Ontario Grade 12 SBI4U Biology (Grade 12, University Preparation)
Chapters: 6
1. A. Scientific Investigation Skills and Career Exploration
A1 Scientific Investigation Skills · A2 Career Exploration
- The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.
2. B. Biochemistry
B1 Relating Science to Technology, Society, and the Environment · B2 Developing Skills of Investigation and Communication · B3 Understanding Basic Concepts
- Biomolecules – A cell is mostly water, plus four big families of carbon compounds: proteins, carbohydrates, lipids and nucleic acids. Grinding tissue in acid separates small molecules (acid-soluble pool) from big ones – proteins, polysaccharides and nucleic acids (acid-insoluble pool). Proteins are chains of amino acids folded into four levels of structure. Polysaccharides are chains of sugars; lipids are fatty acids on glycerol; nucleic acids are chains of nucleotides. Enzymes are protein catalysts that bind a substrate at the active site, lower the activation energy, and are affected by temperature, pH, substrate level and inhibitors.
3. C. Metabolic Processes
C1 Relating Science to Technology, Society, and the Environment · C2 Developing Skills of Investigation and Communication · C3 Understanding Basic Concepts
- Respiration in Plants – Respiration breaks food like glucose to release energy stored as ATP. Plants take in O₂ through stomata and lenticels. Glycolysis in the cytoplasm splits glucose into two pyruvates. Without O₂, pyruvate is fermented to ethanol or lactic acid. With O₂, pyruvate enters the mitochondrion, runs the Krebs cycle, and the electron transport system uses O₂ to make most of the ATP: up to 38 per glucose. The same path also builds molecules (amphibolic). RQ = CO₂ given out ÷ O₂ taken in.
4. D. Molecular Genetics
D1 Relating Science to Technology, Society, and the Environment · D2 Developing Skills of Investigation and Communication · D3 Understanding Basic Concepts
- Molecular Basis of Inheritance – DNA is the genetic material in most living things (some viruses use RNA). It is a double helix: two antiparallel strands of nucleotides, A pairs with T by 2 hydrogen bonds and G with C by 3. Long DNA is packed on histones into nucleosomes and then chromatin. DNA copies itself semi-conservatively (Meselson–Stahl). The central dogma says DNA → RNA → protein. Transcription makes RNA from one strand; in eukaryotes the hnRNA is capped, tailed and spliced. The genetic code is a triplet, has 64 codons (61 for amino acids, 3 stops), starts with AUG, is nearly universal and degenerate. Ribosomes translate mRNA into protein with tRNA adaptors. Genes are switched on and off; the lac operon is the classic example. The Human and Rice Genome Projects read whole genomes, and DNA fingerprinting uses repeat DNA (VNTRs) to identify people.
5. E. Homeostasis
E1 Relating Science to Technology, Society, and the Environment · E2 Developing Skills of Investigation and Communication · E3 Understanding Basic Concepts
- Homeostasis – Homeostasis is how the body keeps its internal environment (blood and tissue fluid) steady even when the outside world changes. It controls body temperature (about 37 °C), blood glucose (about 4–6 mmol/L), water and salt, and blood pH (about 7.4). It mostly uses negative feedback: a receptor senses a change, a control centre decides, and an effector brings the level back to its set point.
6. F. Population Dynamics
F1 Relating Science to Technology, Society, and the Environment · F2 Developing Skills of Investigation and Communication · F3 Understanding Basic Concepts
- Organisms and Populations: Growth and Interactions – A population is a group of the same species living in one area at one time. It has features that a single organism does not have: density, birth rate, death rate, sex ratio and age structure. N grows by births and immigration and shrinks by deaths and emigration. With unlimited food it grows fast (J-curve, dN/dt = rN); with limited food it slows and stops at the carrying capacity K (S-curve, dN/dt = rN(1 − N/K)). Different species affect each other: mutualism (+/+), competition (−/−), predation and parasitism (+/−), commensalism (+/0) and amensalism (−/0).