18.1 Biotechnology

2026 Syllabus Objectives

By the end of these notes, you should be able to:

  1. Explain the role of yeast in the production of bread and ethanol
  2. Understand that bacteria are useful in biotechnology and genetic modification due to their rapid reproduction rate and their ability to make complex molecules
  3. Discuss why bacteria are useful in biotechnology and genetic modification — specifically: (a) no ethical concerns over their manipulation and growth, and (b) the presence of plasmids
  4. Describe how fermenters can be used for the large-scale production of useful products by bacteria and fungi, including the conditions that need to be controlled: temperature, pH, oxygen, nutrient supply, and waste products
  5. Describe the use of: (a) enzymes in biological washing powders, (b) pectinase for fruit juice production, and (c) lactase for lactose-free milk

What is Biotechnology?

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Biotechnology is the use of living organisms — or parts of them, such as enzymes — to make useful products or carry out useful processes. Humans have used biotechnology for thousands of years without even realising it. Baking bread and brewing beer are both ancient examples. Today, biotechnology is also used in medicine, food production, and industry.

Objective 1: The Role of Yeast in the Production of Bread and Ethanol

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What is Yeast?

Yeast is a microscopic (very tiny) single-celled fungus. It is a living organism, and like all living things, it respires — meaning it breaks down sugar to release energy. What makes yeast special and useful is how it respires.

Yeast can respire in two ways:

  • Aerobically — using oxygen (produces carbon dioxide and water)
  • Anaerobically — without oxygen (produces carbon dioxide and ethanol)

It is the anaerobic process — called fermentation — that is important in biotechnology.

The word equation for fermentation in yeast is:

Glucose → Ethanol + Carbon dioxide (+ energy released)

Yeast in Bread Making

When yeast is added to bread dough, it is mixed with flour, water, and sugar. The yeast breaks down the sugar through fermentation and releases carbon dioxide gas.

  • The carbon dioxide gas forms tiny bubbles inside the dough.
  • These bubbles make the dough rise — it gets bigger and lighter.
  • When the dough is baked in the oven, the heat kills the yeast and evaporates the ethanol (so no alcohol remains in the bread).
  • The bubbles are "set" by the heat, giving bread its soft, spongy texture.

In short: Yeast makes bread rise by producing carbon dioxide gas through fermentation.

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