Chapter 8 Photosynthesis

Section 8-1 Energy and Life Energy is the ability to do work Without energy, life would cease to exist The energy in most food comes from the sun

Autotrophs Organisms that make their own food- either photosynthetic or chemosynthetic B. Heterotrophs Obtain energy from the foods they consume-plant, animals or decomposing matter

C. Chemical Energy and ATP 1. Energy comes in different forms a. light, heat, and electricity b. can also be stored in chemical compounds 2. ATP – adenosine triphosphate a. adenine, ribose, and 3 phosphate groups b. 3 phosphates – give the ability to store and release energy

i. Storing Energy - when energy is available it adds a phosphate group to ADP (like a full battery) ii. Releasing Energy - energy released by breaking the bond between the phosphate groups - basic energy source of all cells

DRAW ATP MOLECULE

D. Using Biochemical Energy (Using ATP) 1. Active Transport 2. Motor Proteins- to move organelles 3. Synthesis of proteins and nucleic acids

E. ATP is a useful source of Energy, but it E. ATP is a useful source of Energy, but it is not a good long-term energy storage molecule Most cells only have a small amount of ATP One single molecule of glucose stores 90 times the chemical energy of an ATP molecule Cells can regenerate ATP from ADP as needed by using the energy in foods like glucose

Section 8-2 Photosynthesis: An Overview Photosynthesis – the key cellular process identified with energy production Plants use sunlight to convert water and carbon-dioxide into high energy carbohydrates and oxygen

A. Scientists Investigating Photosynthesis Van Helmont a. concluded that trees gain most of their mass from water b. he did not account for the carbon part of the equation (CO2) 2. Priestley a. candle experiment – jar and the mint plant – release oxygen

3. Jan Ingenhousz -showed Priestley’s effect only occurred in the presence of light - light is necessary for plants to produce oxygen

B. Photosynthesis Equation 6CO2 + 6H2O + Sunlight --> C6H12O6 + 6O2 - Photosynthesis uses energy from sunlight to convert carbon dioxide and water into glucose and oxygen

C. Light and Pigments 1. photosynthesis requires light and chlorophyll – found in chloroplasts 2. Plants use pigments to gather the sun’s energy 3. Chlorophyll – plant’s key pigment - chlorophyll a- absorbs red and violet wavelengths of light - chlorophyll b – absorbs red-orange and blue wavelengths

Section 8-3 The Reactions of Photosynthesis Inside a chloroplast a. Where photosynthesis takes place b. Structures i. Thylakoids – saclike photosynthetic membrane (pancakes) - proteins in the thylakoid organize chlorophyll into clusters called photosystems (light-collecting units) ii. Grana – Stack of thylakoids iii. Stroma – region outside the thylakoid membrane (syrup)

2 reactions -Light-dependent- in the thylakoid membrane - Light-independent (Calvin Cycle) – in the stroma

2. Electron Carriers a. sunlight excites the electrons in chlorophyll – high in energy b. NADP+ - electron carrier - can accept a pair of high energy electrons and a hydrogen ion (H+) - this converts NADP+ to NADPH c. this makes up the Electron Transport Chain (ETC) d. NADPH carries the electrons to Calvin cycle

3. Light-Dependent Reactions a. require light b. produce oxygen gas c. convert ADP and NADP+ into energy carriers ATP and NADPH

Light-Dependent Reactions A. Photosystem II absorb light - electrons absorb energy - passed on to the ETC - thylakoid replaces electrons with electrons from broken apart H20 molecules - Oxygen is released into the air - H+ ions are released inside the thylakoid

B. e- go from PS II to PS I - energy from e- is used to pump the H+ ions from the stroma into the thylakoid membrane

C. Pigment in PS I use energy from light to reenergize the e- - NADP+ then again turns to NADPH D. As the electrons pass to NADP+ more H+ ions are pumped across the membrane - outside of membrane (-) charged - inside of membrane (+) charged - this charge difference provides the energy needed to make ATP

E. ATP synthase – enzyme that allows the H+ ions to cross the membrane - as H+ ions pass through the enzyme it rotates - as it rotates, ATP synthase binds the phosphate group to ADP making ATP - this produces not only high energy electrons but ATP as well

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American scientist Melvin Calvin 4. Light-Independent Reactions (Calvin Cycle)- American scientist Melvin Calvin - Uses ATP and NADPH to produce sugars (short term storage) - contain a lot of chemical energy - does not require light

Light Independent Reactions A. 6 CO2 molecules – enter cycle from atmosphere - combine with (6) 5 Carbon molecules - produce (12) 3-Carbon molecules B. (12) 3-Carbon molecules are converted into high energy forms - energy for conversion comes from ATP and NADPH

C. (2) of the 3-Carbon molecules are removed from the cycle to produce molecules needed by the plant (glucose) D. The remaining (10) 3-Carbon molecules are converted back into (6) 5-Carbon molecules - These return to the beginning of the cycle to restart the next cycle.

Purpose of the Calvin Cycle - It uses (6) CO2 molecules to make a single 6-carbon sugar molecule (glucose) Light-dependent – Trap the energy from the sun in chemical form Light-independent – use the stored chemical energy to produce sugars