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Photosynthesis AP Biology Unit 4.

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Presentation on theme: "Photosynthesis AP Biology Unit 4."— Presentation transcript:

1 Photosynthesis AP Biology Unit 4

2 Vocabulary Review What is an autotroph? What is a heterotroph?
Make their own energy What is a heterotroph? Aren’t able to make own energy– have to get it from another source

3 Photosynthetic Organisms
Photosynthesis is one way to make your own energy Who does it? Plants, algae, some other protists, some prokaryotes (ex. cyanobacteria)

4 Location of Photosynthesis
Photosynthesis occurs in the chloroplasts Organelles that contain the pigment chlorophyll and other pigments Openings in the leaf (stomata) allow CO2 (reactant) to enter and O2 (product) to leave

5 Equation for Photosynthesis
6 CO H2O + ENERGY  C6H12O O2 In terms of reactants and products, it is the reverse of cellular respiration, but process is different.

6 Stages of Photosynthesis
Light Reactions Captures light energy to produce ATP and NADPH Calvin Cycle (“Dark” Reactions) Uses ATP and NADPH to “fix” carbon into a carbohydrate “fix” means to incorporate the carbon into a compound

7 Light Reactions Main point = convert sunlight energy into chemical energy (ATP and NADPH) Sunlight can be divided into different wavelengths of light– only some are useful in photosynthesis

8 Light Reactions Photosynthetic pigments in the chloroplast absorb different wavelengths Chlorophyll a Chlorophyll b Carotenoids

9 Question… Why are most plants green?
The chlorophyll and carotenoid molecules absorb the blue-violet and red light and use it to perform photosynthesis They reflect green light – colors we see are the reflected wavelengths.

10 Light Reactions: Photosystems
Photosystems are the complex of pigments that receives the sunlight to begin the process Photosystems absorb energy to excite an electron in chlorophyll There are 2 different photosystems in chlorophyll – I and II.

11 Light Reactions: Noncyclic Flow
Step 1: Light excites electrons in photosystems I and II Step 2: Excited electrons are passed down an electron transport chain – generates ATP and NADPH

12 Noncyclic Flow Excited electron from Photosystem II fills the space left in Photosystem I Water is split (photolysis) to provide an electron to fill the space left in Photosystem II

13 Cyclic Electron Flow Under certain circumstances, the excited electrons will only flow through Photosystem I (not II)

14 Cyclic Electron Flow Generates ATP Doesn’t generate NADPH
Runs because the Calvin Cycle needs more ATP than NADPH May shift from noncyclic to cyclic flow when NADPH levels are high

15 Electron Transport Chain
very similar to cellular respiration An H+ concentration gradient across the thylakoid membrane drives ATP synthesis

16 Calvin Cycle Also called the Dark Reactions, Non-light Dependent Reactions, or the Calvin Benson Cycle Uses the ATP and NADPH produced in the light reactions to produce glucose using CO2

17 Calvin Cycle: Rubisco Rubisco is the enzyme that first “traps” CO2 into the cycle Through a series of reactions, CO2 is used to eventually make glucose

18 Calvin Cycle CO2 only contributes 1 carbon  6 “turns” of the calvin cycle are needed to produce one glucose. RuBP also has to be regenerated so that cycle can continue

19 The O2 released during photosynthesis comes from
NADPH RuBP (RuDP) C6H12O6 15

20 Carbohydrate-synthesizing reactions of photosynthesis directly require
Light Products of the light reactions Darkness O2 and H2O Chlorophyll and CO2 15

21 The end products of the light-dependent reactions of photosynthesis are

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