Unit 2 - section 5 Flashcards
What is a parasite?
An organism that forms a symbiotic relationship with a host where it benefits at the expense of the host
What is a host?
An organism that harbours a parasite
How common are parasites?
At least 50% of all species are parasitic
How likely are free living organisms to be hosts?
All free living organisms are thought to be hosts
Compare the reproductive potential of host-parasites to predator-prey relationships
When compared to predator-prey relationships the reproductive potential of the parasite is much greater than that of the host
What is an ecological niche?
A complex outline of the tolerances and requirements of a species
Why do parasites have a narrow niche?
Due to high host specificity
Why do parasites have limited structures?
Parasites are degenerate, lacking in structures and organs found in other organisms, because the host provides many of the parasites needs
Compare ectoparasites and endoparasites
Ectoparasites live on the surface of their host eg fleas on cats
Endoparasites live inside their hosts eg tapeworms live in hosts intestine
Compare definitive and intermediate hosts
Definitive - host the organism reaches sexual maturity in/on
Intermediate - host the organism completes some part of its lifecycle in/on
What is a vector?
An organism that plays a role in the transmission of the parasite. Vectors can also be hosts
Describe the two types of niche
Fundamental - niche the organism occupies when there is no other species competing for space or resources
Realised - niche the organism occupies when there is competition from other species
What is competitive exclusion?
When two different species occupy similar niches and are in intense competition with each other the weaker of the two species may die out
What is resource partitioning?
When competing species occupy different realised niches compromising over resources and managing to exist simultaneously
What do transmission and virulence mean?
Transmission is the spread of a parasite to a host
Virulence is the deleterious effect the parasite has on the host
What are 2 qualities of a successful parasite?
Easily transmitted
Evolve rapidly
What factors increase transmission rate of parasites?
Host density is high
Parasite has mechanisms of transmission even when the host is incapacitated
What are 5 aspects of host behaviour that can be altered to exploit the parasite phenotype?
Foraging Movement Sexual behaviour Habitat choice Anti-predator behaviour
Why do parasites often suppress the immune system, size and reproductive rate of the host?
For their own benefit
Describe the distribution of parasites
Non-uniformly
How does parasites having both sexual and asexual phase benefit them in terms of evolution rates?
Allows for rapid evolution and rapid population growth
What are the non-specific barriers mammals have to parasites?
Physical barriers Chemical secretions Inflammatory response Phagocytes Natural killer cells
Describe the process of phagocytosis
Phagocytes are special white blood cells that engulf parasites by enfolding their plasma membrane around the membrane.
The parasite is brought into the phagocyte in a vacuole or vesicle. Phagocytes contain organelles called lysosomes that are filled with digestive enzymes. The lysosomes fuse with the vacuole, releasing the digestive enzymes allowing the enzymes to digest the parasite
What is specific cellular defence?
Responses that are triggered when non-specific responses fail. The response will be specific to the foreign antigen present
What are the 2 types of lymphocytes and what are their roles?
B lymphocytes - produce specific antibodies in response to foreign antigens
T lymphocytes - destroy specific cells or damaged tissue by bringing about cell apoptosis
What is clonal selection of lymphocytes?
Where lymphocytes become amplified with some clones being used for immediate defence and other clones acting as memory cells
What are immunological memory cells?
Cloned lymphocytes that remain in the body allowing it to respond faster if the individual is exposed to the same antigen a second time
What is epidemiology?
The study of the outbreak and spread of infectious diseases
What is herd immunity threshold?
The number of resistant members needed to prevent an epidemic
What are the possible parasite responses to host responses?
Mimicking host antigens
Modifying host-immune response
Antigenic variation
Why do parasites mimic host antigens?
Allows them to evade detection
Why do parasites modify host-immune response?
To suppress the hosts immune system
Why do parasites change their outer antigens?
To evade detection as they change quicker than the host immune system can keep up with
What are the 6 common types of parasites and give examples of each?
Protists - Protozoa, algae, diatoms Plathyhelminthes - flatworms Nematodes - roundworms Arthropods - ectoparasites Bacteria - TB, cholera Viruses - colds, flu
What are two examples of parasites that require more than one host?
Malaria
Schistosomiasis
How are endoparasites and ectoparasites of the main body cavities transited?
Direct contact or by consumption of secondary hosts
How are endoparasites of body tissues often transmitted?
By vectors
Give examples of parasites that can complete their lifecycle in one host
Ectoparasitic arthropods
Endoparasitic protists
Bacteria and viruses
Give an example of a bacterial human disease
Tuberculosis
Give two examples of viral human diseases
Influenza
HIV
What is a virus?
A tiny infectious agent that can only replicate inside a host
What form is genetic information found in viruses?
DNA or RNA packaged in a protective protein coat
Describe the basic structure of a virus
Viruses are composed of a protein coat around some form of nucleus acid (DNA/RNA). Some viruses also have a lipid membrane made out of host resources. The antigens in this protein coat may or may not be recognised by the host immune system
What is a rectotransposon?
Segment of DNA that carries off reverse transcription before being inserted into a new site on the genome
What is thought to be the origin of retrotransposons in the eukaryotic genome?
Retroviruses
What is the role of retrotransposons in host immunity?
??
What is a retrovirus?
They are thought to be the origin of retrotransposons in the eukaryotic genome
What enzyme is involved in DNA formation in retroviruses?
Reverse transcriptase
What are the 3 challenges faced in the treatment and control of parasites?
Some parasites are difficult to culture in the laboratory
Rapid antigen change has to be reflected in the design of vaccinations
Similarities between host and parasite metabolism makes it difficult to find drug compounds that only target the parasite without negatively affecting the host
What are 2 practical control strategies for parasites?
Civil engineering projects to improve sanitation
Coordinated vector control
Under what conditions do parasites thrive and what impact does this have on certain countries in the world?
Thrive in tropical climates and areas where there is overcrowding.
Has the greatest impact on countries where they face the difficulties of war/refugee camps, aftermath of natural disasters or rapidly growing cities in the least developed countries
What are 2 advantages of improving parasite control?
Reduce child mortality
Allows improvement in child development and intelligence
