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8.2Unit 4: Living organisms and classification

Viruses — Cambridge Checkpoint Biology 0893 Revision Notes & Topical Questions

5 min read 10 parts Lesson 2 of 5 1 quiz

📚 Cambridge Checkpoint Biology 0893 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Lesson summary

8.2 Viruses — CHECKPOINT BIOLOGY 0893 notes: Describe the structure of a virus, explain how viruses replicate and cause disease, and describe how the spread of viral diseases can be reduced.A virus is a very small particle, much smaller than a bacterium.It can only be seen with a…

  • Vaccination
  • Electron microscope
  • Viruses have no nucleus, cytoplasm, cell membrane or mitochondria
  • Viruses are not made of cells
  • They do not carry out the life processes, such as respiration, nutrition and growth, on their own
  • Many scientists say that viruses are not living

Part 1 of 8Structure of a virus

1
A virus is a very small particle, much smaller than a bacterium.
2
It can only be seen with an electron microscope.
3
A virus has a protein coat surrounding a small amount of genetic material (RNA or DNA).
  • Pegs or spike proteins on the coat help the virus attach to cells.
4
Viruses have no nucleus, cytoplasm, cell membrane or mitochondria.

Part 2 of 8Are viruses living?

1
Viruses are not made of cells.
2
They do not carry out the life processes, such as respiration, nutrition and growth, on their own.
3
Many scientists say that viruses are not living.
4
Viruses do carry coded genetic instructions and can reproduce, but only inside a living host cell.

Part 3 of 8How a virus reproduces

1
The virus attaches to the surface of a host cell.
2
The virus gets its genetic material into the cell.
3
The cell is forced to copy the genetic material and make many new viruses.
4
New virus particles are assembled inside the cell.
5
The cell bursts and releases many viruses, which infect nearby cells.
How a virus reproduces
This damage to cells causes the symptoms of disease.
A pathogen is a microorganism that causes disease.

Part 4 of 8Examples of viral diseases

  • The common cold.
  • Influenza (flu).
  • Measles.
  • COVID-19.
  • HIV/AIDS.
  • Tobacco mosaic virus affects plants.

Part 5 of 8Spread of viral diseases

Spread of viral diseases
Viruses spread by droplets in the air from coughs and sneezes.
They also spread by direct contact, contaminated surfaces, body fluids and animal vectors.

Part 6 of 8Reducing the spread

  • Wash hands.
  • Cover coughs and sneezes.
  • Isolate infected people.
  • Wear masks.
  • Vaccinate large numbers of people.

Part 7 of 8Vaccination

1
A harmless form of the pathogen (dead, weakened or part of it) is introduced into the body.
2
The immune system makes antibodies and memory cells.
3
If the person is infected later, they are protected and immune.
4
A vaccine does not give the disease and it does not kill the virus directly.

Part 8 of 8Treatment

Treatment
Antibiotics do not kill viruses, because they only work on bacteria.
Some antiviral drugs exist.

Key terms

TermMeaning
VirusA very small particle with a protein coat and genetic material, which reproduces only inside living cells.
PathogenA microorganism that causes disease.
VaccinationGiving a harmless form of a pathogen so the body makes antibodies and memory cells.
AntibodyA protein made by the immune system to fight a pathogen.
Host cellA living cell that a virus uses to reproduce.
Electron microscopeA microscope powerful enough to see a virus.

Avoid these mistakes

1
Saying viruses are tiny bacteria — viruses are much smaller than bacteria and are not cells.
2
Saying antibiotics kill viruses — antibiotics only kill bacteria.
3
Saying the vaccine gives you the disease — it contains a harmless form of the pathogen.
4
Saying viruses reproduce by dividing — they reproduce only inside host cells.
5
Saying the vaccine kills the virus — it causes the body to make antibodies.

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