Describe how a virus replicates inside a host cell.

The virus attaches to the host cell and injects or releases its nucleic acid inside. The cell's machinery copies the viral genome and makes new capsids, and new virus particles are released.

How are new virus particles released from a host cell?

Many viruses burst the cell open, a process called lysis, which kills the cell. Enveloped viruses often bud out through the cell membrane instead.

What is a bacteriophage?

A bacteriophage is a virus that infects bacteria. Phages inject their DNA into the bacterium and often destroy it by lysis.

How large are viruses compared with bacteria?

Most viruses are roughly 20 to 300 nanometres across. Most bacteria are about a micrometre or more, so viruses are far smaller.

CCEA A-Level Life and Health Sciences 0008

Experimental Techniques

Topic overview Standard solutions, titrations and qualitative tests Rates of reaction and organic preparations Physics measurements: oscillations, resistivity, lenses and critical angle Biological tests, colorimetry, chromatography and osmosis

Human Body Systems

Topic overview Blood vessels, the heart and cardiac output Heart sounds, ECG traces, pulse and blood pressure Body fluids, haemoglobin and the Bohr effect The respiratory system, gas exchange and lung disease Monitoring breathing and lung volumes Cellular respiration and ATP Homeostasis, blood glucose and thyroxine Sodium, blood pH and oxygen saturation A balanced diet and nutritional needs through life Cholesterol, minerals, vitamins, alcohol and exercise

Physical Chemistry in Industrial Processes

Topic overview Moles, reacting masses and percentage yield Titration types, indicators and standard solutions Titration calculations and molarity Enthalpy changes and calorimetry Hess's law and average bond enthalpies Collision theory, rates and the Maxwell–Boltzmann distribution Catalysts, chemisorption and catalytic converters Reversible reactions, the Haber process and the Contact process Scale-up, costs and siting a chemical plant

Brain ScienceDouble Award

Topic overview Brain structure and frontal lobe damage Neurones, synapses and the endocrine system Alzheimer's disease, Huntington's disease and stem cell therapy Schizophrenia and mental health awareness in Northern Ireland The biology of aggression and methods of studying the brain Stress, the stress response and stress management Memory models, forgetting and eyewitness testimony Abnormality, phobias, depression and OCD Experiments, observations, self-report and research design Hypotheses, sampling, ethics and descriptive statistics

Material ScienceDouble Award

Topic overview Material properties and selection Stress, strain and the Young modulus Stress–strain graphs, creep and fatigue Density, hardness and conductivity testing Metals, ceramics, glasses, polymers and composites Atomic and microscopic structure of materials Alloys, annealing and biomaterials Smart materials Nanomaterials and semiconductors

Medicine, Drugs and Clinical TrialsDouble Award

Topic overview Categories of medicine and routes to drug discovery Medicines from natural sources, drug names and the ATC system Drug development, preclinical testing and the therapeutic index Phases of clinical trials and trial design Licensing, UK regulators, Yellow Card and trial ethics Formulations, routes of administration and drug absorption Distribution, metabolism, elimination and sites of drug action Quantitative analysis of medicines and antibacterial bioassays

Scientific Method, Investigation, Analysis and Evaluation

Topic overview The scientific method, literature reviews and Harvard referencing Descriptive statistics and the normal distribution Null hypotheses, significance and choosing a statistical test Investigation design, Design of Experiments and project plans Good Laboratory Practice, risk assessment and COSHH Experimental error, scientific writing and evaluation

Organic Chemistry

Topic overview Organic formulae, homologous series and functional groups IUPAC naming and types of organic reaction Structural isomerism and E/Z isomerism Alkanes from crude oil, combustion and halogenation Vehicle pollutants, catalytic converters and biofuels Alkenes, pi bonds and electrophilic addition Classifying alcohols, making ethanol and its effects as a drug Oxidation of alcohols, IR spectroscopy and mass spectrometry Addition polymers, plastic waste and nylon Preparing and purifying aspirin

Medical PhysicsA2 option

Topic overview Body temperature and clinical thermometers Blood pressure readings and the sphygmomanometer Heart activity experiments and EEG traces X-ray tubes, radiographs and CT scans Flexible endoscopes, optical fibres and lasers Ultrasound A-scans, B-scans and acoustic impedance MRI scanning and gamma camera imaging Alpha, beta and gamma radiation and half-life Radiopharmaceuticals, radiotherapy and radiation protection

Sound and LightA2 option

Topic overview Transverse and longitudinal waves and wave graphs Phase difference and the electromagnetic spectrum Outer, middle and inner ear Sound intensity and the decibel scale Standing waves, harmonics and resonance tubes Hearing response, phons and equal loudness curves Structure of the eye, rods and cones Accommodation, lens power and correcting long sight Total internal reflection and fibre-optic communication Dipole antennas, wireless networks and radar Attenuation of radio waves and the Doppler effect

Genetics, Stem Cell Research and CloningA2 option

Topic overview DNA structure and the evidence for the double helix RNA, genes and the triplet code Genotype, phenotype and monohybrid inheritance Dihybrid crosses, epistasis and the chi-squared test DNA replication and the Meselson–Stahl experiment Meiosis and genetic variation Insulin, factor VIII and chymosin from genetically modified microbes Recombinant DNA technology and gene cloning Genetic engineering, food supply and ethics Gene therapy and cystic fibrosis Genetic disease, screening and counselling Genetic fingerprinting and gel electrophoresis Stem cells, therapeutic cloning and their ethics

MicrobiologyDouble Award

Topic overview Bacteria, fungi and protozoa Viruses, viroids and prions Classifying bacteria, fungi and viruses Light and electron microscopy Laboratory safety, biocontainment and quality assurance Aseptic technique, growth media and inoculation Counting and measuring microbial growth Growth requirements and growth inhibition Antibiotics, PCR, gene therapy and pharmaceutical microbiology The gut microbiome in health and disease

Oral Health and DentistryDouble Award

Topic overview Structure of the mouth and the five basic tastes Salivary glands, saliva and the composition of teeth Ingestion, teeth and digestion in the mouth Dental caries and acid erosion Periodontal disease, tooth loss and dental antibiotics Dental materials, prosthodontics and the dental team

Histology and PathologyDouble Award

Topic overview Specimen processing, data protection and safety law Clinical biochemistry tests and electrophoresis Blood smears and identifying blood cells Blood grouping, cross-matching and transfusion Diagnostic and surveillance work in hospital microbiology Preparing and staining tissue sections Recognising tissues, atheroma and emphysema on slides

Analytical Chemistry TechniquesDouble Award

Topic overview Volumetric analysis in industry and healthcare Applied titrations of vinegar, indigestion tablets and bleach Redox titration of iron tablets and evaluating titrations Principles of colorimetry Colorimetric analysis of copper ore, aspirin and iron Thin-layer chromatography and its uses Visualising chromatograms and identifying painkillers and pigments Calorimetry and combustion Molar enthalpy and bond energy calculations Qualitative tests for cations and gases

Enabling TechnologyDouble Award

Topic overview ECG and EEG machines in patient monitoring Ultrasound and IVF equipment in fertility treatment Prosthetic limbs, hearing aids and cochlear implants Workflow and equipment in a medical laboratory Ongoing monitoring of a long-term condition Health data collection, databases and data protection

Microbiology

Viruses, viroids and prions

3 things to know
A2 6

Overview

Virus structure and replication, lysis and budding, bacteriophages, why antibiotics do not work on viruses, viroids, prions and prion diseases.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How does a virus replicate inside a host cell, and how are the new particles released?

Key term

What are the characteristic features of a virus?

Key term

Why are viruses not considered to be living cells?

Questions from this subtopic

Each one with the model answer underneath.

1
What are the characteristic features of a virus?
Model answer
A virus is a non-cellular particle made of DNA or RNA inside a protein coat called a capsid. Some viruses also have an outer lipid envelope.
2
Why are viruses not considered to be living cells?
Model answer
Viruses have no cytoplasm, ribosomes or metabolism of their own. Viruses can only replicate inside a living host cell.
3
Describe how a virus replicates inside a host cell.
Model answer
The virus attaches to the host cell and injects or releases its nucleic acid inside. The cell's machinery copies the viral genome and makes new capsids, and new virus particles are released.
4
How are new virus particles released from a host cell?
Model answer
Many viruses burst the cell open, a process called lysis, which kills the cell. Enveloped viruses often bud out through the cell membrane instead.
5
What is a bacteriophage?
Model answer
A bacteriophage is a virus that infects bacteria. Phages inject their DNA into the bacterium and often destroy it by lysis.
6
How large are viruses compared with bacteria?
Model answer
Most viruses are roughly 20 to 300 nanometres across. Most bacteria are about a micrometre or more, so viruses are far smaller.

See the rest and revise

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.

1Closed book

2Open book

3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Experimental Techniques

Human Body Systems

Physical Chemistry in Industrial Processes

Brain Science

Cram a whole paper in one sitting

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

One cubic equals 1000 cm³.

decimetremetrecentimetre

Blank Blitz makes facts automatic

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

AThe energy of all bonds broken is added up.

BThe energy of all bonds formed is subtracted.

CA negative answer shows an exothermic reaction.

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Acidosis means blood pH falling below 7.35.

TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Every question in Microbiology, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Start revising, £5 a month See how the method works

Or £46 a year, about £3.83 a month. Cancel anytime.