2.5b Parasitic life cycles Flashcards
One host
Some parasites require only one host to complete their life cycle.
Many hosts
Some parasites require more than one host to complete their life cycle. Definitive host and intermediate host.
The definitive host definition
is the organism on or in which the parasite reaches sexual maturity.
The intermediate host definition
The host that the parasite might require in order to complete its life cycle.
Vector
A vector plays an active role in the transmission of the parasite and mat also be a host.
Causing of malaria
An infected mosquito, acting as a vector, bites a human. Plasmodium enters the human bloodstream. Asexual reproduction occurs in the liver and then 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.
Causing of schistosomiasis
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.
What are viruses?
Viruses are parasites that can only replicate inside a host cell.
DNA virus life cycle stages
Virus antigens attach to host cell surface
infection of host cell with genetic material
host cell enzymes replicate viral genome
transcription of viral genes and translation of viral proteins assembly
release of new viral particles.
RNA retroviruses
RNA retroviruses use the enzyme reverse transcriptase to form DNA, which is then inserted into the genome of the host cell.
Viral genes can the be expressed to form the new viral particles.
What is a virus structure?
They contain genetic info stored in nucleic acid (DNA or RNA). The nucleic acid is packaged inside a protective protein coat (capsid). And some are surrounded by a phospholipid membrane derived of the hosts materials.
What are antigens?
Antigens are on the outer surface of a virus. They are proteins that are coded for by the viral genes.
RNA viruses life cycle?
Virus antigens attach to host cell surface
infection of host cell with RNA genetic material
Viral enzyme reverse transcriptase reads viral RNA to form DNA.
Newly formed viral DNA is inserted into genome of host cell.
Virus genes are transcribed to RNA which is translated to make viral protein coats.
New virus particles are assembled and burst out of host cell.
