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Biology IGCSE Edexcel Notes
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Fully inclusive notes of the igcse Biology edexcel syllabus. Includes questions and mark schemes from prepares up to January 2022. Guaranteed 9 :)
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IGCSE biology - TOPIC 4: ECOLOGY AND THE ENVIRONMENT
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IGCSE biology - TOPIC 3: REPRODUCTION AND INHERITANCE
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IGCSE biology - TOPIC 5: USE OF BIOLOGICAL RESOURCES
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Unit 1Chapter 1
Cell: Basic structural unit for living organisms
The eight life processes
1) Movement: An action by which an organism changes place/position in order to obtain food,
water, shelter and to avoid predators, dangerous environment
2) Respiration: The chemical reaction that releases energy
3) Sensitivity: Detecting changes in their environment and respond to stimuli
4) Growth: Increase in size and mass, using materials from their food, by increasing the number
of cells
5) Reproduction: Producing offspring
6) Excretion: The removal of metabolic (=chemical reactions taking place inside cells) waste
7) Nutrition: Taking in food for growth, repair ,and energy (by ingestion for animals and
photosynthesis for plants)
8) Control: Controlling our internal conditions by homeostasis
Cell Structure
Name Description Function
Cytoplasm The jelly-like material that It is the place where most of
makes up a cell and contains all the cell’s chemical reactions
other organelles happen, it contains enzymes
which control these reactions.
Nucleus The largest organelle which has Controls the activities of the
its own membrane and cell
contains genes
Cell Wall Rigid structure made of It supports the cell and
cellulose which surrounds the strengthens it
cell membrane, freely permable
Cell Membrane Thin skin-line layer on the Regulates the movement of
surface of the cell, which forms some substances in and out of
a boundary between the the cell
cytoplasm of the cell and the
outside, it is partially
permeable
Mitochondria They have a characteristic The site of respiration
coiled structure and they have
their own DNA
Vacuole Large central space occupied Acts as a store of sugars, miresl
by a membrane ions ,and other solutes
Chloroplast Green parts of plants that The site of photosynthesis
contain chlorophyll
Describe the role of chlorophyll.
A description that makes reference to two of the following points:
• absorb / trap / captures / eq, light (1)
• photosynthesis (1)
• make carbohydrate / make starch / make glucose / eq (1)
,Enzymes
Metabolism: the sum of all metabolic reactions
Secretion: the release of a fluid or substances from a cell or tissue
Catalyst: a chemical which speeds up a reaction
Substrate: the molecule an enzyme acts on
Enzymes
1) Biological catalysts
2) Proteins
3) Are specific to one substrate
4) Can catalyse reactions without being used up
5) Have an active site in which substrates attach themselves to
Factors affecting enzymes:
1) Temperature: They work fastest at the optimum temperature (the temperature an enzyme
works best) As it is heated up the enzyme and substrate gain kinetic energy meaning that they
move faster and collide more often, forming enzyme-substrate complexes, causing the
reaction to occur faster. If it continues to be heated above the optimum temperature the
proteins get broken down by heat causing the active site to be deformed, this means that the
substrate can no longer fit into the active site. We say that it has been denatured. Ss we
continue heating all the enzymes get denatured and the reaction eventually stops
2) pH: a high or low pH affects the bonds holding the enzyme together, causing the shape of the
active site to change
The birds do not have teeth.
The fish they eat is initially crushed in part of their digestive system called a gizzard.
Suggest why crushing the fish in the gizzard helps the birds to digest the fish
• increase surface area (1)
• enzymes (1)
Practical 1
Amylase: enzyme that breaks starch down to maltose
Notes
1) The digestive enzyme amylase breaks down starch into maltose
2) Iodine solution turns blue-black in the presence of starch
3) Iodine solution remains brown/yellow in maltose
, 4) As the enzyme amylase digests (breaks down) the starch, the blue black colour will disappear
5) If the enzyme amylase is denatured the reaction stops and starch isn’t converted to maltose
6) If the starch isn’t converted to maltose the blue black colour will remain
Why do we need to control variables: to have a valid test, to make sure that our results
are due to only one variable, the independent variable
A control needs to be set up as to have a base line
Method:
1. Add 5cm3 starch solution to a test tube and heat to a set temperature using beaker of
water with a Bunsen burner
2. Add a drop of Iodine to each of the wells of a spotting tile
3. Use a syringe to add 2cm3 amylase to the starch solution and mix well
4. Every minute, transfer a droplet of solution to a new well of iodine solution (which
should turn blue-black)
5. Repeat this transfer process until the iodine solution stops turning blue-black (this
means the amylase has broken down all the starch)
6. Record the time taken for the reaction to be completed
7. Repeat the investigation for a range of temperatures (from 20°C to 60°C)
, Practical 2
Method 1
Buffer solution: solutions of salts that resist changes in pH
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