Photosynthesis : An Overview

1. Photosynthesis: An Overview

2. Photosynthesis: An Overview • The key cellular process identified with energy production is photosynthesis. • Photosynthesis is the process in which green plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates and oxygen.

3. Investigating Photosynthesis • Belgian Jan van Helmont conducted an experiment in the late 1600’s to better understand where a plants mass comes from.   • Planted a small willow tree in a container filled with soil.  • After 5 years of watering it, he found that the tree gained 160 pounds while the soil lost only two ounces.  • Concluded that most of the plants mass came from water, not the soil.

4. Investigating Photosynthesis • Van Helmont’s experiment accounts for the “hydrate,” or water, portion of the carbohydrate produced by photosynthesis. • But where does the carbon of the “carbo” portion come from? • We now know that carbon dioxide in the air is also a major contributor of plant mass. • In photosynthesis, the carbon in carbon dioxide is used to make sugars and other carbohydrates.

5. Investigating Photosynthesis • In 1772, Joseph Priestley made another important discovery.  • Placed a shoot of a green plant into a container of water.  • He then covered the container and lit a candle in it until it completely burned out.  • Later, Priestley was able to both burn the candle again and keep mice alive in the air. • Priestley became the first person ever to observe the respiration of plants - the fact that they take in carbon dioxide and release oxygen.  • Also discovered how to dissolve CO2 in water and invented the first soda pop.

6. Investigating Photosynthesis • Jan Ingenhouz laid the groundwork for understanding photosynthesis when he demonstrated that green leaves absorb carbon dioxide and release oxygen only in sunlight. • In darkness, he showed, leaves absorb oxygen and give off carbon dioxide, just like animals and non-green plant parts.

7. Photosynthesis

8. Light and Pigments • What is the role of light and chlorophyllin photosynthesis? • How do plants capture the energy of sunlight? In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll. • Plants gather the sun's energy with light-absorbing molecules called pigments. • The main pigment in plants is chlorophyll. • There are two main types of chlorophyll: • chlorophyll a • chlorophyll b

9. Light • Visible spectrum – ROYGBIV • Red = longest wavelength • Violet = shortest wavelength • Color of an object is determined by the color the object reflects • Plants gather light using pigments

10. Light and Pigments • Chlorophyll absorbs light well in the blue-violet and red regions of the visible spectrum. 100 80 60 40 20 0 Chlorophyll b Chlorophyll a Estimated Absorption (%) Wavelength (nm) 400 450 500 550 600 650 700 750 Wavelength (nm)

11. Light and Pigments • Chlorophyll does not absorb light well in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green. 100 80 60 40 20 0 Chlorophyll b Chlorophyll a Estimated Absorption (%) 400 450 500 550 600 650 700 750 Wavelength (nm)

12. Lights and Pigments • Carotenoids are accessory pigments that allow plants to absorb light in mainly the blue and green regions of the spectrum and reflect red, yellow, and orange. • These pigments are more prominent in the fall.

13. Light and Pigments • Light is a form of energy, so any compound that absorbs light also absorbs energy from that light. • When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. • These high-energy electrons are what make photosynthesis work.

14. Light and Pigments • Plant pigments can be separated by a process called chromatography. • Chromatography is used to separate mixtures of substances

15. The Photosynthesis Equation • The Photosynthesis Equation • The equation for photosynthesis is: • 6CO2 + 6H2O C6H12O6 + 6O2 • carbon dioxide + water sugars + oxygen • Glucose is theprimary sugarproduced byphotosynthesis Light Light

16. The Photosynthesis Equation • Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.

17. Inside a Chloroplast • thylakoids – saclike photosynthetic membranes • grana – stacks of thylakoids • stroma – space outside the thylakoids

18. Overview of Photosynthesis • photosynthesis occurs only in producers • endergonic reaction – a chemical reaction that uses or stores energy • Two steps of photosynthesis • Light Reactions • Calvin Cycle

19. Light Reactions • require light • use energy from light to produce ATP and NADPH • occurs in the grana • energy from “excited electrons” is used to bond ADP and Pi to form ATP

20. Light Reactions • 3 main events • Light energy is absorbed by the chlorophyll and ATP is made • Water is split into hydrogen ions, oxygen and electrons • The hydrogen ions are used to make NADPH

21. Inputs: Light Water Outputs: ATP NADPH Oxygen (O2) Light Reactions

22. Calvin Cycle • Also called the dark reactions or light-independent reactions • process of synthesizing sugars • occurs in the stroma • does not require light • converts CO2 to sugar

23. Calvin Cycle • 3-carbon sugars are produced • Some used as energy sources • Some converted to lipids, amino acids, parts of nucleic acids • Two can combine to form 6-carbon sugars

24. Calvin Cycle • Inputs: • ATP • NADPH • CO2 • Outputs: • Sugars

25. Photosynthesis Overview Light energy O2 Light-Dependent Reactions (thylakoids) H2O ADPNADP+ ATPNADPH CO2+H20 Sugar Calvin Cycle (stroma)

26. In the end… • a single 6-carbon sugar is formed from 6 molecules of carbon dioxide • plants use the sugar for energy and to build more complex carbohydrates such as starches and cellulose • other organisms eat the plants and use the energy stored in carbohydrates

27. Photosynthesis Overview

28. Quiz • In van Helmont's experiment, most of the added mass of the tree came from • soil and carbon dioxide. • water and carbon dioxide. • oxygen and carbon dioxide. • soil and oxygen.

29. Quiz • Plants use the sugars produced in photosynthesis to make • oxygen. • starches. • carbon dioxide. • protein.

30. Quiz • The raw materials required for plants to carry out photosynthesis are • carbon dioxide and oxygen. • oxygen and sugars. • carbon dioxide and water. • oxygen and water.

31. Quiz • The principal pigment in plants is • chloroplast. • chlorophyll. • carotene. • carbohydrate.

32. Quiz • The colors of light that are absorbed by chlorophylls are • green and yellow. • green, blue, and violet. • blue, violet, and red. • red and yellow.