Introduction to Biology Photosynthesis Introduction to Biology

Photosynthesis Photo = “light”, Synthesis “to make” Photosynthesis is using light energy to make organic compounds such as sugars.

Almost all plants are photoautotrophs. Autotrophs are able to produce the molecules they need for life without eating anything. Photoautotrophs use sunlight as their energy source. Chemoautotrophs use non-living chemicals (like Hydrogen sulfide gas) as their energy source Almost all plants are photoautotrophs. Also includes algae(protists), and some bacteria.

LE 10-2 Plants Unicellular protist Purple sulfur bacteria 10 µm Purple sulfur bacteria 1.5 µm Multicellular algae Cyanobacteria 40 µm

Heterotrophs obtain their organic material by eating other organisms Almost all heterotrophs, including humans, depend on photoautotrophs like plants for food and oxygen

Energy in Sunlight Energy from the sun travels to Earth in the form of light. Sunlight is a mixture of many different types of energy: Ultraviolet: Invisible to us, causes sunburns Visible Light: Wavelengths of light we can see, Infrared: Energy in the form of heat

Energy Our eyes see the different wavelengths of the visible spectrum as different colors: red, orange, yellow, green, blue, indigo, and violet.

Pigments Plants gather the sun’s energy with light-absorbing molecules called pigments. The plants’ principal pigment is chlorophyll. Chlorophyll is a green pigment. Plants are green because chlorophyll reflects green light and absorbs every other wavelength.

Pigments Plant cells contain other pigments besides chlorophyll that increase the wavelengths absorbed. These are called carotenoids. During the summer, so much chlorophyll is produced that the green color overwhelms the other pigments. When temperatures drop, the plants stop producing chlorophyll, and the other pigments may be seen.

Chloroplasts Photosynthesis takes place inside organelles called chloroplasts. Chloroplasts contain stacks called grana. The grana contained stacked membranes called thylakoids, which are interconnected.

Chloroplasts Leaves are the major locations of photosynthesis Their green color is from chlorophyll, the green pigment within chloroplasts Light energy absorbed by chlorophyll drives the reactions needed to produce sugars from carbon dioxide. The plant “breathes” through microscopic pores called stomata. CO2 enters the leaf and O2 exits

Chloroplasts Pigments are located in the thylakoid membranes. The fluid portion outside of the thylakoids is known as the stroma.

Photosynthesis Equation Photosynthesis can be summarized in the following equation:

Stages of Photosynthesis Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part) The light reactions occur in the thylakoids of the chloroplast. Splits water, releases O2, produces ATP and NADPH The Calvin cycle occurs in the stroma of the chloroplast. Forms sugar from CO2 using ATP and NADPH

LE 10-5_1 H2O Light LIGHT REACTIONS Chloroplast

LE 10-5_2 H2O Light LIGHT REACTIONS ATP NADPH Chloroplast O2

LE 10-5_3 H2O CO2 Light NADP+ ADP + CALVIN CYCLE LIGHT REACTIONS ATP NADPH Chloroplast [CH2O] (sugar) O2

ATP and NADPH Chloroplasts are solar-powered chemical factories Their thylakoids transform light energy into the chemical energy of ATP and NADPH. These are small energy-containing molecules that can be used to make glucose later.

LE 10-7 Light Reflected light Chloroplast Absorbed Granum light Transmitted light

Absorption of Sunlight When chlorophyll absorbs light, it goes from a low-energy ground state to an high-energy excited state, which is unstable. When excited electrons fall back to the ground state, photons are given off causing fluorescence.

Building Glucose The Calvin cycle builds sugar from smaller molecules by using ATP and NADPH Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P) To make one G3P, the cycle must take place three times, using up three molecules of CO2