Homeostasis

Q1: How does the fossil record provide evidence for evolution?

The fossil record documents the history of life by preserving remains or traces of organisms in sedimentary rock. It shows: 1) a progression from simple to complex organisms over geological time, 2) transitional fossils linking major groups, 3) the appearance and extinction of species. Radiometric dating provides absolute ages of fossils.

Q2: Explain how comparative anatomy provides evidence for evolution.

Comparative anatomy reveals: Homologous structures — similar bone structure but different functions (e.g. human arm, whale flipper, bat wing), indicating common ancestry. Analogous structures — different structure but similar function (e.g. bird wing, insect wing), indicating convergent evolution. Vestigial structures — reduced or functionless remnants of once-functional organs (e.g. human appendix, whale pelvic bones).

Q3: How does molecular biology provide evidence for evolution?

Molecular evidence compares DNA sequences, amino acid sequences and proteins across species. Closely related species share more similar sequences than distantly related species. Molecular clocks estimate divergence times based on the rate of mutation accumulation. The universal genetic code (shared by all life) supports common ancestry.

Q4: What is biogeography and how does it support evolution?

Biogeography is the study of the geographic distribution of species. It supports evolution because: 1) closely related species are often found in nearby regions, 2) island species resemble mainland species but show unique adaptations, 3) continental drift explains why similar fossils are found on now-separated continents (e.g. Gondwanan distributions).

Q5: State the four conditions required for natural selection to occur.

1) Variation — individuals in a population differ in their traits. 2) Heritability — the variation has a genetic basis that can be inherited. 3) Differential survival and reproduction — some variants are better suited to the environment and produce more offspring. 4) Overproduction — more offspring are produced than can survive, creating competition for resources.

Q6: Distinguish between directional, stabilising and disruptive selection.

Directional selection: one extreme phenotype is favoured, shifting the population mean in one direction. Stabilising selection: intermediate phenotypes are favoured, reducing variation. Disruptive selection: both extreme phenotypes are favoured over the intermediate, potentially leading to bimodal distribution and speciation.

Q7: Explain allopatric speciation and give an Australian example.

Allopatric speciation occurs when a population is geographically separated (e.g. by a river, mountain range or sea-level change). The isolated populations experience different selection pressures and genetic drift, accumulating genetic differences over time until they can no longer interbreed — they become separate species.

Q8: What is sympatric speciation and how does it differ from allopatric?

Sympatric speciation occurs within the same geographic area without physical barriers. It can occur through polyploidy (especially in plants), habitat differentiation or temporal isolation. Unlike allopatric speciation, no geographic barrier separates the populations — reproductive isolation develops while populations overlap.

Q1: The fossil record provides a complete and unbroken history of all life on Earth.

Answer: FALSE

The fossil record is incomplete due to the rarity of fossilisation, destruction of fossils through geological processes, and bias toward organisms with hard body parts. It provides valuable but fragmentary evidence of evolutionary history.

Q2: Homologous structures have similar underlying anatomy but may serve different functions, indicating common ancestry.

Answer: TRUE

Homologous structures (e.g. human arm, whale flipper, bat wing) share a similar bone arrangement inherited from a common ancestor but have been modified for different functions through divergent evolution.

Q3: Analogous structures indicate that two species share a recent common ancestor.

Answer: FALSE

Analogous structures (e.g. bird wing and insect wing) have similar functions but different underlying anatomy. They result from convergent evolution — similar environmental pressures, not common ancestry.

Q4: Molecular comparisons of DNA and protein sequences can be used to construct phylogenetic trees.

Answer: TRUE

Species with more similar DNA/protein sequences are more closely related. The degree of molecular similarity reflects evolutionary distance, allowing construction of phylogenetic trees showing evolutionary relationships.

Q5: Natural selection acts on the genotype of an organism, not its phenotype.

Answer: FALSE

Natural selection acts on the PHENOTYPE (observable traits) because this is what interacts with the environment. Organisms are selected based on their physical characteristics, behaviour and physiology — which are expressions of their genotype.

Stimulus-Response Model

The stimulus-response pathway links a change in the environment to a coordinated body response. Learn the sequence: stimulus, receptor, sensory neuron, integration centre, motor neuron, effector, and response. Practise tracing specific examples such as the withdrawal reflex.

Feedback Mechanisms

Negative feedback returns a variable to its set point, while positive feedback amplifies a change until a process completes. Understand how negative feedback regulates body temperature, blood glucose and blood pressure, and how positive feedback operates during childbirth and blood clotting.

Thermoregulation

The hypothalamus acts as the body's thermostat, coordinating vasodilation, sweating, shivering and vasoconstriction. Study how endotherms and ectotherms differ in maintaining body temperature and relate these mechanisms to Australian wildlife examples.

Endocrine System and Hormonal Control

Hormones such as insulin, glucagon, ADH and adrenaline regulate internal conditions through chemical signalling. Learn how the endocrine system complements the nervous system and be prepared to compare their speed, duration and mode of action in exam responses.

What does WACE Biology Unit 4 Homeostasis cover?

Unit 4 Homeostasis covers the stimulus-response model, receptors and effectors, negative and positive feedback loops, thermoregulation, osmoregulation, glucose regulation, the roles of the nervous and endocrine systems in maintaining internal balance, and the consequences when homeostatic mechanisms fail.

What is a negative feedback loop in homeostasis?

A negative feedback loop is a regulatory mechanism where the output of a system opposes the original change, returning the variable to its set point. For example, when body temperature rises above 37 degrees Celsius, thermoreceptors detect the change and trigger sweating and vasodilation to cool the body back down.

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 Homeostasis, ensuring relevance to your WACE external examination.