KA 5: parasitism: parasitic life cycles

Question 1

some parasites require only…

Answer 1

one host to complete their life cycle

Question 2

many parasites require…

Answer 2

more than one host to complete their life cycle

Question 3

what is the definitive host?

Answer 3

the organism on or in which the parasite reaches sexual maturity

Question 4

what may also be required for the parasite to complete its life cycle?

Answer 4

intermediate hosts

Question 5

what is the role of a vector?

Answer 5

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

Question 6

what is the human disease malaria caused by?

Answer 6

plasmodium

Question 7

describe how the human disease malaria is caused by Plasmodium

Answer 7

• an infected mosquito (vector) bites a human
• plasmodium enters human bloodstream
• asexual reproduction occurs in 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

what causes the human disease schistosomiasis?

Answer 8

schistosomes

Question 9

describe schistosomes causing the human disease schistosomiasis

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

what are viruses?

Answer 10

parasites that can only replicate inside a host cell

Question 11

what do viruses contain?

Answer 11

genetic material (DNA or RNA, packaged in a protective protein coat)

Question 12

what are some viruses surrounded by?

Answer 12

a phospholipid membrane derived from host cell materials

Question 13

what does the outer surface of virus contain?

Answer 13

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

Question 14

list the viral cell cycle stages

Answer 14

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

Question 15

what does RNA retroviruses use to form DNA?

Answer 15

the enzyme reverse transcriptase, which is then inserted into the genome of the host cell

Question 16

what can viral genes be expressed to form?

Answer 16

new viral particles