Topic #4: Photosynthesis

Topic Question+ How do plants and other organisms capture light from the sun?

Section Question How do organisms store energy?

Energy and Life  Living things MUST have the ability to obtain and use energy.  Energy can not be made or destroyed it can only be transferred.  Energy is stored in chemical bonds…the attraction of two or more atoms together caused by the sharing or stealing of electrons.

Chemical Energy and ATP  Adenosine triphosphate (ATP) is the most important chemical compound that cells use to store and release energy.

Chemical Energy and ATP  The energy is stored in the bonds holding together the three phosphate groups.  These bonds hold large amounts of energy AND are easily broken (to release) and reform (to store).

Chemical Energy and ATP  All cell activities are powered (or paid for) by using the energy in ATP. + = FUN + = FUN

Heterotroph vs. Autotroph  Organisms differ in how they get the materials to make ATP and store energy.  Define and give and example of:  Heterotrophs –  Autotrophs –

Photosynthesis  Photosynthesis is the set of chemical reactions some autotrophs use to transform energy from sunlight into glucose which can be made into ATP by the mitochondria.

Section Question What cellular structures and molecules are involved in photosynthesis?

Chlorophyll and Chloroplasts  Plant cells have specialized organelles called chloroplasts which are responsible for photosynthesis.

Chlorophyll and Chloroplasts  The light we see from the sun is called “white light” BUT it is actually a mixture of many different colors.  ROYGBIV  Plants only use red and blue light to undergo photosynthesis.

Chlorophyll and Chloroplasts  Plants absorb the red and blue light from the sun but reflect the green light…that’s why plants look green.  A pigment called chlorophyll is the main pigment in plants which absorbs red and blue light. Chlorophyll A absorbs red light. Chlorophyll A absorbs red light. Chlorophyll B absorbs blue light. Chlorophyll B absorbs blue light.

Chloroplast Strucutre  Define the following terms. Thylakoid – Stroma – Grana(um) –

Sun…to Food…How?  Sunlight comes in contact with the chlorophyll molecules in plants.  These molecules contain electrons that become excited and jump out of their energy level.  These electrons then attach to carrier molecules to be transported to different chemical reactions throughout the chloroplast

An Overview of Photosynthesis light light  Carbon Dioxide + Water Sugar + Oxygen light light  6 CO H 2 O C 6 H 12 O O 2  List the Reactants:  List the Products:

Section Question How do photosynthetic organisms convert the sun’s energy into chemical energy?

Light Dependent Reactions  The first set of reactions are called this because light is required.  Pigments is photosystem 2 absorb light and electrons are pushed off by this absorption.

Light Dependent Reactions  The electrons (high energy) are passed along the Electron Transport Chain (ETC) by electron carrier proteins.  Photosystem 1 has pigments which reenergize the electrons (some energy is lost in transit).  ATP Synthase is a protein at the end of this reaction which pumps the electrons out of the chloroplast and in the process makes ATP

Lets See It in Action… High Energy Molecules

Light Independent Reactions  The small amount of ATP and NADPH made by the light dependent reactions is used to power the Light Independent Reactions AKA the Calvin Cycle.

The Calvin Cycle  Glucose (sugar) is the end result of the Calvin Cycle.  Glucose is a carbon compound so there must be a carbon source for the Calvin Cycle…  CARBON DIOXIDE is that source.

The Calvin Cycle  CO 2 enters the stroma and is broken down in to carbon and oxygen.  The oxygen is released as waste and the carbon is used to assemble carbon chains which will be made into sugars.

Calvin Cycle Summary  6 carbon dioxide molecules are used to make one 6 carbon sugar molecule.  This change is powered by 12 ATP and 12 NADPH molecules form the light dependent reactions.

Factors Affecting Photosynthesis  Using p240 identify how the following affect photosynthesis.  Amount of light  Amount of Water  Temperature

Extreme Photosynthesis  C4 and CAM plants are plants that use alternate forms of photosynthesis because of their environmental conditions.  C4 plants can make more sugar from less CO 2 based on their reactions.  CAM plants can make more sugar with less water based on their reactions.