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AQA A LEVEL BIOLOGY PAPER 1 EXAM 2025|ACTUAL
EXAM QUESTIONS WITH ANSWERS|100% PASS
Water removed from the reactants joining two molecules together forming a chemical bond Condensation The addition of water to the reactants to break a chemical bond between 2 molecules Hydrolysis
- Add Benedict's reagent. 2. Heat the solution in a water bath for 5 minutes at 95 degrees Celsius. 3. Change from blue to brick red as CuO formed Test for Reducing Sugars (3)
Smaller units from which larger molecules are made Monomer
- Add 2cm³ of food sample then add 2cm³ of dilute HCl and heat.
- Add 2cm³ of NaHCO3 then do test for reducing sugars. Non-Reducing Sugars (2) Add drops of iodine to starch solution. Colour change to blue-black Test for Starch (1)
- Mix Test solution with ethanol.
- Shake for 1 minute then add water.
- Cloudy white emulsion Test for Lipids (3)
Competitive inhibition (2)
- Molecule will bind to allosteric site.
- Binding causes a change in active site.
- Permanently preventing further ESC. Non-competitive inhibition (3)
- DNA helicase breaks the hydrogen bonds between the base pairs
- 2 single strands formed as the double helix "unzips".
- Free DNA nucleotides in the nucleoplasm bond to the complementary bases on the strand.
- DNA polymerase forms phosphodiester bonds between adjacent DNA nucleotides via condensation reaction with the hydrolysis of ATP, forming the phosphate backbone DNA Replication: Semiconservative (4)
- ATP stores or releases only a small amount of energy at a time, so no energy is wasted as heat.
- Small and soluble so easily transported
- Easily broken down, so energy is released instantaneously
- Can be quickly re-made
- Can make other molecules more reactive via phosphorylation
- ATP can't pass out of cell, so the cell always has an immediate supply of energy. Describe 6 properties of ATP that make it a good energy source. (6) Prevents the cell from drying out. Allows bacteria to stick to each other Slime capsule (2) Used for attachment of a cell to a surface Fimbria
The mass of organelles at the bottom of the test tube after centrifugation. Pellet Cold. Low temperature slows enzyme activity, minimising self digestion by reducing metabolic rate. Isotonic. Salt and sugar concentration kept the same, minimising organelle size change due to osmosis. Buffered. Minimum changes in pH, so prevents enzymes in organelles denaturing. Solution Required for cell fractionation (6 Marks)
- Homogenisation. Breaking up cells by blending the sample to create a homogenate.
- Filtering. Filtering the large, unwanted sil, producing the filtrate.
- Ultracentrifugation. Spin in a centrifuge so components separate out by weight. Heavier near the bottom of the tube.
- Supernatant is removed and spun again at higher speed. Separation of Organelles From The Cells (4)
The solution not including the pellet at the bottom of the test tube after centrifugation. Supernatant
- Cell wall forms, dividing the two genetically identical daughter cells.
- Same circular DNA. Binary Fission 3 Nuclei, Chloroplasts, Mitochondria, Lysosomes, Endoplasmic Reticulum, Ribosomes Order of Organelles (Pass me a taco chief) Mitosis acronym
- DNA winds up making chromosones from chromatin.
- Centrioles appear at opposite poles of the cell. 3. Nucleolus disappears Prophase (3)
- Nuclear envelope disappears.
- Chromosomes align along the equator of the cell.
- Spindle fibres connect centrioles to chromosomes Metaphase (3)
- Spindle fibres contract pulling daughter chromosomes to opposite poles of the cell. Anaphase (1)
- Spindle fibres disperse.
- Nuclear envelope forms.
- Chromatids uncoil to chromatin Telophase (3)
- Cytoplasm constricts separating the cells into two.
- Membrane forms creating two new genetically identical daughter cells. Cytokinesis (2) number of cells in mitosis/total number of cells Mitotic index
- Circular DNA replicates and both copies attach to the cell membrane.
- Plasmids also replicate.
Fluid: All the components can move around. Mosaic: Many different components all fit together Fluid mosaic Structure [Fluid][Mosaic] (2) The passive transport of large molecules such as amino acids and sugars, but they require integral proteins to pass through. Facilitated Diffusion The passive movement of particles from a high concentration to a region of low concentration, down a concentration gradient. Diffusion
- Add antibody that is specific to antigen. After leaving them to bind, wash the surface to remove unattached antibodies.
- Add a second antibody with an enzyme attached.
- Second antibody binds with first antibody
- Add colourless substrate of enzyme, which the enzyme will act upon to give a coloured product.
- The intensity of the colour is relative to the amount of antigen present. ELISA Test (Enzyme linked Immunosorbent Assay) (5) Small, non-polar molecules (excluding water) freely diffuses in and out of cells through gaps between phospholipids. Simple Lipid Diffusion The passive movement of water molecules across a partially permeable membrane from a high water potential to a low water potential, down a concentration gradient. (Distilled water = 0Ψ) Osmosis Equal concentration solution to the cell
- The simultaneous transport of two different substances through one carrier protein.
- One substance (usually an ion) moves down its concentration (passive) whilst the other substance is transported against its concentration gradient (active transport) Co-transport (2) A molecule, usually a glycoprotein or protein that stimulates an immune response. Antigen A protein molecule that can bind specifically to an antigen Antibody
- Ingestion (phagocytosis).
- Antigen Presentation.
- Clonal Expansion.
- Differentiation (T-cells and cell mediated immunity).
- Differentiation (B-cells and antibody mediated immunity) Stages of response to a non-self antigen found in body fluid Vaccination of a significant portion of a population providing a measure of protection for the individuals who have not developed immunity/have not been vaccinated. Herd immunity Antibodies produced from cloned plasma B lymphocytes Monoclonal Antibodies
- Hydrogen bonds between DNA base pairs are broken
- One DNA strand acts as a template
- Free RNA nucleotides align by complementary base pairing (uracil is used instead of thymine)
- Substrate binds to active site
- ESC forms
- Active site changes shape slightly distorting hydrogen bonds in the substrate.
- Reduces activation energy Describe the Induced fit model of enzyme action and how an enzyme acts as a catalyst. (3 marks) A change in the nucleotide base sequence. Mutations (Normal = BEAST) Substitution in a codon turns it into a stop codon Substitution (Nonsense) Causing a different amino acid to be coded for
Missense (FEAST) Results in a codon coding for the same amino acid creating degenerate code. Silent Nucleotide is gained from a DNA strand, creating a right frameshift. Addition (BREAST) A nucleotide is lost so frameshift to the left. Deletion (BEST) When one or more bases are repeated so shift to the right. Duplication (BEEAST)
