LIFE FUNCTIONS AND ENERGY INTAKE – LIFE SCIENCE

Introduction

Just as a lightbulb needs electricity and a car needs gasoline, cells need a source of energy to function. All organisms obtain energy from food. Most organisms are consumers—they eat other organisms for food. Producers, such as plants, use light energy from the sun to make their own food through a process called photosynthesis.

Photosynthesis

Photosynthesis is a chemical reaction that takes place in the cells of a plant’s leaves. Carbon dioxide enters the leaf through tiny openings called stomata. Water absorbed by the plant’s roots travels to the leaf cells. Inside the cells, structures called chloroplasts use light energy to drive a reaction between carbon dioxide and water. This reaction produces glucose (a type of sugar) and oxygen:
• Glucose travels throughout the plant to be used or stored as energy.
• Oxygen exits the leaf through the same tiny holes.

Carbon dioxide + Water + Light energy – Glucose + Oxygen
Cells obtain energy from food through respiration, which occurs in two main stages:

1. First stage: Glucose from food enters the cell and is broken down into smaller molecules. This process releases a small amount of usable energy.
2. Second stage: The smaller molecules react with oxygen inside the cell’s mitochondria. This reaction produces carbon dioxide, water, and a large amount of energy. This energy powers the cell’s normal functions.

Glucose + Oxygen – Carbon dioxide + Water + Energy

Fermentation

Cells typically use respiration because it produces a large amount of usable energy. However, respiration requires oxygen. When oxygen is not available, some cells can use fermentation, an alternative method for converting energy. Fermentation releases only a small amount of energy but does not require oxygen.
For example, your muscle cells normally use respiration to produce energy. When you exercise intensely, your cells use energy faster than oxygen can be delivered. To keep working, your muscle cells temporarily switch to fermentation, providing a small but critical supply of energy until oxygen levels recover.