The Working Cell Energy from Sunlight Chapter 8

The Working Cell: Energy from Sunlight Chapter 8

What process is this?

Photosynthesis uses light energy to make food • Photosynthesis is the opposite of cellular respiration

• Photosynthesis is the process in which plants and other producers convert the energy of sunlight into energy stored in organic molecules • The cellular organelle in which photosynthesis takes place… Chloroplast • Chloroplasts contain chlorophyll, a chemical compound that give the chloroplast a green color

• In most plants leaves contain the most chloroplasts and are the major site of photosynthesis

• Leaves have tiny pores, called stomata, throughout their surface which allow CO 2 in and O 2 out

• Veins carry water and nutrients from the roots to the stems and leaves • They also deliver organic molecules that are produced in the leaves to the rest of the plant

• Chloroplasts have an inner and outer membrane • Inside the inner membrane is a thick fluid called stroma • Suspended in the stroma are many disk-shaped sacs called thylakoids • A stack of thylakoids is called a grana

Photosynthesis occurs in two stages: 1. The light reactions = convert the energy in sunlight to chemical energy 2. The Calvin cycle = makes sugar from the atoms in carbon dioxide, hydrogen ions, and high-energy electrons

Overview of Photosynthesis

• Electromagnetic energy= a form of energy that exhibits wavelike behavior as it travels through space – Visible light, microwaves, X rays • Wavelength= the shortest distance between equivalent points on a continuous wave

• Electromagnetic spectrum = range of types of electromagnetic energy • The most important segment for life is a narrow band between 380 to 760 nm…visible light • ROY G BIV • A particle of electromagnetic radiation is called a photon

• • Pigments= chemical compounds that determine a substance’s color When light shines on a material that contains pigments, three things can happen: 1. Absorption 2. Transmission (goes through the material) 3. Reflection (bounces back) • Why do leaves look green?

• Chromatography= a laboratory technique used to separate mixtures – Can be used to observe the different pigments in a leaf (Paper chromatography used to separate the dyes in inks)

• Within the thylakoid membrane, chlorophyll and other molecules are arranged in clusters called photosystems – think solar panel! • Each photosystem contains a few hundred pigment molecules, including chlorophyll a, chlorophyll b, and carotenoids – Chlorophyll a, the dominant pigment, absorbs best in the red and blue wavelengths, and least in the green

• Only chlorophyll a participates directly in the light reactions but accessory photosynthetic pigments absorb light and transfer energy to chlorophyll a. – Chlorophyll b, with a slightly different structure than chlorophyll a, has a slightly different absorption spectrum and funnels the energy from these wavelengths to chlorophyll a. – Carotenoids are pigments that range in color from pale yellow to deep red • they are involved in the color changes of leaves in the fall • they funnel the energy from other wavelengths to chlorophyll a.

Carotenoids

Photosynthesis • Overview: Chlorophyll absorbs light ↓ Energy transferred to electrons ↓ Energy level of electrons increased (unstable) ↓ Carbohydrates, oxygen

Light Reactions

• The light reactions involve two photosystems, photosystem I and photosystem II, connected by an electron transport chain • Photons of light, as well as water molecules, come into the thylakoid and strikes photosystem I • The oxygen is “sliced” off of the water molecule and is released through the stomata into the atmosphere – Called photolysis • This leaves hydrogen ions and electrons • The electrons are funneled to the electron transport chain

• The electrons move from carrier to carrier within the electron chain • Each time an electron moves to the next carrier energy is produced • When the electrons exit the electron chain they move to photosystem II • Photosystem II is called the “NADPH producing system” • What is NADPH? Nicotinamide Adenine Dinucleotide Phosphate It’s a carrier molecule!! • What does it carry? Electrons!!!

• The electrons are carried by NADPH to the Calvin cycle • Now, back to the hydrogen ions… • The ETC produces energy by moving the electrons from carrier to carrier • This energy is used to pump hydrogen ions across the membrane from an area of low concentration to area of high concentration • Potential energy builds up and the hydrogen ions rush through the ATP synthase which produces what? ATP • The ATP is then used in the Calvin Cycle

The Calvin cycle makes sugar from carbon dioxide • The light reactions produce oxygen, a very important product for life to exist • But life needs more…organic molecules!

The Calvin cycle • Carbon enters as CO 2 • ATP and NADPH, from the light reactions, provide energy and electrons that are used to make the sugar • The sugar that is produced is called G 3 P, a smaller molecule than glucose (three carbons instead of 6 carbons) • G 3 P exits the cycle • G 3 P is the raw material that plants use to make glucose and other organic molecules

Summary of Photosynthesis • Overall equation for photosynthesis Sunlight + 6 CO 2 + 6 H 2 O C 6 H 1206 + 6 O 2 • Light reactions – – take place in thylakoid membrane use light and water convert light energy to the ATP and NADPH product is oxygen • Calvin cycle – takes place in the stroma – Uses ATP and NADPH to convert carbon dioxide to sugar

Photosynthesis has a global impact • On a global scale, photosynthesis is the most important process to the welfare of life on Earth • Photosynthetic organisms make about 160 billion metric tons of organic material per year

• Earth’s atmosphere • Carbon dioxide traps heat from the sun and prevents it from escaping back out into outer space • The greenhouse effect, keeps the world climate warm enough for life to exist • In recent years the amount of CO 2 in the atmosphere has been rising

Chapter 8 Quiz 1. In a plant cell where do the light reactions occur? 2. The chemical products of the light reactions are ____ and ____. 3. What role do the stomata play in photosynthesis? 4. Which pigment participates directly in the photosynthesis process? (be specific)