2.5b Parasitic life cycles

Question 1

Explain the number of hosts that parasites need to complete their life cycles?

Answer 1

• some only need one
• many need more than one

Question 2

Explain vectors in parasitic life cycles

Answer 2

A vector plays an active role in the transmission of the parasite and may also be a host

Question 3

What is the human disease malaria called?

Answer 3

plasmodium

Question 4

What causes the human disease schistosomiasis?

Answer 4

Schistosomes

Question 5

What are viruses?

Answer 5

Parasites that can only replicate inside a host cell

Question 6

Explain the structure of a virus

Answer 6

• they contain genetic material in the form of DNA or RNA, packaged in a protective protein coat
• Some viruses are surrounded by a phospholipid membrane derived from host cell
  materials
• The outer surface of a virus contains antigens that a host cell may or may not be able to
  detect as foreign

Question 7

What are the viral life cycle stages?

Answer 8

• infection of host cell with genetic material
• host cell enzymes replicate viral genome
• transcription of viral genes and translation of viral proteins
• assembly and release of new viral particles

Question 9

How do RNA retroviruses work?

Answer 9

They use the enzyme reverse transcriptase to form DNA, which is then inserted into the genome of the host cell

Question 10

What is the definitive host?

Answer 10

the organism on or in
which the parasite reaches sexual maturity

Question 11

What is the intermediate host?

Answer 11

Intermediate hosts may also be required for
the parasite to complete its life cycle.

Question 12

What is the life cycle of malaria?

Answer 12

• An infected mosquito, acting as a vector, bites a human.
• Plasmodium enters the
  human bloodstream.
• Asexual reproduction
  occurs in the liver and then in the red blood
  cells.
• When the red blood cells burst gametocytes are released into the
  bloodstream.
• Another mosquito bites an infected human and the gametocytes enter the mosquito, maturing into male and female gametes, allowing sexual reproduction to
  now occur.
• The mosquito can then infect another human host.

Question 13

What is the life cycle of schistosomiasis?

Answer 13

• Schistosomes reproduce sexually in the human intestine.
• The fertilised eggs pass out via faeces into water where they develop into
  larvae.
• The larvae then infect water snails, where asexual reproduction occurs.
• This produces another type of motile larvae, which escape the snail and penetrate the skin of a human, entering the bloodstream.