Drill – February 2012 Overview of Photosynthesis 1.) The process by which autotrophs convert sunlight energy into chemical energy for use by their cells is called 2.) How can it be said that photosynthesis “supports most life on Earth?” With the exception of chemoautotrophs, organisms that make food directly from sunlight (photoautotrophs) form the basis of all food chains on Earth. 3.) Visible light or white light is made up of a spectrum of colors. Each color has a different wavelength and each wavelength contains a different amount of energy. a.Which color (wavelength) contains the most energy? b.Which color contains the least energy? c.Which color is reflected by plants that appear green? photosynthesis. green red violet / blue

4.) Photoautotrophs obtain energy from light wavelengths that they __________, but not from colors that they ________. 5.) A __________ is a molecule that absorbs certain wavelengths (colors) of light and reflects others. Overview of Photosynthesis absorbreflect pigment

Photosynthetic pigment Colors/Wavelengths of Light Absorbed Colors/Wavelengths of Light Reflected chlorophyll a chlorophyll b carotenoids violet / blue / red green / yellow blue / orange blue green / yellow green / yellow / orange / red

6b.) What color(s)/ wavelength(s) of visible light are absorbed by all three of the photosynthetic pigments in the chart? Why might this be so? 6c.) What color(s)/ wavelength(s) of visible light are reflected by all three of these photosynthetic pigments? Overview of Photosynthesis violet / blue green Violet/ blue light contains the most energy, therefore plants might have adapted pigments that can capture this energetic light.

Overview of Photosynthesis 7.) Which of the three photosynthetic pigments in the table is most commonly found in plants? ____________ 8.) Given the information from questions #6 and #7, why do most plants appear green? 9.) Photosynthetic pigments are located in an organelle called a ____________. chlorophyll a Most plants appear green because they contain chlorophyll a, a pigment that reflects green light. chloroplast

10.) Below is a diagram of a chloroplast. Label the following parts: Overview of Photosynthesis granum intermembrane space outer membrane lumen stroma inner membrane thylakoid interior of the thylakoid

Overview of Photosynthesis Photosynthesis occurs in two phases: 1.Light dependent reactions Occur in the thylakoids 2.Light independent reactions / Calvin cycle Sometimes called dark reactions, but this is inaccurate Occur in the stroma Light dependent reactions Calvin cycle Typical chloroplast Glucose

Overview of Photosynthesis Calvin Cycle

Overview of Photosynthesis ADP + P NADP + Calvin Cycle

Light Dependent Reactions

Calvin Cycle ( a.k.a. dark reactions or light independent reactions )

Carbon fixation Carbon fixation: Six CO 2 molecules combine with six 5-carbon compounds and are rearranged into twelve 3-carbon compounds (PGA). STEP 1.

G3P ATP and NADPH from the LD rxn are used to convert twelve PGA molecules into twelve G3P molecules. STEP 2.

Two G3P molecules leave the cycle and are converted into glucose or other compounds. STEP 3.

An enzyme (Rubisco) converts the remaining ten G3P back into six 5-carbon compounds. STEP 4.

Calvin cycle ( recap ) 1.Carbon fixation: Six CO 2 molecules combine with six 5-carbon compounds and are rearranged into twelve 3-carbon compounds (PGA). 2.ATP and NADPH from the LD rxn are used to convert twelve PGA molecules into twelve G3P molecules. 3.Two G3P molecules leave the cycle and are converted into glucose or other compounds. 4.An enzyme (rubisco) converts the remaining ten G3P back into six 5-carbon compounds. Carbon accounting (6*1) + (6*5) = = * 3 = – (2 * 3) = 36 – 6 = 30 (10 * 3) = 30 (6 * 5) = 30

C 4 pathway Fix carbon into 4-carbon compounds instead of 3-carbon compounds. Fix carbon into 4-carbon compounds instead of 3-carbon compounds. Keep the pores in their leaves (called stomata) closed during hot days. Keep the pores in their leaves (called stomata) closed during hot days. Minimizes water loss while allowing these 4-carbon compounds to enter the Calvin cycle Minimizes water loss while allowing these 4-carbon compounds to enter the Calvin cycle Occurs in sugar cane and corn. Occurs in sugar cane and corn.

CAM plants Crassulacean acid metabolism (CAM) photosynthesis Crassulacean acid metabolism (CAM) photosynthesis Allow CO 2 to enter leaves only at night. Allow CO 2 to enter leaves only at night. CO 2 is fixed into organic compounds. CO 2 is fixed into organic compounds. During the day CO 2 can be released from these compounds and used in the Calvin cycle. During the day CO 2 can be released from these compounds and used in the Calvin cycle. Water-conserving plants that live in harsh environments (salt marshes, deserts, high altitude) Water-conserving plants that live in harsh environments (salt marshes, deserts, high altitude) Cacti, orchids, pineapple Cacti, orchids, pineapple