Respiration Showdown

Respiration Showdown 🔥

Every second, in every cell, glucose is being broken down to release the **energy** that keeps you alive. That is **respiration** — and it is not the same as breathing. Meet the two ways cells do it, what changes when you exercise, and the wider web of reactions it all feeds.

Energy from glucose ⚡

**Respiration** is an **exothermic** reaction that transfers **energy** from **glucose**. It happens **continuously** in **all living cells** — not just when you breathe. That energy is used for **movement** (muscle contraction), **keeping warm**, and **building** larger molecules from smaller ones.

Energy in or out?

Respiration is an **exothermic** reaction. What does that tell you?

• It releases (transfers) energy from glucose
• It takes in energy from the surroundings
• No energy is involved
• It is the same as breathing

Aerobic: with oxygen 💨

**Aerobic respiration** uses **oxygen** and releases a **lot** of energy. It happens in the **mitochondria**: **glucose + oxygen → carbon dioxide + water** Higher tier — the balanced symbol equation is `C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O`.

Complete the equation

The word equation for aerobic respiration is: glucose + _____ → _____ + water.

Balance the oxygen

An interactive activity.

Anaerobic: no oxygen 🚫

When oxygen runs short, cells respire **anaerobically** — but it breaks glucose down **incompletely**, releasing **much less** energy. The products depend on the organism: • In your **muscles**: glucose → **lactic acid**. • In **yeast and plant** cells (**fermentation**): glucose → **ethanol + carbon dioxide** (used in brewing and baking).

Products of respiration

Which product?

A yeast cell respires anaerobically to make bread rise. Which products does it produce?

• Ethanol and carbon dioxide
• Lactic acid
• Carbon dioxide and water
• Oxygen and glucose

When you exercise 🏃

Exercising muscles need more energy, so they respire faster — demanding more **oxygen** and **glucose** and making more **CO₂**. Your body responds: **heart rate** rises, and **breathing rate and depth** increase to supply oxygen and remove CO₂. Higher tier — if oxygen can't keep up, muscles respire anaerobically and **lactic acid** builds up, causing muscle **fatigue**.

Paying the debt

Higher tier: after hard exercise you keep breathing heavily to repay an **oxygen debt**. What does that extra oxygen achieve?

• It lets the liver convert the built-up lactic acid back into glucose
• It stores extra oxygen in the muscles for next time
• It cools the muscles down
• It makes more carbon dioxide to breathe out

Metabolism: the whole web ⚗️

Respiration is just one part of **metabolism** — the **sum of all the chemical reactions** in a cell or the body. Metabolism includes: • Turning glucose into **starch, glycogen and cellulose**. • Building **lipids** from glycerol and fatty acids. • Using glucose + **nitrate ions** to make **amino acids**, then **proteins**. • Breaking down excess protein to form **urea**.

Part of metabolism?

Pick the TWO processes that are part of metabolism.

• Using glucose and nitrate ions to make amino acids
• Breaking down excess protein into urea
• Breathing air in and out of the lungs
• Turning oxygen into glucose in the lungs