Photosynthesis Using Light to Make Food AP Biology

Photosynthesis: Using Light to Make Food AP Biology

Introduction: Plant Power § Photosynthesis - a process that converts light energy to chemical energy (sugars – which are carbohydrate!) § Plants use water and carbon dioxide to produce a simple sugar and give off oxygen Copyright © 2009 Pearson Education, Inc.

6 CO 2 + 6 H 2 O Carbon dioxide Water Light energy Photosynthesis C 6 H 12 O 6 + 6 O 2 Glucose Oxygen gas

Energy needs of life § All life needs a constant input of energy u § get their energy from “eating others” w Eat organic molecules consumers u producers Heterotrophs (animals, fungi) Autotrophs (Plants) § produce their own energy (sugars) § Use energy of sunlight to build organic molecules § make energy & synthesize sugars through photosynthesis (use light)

Plant structure § Obtaining raw materials u sunlight § leaves = solar collectors (major sites of chlorophyll & photosynthesis) u CO 2 § In through stomates (stomata) = pores in leaves for gas exchange u H 2 O § uptake from roots u nutrients § N, P, K, S, Mg, Fe… § uptake from roots

Plant structure § Chloroplasts u u double membrane stroma § fluid-filled interior u u Thylakoids – membranous sacs grana – stacks of stroma thylakoids outer membrane § Thylakoid membrane contains u u u chlorophyll molecules electron transport chain ATP synthase § H+ gradient built up within thylakoid sac inner membrane thylakoid granum

In photosynthesis, electrons gain energy – – Light energy captured by chlorophyll pigments provides the boost for the electrons (electrons carry energy) As a result, light energy is converted to chemical energy, which is stored in the chemical bonds of sugar molecules Copyright © 2009 Pearson Education, Inc.

§ photosynthesis occurs in two metabolic stages 1) the light reactions (in thylakoids) 2)

1) the light reactions (in thylakoids) u light energy is converted to chemical energy ATP and NADPH u Water is split to provide the electrons and H+ ions [as well as the oxygen gas (O 2) that is given off] u NADPH (an electron carrier ) and ATP are generated Copyright © 2009 Pearson Education, Inc.

2) Calvin cycle (in stroma) cyclic series of reactions u CO 2 is incorporated into organic compounds (sugars) u NADPH from the light reactions provides the electrons u ATP from the light reactions provides chemical energy u Final outcome builds sugars (glucose) u Copyright © 2009 Pearson Education, Inc.

CO 2 H 2 O Chloroplast Light NADP+ ADP P LIGHT REACTIONS CALVIN CYCLE (in stroma) (in thylakoids) ATP NADPH O 2 Sugar

Photosynthesis gets energy by absorbing wavelengths of light § Chlorophylls & other pigments u u Why are u plants green? Light absorbing molecules embedded in thylakoid membrane inside Chlorophyll § absorbs best in red & blue wavelengths & least in green accessory pigments also absorb light of different wavelengths to add more energy § chlorophyll b, carotenoids, xanthophylls

Photosystems capture solar power § Pigments in chloroplasts are responsible for absorbing light energy

The products of the light reactions § NADPH § ATP § O 2 Copyright

PART 2: THE CALVIN CYCLE: CONVERTING CO 2 TO SUGARS Copyright © 2009 Pearson

ATP and NADPH power sugar synthesis in the Calvin cycle § The Calvin cycle makes sugar within a chloroplast – – – Requires atmospheric CO 2, and the ATP & NADPH generated in the light reactions Produces an energy-rich, three-carbon sugar which the plant uses to make glucose The important enzyme of the Calvin cycle is rubisco Copyright © 2009 Pearson Education, Inc.

Input CO 2 ATP NADPH CALVIN CYCLE Output: G 3 P Which is used to make glucose

Photosynthesis summary § Light reactions produced ATP u produced NADPH u consumed H 2 O u produced O 2 as byproduct u § Calvin cycle consumed CO 2 u Produced sugar u regenerated ADP u regenerated NADP u ADP NADP

Summary of photosynthesis 6 CO 2 + 6 H 2 O + light C 6 H 12 O 6 + 6 O 2 energy § § § § Where did the CO 2 come from? Air through stomates Where did the CO 2 go? Converted to sugars Where did the H 2 O come from? roots Where did the H 2 O go? Split to provide electrons and protons and the Oxygen is given off by the plant (O 2) Where did the energy come from? light What’s the energy used for? Make sugars What will the glucose be used for? energy What else is involved…not listed in this equation? ATP and NADPH – made in light reactions and used in the Calvin cycle