Year 11 Biology – Semester 1 Exam Revision Answers

SCIENTIFIC METHOD VARIABLES

• Independent Variable: This is the variable that is deliberately changed by the experimenter to test its effect.

• Dependent Variable: This is the variable that is measured or observed in response to changes in the independent variable.

• Controlled Variables: These are variables that are kept constant to ensure that the experiment is fair and that the results are valid.

POPULATION SAMPLING & SURVEYING TECHNIQUES

• Transects: A transect is a straight line across a habitat or part of a habitat, along which observations and measurements are made of organisms at regular intervals to study distribution.

• Quadrats: Quadrats are square frames of a known size used to sample and count the number of organisms within a given area, allowing the estimation of population density and abundance.

• Population Density: Population density is calculated by dividing the number of individuals of a species by the area sampled (e.g., individuals per square metre).

• Population Size: Population size can be estimated by multiplying the average number of individuals per quadrat by the total number of quadrats that would fit in the area.

WHAT IS BIODIVERSITY? Biodiversity refers to the variety of life in all its forms, including genetic diversity, species diversity, and ecosystem diversity.

• Genetic Diversity: Variation in the genes of individuals within a species.

• Species Diversity: The number and variety of species in a particular region.

• Ecosystem Diversity: The variety of ecosystems in a given place.

NATURAL SELECTION Natural selection is the process by which individuals with favourable traits are more likely to survive and reproduce, passing on those traits to the next generation.

• Stabilising Selection: Favours the average phenotype and selects against extremes.

• Disruptive Selection: Favours individuals at both extremes of the trait range.

• Directional Selection: Favours one extreme phenotype, causing a shift in the population trait over time.

LEVELS OF CLASSIFICATION The levels of classification in biology are: Kingdom, Phylum, Class, Order, Family, Genus, Species. This hierarchy groups organisms based on shared characteristics and evolutionary relationships.

WHAT DEFINES A SPECIES?

• Morphological Species Concept: Defines species based on shared physical characteristics.

• Biological Species Concept: Defines species as groups of organisms that can interbreed and produce fertile offspring.

• Phylogenetic Species Concept: Defines species based on shared evolutionary history and common ancestors using genetic evidence.

FIVE MAIN CLASSES OF CHORDATA

• Fish: Aquatic vertebrates with gills and fins.

• Amphibia: Vertebrates that start life in water with gills and develop lungs for life on land.

• Reptilia: Vertebrates with scaly skin that lay leathery eggs on land.

• Aves (Birds): Warm-blooded vertebrates with feathers, beaks, and hard-shelled eggs.

• Mammals: Warm-blooded vertebrates with hair or fur that produce milk for their young.

CLASSIFICATION OF KINGDOM PLANTAE Plants are multicellular, photosynthetic organisms classified based on the presence of vascular tissue and seeds.

• Mosses: Non-vascular plants that reproduce using spores.

• Ferns: Vascular plants that also reproduce via spores.

• Conifers: Vascular plants that reproduce using seeds in cones.

• Flowering Plants: Vascular plants that reproduce using seeds in flowers.

  • Monocots: Have one seed leaf, parallel veins, and flower parts in multiples of three.

  • Dicots: Have two seed leaves, net-like veins, and flower parts in multiples of four or five.

PHYLOGENETICS & CLADOGRAMS Phylogenetics is the study of evolutionary relationships between organisms. Cladograms are diagrams that show these relationships based on shared derived characteristics and common ancestry.

COMPETITION

• Intra-specific Competition: Competition between individuals of the same species for resources.

• Inter-specific Competition: Competition between individuals of different species for the same resources.

SYMBIOTIC RELATIONSHIPS

• Mutualism: Both species benefit from the relationship.

• Commensalism: One species benefits while the other is unaffected.

• Parasitism: One species benefits at the expense of the other.

PREDATOR-PREY GRAPHS Predator-prey graphs show the cyclical relationship between predator and prey populations. As prey numbers increase, predator numbers rise shortly after, followed by a decline in prey, and then predators.

FOOD CHAINS & FOOD WEBS Food chains show the linear flow of energy from producers to top consumers. Food webs show interconnected food chains within an ecosystem, representing more complex feeding relationships.

ECOLOGICAL PYRAMIDS

• Numbers: Represents the number of organisms at each trophic level in an ecosystem.

• Biomass: Represents the total mass of organisms at each level, showing the quantity of living or organic matter.

• Energy: Represents the flow of energy through trophic levels, where only about 10% of the energy is transferred to the next level.

NITROGEN CYCLE – KEY PROCESSES Includes nitrogen fixation by bacteria, nitrification (conversion of ammonia to nitrates), assimilation by plants, ammonification (decomposition of organic nitrogen), and denitrification (return of nitrogen to the atmosphere).

CARBON CYCLE – KEY PROCESSES Photosynthesis removes carbon dioxide from the atmosphere; respiration returns it. Decomposition, combustion of fossil fuels, and ocean exchange also cycle carbon.

FUNDAMENTAL NICHE VS. REALISED NICHE

• Fundamental Niche: The full range of environmental conditions a species can potentially occupy.

• Realised Niche: The actual conditions the species occupies due to competition and other biotic factors.

COMPETITIVE EXCLUSION PRINCIPLE States that no two species can occupy the same niche indefinitely in the same environment; one will outcompete the other.

r-SELECTED VS. K-SELECTED SPECIES

• r-Selected: Produce many offspring, mature quickly, little parental care (e.g., insects).

• K-Selected: Fewer offspring, more parental care, longer life spans (e.g., elephants).

CAPTURE – MARK – RECAPTURE A method to estimate population size by capturing individuals, marking them, releasing them, and recapturing to determine the proportion marked. Assumes no migration or significant births/deaths.

POPULATION GROWTH CURVES

• Lag Phase: Slow growth as organisms acclimatise.

• Exponential Phase: Rapid population increase.

• Transitional Phase: Growth slows due to limiting factors.

• Plateau Phase: Population stabilises at carrying capacity.

• Density-Independent Factors: Affect all populations equally (e.g., natural disasters).

• Density-Dependent Factors: Effects increase with population density (e.g., disease, competition).

PRIMARY & SECONDARY SUCCESSION

• Primary Succession: Occurs on surfaces with no soil (e.g., volcanic rock); starts with pioneer species like lichens.

• Secondary Succession: Occurs in areas where an ecosystem existed but was disturbed (e.g., after fire).

INVASIVE SPECIES Species not native to an ecosystem that cause harm by outcompeting native species, spreading disease, or altering habitats.

• Biological Control: Using natural predators to reduce invasive species.

• Chemical Control: Using pesticides or herbicides to manage populations.

• Case Study: Cane toads in Australia were introduced to control pests but became invasive themselves.

AGRICULTURE – DRYLAND SALINITY

• Cause: Clearing of deep-rooted native vegetation raises the water table, bringing salt to the surface.

• Effect: Salt degrades soil and damages crops.

• Management: Replant native vegetation, improve water drainage, use salt-tolerant crops.

EUTROPHICATION

• Cause: Nutrient runoff (e.g., fertilisers) into water bodies.

• Effect: Algal blooms, oxygen depletion, fish death.

• Management: Reduce fertiliser use, restore wetlands, establish buffer zones.

BIOMAGNIFICATION & BIOACCUMULATION

• Cause: Toxins like mercury or DDT accumulate in organisms and increase in concentration up food chains.

• Effect: Top predators suffer toxicity; reproductive failure, death.

• Management: Ban persistent pollutants, monitor wildlife, clean contaminated areas.

CLIMATE CHANGE & GLOBAL WARMING

• Cause: Greenhouse gas emissions from fossil fuel use and deforestation.

• Effect: Global temperature rise, sea level rise, extreme weather, species extinction.

• Management: Use renewable energy, carbon capture, reduce deforestation, international agreements.

CONSERVATION APPROACHES

• Environmental: Habitat protection, restoration of ecosystems.

• Genetic: Captive breeding, gene banks, maintaining genetic diversity.

• Management: National parks, protected areas, wildlife corridors, legislation.

DICHOTOMOUS KEYS Tools used to identify organisms based on a series of choices between two characteristics. Helps classify organisms through elimination.

GRAPH – TURTLE EGGS A graph showing temperature vs. hatchling success would show a peak around the optimal temperature (e.g. 30°C), with lower success at both lower (24°C) and higher (36°C) temperatures, forming a bell-shaped curve.