Paper 1 Summary: Pearson Edexcel GCSE (9-1) Combined Science
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Course
Science
Institution
GCSE
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This set of revision notes goes through Biology Paper 1 [as specified for the Pearson Edexcel course] summarising and explaining everything you need to kn...
Many cells are specialised to carry
out a particular function.
Genes are found in chromosomal
DNA or plasmid DNA in prokaryotic
cells.
Microscopes
Light Microscopes: Uses light to magnify objects. Greatest possible magnification => x 2000.
Electron Microscope: Uses electrons to view an object. Greatest possible magnification => x 10 million.
Resolution: The shortest distance between 2 points on a specimen that can still be seen as 2 different points.
Adjustment knobs bring the sample into focus by moving the stage / objectives up and down.
o Tips for using microscopes:
Measure the image in mm.
Multiply by 1000 to get the measurement in micrometres.
o Drawing Rules:
Use a sharp pencil.
Draw outlines of the main features.
Label using straight, uncrossing lines.
Include magnification & scale.
Drawing should take up at least half of the available space.
Keep the parts in proportion.
÷ 100 Metres [m] X 100
÷ 10 Centimetre [cm] X 10
÷ 1000 Millimetre [mm] X 1000
÷ 1000 Micrometre [μm] X 1000
÷ 1000 Nanometre [nm] X 1000
Picometre [pm]
, Standard Form: Numbers in standard form have 2 parts:
1. The first [number] part has to be >= 1 and < 10.
2. The second part is a power of 10 [the bigger it is the bigger the number].
Enzymes
Special Protein molecules produced by living organisms that act as biological catalysts to speed up the rate
of reactions without being changed themselves.
Enzymes, being proteins, are made by ribosomes.
Enzymes are folded into complex 3D shapes that allow smaller molecules to fit into them. The place where
these molecules fit is called the active site, and the complementary molecules are called substrates.
In the lock and key hypothesis, the shape of the active site matches the shape of its substrate molecules. This
makes enzymes highly specific. Each type of enzyme can usually catalyse only one type of reaction.
Some of the reactions they speed up include photosynthesis; protein synthesis; and respiration.
Synthesis: Building larger molecules from smaller subunits.
The breakdown of large molecules, as well as synthesis reactions, occur much too slowly to supply the body
with all that it needs to stay alive and be active.
The body needs to be able to break down large molecules into smaller components so that they can be
absorbed into the bloodstream and into cells to be used for growth and other life processes.
If enzymes are exposed to extremes of pH or high temperatures the shape of their active site may change. If
this happens then the substrate will no longer fit into the enzymes. This means the key will no longer fit the
lock. The enzyme has now been denatured.
Some important enzymes:
Enzyme Location Digests Produces
Amylase Saliva and small intestine Starch Small sugars, such as maltose
Lipase Pancreas Lipids Fatty acids and glycerol
Protease All living organisms Proteins Amino acids
Particle Movement
Dissolved substances [solutes] move into and out of cells by diffusion and active transport.
Water moves into and out of cells by osmosis.
Diffusion: The net movement of particles from an area of high concentration to an area of lower
concentration.
Osmosis: The net movement of water molecules across a partially permeable membrane from an area of
higher water concentration to an area of lower water concentration.
Active Transport: A process that is required to move molecules against a concentration gradient which
requires energy from respiration.
Cell Cycle
Mitosis: A type of cell division that occurs in body cells [any cell except those that produce gametes].
o Diploid: Refers to the presence of two complete sets of chromosomes [46 for a human].
o The cell is in interphase for most of the time
o The 2 diploid daughter cells are clones of their parent cell. Every base pair of their DNA is identical.
o Mnemonic => IPMAT
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