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PAGE Contents
3 Microscopes
4 Magnification
Movement & stability in cells
5 Vesicles & vacuoles
Plant cell
6 Animal cell
7 More organelles
8 Cell membrane
Membrane functions
9 Phospholipids
Fluid mosaic model
10 Contents of membrane
Functions of contents
11 Communication & cell signalling
12 Crossing cell membranes
13 Further crossing cell membranes
Contents…read more

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Unit 1 biology AS notes - module 1
Light microscope:
Use a number of lenses producing an image that can be viewed directly
at the eyepiece.
Light passes from a bulb under the stage, through a condenser lens,
then through the specimen.…read more

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Cell size and magnification
The unit of measurement...
the micrometre ­ one mm is divided into 1000 equal
divisions m
the nanometre ­ one m is divided into 100 equal divisions nm
It's the smallest distance apart that two separate objects can be seen clearly as two
the better the resolution, the smaller the number
Image size = actual size x magnification
Cells and living processes
Organelles and infrastructure:
There are many other infrastructures than the nucleus, e.g.…read more

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Flagella and cilia (Undulipodia)
These are long extensions from the cell surface which can produce movement. Cilia,
which occur in large numbers, and then flagella is longer, but has the same basic
structure; with only one or two on a cell.
The movement of undulipodia is caused by microtubules which slide against each
other causing the whole structure to bend.
The cilia move in a co-ordinated manner.
Flagella are used in the tail of the sperm, to propel them forward.…read more

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Nucleus ­ structure this is the largest organelle, when stained shows dark
patches (chromatin). It's surrounded by a nuclear envelope, made of two
membranes with fluid between them. Contains holes (nuclear pore) allowing
relatively large molecules to pass through. There's a dense spherical structure,
called the nucleolus.
Function it houses nearly all the genetic material, chromatin consists of DNA
and proteins; some of the proteins regulate the cell's activities. When cells divide, chromatin
condenses into visible chromosomes.…read more

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They're either found free in cytoplasm,
making proteins for the cell or attached to the rough ER, making proteins for export. Often
found in groups called polysomes.
Function site of protein synthesis
Centrioles ­ structure there are two, just outside the nucleus at right
angles to each other. They're hollow cylinders, formed from a ring of
microtubules arranged in 9 triplet groups, they occur in all animal cells.
Function help organise the production of cilia and flagella in animal cells.…read more

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Membranes are partially permeable (some substances pass through and others
don't). The permeability of a substance is determined by the phospholipids & the
They act as a barrier to many water-soluble substances.
Keep many large molecules such as enzymes & pigments within the cell.
Fully permeable to small molecules such as water, oxygen & carbon
Permeable to selected molecules such as glucose and ions.
Permit the movement of substances by endocytosis &
exocytosis: capable of breaking and reforming.…read more

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The fluid mosaic model
The main features of
the fluid mosaic model
1. Bilayer of
2. Various
protein molecules.
3. Some extrinsic
proteins partially
embedded in bilayer,
other intrinsic
proteins completely
spanning the bilayer.
Glycoproteins & glycolipids ­ Some
phospholipid molecules making up the bilayer, & some of
the proteins found in the membrane have carbohydrates
attached to them.
Cholesterol ­ Gives membranes of some eukaryotic cells mechanical stability.…read more

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Carrier proteins ­ actively move substances across the membrane, requiring energy in
the form of ATP.
Recognition & communication ­ Receptor sites ­ some allow hormones to bind
with the cell so that a cell `response' can be carried out. Cells only respond to that hormone
if it has a receptor for that hormone on its cell surface membrane. Glycoproteins &
glycolipids may be involved in cells signalling. Glycoproteins can also bind cells together in
Metabolic processes ­ Enzymes & coenzymes.…read more


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