Summary
OCR A A-level Biology Module 2 Notes Summary PART 1
Concise notes with diagrams and key words highlighted, sticking to the OCR A Biology specification PART 1 - CELLS
[Show more]
Seller
Follow
Content preview
A Level BiologyMICROSCOPY OCR A Module 2
Optical (light) microscopes
• Resolution much lower than electron microscopes
• Magnification → overall magnification calculated by multiplying the eyepiece lens magnification by the
objective lens magnification
• Use light to create colour images
• Used to view whole cells and tissues (most organelles not visible)
• Can be used to view live specimens
• The eyepiece graticule must be calibrated against a stage micrometer (see next page)
Scanning electron microscopes (SEM) Transmission electron microscopes (TEM)
• Resolution and magnification → lower than TEM • Highest resolution
but much higher than optical microscopes • Highest magnification
• Use electrons to scan the surface of cells • Use an electron beam to view internal structure
(cannot see internal structures) of cells and organelles
• Create a 3D image in black and white • Create a 2D image in black and white
• Can only view dead specimens
You need to be able to recognise
• Preparation is more complex than for optical
cellular components of eukaryotic microscopes
cells from microscope images. • Specimens must be very thin
Differential staining in light microscopy
• Allows identification of different cell types and different organelles
• Allows white cells to be visualised and counted, and gives contrast to images
• Many different stains available → Sudan red stains cell membranes
→ Nile blue, methylene blue and haematoxylin all stain nuclei (DNA)
→ eosin stains proteins pink (including the cytoskeleton proteins)
→ iodine in potassium iodide solution stains starch blue-black
Magnification and resolution
• Resolution → the ability to separate two objects
→ a high resolution allows the microscope to distinguish between structures that are very
close
• Magnification → how many times larger the image is than the actual object
image size
10
x x1000 1000
x
magnification
>
-
Cm mi Um, nm
actual size :10 1000
: 1000
:
• To calculate the volume of a cell, use the volume of a sphere formula: V =
ar
Page 1 of 2 © Dr Zoë Huggett
, A Level Biology
MICROSCOPY OCR A Module 2
Calibrating the eyepiece graticule on an optical microscope
• Eyepiece graticule → fixed onto the eyepiece, has divisions with no scale
• Stage micrometer → placed onto the stage, has a scale
• To measure something with the eyepiece graticule
→ calibrate the eyepiece graticule with the stage -
eyepiece graticule
micrometer to find the length of one division on
-
stage micrometer
the graticule 0 1 2 3 5 4
6
(mmdivisions)
7
→ measure the object with the graticule (take
repeat measurements and calculate a mean) one division on the
→ convert the number of graticule divisions into a eyepiece graticule is 0.7mm
length e.g. in millimetres or micrometres
Preparing a microscope slide
• Add a drop of water to a glass microscope slide
• Put a thin section of your sample onto the water drop When taking measurements
using tweezers using a microscope, take
• Pipette a drop of stain at the edge of the sample multiple measurements from
• Carefully lower the cover slip at an angle using a different fields of view and
mounted needle calculate a mean.
• Use blotting paper to remove excess stain
Representing cell structure using annotated diagrams
• Use continuous lines with no shading or cross hatching
• Add a scale bar and title to the diagram Amitochondrion
outer mitochondrial
• Draw label lines using a ruler membrane
matrix
→ do not cross the lines
→ do not add arrowheads to the line
• Use two lines to represent a cell wall
• Annotate colours where appropriate
intermembrane
space we cristal
Make sure to follow these inner mitochondrial
membrane
rules rather than copying my
usual style of diagram! 0.5Mm
Page 2 of 2 © Dr Zoë Huggett
, A Level Biology
EUKARYOTIC CELLS OCR A Module 2
Animal cell structure
• Surrounded by the plasma (cell-surface) membrane
• Contain membrane-bound organelles
nucleus
·in
The cytoplasm contains
:my g
mitochondria smooth
a....
-·
endoplasmic many intracellular enzymes
reticulum and the cytoskeleton.
&
:ii.
-
ribosome ..........
I
o
a
8 ·
1000
·
·
·
·
plasma
membrane
B
·
1
......
·esssssss
·
Algal and fungal cells
- are also eukaryotic.
·
↑
·
-centricle
-
·
cytoplasm ·
·
·
lysosome Golgi apparatus
rough endoplasmic
reticulum
Plant cell structure
• Surrounded by the plasma (cell-surface) membrane and a cellulose cell wall
• Contain membrane-bound organelles
movigrice.
-
cellwall . .......
7
7 smooth
8g
·
-
:iii.
·
-
·
·
⑳ j.ii:
: endoplasmic
.
mR
-
:
I
ooo
- reticulum
Amyloplasts are starch
·
-
&
-
nucleus
grains surrounded by a double ·0- 8 -
·
O
·
membrane. They synthesise plasmodesma-
8 - ......
and store starch.
E· (
s
-
rough endoplasmic
reticulum
·
·
ribosome
-
Plasmodesmata are gaps ·
--
solgi apparatus
&
in the cell wall which allow
~plasma
⑧
·
exchange between cells. S
⑧ 0
membrane
vacuole
↑ -
cytoplasm amyloplast
Page 1 of 4 © Dr Zoë Huggett
The benefits of buying summaries with Stuvia:
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
You can quickly pay through credit card for the summaries. There is no membership needed.
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 abdurrahmaanhasan. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £7.99. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
52510 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now