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Cellular respiration intro


Cells are organic machines. Molecules are constantly being built, broken down, or transported. Every action takes a lot of energy. Where does this energy come from? The process of how a cell gets and uses energy is called cellular respiration.


respiration = breathing in and out air. Brings oxygen into your lungs, then into your bloodstream.

circulation = carries oxygenated blood from your lungs to all body cells

cellular respiration = how cells use oxygen to release chemical energy from food molecules

aerobic = a body process that requires O2 (oxygen gas)

anaerobic = a body process that doesn’t require O2

Main ideas: Why use ATP?

Our bodies don’t directly use energy from our food.

Sugars, fats and proteins all contain energy.

Yet inside our cells, each process use the ATP molecule – for energy.

atp molecule

That’s why weird. Why does our body make these ATP molecules? Why not just directly use the sugars, fats or proteins?

Imagine having a $1000 bill, and needing to buy soda, bread or a chocolate bar. They cost only a few bucks – and the $1000 bill you have is enormous. So we break the $1000 bill down into fifty $20 bills.

The same is true for energy: each sugar or fat contains a lot of energy, but each cell process event only requires a tiny bit of energy. So we “make change.”
Glucose convert to ATP

So sugar is like a $1000 bill, and ATP is like a $20 bill.


Ideally if you break a $1000 bill you should get fifty $20 bills. No money lost. If you ended up with than $1000, you’d have lower efficiency.

But when we break down the energy in a sugar, if we add up all the ATP energy, we only have about 38% of that energy. Where did the rest go?

The rest of the energy is lost as “waste heat.”

No real-world-process is 100% efficient. Every process loses some energy as heat. In fact, that is one of the major laws of the universe – the laws of thermodynamics.

But that’s okay for 2 reasons:

A. Some of this waste heat is useful – it keeps our bodies at 98.6 degrees F, which is necessary for life.

B. Hundreds of millions of years of animal evolution have adapted us to live within these conditions; it is expected and normal. As long as we get more calories each day, we’re fine.

Slide 1: Burning fuel to make energy

Slide 2: A body’s energy budget

Slide 3: Harvesting energy

Slide 4: The energy needs of life

Slide 5: What do we need to male energy?

Slide 6: What happens if oxygen is missing?

Slide 7: Anaerobic respirarion

Sample questions

Feb 2016 MCAS:  In cells, aerobic respiration (cellular respiration in the presence of oxygen) is more efficient than anaerobic respiration (cellular respiration in the absence of oxygen). This is because aerobic respiration produces more of which of the following substances?

A. ATP        B. DNA      C. glucose      D. protein

Learning Standards

Massachusetts Curriculum Frameworks: Biology

8.MS-LS1-7. Use informational text to describe that food molecules, including carbohydrates, proteins, and fats, are broken down and rearranged through chemical reactions forming new molecules that support cell growth and/or release of energy.

HS-LS1-7. Use a model to illustrate that aerobic cellular respiration is a chemical process
whereby the bonds of food molecules and oxygen molecules are broken and new
bonds form, resulting in new compounds and a net transfer of energy.

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