Photosynthesis

Vocabulary Photosynthesis -Process by which plants use light energy to convert water and carbon dioxide into oxygen and sugar. Light Dependent Reactions -The first stage of photosynthesis. Happens in the thylakoid membranes that captures energy from light and drives the production of ATP (stage that splits water and stores energy from the sun). Light Independent Reactions (Calvin Cycle) - A chemical reaction that convert carbon dioxide and other compounds into glucose. These reactions occur in the stroma. Stage that uses energy from light dependent to bond CO2 into sugar. Stroma - the fluid-filled (liquid) area of a chloroplast outside of the thylakoid membranes

What is food and why do organisms eat?

What is Photosynthesis?

What is Photosynthesis? The process in which plants, some bacteria and algae, absorb light energy from the sun to produce glucose, a food molecule high in chemical energy.

What is Chemical Energy? The energy stored in chemical bonds.

Where does all energy come from? Even our energy?

Let me tell you the story about photosynthesis

Once upon a time, there was a man who wondered about how plants grow. How do seeds become trees?

His name was van Helmont Belgian physicist in the 1600’s. He planted some seeds, measured the amount of soil at the beginning and only watered the plants. Once it became a small tree, he measured the amount of soil, which remained for the most part, the same (only 2lbs difference). What can you conclude from this experiment? Why do you think the amount of soil stayed the same?

“164 pounds of wood, barks, and roots arose out of water only.” In 5 years, his tree grew to 164 pounds. Since the soil remained the same for the most part (only lost 2 pounds), and he only watered the plant, van Helmont concluded the plant must get what it needs to grow from the water. The water!

But some folks were not totally convinced… So in the late 1600s, John Woodward,  tried to design an experiment to test Van Helmont hypothesis that water was the source of the extra mass. In a series of experiments over as many as 77 days, Woodward measured the water consumed by plants. John Woodward

Concluded that water and soil together increase plant mass. He grew some mint plants in water. One plant showed a mass gain of about 1 gram, while Woodward had added a total of almost 76,000 grams of water during the 77 days of plant growth - this was a typical result. Woodward correctly suggested that most of this water was “drawn off and conveyed through the pores of the leaves and exhaled into the atmosphere. So the hypothesis that water is the nutrient used by plants was rejected.

But before we continue with our story… We have all heard of oxygen, and we know we need it in order to survive, but how do we know oxygen is real? MIND BLOWN!

How do we know oxygen is real? There was this guy who had a lot of thinking time… he was just a theologian, dissenting clergyman, natural philosopher, chemist, educator, and Liberal political theorist who published over 150 works… Joseph Priestley 1771

So what do you think was his next step? That my friend, was a tragic day for a mouse, but a huge day for mankind! What did Priestley just discovered?

Do you think Priestley's experiment would have the same results under different conditions? So another man decided to take Priestley’s experiment a step further. He also had a lot of free time, after all he was only a Dutch physiologist, biologist and chemist! Jan Ingenhousz 1779 And then there was LIGHT!

Jan Ingenhousz was the first person to show that light is essential to the plant. In 1779 Ingenhousz put a plant and a candle into a transparent closed space. He allowed the system to stand in sunlight for two or three days. This assured that the air inside was pure enough to support a candle flame. But he did not lit the candle. Then, he covered the closed space with a black cloth and let it remain covered for several days. When he tried to light the candle it would not light.  Ingenhousz concluded that somehow the plant must have acted in darkness like an animal. It must have breathed, fouling the air. And in order to purify the air plants need light.

Not totally convinced of his findings, Ingenhousz decided to try it again. This time, he placed a small green aquatic plant in a transparent container of water and exposed the container to bright sunlight. He observed gas bubbles forming around the leaves and the green parts of the stems. When the system was placed in darkness, the bubbles stopped. These bubbles might be what the plant produced that purifies air fouled by animals or candles. In this experiment Ingenhousz demonstrated that plants are dependent on light and their green parts for nutrients and energy.

Jean Senebier 1782 Further investigated Priestly's finding of “injured” air and concluded that it was carbon dioxide. Jean showed that oxygen replaced carbon dioxide as a plant undergoes photosynthesis.

Nicholas Sausurre 1804 Nicholas showed that Van Helmont was wrong. He concluded that the plant mass also came from carbon dioxide. Where do we find carbon dioxide?

By adding together little pieces here and there… The requirements for photosynthesis were discovered in the 1800’s. In the 1950’s scientist began to understand the complex reactions that make this important cellular process possible. Recap: Van Helmont – figured out the soil was not the main source of mass for the plant. He believed most of the mass came from the water. John Woodward – Figured out the water added very little to the mass of the plant. Concluded the plant must get most of its mass from somewhere else. John Priestley – Demonstrated that plants release something that animals need to survive. Jan Ingenhousz – Figured out that plants in the dark cannot release the material animals need to stay alive. Jean Senebier – Showed that oxygen replaced carbon dioxide during photosynthesis. Nicholas Sausure – concluded that most of the plant’s mass comes from carbon dioxide in the atmosphere. We learned about PHOTOSYNTHESIS.

What does this equation represent? 6CO2 + 6H2O + light  C6H12O6 + 6O2 Photosynthesis!

So where in the plant does photosynthesis take place?

Photosynthesis takes place in the leaves of plants! On your notes draw the leaf and label its parts.

If you look at a leaf under a microscope, what do you see? Draw what you observe under the microscope on your notes

What were the many green dots you saw under the microscope? Chloroplasts Chloroplasts have pigments that absorb the sunlight plants use in photosynthesis to obtain energy.

Why some plants have green leaves and others red/orange? Green leaves have a lot of chlorophyll. Chlorophyll is a pigment that absorbs blue and red light and transfers or reflects green light. Orange leaves have a lot of carotenoids. Carotenoid is a pigment that absorbs blue light and transfers or reflects red/yellow light.

Why do leaves change colors? Leaves often contain chlorophyll, carotenoids and anthocyanin pigments. When there is a lot of sunlight, plants produce a lot of chlorophyll. As sunlight goes down, leaves make less chlorophyll and the other two pigments become more visible. Carotenoid and anthocyanin pigments do not depend on amount of sunlight.

Photosynthesis begins with the absorption of light in the chloroplasts.

Inside the Chloroplast

1. Light Dependent Reaction Happens inside the thylakoid membrane. Must have sunlight to occur. Energy travels to the thylakoids. Single Thylakoid Stack of Thylakoid = Grana

What happens in the chloroplast during photosynthesis?

What is ATP & ADP? ATP is a nucleotide Made up of: Adenine Adenosine Triphosphate Adenosine Diphosphate ATP is a nucleotide Made up of: Adenine 5-carbon sugar called ribose 3 phosphate groups Molecules use to store and release energy ADP is a nucleotide Made up of: Adenine 5-carbon sugar called ribose 2 phosphate groups Molecules use to store and release energy When energy is available, a cell can store small amounts of energy by adding a phosphate group to ADP to form ATP (ADP+P->ATP). Energy store in ATP is released by breaking the bond between the second and third phosphate groups (ATP->ADP+P).

Light Dependent Reaction The actual source of energy is the splitting of water from sunlight. For every molecule of water you get: ATP 2 NADPH molecules 1 O2

What is NADP+ and NADPH2? Electron carrier Transports high energy electrons Electron carriers can accept a pair (2) of high-energy electrons and transfer them along with most of their energy to another molecule. This process is known as electron transport. NADP+ takes 2 high-energy electrons and a hydrogen ion (H+). This process converts NADP+ into NADPH.

2. Light Independent Reaction Also known as: Dark Cycle Dark means absence of light. Calvin Cycle Happens in the stroma. The stroma is the fluid in between grana.

Light Independent / Calvin Cycle The Calvin cycle uses the ATP and NADPH that was just made in the light dependent reaction to make high-energy sugar. ATP + NADPH = SUGAR

If ATP and NADPH are high energy molecules why do we need to make sugar? ATP and NADPH are not stable enough to store their chemical energy for more than a few minutes. During the Calvin Cycle, plants use the energy that ATP and NADPH have to build high-energy compounds (sugar) that can be stored for a long time.

Light Dependent / Calvin Cycle Making sugars also uses up 6 NADPH and 6 ATP gained from the Light Reactions. This causes them to be turned back into NADP+ and ADP. 6 CO2 (carbon dioxide) are used to make 1 sugar.

Photosynthesis

Limiting Factors of Photosynthesis Light Intensity Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.

Limiting Factors of Photosynthesis Carbon Dioxide Concentration Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air or water, if an aquatic plant. Even if there is plenty of light, a plant cannot photosynthesize if there is insufficient CO2.

Limiting Factors of Photosynthesis Temperature If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.

Chloroplast Project Use the materials available in class to create a model of a chloroplast. On your model you must include: The parts of a chloroplast Thylakoid Grana Stroma Inner Membrane Outer Membrane Label the 2 reactions and include: Reactants of each reaction Products of each reaction A narrative of each reaction (what happens in each, what is used and what is made) in a paragraph format.

sources http://www.juliantrubin.com/bigten/photosynthesisexperiments.html