Topic 16: Respiration

Electron acceptors

molecules that combine with electrons liberated during metabolic processes

reduction

a gain of electrons or hydrogen atoms

red color

• results indicating nitrite is present

red color

nitrate is reduced to nitrite by zinc (not bacterium)

enzyme catalase breaks down hydrogen peroxide to water and oxygen

catalase test

What are electron acceptors?

molecules that combine with electrons liberated during metabolic processes

What process forms electrons?

ionization of a hydrogen atom

What is reduction?

a gain of electrons or hydrogen atoms

When an electron acceptor picks up an electron, it becomes ___

negatively charged and combines with positively charge hydrogen ion

What act as electron acceptors in fermentative metabolism?

organic molecules

What act as electron acceptors in anaerobic respiration (aka oxidative metabolism)?

inorganic molecules

What acts as electron acceptor in aerobic respiration?

O2

Some bacteria can reduce nitrate to ___ or further reduce to ___ or ___.

nitrities; nitrous oxide; nitrogen gas

What is used to determine a bacterium's ability to reduce nitrates?

nitrate broth

In aerobic bacteria, what carries electrons to the final electron acceptor, O2?

cytochromes

How many classes of bacterial cytochromes are there?

4

What is used to determine the presence of cytochrome c?

oxidase test

Hydrogen atoms combine with oxygen to form ___ which is lethal to the cell.

hydrogen peroxide (H2O2)

What test is used to see if bacterium breaks down hydrogen peroxide to water and oxygen through enzymes?

catalase test