100% satisfaction guarantee Immediately available after payment Both online and in PDF No strings attached
logo-home
Cell structure - A-Level Biology notes $9.18   Add to cart

Class notes

Cell structure - A-Level Biology notes

 37 views  1 purchase
  • Course
  • Institution

Cell structure - A-Level Biology notes

Preview 2 out of 6  pages

  • January 8, 2021
  • 6
  • 2019/2020
  • Class notes
  • Ms. carr
  • All classes
avatar-seller
Chapter 3: Cell structure
3.1 Methods of studying cells

Microscopy:
- Produces a magnified image
- Convex glass lens
- Light microscopes can only distinguish between objects which are 0.2um apart
- Electron microscopes can distinguish objects that are 0.1um apart.




Magnification The size of the image is compared to real life
Resolution The smallest distance where 2 discrete objects will be seen as separate

Cell fractionation Process where cells are broken up and the cells are separated
Conditions necessary:
1. Cold – to reduce enzyme activity
2. Equal water potential as tissue – to prevent organelles from bursting and shrinking
3. Buffered – so pH doesn’t fluctuate
Stage 1:  Cell are broken up by a homogeniser
Homogenation  This releases organelles from the cell = homogenate
 The homogenate is filtered
Stage 2: A process where the homogenate is separated in a centrifuge.
Ultracentrifuge  Tube of filtrate is placed in centrifuge and spun at low speed
 Heaviest organelle (nuclei) is forced to the bottom which forms a sediment/pellet
 The supernatant (fluid on top) is removed, leaving the sediment
 The centrifuge is spun at a faster speed to form a second sediment consisting of the next heaviest
organelle (mitochondria)
 The process continues


3.2 The electron microscope
- Beam has a short wavelength meaning it has a high resolution power
- As electrons are negatively charged the beam can be formed by electromagnets

Transmission Electron Microscope (TEM) Scanning Electron Microscope (SEM)
 Electron gun produces beam  Electron gun produces beam
 Beam focused onto specimen by a condenser electromagnet  Beam focused onto specimen by a condenser
 Beam passes through the specimen. If beam falls onto the electromagnet
specimen, it’s absorbed and that part appear dark. If beam  Beam bounces off the surface of the specimen to
doesn’t fall onto the specimen, it appears white produce a 3D image
- Photomicrograph (it can be photographed) - Photomicrograph (it can be photographed)
Limitation: - Specimen doesn’t need to be thin
- Must be in a vacuum, therefore no living specimen - Lower resolution than TEM
- Complex staining process therefore may contain artefacts
- Image is in black and white and in 2D
- Specimen must be very thin


3.3 Measurements and calculations
You can measure cells by using an eyepiece graticule (a glass disk). Depending on the magnification it will need to be
calibrated. Calibrating the microscope:
1. Place of stage micrometre onto the stage of the light microscope
2. Focus the microscope so that both the stage micrometre and eyepiece graticule are in clear view

, Chapter 3: Cell structure
3. Count the number of divisions of the eyepiece graticule that represents the total length of the stage
micrometre (x)
4. Calculate the actual length (y) represented by one division of the eyepiece graticule
5. The actual length represented by the whole length of the eyepiece graticule (z):
z = y times by the number of divisions on the graphical


3.4 Eukaryotic cell structure




Ultrastructure – each cell has an
internal structure for its function




Nucleus
Nuclear Double membrane; outer layer is
envelope continuous with the endoplasmic
reticulum of the cell and often has
ribosomes on the surface
Nucleoplasm Granular jelly like substance that
makes up the bulk of the of the
nuclei
Nucleolus a small spherical region
within the nucleoplasm which
manufactures ribosomal RNA and
assembles ribosomes there may
be several in one nucleus
Chromosomes Carry genetic material
Nuclear pores Allow passage of big molecules ex.
mRNA
Nucleolus A small spherical region within the
nucleoplasm which manufactures Functions:
ribosomal RNA and assembles - Acts as a control center
ribosomes there may be several in - Retain genetic material
one nucleus - Manufacture ribosomal RNA and ribosomes
Mitochondrion
Double The inner layer is folded to form cristae
membrane (extensions) to give a large surface area
Matrix Makes up the remainder of the cell
Functions:
- Aerobic respiration
- Responsible for ATP

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 polinalobacheva. Stuvia facilitates payment to the seller.

Will I be stuck with a subscription?

No, you only buy these notes for $9.18. You're not tied to anything after your purchase.

Can Stuvia be trusted?

4.6 stars on Google & Trustpilot (+1000 reviews)

81113 documents were sold in the last 30 days

Founded in 2010, the go-to place to buy study notes for 14 years now

Start selling
$9.18  1x  sold
  • (0)
  Add to cart