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ocr a level biology a module 2 - all notes (based on specification)
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This is all of my notes from ocr a level biology a, they are comprehensive notes for all specification points for the ocr a level biology a programme. I have made these notes this year, these notes have helped me achieve A* in all of my mock exams.

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  • June 23, 2023
  • 18
  • 2022/2023
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• (a) the use of microscopy to observe and investigate different types of cell and cell structure in a
range of eukaryotic organisms
• To include an appreciation of the images produced by a range of microscopes; light microscope,
transmission electron microscope, scanning electron microscope and laser scanning confocal
microscope.
• NOTES
• light microscopes - staining required to allow specimens to become visible (name
organelle) and improve the contrast,
• thin specimen required to allow light to pass through,
• artefact - damage to specimen,
• light microscopy used to look at whole cells and tissues,
• transmission electron microscope - pass beams of electrons through specimen,
• TEM - to look at organelle detail, thin specimen required,
• TEM images can appear different because the specimen may be cut along different
planes/angles,
• scanning electron microscope - to look at cell surface, beam of electrons are reflected off
the specimen’s surface,
• laser scanning confocal microscope - specimen has a fluorescent dye and is used to look
at an object at a certain depth within the cell.
• (b) the preparation and examination of microscope slides for use in light microscopy
• Including the use of an eye piece graticule and stage micrometer.
• NOTES
• eyepiece graticule - used to measure width of cell,
• stage micrometer - used to calibrate eyepiece graticule,
• measure the width of cell by the number of eyepieces,
• use stage micrometer to figure out 1 mm = eyepieces,
• then figure out how many micrometers = 1 eyepiece.
• (c) the use of staining in light microscopy
• To include the use of differential staining to identify different cellular components and cell types.
• NOTES
• acetic orcein stains DNA dark red,
• eosin stains cytoplasm pink,
• Sudan black stains membranes and lipids black,
• staining required to allow specimens to become visible (name organelle) and improve
the contrast.
(d) the representation of cell structure as seen under the light microscope using drawings and annotated
diagrams of whole cells or cells in sections of tissue
• NOTES
• for biological drawings: correct proportions, labels, annotations, scale and title included,
drawing should take up half the page, clear and continuous lines.
• (e) the use and manipulation of the magnification formula
• magnifcaton = image size/object size
• NOTES
• use I = A x M because we can’t use micrometer slide in an electron microscope,
•
• when given a scale bar, measure the length of the scale bar and convert to specified
units, then divide by the given scale to find magnification.
• (f) the difference between magnification and resolution
• To include an appreciation of the differences in resolution and magnifcation that can be achieved

, by a light microscope, a transmission electron microscope and a scanning electron microscope.
• NOTES
• magnification - number of times larger the image is in comparison to the object,
• resolution - ability to distinguish between very small structures that are close together.
•
• (g) the ultrastructure of eukaryotic cells and the functions of the different cellular components
• To include the following cellular components and an outline of their functions: nucleus,
nucleolus, nuclear envelope, rough and smooth endoplasmic reticulum (ER), Golgi apparatus,
ribosomes, mitochondria, lysosomes, chloroplasts, plasma membrane, centrioles, cell wall,
fagella and cilia.
• NOTES
• nucleus - controls cell activity, contains DNA and genetic code for proteins,
• nuclear pores - allows substances in and out of nucleus,
• nucleolus - contains dense DNA (in the middle),
• RER - flattened membrane bound sacs (cisternae) that are continuous with nuclear
envelope and contain ribosomes, protein synthesis occurs here,
• SER - flattened membrane bound sacs (cisternae) that are continuous with nuclear
envelope but don’t contain ribosomes, lipid and hormone production occurs here,
• Golgi apparatus - stack of membrane-bound flattened sacs that modify and package
proteins into vesicles,
• ribosome - site of protein synthesis which are either free in cytoplasm or on RER,
• mitochondria - double membrane, which is folded into cristae that contains fluid-filled
matrix, ATP made here during aerobic respiration,
• lysosome - contain powerful digestive/hydrolytic enzymes,
• chloroplast - only in plant cells, double membrane which forms thylakoids that are
stacked into granum, it is the site of photosynthesis,
• plasma/cell surface membrane - phospholipid bilayer that controls what goes in/out of
cell,
• centrioles - tubes of protein fibers that take part in mitosis to form spindle fibres,
• cell wall - provides high tensile strength, insoluble and inert, (cellulose = plant,
peptidoglycan = bacteria),
• flagella - allows whole cell movement and has a 9+2 arrangement,
• cillia - finger-like projections on ciliated epithelial cells that move substances along,
• vacuole - surrounded by tonoplast and can become flaccid/turgid,
• vesicle - membrane bound organelle that transports substances.
• (h) photomicrographs of cellular components in a range of eukaryotic cells
• To include interpretation of transmission and scanning electron microscope images.
• (i) the interrelationship between the organelles involved in the production and secretion of
proteins
• No detail of protein synthesis is required.
• NOTES
• nucleus produces mRNA,
• mRNA leaves nucleus through nuclear pore,
• mRNA attaches to ribosome on RER,
• protein formed in ribosome which is transported to Golgi apparatus via vesicle,
• GA modifies and packages proteins into vesicles,
• vesicle moves to cell surface membrane and fuses,
• mitochondria produces ATP for contractile filaments in cytoskeleton.
• (j) the importance of the cytoskeleton
• To include providing mechanical strength to cells, aiding transport within cells and enabling cell

, movement.
• NOTES
• contains microfilaments, microtubules and intermediate filaments,
• cytoskeleton involved with whole cell support, movement of cilia and flagella, changing
cell shape, moving organelles )name one) and movement of chromosomes,
• microfilaments - changes in cell shape,
• microtubules - moves chromosomes and moves organelles around cell via vesicles,
• intermediate filaments - provides whole cell support,
• flagella - found in prokaryotes and moves the whole organism using ATP,
• cilia - waft substances over the surface.
(k) the similarities and differences in the structure and ultrastructure of prokaryotic and eukaryotic cells.
• NOTES
Eukaryote Prokaryote
membrane bound organelles no membrane bound organelles
nucleus present no distinct nucleus
no cell wall peptidoglycan/murein cell wall
cell surface membrane cell surface membrane
80s ribosome 70s ribosome (smaller)
plasmids (circular DNA - can be exchanged to
linear DNA
other bacteria)
no flagellum flagellum
ATP from mitochondria ATP from mesosome


• (a) how hydrogen bonding occurs between water molecules, and relate this, and other
properties of water, to the roles of water for living organisms
• A range of roles that relate to the properties of water, including solvent, transport medium,
coolant and as a habitat AND roles illustrated using examples of prokaryotes and eukaryotes.
• NOTES
• water is a polar molecule, hydrogen bonds form between negative oxygen of one
molecule and positive hydrogen of another molecule,
• high boiling point = lot of energy need to break bonds, and provides stable water temp
for aquatic animals = less energy spent on temp control,
• ice less dense than water = creates insulating barrier so water below doesn’t freeze,
allows animals to move and provides habitats ontop of ice (polar bears),
• cohesion - attraction between water molecules, creates high surface tension for insects
to walk on,
• adhesion - attraction of water molecules to surfaces,
• water acts as a solvent so allows mineral ions to be transported in animals/plants
(bloodstream),
• water is a transport medium so allows the transport of soluble substances,
• water acts as a coolant through evaporation (sweating and panting),
• water has a high specific heat capacity (lot of energy to heat up water by one degree) =
stable temp, enzymes can work at optimum temp, gases remain soluble for aquatic
animals,
• high latent heat of vaporisation (lot of energy to change water from liquid to gas),
• capillary action = allows water to move up narrow vessels.
(b) the concept of monomers and polymers and the importance of condensation and hydrolysis

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