Biology
Biology: what the CSEC exam tests
CSEC Biology rewards precise vocabulary and the ability to move between a diagram, a data table and a written explanation. The syllabus covers cells and transport, nutrition, respiration, excretion, coordination, reproduction, genetics, ecology and human impact. Paper 1 checks recall and quick interpretation; Paper 2 asks structured and extended answers; Paper 3 assesses practical skills such as drawing, food tests and experimental design.
Core rules and concepts
- Cells: organelles and their functions; plant versus animal cells; specialised cells and surface area to volume ratio.
- Transport: diffusion, osmosis and active transport. Osmosis is the movement of water across a partially permeable membrane from higher to lower water potential.
- Enzymes: specific proteins that catalyse reactions; temperature and pH affect shape and activity, and extremes denature them.
- Nutrition: photosynthesis equation and limiting factors; food tests - iodine for starch, Benedict's for reducing sugar, Biuret for protein, emulsion test for lipid.
- Gas exchange and transport: alveoli and stomata; xylem and phloem; heart, blood vessels and blood.
- Coordination and homeostasis: negative feedback, neurones and hormones.
- Genetics: DNA, genes, alleles, mitosis and meiosis, monohybrid crosses.
- Ecology: food chains, energy flow, nutrient cycles, populations and human impact.
Worked example
In pea plants, tall (T) is dominant to dwarf (t). Cross a heterozygous tall plant with a dwarf plant.
Parent genotypes: Tt × tt. Gametes: the Tt parent gives T or t; the tt parent gives t only. Punnett square gives Tt, tt, Tt, tt. Genotype ratio: 1 Tt : 1 tt. Phenotype ratio: 1 tall : 1 dwarf. The reasoning is that each parent contributes one allele, and the dominant T masks t in the heterozygote.
Traps that cost marks
- Confusing genotype with phenotype; always state both when asked.
- Writing gametes as pairs (Tt) instead of single alleles (T or t).
- Saying solute moves in osmosis instead of water.
- Confusing respiration with breathing.
- Giving food-test results without the reagent or the colour change.
- Describing a process rather than explaining it - link structure to function and cause to effect.