In the Beginning Photosynthesis CP Biology Research into photosynthesis began centuries ago with a simple question When a tiny seedling grows into a tall tree with a mass of several tons, where does the treeʹs increase in mass come from? From the soil? From the water? From the air? NGSS: SC.912.L.18.7, SC.912.L.18.10 SPI.3210.3.4 Photosynthesis Fundamental process where plants manufacture carbohydrates from raw materials using energy from light (sun) Equation How does photosynthesis work? 6CO 2 + 12 H 2 O Memorize this equation!! You will see it again light chlorophyll C 6 H 12 O 6 +6O 2 +6H 2 O Produces glucose and oxygen 2 stages of photosynthesis Light dependent reactions convert sunlight into chemical energy (ATP + NADPH) Light independent reactions use products to form sugars (aka: stored chemical energy) 1
Light Dependent Reactions requires the direct energy of light to make energy carrier molecules that are used in the second process. Light Reactions occur in the grana Light Independent Reactions Occurs when the products of the Light Reaction are used to form C C covalent bonds of carbohydrates. Can occur in the dark if the energy carriers from the light dependent reaction are present take place in the stroma of the chloroplasts Overview Concept Map Photosynthesis includes Chloroplast Light CO 2 NADP + ADP + P Chloroplast use Lightdependent reactions take epa place ein takes place in Calvin cycle uses Light Dependent Reactions ATP NADPH Calvin Cycle Energy from sunlight to produce Thylakoid membranes of Stroma ATP to produce ATP NADPH O 2 Chloroplasts High energy sugars NADPH O 2 Sugars 2
What Are Pigments Pigment A light absorbing molecule Associated with the thylakoid membranes Chlorophyll Chl a and Chl b (Chl c in some algae) Xanthophylls Carotenoids ß carotene The Electromagnetic Spectrum Chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and subsequent storage Starch Pigments absorb light differently Factors Affecting Photosynthesis Many factors affect the rate at which photosynthesis occurs. Water is one of the raw materials of photosynthesis, a shortage of water can slow or even stop photosynthesis. Plants that live in dry conditions, such as desert plants and conifers, have a waxy coating on their leaves that reduces water loss. (Prentice Hall) 3
Factors Affecting Photosynthesis Temperature is also a factor Photosynthesis depends on enzymes that function best between 0 C and 35 C. Temperatures above or below this range may denature the enzymes, slowing down the rate of photosynthesis. At very low temperatures, photosynthesis may stop entirely. (Prentice Hall) Factors Affecting Photosynthesis The intensity of light also affects the rate at which photosynthesis occurs. increasing light intensity increases the rate of photosynthesis. After the light intensity reaches a certain level, however, the plant reaches its maximum rate of photosynthesis. The level at which light intensity no longer affects photosynthesis varies from plant type to plant type. (Prentice Hall) The rate at which a plant carries out photosynthesis depends in part on its environment. Plants that grow in the shade carry out photosynthesis at low levels of light. Plants that grow in the sun, such as desert plants, typically carry out photosynthesis at much higher levels of light. 4
Leaf Structure Cuticle, cellular and tissue structure of a dicotyledonous leaf Leaf Structure Vascular Bundles Chloroplasts photosynthesis Stomata and mesophyll cells gas exchange Vascular bundles (xylem & phloem) Transport and support Mineral Requirements Importance of nitrate ions for protein synthesis Deficiency leads to stunted growth, yellowish leaves More common in fast growing plants Magnesium ions for chlorophyll synthesis Small quantities/ trace elements Nitrogen Fertilizers Dangers of overuse 5
Changing leaves Dunlap, TN October 2011 Mrs. King Chlorophyll The yellows and oranges of autumn leaves are revealed as their chlorophyll breaks down. What do autumn leaves and ripening bananas have in common? The green color in unripe bananas comes from chlorophyll, the same pigment that gives green leaves their color. As bananas ripen, the chlorophyll breaks down and disappears, revealing the yellow color which has been there all along. As bananas ripen the starches change to sugar and the flesh softens as pectin (a carbohydrate) breaks down. Resources Complete Photosynthesis lab: http://www.phschool.com/science/biology_place/bi ocoach/photosynth/intro.html Print out final quiz grade after doing the lab. Write a summary of the lab and reflect on what you learned. Campbell et.al. (2004) Biology: Exploring Life. Prentice Hall Jones, M., Fosbery, R., Taylor, D., & Gregory, J. (2007). AS Level and A Level Biology, 2 nd ed. Cambridge, UK: Cambridge University Press. Mackean, D. (2009). IGCSE Biology, 2 nd ed. London, UK: Hodder Education. Lab 4: Plant Pigments & Photosynthesis Lab 5: Cell Respiration 6