, Electron microscope
• Electrons fired through the electron gun. There is a positively
charged anode which controls the beam.
• There is a vacuum so the electrons travel in a straight line
• Camera at the base to view the image
• More dense tissue will block more electrons to give a darker
image on the fluorescent screen.

Electron microscopes have much higher resolution than optical
microscopes because electrons have a shorter wavelength.

Magnification: how many times enlarged the image is compared
to the real object
Resolution: ability to distinguish between two points

TEM method:
1. Slice the specimen very thin so the electrons can pass
through
2. Fire the electrons through
3. Look at image on the screen

Problems:
• Artefacts: things you can see that aren’t part of the specimen because there are complex
preparation techniques. Early scientists could only distinguish artefacts from organelles by
repeatedly preparing specimens in different ways and if an object was seen in all specimens it
was likely to be an organelle.
• Misleading sections: slicing the cell means there are unusual shapes and sizes in the image
• Expensive, e.g. the vacuum
• Not in colour
• Can only look at dead material because you have to slice the cell and its in a vacuum

2 types of electron microscopy:
TEM - transmission SEM - scanning

Electron beam through thin section of specimen Beam of electrons reflected off the surface of a
specimen, so don’t need thin section

2D images with higher resolution 3D images with lower resolution




Electron vs optical
Similarities: they both…
• magnify
• Use lenses

Differences:
electron Optical

Beam of electrons Light

Vacuum No vacuum

The benefits of buying summaries with Stuvia:

Guaranteed quality through customer reviews

Guaranteed quality through customer reviews

Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.

Quick and easy check-out

Quick and easy check-out

You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.

Focus on what matters

Focus on what matters

Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!

Frequently asked questions

What do I get when I buy this document?

You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.

Satisfaction guarantee: how does it work?

Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.

Who am I buying these notes from?

Stuvia is a marketplace, so you are not buying this document from us, but from seller amybowler. Stuvia facilitates payment to the seller.

Will I be stuck with a subscription?

No, you only buy these notes for $3.97. You're not tied to anything after your purchase.

Can Stuvia be trusted?

4.6 stars on Google & Trustpilot (+1000 reviews)

66184 documents were sold in the last 30 days

Founded in 2010, the go-to place to buy study notes for 15 years now

Start selling
$3.97
  • (0)
Add to cart
Added