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PAGE Contents
3 Microscopes
4 Magnification
Movement & stability in cells
5 Vesicles & vacuoles
Plant cell
6 Animal cell
organelles
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…

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Unit 1 biology AS notes - module 1

Microscopes

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.
Advantages Disadvantages

A wide range of specimens…

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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

Resolution
It's the smallest distance apart that two separate objects can be seen clearly as two
objects
the…

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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…

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Organelles

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…

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the ribosome where it's translated into proteins. 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…

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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
proteins.
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…

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times more permeable to water as they contain aquaporins (protein channel which allows
water through).



The fluid mosaic model
The main features of
the fluid mosaic model
are:
1. Bilayer of
phospholipid
molecules.
2. Various
protein molecules.
3. Some extrinsic
proteins partially
embedded in bilayer,
other intrinsic
proteins completely
spanning…

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leave the cells using these channel proteins.

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…

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