How long do you think someone can hold their breath underwater? 

Why do we need to breath at all?

After Video Question: 

Do you think Vitomir could hold his breath for 29 minutes if he was swimming instead of just floating in the same spot? Why/Why not? 

Cellular Respiration: How Cells Release Energy

All living things need energy to survive, and human cells rely on a process called cellular respiration to get that energy. Although food gives your body nutrients, your cells cannot use food molecules directly. Instead, they break down a simple sugar called glucose in the presence of oxygen to release usable energy. This energy is stored in ATP, which is the main molecule cells use to power their activities.

The chemical equation for cellular respiration can be written in two forms. 

The chemical form is:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

When written in words, the equation is:
glucose + oxygen → carbon dioxide + water + ATP 

In this equation, glucose and oxygen are the reactants. They are the starting materials the cell needs to begin the process. The main product the cell wants is ATP, which supplies energy for life functions.

Cells need ATP for many essential tasks. One major job that requires energy is active transport, which moves molecules across the cell membrane from low concentration to high concentration. This process can only happen if ATP is available. ATP is also required for muscle movement, nerve signals, building new molecules, and repairing cell parts. Without ATP, none of these life processes would be possible.

Most of cellular respiration takes place inside the mitochondria, the energy releasing organelles inside the cell. As glucose and oxygen are broken down in the mitochondria, the cell captures large amounts of energy and converts it into ATP. The process also forms carbon dioxide and water, which are known as byproducts. These byproducts are not useful to the cell and must be removed. Carbon dioxide leaves the body when you exhale, and water can be used in the cell or released through sweat, urine, or vapor when you breathe out.

When cells do not have enough glucose, they cannot produce as much ATP. This may happen during intense activity or when someone has not eaten in a long time. The body can switch to stored fats or proteins, but these sources still do not provide ATP as efficiently as glucose.

When cells do not have enough oxygen, the situation becomes life threatening. Oxygen is required for the mitochondria to release large amounts of ATP from glucose. Without oxygen, ATP levels drop sharply, and the cell must switch to a short backup process that makes very little energy and creates lactic acid instead of carbon dioxide as a byproduct. This backup method cannot sustain the body. This is why people die when they cannot breathe. Without oxygen, cells in the brain, heart, and other organs stop making ATP and begin to shut down.

Key Concepts

• Cells use cellular respiration to release energy from glucose.

• Cellular respiration requires oxygen and glucose and happens in the mitochondria.

• The main product cells want is ATP, which provides energy for life functions (i.e. active transport, protein synthesis)

• Carbon dioxide and water are byproducts that the body removes through breathing and other processes.

• If a person cannot breathe, cells do not get oxygen, and ATP production stops. No energy = death. 

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Reactants: The starting materials of a chemical reaction. For cellular respiration these are glucose and oxygen.

Products: The materials made at the end of a reaction. For this process the product the cell wants is ATP.

Byproducts: Extra materials the cell does not need. Carbon dioxide and water are byproducts of cellular respiration.

ATP: The molecule that stores and releases energy for the cell.