Concept 8.1: Photosynthesis uses light energy to make food

I. The structure of Chloroplasts The structure where photosynthesis takes place is the chloroplast. Chloroplasts contain compounds called pigment that give leaves their color. Leaves contain the most chloroplasts. There are tiny pores called stoma that allows carbon dioxide to enter and oxygen to leave the cell.

I. The structure of Chloroplasts Veins carry CO2 and H2O from the plants roots to the leaves and deliver organic compounds to other parts of the plant. The inner membrane of a chloroplast encloses a thick fluid called stroma. Suspended in the stroma are many disk shaped sacs called thylakoids which are arranged in stacks called grana. These stacks organize the series of reactions that make up photosynthesis.

Photosynthesis

II. Overview of Photosynthesis In cellular respiration, electrons “fall” from glucose to O2 to release energy. In photosynthesis, electrons from water are boosted “uphill” by the energy of sunlight.

III. The Light Reactions These excited electrons, along with carbon dioxide and hydrogen ions produce C6H12O6 molecules Photosynthesis occurs in two main steps: Light Reaction and Calvin Cycle (Dark Reaction).

The Light Reactions…con’t Light Reactions convert the energy in sunlight to chemical energy. Chloroplasts use captured light energy to remove electrons from H2O, splitting it into oxygen and hydrogen ions. The electrons and hydrogen ions are used to make NADPH, which is an electron carrier Chloroplasts also use the captured light energy to generate ATP. The overall result of the light reactions is the conversion of light energy to chemical energy stored in NADPH and ATP.

IV. The Calvin Cycle Calvin Cycle makes sugar from the atoms in carbon dioxide plus the hydrogen ions and high energy electrons carried in NADPH. The ATP made in the light reactions provides the energy to make sugar. The Calvin Cycle is sometimes referred to as the “light-independent reactions” because it does not require light energy to begin.

Concept 8.2 The Light Reactions Convert Light Energy to Chemical Energy

I. Light Energy and Pigments Light is a form of energy that travels in waves and the distance between adjacent waves is called a wavelength. The range of wavelengths is called the electromagnetic spectrum. Visible light only makes up a small portion of the electromagnetic spectrum.

II. Pigments and Color A substances color is due to chemical compounds called pigments. Waves of light shining on a material can be absorbed, transmitted or reflected. Leaves absorb blue-violet and red-orange light very well but either reflect or transmit green light and that is why leaves look green

III. Identifying Chloroplast Pigments Using a technique called chromotography different pigments in a leaf can be observed. Chlorophyll a absorbs mainly blue-violet light while chlorophyll b absorbs mainly red light.

IV. Harvesting Light Energy Within the thylakoid membrane, chlorophyll and other molecules are arranged in clusters called photosystems. Each photosystem contains a few hundred pigment molecules, including chlorophyll a and b as well as carotenoids. Each time a pigment molecule absorbs light energy electrons are raised from a “ground state” to an “excited state”

Concept 8.3: The Calvin Cycle makes sugar from carbon dioxide

A Trip around the Calvin Cycle The Calvin Cycle is the sugar factory within the chloroplasts. The starting material for the Calvin Cycle is regenerated each time the process occurs, the starting material is called RuBP, (a sugar with five carbons) Inputs for the Calvin Cycle are ATP, CO2 and NADPH. (from light reaction and air thus no light) The cycles output is an energy rich sugar molecule called G3P which is not quite like glucose but it used as the raw material to make glucose as the plant needs to.

A Trip around the Calvin Cycle

II. Summary of Photosynthesis The overall equation for photosynthesis is: 6 CO2 + 6 H2O  C6H12O6 + 6 O2 Carbon dioxide + water  Glucose + Oxygen The light reaction take place in the thylakoid membranes and convert light energy into chemical energy in the form of ATP and NADPH. The light reactions use the reactant H2O and release the product O2. The Calvin Cycle takes place in the stroma and uses ATP and NADPH to convert CO2 to C6H12O6.

Summary of Photosynthesis Photosynthesis is the first step in the flow of energy through an ecosystem. Photosynthesis is the ultimate source of all the food that you eat and all the oxygen that you breathe.

Concept 8.4: Photosynthesis has a global impact

I. The Carbon Cycle The Carbon Cycle is the process by which carbon moves from inorganic to organic compounds and back. Through photosynthesis, producers convert inorganic CO2 to organic compounds. (ex: sugar) Cellular Respiration by both producers and consumers return the CO2 to the atmosphere. No other chemical process matches the output of photosynthesis. Earth’s plants and other photosynthetic organisms make up about 160 billion metric tons of organic material per year.

II. Photosynthesis and Global Climate One organism may either produce or use a relatively small amount of CO2, the total effect of all the organisms on Earth has a very large effect. CO2 only made up 0.03% of the Earth’s atmosphere before this century. CO2 traps heat from the sun that would have otherwise escaped back into space, this property is known as the Greenhouse Effect.

Greenhouse Effect

Photosynthesis and Global Climate The greenhouse effect keeps the average temperature on Earth about 10 degrees warmer than it would be otherwise. The amount of CO2 in the atmosphere is rising with no end in sight.