Unit 2: Metabolic Processes Photosynthetic Pigments SBI4U – Ms. Richardson

Light Can behave as a particle (photon) or a wave When light behaves as a wave, the shorter the wavelength, the more energetic the photon Sunlight contains photons of every wavelength Visible light: small part of the electromagnetic spectrum (380 – 750nm)

Photoelectric Effect Formation of electrically charged particles in matter when illuminated by light

Leaves Function: Structure: photosynthesis maximizes surface area exposed to light limits distance for gases to travel to reach chloroplast

Leaves

Transpiration Loss of water vapour in plants, primarily through stomata Assists photosynthesis: Transpiration pull Evaporative cooling

Stomata Controls gas exchange Guard cells swell when K+ ions and water move into guard cells Stomata close (night) When K+ ions and water move out of guard cells, they become flaccid Stomata open (day) CO2 absorbed

Chloroplasts Site of photosynthesis Occurs mainly in stroma and thylakoid membrane Contain their own DNA and ribosomes May contain starch an lipids

Pigment Molecules Molecules that absorb light Many different types of pigments in plants, each absorbing light of different wavelengths Pigment molecules appear the colour that they reflect Eg: chlorophyll reflects green light

Pigment Molecules Carotenoids Orange and yellow accessory pigments B-carotene = orange in carrots/fall leaves Trap energy that is passed to chlorophyll for use in photosynthesis Allow plants to absorb wider range of light

Pigment Molecules Chlorophyll a and b Green pigment molecules Absorb mainly blue and red light Hydrophobic Found in thylakoid membrane

Photosystems Located in thylakoid membrane Network of 40-70 chlorophyll a molecules (antenna pigments) grouped around a central chlorophyll b molecule (reaction centre)

Photosystems Antenna pigments absorb light of various wavelengths and pass energy to reaction centre When pigment molecules absorb light, they eject electrons The energy from the electrons is used in photosynthesis Two photosystems involved in photosynthesis: PSI (P700) – driven by light around 700nm PSII (P680) – driven by light around 680nm Photosynthesis is most effective when PSI and PSII work together (non-cyclic photophosphorylation)