How DNA, chromosomes, genes and alleles relate; the stages of mitosis; and why asexual reproduction gives identical offspring.
6 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
Sugar cane fields are clones. That’s efficient — and dangerous. Here’s why.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Unzip the DNA helix and step through mitosis.
Copy these into your notebook in your own words — that is how they stick.
Molecule carrying genetic information; double helix; base sequence codes for proteins.
Structure of DNA wrapped around histone proteins; found in the nucleus.
A length of DNA that codes for a particular protein/characteristic.
Alternative form of a gene, found at the same locus on homologous chromosomes.
Diploid (2n) body cells; haploid (n) gametes.
Prophase → metaphase → anaphase → telophase; 2 identical diploid cells.
Growth, repair, replacement of cells, asexual reproduction.
Offspring identical because produced by mitosis from one parent — no mixing of genes.
The kind of support a teacher gives after the lesson: worked examples to attempt first, a board illustration, key terms, common misconceptions and memory aids.
Try it in your notebook first, then reveal the solution one step at a time.
Try it in your notebook first, then reveal the solution one step at a time.
| Term | What it is | Recipe-book picture |
|---|---|---|
| DNA | Molecule carrying the genetic code: a double helix with bases A–T and C–G | The letters and words |
| Gene | A section of DNA that codes for one protein (one characteristic) | One recipe |
| Allele | A different form of the same gene | Two versions of the same recipe |
| Chromosome | A long, coiled DNA molecule carrying many genes | A recipe book |
| Nucleus | Holds all the chromosomes (46 in human body cells) | The bookshelf |
Use the analogy to remember how the terms fit inside each other — but give the scientific definition in the exam.
Stages of mitosis: I Prefer My Apple Tart — Interphase, Prophase, Metaphase, Anaphase, Telophase.
Caribbean farmers grow sugar cane from stem cuttings (setts), bananas from suckers and pineapples from crowns. Every new plant is produced by mitosis, so it is a genetically identical clone of the parent.
Model mitosis with two colours of string or pipe cleaners: make 2 pairs of “chromosomes”, copy each one, line them up in the middle, and pull the copies apart into two new “cells”.
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Write full answers, then reveal the mark scheme and tick the points you earned (16 marks in total). Your answers are saved on this device.
Question 1 [10 marks]
Randomly placed diagrams A–E show stages of mitosis in a plant cell; the metaphase cell shows four chromosomes on the equator.
(a) Define gene, allele and chromosome. [3]
(b) How many chromosomes were in the parent cell? State the correct order of stages as prophase → metaphase → anaphase → telophase and describe each. [5]
(c) State TWO reasons why mitosis is important to living organisms. [2]
Question 2 [6 marks]
Sugar cane was once of great economic importance in the Caribbean.
(a) Name the type of cell division that leads to the propagation of sugar cane, and give TWO reasons explaining how it does so. [3]
(b) Explain why the offspring of asexual reproduction are genetically identical, and ONE disadvantage of this. [3]
Find these in your own past-paper booklets for extra timed practice. The practice above is adapted from them.