Cellular Respiration

Chapter 9-1

Chemical Pathways

Biology

Mr. Hines

How do heterotrophs obtain their

energy?

From eating.

Carbohydrates are the main form of food that

is converted into energy.

Carbohydrates include fruits, vegetables,

bread, pasta, candy, and others.

Just about anything that comes from a plant is

a carbohydrate.

Chemical energy and food

There are lots of calories in food.

One gram of sugar (mass of paperclip)

contains 3811 calories.

calorie – the amount of heat energy required

to raise the temperature of 1 gram of water

by 1 degree Celsius.

On food labels, you see calories listed all of the time.

This tells you how much energy is in the food.

Labels are misleading because they are really

reporting “kilocalories”

1 kilocalorie is equal to 1000 calories.

So multiply the number of calories listed on food

items by 1000!

If the “C” is capitalized on Calorie, it is a kilocalorie

In other words 1 Calorie = 1000 calories

Notice the capital C

How cells release the energy stored

in carbohydrates?

In this chapter, we will substitute the word

“carbohydrate” with the word “glucose.”

Glucose is a kind of carbohydrate.

The formula for glucose is C6H12O6.

The process by which cells release energy

from glucose is called “Glycolysis.”

Once glycolysis has completed, it

can take 2 paths

There are 2 paths

1. Cellular respiration – occurs in the

presence of oxygen

2. Fermentation – occurs without oxygen

Cellular Respiration

In the presence of oxygen, cellular respiration

takes on 3 stages

1. Glycolysis

2. Krebs cycle

3. Electron transport chain

The equation for cellular respiration is

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

Cellular respiration uses glucose, oxygen, and

forms carbon dioxide, water, and energy

The equation of cellular respiration seems

relatively simple.

There is more to the story – if all of the

energy stored in glucose were released at

once, it would be explosive.

Cells must release the energy slowly so that it

can be used efficiently.

In order to do this, ATP is necessary

The 3 stages of Cellular respiration

1. Glycolysis – takes place in the cytoplasm

of the cell

2. Krebs cycle – takes place in the

mitochondria

3. Electron transport chain – takes place in

the mitochondria

In order to shorten a long and

difficult story..

Here is what happens with one glucose molecule if oxygen is present.

Glycolysis creates 2 ATP in the cytoplasm

Krebs cycle creates 2 ATP in the mitochondria

Electron Transport chain creates 32 ATP in the mitochondria.

So one molecule of glucose will create 36 total ATP

Glucose Glycolysis

Cytoplasm

Pyruvic

acid

Electrons carried in NADH

Krebs

Cycle

Electrons

carried in

NADH and

FADH2 Electron

Transport

Chain

Mitochondrion

Figure 9–2 Cellular Respiration:

An Overview

Mitochondrion

Section 9-1

How fast?

This happens very quickly – millions of ATP molecules are created each second (per cell)

If there are trillions of cells in an organism and each cell is generating 1 million ATP molecules per second, then a living thing generates almost countless ATP molecules per second.

What happens if there is no oxygen?

Sometimes, a living thing will fall short of

oxygen during physical activities.

When there is not enough oxygen, cellular

respiration cannot occur.

Instead, the cells in mammals will go into

lactic acid fermentation.

There are 2 kinds of Fermentation

1. Lactic Acid Fermentation

2. Alcoholic Fermentation

Fermentation is a process that does not need

oxygen – It is therefore called “anaerobic”

Lactic acid fermentation

Here is the chemical equation for lactic acid fermentation

C6H12O6 → 2C3H6O3 + 4ATP

In this equation, glucose is broken down into two molecules of lactic acid (C3H6O3) and creates 4 ATP.

Lactic acid formation occurs in the cytoplasm.

Which is more efficient?

Cellular respiration is much more efficient

producing 36 ATP over 4 ATP.

Therefore, Cellular respiration is much more

desirable for living things!

Why do we get fatigued when we

exercise?

There are 2 reasons why we get fatigued when we exercise.

1. Not enough oxygen in the bloodstream will cause the body to go into lactic acid fermentation resulting in fewer ATP molecules available for use.

2. Lactic acid builds up in the blood stream which causes pain and burning.

**time to sit down and recharge??

So when you sit down after a

strenuous event,

Your body is recovering by…

1. Breathing heavy to replenish the oxygen so the body can get back to cellular respiration.

2. Breaking down the lactic acid in the blood stream (the liver does this)

**Once oxygen is replenished and the lactic acid is broken down, you can get back to exercise.

**A good athlete is conditioned with a strong cardio/pulmonary system to get the oxygen into the body efficiently.

When oxygen is present, the process is called

“Aerobic Respiration”

This is why we call physical exercise

“Aerobics” It increases your oxygen flow.

Remember - There are 2 kinds of

Fermentation

1. Lactic Acid Fermentation

2. Alcoholic Fermentation

Fermentation is a process that does not need

oxygen – It is therefore called “anaerobic”

Alcoholic Fermentation

Yeast cells (fungi kingdom) will do fermentation differently.

Here is the equation

C6H12O6 → C3H6O3 + C2H6O + CO2 + 4ATP

Notice the ethyl alcohol (C2H6O) – this is how we make beer, wine, and booze.

Also notice the CO2 (a gas) – this is the air in bread when it rises.

Fermentation at home

Notice that fermentation gives off CO2 – a

gas.

Yeast is used to make bread.

The gas given off from this reaction causes

bread to rise (air bubbles – gas)

The alcohol that is produced in this process is

evaporated in the oven.

Summary

Cellular respiration creates 36 ATP (requires

oxygen – AKA areobic)

C6H12O6 + 6O2 → 6CO2 + 6H2O + 36 ATP

Lactic acid fermentation creates 4 ATP (does

not require oxygen – AKA anaerobic)

C6H12O6 → 2C3H6O3 + 4ATP

Alcoholic fermentation creates 4 ATP (does

not require oxygen – anaerobic)

C6H12O6 → C3H6O3 + C2H6O + CO2 + 4ATP