AQA AS Biology 'Unit 1 (BIOL1)' Revision

Comprehensive revision notes for the AQA's specification of Biology Unit 1 (BIOL1).

Note: Everything underlined has been a past paper mark scheme answer.

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Table of Contents
Cells ............................................................................................................................................ 2
Magnification ......................................................................................................................... 2
Organelles............................................................................................................................... 3
Cell Fractionation ................................................................................................................... 5
Lipids....................................................................................................................................... 6
Plasma Membranes ................................................................................................................ 6
Movement .............................................................................................................................. 7
Diseases .................................................................................................................................. 9
The Immune System ................................................................................................................ 10
Risk Factors........................................................................................................................... 10
Pathogens ............................................................................................................................. 10
Defence ................................................................................................................................ 11
Immunity .............................................................................................................................. 12
Artificial Immunity ................................................................................................................ 13
Monoclonal Antibodies ........................................................................................................ 15
The Digestive System ............................................................................................................... 16
Carbohydrates ...................................................................................................................... 17
Proteins ................................................................................................................................ 18
Enzymes................................................................................................................................ 19
The Respiratory System ........................................................................................................... 21
Ventilation ............................................................................................................................ 21
Gaseous Exchange ................................................................................................................ 21
Lung Diseases ....................................................................................................................... 22
The Circulatory System ............................................................................................................ 24
The Cardiac Cycle ................................................................................................................. 24
Coordination......................................................................................................................... 25
Coronary Heart Diseases ...................................................................................................... 26
Risk Factors........................................................................................................................... 28

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Cells
Magnification
Size of image
Magnification =
Size of object
Magnification is number of times bigger the size of the image is compared to the size of the
object. Resolution is the minimum distance for two objects to be identified as separate.
The disadvantages of light microscopes are that the wavelength of light is longer
than the wavelength of an electron beam. This causes the light microscope to have a
lower resolution and lower maximum magnification than electron microscopes.…read more

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Organelles
Eukaryotic cells have a distinct nucleus and membrane-bound organelles. Eukaryotic cells
have a cell membrane, a cytoplasm and ribosomes. Eukaryotic cells also have a nucleus,
mitochondria, smooth endoplasmic reticula, rough endoplasmic reticula, Golgi apparatus,
lysosomes and microvilli. The mitochondria are thin. This decreases the diffusion pathway
and increases the surface area to volume ratio. This increases the rate of diffusion of oxygen
into the mitochondria and carbon dioxide out the mitochondria. Damaged microvilli causes
a decreased surface area.…read more

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Prokaryotic cells do not have a distinct nucleus and do not have membrane-bound
organelles. Prokaryotic cells have a cell membrane, a cytoplasm and ribosomes. Prokaryotic
cells also have a capsule, a cell wall, a chromosome, plasmids and a flagellum.
The ribosomes (i.e. smaller and less dense 70S ribosomes) have a large subunit and a
small subunit. The ribosomes are in the cytoplasm. The ribosomes synthesise
proteins.
The capsule (i.e. glycocalyx) is made from slime.
The cell wall is made from peptidoglycan.
The chromosome (i.e.…read more

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Cell Fractionation
Tissue is homogenised in a cold, isotonic, buffer solution. The cold reduces and prevents
enzyme activity (e.g. autolysis). The isotonic prevents osmosis. This prevents the organelles
from shrivelling or bursting. The buffer prevents the proteins from damage. Organelles can
be separated by cell fractionation because different organelles have different masses and
densities.
During homogenisation, the cell membrane is disrupted. This causes cells to break
open. This causes cells to release contents.
During filtration, the complete cells and cell debris are removed.…read more

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Lipids
Triglycerides are made of one glycerol molecule and three hydrophobic fatty acid
tails joined by condensation reactions to release three water molecules to form ester
bonds. Saturated fatty acid chains do not have carbon-carbon double bonds between
carbon atoms. This causes saturated fatty acid chains to be saturated with hydrogen
atoms. Unsaturated fatty acid chains have carbon-carbon double bonds between
carbon atoms. This causes unsaturated fatty acid chains to not be saturated with
hydrogen atoms.…read more

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Movement
Osmosis is the net movement of water molecules from an area of high water
potential down the water potential gradient to an area of low water potential
through a partially-permeable membrane. Osmosis is a passive process so does not
require energy.
Diffusion is the net movement of molecules from an area of high concentration to an
area of low concentration down the concentration gradient. Diffusion is a passive
process so does not require energy.…read more

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Water moves through the phospholipid bilayer from a higher water potential to a lower
water potential down the water potential gradient by osmosis through water channels (i.e.
aquaporins). Small, non-polar, lipid-soluble molecules move through the phospholipid
bilayer from a higher concentration to a lower concentration down the concentration
gradient by simple diffusion. Large, polar, water-soluble molecules move through the
phospholipid bilayer from a higher concentration to a lower concentration down the
concentration gradient by facilitated diffusion through carrier proteins or channel proteins.…read more

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Diseases
Cholera
Cholera bacteria produce and release toxins which open the chloride channel proteins. This
causes the chloride ions to move into the small intestinal lumen by diffusion. This decreases
the water potential of the small intestinal lumen. This causes water to move into the small
intestinal lumen by osmosis. Less water is reabsorbed. This causes diarrhoea. Oral
rehydration therapy replaces lost water and lost salts. This treats diarrhoea.
Boiled water is present to kill bacteria.…read more

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The Immune System
Risk Factors
Risk factors are something that increase the probability. Changing lifestyle reduces the risk
of the development of some diseases but does not prevent the development of these
diseases.
Risk factors of coronary heart disease include age, sex, genes and obesity. Other risk
factors include smoking, excessive alcohol intake, high salt intake, little exercise and
high stress. These risk factors increase the probability of high blood pressure.
Risk factors of cancer include age, sex and genes.…read more

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