Biology Practice Test: Viruses and Bacteria

A virus is genetic material enclosed in a protein coat called a capsid, and some also have an outer envelope. It has no cytoplasm, ribosomes or organelles.

Viruses have no metabolism of their own and must use a host cell's machinery to make copies. Being small is not a rule for life, since many bacteria are tiny too.

Antibiotics target parts of bacterial cells. The flu is caused by a virus, which has no cell wall or ribosomes of its own, so the drug has nothing to act on.

In the lysogenic cycle the viral DNA hides in the host's chromosome and is passed on with it. In the lytic cycle the virus makes new viruses right away and bursts the cell.

In binary fission a bacterium copies its single circular chromosome and splits into two identical cells. Mitosis, meiosis and fertilization happen only in eukaryotes.

Rod-shaped bacteria are bacilli. Round bacteria are cocci, spiral-shaped bacteria are spirilla, and comma-shaped bacteria are vibrios.

Lactobacillus ferments the sugar in milk into lactic acid, which thickens it into yogurt. The other options describe bacteria that cause illness or tooth decay.

Conjugation is the direct transfer of DNA, often a plasmid, from one bacterium to another. It helps antibiotic resistance spread quickly between bacteria.

An endospore is a tough, dormant structure with a thick coat around the DNA. It can survive conditions that kill active cells and becomes an active cell again when conditions improve.

Reverse transcriptase copies the viral RNA into DNA, which is the reverse of normal transcription. This DNA is then inserted into the host cell's chromosome.