 Energy is the ability to do work How Organisms Obtain Energy  Thermodynamics is the study of the flow & transformation of energy in the universe

Laws of Thermodynamics  First law—energy can be converted from one form to another, but it cannot be created nor destroyed.  Second law—energy cannot be converted without the loss of usable energy

Autotrophs and Heterotrophs  Autotrophs use energy from sunlight or chemical bonds in inorganic substances to make organic compounds  Heterotrophs are organisms that need to ingest food to obtain energy

What was the best item you ate for lunch today?

Metabolism  All of the chemical reactions in a cell  Anabolic reactions- simpler substances combine to make more complex molecules or store energy-usually requires energy  Catabolic reactions-break down more complex molecules into simpler substances- usually releases energy-drives chemical rxns

 Photosynthesis—light energy from the Sun is converted to chemical energy for use by the cell (anabolic)  Cellular respiration—organic molecules are broken down to release energy for use by the cell (catabolic) Biochemical Pathways

 Photosynthesis uses CO 2, water and sunlight (energy) to make organic compounds and O 2  Cellular respiration uses organic compounds and O 2 to make CO 2, water and energy

In 1648, a Flemish alchemist, Jan van Helmont, had a theory. To test it, he grew a tree in a tub of soil, adding nothing but measured quantities of water for five years. During that time he kept track of the weight of the soil and the tree. At the end of the experiment the tree had gained 164 pounds and the soil had lost 2 ounces. What could von Helmont conclude from his experiment?

Overview of Photosynthesis  Photosynthesis occurs in 2 phases:  Light reactions-light energy is absorbed and temporarily stored in ATP and NADPH  Calvin Cycle (carbon fixation)- organic compounds formed using CO 2 and energy in ATP and NADPH

What is an organic molecule?

 1. Build a carbon dioxide – what type of bonds does it have?  2. Build a water molecule- what type of bonds does it have?  3. Begin bonding the 6 carbons together for glucose-note 1 is not in the ring

Phase One: Light Reactions  The absorption of light is the first step in photosynthesis  How does a leaf absorb light? They contain light-absorbing pigments in the chloroplasts

 Chlorophyll the primary pigment in photosynthesis, absorbs mostly blue and red light and reflects green and yellow light

Plants contain two types of chlorophyll, chlorophyll a and chlorophyll b

 The pigments that produce yellow and orange fall leaf colors, also the colors of many fruits, vegetables, flowers, are called carotenoids.

 Carotenoids absorb wavelengths different from chlorophyll, both pigments allow plants to absorb more light energy

Absorption Spectra of Photosynthetic Pigments

Pigments are embedded in the membranes of thylakoids- photosystem I and II

 When light strikes a thylakoid in a chloroplast, energy is transferred to electrons in chlorophyll.  This energy transfer causes the electrons to jump to a higher energy level.

 The excited electrons that leave chlorophyll molecules must be replaced by other electrons  Plants get replacement electrons from water molecules. Photolysis is the splitting of water by light  form oxygen gas, O 2  2H 2 O 4 H + + 4e - + O 2

 Hydrogen ions (H +, protons) are released into the lumen of the thylakoid  Here H + ions build up and when H + passes through ATP synthase into the stroma of the chloroplast, ADP + Pi are converted into ATP - chemiosmosis

 The excited electrons move from photosystem II to an electron-acceptor molecule in the thylakoid membrane  The electron-acceptor molecule transfers the electrons along a series of electron-carriers to photosystem I  electrons are released into the electron transport system

 Photosystem I transfers the electrons to a protein called ferrodoxin  Ferrodoxin transfers the electrons and a proton to the electron carrier NADP +, forming the energy-storing molecule NADPH

Phase Two: The Calvin Cycle-Carbon Fixation  In the second phase of photosynthesis, called the Calvin cycle, energy is stored in organic molecules such as glucose

 Six CO 2 molecules combine with six 5-carbon compounds to form twelve 3-carbon molecules called 3-PGA  The chemical energy stored in ATP and NADPH is transferred to the 3-PGA molecules to form high-energy molecules called G3P

 Two G3P molecules leave the cycle to be used for the production of glucose and other organic compounds  An enzyme called rubisco converts the remaining ten G3P molecules into 5-carbon molecules called RuBP  These molecules combine with new carbon dioxide molecules to continue the cycle

How does the essential CO 2 get into the plant? How does O 2 leave?

Alternative Pathways  C 4 plants-corn, sugarcane, crabgrass – plants that keep stomata partially closed during the hottest part of the day  CAM plants-cacti, orchids, pineapples- stomata only open at night, grow slowly but lose little water

Factors that affect Photosynthesis  Light Intensity  CO 2 level  Temperature  All increase photosynthesis as factor increases to a terminal point