Source: https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-5-stem-cells

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# Stem Cells

Biology: Cambridge International A Level, topic 5.1.5

## Stem Cells

Stem cells are unspecialised cells. Unspecialised cells are capable of dividing and differentiating into any type of cell. Stem cells divide by mitosis and are important in tissue repair.

### Totipotent cells

![Totipotent cells](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/6.2.3%20-%20Cloning/embryo-1514192_640-min-min.jpg)

- Totipotent cells exist for only a very limited time during embryonic development in mammals (the first few cell divisions).
- During development, totipotent cells translate only part of their DNA. This means that the cells remain unspecialised.
- Totipotent cells are able to produce any type of body cell, as well as cells of supportive structures such as the placenta.
- They are the most unspecialised stem cell.

### Pluripotent cells

![Pluripotent cells](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/6.2.3%20-%20Cloning/stem-cell-163711_640-min.jpg)

- Totipotent cells develop into pluripotent cells in embryos. 
- Pluripotent cells are able to divide in unlimited numbers and produce any type of cell that makes up the body.
- Pluripotent cells can be used to treat human disorders.

### Multipotent cells

![Multipotent cells](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/1.2.1%20Chromosomes%20and%20mitosis/bone-316228_640.jpg)

- Multipotent cells are found in mature mammals.
- Multipotent cells can develop into a limited number of cell types.
 - E.g. Multipotent cells in the bone marrow can produce a range of blood cells.

### Unipotent cells

![Unipotent cells](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/OCR%20Gateway/3.1.2/muscle%20man.jpg)

- Unipotent cells are found in mature mammals.
- Unipotent cells can divide to produce new cells but can only produce one type of cell.
 - E.g. Cardiomyocytes are unipotent cells that can produce new muscle cells.

## Specialisation of Stem Cells

Stem cells become specialised during embryonic development. Specialised cells only express some of the genes in their DNA.

### Totipotent cells

![Totipotent cells](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/6.2.3%20-%20Cloning/embryo-1514192_640-min-min.jpg)

- Totipotent cells become specialised during embryonic development.
- When the cells become specialised, only some genes in the cell are activated.
 - Only the activated genes are expressed.

### Proteins in differentiation

![Proteins in differentiation](https://image-v2.cdn.app.senecalearning.com/2018-09/3bca9e63-02ac-45d0-832a-5c8af2d2cbe9/rna-protein-synthesis.jpg)

- If a gene is expressed, it is transcribed into mRNA and translated into a protein.
- Differentiation happens as certain proteins are made.
- The presence of certain proteins means a cell has become specialised.

## Test yourself on Stem Cells

- What is the most unspecialised stem cell?
- Which of the following statements about stem cells are true?
- Stages in Specialisation of Stem Cells
- When do totipotent cells become specialised?
- Which of the following statements about cell specialisation are true?

[Practise this topic for free](https://app.senecalearning.com/classroom/course/8d1a05c1-df92-4b13-9a69-b60acc7af79a/section/768c3780-56fa-4a06-9354-03e74b7a5b7e/session)

- Previous topic: [5.1.4 Role of Mitosis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-4-role-of-mitosis.md)
- Next topic: [5.1.6 Mitosis & Cancer](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-6-mitosis-and-cancer.md)

## Biology: Cambridge International A Level contents

### 1 Cell Structure
- 1.1 Cell Structure
  - [1.1.1 Studying Cells - Microscopes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-1-studying-cells-microscopes.md)
  - [1.1.2 Introduction to Eukaryotic & Prokaryotic Cells](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-2-introduction-to-eukaryotic-and-prokaryotic-cells.md)
  - [1.1.3 Ultrastructure of Eukaryotic Cells](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-3-ultrastructure-of-eukaryotic-cells.md)
  - [1.1.4 Ultrastructure of Eukaryotic Cells 2](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-4-ultrastructure-of-eukaryotic-cells-2.md)
  - [1.1.5 Ultrastructure of Eukaryotic Cells 3](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-5-ultrastructure-of-eukaryotic-cells-3.md)
  - [1.1.6 Prokaryotic Cells](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-6-prokaryotic-cells.md)
  - [1.1.7 Viruses](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-7-viruses.md)
  - [1.1.8 End of Topic Test - Cell Structure](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-8-end-of-topic-test-cell-structure.md)
  - [1.1.9 Exam-Style Question - Microscopes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-9-exam-style-question-microscopes.md)
  - [1.1.10 A-A* (AO2/3) - Cell Structure](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/1-1-10-a-a-ao23-cell-structure.md)

### 2 Biological Molecules
- 2.1 Testing for Biological Modules
  - [2.1.1 Tests for Sugars & Starch](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-1-1-tests-for-sugars-and-starch.md)
  - [2.1.2 Tests for Lipids & Proteins](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-1-2-tests-for-lipids-and-proteins.md)
- 2.2 Carbohydrates & Lipids
  - [2.2.1 Monomers & Polymers](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-2-1-monomers-and-polymers.md)
  - [2.2.2 Carbohydrates](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-2-2-carbohydrates.md)
  - [2.2.3 Examples of Carbohydrates](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-2-3-examples-of-carbohydrates.md)
  - [2.2.4 Triglycerides & Phospholipids](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-2-4-triglycerides-and-phospholipids.md)
  - [2.2.5 Types of Fatty Acids](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-2-5-types-of-fatty-acids.md)
  - [2.2.6 Exam-Style Question - Carbohydrates](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-2-6-exam-style-question-carbohydrates.md)
  - [2.2.7 End of Topic Test - Carbohydrates & Lipids](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-2-7-end-of-topic-test-carbohydrates-and-lipids.md)
- 2.3 Proteins
  - [2.3.1 Amino Acids & Overview of Protein Structure](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-3-1-amino-acids-and-overview-of-protein-structure.md)
  - [2.3.2 Primary & Secondary Structure](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-3-2-primary-and-secondary-structure.md)
  - [2.3.3 Tertiary & Quaternary Structure](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-3-3-tertiary-and-quaternary-structure.md)
  - [2.3.4 Globular & Fibrous Proteins](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-3-4-globular-and-fibrous-proteins.md)
  - [2.3.5 Haemoglobin](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-3-5-haemoglobin.md)
  - [2.3.6 Collagen](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-3-6-collagen.md)
  - [2.3.7 End of Topic Test  - Proteins](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-3-7-end-of-topic-test-proteins.md)
- 2.4 Water
  - [2.4.1 Water Structure & Function](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-4-1-water-structure-and-function.md)
  - [2.4.2 End of Topic Test - Water](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/2-4-2-end-of-topic-test-water.md)

### 3 Enzymes
- 3.1 Enzymes
  - [3.1.1 Enzyme Action](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/3-1-1-enzyme-action.md)
  - [3.1.2 Factors Affecting Enzyme Activity](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/3-1-2-factors-affecting-enzyme-activity.md)
  - [3.1.3 Factors Affecting Enzyme Activity 2](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/3-1-3-factors-affecting-enzyme-activity-2.md)
  - [3.1.4 A-A* (AO2/3) - Enzymes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/3-1-4-a-a-ao23-enzymes.md)

### 4 Cell Membranes & Transport
- 4.1 Biological Membranes
  - [4.1.1 Fluid Mosaic Model](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-1-1-fluid-mosaic-model.md)
  - [4.1.2 Cell Signalling](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-1-2-cell-signalling.md)
  - [4.1.3 End of Topic Test - Biological Membranes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-1-3-end-of-topic-test-biological-membranes.md)
  - [4.1.4 Exam-Style Question - Membranes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-1-4-exam-style-question-membranes.md)
- 4.2 Movement Into & Out of Cells
  - [4.2.1 Passive Movement Across the Membrane](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-2-1-passive-movement-across-the-membrane.md)
  - [4.2.2 Active Movement Across the Membrane](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-2-2-active-movement-across-the-membrane.md)
  - [4.2.3 Osmosis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-2-3-osmosis.md)
  - [4.2.4 Osmosis & Plant Cells](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-2-4-osmosis-and-plant-cells.md)
  - [4.2.5 Surface Area to Volume Ratio](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-2-5-surface-area-to-volume-ratio.md)
  - [4.2.6 Adaptions to Surface Area to Volume Ratio](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-2-6-adaptions-to-surface-area-to-volume-ratio.md)
  - [4.2.7 Calculations - Volume](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-2-7-calculations-volume.md)
  - [4.2.8 Calculations - Surface Area](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/4-2-8-calculations-surface-area.md)

### 5 The Mitotic Cell Cycle
- 5.1 Replication & Division of Nuclei
  - [5.1.1 Chromosomes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-1-chromosomes.md)
  - [5.1.2 The Cell Cycle](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-2-the-cell-cycle.md)
  - [5.1.3 Mitosis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-3-mitosis.md)
  - [5.1.4 Role of Mitosis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-4-role-of-mitosis.md)
  - [5.1.5 Stem Cells](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-5-stem-cells.md)
  - [5.1.6 Mitosis & Cancer](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-6-mitosis-and-cancer.md)
  - [5.1.7 End of Topic Test - Replication & Division](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-7-end-of-topic-test-replication-and-division.md)
  - [5.1.8 A-A* (AO2/3) - Cell Cycle & Transport](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/5-1-8-a-a-ao23-cell-cycle-and-transport.md)

### 6 Nucleic Acids & Protein Synthesis
- 6.1 Nucleic Acids
  - [6.1.1 Introduction to DNA & RNA](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-1-1-introduction-to-dna-and-rna.md)
  - [6.1.2 Nucleotides](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-1-2-nucleotides.md)
  - [6.1.3 Polynucleotides](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-1-3-polynucleotides.md)
  - [6.1.4 ADP & ATP](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-1-4-adp-and-atp.md)
  - [6.1.5 DNA](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-1-5-dna.md)
  - [6.1.6 DNA Replication](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-1-6-dna-replication.md)
  - [6.1.7 RNA](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-1-7-rna.md)
  - [6.1.8 End of Topic Test - Nucleic Acids & ATP](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-1-8-end-of-topic-test-nucleic-acids-and-atp.md)
- 6.2 Protein Synthesis
  - [6.2.1 The Genetic Code](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-2-1-the-genetic-code.md)
  - [6.2.2 Polypeptide Synthesis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-2-2-polypeptide-synthesis.md)
  - [6.2.3 RNA Processing in Eukaryotes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-2-3-rna-processing-in-eukaryotes.md)
  - [6.2.4 Mutations](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-2-4-mutations.md)
  - [6.2.5 Exam-Style Question - Protein Synthesis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-2-5-exam-style-question-protein-synthesis.md)
  - [6.2.6 A-A* (AO2/3) - Coronavirus Translation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/6-2-6-a-a-ao23-coronavirus-translation.md)

### 7 Transport in Plants
- 7.1 Transport in Plants
  - [7.1.1 Plant Vessels](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/7-1-1-plant-vessels.md)
  - [7.1.2 Xylem](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/7-1-2-xylem.md)
  - [7.1.3 Investigating Transpiration](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/7-1-3-investigating-transpiration.md)
  - [7.1.4 Adaptations to Water Availability](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/7-1-4-adaptations-to-water-availability.md)
  - [7.1.5 Phloem](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/7-1-5-phloem.md)
  - [7.1.6 End of Topic Test - Transport in Animals & Plants](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/7-1-6-end-of-topic-test-transport-in-animals-and-plants.md)
  - [7.1.7 A-A* (AO2/3) - Transport in Animals & Plants](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/7-1-7-a-a-ao23-transport-in-animals-and-plants.md)

### 8 Transport in Mammals
- 8.1 Circulatory System
  - [8.1.1 Double Circulation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-1-1-double-circulation.md)
  - [8.1.2 Blood Vessels](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-1-2-blood-vessels.md)
  - [8.1.3 Important Blood Vessels](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-1-3-important-blood-vessels.md)
  - [8.1.4 Blood Cells](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-1-4-blood-cells.md)
  - [8.1.5 Tissue Fluid](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-1-5-tissue-fluid.md)
- 8.2 Transport of Oxygen & Carbon Dioxide
  - [8.2.1 Haemoglobin](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-2-1-haemoglobin.md)
  - [8.2.2 Oxygen Dissociation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-2-2-oxygen-dissociation.md)
- 8.3 The Heart
  - [8.3.1 Structure of the Heart](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-3-1-structure-of-the-heart.md)
  - [8.3.2 The Cardiac Cycle](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-3-2-the-cardiac-cycle.md)
  - [8.3.3 Coordination of Heart Action](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/8-3-3-coordination-of-heart-action.md)

### 9 Gas Exchange
- 9.1 Gas Exchange System
  - [9.1.1 Mammalian Gas Exchange](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/9-1-1-mammalian-gas-exchange.md)
  - [9.1.2 Smoking](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/9-1-2-smoking.md)

### 10 Infectious Diseases
- 10.1 Infectious Diseases
  - [10.1.1 Transmission of Disease](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/10-1-1-transmission-of-disease.md)
  - [10.1.2 Tuberculosis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/10-1-2-tuberculosis.md)
  - [10.1.3 HIV](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/10-1-3-hiv.md)
  - [10.1.4 Malaria](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/10-1-4-malaria.md)
  - [10.1.5 Cholera](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/10-1-5-cholera.md)
  - [10.1.6 Measles](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/10-1-6-measles.md)
- 10.2 Antibiotics
  - [10.2.1 Antibiotics](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/10-2-1-antibiotics.md)

### 11 Immunity
- 11.1 The Immune System
  - [11.1.1 Phagocytes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-1-1-phagocytes.md)
  - [11.1.2 Antigens](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-1-2-antigens.md)
  - [11.1.3 Lymphocytes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-1-3-lymphocytes.md)
  - [11.1.4 Primary & Secondary Response](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-1-4-primary-and-secondary-response.md)
- 11.2 Antibodies & Vaccination
  - [11.2.1 Antibodies](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-2-1-antibodies.md)
  - [11.2.2 Monoclonal Antibodies](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-2-2-monoclonal-antibodies.md)
  - [11.2.3 Immunity](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-2-3-immunity.md)
  - [11.2.4 Vaccines](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-2-4-vaccines.md)
  - [11.2.5 Exam-Style Question - Immune System](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-2-5-exam-style-question-immune-system.md)
  - [11.2.6 A-A* (AO2/3) - Disease & Immune System](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/11-2-6-a-a-ao23-disease-and-immune-system.md)

### 12 Energy & Respiration (A2 Only)
- 12.1 Energy
  - [12.1.1 Energy & ATP](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-1-1-energy-and-atp.md)
  - [12.1.2 Respiratory Substrates & Quotient](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-1-2-respiratory-substrates-and-quotient.md)
  - [12.1.3 Respirometers](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-1-3-respirometers.md)
- 12.2 Respiration
  - [12.2.1 Introduction to Respiration](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-2-1-introduction-to-respiration.md)
  - [12.2.2 Anaerobic Respiration](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-2-2-anaerobic-respiration.md)
  - [12.2.3 Aerobic Respiration](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-2-3-aerobic-respiration.md)
  - [12.2.4 Chemiosmosis & Coenzymes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-2-4-chemiosmosis-and-coenzymes.md)
  - [12.2.5 Mitochondria](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-2-5-mitochondria.md)
  - [12.2.6 Respiration Experiments](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-2-6-respiration-experiments.md)
  - [12.2.7 End of Topic Test - Respiration](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-2-7-end-of-topic-test-respiration.md)
  - [12.2.8 A-A* (AO3/4) - Respiration](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/12-2-8-a-a-ao34-respiration.md)

### 13 Photosynthesis (A2 Only)
- 13.1 Photosynthesis
  - [13.1.1 Introduction to Photosynthesis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/13-1-1-introduction-to-photosynthesis.md)
  - [13.1.2 Light-Dependent Reactions](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/13-1-2-light-dependent-reactions.md)
  - [13.1.3 Light-Independent Reactions](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/13-1-3-light-independent-reactions.md)
  - [13.1.4 Limiting Factors](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/13-1-4-limiting-factors.md)
  - [13.1.5 Investigating Photosynthesis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/13-1-5-investigating-photosynthesis.md)
  - [13.1.6 End of Topic Test - Photosynthesis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/13-1-6-end-of-topic-test-photosynthesis.md)
  - [13.1.7 A-A* (AO3/4) - Photosynthesis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/13-1-7-a-a-ao34-photosynthesis.md)

### 14 Homeostasis (A2 Only)
- 14.1 Homeostasis
  - [14.1.1 Homeostasis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/14-1-1-homeostasis.md)
  - [14.1.2 Negative Feedback](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/14-1-2-negative-feedback.md)
- 14.2 The Kidney
  - [14.2.1 Kidneys & Osmoregulation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/14-2-1-kidneys-and-osmoregulation.md)
- 14.3 Cell Signalling
  - [14.3.1 Messengers & cAMP](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/14-3-1-messengers-and-camp.md)
- 14.4 Blood Glucose Concentration
  - [14.4.1 Blood Glucose Concentration](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/14-4-1-blood-glucose-concentration.md)
  - [14.4.2 Controlling Blood Glucose](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/14-4-2-controlling-blood-glucose.md)
  - [14.4.3 Urinalysis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/14-4-3-urinalysis.md)
- 14.5 Homeostasis in Plants
  - [14.5.1 Stomata & Guard Cells](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/14-5-1-stomata-and-guard-cells.md)

### 15 Control & Coordination (A2 Only)
- 15.1 Control & Coordination in Mammals
  - [15.1.1 Neurones](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-1-neurones.md)
  - [15.1.2 Receptors](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-2-receptors.md)
  - [15.1.3 Taste](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-3-taste.md)
  - [15.1.4 Reflexes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-4-reflexes.md)
  - [15.1.5 Action Potentials](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-5-action-potentials.md)
  - [15.1.6 Saltatory Conduction](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-6-saltatory-conduction.md)
  - [15.1.7 Synapses](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-7-synapses.md)
  - [15.1.8 Cholinergic Synnapses](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-8-cholinergic-synnapses.md)
  - [15.1.9 Neuromuscular Junction](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-9-neuromuscular-junction.md)
  - [15.1.10 Skeletal Muscle](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-10-skeletal-muscle.md)
  - [15.1.11 Sliding Filament Theory Contraction](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-11-sliding-filament-theory-contraction.md)
  - [15.1.12 Sliding Filament Theory Contraction 2](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-12-sliding-filament-theory-contraction-2.md)
  - [15.1.13 Menstruation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-13-menstruation.md)
  - [15.1.14 Contraceptive Pill](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-1-14-contraceptive-pill.md)
- 15.2 Control & Co-Ordination in Plants
  - [15.2.1 Venus Flytrap](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-2-1-venus-flytrap.md)
  - [15.2.2 Auixns](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-2-2-auixns.md)
  - [15.2.3 Gibberellins](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/15-2-3-gibberellins.md)

### 16 Inherited Change (A2 Only)
- 16.1 Passage of Information to Offspring
  - [16.1.1 Meiosis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-1-1-meiosis.md)
  - [16.1.2 Gametogenesis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-1-2-gametogenesis.md)
  - [16.1.3 Meiosis & Genetic Diversity](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-1-3-meiosis-and-genetic-diversity.md)
- 16.2 Genes & Phenotype
  - [16.2.1 Key Terms in Genetics](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-2-1-key-terms-in-genetics.md)
  - [16.2.2 Inheritance](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-2-2-inheritance.md)
  - [16.2.3 Linkage](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-2-3-linkage.md)
  - [16.2.4 Multiple Alleles](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-2-4-multiple-alleles.md)
  - [16.2.5 Chi-Squared Test](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-2-5-chi-squared-test.md)
  - [16.2.6 Mutations](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-2-6-mutations.md)
  - [16.2.7 Specific Mutations](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-2-7-specific-mutations.md)
  - [16.2.8 End of Topic Test - Genetics](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-2-8-end-of-topic-test-genetics.md)
  - [16.2.9 A-A* (AO2/3) - Genetics](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-2-9-a-a-ao23-genetics.md)
- 16.3 Gene Control
  - [16.3.1 lac Operon](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-3-1-lac-operon.md)
  - [16.3.2 Transcription Factors](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-3-2-transcription-factors.md)
  - [16.3.3 Gibberellins & DELLA Proteins](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/16-3-3-gibberellins-and-della-proteins.md)

### 17 Selection & Evolution (A2 Only)
- 17.1 Variation
  - [17.1.1 Phenotypic Variation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-1-1-phenotypic-variation.md)
  - [17.1.2 Continuous & Discontinuous Variation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-1-2-continuous-and-discontinuous-variation.md)
  - [17.1.3 t-Tests](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-1-3-t-tests.md)
- 17.2 Natural & Artificial Selection
  - [17.2.1 Natural Selection & Evolution](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-2-1-natural-selection-and-evolution.md)
  - [17.2.2 Types of Selection](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-2-2-types-of-selection.md)
  - [17.2.3 Types of Selection Summary](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-2-3-types-of-selection-summary.md)
  - [17.2.4 Genetic Drift & Founder Effect](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-2-4-genetic-drift-and-founder-effect.md)
  - [17.2.5 Populations](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-2-5-populations.md)
  - [17.2.6 Hardy-Weinberg Principle](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-2-6-hardy-weinberg-principle.md)
  - [17.2.7 Artificial Selection](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-2-7-artificial-selection.md)
- 17.3 Evolution
  - [17.3.1 Evolution by Natural Selection](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-3-1-evolution-by-natural-selection.md)
  - [17.3.2 Evidence for Evolution](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-3-2-evidence-for-evolution.md)
  - [17.3.3 Speciation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-3-3-speciation.md)
  - [17.3.4 Extinction](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/17-3-4-extinction.md)

### 18 Classification & Conservation (A2 Only)
- 18.1 Biodiversity
  - [18.1.1 Key Terms](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-1-1-key-terms.md)
  - [18.1.2 Biodiversity](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-1-2-biodiversity.md)
  - [18.1.3 Sampling Methods](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-1-3-sampling-methods.md)
  - [18.1.4 Correlation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-1-4-correlation.md)
  - [18.1.5 Spearman’s Rank](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-1-5-spearmans-rank.md)
  - [18.1.6 Measuring Biodiversity](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-1-6-measuring-biodiversity.md)
- 18.2 Classification
  - [18.2.1 3-Domain Classification System](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-2-1-3-domain-classification-system.md)
  - [18.2.2 Linnaean Classification System](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-2-2-linnaean-classification-system.md)
- 18.3 Conservation
  - [18.3.1 Importance of Biodiversity](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-3-1-importance-of-biodiversity.md)
  - [18.3.2 Conservation](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-3-2-conservation.md)
  - [18.3.3 Zoos, Seedbanks, & Other Conservation Methods](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-3-3-zoos-seedbanks-and-other-conservation-methods.md)
  - [18.3.4 Assisted Reproduction & Contraception](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-3-4-assisted-reproduction-and-contraception.md)
  - [18.3.5 Non-Governmental Organisations](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/18-3-5-non-governmental-organisations.md)

### 19 Genetic Technology (A2 Only)
- 19.1 Manipulating Genomes
  - [19.1.1 Recombinant DNA & Genetic Engineering](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-1-1-recombinant-dna-and-genetic-engineering.md)
  - [19.1.2 Restriction Endonucleases](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-1-2-restriction-endonucleases.md)
  - [19.1.3 Gel Electrophoresis](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-1-3-gel-electrophoresis.md)
  - [19.1.4 DNA Probes & Microarrays](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-1-4-dna-probes-and-microarrays.md)
  - [19.1.5 End of Topic Test - Manipulating Genomes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-1-5-end-of-topic-test-manipulating-genomes.md)
  - [19.1.6 A-A* (AO2/3) - Manipulating Genomes](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-1-6-a-a-ao23-manipulating-genomes.md)
- 19.2 Genetic Technology Applied to Medicine
  - [19.2.1 Bioinformatics](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-2-1-bioinformatics.md)
  - [19.2.2 Applications of Recombinant DNA](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-2-2-applications-of-recombinant-dna.md)
  - [19.2.3 Genetic Screening](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-2-3-genetic-screening.md)
  - [19.2.4 Gene Therapy](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-2-4-gene-therapy.md)
  - [19.2.5 Ethics](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-2-5-ethics.md)
  - [19.2.6 DNA Profiling & Forensics](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-2-6-dna-profiling-and-forensics.md)
- 19.3 Genetically Modified Organisms in Agriculture
  - [19.3.1 GM Crops & Livestock](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-3-1-gm-crops-and-livestock.md)
  - [19.3.2 Ethics](https://senecalearning.com/en-gb/revision-notes/international-a-level/biology/cambridge-international/19-3-2-ethics.md)