Cell Energy

Accessing energy stored by photosynthesis

Photosynthesis

Plants harvest energy from photons of light

Use it to excite electrons Use excited electrons to form the bonds in

a sugar molecule

6H2O + 6CO2--------- C6H12O6 + 6O2

Cellular Energy

Animal (and fungi and protist) cells need to access the energy stored by photosynthesis.

They release the energy stored in sugars in a process that is the reverse of photosynthesis

C6H12O6 + 6O2 -------- 6H2O + 6CO2

Glycolysis

The very first reaction

Breaks Glucose into smaller sugar molecules

Different Pathways after Glycolysis

There are two main pathways to release energy from glucose

The amount of oxygen available controls the pathway

Plenty of Oxygen = Cellular RespirationNot much Oxygen = Fermentation

Two types of Fermentation

Lactic Acid Fermentation: Our muscles carry this out when they run low on oxygen, producing ATP and Lactic Acid

Alcoholic Fermentation: Yeast cells carry this out, producing ATP and Alcohol.

Picture of Pathway

Glycolysis

Lots

of Oxy

gen

Not enough Oxygen

Cellular Respiration Alcoholic Fermentation

Lactic Acid Fermentation

Cellular Respiration

Using Oxygen to break apart food molecules (sugars)

Takes place in the mitochondria Produces lots of ATP and releases CO2

and H2O as byproducts Muscles will do this as long as they don’t

run out of oxygen

Lactic Acid Fermentation

Takes place when there’s not enough oxygen for cellular respiration

Produces ATP, but also Lactic Acid Muscles do this when they run low on

oxygen

Lactic Acid causes the burning sensation

Alcoholic Fermentation

Occurs in organisms that do not carry out cellular respiration or lactic acid fermentation

Produces ATP, but also Alcohol and CO2 as byproducts.

Yeast cells do this—we use them to make beer, wine, and bread.

Our Cells

Will either do:Cellular respiration: During slow, steady

exerciseLactic Acid Fermentation: During strenuous

exercise like sprinting, or lifting heavy weights.

Do not carry out alcoholic fermentation—it would kill your cells

What happens during exercise?

First 90 Seconds: Cells carry out cellular respiration, burning mostly ATP.

Next approximately 20 minutes: Cells carry out cellular respiration, but burn glycogen (a small sugar) and other simple carbohydrates.

Only after about 20 minutes: Cells burn fat reserves.

What Metabolism Really Is

Metabolism is how fast your body burns energy reserves.Fast metabolism—you burn them fast, and it

seems like you are always hungry and don’t gain much weight

Slow metabolism—you are better at storing reserves than others. You may feel hungry, but find you gain weight easily

Can Metabolism Change?

As we age, our bodies tend to slow down. We can’t exercise the way we once could. Sometimes metabolism slows, but mostly we

just don’t burn as many calories.

Maintaining an exercise routine, especially one that runs longer than 20 minutes, can maintain your metabolism level.

Why is it hard to lose weight?

Body is good at changing systems to maintain the weight it wants.

When you start to burn fat, your body makes you feel tired and may make you crave more sugar.

If you try to control weight just by diet alone, your body will slow down in an attempt to save your fat reserves.