Biology - Unit 2: Metabolism Pt. 2, Photosynthesis

Pigments

• molecules that absorb some wavelength & reflect some others

• causing things to appear as the colour that is reflected

Electromagnetic Spectrum

• longer wavelength → less energy (e.g. red)

• shorter wavelength → more energy (e.g. violet)

• white light - all colours

Chloroplasts

• double membrane

• contains pigments - chlorophylls and carotenoids

• all green parts of plants have chloroplasts - leaves have the most (palisade mesophyll)

Thylakoids

• membrane-bound disk-like structure where light-dependent reactions take place

• filled with fluid

Grana

• stacks of thylakoids (granum - stack of thylakoids)

• stacking → increases surface area

Thylakoid Space (Thylakoid Lumen)

• space inside the thylakoid, filled with fluid

Stroma

• space outside of the thylakoids filled with fluid in the chloroplast

Chlorophyll a

• has a methyl group, photosynthetic

• the special pair in light-dependent reactions

• main pigment

• absorbs red & blue light (also orange and violet), transmits green/yellow

Chlorophyll b

• has an aldehyde group, photosynthetic

• absorbs light and transfers the excitation energy to chlorophyll a

• accessory pigment

• absorbs blue light (also red/orange), transmits green/yellow

Beta-Carotene

• absorbs green/blue/violet, transmits red/orange/yellow

• type of carotenoid (non-photosynthetic)

Absorption Spectrum

• shows the amount of energy absorbed at a range of wavelengths by certain pigments

Action Spectrum

• shows the amount of oxygen produced (rate of photosynthesis) at each wavelength

Autumn Leaves

• chlorophyll gives green colour

• plants need warm temperatures to make chlorophyll - in autumn, less chlorophyll is made

• xanthophylls (a carotenoid), flavonoids, and other carotenoids → yellow

• beta-carotene → orange

• anthocyanins & carotenoids → red

Photosystems

• a protein complex in the thylakoid membrane

• antenna complex + reaction center

• 2 photosystems - photosystem I (PSI) and photosystem 2 (PSII)

Antenna Complex

• cluster of pigments that absorb and transfer energy to the reaction center

Reaction Center

• has proteins + chlorophyll a special pair

Special Pair

• a pair of chlorophyll a molecules in the reaction center

• initiates the conversion of light energy into chemical energy (ATP)

Photosynthesis

• light reaction to make glucose

• performed by photoautotrophs (plants, cyanobacteria, euglena)

• products are needed by all organisms (glucose & oxygen)

Light-Dependent Reactions

• first part of photosynthesis, makes ATP and NADPH for dark reactions

• occurs on thylakoid membranes

• electrons are shuttled in an ETC

Non-Cyclic Photophosphorylation

• make 1 ATP:1 NADPH

• PSI & PSII used

• ferredoxin goes to NADP reductase for NADPH to be made

Cyclic Photophosphorylation

• only makes ATP to make up for difference

• no water is split, no oxygen production

• ferredoxin goes to b₆-f complex instead of NADP reductase

Photophosphorylation

• chemiosmosis in plants

• occurs through ATP synthase, electrochemical gradient is given by b₆-f complex

Paper Chromatography

• technique used to separate a mixture into its components

• leaf chromatography - pigments have different solubilities, will travel at different rates/distances

Reference Front

• R_f = migration of pigment/migration of solvent

• different pigments have different R_f values

Carotenoids

• absorbs some green and a lot of blue

Photolysis of Water

• splitting of water using light energy

• H₂O → 2H⁺ + ½ O₂ + 2e^-

Photosystem II

• initiates photosynthesis for non-cyclic

• splits water

Photosystem I

• allows for production of NADPH or ATP by transporting electrons to b6-f or NADP reductase

Rubisco

• enzyme used in carbon fixation for the Calvin Cycle

Calvin Cycle

• light-independent reaction/dark reaction

• makes one glucose per 2 turns of the cycle

• 18 ATP & 12 NADPH are used, 16 P_i are released

• 3 phases - carbon fixation, reduction, RuBP regeneration