HSC Biology cheat sheet

Cell theory: all living things are composed of cells, the cell is the basic structural and functional unit, and all cells arise from pre-existing cells by division.

Prokaryotic cells lack membrane-bound organelles and a nucleus; eukaryotic cells have a nucleus and membrane-bound organelles such as mitochondria and chloroplasts.

Surface area to volume ratio decreases as cell size increases, so large cells must divide or develop folded membranes to maintain efficient exchange.

The fluid mosaic model describes the membrane as a phospholipid bilayer with embedded proteins, cholesterol and glycolipids that move laterally.

Passive transport (diffusion, osmosis, facilitated diffusion) moves substances down a concentration gradient without ATP; active transport requires ATP and can move substances against a gradient.

Osmosis is the net movement of water across a semipermeable membrane from low solute concentration to high solute concentration.

Enzymes are biological catalysts that lower activation energy; they are specific to substrates and denature at high temperature or extreme pH.

Cellular respiration converts glucose and oxygen into ATP, carbon dioxide and water; photosynthesis converts light, carbon dioxide and water into glucose and oxygen.

Levels of organisation from smallest to largest: organelle, cell, tissue, organ, organ system, organism.

Plants have three tissue systems: dermal (protection), vascular (xylem transports water and minerals upward; phloem transports sugars) and ground tissue (photosynthesis and storage).

Mammals have four tissue types: epithelial, connective, muscle and nervous tissue.

Autotrophs synthesise organic compounds from inorganic sources; heterotrophs obtain organic compounds by consuming other organisms.

Gas exchange surfaces share features: large surface area, thin barrier, moist surface and a concentration gradient maintained by ventilation and blood flow.

Mammalian lungs use alveoli; fish use gills with counter-current flow of water and blood to maximise oxygen uptake.

Transport in mammals relies on a closed circulatory system with a four-chambered heart separating oxygenated and deoxygenated blood.

Xylem vessels are dead, lignified and continuous tubes; transpiration pull and cohesion-tension drive water movement up the plant.

A species is a group of organisms that can interbreed in nature to produce fertile offspring.

Binomial nomenclature uses genus and species names, italicised or underlined, with the genus capitalised.

Classification hierarchy: domain, kingdom, phylum, class, order, family, genus, species.

Biological diversity includes genetic diversity, species diversity and ecosystem diversity.

Adaptations may be structural (body form), physiological (internal processes) or behavioural (actions).

Natural selection requires heritable variation, environmental selection pressure and differential reproductive success.

Reproductive isolating mechanisms (geographic, temporal, behavioural, mechanical) prevent gene flow and can lead to speciation.

Phylogenetic trees and DNA sequencing are used to infer evolutionary relationships where morphology is unreliable.

An ecosystem comprises biotic factors (living organisms) and abiotic factors (light, temperature, water, soil, salinity).

Trophic levels: producers, primary consumers, secondary consumers, tertiary consumers, with decomposers recycling nutrients.

Energy transfer between trophic levels is about 10 percent, so food chains rarely exceed four or five levels.

Photosynthesis and respiration form the carbon cycle; nitrogen fixation, nitrification, denitrification and decomposition form the nitrogen cycle.

Population size is affected by birth rate, death rate, immigration and emigration.

Interspecific relationships include competition, predation, parasitism, mutualism and commensalism.

Keystone species have a disproportionately large effect on community structure relative to their abundance.

Ecological succession is the change in species composition over time; primary succession begins on bare substrate, secondary succession follows disturbance.

DNA is a double helix of nucleotides; adenine pairs with thymine (two hydrogen bonds) and guanine pairs with cytosine (three hydrogen bonds).

DNA replication is semi-conservative; each new molecule retains one parental strand.

Transcription produces mRNA from a DNA template in the nucleus; translation at ribosomes assembles amino acids using codons and tRNA.

A gene is a sequence of DNA that codes for a polypeptide or functional RNA; alleles are alternative forms of a gene.

Genotype is the allele combination; phenotype is the observable trait resulting from genotype and environment.

Punnett squares predict offspring ratios; a monohybrid cross of heterozygotes gives a 3:1 phenotypic ratio and 1:2:1 genotypic ratio.

Incomplete dominance produces an intermediate phenotype; codominance expresses both alleles simultaneously.

Sex-linked traits are carried on sex chromosomes; X-linked recessive traits appear more often in males because they have one X chromosome.

A mutation is a permanent change in DNA sequence; point mutations include substitution, insertion and deletion.

Insertions and deletions cause frameshifts, altering every subsequent codon and often producing non-functional proteins.

Mutagens such as UV radiation, ionising radiation and certain chemicals increase mutation rate.

Meiosis produces genetic variation through crossing over in prophase I and independent assortment in metaphase I.

Fertilisation further increases variation by combining haploid gametes from two parents.

Biotechnology techniques include gene cloning, polymerase chain reaction, gel electrophoresis and recombinant DNA technology.

Transgenic organisms contain genes from another species introduced by vectors such as plasmids.

Ethical issues in genetic technology include privacy of genetic data, consent, equity of access and ecological risk of releasing modified organisms.

Pathogens include bacteria, viruses, fungi, protozoa and prions; they cause disease by direct damage or toxin production.

A disease is infectious if its causative agent can be transmitted from one host to another.

Transmission modes include direct contact, droplet, airborne, vector-borne, and food or water-borne routes.

The first line of defence comprises physical and chemical barriers: intact skin, mucus, cilia, stomach acid and lysozyme.

The second line of defence is non-specific and includes inflammation, phagocytosis and fever.

The third line of defence is specific and adaptive, involving B cells producing antibodies and T cells destroying infected cells.

Vaccination exposes the immune system to antigens, producing memory cells that give a faster, stronger secondary response.

Antibiotics target bacterial structures such as cell walls or ribosomes and are ineffective against viruses; misuse promotes antibiotic resistance.

Non-infectious diseases are not caused by pathogens and cannot be transmitted between individuals.

Causes include genetic inheritance, environmental exposure, nutritional deficiency and lifestyle factors.

Single-gene disorders follow Mendelian inheritance; examples include cystic fibrosis (autosomal recessive) and Huntington disease (autosomal dominant).

Chromosomal disorders arise from abnormal chromosome number or structure, such as trisomy 21.

Multifactorial diseases result from combined genetic and environmental influences, such as type 2 diabetes and cardiovascular disease.

Cancer arises from mutations in genes controlling cell division, leading to uncontrolled proliferation and tumour formation.

Epidemiology studies the distribution and determinants of disease in populations to identify risk factors.

Prevention strategies target modifiable risk factors such as smoking, diet, physical activity and sun exposure.