Standard IIObjective C (continued)

Objectives• Write and explain the chemical formula for cellular respiration.• Compare photosynthesis with cellular respiration.• Describe the results of fermentation and understand when fermentation is needed.• Where does the energy captured at the beginning of photosynthesis originate from?• What is the form of chemical energy produced by photosynthesis?

Cellular RespirationHow does the food you eat provide energy? When you need a quick boost of energy, you might reach for an apple or a candy bar. Although foods with sugars can give you a quick boost of energy, they cannot be used for energy directly by your cells. Energy is simply stored in these foods. Through the process of cellular respiration, the energy in

food is converted into energy that can be used by the body's cells. Glucose and O2 is converted into ATP and CO2 and H2O. ATP is the molecule that provides energy for your cells to

perform work.Cellular respiration a process that converts one type of

chemical energy, the energy stored in sugar, into another type, ATP.

Overview of Cellular RespirationMost often, cellular respiration proceeds by breaking down

glucose into carbon dioxide and water. As this breakdown of glucose occurs, energy is released.

The process of cellular respiration includes the conversion of this stored energy into ATP.

This exchange of carbon dioxide and oxygen in all the organisms that use photosynthesis and/or cellular respiration worldwide, helps to keep atmospheric oxygen and carbon dioxide at somewhat stable levels.

Glucose is broken down slowly so that cells convert as much sugar as possible into the usable form of energy, ATP.

Some energy is lost in the process in the form of heat. When one molecule of glucose is broken down, it can be

converted to a net total of 36 or 38 molecules of ATP.

Cellular respiration can be divided into three phases.1. Glycolysis: the breakdown of glucose.2. The Krebs Cycle (citric acid cycle): the

formation of electron carriers.3. The electron transport chain: use of oxygen

to make ATP.In eukaryotic cells, the first phase takes place in the cytoplasm of the cell, while the other phases are carried out in the mitochondria.

MitochondriaThis organelle is known as the “powerhouse”

of the cell because this is the organelle where the ATP that powers the cell is produced.

1st step - GlycolysisDuring glycolysis, glucose is converted into

Pyruvate and energy. After glycolysis, the pyruvate can go down

several different paths. If there is oxygen available, the pyruvate

moves inside the mitochondrion to produce more ATP during further break-down stages.

In the absence of oxygen, the fermentation process begins.

2nd step – The Krebs CycleInside the Mitochondria if oxygen is available,

the next step of cellular respiration is moving the pyruvate into the mitochondria.

The mitochondria’s unique shape makes it possible to carry out the Krebs Cycle.

The Krebs cycle starts with pyruvic acid (pyruvate) and produces energy.

Within the mitochondria the Krebs Cycle or citric acid cycle occurs.

The citric acid cycle is a series of steps that produce Carbon dioxide, ATP, NADH and FADH2.

The Electron Transport Chain takes place in the Mitochondria and changes NADH and FADH into ATP. What is the final product of the ETC?

3rd step – The Electron Transport Chain

During this energy conversion oxygen, which is necessary, combines with hydrogens and becomes water.

That is the key reason why this process only occurs in the presence of oxygen.

This is known as aerobic respiration. The Electron Transport Chain takes place in the

Mitochondria and changes NADH and FADH in to ATP.However, there is not always enough oxygen present for aerobic respiration to occur. In this case, the next step after glycolysis will be fermentation instead of the citric acid cycle.

What is the final product of the ETC?

FermentationSometimes cellular respiration is anaerobic,

occurring in the absence of oxygen. In the process of fermentation, the NAD+ is recycled so that is can be reused in the glycolysis process. No additional ATP is produced during fermentation. Yeasts (single-celled eukaryotic organisms) carry

on alcoholic fermentation in the absence of oxygen, making ethyl alcohol and carbon dioxide.

Animals and some bacteria and fungi carry out lactic acid fermentation.

Why do your muscles get sore after vigorous exercise?

What is the purpose of fermentation?

Lactate (lactic acid) is a waste product of lactic acid fermentation. Our muscles undergo lactic acid fermentation

during strenuous exercise, when oxygen cannot be delivered to the muscles quickly enough.

The buildup of lactate is what makes your muscles sore after vigorous exercise.

Bacteria that produce lactate are used to make cheese and yogurt.

Tooth decay is also accelerated by lactate from the bacteria that use the sugars in your mouth.

In all these types of fermentation, the goal is the same: to recycle NAD+ for glycolysis.

Products of fermentation include cheese (lactic acid fermentation) and wine (alcoholic fermentation).

• Alcoholic fermentation is central to bread baking.

• The carbon dioxide bubbles allow the bread to rise, and the alcohol evaporates.

• In wine making, the sugars of grapes are fermented to produce the wine.

SummaryCellular respiration is the breakdown of glucose to

release energy in the form of ATP.Glycolysis, the conversion of glucose into two 3-

carbon pyruvate molecules, is the first step of cellular respiration.

If oxygen is available, the pyruvate enters the mitochondria and goes through a series of reactions, including the citric acid cycle, to produce more ATP.

If oxygen is not available, the pyruvate is reduced during the process of fermentation to free up more NAD+ for glycolysis, and there is no net gain of ATP.

Review Questions1. What are the products of alcoholic

fermentation?2. What is the metabolic process where glucose is

ultimately converted to two molecules of pyruvate?

3. What is the purpose of fermentation?4. Where does the citric acid cycle take place?5. Write the chemical reaction for the overall

process of cellular respiration.6. Which is more efficient, aerobic or anaerobic

cellular respiration?

Vocabulary

• ATP• Chlorophyll• Photosynthesis• Cellular

Respiration

• Homeostasis• Fermentation• Anaerobic

respiration• Aerobic

respiration

Points to Consider1. Now that we know how the cell gets its

energy, we are going to turn our attention to cell division. Cell division is a highly regulated process.

2. What do you think could happen if your cells divide uncontrollably?

3. When new life is formed, do you think it receives all the DNA of the mother and the father?

4. Why do you think you might need new cells throughout your life?