OCR Biology F211

Notes on Unit 1 for OCR AS Biology.

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Nicola Fitzhugh
Biology Unit 1 Revision
Observing Cell Structure
There are two types of microscopes:
1. Light (up to X1500 and low resolution)
2. Electron (up to X500000 and high resolution)
Resolution is how well small, close objects can be seen
separately. High resolution produces detailed images of
Specimens need preparation to make structures visible.
1. Light ­ stains
2. Electron ­ lead salts to scatter electrons and produce
3. The pictures produced are called micrographs
The magnification of a micrograph is the image size/actuak
Cell Structure and Function
1. Nucleus
2. Nucleolus (Makes Ribosomes)
3. Mitochondria (Makes ATP for cellular energy)
4. Lysosomes (Contain lytic enzymes)
5. Chloroplasts (Plant cells only, photosynthesis)
6. Centrioles (Animal cells only, aid cell division)
7. Cilia and Flagella (Beat to produce cell movements)
Ribosomes make proteins, rough endoplasmic reticulum
transports the protein to Golgi apparatus, which packages
and secretes it out of the cell.
Eukaryotic cells have a true nucleus and membrane-bound
Prokaryotes have naked DNA and small organelles with no
membranes around them.
Cell Membranes

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Nicola Fitzhugh
The fluid mosaic is a phospholipid bilayer with scattered
The cell surface membrane is for transport (partially
permeable) and recognition or signalling (e.g. receptor
molecules for hormones).
Passive transport (diffusion/facilitated diffusion) does not
use energy, while active transport does and is against a
concentration gradient.
Osmosis is diffusion of water from high water potential to
low across a cell membrane.
Endocytosis is bulk movement of fluid/particles into a cell.
Exocytosis is movement to the outside of the cell.…read more

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Nicola Fitzhugh
They are specialised for their function (e.g. epithelial or
guard cells).
Cells are organised into tissues (e.g. squamous or ciliated
epithelium; xylem/phloem), which are organised into organ
Gaseous Exchange
The alveolus wall is an efficient exchange surface as it is
only one cell thick. It is moist and is highly folded for a large
surface area.
Alveoli are supplied with a rich network of capillaries,
which carry blood close to the alveolus wall (the exchange
surface).…read more

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Nicola Fitzhugh
Inhaling (inspiration):
1. Diaphragm contracts to become flatter and pushes
digestive organs down.
2. External intercostal muscles contract to raise ribs.
3. Volume of chest cavity increases.
4. Pressure in chest cavity drops below atmospheric
5. Air moves into lungs.
Exhaling (expiration)
1. Diaphragm relaxes and is pushed up by the displaced
organs underneath.
2. External intercostal muscles relax and ribs fall.
3. Volume or chest cavity decreases.
4. Pressure in lungs increases and rises above
atmospheric pressure.
5.…read more

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Nicola Fitzhugh
The right ventricle wall (thinner) only has to pump blood to
the lungs.
Atrial walls are very thin since they only have to pump
blood a short distance into the ventricles.
Cardiac cycle: chambers fill; ventricles contract (cuspid
valves close, "lub" sound); atria contract (semi-lunar
valves close, "dub' sound).
The Sino-Atrial Node (in right atrium) maintains beat
The AtrioVentricular Node and Purkyne fibres pass the beat
on to ventricles.
Blood contains cells, plasma proteins and dissolved
substances.…read more

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Nicola Fitzhugh
The waterproof Casparian strip in endodermis cells forces
water into the symplast. This creates root pressure in the
The transpiration stream pulls water up the xylem.
Cohesion holds water molecules together.
Adhesion holds them to the xylem walls.
Plant Transport ­ Translocation and Phloem
Phloem is a living tissue, which carries substances (e.g.
sucrose, growth substances) around the plant. This is
called translocation.
Translocation occurs from where sucrose is produced (the
source, e.g. leaves) to where they are used (the sink, e.g.…read more


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