Infectious Disease

Q1: Distinguish between biotic and abiotic factors in an ecosystem.

Biotic factors are the living components of an ecosystem — producers, consumers, decomposers, parasites and their interactions (predation, competition, mutualism). Abiotic factors are the non-living physical and chemical components — temperature, rainfall, light intensity, soil type, pH, salinity, wind and nutrient availability.

Q2: Define the terms habitat, niche and community.

Habitat: the physical environment where an organism lives (its "address"). Niche: the functional role of an organism in its ecosystem, including what it eats, when it is active, how it reproduces and its interactions with other species (its "job"). Community: all the populations of different species living and interacting in the same area at the same time.

Q3: Explain the difference between a food chain and a food web.

A food chain is a single linear pathway showing the flow of energy from one organism to the next (producer → primary consumer → secondary consumer → tertiary consumer). A food web is a network of interconnected food chains showing the complex feeding relationships within an ecosystem, providing a more realistic picture of energy flow.

Q4: Name and describe the four main trophic levels.

1) Producers (autotrophs) — photosynthetic organisms (plants, algae, cyanobacteria) that convert light energy to chemical energy. 2) Primary consumers (herbivores) — eat producers. 3) Secondary consumers (carnivores/omnivores) — eat primary consumers. 4) Tertiary consumers (top predators) — eat secondary consumers. Decomposers (bacteria, fungi) break down dead organisms at all levels, recycling nutrients.

Q5: Explain the 10% rule and why energy decreases at each trophic level.

Approximately only 10% of energy at one trophic level is transferred to the next. The remaining ~90% is lost as: heat from cellular respiration, energy used for life processes (movement, growth, reproduction), energy in uneaten parts, and energy in undigested waste (faeces). This progressive energy loss limits food chains to typically 4-5 trophic levels.

Q6: What is the difference between gross primary productivity and net primary productivity?

Gross primary productivity (GPP) is the total amount of energy (or carbon) fixed by photosynthesis in producers per unit area per unit time. Net primary productivity (NPP) is GPP minus the energy used by producers for their own respiration: NPP = GPP − R. NPP represents the energy available for consumption by primary consumers.

Q7: Describe the carbon cycle, including the role of photosynthesis and respiration.

The carbon cycle moves carbon through the biosphere, atmosphere, hydrosphere and lithosphere. Key processes: Photosynthesis removes CO₂ from the atmosphere, converting it to organic carbon in producers. Respiration (all organisms) releases CO₂ back to the atmosphere. Decomposition releases carbon from dead organisms. Combustion of fossil fuels releases stored carbon. Ocean absorption dissolves atmospheric CO₂.

Q8: Outline the nitrogen cycle and explain the role of nitrogen-fixing bacteria.

The nitrogen cycle converts nitrogen between forms: 1) Nitrogen fixation — N₂ converted to NH₃ (ammonia) by nitrogen-fixing bacteria (Rhizobium in legume root nodules, or free-living Azotobacter). 2) Nitrification — NH₃ oxidised to NO₂⁻ then NO₃⁻ by nitrifying bacteria (Nitrosomonas, Nitrobacter). 3) Assimilation — plants absorb NO₃⁻ to make amino acids/proteins. 4) Ammonification — decomposers convert organic nitrogen back to NH₃. 5) Denitrification — bacteria convert NO₃⁻ back to N₂ gas.

Q1: Temperature, rainfall and soil pH are examples of biotic factors in an ecosystem.

Answer: FALSE

Temperature, rainfall and soil pH are abiotic (non-living) factors. Biotic factors are living components such as producers, consumers, decomposers and their interactions.

Q2: An organism's niche describes its functional role in the ecosystem, including its feeding relationships and habitat requirements.

Answer: TRUE

A niche encompasses an organism's complete ecological role — what it eats, what eats it, when and where it is active, how it reproduces, and all its interactions with biotic and abiotic factors.

Q3: A food web provides a less accurate representation of feeding relationships than a single food chain.

Answer: FALSE

A food web is MORE accurate than a single food chain because it shows the complex, interconnected feeding relationships in an ecosystem. Food chains oversimplify by showing only one linear pathway.

Q4: Producers (autotrophs) form the first trophic level in all ecosystems.

Answer: TRUE

Producers (plants, algae, photosynthetic bacteria) are always the first trophic level because they convert light energy into chemical energy through photosynthesis, forming the base of all food chains.

Q5: Approximately 90% of energy at one trophic level is transferred to the next level.

Answer: FALSE

Only approximately 10% of energy is transferred between trophic levels. The remaining ~90% is lost as heat from respiration, used for life processes, or lost in undigested waste.

Pathogen Types and Transmission

Pathogens include bacteria, viruses, fungi, prions and parasites, each with distinct structures and modes of infection. Study how diseases spread through direct contact, droplets, vectors, contaminated food and water. Understand Koch's postulates for establishing a causal link between a microorganism and a disease.

Innate Immune System

The first line of defence includes physical barriers (skin, mucous membranes) and chemical barriers (lysozyme, stomach acid, antimicrobial peptides). The second line involves phagocytes, natural killer cells, the complement system and the inflammatory response. These defences are rapid but non-specific.

Adaptive Immune System

The adaptive immune response involves B lymphocytes producing specific antibodies and T lymphocytes (helper and cytotoxic) coordinating and executing targeted attacks. Study clonal selection, immunological memory, and the difference between humoral and cell-mediated immunity.

Epidemiology and Disease Prevention

Epidemiology tracks disease patterns in populations using incidence, prevalence and mortality rates. Study vaccination principles (herd immunity, active vs passive immunity), antibiotic resistance mechanisms, quarantine measures and public health strategies for controlling outbreaks.

What does WACE Biology Unit 4 Infectious Disease cover?

Unit 4 Infectious Disease covers types of pathogens (bacteria, viruses, fungi, prions, parasites), modes of transmission, Koch's postulates, innate immunity (physical and chemical barriers, phagocytes, inflammation), adaptive immunity (B cells, T cells, antibodies, immunological memory), vaccination, epidemiology, disease prevention and the impact of emerging diseases on global health.

What is the difference between innate and adaptive immunity?

Innate immunity provides immediate, non-specific defence through physical barriers (skin, mucous membranes), chemical barriers (lysozyme, stomach acid) and cellular responses (phagocytes, natural killer cells, inflammation). Adaptive immunity is slower but highly specific, involving B lymphocytes that produce antibodies and T lymphocytes that destroy infected cells, and it creates immunological memory for faster future responses.

Are these flashcards aligned to the SCSA WACE syllabus?

Yes — every flashcard and quiz question is mapped to the SCSA Biology ATAR Unit 4 syllabus content for Infectious Disease, ensuring relevance to your WACE external examination.