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AQA A-Level Biology 7402

Biological Molecules

Topic overview Monomers, polymers, condensation and hydrolysis Monosaccharides, disaccharides and glycosidic bonds Alpha and beta glucose, amylose and amylopectin How starch, glycogen and cellulose suit their functions Cellulose microfibrils and tests for sugars and starch Triglycerides, fatty acids and phospholipid structure Properties of lipids and the emulsion test The general structure of amino acids Peptide bonds, polypeptides and bonds in proteins Levels of protein structure, the biuret test and chromatography Activation energy, induced fit and enzyme specificity Enzyme and substrate concentration and inhibition pH, temperature, initial rates and measurement uncertainty DNA, RNA and the components of a nucleotide Base pairing in DNA and RNA Phosphodiester bonds and the DNA double helix Doubts about DNA, base ratios and RNA structure Semi-conservative replication, helicase and DNA polymerase Steps of replication and the Meselson-Stahl experiment ATP structure, hydrolysis and resynthesis Water as a metabolite, solvent and coolant Hydrogen, iron, sodium and phosphate ions

Cells

Topic overview Cell-surface membrane, nucleus and mitochondria Chloroplasts, Golgi apparatus and lysosomes Ribosomes, endoplasmic reticulum, cell walls and vacuoles Cell specialisation, levels of organisation and organelle roles Prokaryotic cell structure and virus particles Optical and transmission electron microscopes Scanning electron microscopes, magnification and graticules Cell fractionation, homogenisation and ultracentrifugation Order of sedimentation, artefacts and fractionation conditions The cell cycle, interphase and the stages of mitosis Spindle fibres, cytokinesis and uncontrolled cell division Binary fission, viral replication and root tip squashes Mitotic index, mitosis stages and size calculations The fluid-mosaic model and cholesterol Simple diffusion, facilitated diffusion and membrane proteins Osmosis, water potential and active transport Co-transport in the ileum and adaptations for rapid transport Transport rates, dilution series and membrane permeability Antigens, cell recognition and phagocytosis Antigen-presenting cells, T cells and clonal selection Antibody structure, agglutination and antigen-antibody complexes Memory cells, vaccination and active and passive immunity HIV structure and replication AIDS, monoclonal antibodies, ELISA and clinical trials

Organisms Exchange Substances with Their Environment

Topic overview Surface area to volume ratio, metabolic rate and calculations Gas exchange in single-celled organisms, insects and fish Leaf gas exchange, insect water loss and xerophytes Trachea, bronchi, alveoli and lung dissection Inspiration, expiration and pulmonary ventilation rate Lung disease, correlation, insect tracheae and Spearman's rank Digestion of carbohydrates and lipids Endopeptidases, exopeptidases and dipeptidases Co-transport of amino acids, micelles and chylomicrons Haemoglobin, red blood cells and the dissociation curve Cooperative binding, the Bohr effect and different haemoglobins Double circulation and the major blood vessels Heart chambers, the cardiac cycle and heart dissection Arteries, arterioles, veins and capillaries Tissue fluid, cardiovascular risk factors and semilunar valves Xylem structure and the cohesion-tension theory Phloem structure, companion cells and translocation Mass flow from source to sink, tracers and ringing Evaluating mass flow, potometers and transpiration rate

Genetic Information, Variation and Relationships Between Organisms

Topic overview Prokaryotic and eukaryotic DNA, chromosomes and histones DNA in mitochondria and chloroplasts, genes and loci Features of the genetic code, exons and introns Genome, proteome, mRNA and tRNA Transcription, RNA polymerase and splicing Translation at the ribosome and the role of tRNA Gene mutations, mutagens and chromosome non-disjunction Meiosis, independent segregation and crossing over Meiosis compared with mitosis and random fertilisation Genetic diversity and the spread of advantageous alleles Directional and stabilising selection Defining adaptations and how antibiotic resistance spreads Selection on birth weight, aseptic technique and antimicrobials Classifying anatomical, physiological and behavioural adaptations Defining a species, courtship and phylogenetic classification The taxonomic hierarchy, binomial names and molecular evidence Species richness, the index of diversity and farming Comparing genetic diversity, standard deviation and the t-test

Energy Transfers in and Between Organisms

Topic overview Photoionisation and ATP from the light-dependent reaction Chemiosmosis, photolysis and products for the Calvin cycle Carbon fixation, triose phosphate and limiting factors Glasshouse conditions, pigment chromatography and DCPIP Glycolysis and its products Anaerobic respiration and the oxidation of pyruvate Acetylcoenzyme A and the Krebs cycle Oxidative phosphorylation, other substrates and respirometers Biomass and gross and net primary production Net production of consumers and productivity Farming practices, transfer efficiency and the production equations Saprobionts and the phosphorus cycle Mycorrhizae, ammonification and nitrification Nitrogen fixation, denitrification and fertilisers Leaching, eutrophication and nutrient cycles reviewed

Organisms Respond to Changes in Their Internal and External Environments

Topic overview IAA, gravitropism and phototropism Taxes, kineses, reflex arcs and choice chambers The Pacinian corpuscle and generator potentials Rods, cones, colour vision and visual acuity The SAN, AVN, bundle of His and Purkyne tissue Chemoreceptors, baroreceptors and cardiac output Motor neurone structure and the resting potential Depolarisation, action potentials and saltatory conduction The refractory period and speed of conduction Synapse structure and the neuromuscular junction Transmission at a cholinergic synapse Acetylcholinesterase, summation and inhibitory synapses Neuromuscular junctions compared, agonists and antagonists Drug effects and potassium channels in hyperpolarisation Antagonistic muscle pairs and muscle fibre structure Sarcomere bands, actin, myosin and tropomyosin The sliding filament cycle, ATP and phosphocreatine Slow twitch and fast twitch muscle fibres Control systems and why temperature, pH and glucose matter Negative and positive feedback Glycogenesis, glycogenolysis and gluconeogenesis How insulin, glucagon and adrenaline act The second messenger model, diabetes and the sugar debate Glucose calibration curves and hormones affecting blood glucose Osmoregulation, osmoreceptors and ADH Nephron structure and ultrafiltration The proximal convoluted tubule and the loop of Henle The distal tubule, collecting duct and urine concentration

Genetics, Populations, Evolution and Ecosystems

Topic overview Genotype, phenotype and types of allele Monohybrid and dihybrid crosses, sex linkage and autosomal linkage Epistasis, genetic diagrams and the chi-squared test Gene pools, allele frequency and Hardy–Weinberg Sources of variation and selection pressures Types of selection and allopatric and sympatric speciation Genetic drift, founder effects and the route to speciation Communities, ecosystems, niches and carrying capacity Competition, predation, quadrats and mark-release-recapture Mark-release-recapture assumptions and succession Succession, conservation and evaluating the evidence

The Control of Gene Expression

Topic overview Types of gene mutation and mutagenic agents Silent, frameshift, missense and nonsense mutations Totipotent, pluripotent and induced pluripotent stem cells Transcription factors, oestrogen, epigenetics and twin studies DNA methylation, histone acetylation and cancer RNA interference and epigenetic drug targets Benign and malignant tumours, suppressor genes and oncogenes Abnormal methylation, oestrogen and evidence on causes of cancer Genome projects, the proteome and sequencing methods Transgenic organisms and making DNA fragments The polymerase chain reaction Promoters, restriction endonucleases, sticky ends and ligase Transformation, marker genes and uses of recombinant DNA The humanitarian debate, cDNA and in vivo cloning DNA probes, hybridisation and screening for alleles Genetic counselling, personalised medicine and screening ethics VNTRs, PCR and gel electrophoresis Using and interpreting genetic fingerprints

Cells

Scanning electron microscopes, magnification and graticules

3 things to know
Papers 1 and 3

Overview

Recall questions on the scanning electron microscope, the limitations of electron microscopy, resolution and magnification, the magnification formula, and calibrating an eyepiece graticule with a stage micrometer.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What type of image does an SEM produce?

Key term

What is the resolution of a scanning electron microscope?

Process

Describe the preparation steps required for electron microscope specimens.

Questions from this subtopic

Each one with the model answer underneath.

1
Why must specimens for TEM be very thin?
Model answer
So that electrons can pass through the specimen.
2
How does a scanning electron microscope form an image?
Model answer
It bounces electrons off the surface of a specimen to form an image.
3
What type of image does an SEM produce?
Model answer
Three-dimensional images of surface features.
4
What is the resolution of a scanning electron microscope?
Model answer
Approximately 3–10 nm.
5
Why can electron microscopes not be used to view living specimens?
Model answer
Because specimens must be placed in a vacuum.
6
Describe the preparation steps required for electron microscope specimens.
Model answer
Complex preparation including fixation, dehydration and staining with heavy metals.

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Biological Molecules

Cells

Organisms Exchange Substances with Their Environment

Genetic Information, Variation and Relationships Between Organisms

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Sort every topic into what you know and what you do not, then drill only the weak ones.

A bond.

phosphodiesterglycosidicpeptide

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Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AOne glycerol molecule.

BThree fatty acid molecules.

CAn ester bond.

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Genotype means the genetic constitution of an organism.

TrueFalse

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