Cells 29

What is binary fission?

Asexual reproduction in which one bacterial cell divides into two genetically identical daughter cells.

What type of reproduction do prokaryotes use?

Asexual reproduction by binary fission.

What is the first step of binary fission?

Chromosome replication begins.

What happens after chromosome replication during binary fission?

The origins move apart as the cell elongates.

What forms before bacterial cell division is completed?

A septum.

What is produced at the end of binary fission?

Two genetically identical daughter cells.

Why are prokaryotes so dominant?

Fast growth, rapid adaptation, and metabolic/ecological diversity.

Why does fast bacterial growth matter?

It allows rapid evolution and antimicrobial resistance.

What is a closed batch culture system?

A microbial culture system with limited nutrients.

Why does growth eventually stop in a closed batch culture?

Nutrients become depleted and waste accumulates.

What are the four phases of microbial growth?

Lag, exponential (log), stationary, and death phases.

What happens during the lag phase?

Cells adapt to the environment and prepare for growth.

What determines the length of the lag phase?

The history of the inoculum.

What happens during exponential (log) phase?

Cells divide at a constant maximum rate.

Why is exponential phase important clinically?

Cells are most metabolically active and sensitive to antibiotics.

What happens to the population during log phase?

It doubles at regular intervals.

What happens during stationary phase?

Growth rate equals death rate.

Why is stationary phase considered dynamic?

Cells are still dividing and dying.

What causes stationary phase?

Nutrient depletion and waste accumulation.

What is cryptic growth?

Surviving cells consume nutrients released from dead cells.

What happens during death phase?

Death rate exceeds growth rate.

What do batch culture assays measure?

The average behaviour of cells.

What are the 3 major requirements for microbial growth?

Carbon source, energy source, and reducing power.

What is the role of a carbon source?

Provides building blocks for macromolecule synthesis.

What is the role of an energy source?

Provides energy/electrons for metabolism.

What is reducing power?

Electron carriers used in metabolism such as NADH and NADPH.

What is ATP?

The main energy currency of the cell.

How is energy released from ATP?

ATP is hydrolysed to ADP + Pi.

What are redox reactions?

Oxidation-reduction reactions involved in energy transfer.

What is catabolism?

Breakdown reactions that release energy.

What does catabolism produce?

ATP and building blocks.

What is anabolism?

Biosynthetic reactions that consume energy.

What is the difference between catabolism and anabolism?

Catabolism breaks down molecules and releases energy; anabolism builds molecules and uses energy.

How are microbes classified into trophic groups?

By their carbon source and energy source.

What are photoautotrophs?

Organisms that use light for energy and CO2 as a carbon source.

Give examples of photoautotrophs.

Plants, algae, and cyanobacteria.

What are chemoautotrophs?

Organisms that obtain energy from chemicals and carbon from CO2.

What are photoheterotrophs?

Organisms that use light for energy and organic compounds for carbon.

What are chemoheterotrophs?

Organisms that obtain energy and carbon from organic compounds.

Give examples of chemoheterotrophs.

Animals, fungi, and many bacteria.

What is an auxotroph?

An organism unable to synthesize an essential growth factor.

Why can’t auxotrophs grow independently?

They lack genes needed to synthesize essential compounds.

What is a wild-type strain?

An organism with all essential genes that can grow independently.

What is cross-feeding (syntrophy)?

When one species uses metabolic products produced by another species.

Why is cross-feeding important?

It allows auxotrophs and microbial communities to survive.

Why are many microbes difficult to culture?

Many depend on nutrients provided by other microbes.

What is microbiota?

The individual microbial species in an environment.

What is a microbiome?

The complete collection of microorganisms and their genes in an environment.

What are culture-dependent methods?

Methods that rely on growing microbes in the lab.

What are the advantages of culture-dependent methods?

Access to phenotype, manipulation of conditions, and study of individual organisms.

What are the disadvantages of culture-dependent methods?

Many microbes cannot be cultured and lab conditions may not reflect nature.

What are culture-independent methods?

Methods that study microbes without culturing them.

What are the advantages of culture-independent methods?

Can study entire communities and unculturable organisms.

What are the disadvantages of culture-independent methods?

Expensive, complex, and cannot manipulate pure cultures.

What is metagenomics?

Sequencing to determine which organisms are present.

What is metatranscriptomics?

Studying what microbial communities are doing functionally.

What is metabolomics?

Studying metabolites and by-products produced by microbes.

What happens to nutrients in a closed batch culture over time?

They become limited.

What is the main energy storage molecule in cells?

ATP.

What is the relationship between ATP and ADP?

ATP releases energy when converted to ADP + Pi.

Why are microbes important in ecosystems?

They colonise nearly all ecosystems and drive energy and nutrient flow.