4.3 Photosynthesis in Detail

Topic: PhotosynthesisObjective: Describe the 2 parts of photosynthesis:

light dependent and light independent reactions

4.3 Photosynthesis in Detail

• Energy is CAPTURED FROM SUNLIGHT• Plants absorb mostly blue and red wavelength light• Plants reflect back the other colors of the visible spectrum

– So plants look green– Pigments break down in cool weather to show different colors

• Pigments are molecules that absorb light of certain wavelengths

Plants and Visible Light

4.3 Photosynthesis in Detail

• Photosynthesis occurs in plants in plant cells.• Parts of plant involved in photosynthesis:

– Stomata

- On outside of plant leaf—allows for oxygen and carbon dioxide exchange….like a plant’s mouth

– Chloroplasts

- Thylakoid –stacks where light-dependent reactions occur

- Stroma – fluid portion inside chloroplast where light-independent reactions occur

– Pigments

- Green plants have 4 closely-related photosynthetic pigments

- Carotene - an orange pigment (carotenoids)

- Xanthophyll - a yellow pigment

- Chlorophyll a - a blue-green pigment

- Chlorophyll b - a yellow-green pigment

4.3 Photosynthesis in Detail

The first stage of photosynthesis captures and transfers energy.

• The light-dependent reactions include groups of molecules called photosystems in thylakoid– Are 2 of them

4.3 Photosynthesis in Detail

• Photosystem II captures and transfers energy (in thylakoid).

1. Chlorophyll molecules in Photosystem II absorb energy from sunlight, electrons get excited and enter the electron transport chain (ETC)

2. water molecules are split and H, e, and oxygen is released for us to breathe

3. hydrogen ions (H+) are transported across thylakoid membrane

4.3 Photosynthesis in Detail

• Photosystem I captures energy and produces energy-carrying molecules.

4. chlorophyll absorbs energy again from sunlight in photosystem I

5. Energized (excited) electrons are used to make NADPH

(another energy carrying

molecule)

6. Hydrogen ions diffuse

through a protein channel

7. ATP is made as H’s flow through the channel…goes from ADP to ATP

4.3 Photosynthesis in Detail

• SO the products of the light dependent reactions are:

1.Oxygen

2.ATP and NADPH to make sugars in the Calvin Cycle

4.3 Photosynthesis in Detail

• Light-independent reactions occur in the stroma and use CO2 molecules to make glucose.

The second stage of photosynthesis uses energy from the first stage to make sugars.

4.3 Photosynthesis in Detail

• A molecule of glucose is formed as it stores some of the energy captured from sunlight (in stroma).

1. carbon dioxide molecules (that we have exhaled) enter the Calvin cycle

2. energy is added (ATP and NADPH from light reactions) and carbon molecules are rearranged

3. two high-energy three-carbon molecule make a sugar = C6H12O6

4. Plants use the sugars, proteins, and lipids as energy

4.3 Photosynthesis in Detail

• SO the product of the light independent reactions = Calvin Cycle is:1. Glucose = sugar for the plant = C6H12O6 because they produce their own food (the C comes from CO2)

4.3 Photosynthesis in Detail

Equation in WORDS!

• Water + Carbon Dioxide YIELDS Oxygen + Glucose

(in soil) + (we exhale) YIELDS (from water + (plant food

splitting) from the C in CO2)