Unit 3 Notes
“Energy of Life”
8-1 Objectives:
1. Compare and contrast autotrophs and heterotrophs.
2. Describe how ATP works in a cell.
How Organisms Obtain Energy
Chapter 8, Section 1
A. Energy
1. Energy is the ability to do work
2. Nearly every activity in modern society depends on one kind of energy or another.
a. When a car runs out of gas, it comes to a sputtering halt
b. Without electrical energy, lights, appliances, computers stop working.
3. All living things need energy too
B. Autotrophs and Heterotrophs
1. Plants and some other types of organisms are able to use light energy from the sun to
produce food
2. Autotroph—organisms that make their own food Example: plants
3. Heterotroph—obtain energy from the foods they consume
Example: animals
C. Chemical Energy and ATP
1. Forms of energy:
a. Light
b. Heat
c. Electricity
d. Chemical compounds
2. Living things use energy in the form of chemical compounds
3. Adenosine triphosphate (ATP)—main chemical compound used to store and release
energy; consists of Adenine, Ribose (5-carbon sugar), three phosphate groups
4. Storing Energy
a. Adenosine diphosphate (ADP)—same at ATP, but only has two phosphate
groups
b. When a cell has energy, it can store small amounts of it by adding a phosphate
group to ADP, making ATP.
c. In a way, ATP is like a fully charged battery, ready to power the machinery of the
cell
5. Releasing Energy
a. To release energy, the bond between the 2nd and 3rd phosphate is broken
b. ATP is the basic source of energy for all cells
c. ATP powers events in the cell, including active transport across cell membranes,
protein synthesis, and muscle contractions.
Energy Bond Forms
Energy Bond Breaks
8-2 Objectives:
1. Summarize the two phases of photosynthesis.
2. Explain the function of a chloroplast during the light reactions.
Photosynthesis: An Overview
Chapter 8, Section 2
A. Overview of Photosynthesis
1. Photosynthesis—plants use energy from sunlight to convert water and carbon dioxide
into sugar and oxygen.
B. The Photosynthesis Equation
6CO₂
+ 6H₂O  C₆H₁₂O₆ + 6O₂
Carbon dioxide + water 
sugars
+ oxygen
C. Light and Pigments
1. In addition to carbon dioxide and water, photosynthesis requires light and chlorophyll.
2. Pigment—light absorbing molecule
3. Chlorophyll—main pigment in plants;
a. reflects green light waves, which is why leaves appear green
b. absorbs light very well in the blue-violet and red regions of the visible spectrum
4. Plants also contain red and orange pigments such as carotene that absorb light
5. Other pigments in plants (Not Tested)
a. Anthocyanin—blue-green color
b. Chlorophyll a—yellow color
c. Chlorophyll b—yellow-green color
D. Inside a Chloroplast (Not Tested)
1. Photosynthesis takes place in chloroplasts
2. Structures in a chloroplast:
a. Thylakoids—saclike photosynthetic membranes that are arranged in stacks
b. Grana—stacks of the thylakoid
c. Photosystems—organized chlorophyll and other pigments into groups
d. Stroma—region outside the thylakoid membrane; Calvin cycle takes place here
E. Factors Affecting Photosynthesis
1. Water
a. Shortage of water can slow or even stop photosynthesis
b. Plants that live in dry conditions, such as desert plants, have a waxy coating on
their leaves that reduce water loss
2. Temperature
a. Photosynthesis depends on enzymes that function best between 0°C and 35°C.
b. Temperatures above or below this range may damage the enzymes, slowing
down the rate of photosynthesis
3. Light intensity
a. Increasing light intensity increases the rate of photosynthesis
b. However, after the light intensity reaches a certain level, the plant reaches its
maximum rate of photosynthesis
F. There are two stages to Photosynthesis
1. Light-dependent reactions (First)
a. Chlorophyll absorbs energy from sunlight and energy is transferred along
thylakoids, Water is broken down and Oxygen is produced
b. Energy that is carried along thylakoids is transferred in molecules of ATP
2. Light-independent reactions (Second)
a. Carbon Dioxide is added to a cycle of chemical reactions building larger
molecules of sugars
b. Energy, ATP, from the light-dependent reaction is used to form these simple
sugars
8-3 Objectives:
1. Summarize the stages of cellular respiration.
2. Compare alcoholic fermentation and lactic acid fermentation.
Cellular Respiration
Chapter 8, Section 3
A. Overview of Cellular Respiration
1. The process that releases energy by breaking down glucose and other food molecules in
the presence of oxygen
2. Equation for cellular respiration:
6O₂ + C₆H₁₂O₆  6CO₂ + 6H₂O + Energy
Oxygen + glucose  carbon dioxide + water + energy
B. Fermentation
1. Fermentation—releases energy from food molecules by producing ATP without oxygen
a. Anaerobic—“not in air”—does not require oxygen
b. The two main types of fermentation are alcoholic fermentation and lactic acid
fermentation.
2. Alcoholic Fermentation
a. Produces carbon dioxide and ethyl alcohol
b. Causes bread dough to rise; when yeast in the dough runs out of oxygen, it
begins to ferment, giving off bubbles of carbon dioxide that form the air spaces
you see in a slice of bread
c. The small amount of alcohol produced in the dough evaporates when the bread
is baked
3. Lactic Acid Fermentation
a. Produces lactic acid
b. Lactic acid is found in your muscles and used when your cells run out of oxygen
to make ATP; the buildup of lactic acid causes a painful, burning sensation.
c. This is why muscles may feel sore after only a few seconds of intense activity
d. Unicellular organisms also use lactic acid as a waste product
e. Example: prokaryotes are used in the production of a wide variety of foods and
beverages such as cheese, yogurt, buttermilk, and sour cream. Pickles and
sauerkraut are also produced using lactic acid fermentation.
C. Comparing Photosynthesis and Cellular Respiration
1. The energy flows in photosynthesis and cellular respiration take place in opposite
directions.
2. Photosynthesis and cellular respiration are complete opposites.
a. Photosynthesis removes carbon dioxide from the atmosphere and cellular
respiration puts it back
b. Photosynthesis releases oxygen into the atmosphere and cellular respiration
uses that oxygen to release energy from food
Comparing Photosynthesis to Cellular Respiration
Photosynthesis
Function
Location
Reactants
Products
Equation
Cellular Respiration
Energy capture
Energy release
Chloroplasts
Mitochondria
CO₂ and H₂0
C₆H₁₂O₆ and O₂
C₆H₁₂O₆ and O₂
CO₂ and H₂0
6CO₂ + 6H₂O  C₆H₁₂O₆ + 6O₂
6O₂ + C₆H₁₂O₆  6CO₂ + 6H₂O
ENERGY!
ENERGY