Photosynthesis

Autotrophs & Heterotrophs Autotrophs – organisms use can make their own food Some autotrophs capture light energy from the sun in the process of photosynthesis Heterotrophs – obtain energy from the foods they consume

ATP & Energy Structure of ATP ATP (Adenosine Triphosphate) – shuttles energy for cells ATP is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups

ATP & Glucose ATP is not good for storing energy for a long time. Cells only have a small amount of ATP. One Glucose can store more than 90 times more energy than one ATP. Cells store glucose, and use glucose to regenerate ATP as needed (cellular respiration).

*Photosynthesis – process of capturing light energy from the sun to convert water & CO2 into oxygen and high energy carbohydrates (food, ex: glucose, starch, & other sugars) Equation: Energy (light) + 6CO2 + 6H2O  6O2 + C6H12O6

Investigating Photosynthesis Van Helmont’s Experiment – do plant’s grow by taking material from the soil? Found mass of dry soil Planted a seedling, watered it at regular intervals until it grew to a mass of 75kg. Found mass of soil to be unchanged Concluded the mass the plant gained came from the water he added. Partially correct, but did not determine where the carbon in the carbohydrate comes from

Priestley’s Experiment – oxygen is produced by plants Determined that oxygen was required to keep a flame lit/burning. Removed oxygen from a jar by placing a lit candle under it until the flame went out. Then placed a sprig of mint in the jar (empty of oxygen) After a few days, he found he could relight a candle in this jar and it would remain lit for a while!

Jan Ingenhousz – light is essential to photosynthesis! Showed the effect observed by Priestley occurred only when the plant is exposed to light! Together, Priestly and Ingenhousz showed the plants need light and water to produce oxygen.

Photosynthesis Basics – occurs in the chloroplasts of plants, protists, and some bacteria cells. Chloroplast – organelle where photosynthesis occurs Surrounded by 2 membranes. Thylakoid – flattened sac made of membrane inside the chloroplast Granum – stack of multiple thylakoids Stroma – fluid that surrounds the grana and fills the chloroplast

B. Pigments – compound that absorbs light 1. Chlorophyll – pigment on thylakoid membrane that absorbs light for photosynthesis Chlorophyll a – absorbs less blue and more red light; directly absorbs sunlight Chlorophyll b – absorbs more blue and less red light; helps chlorophyll a absorb light Both chlorophyll a and b reflect green light Caretenoid – another pigment that absorbs blue and green light, but not orange; also helps chlorophyl a absorb light.

**Equations are also the reverse! C. Photosynthesis is chemically the opposite of Respiration. Respiration Photosynthesis Uses glucose to make ATP 1st converts light to ATP 2nd uses ATP to make glucose **Equations are also the reverse!

NAPDH As chlorophyll absorb sunlight, their electrons become excited (gain a lot of energy). These high energy electrons require a special carrier called NADP+ NADP+ holds and carries 2 high energy electrons, along with a H+ ion to become NADPH

Light-Dependent Reactions – first step of photosynthesis, converts sunlight to ATP Occurs on the thylakoid membrane. Light is absorbed by a chlorophyll. The light energy provides electrons for the Electron Transport Chain (chain of proteins). The ETC splits water (H+ & O2 are released). Some H+ is added to NADP+ and produces NADPH. The O2 is released to the atmosphere.

*Chemiosmosis and the ETC happen at the same time!!! Also happens on the membrane of the thylakoids. Rest of the H+ (from the splitting of water) drives ATP Synthase proteins to make ATP. *Chemiosmosis and the ETC happen at the same time!!!

Uses ATP to make Glucose Calvin Cycle – the 2nd step of photosynthesis. Also called the Light-independent Reactions (used to be called Dark Reactions), as light does not play any direct role. Uses ATP to make Glucose

Steps of the Calvin Cycle RuBP (carbohydrate in plants) reacts with NADPH, CO2 (from the atmosphere), and ATP to make Glucose. In the final step, RuBP is remade so the cycle can occur again.

Factors Affecting Photosynthesis Water – is a needed raw material; shortage of water slows or even stops photosynthesis Temperature – photosynthesis relies on enzymes, which only function between 0oC and 35oC Intensity of Light – up to a specific level, as light intensity increases, so does the rate of photosynthesis