Photosynthesis Plant – multicellular eukaryotes that have cell walls made of cellulose and photosynthesize. “stationary animals that eat sunlight”

Adenosine Triphosphate (ATP) One of the most important compounds that cells use. Stores and releases energy - adenosine triphosphate (ATP). ATP consists of adenine, a 5-carbon sugar called ribose, and three phosphate groups.

Adenosine Triphosphate (ATP) Adenosine diphosphate (ADP) has two phosphate groups instead of three. ADP does not contain as much energy as ATP. Another P is added to ADP to form ATP. Cells release the energy stored in ATP by breaking the bonds between the second and third phosphate groups.

Uses of ATP Powers protein pumps in the cell membrane Powers cilia and flagella Power for synthesis of proteins Powers motor proteins that contract muscles Provides cell energy

How could a small seed become a giant tree? Heterotroph – obtains energy from food it consumes Autotroph – uses energy from the sun to produce food Photosynthesis - the process by which autotrophs use the energy of sunlight to produce high- energy carbohydrates that can be used for food.

Autotroph or Heterotroph

Photosynthesis 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 LIGHT Carbon Dioxide Water Glucose Oxygen

What is Light? Light Speed, c = x 10 8 m/s Or million mph Which type of light carries more energy, blue or red?

Why are plants usually green? Electromagnetic Spectrum Wave length and energy are inversely proportional The smaller the wave length, the more energy Blue light is high energy Red light is low energy They reflect green light

Plant Pigments Pigments – light absorbing molecules Chlorophyll – the most abundant pigment in plants, that absorbs blue and red light. Chlorophyll a - a blue-green pigment Chlorophyll b - a yellow-green pigment

Accessory Pigments Carotene - an orange pigment Xanthophyll - a yellow pigment Anthocyanin – a red pigment

Accessory Pigments Why do plants need accessory pigments? They absorb light in other regions of the spectrum The accessory pigments are always present in most plants but masked by the chlorophyll.

Pigments Why do leaves change color in the fall? Answer: Shorter day lengths stop chlorophyll production, and expose accessory pigments

Photosynthesis Takes place in the chloroplast Thylakoids – saclike photosynthetic membrane in the chloroplast Grana – stacks of thylakoids Stroma - the region outside of the thylakoid membranes

Photosynthesis (Overall) Light CO 2 H2OH2O Chloroplast LIGHT REACTIONS (in thylakoids) CALVIN CYCLE (in stroma) NADP + ADP +P ATP NADPH OSugar Electrons Light Dark

Connection between light and dark reactions The electron acceptor NADP + and ADP enter the light reaction NADP + accepts 2 high energy electrons and a hydrogen ion making NADPH. ADP is converted to ATP Without these products from the light reaction the dark reaction could not proceed.

Light-Dependent Reaction Inputs = Light, Water, NADP+, ADP Occurs in the thylakoid membranes Conversion of light energy to ATP and NADPH Oxygen is released through the stoma.

Light Reaction

Light Reaction Steps 1. Photosystem II – light energy is absorbed and sends electrons through electron transport chain (ETC). Note: H 2 O is the source of electrons, hydrogen and oxygen 2. Electrons move along ETC and pump H + into the thylakoid space 3. Photosystem I – electrons are re-energized and NADP+ picks up electrons and H + (NADPH formed) 4. H+ builds up in thylakoid space, exits from high to low to stroma THROUGH ATP SYNTHASE (a turbine that adds P to ADP = ATP)

THE DARK SIDE

Dark Reaction (Calvin Cycle) Takes place in the stroma Use ATP and NADPH to make carbohydrates Glucose Starch – long chain of stored glucose. Cellulose – tough fibers that give plants strength and rigidity

Dark Reaction (Calvin Cycle) (PGAL)

Dark Reaction (Calvin Cycle) Steps 1. CO 2 enters the Calvin Cycle from the atmosphere. The enzyme rubisco combines CO 2 with a 5 carbon compound called Ribulose biphosphate (RuBP). 2. The result are six 3 carbon compounds that are reduced and combine with ATP and NADPH to make Glyceraldehyde 3- phosphate (PGAL), a sugar. 3. One PGAL leaves the cycle at midpoint and becomes the building block for glucose 4. The remaining five 3 carbon compounds continue through the cycle to reform the 5 carbon compound RuBP

Photosynthesis The products of the light reaction fuel the Calvin cycle. The products of the Calvin cycle fuel the light reaction. Light CO 2 H2OH2O Chloroplast LIGHT REACTIONS (in thylakoids) CALVIN CYCLE (in stroma) NADP + ADP +P ATP NADPH OSugar Electrons

Factors Affecting Photosynthesis Shortage of water H2O acts as the electron donor in the light dependent reaction Temperature Photosynthesis is controlled by enzymes that work best between 0 C and 35 C. Light Intensity More light increases rate of photosynthesis