Lesson Overview 8.2 Photosynthesis: An Overview
Light and pigments Energy from the sun travels to Earth in the form of light. Sunlight is a mixture of different wavelengths. The wavelengths we see is known as the visible spectrum: The colors of the visible spectrum are red, orange, yellow, green, blue, indigo, and violet.
Plants gather the sun s energy with light-absorbing molecules called pigments. Chlorophyll absorbs all colors in light but reflects green (so, plants appear green) Chlorophyll is the main pigment in plants Carotenoids (Carotene) - an accessory pigment in plants that absorbs all light except for red, orange, or yellow (usually seen in Autumn leaves)
Pigments We see the green colors of plants most of the time, because the green color of the chlorophyll overwhelms the other pigments. As temperatures drop, chlorophyll molecules break down, the red and orange pigments may be seen. Pigments absorb the light energy needed for photosynthesis.
The Chloroplast Structure Grana - Stacks of membrane sacks (singular = Granum) Thylakoid the individual membrane sacks of grana Chlorophyll is located on membrane of thylakoid, where light absorption occurs Stroma fluid space surrounding grana http://www.youtube.com/watch?v=scl K6duS9zQ
The Process of Photosynthesis 2 Steps: 1. Light-dependent reactions uses sunlight to produce two energy carriers: NADPH and ATP 2. Light-independent reactions uses carbon dioxide (CO 2 ) to produce glucose, using energy from NADPH and ATP (from step 1)
1. Light-dependent Reactions Requires sunlight to work Occurs on the membrane of the thylakoid in the chloroplast Clusters of chlorophyll, called photosystems, absorb sunlight and excite electrons Water is required as a source of electrons and hydrogen ions. Oxygen is released as a byproduct (waste).
Electrons are passed along a chain of molecules Energy from this is used to produce 2 molecules: NADPH is made from NADP+ ATP is made from ADP
High-Energy Electrons (R-Track) NADP + (nicotinamide adenine dinucleotide phosphate) is a carrier molecule. NADP + accepts and holds two high-energy electrons, along with a hydrogen ion (H + ). In this way, it is converted into NADPH.
2. Light-independent reactions-no light required Also called the Calvin Cycle Calvin Cycle- a series of reactions that produces the organic molecule (carbohydrates). Occurs in the stroma (open space) of the chloroplast The light-independent reaction is a continuous chain of chemical reactions in which energy is used to convert CO 2 into glucose ATP and NADPH molecules produced in the lightdependent reactions are used to produce high-energy sugars (carbohydrates) from carbon dioxide (in the air).
An Overview of Photosynthesis (you must know this equation!) Reactants: carbon dioxide & water Products: sugar (carbohydrates) & oxygen Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen. Light In symbols: 6 CO 2 + 6 H 2 O -------> C 6 H 12 O 6 + 6 O 2 Light 6 molecules Carbon dioxide +6 molecules Water ----> 1 molecule Sugar + 6 molecules Oxygen
Summary of Photosynthesis (Do not Write) Stage 1 Light energy is captured
Summary of Photosynthesis (Do not Write) Stage 2. Light energy is used to make ATP & NADPH CO 2 + H 2 O Photosynthesis Carbs Proteins Lipids + O 2 Cellular (Aerobic) Respiration (ATP Produced)
Summary of Photosynthesis (Do not Write) Stage 3. ATP & NADPH are used to power the manufacture of energy rich carbohydrates using CO2 from the air
An Overview of Photosynthesis
Photosynthesis animation http://www.youtube.com/ watch?v=1gla5ewn9oi
Factors Affecting Photosynthesis Factors that affect photosynthesis are: Temperature: enzymes that affect photosynthesis function best between 0 C and 35 C. Light intensity: High light intensity increases the rate of photosynthesis Availability of water: a shortage of water can slow or even stop photosynthesis.
Photosynthesis Under Extreme Conditions Plants that live in dry conditions: Often have waxy coatings on their leaves to reduce water loss. C4 and CAM plants have biochemical adaptations that make photosynthesis more efficient under dry conditions. plants in dry conditions adaptations
C4 Photosynthesis C4 plant -named from the fact that the first compound formed in this pathway contains 4 carbon atoms. They can capture even very low levels of carbon dioxide and pass it to the Calvin cycle (where carbohydrates are formed). Require extra ATP to function. C4 organisms include crop plants like corn, sugar cane, and sorghum. sugar cane sorghum corn
CAM Plants Use a process called Crassulacean Acid Metabolism (CAM) to make carbs. At night, they take in CO2 to produce organic acids, trapping the carbon within the leaves. In the daytime, when leaves are tightly sealed to prevent water loss, these compounds release carbon dioxide, enabling carbohydrate production. Ex. pineapple, many desert cacti, and ice plants. cacti pineapple ice plants