Asexual reproduction in which the parent cell divides in two budding 2. the ability of a virus to cause disease fermentation 3. an organism or substance that causes disease conjugation 4. sexual reproduction in some protozoans pathogen 5. the breakdown of complex molecules into simpler ones symbiosis 6. a mutually positive arrangement between species homeostasis

1. Budding is a type of asexual reproduction in which the parent cell divides in two. A new organism develops from the bud and it is genetically identical to its parent. This type of reproduction is characteristic for the yeast.

2. Virulence is the ability of a virus to cause a disease. It refers to ability of a virus (or bacteria) to infect or damage a host organism. Virulence is determined by its virulence factors (products of the viruses).

3. Pathogen is an organism or substance that causes disease. It is usually an infectious microorganism such as a virus, bacterium or protozoa. Disease-causing capacity of pathogens is called pathogenicity.

4. Conjugation is type of sexual reproduction in some protozoans. It includes the exchange of genetic material through a bridge between two protozoan organisms. Two filaments of opposing mating types come close together, conjugation tube is formed and then one cell balls up and crawls through the tube into the other cell. The fusion forms a zygote.

5. Fermentation is the breakdown of complex molecules into simpler ones. It refers to metabolic processes of carbohydrates, which are broken down in the absence of oxygen via the action of enzymes. It is the main source of ATP producing anaerobically in microorganisms.

6. Symbiosis is a mutually positive arrangement between species. Symbiosis can be obligatory (when one or both of the symbionts entirely depend on each other for survival) or facultative (when they can generally live independently).

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.