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BIO CH09 Foundations.pdf (2)
biology (bio120)
Florida International College
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CHAPTER
####### 9 LESSON
1
Energy and Life
Chemical Energy and ATP
KEY QUESTION Why is ATP useful to cells? Cells require energy to perform work, and energy makes life possible. We humans cannot use sunlight as a source of energy, but must take in food made by other organisms, plant or animal, to acquire energy. We are heterotrophs.
Heading Main Idea
Chemical Energy and ATP Chemical energy is contained in the bonds between atoms. ATP is the molecule that organisms use to temporarily store energy.
Storing Energy
Releasing Energy
How Cells Use ATP
Heterotrophs and Autotrophs
As you read, circle the answers to each Key Question. Underline any words you do not understand.
READING TOOL Main Idea As you read the lesson, complete the main idea
table for each heading. The first one has been completed for you.
Lesson Summary
106 Chapter 9 Photosynthesis Copyright © by Savvas Learning Company LLC. All Rights Reserved.
Energy comes in many forms, including light, heat, and electricity. Energy can be stored in chemical compounds, too. For example, when you light a candle, the wax melts, soaks into the wick, and is burned. As the candle burns, chemical bonds between carbon and hydrogen atoms in the wax are broken. New bonds then form between these atoms and oxygen, producing CO 2 and H 2 O (carbon dioxide and water). These new bonds are at a lower energy state than the original chemical bonds in the wax. The energy is released as heat and light in the glow of the candle’s flame.
Storing Energy All living cells store energy in the chemical
bonds of certain compounds. Of these compounds, one of the most important is adenosine triphosphate (ATP). ATP consists of adenine, a 5-carbon sugar called ribose, and three phosphate groups. The phosphate groups are the key to ATP’s ability to store and release energy. Adding a phosphate group to adensosine diphosphate (ADP) adds energy to the molecule and changes it to ATP. When a cell requires this energy, it removes the third phosphate group from ATP, changing it to ADP again.
Releasing Energy ATP can release energy by breaking the
bonds between its phosphate groups. This characteristic of ATP makes it exceptionally useful as a basic energy source for all cells. ATP is the most immediate source of energy for cells.
How Cells Use ATP Cells use the energy provided by ATP
to carry out active transport. Many cell membranes contain sodium-potassium pumps, which are membrane proteins that pump sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. ATP provides the energy that keeps this pump working, which involves maintaining a carefully-regulated balance of ions on both sides of the cell membrane. The energy stored in ATP also enables cells to move, providing power for motor proteins that contract muscles and generate the wavelike movement of cilia and flagella. Energy from ATP can be transferred to other molecules in the cell to power processes such as protein synthesis. The chemical energy from ATP can even be converted to light. In fact, the blink of a firefly comes from an enzyme that is powered by ATP! Most cells have only enough ATP to last for a few seconds of activity. ATP is not a good molecule for storing large amounts of energy over the long term. A single molecule of the sugar glucose, for example, stores more than 90 times the energy required to add a phosphate group to ADP to produce ATP. Therefore, it is more efficient for cells to keep only a small supply of ATP on hand. Cells regenerate ATP from ADP as needed by using the energy in sugars and other sources.
BUILD Vocabulary
adenosine triphosphate (ATP) compound used by cells to store and release energy Word Origins The name photosynthesis comes from the Greek words phós (light) and synthesis (putting together). What other words do you know that begin with the prefix photo-?
Copyright © by Savvas Learning Company LLC. All Rights Reserved. 9 Energy and Life 107
CHAPTER
####### 9 LESSON
2
Photosynthesis: An Overview
READING TOOL Make Connections Fill in the concept map to show the
organization of a chloroplast. Then below, answer the questions to describe how the different parts are related to each other.
Chlorophyll and Chloroplasts
KEY QUESTION What role do pigments play in the process of photosynthesis?
Our lives, and the lives of nearly every living thing on the surface of Earth, are made possible by the sun and the process of photosynthesis. In order for photosynthesis to occur, light energy from the sun must somehow be captured.
As you read, circle the answers to each Key Question. Underline any words you do not understand.
Complete each of the following sentences.
Saclike membranes that contain chlorophyll are known as.
is a stack of thylakoids.
is the fluid portion of the chloroplast outside of the thylakoids.
Two surround and enclose the chloroplasts.
Chloroplast
Lesson Summary
Copyright © by Savvas Learning Company LLC. All Rights Reserved. 9 Photosynthesis: An Overview 109
Light The sun’s energy travels to Earth in the form of light.
Sunlight, which our eyes perceive as “white” light, is actually a mixture of different wavelengths. Our eyes see the different wavelengths of the visible spectrum as different colors: shades of red, orange, yellow, green, blue, indigo, and violet.
Pigments Light-absorbing compounds are known as
pigments. Photosynthetic organisms primarily use the pigment chlorophyll to capture the energy in sunlight. The principal pigment of green plants is known as chlorophyll. Two types of chlorophyll, a and b, are found in plants, and are available to absorb different parts of the visible light spectrum, primarily blue-violet and red. Chlorophyll does not absorb the color green. Leaves appear green because they reflect these wavelengths. Plants also have red and orange carotene pigments, which we can only see when leaves begin to die during the fall.
Chloroplasts The plant organelle known as a chloroplast
is where photosynthesis takes place. Within chloroplasts are grana, which are stacks of thylakoids that contain chlorophyll. The rest of the fluid outside of this is called stroma. The number of chloroplasts per cell varies across different plants. Chloroplasts can sometimes move within plants, as well as duplicate themselves.
Energy Collection The light energy collected by a cluster
of pigments, including chlorophyll, is transferred to the reaction center in the center of the cluster where a particular chlorophyll molecule is excited and releases energized electrons. These high-energy electrons are vital to later steps of photosynthesis.
High-Energy Electrons
KEY QUESTION What are electron carrier molecules?
Specific molecules called electron carriers are necessary to convey the highly reactive and high-energy electrons that are produced by chlorophyll. The electron carrier moves the electrons with their energy to other molecules where they are needed. Nicotinamide adenine dinucleotide phosphate, or NADP+, is one such electron carrier. When it accepts two high-energy electrons, NADP + also bonds a hydrogen ion, which turns it into NADPH. Now the captured energy can be moved to the location in the chloroplast where sugars are manufactured.
BUILD Vocabulary
pigment light-absorbing molecules used by plants to gather the sun’s energy
chlorophyll principal pigment of plants and other photosynthetic organisms
thylakoid saclike membranes found in chloroplasts, the location of the light-dependent reactions
stroma fluid portion of the chloroplasts; outside of the thylakoids, location of the light- independent reactions (Calvin cycle)
NADP+ (nicotinamide adenine dinucleotide phosphate) carrier molecule that transfers high-energy electrons from chlorophyll to the Calvin cycle
Word Origins The word “thylakoid” comes from the Greek word thylakos, meaning sac or pouch. There once was a species of marsupials called the thylacine that went extinct in the 1930’s. Based upon what you know about the Greek word thylakos, how do you think the thylacines carried their young?
110 Chapter 9 Photosynthesis Copyright © by Savvas Learning Company LLC. All Rights Reserved.
CHAPTER
9
The Process of Photosynthesis
####### LESSON
3
The Light-Dependent Reactions:
Generating ATP and NADPH
KEY QUESTION What happens during the light-dependent reactions? The light-dependent reactions use solar energy to convert ADP and NADP+ into the energy and electron carriers ATP and NADPH. Oxygen is produced as a by-product of this reaction. The light-dependent reactions occur across the thylakoids of chloroplasts. Thylakoids are saclike membranes that contain most of the machinery needed to carry out photosynthesis, including clusters of chlorophyll and proteins known as photosystems.
Photosystem II The light-dependent reactions begin in
photosystem II. Chlorophyll molecules in the photosystem ab- sorb light. This absorption of light raises electrons in chlorophyll to a higher energy level, and these high-energy electrons (e–) are passed from chlorophyll to the electron transport chain.
READING TOOL Main Idea As you read the lesson, complete the main idea table for the primary headings below.
Heading Main Idea The Light-Dependent Reactions: Generating ATP and NADPH
The Light-Independent Reactions: Producing Sugars
Factors Affecting Photosynthesis
As you read, circle the answers to each Key Question. Underline any words you do not understand.
BUILD Vocabulary
photosystem cluster of chlorophyll and proteins found in thylakoids
Lesson Summary
112 Chapter 9 Photosynthesis Copyright © by Savvas Learning Company LLC. All Rights Reserved.
BUILD Vocabulary
electron transport chain series of electron carrier proteins that shuttle high-energy electrons in preparation for ATP-generating reactions ATP synthase enzyme that spans the thylakoid membrane and produces ATP from ADP when hydrogen ions (H +) pass through it Calvin Cycle the light- independent reactions of photosynthesis in which energy from ATP and NADPH is used to build high-energy compounds such as sugar Suffixes When words end in -ase this usually indicates an enzymatic protein. ATP synthase is an enzymatic protein that creates ATP. What molecules need to travel through ATP synthase to help it create ATP?
Electron Transport Chain The Electron Transport Chain
(ETC) uses energy from the electrons to pump protons (H+) through the proteins in the chain from the stroma to the inside of the thylakoid sac. At the end of the electron transport chain, the electrons themselves pass to a second photosystem called photosystem I.
Photosystem I In Photosystem I the low-energy electrons
from the ETC are passed to chlorophyll molecules and re-energized using light energy. The energized electrons are passed on to an enzyme that facilitates the production of NADPH from NADP+ and hydrogen ions. The NADPH can now move on to the light-independent reactions.
Hydrogen Ion Movement and ATP Formation All
of the prior steps involved some increasing of H+ concentration inside the thylakoids. Now there is a concentration gradient between the inside and outside of the thylakoid. Because molecules tend to move from a high to low concentration, the H + ions will move back across the thylakoid, if given the opportunity. ATP synthase provides a pathway for the hydrogen ions. As H+ ions move across the thylakoid, through the ATP synthase protein, ADP is converted into ATP by the addition of a phosphate group.
Summary of Light-Dependent Reactions Light
energy is used to convert ADP to ATP, and NADPH+ to NADPH. Water is split apart to make electrons available to PS II, which produces O 2 and hydrogen ions.
The Light-Independent
Reactions
KEY QUESTION What happens during the light-independent reactions?
During the light-independent reactions, ATP and NADPH from the light-dependent reactions are used to synthesize high- energy sugars. The light-independent reactions are commonly referred to as the Calvin cycle. The Calvin cycle occurs in the stroma of the chloroplast.
Carbon Dioxide Enters the Cell Carbon dioxide that
has entered the leaves through the stomata is used in the Calvin cycle to produce higher energy sugars. An enzyme called RuBisCO “grabs” the CO 2 and brings it into the cycle where the energy from ATP and NADPH is used, through a series of steps, to produce a simple 3-carbon sugar for every 3 carbon dioxides that enter the cycle.
Sugar Production The two 3-carbon compounds are vital
later on, helping to make other carbon-based compounds. One glucose molecule is a 6-carbon compound and would require 6 “turns” of the Calvin cycle.
Copyright © by Savvas Learning Company LLC. All Rights Reserved. 9 The Process of Photosynthesis 113
CAM Plants Crassulacean acid metabolism (CAM) plants
open their stomata at night to allow for gas exchange when water loss will be minimized. They store the CO 2 that they collect at night as in an organic acid. When day comes, they then release the CO 2 in order to perform photosynthesis as usual. This evolved in some plants as an adaptation to arid conditions. The jade plant is one example of the Crassulacea family.
Where does the ATP and NADPH get created?
How many molecules of carbon dioxide are required to produce a 6-carbon sugar?
Label the diagram with the four molecules that carry energy through photosynthesis.
Visual Reading Tool: The Light-Independent Reactions
ATP
ADP
CO 2
Sugars and Other Compounds
6
6
12
10 12
6
2
STROMA
CYTOPLASM
From Light-Dependent Reactions
From Light-Dependent Reactions
12
12
12
12
6
6
Copyright © by Savvas Learning Company LLC. All Rights Reserved. 9 The Process of Photosynthesis 115
9 Chapter Review
Review Vocabulary
Choose the letter of the best answer.
The main pigment of green plants is: A. thylakoid B. carotene C. chlorophyll D. chloroplast
What concentration gradient powers ATP synthase? A. O 2 B. CO 2 C. H+ D. H 2 O
Match the vocabulary term to its definition.
material that absorbs light energy
source of temporary energy
reactions that occur in the thylakoid membrane
fluid matrix of chloroplasts
a. stroma
b. pigment
c. ATP
d. light-dependent
Review Key Questions
Provide evidence and details to support your answers.
What is the importance of photosynthesis for all life?
How is energy captured from the sun?
In what stages are carbon dioxide and oxygen involved in photosynthesis ATP production?
116 Chapter 9 Photosynthesis Copyright © by Savvas Learning Company LLC. All Rights Reserved.
BIO CH09 Foundations.pdf (2)
Course: biology (bio120)
University: Florida International College
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