1. Photosynthesis

2. I. Energy What do cells need in order to grow & repair, preform active transport across cell membranes, reproduce, synthesize cellular products, etc? What do cells need in order to grow & repair, preform active transport across cell membranes, reproduce, synthesize cellular products, etc? All organisms require energy. All organisms require energy. Some organisms (autotrophs) obtain energy in the form of light directly from the sun and store it in organic compounds (glucose) during a process called photosynthesis. Some organisms (autotrophs) obtain energy in the form of light directly from the sun and store it in organic compounds (glucose) during a process called photosynthesis.

3. Autotrophs vs. Heterotrophs Autotroph (Producers) Heterotroph (Consumers) Make their own foodCannot make their own food. by converting:They get energy by eating Sunlight(consuming) other organisms. Sunlight(consuming) other organisms. CO 2 CO 2 H 2 O H 2 O into glucose (their food) and Oxygen via a biochemical pathway called Photosynthesis. Chemosynthesis: A biochemical Pathway in which autotrophs use inorganic compounds instead of sunlight to make food.

4. Autotrophs vs. Heterotrophs Autotroph Heterotroph (Producers) (Consumers)

5. Photosynthesis: A Biochemical Pathway 6CO 2 + 6H 2 O + energy --> 6O 2 + C 6 H 12 O 6 6CO 2 + 6H 2 O + energy --> 6O 2 + C 6 H 12 O 6

6. Photosynthesis: Step 1: Light Absorption in Chloroplasts Hours of sunlight in a day decrease. Days become shorter. Nights get longer. Temperature decreases. Tree’s respond by producing less and less chlorophyll. Eventually, a tree stops producing chlorophyll and accessory pigments such as, carotenoids, can finally show through.

7. Photosynthesis: Step 1: Light Absorption in Chloroplasts Sunlight or white light is made of different wavelengths or colors carrying different amounts of energy Sunlight or white light is made of different wavelengths or colors carrying different amounts of energy A prism separates white light into 7 colors (red, orange, yellow, green, blue, indigo, & violet) ROY G. BIV A prism separates white light into 7 colors (red, orange, yellow, green, blue, indigo, & violet) ROY G. BIV These colors are called the visible spectrum These colors are called the visible spectrum

8. Photosynthesis: Step 1: Light Absorption in Chloroplasts

9. Photosynthesis: Step 1: Light Absorption in Chloroplasts Photosynthesis: Step 1: Light Absorption in Chloroplasts When light strikes an object it is: When light strikes an object it is: absorbed, transmitted, or reflected absorbed, transmitted, or reflected When all colors are absorbed, the object appears black When all colors are absorbed, the object appears black When all colors are reflected, the object appears white When all colors are reflected, the object appears white If only one color is reflected (green), the object appears that color (e.g. Chlorophyll) If only one color is reflected (green), the object appears that color (e.g. Chlorophyll)

11. Photosynthesis: Step 1: Light Absorption in Chloroplasts Chloroplasts in plant & algal cells absorb light energy from the sun during the light dependent reactions Chloroplasts in plant & algal cells absorb light energy from the sun during the light dependent reactions Photosynthetic cells may have thousands of chloroplasts Photosynthetic cells may have thousands of chloroplasts Chloroplasts are double membrane organelles with the an inner membrane folded into disc- shaped sacs called thylakoids Chloroplasts are double membrane organelles with the an inner membrane folded into disc- shaped sacs called thylakoids

12. Photosynthesis: Step 1: Light Absorption in Chloroplasts Thylakoids, containing chlorophyll and other accessory pigments, are in stacks called granum (grana, plural) Thylakoids, containing chlorophyll and other accessory pigments, are in stacks called granum (grana, plural) Grana are connected to each other & surrounded by a gel-like material called stroma Grana are connected to each other & surrounded by a gel-like material called stroma Light-capturing pigments in the grana are organized into photosystems Light-capturing pigments in the grana are organized into photosystems

13. Photosynthesis: Step 1 Pigments in the Chloroplasts Carotenoids are accessory pigments in the thylakoids & include yellow, orange, & red Carotenoids are accessory pigments in the thylakoids & include yellow, orange, & red

14. Photosynthesis Step 1: Light Absorption in Chloroplasts Thylakoids contain a variety of pigments ( green red, orange, yellow...) Thylakoids contain a variety of pigments ( green red, orange, yellow...) Chlorophyll (C55H70MgN4O6) is the most common pigment in plants & algae Chlorophyll (C55H70MgN4O6) is the most common pigment in plants & algae Chlorophyll a & chlorophyll b are the 2 most common types of chlorophyll in autotrophs Chlorophyll a & chlorophyll b are the 2 most common types of chlorophyll in autotrophs Chlorophyll absorbs only red, blue, & violet light Chlorophyll absorbs only red, blue, & violet light Chlorophyll b absorbs colors or light energy NOT absorbed by chlorophyll a Chlorophyll b absorbs colors or light energy NOT absorbed by chlorophyll a The light energy absorbed by chlorophyll b is transferred to chlorophyll a in the light reactions The light energy absorbed by chlorophyll b is transferred to chlorophyll a in the light reactions

15. Energy for Life Processes

16. Biochemical Pathways Biochemical Pathways Photosynthesis and cellular respiration are biochemical pathways Photosynthesis and cellular respiration are biochemical pathways Biochemical pathways are a series of reactions where the product of one reaction is the reactant of the next Biochemical pathways are a series of reactions where the product of one reaction is the reactant of the next Only autotrophs are capable of photosynthesis Only autotrophs are capable of photosynthesis Both autotrophs & heterotrophs perform cellular respiration to release energy to do work Both autotrophs & heterotrophs perform cellular respiration to release energy to do work In photosynthesis, CO 2 (carbon dioxide) and H 2 O (water) are combined to form C 6 H 12 O 6 (glucose) & O 2 (oxygen) In photosynthesis, CO 2 (carbon dioxide) and H 2 O (water) are combined to form C 6 H 12 O 6 (glucose) & O 2 (oxygen) 6CO 2 + 6H 2 O + energy --> 6O 2 + C 6 H 12 O 6 6CO 2 + 6H 2 O + energy --> 6O 2 + C 6 H 12 O 6

17. Overview of Photosynthesis Photosynthesis is not a simple one step reaction but a biochemical pathway involving many steps Photosynthesis is not a simple one step reaction but a biochemical pathway involving many steps This complex reaction can be broken down into two reaction systems --- light dependent & light independent or dark reactions This complex reaction can be broken down into two reaction systems --- light dependent & light independent or dark reactions

18. Overview of Photosynthesis Light Reaction: H 2 O --> O 2 + ATP + NADPH Light Reaction: H 2 O --> O 2 + ATP + NADPH 1. Water is split, giving off oxygen. 2. This system depends on sunlight for activation energy. 3. Light is absorbed by chlorophyll a which "excites" the electrons in the chlorophyll molecule. 4. Electrons are passed through a series of carriers and adenosine triphosphate or ATP (energy) is produced. 5. Takes place in the thylakoids.

19. Overview of Photosynthesis Dark Reaction: ATP + NADPH + CO 2 --> C 6 H 12 O 6 Dark Reaction: ATP + NADPH + CO 2 --> C 6 H 12 O 6 1. Carbon dioxide is split, providing carbon to make sugars. 2. The ultimate product is glucose. 3. While this system depends on the products from the light reactions, it does not directly require light energy. 4. Includes the Calvin Cycle. 5. Takes place in the stroma.

20. Biochemical Pathways Biochemical Pathways The second set of reactions in photosynthesis involves a biochemical pathway known as the Calvin cycle. The second set of reactions in photosynthesis involves a biochemical pathway known as the Calvin cycle. This Calvin cycle is also known as the light- independent reactions. This Calvin cycle is also known as the light- independent reactions.

21. Biochemical Pathways Biochemical Pathways The biochemical pathway of light-independent reactions in photosynthesis also are known as carbon fixation. The biochemical pathway of light-independent reactions in photosynthesis also are known as carbon fixation. In science, the word “fixation” just describes how an element is put into a usable form. In science, the word “fixation” just describes how an element is put into a usable form. Therefore carbon fixation is the building of glucose or other sugars using carbon dioxide from the air. Therefore carbon fixation is the building of glucose or other sugars using carbon dioxide from the air.

22. Calvin Cycle Carbon atoms from CO 2 are bonded or "fixed" into organic compounds during a process called carbon fixation Carbon atoms from CO 2 are bonded or "fixed" into organic compounds during a process called carbon fixation The energy stored in ATP and NADPH during the Light Reactions is used in the Calvin cycle The energy stored in ATP and NADPH during the Light Reactions is used in the Calvin cycle The Calvin cycle has 3 main steps occurring within the stroma of the Chloroplast The Calvin cycle has 3 main steps occurring within the stroma of the Chloroplast

23. Remember our products from the light-dependent reactions:

25. Calvin Cycle

26. Step 1: Step 1: 1. CO 2 diffuses into the stroma from surrounding cytosol 2. An enzyme combines a CO 2 molecule with a five- carbon carbohydrate called RuBP 3. The six-carbon molecule produced then splits immediately into a pair of three-carbon molecules known as PGA

27. Calvin Cycle Step 2: Step 2: 1. Each PGA molecule receives a phosphate group from a molecule of ATP 2. This compound then receives a proton from NADPH and releases a phosphate group producing PGAL 3. These reactions produce ADP, NADP+, and phosphate which are used again in the Light Reactions

28. Calvin Cycle Step 3: Step 3: 1. Most PGAL is converted back to RuBP to keep the Calvin cycle going 2. Some PGAL leaves the Calvin Cycle and is used to make other organic compounds including amino acids, lipids, and carbohydrates 3. PGAL serves as the starting material for the synthesis of glucose and fructose 4. Glucose and fructose make the disaccharide sucrose, which travels in solution to other parts of the plant (e.g., fruit, roots)

29. Calvin Cycle Step 3: Step 3: 5. Glucose is also the monomer used in the synthesis of the polysaccharides starch and cellulose

30. Final Overview of Photosynthesis

31. Alternate Pathways The Calvin cycle is the most common pathway used by autotrophs called C3 Plants The Calvin cycle is the most common pathway used by autotrophs called C3 Plants Plants in hot, dry climates use alternate pathways to fix carbon & then transfer it to the Calvin cycle Plants in hot, dry climates use alternate pathways to fix carbon & then transfer it to the Calvin cycle Stomata are small openings on the underside of leaves for gas exchange (O2 & CO2) Stomata are small openings on the underside of leaves for gas exchange (O2 & CO2) Guard cells on each side of the stoma help open & close the stomata Guard cells on each side of the stoma help open & close the stomata Plants also lose H2O through stoma so they are closed during the hottest part of the day Plants also lose H2O through stoma so they are closed during the hottest part of the day

32. Alternate Pathways

33. C 4 plants fix CO2 into 4-Carbon Compounds during the hottest part of the day when their stomata are partially closed C 4 plants fix CO2 into 4-Carbon Compounds during the hottest part of the day when their stomata are partially closed C 4 plants include corn, sugar cane and crabgrass C 4 plants include corn, sugar cane and crabgrass CAM plants include cactus & pineapples CAM plants include cactus & pineapples CAM plants open their stomata at night and close during the day so CO2 is fixed at night CAM plants open their stomata at night and close during the day so CO2 is fixed at night During the day, the CO2 is released from these compounds and enters the Calvin Cycle During the day, the CO2 is released from these compounds and enters the Calvin Cycle

34. Factors Determining the Rate of Photosynthesis Light intensity - As light intensity increases, the rate of photosynthesis initially increases and then levels off to a plateau Light intensity - As light intensity increases, the rate of photosynthesis initially increases and then levels off to a plateau Temperature - Only the dark, not the light reactions are temperature dependent because of the enzymes they use (25 o C to 37 o C) Temperature - Only the dark, not the light reactions are temperature dependent because of the enzymes they use (25 o C to 37 o C) Length of day Length of day Increasing the amount of carbon dioxide available improves the photosynthesis rate Increasing the amount of carbon dioxide available improves the photosynthesis rate Level of air pollution Level of air pollution

35. XII. Factors Determining the Rate of Photosynthesis