SECTION 4.2 Photosynthetic organisms are producers. Some organisms are called producers because they produce their own sources of chemical energy. Other organisms also use the chemical energy that producers make. Plants are producers. Plants capture energy from sunlight, and store it as chemical energy in the form of sugars. These sugars are made through photosynthesis. Remember from Section 3.2 that chloroplasts are organelles in plant cells where photo- synthesis takes place. Chlorophyll (KLAWR-uh-fihl) is a molecule in chloroplasts that absorbs some of the energy in visible* light. Plants use energy in visible light for photosynthesis. Visible light looks white, but it is made up of different wavelengths, or colors, of light. Plants have two kinds of chlorophyll, called chlorophyll a and chloro- phyll b. These two types of chlorophyll absorb red and blue wavelengths of light. Neither type of chlorophyll absorbs much green light. Plants are green because green wavelengths of light are reflected by chlorophyll. What is the role of chlorophyll in photosynthesis? Photosynthesis in plants occurs in chloroplasts. Chloroplasts are plant cell organelles. Two main parts of chloroplasts are needed for photosynthesis: • The grana (singular, granum) are stacks of compartments called thylakoids (THY-luh-KOYDZ). Thylakoids are shaped like coins, flat and circular. The thylakoid compartments are enclosed by mem- branes. These membranes contain chlorophyll. • The stroma is fluid that is all around the grana inside the chloroplast. There are two stages of photosynthesis, which are called the light- dependent reactions and the light-independent reactions. The light-dependent* reactions capture energy from sunlight. These reactions happen in the thylakoids and their membranes. Chlorophyll Overview of Photosynthesis KEY CONCEPT The overall process of photosynthesis produces sugars that store chemical energy. * ACADEMIC VOCABULARY dependent needs something to function visible able to be seen Student text pages 103–105 Chloroplasts in plant cells contain a light- absorbing molecule called chlorophyll, not shown here. chloroplast McDougal Littell Biology 56 SC.912.L.18.7
Transcript
SECTION
4.2
Photosynthetic organisms are producers. Some organisms are called producers because they produce their own sources of chemical energy. Other organisms also use the chemical energy that producers make. Plants are producers. Plants capture energy from sunlight, and store it as chemical energy in the form of sugars. These sugars are made through photosynthesis. Remember from Section 3.2 that chloroplasts are organelles in plant cells where photo-synthesis takes place.
Chlorophyll (KLAWR-uh-fihl) is a molecule in chloroplasts that absorbs some of the energy in visible* light. Plants use energy in visible light for photosynthesis. Visible light looks white, but it is made up of different wavelengths, or colors, of light.
Plants have two kinds of chlorophyll, called chlorophyll a and chloro-phyll b. These two types of chlorophyll absorb red and blue wavelengths of light. Neither type of chlorophyll absorbs much green light. Plants are green because green wavelengths of light are reflected by chlorophyll.
What is the role of chlorophyll in photosynthesis?
Photosynthesis in plants occurs in chloroplasts.Chloroplasts are plant cell organelles. Two main parts of chloroplasts are needed for photosynthesis:
• The grana (singular, granum) are stacks of compartments called thylakoids (THY-luh-KOYDZ). Thylakoids are shaped like coins, flat and circular. The thylakoid compartments are enclosed by mem-branes. These membranes contain chlorophyll.
• The stroma is fluid that is all around the grana inside the chloroplast.
There are two stages of photosynthesis, which are called the light-dependent reactions and the light-independent reactions.
The light-dependent* reactions capture energy from sunlight. These reactions happen in the thylakoids and their membranes. Chlorophyll
Overview of PhotosynthesisKEY CONCEPT The overall process of photosynthesis produces sugars that store chemical energy.
* ACADEMIC VOCABULARY
dependent needs something to function
visible able to be seen
Student text pages 103–105
Chloroplasts in plant cells contain a light-absorbing molecule called chlorophyll, not shown here.
absorbs energy from sunlight. The energy moves along the thylakoid membrane and is transferred to molecules that carry energy, such as ATP. During this process, water (H2O) molecules are broken down, and oxygen (O2) molecules are released.
The light-independent* reactions use the energy from the light-dependent reactions to make sugars. These reactions happen in the stroma. During this process, carbon dioxide (CO2) and energy from the light-dependent reactions are used to build sugars, usually glucose (C6H12O6).
The equation for the whole process of photosynthesis is shown below. You can see that there are many arrows between the reactants—6CO2 and 6H2O—and the products—C6H12O6 and 6O2. Although there is only one arrow, there are many steps in the process.
6CO2 � 6H2O C6H12O6 � 6O2
Carbon Dioxide Water light, enzymes a sugar oxygen
Circle the four main steps of photosynthesis shown on the diagram.
* ACADEMIC VOCABULARY
independent can function without something
OVERVIEW OF PHOTOSYNTHESIS
STAGE 1: Light-Dependent Reactions
1 Energy from sunlight is absorbed. Water mol-ecules are broken down and oxygen is released.
STAGE 2: Light-Independent Reactions
6H2O
chloroplast
sunlight
chloroplast ( the plant cell organelle where photosynthesis takes place)
6O2
3 Carbon dioxide molecules are used to build sugars.
1 six-carbon sugar
C6H12O6
6CO2
4 Six-carbon simple sugars are produced. The sugars are often used to build starches and cellulose.
stroma (fluid outside the thylakoids)
granum (stack of thylakoids)
thylakoid 2energy
Energy-carrying molecules, including ATP, transfer energy.
Interactive Reader 57
Circle the four main steps of photosynthesis shown on the diagram
Simple sugars, such as glucose, are not the only carbohydrates that come from photosynthesis. Plants use simple sugars to build starch and cellulose molecules. Another important product of photosynthesis is oxygen. You will read more about that in Sections 4.4 and 4.5.
photosynthesis light-dependent reactions
chlorophyll light-independent reactions
thylakoid
1. Which two terms are things that are found in the chloroplast?
2. Which term is a process that is made up of two other terms?
3. Which term is the part of photosynthesis when light energy is cap-tured and transferred to a molecule, such as ATP?
4. Which term is the part of photosynthesis when energy is used to make sugars like glucose?
5. Where in the plant cell does photosynthesis take place?
6. What molecule absorbs sunlight for photosynthesis?
7. Why are plants called producers?
8. Complete the chart below.
REACTION WHERE DOES IT HAPPEN? WHAT IS NEEDED IN THE REACTION?
WHAT IS PRODUCED BY THE REACTION?
Light-dependent reactions
water (H2O) and sunlight
Light-independent reactions
sugar (C6H12O6)
4.2 Vocabulary Check
Go back and highlight each sentence that has a vocabulary word in bold.
Mark It Up4.2 Vocabulary Check
Go back and highlight each sentence that has a vocabulary word in bold.
Mark It Up
4.2 The Big Picture4.2 The Big Picture
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