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Advanced Higher Biology > Unit 2: Key Area 5 - Parasitism > Flashcards

Unit 2: Key Area 5 - Parasitism Flashcards

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1
Q

Define an ecological niche

A

An ecological niche is a multi-dimensional summary of tolerances and requirements of a species

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2
Q

Why do species have a niche

A

A species has a fundamental niche that it occupies in the absence of any interspecific competition

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3
Q

Define a realised niche

A

A realised niche is occupied in response to interspecific competition

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4
Q

What is a result of interspecific competition

A

As a result of interspecific competition, competitive exclusion can occur, where the niches of two species are so similar that one declines to local extinction

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5
Q

What happens when realised niches are sufficiently different

A

Where the realised niches are sufficiently different, potential competitors can co-exist by resource partitioning

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6
Q

Define Parasitism

A

Parasitism is a symbiotic interaction between a parasite and its host (+/-)
A parasite gains benefit in terms of nutrients at the expense of its host

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7
Q

Describe the relationship of a parasite and host

A

Unlike in a predator-prey relationship, the reproductive potential of the parasite is greater than that of the host

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8
Q

Describe parasite niches

A

Most parasites have a narrow (specialised) niche as they are very host-specific

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9
Q

Compare a ectoparasite to an endoparasite

A

An ectoparasite lives on the surface of its host, whereas an endoparasite lives within the tissues of its host

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10
Q

What is the result of the host providing resources for the parasite

A

As the host provides so many of the parasite’s needs, many parasites are degenerate, lacking structures and organs found in other organisms

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11
Q

How many hosts do parasites require in their life cycle

A

Some parasites require only one host to complete their life cycle
Many parasites require more than one host to complete their life cycle

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12
Q

Define a definitive host

A

The definitive host is the organism on or in which the parasite reaches sexual maturity.

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13
Q

Define an intermediate host

A

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

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14
Q

Describe the role of a vector

A

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

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15
Q

How is the human disease malaria caused

A

The human disease malaria is caused by Plasmodium

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16
Q

Describe how malaria is caused in humans

A
  • 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.
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17
Q

What causes the human disease schistosomiasis

A

Schistosomes cause the human disease schistosomiasis

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18
Q

Describe how schistosomiasis is caused in humans

A
  • 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.
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19
Q

Define a virus

A

Viruses are parasites that can only replicate inside a host cell

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20
Q

Describe the inner structure of viruses

A

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

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21
Q

What are some viruses surrounded by

A

Some viruses are surrounded by a phospholipid membrane derived from host cell materials

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22
Q

Describe

a) the outer surface of a virus structure
b) how a host can detect the virus is not a part of itself

A

a) The outer surface of a virus contains antigens

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

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23
Q

Describe the stages of the Viral life cycle stages (how new viruses are made within a host cell)

A

Viral life cycle stages:

  • 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
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24
Q

Describe

a) what enzyme RNA retroviruses use
b) what effect does this enzyme have
c) what happens after this enzyme is used

A

a) RNA retroviruses use the enzyme reverse transcriptase
b) to form DNA, which is then inserted into the genome of the host cell
c) Viral genes can then be expressed to form new viral particles

25
Q

Define Transmission

A

Transmission is the spread of a parasite to a host

26
Q

Define Virulence

A

Virulence is the harm caused to a host species by a parasite

27
Q

What factors increase transmission rates

A

Factors that increase transmission rates:

  • the overcrowding of hosts when they are at high density
  • mechanisms, such as vectors and waterborne dispersal stages, that allow the parasite to spread even if infected hosts are incapacitated
28
Q

What do parasites often do to maximise transmission

A

Host behaviour is often exploited and modified by parasites to maximise transmission

29
Q

What happens to the host’s behaviour afterwards

A

The host behaviour becomes part of the extended phenotype of the parasite

30
Q

How else does the parasite use its host to benefit itself

A

Alteration of host foraging, movement, sexual behaviour, habitat choice or anti-predator behaviour

31
Q

What type of immune responses do mammals have

A

Immune response in mammals has both non-specific and specific aspects

32
Q

Give examples of non-specific defences

A
  • Physical barriers
  • chemical secretions
  • inflammatory response
  • phagocytes
  • natural killer cells destroying cells infected with viruses
33
Q

Give an example of a physical barrier response within the body

A

Epithelial tissue (skin) blocks the entry of parasites

34
Q

Give examples of chemical secretion responses within the body

A
  • hydrolytic enzymes in mucus, saliva and tears destroy bacterial cell walls
  • low pH environments of the secretions of stomach,
    vagina and sweat glands denatures cellular proteins of pathogens
35
Q

Describe why does more blood flow to the site of wounds and what the blood carries

A

Injured cells release signalling molecules. This results in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes

36
Q

Describe the process of phagocytosis

A

Killing of parasites using powerful enzymes contained in lysosomes, by engulfing them and storing them inside a vacuole in the process of phagocytosis

37
Q

What do natural killer cells do

A

Natural killer cells can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis

38
Q

Which cells constantly circulate to monitor body tissues as part of a specific cellular defence

A

Specific cellular defences

A range of white blood cells constantly circulate, monitoring the tissues

39
Q

Describe what happens

a) If tissues become damaged or invaded what do the cells release
b) what is the result of this

A

a) If tissues become damaged or invaded, cells release cytokines
b) that increase blood flow resulting in non-specific and specific white blood cells accumulating at the site of infection or tissue damage

40
Q

Describe

a) the structure of lymphocytes
b) what does it do

A

a) Mammals contain many different lymphocytes, each possessing a receptor on its surface
b) which can potentially recognise a parasite antigen

41
Q

What happens as a result of a binding of an antigen to a lymphocyte’s receptor

A

Binding of an antigen to a lymphocyte’s receptor selects that lymphocyte to then divide and produce a clonal population of this lymphocyte

42
Q

What do selected lymphocytes produce

A

Some selected lymphocytes will produce antibodies, others can induce apoptosis in parasite-infected cells

43
Q

What do regions of antibodies posses

A

Antibodies possess regions where the amino acid sequence varies greatly between different antibodies

44
Q

What does the variable region give the antibody

A

This variable region gives the antibody its specificity for binding antigen

45
Q

Describe

a) what is formed when the antigen bind to the binding site of the antibody
b) what are the 2 results

A

a) When the antigen binds to this binding site the antigen-antibody complex formed
b) (1) can result in inactivation of the parasite, rendering it susceptible to a phagocytes,
(2) or can stimulate a response that results in cell lysis (bursting)

46
Q

Describe

a) what else can be formed from antigen-antibody binding
b) how?
c) how is this of advantage to the host

A

a) Memory lymphocyte cells are also formed
b) Initial antigen exposure produces memory lymphocyte cells specific for that antigen that can produce a secondary response when the same antigen enters the body in the future.
c) When this occurs antibody production is enhanced in terms of speed of production, concentration in blood and duration.

47
Q

Parasites have evolved ways of evading the immune system to reduce their chances of being detected. How do endoparasites do this?

A

Endoparasites mimic host antigens to evade detection and modify host immune response to reduce their chances of destruction

48
Q

Describe

a) antigenic variation in parasites
b) give another advantage of antigenic variation for parasites

A

a) Antigenic variation in some parasites allows them to change between different antigens during the course of infection of a host
b) It may also allow re-infection of the same host with the new variant

49
Q

Describe latency

A

Some viruses escape immune surveillance by integrating their genome into host genomes, existing in an inactive state known as latency

50
Q

When does latency end

A

Latency ends when favourable conditions arise resulting in the virus becoming active again

51
Q

What is epidemiology

A

Epidemiology is the study of the outbreak and spread of infectious disease

52
Q

What is herd immunity threshold

A

The herd immunity threshold is the density of resistant hosts in the population required to prevent an epidemic

53
Q

Why are vaccines important during an epidemic

A

As vaccines contain antigens that will elicit an immune response

54
Q

Why is it difficult to design a vaccine

A

Because the similarities between host and parasite metabolism makes it difficult to find drug compounds that only target the parasite
AND
Antigenic variation has to be reflected in the
design of vaccines
AND
Some parasites are difficult to culture in the laboratory making it difficult to design vaccines

55
Q

What conditions make co-ordinated treatment and control programs difficult to achieve

A

Challenges arise where parasites spread most rapidly as a result of overcrowding (condition 1) or tropical climates (condition 2)

56
Q

How and where can overcrowding occur

A

Overcrowding can occur in refugee camps that result from war or natural disaster or rapidly growing cities in LEDCs.

57
Q

What are often the only practical control strategies

A

Civil engineering projects to improve sanitation combined with co-ordinated vector control may often be the only practical control strategies

58
Q

What are the wider impacts of controlling a parasite within a population

A

Improvements in parasite control reduce child mortality and result in population-wide improvements in child development and intelligence, as individuals have more resources for growth and development

Advanced Higher Biology (12 decks)

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