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 6H 2 O + 6CO  C 6 H 12 O 6 + 6O 2

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 C 6 H 12 O 6 + 6O  6H 2 O + 6CO 2

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 Respiration  Not 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 Oxygen Not enough Oxygen Cellular RespirationAlcoholic 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 exercise  Lactic 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.