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PHOTOSYNTHESIS

PHOTOSYNTHESIS. Primary Productivity. Overview Lessons 1. ATP – The Energy Currency 2. Chloroplasts Photosynthesis – Capturing Light Photosynthesis - Light Dependent Reactions Photosynthesis – Light Independent Reactions Assessment. LESSON 1 A Review of ATP.

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PHOTOSYNTHESIS

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  1. PHOTOSYNTHESIS Primary Productivity

  2. Overview Lessons 1. ATP – The Energy Currency 2. Chloroplasts Photosynthesis – Capturing Light Photosynthesis - Light Dependent Reactions Photosynthesis – Light Independent Reactions Assessment

  3. LESSON 1 A Review of ATP Have you ever used a rechargeable battery? Well, every living thing uses the same molecule for the short-term storage of energy. It is called ATP. The function of this molecule can be compared to a rechargeable battery. This molecule is called the energy currency of ALL living things! What does this word currency mean? a unit of exchange, facilitating the transfer of goods and/or services

  4. So by calling ATP the energy currency of all cells we mean that different parts of cells exchange this molecule when energy is needed and consumed. Since all living organisms use this same ATP molecule, an analogy to this would be going anywhere in the world and being able to buy goods with dollars, quarters, and nickels and other U.S. currency. So how is this molecule like a re-chargeable battery? Let’s find out!

  5. This is a graphic representation of ATP Three parts Adenine – a nitrogenous base (nucleotide base) Ribose – a sugar 3 Phosphate molecules (energy is stored in the bonds) Chemical bonds broken energy is released Chemical bonds formed energy is absorbed

  6. What about the re-chargeable battery analogy? Adenosine triphosphate (Fully charged battery) Adenosine monophosphate (dead battery) Adenosine diphosphate (Half-charged battery) Every time a phosphate bond is broken, energy is released. To recharge the battery, the phosphate must be reattached. (energy is captured) This concludes lesson 1.

  7. LESSON 2 Chloroplasts Chloroplasts are the specialized organelle in plants and some algae where photosynthesis occurs. This view would be through a cross-section of the leaf Image source: http://www.daviddarling.info/encyclopedia/C/chloroplasts.html

  8. Chloroplasts • Have TWO membranes • The inner membrane is called the thylakoid. • The thylakoid is folded and looks like stacks of coins called granum (grana singular). • The side of the granum is oriented towards the sun for maximum light exposure. • The light dependent reactions (lesson 4) occur in the thylakoid membrane . • The stroma is the space surrounding the granum • The light independent reactions (lesson 5) occur in the stroma. This concludes lesson 2.

  9. LESSON 3 Photosynthesis - Light Capture • Light behaves as both a wave and a particle • Wavelength is defined as the distance from peak to peak (or trough to trough). • The energy of is inversely proportional to the wavelength: longer wavelengths have less energy than do shorter ones. The Nature of Light

  10. Visible Light • Visible light is one small part of the electromagnetic spectrum. • The order of colors is determined by the wavelength of light. • Longer wavelength - the more red the color. • Shorter wavelengths - the violet side of the spectrum. • Wavelengths longer than red are referred to as infrared, while those shorter than violet are ultraviolet.

  11. Pigments • Pigments are lipids • Plants use PIGMENTS to capture sun’s energy • A pigment is a substance that absorbs and reflects light. • The main pigment in plants is chlorophyll a • Chlorophyll b • Carotenoids

  12. How Does It Work? • Molecules, when struck by a wave or photon of light • Reflect some of its energy back out, or • Absorb the energy, and thus enter into a higher energy or excited state. • Each molecule absorbs or reflects its own characteristic wavelengths of light.

  13. Chlorophyll • Chlorophyll absorbs blue and red regions of the spectrum • Reflects the green region so we see green • The color of the pigment comes from the wavelengths of light reflected (in other words, those not absorbed).

  14. Chlorophyll • Chlorophyll molecules are embedded in the thylakoid membrane • Act like a light “antenna” • These molecules can absorb sunlight energy.

  15. Photosynthesis If a pigment absorbs light energy, one of three things will occur Energy is dissipated as heat. The energy may be emitted immediately as a longer wavelength, a phenomenon known as fluorescence. Energy may trigger a chemical reaction, as in photosynthesis. Chlorophyll only triggers a chemical reaction when it is associated with proteins embedded in a membrane (as in a chloroplast) This concludes lesson 3.

  16. Plant Photosynthesis internal leaf structure chloroplasts outer membrane inner membrane thylakoid

  17. Plant Photosynthesis • Photosynthesis is the process by which plants, algae, cyanobacteria and some protists use the energy from sunlight to produce carbohydrates. • A way of converting light energy into chemical energy. • Associated with the actions of the green pigment chlorophyll.

  18. Overall Reaction What is the equation for photosynthesis? carbon dioxide + water  glucose + oxygen + water + energy 6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O + 686 kcal/mol

  19. LESSON 4 Photosynthesis - Light Dependent Reaction • Happens ONLY in sunlight • Occurs along the thylakoid membrane • The light dependent reactions capture the energy of the sun • Two sets of reactions called photosystems. • Begins with Photosystem II because it was the first set of reactions discovered. Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto. 2003.

  20. REMINDER! • Electrons are a tiny, energetic part of an atom.

  21. Photosystem II Begins with absorption of energy (photon) by a chlorophyll molecule (Chl). The chlorophyll molecule is raised to an excited state. (The electrons in the valence shells jump ship) The electron lost by the chlorophyll is replaced by the enzymatic splitting of water

  22. This electron is passed down a chain of molecules called the electron transport chain or redox chain. It’s like pass the ball around a circle, but each time the ball is passed some energy is released and captured by… Wait for it…..ATP!!!! Energy from this transfer of electrons is used to produce ATP, leaving the electron in a low energy state to be recharged by Photosystem I Photosystem II

  23. Photosystem I The low energy electron from photosystem II replaces one in photosystem I that has become energized and left the chlorophyll molecule in photosystem II. Energy from this excited electron is exchanged across different molecules (called carriers) ultimately being used to convert NADP+ to NADPH. NADPH stores this electrical energy for use in the light independent reactions.

  24. Where did the light dependent reactions take place again? In the stroma In the thylakoid membranes

  25. The Light Dependent Reactions (Overview) This completes lesson 4 http://www.fw.vt.edu/dendro/forestbiology/photosynthesis.swf

  26. LESSON 5Photosynthesis - Light Independent Reaction • Happens in sunlight and in the dark. • Occurs in the stroma of the chloroplast. • ATP generated by sunlight drives the Calvin Cycle. • Monosaccharides (eg. glucose) are manufactured -are used to “build” polysaccharides (eg. Cellulose - starch). Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto. 2003.

  27. The Calvin Cycle • a.k.a. the “dark reactions” • WARNING: DOES NOT ONLY TAKE PLACE IN THE DARK! • Accomplishes “carbon fixation” taking carbon from inorganic molecules and putting it into organic molecules (CO2 sugars) .

  28. Here’s an overview of the Calvin Cycle. Next we’ll break it down in stages. The quantities listed are for the production of one glucose molecule which is produced from six turns of the cycle Acronyms we’ll use RuBP - ribulose biphosphate PGA - phosphoglycerate PGAP - diphosphoglycerate PGAL - phosphoglyceraldehyde .

  29. The cycle starts when (3) 5-carbon molecules (from the previous cycle) of RuBP combine with (3)CO2. molecules from the atmosphere. This combination of molecules forms six molecules of the 3-carbon compound PGA. .

  30. The energy and phosphates from six ATP’s is taken to convert the 6 PGA’s to 6 PGAP’s .

  31. Where did these ATP’s come from? The Light dependent reactions The mitochondria .

  32. You are right! In this next step the energy from 6 NADPH’s is used to remove the phosphate molecules forming 6 PGAL’s .

  33. Where did these NADHP’s come from? The cytoplasm The Light dependent reactions .

  34. You are correct! At this point (after three turns of the cycle) one of these PGAL’s leaves the cycle. Six turns of the cycle produces 2 of these PGAL molecules which combine to form a glucose molecules. .

  35. The remaining 5 PGAL molecules are converted to (3) 5-carbon intermediates, then back to 3 RuBP molecules to start the cycle again. This completes lesson 5 .

  36. Here’s a graphic representation of the two series of reactions. .

  37. Let’s Review The two series of chemical reactions that comprise Photosynthesis are called? Photosystem I and Photosystem II Light dependent and Light independent .

  38. Correct! The two series of chemical reactions that comprise photosynthesis are called the: Light dependent reactions – they require light and therefore occur in the thylakoid membrane Light independent reactions – these don’t require light and occur in the stroma .

  39. ASSESSMENT Question 1 of 5 The energy currency of all cells in all organisms is Adenosine diphosphate Adenosine triphosphate Adenosine monophosphate .

  40. ASSESSMENT Question 2 of 5 The two series of chemical reactions that comprise photosynthesis are called Photosystem I and photosystem II Cellular Respiration Light dependent and light independent .

  41. ASSESSMENT Question 3 of 5 The light independent (also called dark reactions) occur in the stroma thylakoid membrane cytoplasm .

  42. ASSESSMENT Question 4 of 5 The three parts of ATP are adenine, thylakoids, stroma stroma, grana, chlorophyll adenine, ribose, phosphate .

  43. ASSESSMENT Question 5 of 5 What are products of the light dependent reactions? oxygen gas ATP NADPH All of the above .

  44. The End .

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