Biology OCR AS Unit 1 - Module 1

I basically made some notes for each spread , answered all the objectives in the module and listed key points which I thought were important :)  

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AS Biology Unit 1 Module 1 Revision Notes OCR
Spread 1 ­ Living organisms consist of cells
1. State the resolution and magnification that can be achieved by a light microscope.
Light microscopes have a number of different magnifications because it has many different object lenses which are responsible
for the magnifications.
Light passes from a bulb which is under the stage then through a condenser lenses and into the eye piece.
Advantages and limitations : Magnification can go up to x1500
Resolution: has the maximum of 200nm so any object closer together than that width will be seen as one object.
Specimens: can be a range of living things such as plant and animal cells but the disadvantage is that you cannot see the ultra
structure within the cell.
2. Explain the differences between magnification and resolution.
Magnification is the degree to which the size of an image is larger than the object it's self.
Resolution is the degree to which it is possible to distinguish between two objects that are very close together, the higher the
resolution the clearer the image will be.
3. Explain the need for staining samples in a light microscope.
Staining is used so more detail can be seen within the cell, coloured staining are chemicals that bind onto chemicals in the
specimen, and some stains bind to specific parts of the cell.
Sectioning is a way to avoid damaging the structure of the specimen when needed to cut a sample for a slide , the specimen is
embedded in wax and then cut thinly.
Spread 3-Electron microscope and cells in detail
1. State that resolution and magnification can be achieved with the electron microscope.
Higher resolution can be achieved using a electron microscope.
This is how it works ...
Beams of electrons are generated
The electrons are focused onto the specimen using magnets which as a result produces a black and white image on a
projector screen which are called micrographs
Types of electron microscope TEM and SEM
TEM ­ Transition electron microscope
Electrons pass through thin samples and do not easily pass through thicker parts of the sample creating a contrast in the
image produced which is 2D
SEM ­ Scanning electron microscope
Electrons are beamed at the specimen but are not pass through they are reflected and as a result create a 3D image.
Advantages and Limitations :
Higher resolution compared to a light microscope so it can produce detailed images and SEM can help show cellular structure.
Samples have to be done in vacuums because electrons can be disrupted by air.
Very expensive.
High degree of skill and training is needed to prepare an electron microscope sample.
2. Explain the need for staining samples for the use in electron microscopy
To help reveal and distinguish different features in EM the colours are fluorescent and they are metal particles or metal salts.
Spread 4- Cells and living processes
1. Explain the importance of the cytoskeleton in providing mechanical strength to cells aiding transport within cells
enabling cell movement.
Ulrastructure: is the detail within a cell or all the organelles.
Division on labour: is when every organelle within the cell has its own role all organelles work together doing their role for
the survival of the cell the work is divide amongst the organelles.
The Cytoskeleton :is made out of fibres which are made from proteins , the structures provide a frame work of the cell , there
are different types of protein fibres actin filaments which move organelles around.
Microtubules made form a protein called tubulin, they can move micro organisms through liquids and also move different
organelles around the cells such a vesicles ECT... APT is used to carry out these processes.
2. Recognise structures of undulipodia (flagella) and cilia, and outline their functions

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Flagella (undulipodia) are hair like extensions which stick out from the surface and are made from 9 microtubules arranged in
a cylinder shape , an example is the tail of a sperm this helps the sperm move as it is used as a motor you will normally find 1 or
two within a cell structure .…read more

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The protein is then packaged into a vesicle and then transported to the Golgi apparatus which modifies the protein and
packaged again so it can moved out the cell by exocytosis.
2. Comparing the structure of eukaryotes and prokaryotes.
Prokaryotic features ...
They are bacteria and are smaller than eukaryotic cells.
They have one membrane and have no organelles such as mitochondria or chloroplast.
They have a cell wall.
Ribosomes are smaller in size compared to eukaryotic.
DNA is free and looped.…read more

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Increasing temperature increases kinetic energy in the molecule, this also increases movement and makes the membranes
leaky which would allow substances which normally wouldn't enter, more cholesterol helps with cell stability so membranes
present in hotter environments have to adjust.
Spread 9 ­ Communication and cell signalling
1. Explain the term cell signalling
Cell signalling is how cells communicate with one another by molecules acting as signals an example is cytokines. For cell
signalling to occur there must be receptors present on the membrane.
2.…read more

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Example of active transport is calcium ions when a muscle is stimulated, there's a high concentration of calcium ions in the
endolplasmic reticulum, they are released by diffusion but when needed to be stored again protein calcium ion pumps are
used to restore the calcium ions.
Endocytosis is when materials are brought into the cell and exocytosis is when material is released from the cell, this happens
with the use of vesicles; vesicles can fuse with the membrane to either release or intake material.…read more

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Prophase- Chromosomes are replicated in Interphase, then they super coil in prophase , the nuclear envelope breaks down
and centrioles divide into two and move to opposite poles of the cell and produce spindle fibres which will be used later in
Metaphase ­ replicated chromosomes line up in the centre of the cell and bind to the spindle fibres at their centromeres
Anaphase- replicated chromosomes are pulled apart to opposite poles of the cell by the spindle fibres which shorten
Telaphase- as the chromosomes…read more

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Xylem and phloem are produced from divided meristem cells such as cambium; they undergo differentiation to form all the
different kinds of transport tissue
Xylem consists of xylem vessels with parenchyma cells and fibres, meristem cells produce small cells that elongate and become
water proof by lignin, this kills the cells contents inside so that the long tubes become hollow and a lumen is formed.…read more


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