Photosynthesis September 25th/26th, 2008

Q: Where do plants get the energy they need to produce food? Plants and some other types of organisms are able to use light energy from the sun to produce food. These organisms are called autotrophs. In Italian, the prefix “auto” means “self” and the suffix “trophs” means “feeder”.

Q: Who was Jan van Helmont? It was first thought that plants grew by taking material from the soil. To determine if this was correct, van Helmont measured the mass of a pot of dry soil and a small seedling. Over the next five years, he did nothing but water the plant. In the end, the plant had grown into a small tree, increasing in mass by about 75 kg. The pot of soil, however, still weighed the same. Van Helmont concluded that most of the gain in mass of the tree came from the water, not the soil. He was only half right…

Q: Who was Joseph Priestly? Joseph Priestly was the first to determine that plants gave off Oxygen. In his experiment, Priestly placed a lit candle under a glass jar, and watched as the flame went out. Priestly decided that there must be something in the jar, keeping the flame lit, and when it was all used up, the flame went out. He then found that putting a sprig of mint (a small piece of a mint plant) into the jar with the candle, that the flame would remain lit for a longer period of time. He therefore concluded that this plant had produced the substance that was needed for a flame to burn. This substance that Priestly discovered was Oxygen.

Q: Who was Jan Ingenhousz? Ingenhousz showed that the effect observed by Priestly occurred only when the plant was exposed to light.

Q: What did the experiments of these three men reveal about how plants grow? In the end, the experiments preformed by these three men eventually led scientists after them to discover that in the presence of light, plants are able to change carbon dioxide and water into carbohydrates, and in the process, release oxygen as a waste product.

Photosynthesis Equation Reactants Products 6 CO2 + 6 H2O + Energy → C6H12O6 + 6 O2 Carbon Dioxide Light Energy From the Sun Water Glucose Oxygen

Q: Where did all the reactants go? 6 CO2 + 6 H2O + Energy → C6H12O6 + 6 O2

Q: Where does photosynthesis occur? Photosynthesis occurs in the chloroplasts of a plant cell. Chloroplasts are found mostly in the leaves of plants.

The Chloroplast !

Q: What is the role of chlorophyll in photosynthesis? In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule found in chloroplasts. Plants gather the sun’s energy with light-absorbing molecules called pigments. The color of the leaf comes from chlorophyll, the green pigment found in chloroplasts.

Important Pigments Each pigment absorb light at different wavelengths. Chlorophyll a – absorbs purple and red light Chlorophyll b – absorbs blue and orange light Carotenoids – absorb purple and blue light

Reflection _____ + 6 H2O + _____→ C6H12O6 + ____ The main source of energy used by cells is _________. In what part of the plant cell does photosynthesis occur? Fill in the blanks in the photosynthesis equation below. What is the pigment called that gives chloroplasts their green color? _____ + 6 H2O + _____→ C6H12O6 + ____

ATP vs. ADP NADPH vs. NADP+ September 29th, 2008

Q: How important is the light in photosynthesis? Light energy from the sun is what drives photosynthesis. It’s what sets everything in motion. Once things are set in motion, the energy used by the cell to carry out the rest of the process is in the form of ATP.

Q: What is ATP ATP is one of the principle sources of energy used by cells. ATP stands for adenosine triphosphate. ATP is composed of the DNA nucleotide adenine, the sugar ribose, and three phosphate groups. adenine phosphate ribose

Q: What is the role of ATP in cellular activities? ATP has two roles within the cell. One is to store/carry energy, the other is to release energy. Storing/Carrying Energy: ATP IS stored energy! One molecule of ATP is like one fully charged battery, waiting to be used.

Releasing Energy: When the cell needs to use this energy is simply breaks off the third phosphate group at the end the ATP molecule, which releases energy. The new molecule is called ADP – adenosine diphosphate.

Adenosine Diphosphate - ADP Adenosine Triphosphate - ATP Partially charged battery Fully charged battery

Q: What is NADPH? Just like ATP, NADPH is an energy carrier. It is like the fully charged battery. The partially charged battery (after the energy has been used) is called NADP+.

Reflection If ATP is the energy for photosynthesis, what is the role of light energy from the sun? How does ATP release its stored energy? Use an analogy to explain the difference between ATP and ADP.

The Reactions of Photosynthesis September 30th, 2008

Q: What happens in the light-dependent reaction? In the light-dependent reactions, photosynthesis uses light energy from the sun to break apart H2O into H+ and oxygen, and recharge ADP and NADP+ back into ATP and NADPH. The Oxygen (O2) from water is a byproduct of photosynthesis and is released into the atmosphere.

The newly charged ATP and NADPH goes on to be used in the next step of photosynthesis. The light-dependent reactions MUST happen in the thylakoid (where chlorophyll is located) because it is chlorophyll that captures the energy from the sun.

Light Reactions Reactants (things that go into the thylakoid): Light energy from the sun H2O (water) NADP+ ADP + Phosphate Products (things that leave the thylakoid): O2 (Oxygen) NADPH ATP

Q: What is the Calvin Cycle? The Calvin Cycle, photosynthesis uses ATP and NADPH from the light-dependent reactions, as well as Carbon Dioxide (CO2) from the atmosphere, to produce glucose (C6H12O6).

Because this reaction does not directly require light, it is sometimes referred to as the dark reaction. Also, because it does not require light, the Calvin cycle does not need to happen in the thylakoid.

The Calvin cycle Reactants (things that go into the Calvin Cycle): NADPH ATP CO2 Products (things that leave the Calvin Cycle): NADP+ ADP C6H12O6 (glucose)

Exit Slip Quiz Name 2 reactants of the light reactions. Name 1 product of the light reactions. Name 2 reactants of the Calvin Cycle. Name 1 product of the Calvin Cycle.