Parasitism

Question 1

What is a fundamental niche?

Answer 1

A niche that a species occupies in absence of interspecific competition.

Question 2

What is a realised niche?

Answer 2

A niche a species occupies in response to interspecific competition.

Question 3

What can interspecific competition lead to?

Answer 3

Competitive exclusion

Question 4

What is competitive exclusion?

Answer 4

Competitive exclusion is where the niches of two species are so similar that one declines to local extinction.

Question 5

When does resource partitioning occur?

Answer 5

When the realised niches are sufficiently different,

Question 6

What is parasitism?

Answer 6

Parasitism is a symbiotic interaction between a parasite and its host in which the parasite benefits (+) in terms of nutrients at the expense of its host, which loses these (-).

Question 7

Which has the greater reproductive potential, the parasite or the host?

Answer 7

The parasite.

Question 8

Describe the niches of parasites.

Answer 8

Parasites have a narrow, specialised niche as they are very host-specific.

Question 9

What may happen to a parasite when the host provides so many of it’s needs?

Answer 9

They may become degenerate.

Question 10

What is meant by a parasite that is degenerate?

Answer 10

A parasite that is lacking structures and organs such as digestive systems.

Question 11

What is an ectoparasite?

Answer 11

A parasite that lives on the surface of its host.

Question 12

What is an endoparasite?

Answer 12

A parasite that lives within the tissues of its host.

Question 13

Explain what is meant by the definitive host.

Answer 13

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

Question 14

What is a vector?

Answer 14

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

Question 15

Explain the process of the parasite Plasmodium.

Answer 15

• an infected mosquito, acting as a vector, bites a human and plasmodium enters the bloodstream
• asexual reproduction occurs in the liver and then in the red blood cells, which burst burst to release gametocytes into the bloodstream
• if a mosquito bites an infected human, gametocytes enter the mosquito, maturing into male and female gametes, allowing sexual reproduction to occur.

Question 16

Explain the process of Schistosomes.

Answer 16

Schistosomes reproduce sexually in the human intestine and fertilised eggs pass out via faeces into water where they develop into larvae that infect water snails, where asexual reproduction occurs reproducing another type of motile larvae that escape the snail and penetrate the skin of humans, entering the bloodstream.

Question 17

What are viruses?

Answer 17

Viruses are parasites that can only replicate inside a host cell.

Question 18

Explain the structure of a virus.

Answer 18

Viruses contain genetic material in the form of RNA or DNA, packaged ina protective protein coat (capsid). Some virsues are surrounded by a phospholipid membrane derived from host mammal cells. The outer surface of a virus contains antigens that a host cell may or may not be able to detect as foreign.

Question 19

What do RNA retroviruses use to form DNA?

Answer 19

The enzyme reverse transcriptase.

Question 20

Explain the process of viral multiplication.

Answer 20

• viruses adheres to cell surface
• viral material, including genetic material, enters cell
• viral genetic information replicated, transcribed and translated (is inserted into host DNA for this to happen)
• new viral particles assembled then released from cell.

Question 21

What is meant by transmision?

Answer 21

Transmission is the spread of a parasite to a host.

Question 22

What is virulence?

Answer 22

The harm caused to a host species by a parasite.

Question 23

How are ectoparasites generally transmitted?

Answer 23

Through direct contact or by comsumption of intermediate hosts.

Question 24

How are endoparasites often transmitted?

Answer 24

By vectors.

Question 25

Explain some of the factors which increase transmission rates.

Answer 25

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

Question 26

What do parasites do to host behaviour?

Answer 26

They often exploit and modify them to maximise transmission.

Question 27

What do alteration of host foraging, movement, sexual behaviour, habitat choice or anti-predator behaviour become part of?

Answer 27

The extended phenotype of the parasite.

Question 28

What do parasites often do to benefit parasite growth, reproduction or transmission?

Answer 28

Suppress the host immune system and modify host size and reproductive rate.

Question 29

State the 5 types of responses in the non-specific defences.

Answer 29

• physical barriers
• chemical secretions
• inflammatory response
• phagocytes
• NK cells

Question 30

Give an example of a physical barrier in non-specific defences.

Answer 30

Epithelial tissues blocks the entry of pathogens.

Question 31

Give some examples of chemical secretions in non-specific defence.

Answer 31

• hydrolytic enzymes in mucus, saliva and tears destroy bacterial cell walls
• low pH environments created by the secretions of the stomach, vagina and sweat glands denature the cellular proteins of pathogens.

Question 32

Breifly explain the inflammatory response.

Answer 32

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

Question 33

Briefly explain the process of phagocytosis.

Answer 33

Phagocytes engulf pathogens into a vacuole and release powerful enzymes, contained in lysosomes.

Question 34

Briefly explain what natural killer cells do.

Answer 34

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

Question 35

What kinds of cell constantly circulate the blood, monitoring the tissue?

Answer 35

A range of white blood cells.

Question 36

What do cells release if tissues become damaged or invaded and explain what these do.

Answer 36

Cells release cytokines that increase blood flow, resulting in non-specific and specific white blood cells accumulating at the site of infection or tissue damage.

Question 37

What do lymphocytes have on their surfaces? And what do they do?

Answer 37

They have receptors that can potentially recognise a parasite antigen.

Question 38

How is a clonal population produced?

Answer 38

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

Question 39

What are the two different functions carried out by the two different lymphocytes?

Answer 39

One can produce antibodies while the other can induce apoptosis in parasite infected cells.

Question 40

Explain the structure of antibodies and why this is important.

Answer 40

Antibodies possess regions where the amino acid sequence varies greatly between different antibodies; this variable region gives the antibodies its specificity for binding to an antigen.

Question 41

Other than a clonal population being formed what else happens once an antibody binds to an antigen.

Answer 41

The antigen-antibody complex is formed, which can result in the inactivation of the parasite, rendering it susceptible to a phagocyte, or it can stimulate a response that results in cell lysis.

Question 42

What does inital antigen exposure produce?

Answer 42

Memory lymphocytes.

Question 43

What can memory lymphocytes prodcue?

Answer 43

A secondary response when the same antigen enters the body in the future. In a secondary response, antibody production is enhanced in terms of speed of production, concentraion in the blood and duration.

Question 44

Explain some of the ways that parasites have evolved to evade the immune system.

Answer 44

• some endoparasites minic host antigens to evade detection and modify the host immune response to reduce their chances of destruction
• antigen variation = allows them to change antigens during the course of an infection of a host, may allow reinfection of same host with new variant
• latency = integrating their genome into host genomes, existing in an inactive state and virus emeges when favourable conditions arise.

Question 45

What is the study of outbreak and spread of infectious disease called?

Answer 45

Epidemiology

Question 46

What is meant by the herd immunity threshold?

Answer 46

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

Question 47

Explain some difficulties of treatment and control of viruses.

Answer 47

• the similarities between host and parasite metabolism makes it hard to mind drug compounds that only target the parasite
• antigenic variation makes vaccines tricky to make
• some parasites difficult to culture in laboratory

Question 48

Give an example of overcrowding that increase transmission of virus and that make co-ordinated treatment and control programmes difficult.

Answer 48

In refugee camps that result from war or natural disasters, or rapidly growing cities in less economically developed countries (LEDCs).

Question 49

When vaccines are difficult to produce or roll out what other strategies can be used?

Answer 49

Civil engineering projects to improve sanitation, combined with co-ordinated vector control.

Question 50

What does improvemnts in parasite control lead to?

Answer 50

Reductions in child mortality and population-wide improvements in child development and intelligence, as individuals have more resources for growth and development.