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Chapter 8: Photosynthesis Big Idea: How do plants and other organisms capture energy from the Sun?

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Presentation on theme: "Chapter 8: Photosynthesis Big Idea: How do plants and other organisms capture energy from the Sun?"— Presentation transcript:

1 Chapter 8: Photosynthesis Big Idea: How do plants and other organisms capture energy from the Sun?

2 8.1 Energy and Life Why is ATP useful to cells?  ATP (Adenosine triphosphate) is cellular energy. It is used by all cell types.  Without the ability to obtain and use energy life would not exist.  Energy is needed to grow, respond, move materials, and build new molecules

3  ADP (has 1 less phosphate group) and is how energy is stored. Once the extra phosphate group is added the cell has enough energy to be used.  ATP can easily release and store energy by breaking and re-forming the bonds between its phosphate groups. This characteristic makes ATP very useful as a basic energy source for all cells.

4  One way cells use energy is active transport.  Many membranes have sodium- potassium pumps (Na-K), which powers movement, and keeps ions balanced on both sides of the membrane.  ATP molecules are large so it is more efficient for cells to only store a small amount at a time.

5 What happens during the process of photosynthesis? Heterotrophs vs. Autotrophs Heterotrophs are organisms that obtain food by consuming other living things (Ex: mammals, insects, amphibians, reptiles, birds, fish, decomposers). Autotrophs are organisms that make their own food (Ex: plants) In the process of photosynthesis, plants convert the energy of sunlight into chemical energy stored in the bonds of carbohydrates

6 History of Photosynthesis Many scientists have contributed to understanding how plants carry out photosynthesis. Early research focused on the overall process. Later, researchers investigated the detailed chemical pathways.

7 8.2 Overview of Photosynthesis What role do pigments play in photosynthesis?  Pigments are light absorbing molecules that capture energy from sunlight.  A plants main pigments are chlorophyll a and chlorophyll b. They do not absorb green light on the light spectrum, but reflect green very well (which makes plants green).

8 Thylakoids are sac-like photosynthetic membranes that are arranged in stacks, known as grana. This is where chlorophyll is located Stroma is the fluid- portion of a chloroplast

9 A fraction of the light energy absorbed by plants goes directly to the electrons in the chlorophyll molecule. This raises the energy, giving the plant a steady supply of electrons to help photosynthesis occur What is an electron carrier molecule? A molecule that can accept a pair of high-energy electrons, and transfer them, along w/ most of their energy, to another molecule

10  Ex of a carrier molecule: NADP + accepts and holds 2 high-energy electrons and a hydrogen ion, which helps to trap light energy and convert it into a chemical form. What are the reactants and products of photosynthesis?  Photosynthesis used the energy of sunlight to convert water and carbon dioxide (reactants) into high-energy sugars and oxygen (products)

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12 Light-dependent vs. Light-independent reactions Photosynthesis involves 2 sets of reactions  The first are light-dependent reactions, which use energy from sunlight to produce energy rich compounds such as ATP -Occur in the thylakoid membranes, oxygen is produced as a byproduct  The second reactions are light-independent use ATP and NADPH to produce high-energy sugars. -occur in the stroma

13 8.3 The Process of Photosynthesis  The light-dependent reactions use energy from sunlight to produce oxygen and convert ADP to NADP + into the energy carriers ATP and NADPH  Photosystems are proteins located in thylakoids that absorb light and generate high energy electrons, that generate the light-independent reactions

14 The electron-transport chain is a series of electron-carrier proteins shuttling high- energy electrons from photosystem II  photosystem I. In photosystem I electrons are reenergized and carried into another electron transport chain The pumping of electrons builds a gradient on both sides of the thylakoids, giving the chloroplast energy to make ATP

15 The light-independent reactions do NOT require light to occur and are commonly called the Calvin cycle During the light-independent reactions, ATP and NADPH from the light-dependent reactions are used to produce high-energy sugars. The Calvin cycle used 6 molecules of CO 2 to produce a single 6-carbon sugar. It uses energy produced from the light-dependent reactions and CO 2

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17 The most important factors that affect the rate of photosynthesis are temperature, light intensity, and the availability of water. Extreme conditions: C4 Photosynthesis: allows photosynthesis to occur in plants located in hot, dry conditions w/ low levels of CO 2 CAM Plants: Present in dry climates. Allow plant to obtain CO 2 While minimizing water loss by sealing the leaves pores during the day and opening them during night.


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