Look through the passages. Title them using the given titles.

Structure of viruses	General characteristics	Spread of viruses
Origin of viruses	Treatment of viral diseases

1.____________________________. A virus is a biological agent that reproduces inside the cells of living hosts. When infected by a virus, a host cell is forced to produce many thousands of identical copies of the original virus, at an extraordinary rate. Unlike most living things, viruses do not have cells that divide; new viruses are assembled in the infected host cell. Over 2,000 species of viruses have been discovered.

2.____________________________.A virus consists of two or three parts: genes, made from either DNA or RNA, long molecules that carry the genetic information; a protein coat that protects the genes; and some viruses have an envelope of fat that surrounds and protects them when they are not contained within a host cell. Viruses vary in shape from the simple helical and icosahedral to more complex structures. Viruses are about 100 times smaller than bacteria.

3.____________________________.Viruses spread in many different ways. Plant viruses are often spread from plant to plant by insects and other organisms, known as vectors. Some viruses of animals are spread by blood-sucking insects. Each species of virus relies on a particular method. Influenza viruses are spread through the air by people when they cough or sneeze, noroviruses are transmitted by the faecal-oral route, contaminate hands, food and water. Rotavirus is often spread by direct contact with infected children. Human Immuno-deficiency Virus HIV, is transmitted during sexual contact and by the exposure of infected blood.

4._____________________________.The origins of viruses is unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria.

5._____________________________.Viral infections often cause disease in humans and animals, however they are usually eliminated by the immune system. Examples of common human diseases caused by viruses include the common cold, influenza, chickenpox and measles. Many serious diseases such as AIDS and hepatitis are caused by viruses. Antibiotics have no effect on viruses, but antiviral drugs have been developed to treat life-threatening infections. Vaccines that produce lifelong immunity can prevent some viral infections.

3.Translate the 1^stpassage into Russian.

Read the 2d passage and do the tasks A and B.

A. Name three parts of a virus.

1.______________________ 2.________________________ 3._____________________

B. Complete the sentences and translate them.

1. Genes are made of __________________________________________________

2. Genes are __________________________________________________________

3. A protein coat ______________________________________________________

4. An envelope of fats __________________________________________________

5. Viruses may be ______________________________________________________

Read the 3d passage. Say if the statements are true or false. Correct the mistakes. Translate the sentences.

1. Viruses spread in different ways.

2. Plant viruses are often spread by vectors.

3. Some viruses of animals are spread by butterflies.

4. Influenza viruses are spread through the food by people when they cough or sneeze.

5. Noroviruses are transmitted by the faecal-oral route, contaminate hands, food and water.

6. Rotavirus is often spread by indirect contact with infected children.

7. Human Immuno-deficiency Virus HIV is transmitted during sexual contact and by the exposure of infected blood.

6.Read the 4^thand 5^thpassages. Answer the questions. Translate the answers.

1. Where have viruses evolved from?

2. What do viral infections cause?

3. What system eliminates viruses?

4. What diseases are caused by viruses?

5. What drugs can help to treat viral infections?

6. What can prevent some viral infections?

Fill in the gaps using the given words.

long molecules / helical / eliminate / viral infections / protects / influenza / protein coat / measles / genetic / complex / prevent / surrounds / antiviral drugs

A virus consists of two or three parts: genes, a _____________ and an envelope of fat. DNA or RNA are _________ that carry the ___________ information. A protein coat ________ the genes. An envelope of fat __________ and protects viruses. Viruses may be __________ and icosahedral or have more _________ structures. __________________ cause diseases in human and animals. Common colds, ___________, chicken-pox and _____________ are caused by viruses. The immune system helps to ______________ viruses. ________________ treat viral infections. Vaccines can ____________ some viral infections.

TOPIC 42. BACTERIA

Do you know that the term bacteria was introduced in the 19th century by the German botanist Ferdinand Cohn (1828-98)? Studying this topic you’ll be able to enrich your knowledge about bacteria, their shapes, habitant and influence on the living organisms.