Photosynthesis

Autotrophs & Heterotrophs Autotrophs, such as plants and other types of organisms can convert light energy into food Heterotrophs obtain energy from food that they consume YOU are a heterotroph!

ENERGY Energy comes in many forms such as light, heat, electricity and can be stored in chemical compounds. ADP (adenine di-phosphate) has 2 phosphates and resembles a partially charged battery When ADP gains another phosphate it turns into ATP (Adenine Tri-phosphate, 3 phosphates)which stores tons of energy and resembles a fully charged battery ADP turns into ATP when sugars such as glucose are broken down

History 1643 Jan van Helmont 1771-Joseph Priestly 1779-Jan Ingenhousz 1845-Julius Robert Mayer 1941-Samuel Ruben/Martin Kamen 1948-Melvin Calvin 1992-Rudolph Marcus

Photosynthesis Equation CO 2 + H 2 O + SUNLIGHT  C 6 H 12 O 6 + O 2 Photosynthesis: to convert light energy from the sun into chemical energy in the form of organic compounds such as carbohydrates (glucose) Photosynthesis involves many steps, it is called a biochemical pathway.

Parts of a chloroplast

Light and Pigment Chloroplasts have pigments, which are compounds that absorb light Chlorophyll a and chlorophyll b absorb blues and reds and reflect green, this why leaves look green! Other colors can be absorbed such as browns, orange and yellows, these colors are called carotenoids. Pigments that absorb these colors are called accessory pigments.

Chlorophyll a absorbs reds, chlorophyll b absorbs blues-----together, with accessory pigments, they reflect green

Photosynthesis occurs in 2 steps Step 1-the light reaction – Occurs in the day time (stomata are open) – Uses light to make energy for dark reaction Step 2-the dark reaction or Calvin Cycle – Occurs usually at night (stomata are closed) – Uses energy made from light reaction to “fix carbon” or make glucose

The Light Reaction 1-light is absorbed in the thylakoid membrane of the chloroplast 2-Light energy breaks apart water molecules to make H and O. 3-Oxygen is let off into the atmosphere 4-Hydrogen gets converted to electrons and stays around to make ATP 5-NADPH, an energy carrier, “plays catch” with the electrons through the thylokoid membrane, generating ATP for the next reaction

The light reaction happens inside the thylakoid membrane

The Calvin Cycle 1. ATP made from the light reaction move to the stroma (fluid inside the chloroplast) 2. 3 CO 2 molecules enter the stroma from diffusion 3. each CO 2 molecule gets enzymatically combined with a 5 carbon compound called RuBP (Rubisco) 4. A 6 carbon molecule results and immediately splits into a 3 carbon molecule called 3-PGA

Last step 5. ATP and NADPH use energy to turn 3PGA into G3P (a 3 carbon compound) which is an organic compound that the plant can use as food. 2 G3P’s can hook together to make glucose!!!!! This is CARBON FIXATION ** Since glucose has to be broken down to use again, the plant will use this 3 carbon (G3P) instead of having to break down glucose which will require more energy

The Calvin Cycle (In the stroma)

Where to next? Organic compounds (food or G3P, glucose) made during photosynthesis is now sent to the mitochondria to gain energy. O 2 not released from photosynthesis can be used for cellular respiration. CO 2 released from cellular respiration is recycled back for use in photosynthesis!

Recap CO 2 +H 2 O+ sunlight  C 6 H 12 O 6 +O 2 – Equation for photosynthesis – Occurs in chloroplast Products from above now go into the mitochondria for cellular respiration: C 6 H 12 O 6 +O 2 +H 2 O  ATP+ CO 2 +H 2 O

Alternative Pathways of Photosynthesis There are 3 different ways plants can perform photosynthesis. Each way depends on its environment and how the plant has evolved or adapted to its surroundings The pathways are: C3, C4 and CAM

C3 Open stomata during the day and close them at night Hooks 3 carbons together during carbon fixation-the goal is to make 6 (glucose) This is USUALLY the way most plants photosynthesize in temperate climates like NJ

C4 Stomata are partially closed during the day (to conserve water) Certain enzymes can fix 4 carbons together at once, since the goal is 6 (glucose), they are automatically closer to their goal! These plants originated in the tropics and have evolved this special enzyme Examples are crabgrass, corn and sugar cane

CAM Pathway Open stomata at night and close them during the day (ultimate water conservations) During the night, they take in CO2 and fix it (Calvin cycle) during the day  opposite of what most plants do!! They grow slower, but conserve a lot of water since they have evolved to adapt in extremely hot and dry climates. Examples: cactus and pineapples