Life Sciences Paper 2 Revision Guide: Term 2
This guide is designed to help you master the core concepts of Life Sciences Paper 2,
focusing on the South African CAPS curriculum. We will cover the molecular basis of
life, how traits are passed down, and how life changes over time.
1. DNA: The Code of Life
DNA (Deoxyribonucleic acid) is the blueprint for every living organism. It is located in
the nucleus (nuclear DNA) and mitochondria (mitochondrial DNA).
• Structure of DNA: It is a double-stranded molecule twisted into a double helix.
• Nucleotides: The building blocks of DNA. Each nucleotide consists of:
o A Phosphate group.
o A Deoxyribose sugar.
o One of four Nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C),
and Guanine (G).
• Base Pairing Rule: Adenine always bonds with Thymine (A-T), and Cytosine
always bonds with Guanine (C-G).
2. Meiosis: Making Gametes
Meiosis is a type of cell division that reduces the chromosome number by half (from
diploid to haploid) to produce gametes (sperm and eggs).
• Importance: It ensures that the chromosome number stays the same from
generation to generation and introduces genetic variation.
, • Variation Mechanisms:
o Crossing Over: Occurs during Prophase I where homologous
chromosomes exchange genetic material.
o Independent Assortment: Occurs during Metaphase I where
chromosomes line up randomly at the equator.
3. Genetics and Inheritance
This topic looks at how traits are passed from parents to offspring.
• Alleles: Alternative forms of a gene (e.g., 𝐵 for brown eyes, 𝑏 for blue eyes).
• Genotype: The genetic makeup (the letters, like 𝐵𝑏).
• Phenotype: The physical appearance (what you see, like “brown eyes”).
• Homozygous: Two of the same alleles (𝐵𝐵 or 𝑏𝑏).
• Heterozygous: Two different alleles (𝐵𝑏).
4. Evolution: Change over Time
Evolution explains how species change over millions of years.
• Lamarckism: Proposed that organisms change because they “want” to or
through “use and disuse.” He believed in the inheritance of acquired
characteristics (which is now known to be incorrect).
• Darwinism: Proposed the theory of Natural Selection. Individuals with favorable
traits survive and reproduce, passing those traits to the next generation.
Practice Problems
Problem 1: DNA Composition A sample of DNA is analyzed and found to contain 22%
Adenine. Calculate the percentage of Guanine present in this sample.
Problem 2: Genetic Cross In pea plants, tallness (𝑇) is dominant over sequence
shortness (𝑡). A heterozygous tall plant is crossed with a short plant. Use a Punnett
square to determine the phenotypic ratio of the offspring.
Problem 3: Evolution Case Study Explain how Darwin would explain the evolution of
long necks in giraffes compared to how Lamarck would explain it.
This guide is designed to help you master the core concepts of Life Sciences Paper 2,
focusing on the South African CAPS curriculum. We will cover the molecular basis of
life, how traits are passed down, and how life changes over time.
1. DNA: The Code of Life
DNA (Deoxyribonucleic acid) is the blueprint for every living organism. It is located in
the nucleus (nuclear DNA) and mitochondria (mitochondrial DNA).
• Structure of DNA: It is a double-stranded molecule twisted into a double helix.
• Nucleotides: The building blocks of DNA. Each nucleotide consists of:
o A Phosphate group.
o A Deoxyribose sugar.
o One of four Nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C),
and Guanine (G).
• Base Pairing Rule: Adenine always bonds with Thymine (A-T), and Cytosine
always bonds with Guanine (C-G).
2. Meiosis: Making Gametes
Meiosis is a type of cell division that reduces the chromosome number by half (from
diploid to haploid) to produce gametes (sperm and eggs).
• Importance: It ensures that the chromosome number stays the same from
generation to generation and introduces genetic variation.
, • Variation Mechanisms:
o Crossing Over: Occurs during Prophase I where homologous
chromosomes exchange genetic material.
o Independent Assortment: Occurs during Metaphase I where
chromosomes line up randomly at the equator.
3. Genetics and Inheritance
This topic looks at how traits are passed from parents to offspring.
• Alleles: Alternative forms of a gene (e.g., 𝐵 for brown eyes, 𝑏 for blue eyes).
• Genotype: The genetic makeup (the letters, like 𝐵𝑏).
• Phenotype: The physical appearance (what you see, like “brown eyes”).
• Homozygous: Two of the same alleles (𝐵𝐵 or 𝑏𝑏).
• Heterozygous: Two different alleles (𝐵𝑏).
4. Evolution: Change over Time
Evolution explains how species change over millions of years.
• Lamarckism: Proposed that organisms change because they “want” to or
through “use and disuse.” He believed in the inheritance of acquired
characteristics (which is now known to be incorrect).
• Darwinism: Proposed the theory of Natural Selection. Individuals with favorable
traits survive and reproduce, passing those traits to the next generation.
Practice Problems
Problem 1: DNA Composition A sample of DNA is analyzed and found to contain 22%
Adenine. Calculate the percentage of Guanine present in this sample.
Problem 2: Genetic Cross In pea plants, tallness (𝑇) is dominant over sequence
shortness (𝑡). A heterozygous tall plant is crossed with a short plant. Use a Punnett
square to determine the phenotypic ratio of the offspring.
Problem 3: Evolution Case Study Explain how Darwin would explain the evolution of
long necks in giraffes compared to how Lamarck would explain it.
