Chapter 8 Photosynthesis (Page 200) Section 8 1: Energy and Life (Page 201) Energy is the ability to do work. Living things depend on energy. Without the ability to obtain and use energy, life would cease to exist. 1
Chapter 8 Photosynthesis (Page 200) 1. What is energy? Energy is the ability to do work. 2. Where does the energy that living things need come from? It comes from food though most energy in food comes from the sun. 3. How do autotrophs and heterotrophs differ? Autotrophs are organisms that use light energy from the sun to make their own food. Heterotrophs obtain energy from the foods they consume. 4. What is one of the principal chemical compounds that cells use to store and release energy? Provide the compound's name and abbreviation. The compound is adenosine triphosphate or ATP. 5. What does the principal compound consist of? It consists of adenine (a nitrogen base), ribose (a five carbon sugar) and three phosphate groups. 6. Copy Figure 8 2 from page 202 into your notebook. Label it. adenine ribose 3 phosphate groups P P P P 7. What are the keys to the compounds ability to store and release energy? The three phosphate groups are the keys. 2
8. Explain how energy is stored and released in the compound. When a cell has energy available, it can store small amounts by of it by adding a phosphate group to ADP (a process called phosphorylation). By breaking the chemical bond between the second and third phosphate groups in ATP, energy is released. + energy + energy + 9. See page 204 for a list of scientists who have contributed to the understanding of how plants carry out photosynthesis. List the scientists in your notebook and be able to state the contribution of each. van Helmont concluded that trees gain most of their mass from water (1643) Priestley found that plants release oxygen (1771) Ingenhousz concludes that plants need sunlight to produce oxygen (1779) Mayer proposed that plants convert light energy into chemical energy (1845) Calvin traced the chemical path that carbon follows to form glucose (1948) 10. What is the overall equation for photosynthesis? Write a word equation and balanced chemical equation. light carbon dioxide + water sugars + oxygen light 6CO 2 + 6 H 2 O C 6 H 12 O 6 + 6O 2 11. Read "Light and Pigments" starting on page 207. 12. Read "The Reactions of Photosynthesis" starting on page 208. 3
Autotrophs and Heterotrophs Greek: trophe > food autos > self heteros > other Autotrophs are organisms that use light energy from the sun to make food for themselves. Heterotrophs are organisms that obtain energy from the foods they consume. To live, all organisms must release the energy in sugars and other compounds. 4
Chemical Energy and ATP One of the principal chemical compounds that cells use to store and release energy is adenosine triphosphate, ATP. NH 2 OH OH OH N HC C N C C N N CH HO P O P O P O O O O CH 2 O C H C H H C C H OH OH 5
ATP consists of adenine (a nitrogenous base), 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. adenine ribose 3 phosphate groups ATP Nitrogenous base: A molecule that contains nitrogen and has the chemical properties of a base. The nitrogenous bases in DNA are adenine (A), guanine (G), thymine (T), and cytosine (C). The nitrogenous bases in RNA are the same with one exception: adenine (A), guanine (G), uracil (U), and cytosine (C) 6
When a cell has energy available, it can store small amounts of it by adding a phosphate group to ADP molecules, producing ATP. + energy adenosine diphosphate ADP energy + phosphate adenosine triphosphate ATP "partially charge battery" "fully charged battery" The addition of a phosphate group is called phosphorylation. 7
Occasionally... + + energy adenosine diphosphate ADP adenosine monophosphate AMP 8
ATP has enough energy to power a variety of cellular activities, including active transport across cell membranes, protein synthesis and muscle contraction. Most cells have only a small amount of ATP enough to last a few minutes of activity. A single molecule of glucose stores more than 90 times the chemical energy of a molecule of ATP. It is more efficient for cells to keep only a small supply of ATP on hand. Exergonic chemical reactions release energy. They supply needed energy for the synthesis of ATP. 9
Photosynthesis (Page 204) The key cellular process identified with energy production is photosynthesis a process in which plants use the energy of sunlight to convert water and carbon dioxide into high energy carbohydrates (sugars and starches) and oxygen, a waste product. Greek: photo > light synthesis > putting together 10
The Photosynthesis Equation (Page 206) Word Equation carbon dioxide + water light sugars + oxygen Balanced Chemical Equation light 6CO 2 + 6 H 2 O C 6 H 12 O 6 + 6O 2 11
What contributions did the following make to the understanding of how plants carry out photosynthesis? (Page 204 205) Jan van Helmont Joseph Priestley Jan Ingenhousz Julius Robert Mayer Melvin Calvin Rudolph Marcus 12
Jan van Helmont 1643 After careful measurements of a plant's water intake and mass increase, he concludes that trees gain most of their mass from water. Joseph Priestley 1771 Using a bell jar, a candle and a plant, he finds that the plant releases oxygen. Jan Ingenhousz 1779 He finds that aquatic plants produce oxygen bubbles in the light but not in the dark. He concludes that plants need sunlight to produce oxygen. Julius Robert Mayer 1845 Mayer proposes that plants convert light energy into chemical energy. Melvin Calvin 1948 He traces the chemical path that carbon follows to form glucose. These reactions are also known as the Calvin cycle. Rudolph Marcus 1992 He wins the Nobel Prize in chemistry for describing the process by which electrons are transferred from one molecule to another in the electron transport chain. 13
Chloroplasts In plants and other photosynthetic eukaryotes, photosynthesis takes place inside chloroplasts. Plant Plant Cells (500x) Chloroplast (10000x) 14
Plant Cell Chloroplast Structure *two membranes* thylakoid > saclike photosynthetic membrane granum > a stack of thylakoids photosystems > clusters of chlorophyll and other pigments found in the membranes of the thylakoids that absorb light energy stroma > semi fluid material that contains enzymes and makes up most of the chloroplast's volume stroma lamellae act like the skeleton of the chloroplast 15
Light and Pigments Plants gather the sun's energy with light absorbing molecules called pigments. The plant's principal pigment is chlorophyll which is found in chloroplasts. There are two types of chlorophyll, chlorophyll a and chlorophyll b. Page 207 When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule raising the energy levels of these electrons. The high energy electrons make photosynthesis work. 16
Carrier Molecules A carrier molecule is a compound that can accept a pair of high energy electrons and transfer them along with most of their energy to another molecule. This process is called electron transport and the electron carriers form an electron transport chain. One of these carrier molecules is the compound nicotinamide adenine dinucleotide phosphate or NADP +. NADP + accepts and holds 2 high energy electrons along with a hydrogen ion (H + ). This converts NADP + into NADPH. This is one way the energy of sunlight can be trapped in chemical form. NADP + + 2e + H + > NADPH The NADPH carry high energy electrons to chemical reactions elsewhere in the cell. 17
Reactions of Photosynthesis (Page 210) I. Light dependent Reactions The light dependent reactions require light and take place within the thylakoid membranes of chloroplasts. They produce oxygen gas and convert ADP and NADP + into energy carriers ATP and NADPH. Summary Light Dependent Reactions light water NADP + ADP O 2 NADPH ATP light 6CO 2 + 6 H 2 O C 6 H 12 O 6 + 6O 2 18
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The NADPH and ATP formed by the light dependent reactions contain a lot of energy, but they are not stable enough to store that energy for more than a few minutes. 20
II. Light independent Reactions The light independent reactions (Calvin cycle) do not require light and take place in the stroma of chloroplasts. The Calvin cycle uses ATP and NADPH from the light dependent reactions to produce high energy sugars. Summary Light independent Reactions CO 2 NADPH ATP C 6 H 12 O 6 NADP + ADP light 6CO 2 + 6 H 2 O C 6 H 12 O 6 + 6O 2 21
Calvin Cycle of Photosynthesis Page 212 22
What Factors Affect Photosynthesis? (Page 214) 1. amount of water available shortage of water can slow or stop photosynthesis 2. temperature photosynthesis depends on enzymes that function best between 0 o C and 35 o C 3. intensity of light increasing the intensity of light increases the rate of photosynthesis after the light intensity reaches a certain level, the plant reaches its maximum rate of photosynthesis 23
Complete: Thinking Visually (Page 216) Review Content: #1 10 (Page 217) Understanding Concepts: #11 14, 16 23 (Page 217) 24