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Photosynthesis – Lesson # 1

Photosynthesis – Lesson # 1. Introduction. Why study photosynthesis?. Practical reasons: Photosynthetic organisms are autotrophs (they make their own food) Without autotrophs, heterotrophs (organisms that eat other organisms) would not have a source of food/energy.

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Photosynthesis – Lesson # 1

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  1. Photosynthesis – Lesson # 1 Introduction

  2. Why study photosynthesis? • Practical reasons: • Photosynthetic organisms are autotrophs (they make their own food) • Without autotrophs, heterotrophs (organisms that eat other organisms) would not have a source of food/energy

  3. Photosynthesis – What is it? • The conversion of light energy, carbon dioxide and water into high energy compounds (e.g. Glucose). • The general equation for photosynthesis is: CO2(g) + H2O(l) + light energy [CH2O](aq) + O2(g) • Photosynthesis can be thought of as the reverse of cellular respiration. Why ?

  4. Where in a plant does photosynthesis take place? (Cross section of a leaf)

  5. Leaves – Getting the Raw Materials • Light passes through the upper epidermis to reach the mesophyll layers. • Water is absorbed by plant roots, and is delivered to the leaf via the vascular bundle. • Carbon Dioxide gets into the leaf through the stoma (see picture below)

  6. Guard Cells and Stomata • Guard cells control the diameter of the stoma • The stoma opens during the day and closes at night (usually) • Sunlight activates a proton pump in the guard cells causing H+ to exit the cells. • The electrical potential of the cells becomes negative • K+ ions flow in to correct this difference • The influx of K+ ions draws water into the guard cell making them turgid • The swelling of the guard cells opens the stoma

  7. Guard Cells and Stomata • See animation: • http://academic.kellogg.cc.mi.us/herbrandsonc/bio111/animations/0021.swf • So what?

  8. Photosynthesis - Overview • Photosynthesis takes place in the chloroplast. • The following structures inside the chloroplast are important: • thylakoids • stroma • Why are these structures important? • Photosynthesis is a 2 step process. Step 1 (the light reactions) occurs in the thylakoids. Step 2 (the Calvin Cycle) occurs in the stroma

  9. Photosynthesis - Overview

  10. Light Reactions - Overview • Light Reactions: light is absorbed by chlorophyll which drives the transfer of electrons to (NADP+). NADP+ is reduced to form NADPH. • ATP is also produced during the light reactions in a process known as photophosphorylation Take home point: Light reactions produce ATP and NADPH which are used in the Calvin Cycle to make sugar. Oxygen is also produced (as a result of the water splitting) as a by-product.

  11. Calvin Cycle - Overview • Calvin Cycle: begins with carbon fixation. The Calvin Cycle uses NADPH and ATP from the light reactions to reduce carbon dioxide to carbohydrates (e.g. Glucose). • The Calvin Cycle is sometimes referred to as the “light independent reactions”. Why?

  12. Tomorrow: • More detail on light reactions and Calvin Cycle • You need to work on a photosynthesis cheat sheet (4 pages) and have a format like this:

  13. Homework • Read section 3.1 in your text (pp 138-144) • Try questions 1, 2a, 4, and 5 on page 145 of your textbook • Wednesday: Quiz on Cellular Respiration (Can use cheat sheet)

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