Photosynthesis

1. Photosynthesis Basic concepts and Leaf Chromatography Lab

2. Autotrophs vs. heterotrophs • Autotrophs create glucose and they are able to sustain themselves. • Use energy from sunlight or from chemical bonds in inorganic substances to make organic compounds (food) • Heterotrophs are the consumers of the Autotrophs and of other species. • Obtain energy from the food they consume

3. Photo-synthesis • Putting together with sunlight • Plants use sunlight to convert water and carbon dioxide into Glucose and oxygen. • This occurs through a series of reactions known as Biochemical Pathways.

4. Photosynthesis equation sunlight • Carbon dioxide + water  Glucose + Oxygen • Where do you think the reactants CO2 and H20 come from in a plants environment? Absorbed by chlorophyll

5. Where does photosynthesis take place? The Chloroplast is an organelle only found in plants cells and in some algae.

6. Stoma • This opening is how the plants exchange gasses. • Can anyone tell me which two gasses are exchanged? • Why are the stomata on the underside of the leaves?

7. Photosynthesis • The process of photosynthesis first begins when plants capture sunlight through their leaves (or other green parts of the autotroph)

8. Photosynthesis • The process of photosynthesis can be divided into two stages: Light Reactions and Calvin Cycle. • In the Light Reactions, light energy is converted to chemical energy, which is temporarily stored in ATP and the energy carrier molecule NADPH. • In the Calvin Cycle, organic compounds are formed using CO2 and the chemical energy stored in ATP and NADPH.

9. Why ARE LEAVES GREEN? Now that we have reviewed the basic concepts of photosynthesis, let us now hypothesize why leaves are green!

10. WHY ARE THE LEAVES GREEN? • Plants gather the sun’s energy with light absorbing molecules called pigments • A plant’s principle pigment is chlorophyll • Leaves appear to be green because chlorophyll does not absorb light well in the green region of the light spectrum. This causes green light to be reflected by the leaves.

11. Other pigments found in leaves • All Pigments found in leaves, are organized into clusters known as Photosystems • These Photosystems are located in the Thylakoids of the chloroplast • There are three main types of pigments are: • Chlorophyll- the pigment representing the green color • Carotenoids (sometimes called Carotene)- The pigment representing the colors yellow and orange • Anthocyanins- the pigments representing the colors red and purple

12. Why aren’t the other pigments visible in green leaves? • Chlorophyll is the main pigment found in plants. • During the growing season (spring and summer), Chlorophyll is being produced insuch high levels that it masks the appearances of the other pigments. During what time of the year are the other pigments visible?

13. Autumn season • How do you think the Autumn season affects photosynthesis and the color of the leaves?

14. How Autumn affects Photosynthesis • During the Autumn season, the environment undergoes a few changes: • Days become shorter • Carbon Dioxide Levels vary • Temperatures lower • Precipitation levels can greatly vary

15. Shorter days- Light becomes less intense • Shorter days, means less intense light being absorbed by the plant. • Less light being absorbed by the plant, means less chlorophyll being produced. • Less chlorophyll being produced, allows other pigments to shine through the leaf.

16. Carbon Dioxide Levels • As with increasing light intensity, increasing levels of carbon dioxide also stimulate photosynthesis until the rate levels off.

17. Colder Temperatures • During the autumn seasons, the temperatures tend to become colder • Temperature does not affect the light dependent reactions of photosynthesis, but rather the light independent reactions. • The light independent reactions are catalyzed by enzymes • Enzymes are proteins that increase the rate of chemical reactions.

18. Colder temperatures • The enzymes needed for the light independent reactions work best at a temperature range of 32°F to 86°F • During Autumn, temperature may reach below this range, causing damage to the enzymes and slowing the rate of photosynthesis. • In places of low temperatures, photosynthesis may stop altogether. • Once again, the slowing rate of photosynthesis results in less chlorophyll being produced. This allows the other pigments to shine through

20. Varying levels of Precipitation • Depending on your location, precipitation levels may decline during the autumn season. • Water is one of the reactants of photosynthesis, so a shortage of water will slow down or completely stop the reaction of photosynthesis altogether.

21. Light Dependent reaction Photosynthesis can be broken down into two categories of reactions: Light dependent reactions & Light independent reactions • In light dependent reactions, Sun energy is absorbed by Chlorophyll  Converted into stored chemical energy

22. Light dependent reaction • Chemical energy is in the form of NADPH and ATP (products of Light dependent reaction) • NADPH- is the electron carrier molecule • ATP- the energy currency molecule • Use ATP to spend energy for reactions to occur

23. Light dependent Reaction • Takes place in the Thylakoid Membrane in the granum • Granum- stack of thylakoids • Within the Chloroplast

24. Photosystems 1 and Photosystems 2 • In each photosystem, the acquire energy is passes quickly to other pigment molecules until it reaches a specific pair of chlorophyll a molecules. • This energy forces the electrons to enter a higher energy level in the two chlorophyll a molecules of photosystem II. • The excited electrons have enough energy to leave the chlorophyll a molecules.

25. Continued.. • The acceptor of these electrons from photosystem II is a molecule called the primary electron acceptor, which donates the electrons to the electron transport chain. • As the electrons move from molecule to molecule in the chain, they lose most of the acquire energy. • The energy they lose is used to move protons into the Thylakoid.

26. Light reactions in photosynthesis

27. Light is absorbed by photosystem I at the same time it is absorbed by photosystem II. • Electrons move from chlorophyll a molecules to another primary electron acceptor. • The electrons lost from photosystem I are replaced by electrons that have passed through the electron transport chain from photosystem II.

28. These electrons are then donated to another electron transport chain, which brings the electrons to the side of the thylakoid membrane that faces the stroma. • In the stroma, the electrons combine with a proton and NADP+. • This causes NADP+ to be reduced to NADPH.

29. Replacing Electrons in Light Reactions • Electrons from photosystem II replace electrons that leave photosystem I. Replacement electrons for photosystem II are provided by the splitting of water molecules • Oxygen produced when water molecules are split diffuses out of the chloroplast and the leaved the plant.

30. Making ATP in Light Reactions • An important part of the light reactions is that synthesis of ATP. • During Chemiosmosis, the movements of protons through ATP synthase into the stroma releases energy, which is used to produced ATP

32. Light independent Reaction/ Calvin cycle The next phase is called the Light Independent Reactions, as it does not requiresunlight to begin its reaction • The energized products, NADPH and ATP, from the light dependent reactions provide the energy • The light independent reaction occurs in the stroma of the chloroplasts Do you think this reaction will occur during the day, night, or both? Why?

33. Carbon fixation • In the Calvin cycle, CO2 is incorporated into organic compound, a process called carbon fixation.

34. Carbon fixation continued.. • The Calvin cycle, which occurs in the stroma of the chloroplast, is a series of enzyme-assisted chemical reactions that produces a three-carbon sugar. • Most of the three-carbon sugars (G3P) generated in the Calvin cycle are converted to a five-carbon sugar (RuBP) to keep the Calvin cycle operating. But some of the three-carbon sugars leave the Calvin cycle and are used to make organic compounds, in which energy is stored for later use.

36. Light independent Reaction After the energy is transferred, the energy carrier molecules return to light dependent reactions.

37. Alternative pathways • The C4Pathway • Some plants that evolved in hot, dry climates fix carbon through the C4 pathway. These plants have their stomata partially closed during the hottest part of the day. • Certain cells in these plants have an enzyme that can fix CO2 into four-carbon compounds even when the CO2 level is low and the O2 level is high. These compounds are then transported to other cells, where the Calvin cycle ensues.

38. Alternative pathways • The CAM Pathways • Some other plants that evolved in hot, dry climates fix carbon through the CAM Pathway. These plants carry out carbon fixation at night and the Calvin cycle during the day to minimize water loss.

39. Ongoing cycle of photosynthesis

40. Leaf Chromatography activity • We will now look at how various pigments within leaves are present in autumn leaves. • Students will participate in a leaf chromatography activity with the guidance of Mrs. Yahner and Mrs. K . • Students will complete a guided activity worksheet to be handed in at the end of class.