U2)KA5)- the parasite niche and lifecycle

Question 1

what is an ecological niche

• definition
• more detailed explanation

Answer 1

• an ecological niche is a multi dimensional summary of tolerances and requirements of a species
• ecological niche - attempts to summarise all factors that influence the distribution of individual species. At the simplest level is described as the role an organism plays in the living community. eg ‘woodland herbivore’
• factors that should be considered are abiotic factors (temp, ph , light intensity humidity) and biotic interactions (predator-prey interactions, competition , parasitism)

Question 2

what is interspecific and intraspecific competition

Answer 2

interspecific - occurs between individuals of different species
intraspecific- occurs between individuals of the same species

Question 3

what is the

• fundamental niche
• realised niche

Answer 3

• fundamental niche of a species is the set of resources that it is capable of using in the absence of any interspecific competition
• the realised niche is the set of resources that the species actually uses in response to the presence of interspecific competition

Question 4

fundamental and realised niche basic definition

Answer 4

• a species has a fundamental niche that it occupies in the absence of any interspecific competition
• a realised niche is occupied in response to interspecific competition

Question 5

explain the competitive exclusion principle

Answer 5

• in some cases of interspecific competition , the realised niche of the two species is so similar that one species will lose out more in the competition , so its population will decline , leading to local extinction

Question 6

example of competitive exclusion principle

Answer 6

grey squirrels which were introduced in the UK , are able to eat seeds from deciduous trees before they are fully ripe and so are able to out compete red squirrels in these habitats

Question 7

what is resource partitioning and give an example

Answer 7

• where two species living in a habitat have similar requirements it may be that the realised niches are sufficiently different so that they can co exist.
  ( resource partitioning can occur when the two species exploit different components / parts of the resource so reducing potential competition
  (eg evolution of different beak lengths and foraging behaviours in waders has allowed various species to exploit food at different depths in their shared habitat)

Question 8

what is symbiosis

Answer 8

symbiosis is co evolved and intimate relationship between 2 different species.

Question 9

what is parasitism

Answer 9

• parasitism is a symbiotic intereaction between a parasite and its host , which can be described using a +/- /0 notation.
• the parasite benefits + in terms of nutrients at the expense - of its host

Question 10

how does the parasite gain benefit in terms of nutrients at the expense of the host
what other expenses does the host have to deal with

Answer 10

• the parasite uses the hosts resources for growth and reproduction
• as well as losing resources the host incurs further costs in defending its tissue from parasitic attack ( technically the parasite is harmful to the host)

Question 11

who’s reproductive potential is greater - the parasite or host

Answer 11

the reproductive potential of the parasite is greater than that of the host

Question 12

• most parasite have a specialised niche as they are very ____ ______
• as the host provides so many of the parasites needs , many parasites are degenerate , what does this mean?

Answer 12

• host specific

- they lack the structure and organs found in other organisms

Question 13

what are

• ectoparasites
• endoparasites

Answer 13

• ectoparasites live and feed on the surface of their host (eg ticks, lice, fleas)
• Endoparasites live within the host ( eg tapeworm , plasmodium (causes malaria) , rhinovirus (causes common cold)

Question 14

some parasites require only one host to complete their life cycle. many parasitic lifecycles can involve more than one species.
what is
- definitive host
- intermediate host

Answer 14

• the definitive host is the organism on which or in which the parasite reaches sexual maturity and so carries out sexual reproduction
• an intermediate host is one in which developmental stages happen to complete the parasites life cycle.

Question 15

what are vectors

Answer 15

• species in the parasite lifecycle that play an active part in the transmission of the parasite. they can also be hosts
  eg the mosquito is the vector for the malarial parasite and it is also the definitive host. but vectors are not always hosts : aphids are vectors for plant viruses , but the viruses have no lifecycle stages in the aphids

Question 16

what is malaria caused by

Answer 16

caused by an endoparasite called plasmodium

Question 17

how does malaria pass to a human

Answer 17

an infected mosquito (acting as a vector and definitive host) bites a human (the intermediate host)

Question 18

plasmodium enters the human bloodstream in _____ in the bite

Answer 18

saliva

Question 19

why does the plasmodium parasite have to spend time in the human

Answer 19

the parasites have to spend time in the human so that they can develop into male and female forms ready to infect a mosquito , its definitive host

Question 20

malaria - parasite in body cycle

Answer 20

1) - an infected mosquito acting as a vector and the definitive host ,bites the human - the intermediate host
- plasmodium ( the endoparasite) then enters the bloodstream in saliva in the bite
2) parasites reproduce asexually in liver then in red blood cells. red blood cells burst and gametocytes are released into the bloodstream ( parasites are now in male and female forms)
3) another mosquito bites the infected human and the gametocytes enter its body , and mature into male and female gametes and so allowing fertilisation and sexual reproduction to occur.
- the zygote develops in the mosquitos gut , the mosquito can infect another human host when it bites

Question 21

what causes schistosomiasis

Answer 21

the schistosomiasis parasite causes the human disease schistosomiasis

Question 22

schistosomiasis cycle

Answer 22

1) schistosomiasis reproduce sexually in the human intestine (making the human the primary host)
2) their fertilised eggs pass out via faeces into water where they develop into larvae
3) the larvae then infect water snails, the intermediate host, where asexual reproduction occurs producing another type of motile larvae.
4) they then escape the snail into the water and penetrate the skin of humans wading in the water and enter their bloodstream

Question 23

what are viruses

Answer 23

• infectious parasites that can only replicate inside a host cell ( can only reproduce in a living organism)

Question 24

what is the structure of a virus

• what do they contain
• what are they surrounded by
• what does the outer surface contain

Answer 24

• viruses contain genetic info stored in a nucleic acid (DNA or RNA) , which is packaged inside a protective protein coat (capsid)
• some viruses are surrounded by a phospholipid membrane derived by host cell materials.
• the outer surface of a virus contains antigens( these are coded for by viral genes) that host cells might be able to detect as foreign

Question 25

DNA viruses - what are they

examples

Answer 25

• DNA viruses have their genetic material in the form of DNA
• include smallpox, herpes, chickenpox

Question 26

how do DNA viruses reproduce steps

Answer 26

1) virus (its antigens) attach to the surface of the host cell and infect the host cell with genetic material
2) host enzymes replicate the virus genome
3) virus genes are transcribed to RNA , which is then translated to make viral proteins including coats
4) replicated viral genes and new coats are assembled to form new viral particles that can be released by the host cell

Question 27

RNA viruses
example
how it reproduces

Answer 27

• RNA viruses have an RNA genome
• eg influenza, Ebola , C polio, measles
• reproduces the exact same way , apart from the fact that the viral RNA genome is replicated directly using an enzyme from the virus (viral DNA is never made)

Question 28

RNA retrovirus

Answer 28

eg HIV

Question 29

RNA retrovirus cycle

what does RNA retrovirus use

Answer 29

1) virus antigens attach to host cell surface
2) Virus RNA inserted into host cell
3) Viral enzyme called reverse transcriptase reads viral RNA to form DNA , and so newly formed DNA is inserted into genome of host cell
4) Virus genes are transcribed to RNA which is translated to make viral protein coats
5) new virus particles are assembled and burst out of host cell

• RNA retrovirus uses the enzyme reverse transcriptase to form DNA which is then inserted in the genome of the cell