unit 2 key area 5- parasitism

from course spec (plus chat gpt add ons for additional key terms)

define an ecological niche 

multi-dimensional summary of tolerances and requirements of a species. 

define fundamental niche

a niche that a species occupies in the absence of any interspecific competition. 

define a realised niche 

niche occupied in response to interspecific competition. 

What is competitive exclusion 

As a result of interspecific competition the niches of two species are so similar that one declines to local extinction. 

what is resource partitioning?

The process by which different species in an ecological community use a limited resource in different ways, places, or at different times, to avoid direct competition and allow for their stable coexistence. Potential competitors can co-exist.

define parasitism

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

True or false? is the reproductive potential of a parasite greater than that of the host

true

Describe a parasites niche

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

Why are many parasites degenerate, lacking structures and organs found in other organisms?

Because the host provides so many of the parasite’s needs, many parasites have lost the need for certain structures and organs.

what is an ectoparasite 

lives on the surface of its host 

what is an endoparasite

lives within the tissues of its host

Q: What type of parasites require only one host to complete their life cycle?

A: Parasites that have a direct life cycle require only one host.

Q: What type of parasites require more than one host to complete their life cycle?

A: Parasites with an indirect life cycle require more than one host.

Q: What is the role of a vector in a parasitic life cycle?

A: A vector plays an active role in transmitting the parasite and may also serve as a host.

Q: Which parasite causes the human disease malaria?

A: Malaria is caused by Plasmodium.

Q: Which parasites cause the human disease schistosomiasis?

A: Schistosomiasis is caused by Schistosomes.

Q: What is unique about viruses in terms of replication?

A: Viruses can only replicate inside a host cell.

Q: What is the structure of a virus composed of?

A: Viruses contain genetic material (DNA or RNA) packaged in a protective protein coat.

Q: What additional structure do some viruses have surrounding their protein coat?

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

Q: What is found on the outer surface of a virus that helps determine host recognition?

A: Viral antigens, which a host cell may or may not recognize as foreign.

Q: What are the main stages of a viral life cycle?

Infection of host cell → Replication of viral genome by host enzymes → Transcription and translation of viral genes → Assembly and release of new viral particles.

Q: What enzyme do RNA retroviruses use to form DNA from RNA?

A: They use the enzyme reverse transcriptase.

Q: What happens to the DNA formed by reverse transcriptase in RNA retroviruses?

A: It is inserted into the genome of the host cell.

Q: How do viral genes lead to the production of new viruses?

A: Viral genes are expressed by the host cell to form new viral particles.

What is transmission in relation to parasites?

Transmission is the spread of a parasite to a host

what is virulence

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

how are ectoparasites generally transmitted 

through direct contact 

how are endoparasites of body tissues often transmitted?

they are often transmitted by vectors or be consumption of intermediate hosts.

what factors can increase transmission rates of parasites? (2)

1. overcrowding of hosts at high density

2. mechanisms such as vectors or waterborne dispersal stages that all spread even when hosts are incapacitated.

how do parasites exploit host behaviour to aid transmission?

Parasites can alter or exploit host behaviour to maximise their own transmission. 

What is meant by the ‘extended phenotype’ of a parasite?

It refers to changes in the host’s behaviour caused by the parasite’s transmission.

In what way can parasites manipulate their host’s biology to benefit themselves?

They can suppress the host’s immune system and modify the host’s size or reproductive rate to enhance parasite growth, reproduction, or transmission.

Q: What are the two main aspects of the immune response in mammals?

A: The immune response has both non-specific and specific aspects.

Q: What are examples of non-specific defences in mammals?

A: Physical barriers, chemical secretions, the inflammatory response, phagocytes, and natural killer cells that destroy virus-infected cells.

Q: What do non-specific defences protect against?

A: They act as general defences against a wide range of pathogens, not just specific ones.

Q: What cells are responsible for specific cellular defences?

A: A range of white blood cells (lymphocytes) that monitor body tissues.

Q: What happens when tissues become damaged or invaded?

A: Cells release cytokines that increase blood flow, leading to accumulation of non-specific and specific white blood cells at the infection or injury site.

Q: What are lymphocytes and what role do they play in immunity?

A: Lymphocytes are white blood cells that have surface receptors capable of recognising specific parasite antigens.

Q: What happens when an antigen binds to a lymphocyte receptor?

A: That lymphocyte is selected to divide and form a clonal population of identical cells.

Q: What do the selected lymphocytes do after clonal expansion?

A: Some produce antibodies, while others induce apoptosis (programmed cell death) in parasite-infected cells.

Q: What gives antibodies their specificity?

A: Antibodies have variable regions where the amino acid sequence differs greatly between antibodies, allowing them to bind specific antigens.

Q: What happens when an antibody binds to its specific antigen?

A: An antigen–antibody complex forms, which can inactivate the parasite, make it susceptible to phagocytosis, or trigger cell lysis.

Q: What are memory lymphocytes?

A: Cells formed after infection that remain in the body to provide long-term immunity by responding quickly to future infections by the same pathogen.

Q: Why have parasites evolved immune evasion mechanisms?

A: To avoid detection and destruction by the host’s immune system.

Q: How do endoparasites evade the immune system?

A: They can mimic host antigens and modify the host’s immune response to reduce their chances of destruction.

Q: What is antigenic variation and how does it benefit parasites?

A: Antigenic variation is when parasites change their surface antigens during infection to evade immune detection; it can also allow re-infection of the same host with a new variant.

Q: How do some viruses escape immune surveillance?

A: They integrate their genome into the host’s DNA and remain inactive in a latent state.

Q: What happens when a latent virus becomes active again?

A: It resumes replication and causes infection when favourable conditions arise.

Q: What is epidemiology?

A: The study of the outbreak and spread of infectious diseases.

Q: What is the herd immunity threshold?

A: The density of resistant hosts in a population required to prevent an epidemic.

Q: What do vaccines contain and how do they work?

A: Vaccines contain antigens that elicit an immune response, preparing the immune system to fight future infections.

Q: Why is it difficult to design drugs that target parasites?

A: Because host and parasite metabolisms are very similar, making it hard to find drugs that harm the parasite but not the host.

Q: How does antigenic variation affect vaccine design?

A: Vaccines must account for antigenic variation since parasites can change their surface antigens.

Q: Why are some parasites difficult to develop vaccines for in the lab?

A: Because some parasites are difficult to culture under laboratory conditions.

Q: In what environments do parasites tend to spread most rapidly?

A: In overcrowded conditions and tropical climates.

Q: Why are treatment and control programs challenging in such environments?

A: Overcrowding and poor infrastructure make coordinated efforts difficult to achieve.

Q: What combined strategies can help control parasites in such regions?

A: Civil engineering projects to improve sanitation and coordinated vector control programs.

Q: What are the long-term benefits of improved parasite control?

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

(AKT) Q: What are cytokines?

A: Cytokines are signalling proteins released by damaged or infected cells that increase blood flow and attract white blood cells to the site of infection.

AKT Q: What is apoptosis?

A: Apoptosis is programmed cell death — a controlled process where infected or damaged cells are deliberately destroyed to prevent infection spread.

AKT Q: What is the variable region of an antibody?

A: The variable region is the part of an antibody where the amino acid sequence differs between antibodies, giving each antibody its specific antigen-binding ability.

AKT Q: What is an antigen–antibody complex?

A: It is the structure formed when an antibody binds to a specific antigen, which can neutralise the pathogen or signal it for destruction.

AKT Q: What is meant by cell lysis?

A: Cell lysis is the breaking or bursting of a cell’s membrane, leading to cell death, often caused by immune responses or viral replication.

AKT Q: What does mimic host antigens mean in relation to parasites?

A: It means the parasite produces molecules similar to the host’s own antigens so the immune system fails to recognise it as foreign.

AKT Q: What is antigenic variation?

A: Antigenic variation is when a parasite changes its surface antigens during infection to avoid being recognised by the host’s immune system.

AKT Q: What is immune surveillance?

A: Immune surveillance is the constant monitoring of the body by immune cells to detect and eliminate infected or abnormal cells.

AKT Q: What is latency in viral infections?

A: Latency is an inactive state in which a virus’s genome remains in the host’s DNA without producing new viruses until conditions become favourable.

AKT Q: What is epidemiology?

A: Epidemiology is the study of how infectious diseases originate, spread, and can be controlled within populations.

AKT Q: What is a vector in disease transmission?

A: A vector is an organism (such as a mosquito or tick) that actively transmits a parasite from one host to another.

AKT Q: What does herd immunity threshold mean?

A: It’s the minimum proportion of immune individuals in a population required to stop the spread of an infectious disease.

AKT Q: What does antigenic variation has to be reflected in vaccine design mean?

A: It means vaccines must target several antigen variants because the parasite’s surface antigens can change over time.

AKT Q: What does vector control mean?

A: Vector control refers to methods that reduce or eliminate organisms (like mosquitoes) that spread disease-causing parasites.

AKT Q: What are civil engineering projects in the context of disease control?

A: These are large-scale public works, such as improved sanitation systems or clean water supplies, that reduce parasite transmission.

AKT Q: What is meant by host metabolism and why is it relevant to parasite treatment?

A: Host metabolism refers to the chemical processes in host cells; because parasites share many of these pathways, it’s hard to design drugs that kill parasites without harming the host.

AKT Q: What is the extended phenotype?

A: The extended phenotype is when a parasite influences or alters a host’s behaviour or physiology in ways that benefit the parasite’s survival or transmission.