Essay Model Answers Flashcards
AO1 SynapsesAO2 Control of Heart Rate
AO1
Action potential reaches pre-synaptic membrane allowing Ca2+ channels to open and Ca2+ enters by facilitated diffusion
Vesicles containing Acetylcholine (Ach) fuse with the pre-synaptic membrane and Ach is released
Ach diffuses across the synaptic cleft
Ach binds to the receptors on the post-synaptic membrane.
Na+ channels open and Na+ moves in by facilitated diffusion
Leading to depolarisation and action potential of threshold is exceeded
Acetylcholinesterase hydrolyses Ach to acetic acid and choline to be returned to the presynaptic neurone
AO2
The role of ______________ (insert title here) in synapses is/are important because…
Synapses are required to propagate impulses from one neurone to another.
When too much CO2 is present in the blood it is detected by chemoreceptors where more impulses are sent along neurons to the medulla and along the sympathetic nerve to the SAN which increases heart rate.
AO1 Oxidative PhosphorylationAO2 Co-Transport
AO1
FADH and NADH are oxidised and lose e- and H+
The e- are passed from carrier protein to carrier protein in the mitochondria inner membrane in a series of redox reactions. This releases energy
The energy is used to pump H+ through the membrane into the inner membrane space building a chemiosmotic gradient
H+ moves back through the membrane through ATP synthase
ADP + Pi ATP
Oxygen is the terminal electron acceptor forming water
AO2
The role of ______________ (insert title here) in Oxidative Phosphorylation is/are important because…
ATP that is generated may can be used in active transport across membranes. An example of this is when the Na+/K+ pump pumps Na+ out of the ileum epithelial cells into the blood to generating a concentration gradient that allows the absorption of glucose during co-transport.
AO1 PhotophosphorylationAO2 Light Independent Reaction
AO1
Chlorophyll is excited by light in photoionisation
The e- are passed from carrier protein to carrier protein in the thylokoid membrane in a series of redox reactions. This releases energy
The energy is used to pump H+ through the membrane into the inside of the thylakoid building a chemiosmotic gradient
H+ moves back through the membrane through ATP synthase
ADP + Pi ATP
The electrons are eventually used to reduce NADP with the H+ from photolysis
AO2
The role of ______________ (insert title here) in Photophosphorylation is/are important because…
ATP that is generated is required for the light independent reaction where it is used to aid reduction of glycerate-3-phosphate to Triose phosphate and in the regeneration of RuBP. This allows more CO2 to be fixed in further light independent reactions
AO1 Protein DigestionAO2 Co-Transport
AO1
Endopeptidase hydrolyse peptide bonds by adding a water molecul in the middle of protein/polypeptide in the stomach and produces shorter polypeptides, increasing the number of ends
Exopeptidases hydrolyse peptide bonds at end of protein/polypeptide and in the stomach and produce dipeptides.
Dipeptidases are membrane bound enzymes in the ileum which hydrolyse peptide bonds in dipeptides and produce single amino acids
AO2
The role of ______________ (insert title here) in protein digestion is/are important because…
Dipeptidases produce single amino acids, these are small enough to be able to be co-transported through the ileum epithelium cells with Na+. This increased the concentration of amino acids in cells so they can move into the blood by facilitated diffusion down a concentration gradient.
AO1 Co-TransportAO2 Glycolysis
AO1
Na+ is actively pumped out of the cell into the blood by the sodium potassium pump
This lowers the concentration of sodium in the epithelium cell
Na+ moves into the cell from the lumen by facilitated diffusion and glucose/amino acids are co-transported with it
Glucose/amino acids are then transported into the blood by facilitated diffusion
AO2
The role of ______________ (insert title here) in co-transport is/are important because…
Glucose that is absorbed by co-transport is required for glycolysis. A molecule of glucose is phosphorylated by ATP and then oxidised to form two molecules of pyruvate and NADH that are required for later stages of respiration.
AO1 PCRAO2 DNA fingerprinting
AO1
DNA is heated to 95°C to break the hydrogen bonds between bases and separate the DNA strands
DNA is cooled to 55 °C to allow primers to anneal.
Free nucleotides complementary base pair to the template DNA
DNA is heated to 72 °C so Taq DNA polymerase can bind and join the free nucleotides together forming phosphodiester bonds
AO2
The role of ______________ (insert title here) in PCR is/are important because…
PCR can be used to create large volumes of DNA sequences from small amounts.
These can be run on a gel during electrophoresis and specific fluorescent or radioactively labelled probes can be used to diagnose diseases or during identification at crime scenes using Southern blotting.
AO1 Phospholipid BilayerAO2 Oxygen absorption
AO1
The phospholipid bilayer is made of phospholipids with hydrophilic/polar phosphate heads and non-polar/hydrophobic fatty acid tails
This bilayer limits the movement of substances through the membrane so that only small non-polar molecules like oxygen can freely diffuse through
Embedded in the membrane are transmembrane proteins that can act as carrier and channel proteins. Chanel proteins allow facilitated diffusion of ions, while carrier proteins can perform facilitated diffusion, they can also transport molecules across the membrane using energy from ATP in active transport
Glycoproteins are embedded in the membrane and act as antigens for cell recognition, they also increase stability and adhesion of the cells
Glycolipids are part of the membrane and increase stability and allow for adhesion of cells.
AO2
The role of ______________ (insert title here) in the phospholipid bilayer is/are important because…
The structure of the membrane allows small non-polar molecules like oxygen to pass through, this can be used as the terminal electron accepter in oxidative phosphorylation. However, larger and polar substance can be excluded allowing the control of absorption of these substances such as when ADH controls the absorption of water reabsorption by stimulating aquaporin activation.
AO1 DNA ReplicationAO2 Cell Cycle/Mitosis
AO1
DNA helicase breaks the hydrogen bonds causing the strands to separate
Both strands act as a template
Free nucleotides complementary base pair to the template A-T and G-C
DNA polymerase joins adjacent nucleotides together forming a phosphodiester bond
Hydrogen bonds form between the old strand and the newly synthesised strand
DNA replication is semi-conservative replication
AO2
The role of ______________ (insert title here) in DNA Replication is/are important because…
DNA replication ensures faithful copying of DNA. This ensures sister chromatids do not have any mutations or differences so that they can be segregated correctly at anaphase. It also ensures that the cell cycle remains controlled and prevents mutations leading to the development of oncogenes.
AO1 ADHAO2 Hydrolysis
AO1
Water potential in the blood decreases. Osmoreceptors in the hypothalamus shrink
Stimulates the hypothalamus. Increases ADH release by posterior pituitary gland
ADH carried in the blood to the distal convoluted tubule and the collecting duct
ADH binds to complementary receptors on specific target cells in the collecting duct and distal convoluted tubule (DCT)
The enzyme phosphorylase is activated by this binding. Leading to aquaporins fusing with the membrane of the epithelial cells in the collecting duct (DCT)
Membrane permeability to water increases
Water moves from a high water potential in the collecting duct to a low water potential in the blood via osmosis
AO2
The role of ______________ (insert title here) in ADH is/are important because…
ADH allows the cells to contain the right amount of water. Cells need that water as it is a universal solvent so many reactions occur when reactants are dissolved in the cytoplasm. Water itself is a reactant in many cell processes and is essential for hydrolysis reactions e.g. maltose 2 x alpha glucose.
AO1 PhagocytosisAO2 Immune Response
AO1
Phagocyte receptors recognizes foreign antigen
Pathogen is engulfed into a Phagosome
Lysosome fuses with phagosome forming a phagolysosome
Lysozyme enzymes Hydrolyse pathogen
Antigens from pathogen may be presented on the surface of the cell
AO2
The role of ______________ (insert title here) in phagocytosis is/are important because…
The antigens that are presented on the outside of the phagocyte trigger further action of the immune system. T Helper cells with the complimentary receptor will bing to the antigen becoming activated. They will go on to divide through mitosis forming cytotoxic T cells and further T Helper cells that can activate B cells.
AO1 Cell mediated responseAO2 Humoral response
AO1
Antigen is presented by an antigen presenting cell
Helper T Cells with the complementary receptor binds to the presented antigen
Helper T cell is activated and goes through mitosis, forming cytotoxic T cells and more Helper T cells
Cytotoxic T cells produce perforins to kill cells by making holes in their cell surface membrane, water enters causing cells to burst
Only works on whole cells e.g. cancer cells or those infected with viruses
AO2
The role of ______________ (insert title here) in cell mediated response is/are important because…
T helper cells are needed in clonal selection and to activate specific B cells. These then divide by mitosis in clonal expansion, producing plasma and memory B cells. This is clonal expansion. Without plasma cells antibodies could not be produced, which are needed to destroy pathogens with antigens complementary to their receptos.
AO1 TranscriptionAO2 Translation
AO1
DNA strands are separated by breaking hydrogen bonds
Transcription is the synthesis of an mRNA copy of a gene;
The copy is complementary to the DNA template/antisense strand;
RNA polymerase attaches to DNA
RNA nucleotides matched to exposed complementary bases;
Adjacent nucleotides are joined by a phosphodiester bond together to make a strand of mRNA;
mRNA molecule separates from DNA
In eukaryotes only: mRNA is spliced to remove introns
Mature mRNA leaves the nucleus through nuclear pores
AO2
The role of ______________ (insert title here) in Transcription is/are important because…
Transcription generates mRNA which is essential for making proteins, during translation the mRNA codons bind to tRNAs complementary anticodons inside the ribosome. This allows specific amino acids to be brough together and joined by a peptide bond in a condensation reaction.
AO1 TranspirationAO2 Translocation
AO1
Water evaporates from the leaves/transpiration
Due to heat/kinetic energy from sunlight
Water diffuses out of the stomata from a high water potential to low
The diffusion of water causes tension in the xylem
This is due to water potential gradient
Cohesion tension forms a continuous column of water that is pulled through the xylem in a transpiration stream
Water’s adhesive properties aid the movement through the xylem
Transpiration stream lowers water potential in the root cells
Water is absorbed through the root hair cells by osmosis from a higher water potential to low.
AO2
The role of ______________ (insert title here) in transpiraton is/are important because…
The water present in the xylem is also necessary for the movement of solutes in the plant phloem. Solutes are actively transported into the phloem reducing the water potential. This leads water moving into the phloem by osmosis and increasing the hydrostatic pressure allowing substances to move by mass flow.
AO1 Induced Fit (Enzymes)AO2 Digestion of maltose
AO1
An enzyme and its substrate are complementary due to the enzymes tertiary structure, however they are not a perfect fit.
When an enzyme binds to a substrate it changes shape slightly which stresses the hydrogen, ionic and disulphide bonds of the substrate.
This lowers the activation energy required to break and make bonds meaning the reaction occurs more quickly.
The products are formed and the product is released and the enzyme is able to catalyse the reaction again.
AO2
The role of ______________ (insert title here) in enzyme action is/are important because…
Maltose is complementary to the enzyme maltase which works by the induced fit mechanism. The enzyme maltase hydrolyses the glycosidic bond in maltose forming α-glucose. Glucose is then absorbed by co-transport
AO1 Natural SelectionAO2 Protein Structure/Mutations
AO1
Mutation leads to variation in a species by developing a new allele
The new allele provides an advantage e.g. give an example from the question
Organisms with the new allele can survive and reproduce
Advantageous allele is passed on to offspring
The advantageous allele increases in frequency in the population
AO2
The role of ______________ (insert title here) in natural selection is/are important because…
Natural selection allows for the increase of favourable alleles in a population, this can lead to a change in protein structure as the primary of sequence of amino acids may change resulting in a further change in the secondary and tertiary structure. This can impact the functioning of a protein and in some cases leading to an advantage e.g. production of lactase that allows lactose digestion in adulthood.
