ESSAY Flashcards
How long should you spend on the essay?
NO LONGER than 45 mins
This includes planning & writing!
Do I need to write an introduction or a conclusion?
NO
Should I plan both essay titles?
YES.
This will help you decide which essay you can write about in the most detail.
Which topics can fit into (almost) EVERY essay title?
- Photosynthesis
- Respiration
- Protein synthesis/Control of gene expression
- Immunology
- Synapse
- Receptors & Homeostasis
Describe the light dependent reaction (6)
- Chlorophyll absorbs light energy & Excites electrons
- electrons removed (Oxidation of chlorophyll) via photoionisation;
- Electrons move along carriers/electron transport chain releasing energy (Series of REDOX reactions)
- Energy released (by electrons) used to form proton gradient;
- H+ ions move through ATP synthase;
- providing energy to join ADP and Pi to form ATP;
- Photolysis of water produces 2 protons, 2 electrons and ½ oxygen;
- NADP reduced by electrons / electrons and protons / hydrogen;
Describe the light independent reaction (6)
- Carbon dioxide combines/reacts with ribulose bisphosphate/RuBP;
- Produces two glycerate (3- )phosphate/GP using (enzyme) Rubisco;
- GP reduced to triose phosphate;
- Using reduced NADP;
- Using energy from ATP;
- Triose phosphate converted to glucose/hexose/RuBP/ribulose bisphosphate/named organic substance;
Explain why plants that have more chlorophyll will grow faster than plants with less chlorophyll.
- Have faster production of ATP and reduced NADP;
- (So) have faster / more light-independent reaction;
- (So) produce more sugars that can be used in respiration;
- (So) have more energy for growth;
- Have faster / more synthesis of new organic materials.
Describe the process of glycolysis. [4]
- Phosphorylation of glucose using ATP;
- Oxidation of triose phosphate to pyruvate;
- Net gain of ATP;
- NAD reduced;
Describe how oxidation takes place in glycolysis and in the Krebs cycle. [4]
- removal of hydrogen/dehydrogenation;
- by enzymes/dehydrogenases;
- H accepted by NAD/reduced NAD formed;
- in Krebs cycle, FAD (used as well);
Explain how the amount of ATP is increased by reactions occurring inside a mitochondrion. [6]
- oxidation of/removal of electrons and H+
- from pyruvate
- acetyl CoA / 6 carbon compound; (credit oxidative decarboxylation)
- substrate level production of ATP / ATP produced in Krebs cycle;
- production of reduced NAD / FAD (allow they take up hydrogen);
- in matrix of mitochondria;
- electrons fed into electron transport chain / used in oxidative
- (Electrons) pass along carriers/through electron transport chain/through series of redox reactions;
- Energy released;
- Protons move into intermembrane space;
- ADP/ADP + Pi;
- ATP synthase;
The mitochondria in muscles contain many cristae. Explain the advantage of this. [2]
- larger surface area for electron carrier system / MORE oxidative phosphorylation;
- provide MORE ATP / energy for contraction
Describe Transcription in Eukaryotes [5]
- Hydrogen bonds (between DNA bases) break;
- (Only) one DNA strand acts as a template;
- (Free) RNA nucleotides align by complementary base pairing;
- (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;
- RNA polymerase joins (adjacent RNA) nucleotides;
- (By) phosphodiester bonds (between adjacent nucleotides);
- Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA);
Describe Translation [5]
- (mRNA attaches) to ribosomes OR (mRNA attaches) to rough endoplasmic reticulum;
- (tRNA) anticodons (bind to) complementary (mRNA) codons;
- tRNA brings a specific amino acid;
- Amino acids join by peptide bonds via condensation reaction;
- (Amino acids join together) with the use of ATP;
- tRNA released (after amino acid joined to polypeptide);
- The ribosome moves along the mRNA to form the polypeptide;
A mutation in a gene coding for an enzyme
could lead to the production of a non-functional enzyme. Explain how [5]
- Change in base sequence (of DNA/gene);
- Change in amino acid sequence / primary structure (of enzyme);
- Change in hydrogen/ionic/ disulphide bonds;
- Change in the tertiary structure/active site (of enzyme);
- Substrate not complementary/cannot bind (to enzyme / active site) / no enzyme-substrate complexes form;
Eukaryotic cells produce and release proteins.
Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. [5]
- DNA in nucleus is code (for protein);
- Ribosomes/rough endoplasmic reticulum produce (protein);
- Mitochondria produce ATP (for protein synthesis);
4 Golgi apparatus package/modify; OR Carbohydrate added/glycoprotein produced by Golgi apparatus;
5 Vesicles transport OR Rough endoplasmic reticulum transports; - (Vesicles) fuse with cell(-surface) membrane;
Describe the non-specific defence mechanisms the body may launch against pathogens (5 marks)
The process is called phagocytosis – No Mark
1. Pathogen is engulfed by the phagocyte.
2. Engulfed pathogen enters the cytoplasm of the phagocyte in a vesicle [phagosome];
3. Lysosomes fuse with vesicle releasing hydrolytic enzymes [phagolysosome];
4. Lysosome enzymes hydrolyse/digest the pathogen.
5. Waste materials are ejected from the cell by exocytosis;
6. Antigen is presented on surface membrane.
Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). [4]
- RNA converted into DNA using reverse transcriptase;
- DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
- DNA transcribed into (HIV m)RNA;
- (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles);
AO2 (More or Less)
Describe how a person infected with HIV will develop AIDS (if untreated) and die of secondary infections. [4]
- High viral load leads to increased destruction of helper T/CD4 cells;
- Less activation of B cells/cytotoxic T cells/phagocytes;
- Less production of plasma cells/antibodies OR (With cytotoxic T cells) less able to kill virus infected cells;
- (Less able to) destroy other microbes/pathogens OR (Less able to) destroy mutated/cancer cells;
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how. [6]
- Vaccine contains (specific) antigen from pathogen;
- Macrophage presents antigen on its surface;
- T (helper) cell with complementary receptor protein binds to antigen & becomes activated;
- T cell stimulates B cell by complementary receptor binding and releases cytokines;
- (With) complementary antibody on its surface;
- B cell divides to form clone secreting / producing same antibody;
- B cell secretes large amounts of (monoclonal) antibody;
How should I set out my essay on the importance of membranes?
Write about a relevant topic / process (AO1 Key points 5 marker) that includes a membrane. E.g. Thylakoid membrane in photosynthesis.
THEN
Write 2 or 3 sentances about why the thylakoid membrane is important. (AO2)
e.g., without the thylakoid membrane, proton gradient could not form so protons could not diffuse through ATP synthase, so less ATP would be produced, less GP would be reduced into triose phosphate, so less glucose, less cellulose synthesised so new plant cells would have weaker cell walls and may undergo osmotic lysis.
Now repeat this another FOUR times with different topics.
How are the marks allocated?
AO1 = 15 marks
AO2 = 10 marks
What are the maximum number of marks for an essay with NO LINKS?
15 Max (so long as you have covered at least 3 topics)
3 x (relevant) 5 markers
How do I get 25 marks?
5 x AO1 5 markers (different topics)
All topics are relevant and linked to the importance of “essay focus”
One topic is ‘off-spec’ at least to A Level standard
NO Significant errors (Biologically incorrect)
NO Irrelevant content (waffle / does not address the essay theme)
Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane.
- Depolarisation of presynaptic membrane;
- Ca2+ channels open and calcium ions enter (synaptic knob);
- (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine / neurotransmitter;
- Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
- (Acetylcholine attaches) binds to receptors on the postsynaptic membrane;
- Sodium ions enter (postsynaptic neurone) leading to depolarisation;
