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?

A student records a small temperature RISE in a flask of germinating peas, but no rise at all in a flask of dead peas. What does that show?

• The living peas are respiring, and respiration is exothermic so it releases energy as heat
• The living peas are respiring, and respiration is endothermic so it takes heat from the flask
• The living peas are breathing, and that warms the air trapped inside the flask
• The living peas are photosynthesising, and that releases heat into the flask

The showdown

Two ways to release energy from glucose, and the anaerobic route splits again depending on the organism. Mixing up the last two columns is the easiest mark to lose in this whole topic.

Complete the equations

Aerobic: glucose + _____ → carbon dioxide + water. Anaerobic in muscle: glucose → _____. Anaerobic in yeast: glucose → _____ + carbon dioxide.

Balance the oxygen

Higher tier: in `C₆H₁₂O₆ + ?O₂ → 6CO₂ + 6H₂O`, what number balances the oxygen (the O₂ coefficient)?

Products of respiration

Which product?

A baker's dough rises in a warm covered bowl with no air getting in. Which process is raising it, and what is the gas?

• Anaerobic respiration in the yeast, giving carbon dioxide alongside ethanol
• Anaerobic respiration as it happens in muscle, giving carbon dioxide alongside lactic acid
• Aerobic respiration in the yeast, giving carbon dioxide and water
• Photosynthesis in the flour, giving oxygen as the gas

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**.

Read the race report

Tap the phrase that describes **anaerobic respiration** happening in the runner's muscles.

• Off the gun her
• heart rate climbed to deliver more oxygen
• , then over the final bend
• her legs filled with lactic acid and began to fatigue
• . Across the line
• she stood bent double, breathing hard for several minutes
• .

The sprint

Follow what happens in a sprinter's muscles from the gun to well past the finish line.

• Twenty seconds in, her muscles need energy faster than her blood can deliver oxygen. What do they do?
• Something builds up in her muscles as a result. What is it, and what does it cause?
• She crosses the line and keeps breathing hard for several minutes. What is that extra oxygen called, and what is it for?
• Higher tier. Where does the lactic acid actually go, and what becomes of it?

Metabolism: the whole web

Respiration is just one part of **metabolism**: the **sum of all the chemical reactions** in a cell or the body. These are the reactions AQA names.

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 to form urea
• Breathing air in and out of the lungs
• Turning oxygen into glucose in the lungs
• Pumping blood from the heart around the body

Compare them

Compare aerobic and anaerobic respiration in a human. Then explain why a sprinter keeps breathing hard for several minutes after crossing the line.

• Say whether each one uses oxygen, and give the products of each.
• Say which releases more energy, and WHY: one breaks glucose down completely, the other does not.
• Name what builds up in the muscles during anaerobic respiration, and what it causes.
• For the second part, name the oxygen debt and say what the extra oxygen is for.
• Higher tier: say where the lactic acid is carried to, and what the liver converts it back into.