A Level Biology Lesson 1: -

The Biochemical Basis of Life.

Task 1. Check Where this Lesson fits into your Exam Specification!

Task 2. Watch the Revision Notes Lesson in Full.

00:00 Learning Outcomes

00:41 Introduction

01:13 Phylogenetic Tree

01:52 Biochemical Similarities Support The Theory of Evolution

02:20 The 4 Biological Molecules you Must Know.

03:10 Summary.

Task 3. 

Download, Print out & complete the accompanying Interactive Worksheet.

A-Level Biology "The Biochemical Basis of Life" Lesson 1. Summary.


Despite the variety of life on Earth being extensive, ALL organisms share the same basic biochemistry. Specifically, Carbon-based compounds such as: -

  • Nucleotides, which form DNA and RNA

  • Amino Acids, which form Polypeptides (proteins)

  • Monosaccharides, which form Polysaccharides.


Definition of a Monomer: “The single unit from which a polymer is made” monomers join together to form long complex polymers.


Definition of a Polymer: “A Long complex molecule composed of many repeating monomers”


The 4 Biological Molecules you have to know are: -

  1. Nucleic acids (DNA & RNA) – Which are made up from Nucleotides.

  2. Proteins (polypeptides) - Which are made up from Amino Acids.

  3. Carbohydrates – Which are made up from Monosaccharides.

  4. Lipids – Which are NOT polymers, since they are made up from Glycerol + Fatty Acids.


Shared common ancestry can be depicted by means of a phylogenetic tree – a diagram that represents the relatedness and evolutionary history of a given species. The branch points on the diagram relate to a shared common ancestor between species.

Check Your Spec!

AQA Specification Reference: - 3.1 Biological molecules. 3.1.1 Monomers and polymers. All life on Earth shares a common chemistry. This provides indirect evidence for evolution. Despite their great variety, the cells of all living organisms contain only a few groups of carbon-based compounds that interact in similar ways.


CIE Specification Reference: - 2 Biological molecules. Candidates will be expected to use the knowledge gained in this section to solve problems in familiar and unfamiliar contexts.


Edexcel (Biology A – Salters-Nuffield) Specification Reference: - Topic 4: Biodiversity and Natural Resources.


Edexcel (Biology B) Specification Reference: - Topic 1: Biological Molecules & Topic 3: Classification and Biodiversity.


OCR (Biology A) Specification Reference: - Module 2: Foundations in biology: The cells of all living organisms are composed of biological molecules. Proteins, carbohydrates and lipids are three of the key groups of biological macromolecules that are essential for life. A study of the structure of these macromolecules allows a better understanding of their functions in living organisms.


OCR (Biology B) Specification Reference: - Module 2: Cells, chemicals for life, transport and gas exchange: biologically important molecules in animals and plants, including DNA, natural polymers,


WJEC Specification Reference: - Core Concepts 1. Chemical elements are joined together to form biological compounds. All organisms are composed of biological molecules. These are fundamental to the functioning of living organisms. It is essential to understand how the structure of these molecules is related to their function.


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