2.5b - Parasitic Life Cycles

Question 1

Some parasites require only one…

Answer 1

host to complete their life cycle

Question 2

Many parasites require more than one…

Answer 2

host to complete their lifecycle

Question 3

The definitive host is…

Answer 3

the organism on or in which the parasite reaches sexual maturity

Question 4

Intermediate hosts may also be required for…

Answer 4

the parasite to complete its life cycle

Question 5

A vector plays…

Answer 5

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

Question 6

The human disease malaria is caused by…

Answer 6

Plasmodium

Question 7

Malaria life cycle

Answer 7

• an infected mosquito, acting as a vector, bites an infected human and the gametocytes enter the 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 8

Schistosomes cause…

Answer 8

the human disease schistosomiasis

Question 9

Schistosomiasis life cycle

Answer 9

• 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

Question 10

Viruses are…

Answer 10

parasites that can only replicate inside a host cell

Question 11

Viruses contain…

Answer 11

genetic material in the form of DNA or RNA, packaged in a protective protein coat

Question 12

Some viruses are surrounded by…

Answer 12

a phospholipid membrane derived from the host materials

Question 13

The outer surface of a virus contains…

Answer 13

antigens that a host cell may or may not able to detect as foreign

Question 14

Viral life cycle stages:

Answer 14

• 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 15

RNA retroviruses use the enzyme reverse transcriptase to form…

Answer 15

DNA, which is then inserted into the genome of the host cell

Question 16

Viral genes can then be…

Answer 16

expressed to form new viral particles