38 - Viruses

To be accompanied with past exam questions

Explain the difficulty in describing viruses as living organisms

Non-cellular or no metabolism

Name the two biochemical components that make up all viruses

Protein

Nucleic acid (or DNA or RNA)

Describe the process of viral replication

Virus attaches or DNA enters / DNA replication and protein synthesis / using host cell organelles / viruses assembled / viruses released

Give two examples of a harmful virus

Common cold virus or coronavirus or HIV or hepatitis virus

Give one way in which viruses can be beneficial

Can be used in genetic engineering or vaccine production

Give a brief biological explanation for the following:

Doctors do not prescribe antibiotics for viral infections

Antibiotics do not affect viruses or antibiotics only kill bacteria

Distinguish between the terms asepsis and sterility, as applied to living organisms

Asepsis: Free from pathogens

Sterility: Free from microorganisms

The diagram shows a typical spherical-shaped virus.

Name the structures B and Y

X: protein coat

Y: nucleic acid

Explain the term obligate parasite

Needs a host cell //

to reproduce

Antigens are present in viruses. On the diagram, draw an arrow from ‘X’ to accurately show the location of an antigen

Explain in detail the term vaccination

What it is: Administration of a non-disease causing dose of a pathogen

What it does: Stimulates production of antibodies or stimulates active immunity or stimulates memory cells

True or False:

A virus particle contains both DNA and RNA

False

Viruses can be classified based on their shape.

Name any two shapes of viruses

Round / rod / complex

Immunity is the ability to resist infection. Name two types of induced immunity

Active

Passive

Why type of immunity occurs after vaccination?

Active

Give one difference between active and passive immunity

Active is longer lasting than passive

or active the body makes antibodies and passive the body receives antibodies

Name one virus that causes disease in plants

Mosaic (virus)

How do scientists distinguish between different viruses?

Shape of coat or type of nucleic acid or antibody reaction or size or host species or structure

Viruses are difficult to classify into a kingdom. Why is this so?

Non cellular or no cell organelles