Microorganisms

Question 1

Bacteria

Answer 1

• Single-celled microorganism
• Prokaryotic and do not have a nucleus
• They are very small

Question 2

Structure of a Bacterium

Answer 2

• Ribosomes: Produces proteins from mRNA
• Cell wall: Supports cell and is made of glycoproteins
• Plasma membrane: Contains mesosome folds
• Slime capsule: Protects the bacteria and allows easy access
• Plasmids: Small loops of DNA
• Bacterial chromosome: Long, circular coiled strand contains the genetic information
• Pili: Short hair like structures and allow the transfer of genes
• Flagellum: A Long structure that rotates to move the bacterium

Question 3

Viruses

Answer 3

• Nucleic acids surrounded by a protein coat
• Smaller than bacteria
• They have no plasma membrane, cytoplasm or ribosomes

Question 4

Structure of Viruses

Answer 4

• DNA or RNA: The genetic material
• Protein coat: Also called the capsid
• Envelope: Stolen membrane from a previous host cell
• Attachment proteins: Stick out from the capsid allowing the virus to bind to host cell
• Proteins: Some carry proteins eg Reverse Transcriptase

Question 5

Pathogens

Answer 5

A pathogen is any organism that causes disease. A disease caused by a pathogen is called an infectious disease.

4 types of Pathogens:

• Virus
• Bacteria
• Fungi
• Protozoa

Question 6

How do Pathogens cause disease?

Answer 6

They do this in 2 ways:

• Damage cells: Pathogens reproduce quickly and cause damage to cells and cell walls causing them to lyse and burst.
• Produce Toxins: Harmful substances that poison the tissues and enzymes

Question 7

Good Microorganisms

Answer 7

Gut flora and skin flora: These compete with pathogens for space and nutrients, lowering the number of pathogens

Question 8

How do pathogens invade the body?

Answer 8

• Ingestion: Eating or drinking contaminated substances
• Inhalation: Inhaling contaminated particles
• Direct contact: Through cuts in the skin
• Fomites: By touching infected objects eg toilets

Question 9

Barriers to Infection:

Answer 9

• Stomach Acid: The PH of stomach acid is so acidic that pathogens will be destroyed in the stomach
• Skin: This acts as a physical barrier to pathogens however if the skin is damaged, blood clots can form to protect the wound.
• Gut and Skin Flora: Compete with pathogens for space and nutrients
• Lysozyme: Mucosal surfaces contain the enzyme Lysozyme that kills bacteria by damaging the cell wall

Question 10

Bacterial Reproduction

Answer 10

Asexual Reproduction:
- When a bacteria reaches a certain size it’s DNA replicates and the cell wall breaks down. A septum is created with the new cell membrane and eventually, the bacteria splits into 2 cells.

Sexual Reproduction:

• Genes are transferred between the bacteria
• Transformation: Short DNA pieces are taken up by another bacteria
• Transduction: Bacteriophage transfers DNA to another bacteria

Question 11

Viral Reproduction

Answer 11

Viruses can ONLY reproduce in host cells. They use vectors or host cells to replicate.

• Lysogenic pathway:
• Virus inserts DNA into a host cell and is replicated
• Viral repressor protein is produced so mRNA is not formed and genetic material is not translated
• Lytic Pathway:
• Viral DNA is independently replicated
• Mature viruses are made and host cell bursts
• This releases viruses that invade other cells.

Question 12

Retroviruses

Answer 12

These contain viral RNA. Reverse Transcriptase translates this into DNA