Photosynthesis

Energy and Life  Autotroph: organisms that make their own food  Heterotrophs: organisms that obtain energy from the foods they consume  To live, all organisms, including plants, must release the energy in sugars and other compounds

Chemical Energy and ATP  ATP: (adenosine triphosphate) used by all cells as their basic energy source.  ATP consists of adenine, a 5-carbon sugar called ribose, and three phosphate groups.  The bonds between the last two phosphates is where the energy is stored!  ADP + P + energy  ATP

Photosynthesis – plants use the energy of sunlight to convert water and carbon dioxide into high energy carbs. (glucose) and oxygen (waste)

The Photosynthesis Equation  The overall reaction is: 6CO 2 + 6H 2 O LIGHT > C 6 H 12 O 6 + 6O 2 OR Carbon Dioxide + Water light > Glucose + Oxygen

The Importance of Photosynthesis 1. The oxygen in the air comes from photosynthesis. The plants continue to replenish the oxygen in the air. 2. All of our food comes directly or indirectly from photosynthesis.

What Is a Plant?  Nearly all plants are autotrophs.  All are multi-cellular  All plants are eukaryotes.  Plants cells are surrounded by cell walls.

Plant Parts Roots anchor a plant in the ground, absorb water and minerals from the soil, and sometimes store food.

Stems  Contains the vascular tissue.  Helps Supports the plants.

LLeaves capture and use the sun’s energy to make food (photosynthesis) LLeaf Structure BBlade: the most important part; food-making part VVeins: contains the vascular tissue SStomata: tiny openings on the underside of the leaf Leaves

Leaf Structure  Epidermis: a protective cover that prevent excess loss of water.  Mesophyll: the layer underneath epidermis that contains the chloroplast Stoma Mesophyll Cell Chloroplast

Stomata (stoma) Pores in a plant’s cuticle through which water and gases are exchanged between the plant and the atmosphere. Guard Cell Carbon Dioxide (CO 2 ) Oxygen (O 2 ) Found on the underside of leaves

Chloroplast Organellephotosynthesis Organelle where photosynthesis takes place. Granum Thylakoid Stroma Outer Membrane Inner Membrane Thylakoid stacks are connected together

Thylakoid: Thylakoid: sac-like photosynthetic membranes Thylakoid Membrane Thylakoid Space Granum Grana are stacks of thylakoids

Chlorophyll Molecules  Located in the thylakoid membranes  Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red-660 nm are most important)  Plants are green because the green wavelength is reflected, not absorbed  Plants are green because the green wavelength is reflected, not absorbed.

wavelength Absorption violet blue green yellow orange red Absorption of Light by Chlorophyll

Fall Colors  In addition to the chlorophyll pigments, there are other pigments present  During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments  Carotenoids are pigments that are either red, orange, or yellow

Stage of Photosynthesis

Redox Reaction The transfer of one or more electrons from one reactant to another Two types: 1.Oxidation is the loss of e - 2.Reduction is the gain of e -

Oxidation Reaction The loss of electrons from a substance or the gain of oxygen. (in this case splitting of water using energy from the sun) glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Oxidation

Reduction Reaction The gain of electrons to a substance or the loss of oxygen. (Carbon Fixation – building of glucose) glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Reduction

22 Two Parts of Photosynthesis Two reactions make up photosynthesis: 1.Light Reaction or Light Dependent Reaction – Happens in the thylakoid Produces energy from solar power (photons) in the form of ATP and NADPH.

Two Parts of Photosynthesis 2. Calvin Cycle or Light Independent Reaction or Dark Reaction  Happens in the stroma  Also called Carbon Fixation  Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).

Factors Affecting Photosynthesis  The amount of water  Temperature.  Best between 0 and 35 ºC.  Intensity of light  The Concentration of CO 2

Electron Carriers  Electron carriers are molecules that can accept a pair of high-energy electrons and later transfer them along with most of the energy to another compound.  Example:  NADPH – which carry the high-energy electrons elsewhere in the cell.  High energy electrons are used to build a variety of molecules the cell needs like glucose.  Electron transport chain: uses electron carriers to pass electrons to other carriers, releasing energy as they are transferred.

Light Reactions  Requires light  Happens in the thylakoids of the chloroplast  Produces ATP and NADPH and oxygen gas by splitting water molecules.  ATP synthase is a membrane protein (enzyme)  Allows H+ ions to pass through the cell membrane in order to make ATP  Overall result of the light reactions is the conversion of light energy to chemical energy stored in two compounds: NADPH and ATP

The Dark Reactions or Light- Independent Reactions  Takes place outside the thylakoid membrane in the stroma.  Uses ATP and NADPH from the light reactions along with CO 2 to produce glucose  Carbon dioxide is broken and “fixed” into glucose or fructose molecules in the CALVIN CYCLE!

Stage of Photosynthesis 1.2. Chloroplast Thylakoid Stroma