PHOTOSYNTHESIS Providing Energy for Life

Do you remember food web terminology? Autotrophs = producers Autotrophs = producers Photoautotrophs Photoautotrophs Chemoautotrophs Chemoautotrophs Heterotrophs = consumers Heterotrophs = consumers Primary consumers, secondary consumers, etc Primary consumers, secondary consumers, etc decomposers decomposers

Photosynthesis Photoautotrophic cells contain pigments that absorb visible light Photoautotrophic cells contain pigments that absorb visible light This is their source of ENERGY This is their source of ENERGY

Where does photosynthesis occur? Leaf: cross section Leaf: cross section

Photosynthesis Most occurs in the mesophyll layer of the leaf Most occurs in the mesophyll layer of the leaf Each mesophyll cell contains chloroplasts Each mesophyll cell contains chloroplasts

CHLOROPLAST

CHLOROPLAST

CHLOROPLAST

CHLOROPLAST Light-absorbing pigments are embedded in thylakoid membranes Light-absorbing pigments are embedded in thylakoid membranes A stack of thylakoids is called a granum A stack of thylakoids is called a granum Plural = grana Plural = grana Grana have a large surface area to allow greater diffusion of materials Grana have a large surface area to allow greater diffusion of materials

CHLOROPLAST STROMA STROMA Surrounds the thylakoid membranes Surrounds the thylakoid membranes Contains enzymes, DNA, RNA Contains enzymes, DNA, RNA

Electromagnetic Spectrum

Electromagnetic spectrum Visible light drives photosynthesis Visible light drives photosynthesis Substances that absorb visible light are called pigments Substances that absorb visible light are called pigments Pigments appear different colors because they reflect different wavelengths (and thus absorb different wavelengths) Pigments appear different colors because they reflect different wavelengths (and thus absorb different wavelengths) Spectrophotometer measures the ability of a pigment to absorb different wavelengths of light Spectrophotometer measures the ability of a pigment to absorb different wavelengths of light

CHLOROPLAST PIGMENTS CHLOROPHYLL = green pigment CHLOROPHYLL = green pigment Two forms of chlorophyll Two forms of chlorophyll Chlorophyll a Chlorophyll a Chlorophyll b Chlorophyll b Chlorophyll absorbs light energy in the violet/blue and orange/red ranges Chlorophyll absorbs light energy in the violet/blue and orange/red ranges REFLECTS in the green range REFLECTS in the green range

Chlorophyll The color that we see is the color that is REFLECTED, not absorbed The color that we see is the color that is REFLECTED, not absorbed Therefore, chlorophyll appears GREEN, because green wavelength light is reflected Therefore, chlorophyll appears GREEN, because green wavelength light is reflected

Other Pigments in Chloroplasts Xanthophyll: yellow Xanthophyll: yellow Carotene: orange Carotene: orange Different colors indicate that they absorb (and therefore reflect) energy at different wavelengths Different colors indicate that they absorb (and therefore reflect) energy at different wavelengths

Absorption Spectra

Plant Pigments Located in the thylakoid membrane Located in the thylakoid membrane Absorption spectrum tells us which wavelengths are absorbed best Absorption spectrum tells us which wavelengths are absorbed best Why is this important? HINT: it has to do with amount of energy absorbed! Why is this important? HINT: it has to do with amount of energy absorbed!

PHOTOSYNTHESIS Overview Photosynthesis involves 3 energy conversions Photosynthesis involves 3 energy conversions 1. absorption of light energy 1. absorption of light energy 2. conversion of light energy into chemical energy 2. conversion of light energy into chemical energy 3. storage of chemical energy as sugars (carbon- containing compounds) 3. storage of chemical energy as sugars (carbon- containing compounds)

Law of Conservation of Energy REMEMBER!!! REMEMBER!!! Energy cannot be created or destroyed, only converted into different forms Energy cannot be created or destroyed, only converted into different forms

PHOTOSYNTHESIS overall summary KNOW THIS!!!!! KNOW THIS!!!!! Carbon dioxide gas combines with water in the presence of light energy and chlorophyll to form sugar and oxygen gas

PHOTOSYNTHESIS

PHOTOSYNTHESIS Photosynthesis occurs in 2 groups of reactions Photosynthesis occurs in 2 groups of reactions LIGHT REACTIONS LIGHT REACTIONS CALVIN CYCLE OR DARK REACTIONS CALVIN CYCLE OR DARK REACTIONS

PHOTOSYNTHESIS I’M NOT GONNA DENY IT….THIS IS GOING TO INVOLVE MEMORIZATION!! I’M NOT GONNA DENY IT….THIS IS GOING TO INVOLVE MEMORIZATION!!

LIGHT REACTIONS Pigment molecules in the thylakoids absorb light energy Pigment molecules in the thylakoids absorb light energy Light energy is converted to short-lived chemical energy in carrier molecules Light energy is converted to short-lived chemical energy in carrier molecules Conversion to chemical energy has to do with transfer of electrons from one molecule to another Conversion to chemical energy has to do with transfer of electrons from one molecule to another Remember Oxidation-Reduction reactions???? Remember Oxidation-Reduction reactions????

Light Reactions

CALVIN CYCLE Energy molecules from the light reactions are used to make sugar Energy molecules from the light reactions are used to make sugar Also known as the DARK REACTIONS Also known as the DARK REACTIONS

Calvin Cycle

PHOTOSYNTHESIS: SUMMARY

Assignment Define/describe a PHOTOSYSTEM Define/describe a PHOTOSYSTEM Diagram (and label) the light reactions of photosynthesis Diagram (and label) the light reactions of photosynthesis Diagram the dark reaction of photosynthesis Diagram the dark reaction of photosynthesis