These notes got me an A* in OCR A-Level Biology. These notes were made to be bite-sized and straight to the point. Best part? They incorporate MARK SCHEMES answers (in blue) from previous OCR past paper questions so you can get an exact idea of what the exam wants from you. There's also a column fo...
, 2.1.1 Cell Structure
(a) the use of microscopy to observe Types of microscopes:
and investigate different types of cell
Advantages Disadvantages
and cell structure in a range of
eukaryotic organisms. Light Observe living organisms Low resolution + magnification
To include an appreciation of the TEM Highest resolution + magnification Not 3D, thinly sliced specimen
images produced by a range of
microscopes; light microscope, SEM 3D, high R + M Lower R + M than SEM
transmission electron microscope,
scanning electron microscope and LSCF Observe living organisms, in Lower R + M
laser scanning confocal microscope. colour, 3D
State the resolution that can be achieved by the following microscope. (2)
● Light: 200nm/ SEM: 4nm/ TEM: 1nm
A student says that the details of __ could be seen clearly with a very good
light microscope. Explain why the student is not correct. (2)
● TOO small (do not say VERY small)
● Resolution is not high enough
(b) the preparation and examination 1) Thinly slice the specimen → add to the slide → add drop of stain → place
of microscope slides for use in light the coverslip above
microscopy. 2) If a liquid mount, pipette water→add specimen [+ stain] → lower the
coverslip at an angle [avoid air bubbles]
3) Place slide on the stage
4) Start with lowest power of magnification → course adjusting knob to raise
the stage → fine adjustment knob to focus on image
Eyepiece graticule: varies
Including the use of an eyepiece Stage micrometer: fixed (e.g 1mm)
graticule and stage micrometer. 1) Line up the eyepiece graticule and stage micrometer
PAG1 HSW4 2) 1 SM division = 0.1mm
3) Count how many EPG divisions in 1 SM division
E.g
4 EPG = 0.1mm (1 SM division)
1 EPG = 0.025mm (0.1 ÷ 4)
So if object is 3 EPGs long, it’s 0.025 × 3 = 0.075mm
(c) the use of staining in light Why stain…? (2)
microscopy. To include the use of ● So internal organelles/ structures are visible (1) increase contrast (1)
differential staining to identify Differential staining: staining that distinguishes between two cells/ organisms
different cellular components and
cell types. PAG1 HSW4, HSW5
(d) the representation of cell Rules for Drawing diagrams:
structure as seen under the light ● No shading
microscope using drawings and ● Straight horizontal lines for labels
annotated diagrams of whole cells ● No arrowheads in labels
or cells in sections of tissue ● Add scale for magnification
, (e) the use and manipulation of the
magnification formula
In I = AM, A & M must be same units
(f) the difference between Explain the difference between resolution and magnification. (2)
magnification and resolution ● Resolution is the ability to distinguish the smallest distance between two
distinct points + SEE DETAIL (1)
● Magnification is how many times larger an image is compared to the
object (1)
State the resolution that can be achieved by the following microscope. (2)
● Light: 200nm/ SEM: 4nm/ TEM: 1nm
(g) the ultrastructure of eukaryotic
cells and the functions of the
Nucleus Contains genetic material, Contains chromatin (DNA +
different cellular components.
controls cell activity proteins)
To include the following cellular Nucleolus Produces ribosomes Dense part of nucleus
components and an outline of their
functions: Nuclear Allows stuff to enter or leave the Double membrane with
Nucleus, nucleolus, nuclear envelope nucleus (e.g mRNA) pores
envelope, rough and smooth
endoplasmic reticulum (ER), Golgi RER Involved in protein synthesis - Surface covered by
apparatus, ribosomes, mitochondria, folds proteins made at ribosomes
lysosomes, chloroplasts, plasma ribosomes
membrane, centrioles, cell wall,
flagella and cilia. SER Synthesis of lipids & No ribosomes on surface
carbohydrates (1)
Golgi Modifies protein (1) and
Apparatus repackages into vesicles (1)
Ribosomes Protein synthesis (1)
Mitochondria Respiration to produce ATP Cristae, matrix, double
membrane (A2)
Lysosomes Break down organelles (1) Contains hydrolysing
enzymes (1)
Chloroplasts Site of photosynthesis Thylakoid, stroma, granum,
double membrane (A2)
Plasma Allow stuff in/ out & is selectively Phospholipid bilayer,
membrane permeable to stuff cholesterol, proteins
Centrioles Form spindle fibres in mitosis Made up of microtubules
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