Photosynthesis
● Autotrophs such as plants, algae, and bacteria make organic compounds such as sugar
by photosynthesis.
○ Photo.= process in which light energy is converted into chemical energy.
○ 6CO​2​+6H​2​O (light)→ C​6​H​12​O​6​ + 6O​2
● Two phases:
○ light dependent reactions (phase 1): light energy absorbed and converted to
chemical energy in the form of ATP and NADPH (nicotinamide adenine
dinucleotide phosphate) (energy storage molecules)
○ light independent reactions (phase 2): ATP and NADPH energy made in phase 1
are used to make glucose
■ Glucose is a simple sugar and can be used to form more complex
molecules such as starch.
■ Products of photo can also be used to make lipids, nucleic acids, and
proteins.
Phase 1: Light-Dependent Reactions
● Light is captured by chloroplasts which are mainly found in leaves.
● Chloroplasts are disk shaped and contain 2 compartments:
○ thylakoid: flattened sac-like membranes arranged in stacks; light-dep. reactions
occur here
■ each stack is called a grana (sing. granum)
○ stroma: fluid-filled space outside the grana; location of the light independent
reactions
Pigments
● Thylakoids contain the pigment chlorophyll.
○ Pigments are light absorbing colored molecules.
○ Different pigments absorb different wavelengths of light.
■ Chlorophyll is the main light-absorbing pigment. It is rich in magnesium. It
absorbs most wavelengths of light except green light (which it reflects,
making it appear green).
■ See Figure 6 page 223. -​Ask students to interpret this figure.
○ Two types of chlorophyll:
■ Chloro ​a​: primarily absorbs wavelengths of violet-blue light and
red-orange light
■ Chloro ​b​: primarily absorbs blue and red light (accessory pigment)
● Other pigments called accessory pigments. They allow plants to absorb other
wavelengths of light on the visible light spectrum.
○ carotenoids: absorb blue and green regions of the spectrum and reflect most light
in the red, yellow, and orange regions (they produce the colors of sweet potatoes
and carrots)
○ xanthophylls: reflect yellow light
○ anthocyanins: absorb blue-green light and aid chloro ​a​. Reflect reddish, blue, and
violet light