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Pearson Edexcel GCSE Triple Science Biology Notes
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Pearson Edexcel GCSE/iGCSE Triple Science Biology Notes covering every specification point.
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Biology Unit 1 Revision (The Nature and Variety of Living Organisms)Characteristics of Living Organisms:
Characteristics:
Movement: All living organisms move (eg, to move we use muscles and phototropism
in plants)
Reproduction: All living organisms can produce offspring (eg, sexual reproduction)
Sensitivity: All living organisms respond to stimuli (eg, sense changes around them)
Nutrition: All living organisms need nutrition (eg, animals eat other organisms while plants use photosynthesis)
Excretion: All living organisms excrete (eg, they get rid of waste products)
Respiration: All living organisms respire (eg, they release energy from their food)
Homeostasis: All living organisms can control their internal conditions (eg, They can control water levels)
Growth: All living organisms can grow and develop (eg, Increase in size and complexity or more cells)
Variety of Living Organisms:
Plants:
- Multicellular (eukaryotic)
- Can carry out photosynthesis
- Cellulose cell walls
- Store carbohydrates as starch or sucrose
- Eg, cereals (maize), herbaceous legumes (pea)
Animals:
- Multicellular (eukaryotic)
- Can’t carry out photosynthesis
- No cell walls
- Have nervous coordination and can move in different directions
- Eg, mammals (humans) and insects (mosquitos)
Fungi:
- Single celled (yeast) and multicellular (Mucor) (eukaryotic)
- Can’t carry out photosynthesis
- Bodies of mycelium made from hyphae (thread-like)
- Cell walls of chitin
- Feed by saprotrophic nutrition (excrete extracellular enzymes onto food and absorb organic products)
- Store carbs as glycogen
Protoctists:
- Single-celled and microscopic (eukaryotic)
- Some are like animal cells (eg, amoeba) and others like plant cells (eg, chlorella)
- Eg, plasmodium causes malaria
Bacteria:
- Microscopic and single-celled (prokaryotic)
- Have cell wall, cell membrane, cytoplasm, no nucleus only a circular chromosome of DNA, plasmids,
flagellum
- Some carry out photosynthesis while some feed off other organisms
- Eg, lactobacillus bulgaricus (rod shaped used to make yoghurt) and Pneumococcus (spherical and causes
pneumonia)
Viruses:
- Not living organisms
- Smaller than bacteria
- Can only reproduce inside living cells
- Have a protein coat around nucleic acid (eg, RNA or DNA)
- Eg, Tobacco Mosaic Virus (causes discolouration of leaves as no chloroplasts), influenza (causes flu) and
HIV (causes AIDS)
Pathogens:
- A microorganism that causes disease
- Can be fungi, bacteria (pneumococcus), protoctists (plasmodium) and viruses (HIV)
, Biology Unit 2 Revision (The Structure and Functions of Living Organisms)
Level of Organisation:
Levels of Organisation:
- Organelles, Cells, Tissues, Organs, Organ Systems
- Organelle: Organised structures that have specific functions in a cell. Eg mitochondria.
- Cells: Made up of organelles and is the basis of living things. Eg, skin cells
- Tissues: Collection of similar cells that carry out a specific function. Eg, muscular tissues
- Organs: Made up of several different tissues that work together to perform a specific function. Eg, heart
- Organ Systems: Made up of several different organs that work together to perform a specific function. Eg,
cardiovascular system
Cell Structure:
Animal Cells:
- Nucleus: Contains genetic info of the cell and controls its activities.
- Cytoplasm: A substance where most of the chemical reactions take place.
- Cell Membrane: controls the movement of substances in and out of the cell
- Mitochondria: Carries out cell respiration and releases energy for the cell.
- Ribosomes: Site of protein synthesis
Plant Cells:
- Cell Wall: Protects and maintains the shape of the cell
- Vacuole: Stores water and dissolved substances in the cell sap
- Chloroplast: Has chlorophyll and carries out photosynthesis
Cell Differentiation (T):
- All specialised cells have developed by cell differentiation
- Undifferentiated cells (eg, stem cells) get signals which stimulates the genes for the cell to change itself to
carry out specific functions.
- This allows cells to develop features that can help the cell adapt to its function.
Stem Cells (T):
- Stem cells are cells that are capable of replicating and can differentiate into different specialised cells. They
can be used in medicine to help cure diseases.
- Advantages: Heal illnesses, can help therapeutic cloning, ability to test drugs without simulation, reduced
risk of rejection as it’s the patient's own cells
- Disadvantages: Ethical issues that they are from embryos that have rights, uncertainty in the long term,
may be rejected, expensive, difficult in controlling differentiation.
Biological Molecules:
Chemical Elements of Molecules:
- Carbohydrates: Carbon, Oxygen, Hydrogen
- Protein: Carbon, Oxygen, Hydrogen, Sulfur, Nitrogen
- Lipids: Carbon, Oxygen and Hydrogen
Structure of Molecules:
- Starch and Glycogen: Chains of Simple Sugars (ie, glucose)
- Protein: Chains of Amino Acids
- Lipids: Chains of Glycerol and Fatty Acids
Food Tests Practicals:
- Glucose:
- Add drops of Benedict’s solution in a test tube with sample
- Heat test tube in water bath for 5 mins
- Remove and see colour, brick red from blue if present
- Starch:
- Use a pipette to drop iodine on sample
- If colour changes from bule-black to brown, it is present
- Protein:
- Add a few drops of Biuret solution in a test tube with sample
, - If colour changes from blue to violet, it is present
- Lipids:
- Add ethanol to distilled water
- If the solution changes from colourless to milky with white emulsion, it is present
Enzymes:
- Enzymes: Protein molecules that are biological catalysts as they speed up the rate of reaction without
being used up.
- They catalyse metabolic reactions by binding the substrate to the enzyme active site and they break down
the substrate
- Substrate collides with the active site of the enzyme and attach
- Enzyme catalyses breakdown of substrate
- Products released and enzyme remains unchanged and can be reused
- Carbohydrase: carbs → reducing sugars (eg, amylase maltase)(salivary glands, small intestine, pancreas)
- Protease: protein → amino acids (eg, pepsin, trypsin, peptidases)(stomach, small intestine, pancreas)
- Lipases: lipids → fatty acids and glycerol (eg, lipase)(pancreas)
Factors Affecting Enzyme Activity:
- Temperature:
- As temperature increases to optimum temp, rate of enzyme activity increases. This is because
the enzyme and substrates get more kinetic energy and so allows more frequent collisions so
more substrates are broken down.
- If the temp increases past optimum, the enzyme denatures as the bonds of the enzyme vibrate
more and get broken, distorting the shape of the active site and it won’t be complementary to the
substrate and there can’t be any more enzyme activity.
- pH:
- As it increases to optimum, active site and substrate shape will be optimal so more frequent
collisions occur and this increases the rate of substrates being broken down.
- As pH exceeds optimum, the shape of the active site changes so the substrate can’t fit and this
allows no enzyme activity
Temperature and Enzymes Practical:
- Get starch in a test tube and heat in water bath to set temp
- Add amylase to solution
- Quickly pipette the solution onto wells on spotting tile
- After the solution is added add drops of iodine to each spot.
- Repeat for each temp until iodine is orange which means that starch is completely broken down
- Record time taken
- Independent variable (Starch Temp)
pH and Enzymes Practical (T):
- Test tube of starch and place it in water bath w set optimum temp
- Add amylase to solution
- Add buffer solution to solution to keep pH constant
- Pipette solution into wells and add iodine to each one
- Repeat until iodine turns orange as starch is completely broken down
- Record time taken
- Independent Variable (pH of buffer solution)
Movement of Substances:
Diffusion:
- The passive net movement of particles from an area of high to low concentration (down a concentration
gradient) until equilibrium.
Osmosis:
- The passive net movement of water molecules from an area of high to low water potential across a partially
permeable membrane
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