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