Photosynthesis

CA Biology Standards Cell Biology Students know usable energy is captured from sunlight by chloroplasts and is stored through the synthesis of sugar from carbon dioxide. Ecology Students know how water, carbon, and nitrogen cycle between abiotic resources and organic matter in the ecosystem and how oxygen cycles through photosynthesis and respiration.

Photosynthesis Chapter 8 Summarize how energy is captured from sunlight during the light dependent reactions of photosynthesis. Analyze the function of electron transport chains during the light dependent reactions of photosynthesis. Relate the Calvin cycle to carbon dioxide fixation in photosynthesis. Identify three environmental factors that affect the rate of photosynthesis.

Photosynthesis Song!

Using the Energy in Sunlight Plants, algae, and some bacteria capture 1% of the sunlight that reaches earth and convert it to chemical energy through the process of photosynthesis.

History of the Discovery of Photosynthesis The following people all contributed to the discovery of photosynthesis. Van Helmont (1600’s) Priestley (1700’s) Ingenhousz (1779) Mayer (1845) Ruben and Kamen (1941) Melvin Calvin (1948) Rudolph Marcus (1992)

Jan van Helmont He wondered where the mass of a tree came from- perhaps the soil? To find out, he did an experiment where he weighed a seedling and a pot of soil. After 5 years, he reweighed them both. The soil was the same mass but the tree had gained mass. Where did it come from? He concluded it came from the water!

Joseph Priestley (1700’s) He put a jar over a candle and found? The candle went out! But when he placed a living plant under the jar with the candle, it stayed lit longer. Why??? The plant produced….OXYGEN!

Jan Ingenhousz He did the same experiment as Priestley, but in the dark and in the light. It only worked in the light, proving that plants need light to make oxygen!

What is the equation for photosynthesis?

Photosynthesis Equation Oxygen What we breathe 6 CO2 + 6 H2O  C6H12O6 + 6O2 Carbon Dioxide What we exhale Glucose What we use for energy Water

Photosynthesis is… The process where plants, algae and some bacteria convert light energy into chemical energy (glucose), using water and carbon dioxide and releasing oxygen gas as a byproduct.

Where does photosynthesis occur in a plant? Usually in the leaves, but anywhere it is green!

Photosynthesis The raw materials of photosynthesis, water and carbon dioxide, enter the cells of the leaf, and the products of photosynthesis, sugar and oxygen, leave the leaf.

Cross section of a leaf, showing the anatomical features important to the study of photosynthesis: stoma, guard cell, mesophyll cells, and vein.

Water enters the root and is transported up to the leaves through specialized plant cells known as xylem (pronounced zigh-lem).

Land plants must guard against desiccation (drying out) and so have evolved specialized structures known as stomata to allow gas to enter and leave the leaf. (stoma = singular; stomata = plural; Greek for mouth)

Stomata Consists of: Stomatal Opening and 2 Guard Cells

What enters and exits the stomata? CO2 CO2 enters the leaf through the stomata. O2 exits the leaf through the stomata. H2O can also escape through the stomata, especially on hot, dry days. This is called transpiration, or the evaporation of water through plants. So when it’s hot, the stomata close.

Carbon dioxide enter the leaf through the stoma flanked by two guard cells. Oxygen produced during photosynthesis can only pass out of the leaf through the opened stomata.

How would stomata closure affect photosynthesis? When the stomata close, CO2 levels drop rapidly within the leaf, inhibiting the light-independent reactions. This then causes photosynthesis to stop.

Stomata on a leaf of corn.

Stomata and Guard cells

LIGHT AND PIGMENTS Light has different wavelengths. You can only see visible light.

Visible spectrum Sunlight contains a mixture of all the wavelengths (colors) of visible light. When sunlight passes through a prism, the prism separates the light into different colors.

Pigments Pigments are light-absorbing molecules which absorb only certain wavelengths and reflect all of the others. Chlorophyll is the pigment in plants that makes them appear green. GREEN is reflected, while all other colors are absorbed. Period 1 stopped here 10/19/10

Absorbs mostly blue and red light and reflects green and yellow light. Thus, the plant looks green. Chlorophyll

Carotenoids Pigments in plants that absorb blue and green light and reflect yellow and orange.

Autumn Colors In the fall, as it gets colder, chlorophyll gets broken down because photosynthesis can’t occur in the winter. Why? Water freezes! And if water freezes, it can’t do its part in photosynthesis.

Pigments are located in the chloroplasts of leaf cells

What are the little green dots? Chloroplasts!

PLANT CELL Chloroplasts

Inside a Chloroplast

CHLOROPLAST STRUCTURE Period 0 stopped here

Thylakoids Are disk shaped structures containing clusters of pigments embedded in their membranes. This is where the Light-Dependent Reactions occur.

Great Animation of Photosynthesis! http://www.fw.vt.edu/dendro/forestbiology/photosynthesis.swf

Fun Overview of Photosynthesis Animation http://www.pbs.org/wgbh/nova/methuselah/photosynthesis.html

Photosynthesis Occurs in Two Stages: The Light-Dependent Reactions (occur in the thylakoid membranes) The Calvin Cycle (occurs in the stroma)

Overview of The Light-Dependent Reactions Where do they occur? What are they? The Thylakoid Membranes where there is chlorophyll! The light-dependent reactions use water, produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH.

Overview of The Light-Dependent Reactions What part of the photosynthesis equation is involved? Water (H2O) is broken apart for its electrons. Oxygen gas (O2) is given off as a waste product.

Glucose

STEPS OF THE LIGHT DEPENDENT REACTIONS

Light strikes 1. Light strikes chlorophyll in the thylakoid membrane and transfers solar energy to its electrons.

2. This energy transfer from light causes the electrons to become “excited”. 3. These high-energy electrons are transferred to NADP+.

NADP+ is an energy carrier molecule. It can accept high-energy electrons (e-) from chlorophyll and become NADPH (the negative electrons attract a hydrogen ion). This is how the energy from sunlight is converted into chemical energy! COOL! But now chlorophyll is missing electrons… Where does it get more? WATER!

Glucose

4. Water molecules are split by enzymes to form electrons (from the H atoms) which the chlorophyll takes to replace lost e-’s.

5. Leftover oxygen atoms from water combine to make oxygen gas.

6. Electrons begin to move along the Electron Transport chain

6. Electron Transport chain A. Hydrogen ions move into the thylakoid and become concentrated inside. 2nd period stopped here 9/29/10

6. Electron Transport chain B. Hydrogen ions pass through ATP synthase (a protein in the thylakoid membrane) which catalyzes the reaction where a phosphate group is added to ADP to become ATP!

ATP Synthase Animation http://www.stolaf.edu/people/giannini/flashanimat/metabolism/photosynthesis.swf Period 1 stopped here 10/21/10

6. Electron Transport Chain C. NADPH is made by adding H+ ions to NADP+

Remember: NADPH is an electron carrier that provides the high-energy electrons needed to make carbon-hydrogen bonds in the third stage of photosynthesis.

ATP is the molecule that provides energy for the plant to make glucose ATP is the molecule that provides energy for the plant to make glucose! NADPH provides hydrogen atoms for the plant to make glucose!

Summary of Light dependent reaction Pigments in the thylakoids of chloroplasts absorb light energy. Electrons in the pigments are excited by light and move through electron transport chains in thylakoid membranes. These electrons are replaced by electrons from water molecules, which are split by an enzyme. Oxygen atoms from water molecules combine to form oxygen gas. Hydrogen ions accumulate inside thylakoids, setting up a concentration gradient that provides the energy to make ATP.

Light Dependent Reactions

Review of Light Dependent Reactions!

Pigment molecules absorb energy at which stage of photosynthesis? The beginning of the Light-Dependent Reactions!

At which stage of photosynthesis is light energy stored as ATP and NADPH? The end of the Light-Dependent Reactions!

At which stage of photosynthesis are excited electrons passed along an electron transport chain? Light-Dependent Reactions!

Where do the light-dependent reactions occur? The thylakoid membranes!

What goes into the light-dependent reactions? Light excites the electrons of chlorophyll. Water is split to replace lost e-’s in chlorophyll. ADP gets a phosphate group to become ATP. NADP+ gets hydrogen ions to become NADPH.

What is produced in the light-dependent reactions? ATP and NADPH go into the Calvin Cycle. Oxygen gas is released into the atmosphere.

Light Reactions Animation http://www.johnkyrk.com/photosynthesis.html

Glucose

The Calvin Cycle! What is it? The Calvin Cycle uses ATP and NADPH from the light-dependent reactions and CO2 from the air to make high-energy sugars (glucose)! Glucose

Where does the Calvin Cycle occur? The Calvin Cycle occurs in the stroma of the chloroplast.

What parts of the photosynthesis equation are involved in the Calvin Cycle? CO2 is broken down to create glucose (C6H12O6) C6H12O6

Steps of the Calvin Cycle

Calvin Cycle 1. Six CO2 molecules enter the leaf through the stoma and diffuse into the stroma. They are added to a 5 carbon compound by an enzyme.

Calvin Cycle They are split into twelve 3-carbon compounds. 3. Energy from ATP and electrons from NADPH are used to convert the 3-carbon compounds into 3-carbon sugars. Calvin Cycle

Calvin Cycle 4. Two of the resulting 3-carbon sugars is used to make organic compounds – including GLUCOSE, starch and sucrose – in which energy is stored for later use by the organism.

Calvin Cycle 5. The other ten 3-carbon sugars are used to regenerate the initial 5-carbon compound, thereby completing the cycle.

Review of Calvin Cycle

Where does the Calvin Cycle occur? In the stroma of the chloroplast!

What goes into the Calvin Cycle? ATP and NADPH are used for energy CO2 is broken apart to create C6H12O6

Animation of Overview of Photosynthesis http://wps.prenhall.com/wps/media/objects/486/498596/CDA7_1/CDA7_1d/CDA7_1d.htm

Factors that Affect Photosynthesis Photosynthesis is directly affected by environmental factors such as: The intensity of light The concentration of carbon dioxide Temperature. Period 4 stopped here 10-7/10

PHOTOSYNTHESIS QUIZ 15 points Where in a plant cell does photosynthesis occur? What are the 2 stages of photosynthesis and where do they occur? Why are plants green? What is the balanced equation for photosynthesis? What are the reactants and products of the light dependent reactions? What are the reactants and products of the Calvin Cycle? What are two reasons we depend on plants for our survival?

Review Summarize how photosynthetic organisms capture the energy in sunlight. Compare the roles of water molecules and hydrogen ions in electron transport chains. Describe the role of the Calvin cycle in photosynthesis. Critical Thinking Organizing Information Make a table in which you identify the role of each of the following in photosynthesis: light, water, pigments. ATP. NADPH. and carbon dioxide.

5. Critical Thinking Inferring Relationships What combination of environmental factors affects the rate of photosynthesis? 6. Standardized Test Prep During photosynthesis, plants store energy in A ADP. B carbon dioxide. C 3-carbon sugars. D water.

What happens when a phosphate group is removed from an ATP molecule? Energy is released

What happens to the electrons of a chlorophyll molecule that are raised to a higher energy level They enter the electron transport chain.

Why does chlorophyll look green? Because it reflects green wavelengths of light.

Because of photosynthesis the atmosphere is rich in which gas? oxygen

1. Energy is captured from sunlight Photosynthesis

2. Light energy is converted to chemical energy, which is temporarily stored as ATP and the energy carrier molecule NADPH Photosynthesis

3. The chemical energy stored in ATP and NADPH powers the formation of organic compounds, using carbon dioxide, CO2. Photosynthesis

photosynthesis 6CO2 + 6H2O + light  C6H12O6 + 6O2

photosynthesis 6CO2 + 6H2O + light  C6H12O6 + 6O2

photosynthesis 6CO2 + 6H2O + light  C6H12O6 + 6O2

photosynthesis 6CO2 + 6H2O + light  C6H12O6 + 6O2

photosynthesis 6CO2 + 6H2O + light C6H12O6 + 6O2

At which stage of photosynthesis do the pigment molecules absorb energy?

Light energy is converted to chemical energy by what process? Photosynthesis

What is the major by-product of photosynthesis which goes into the atmosphere? Oxygen

photosynthesis 6CO2 + 6H2O + light  C6H12O6 + 6O2 Plants use the organic compounds to carry out their life processes. Starch is stored in the plant to be used later to be broken down into sugar and ATP.

photosynthesis ATP is used to power metabolism. All proteins, nucleic acids and other molecules are assembled from fragments of organic compounds being made into sugar.