The tour

Welcome Folks! My name is Ernie, and you are about to see how plants make energy using only water, sunlight, and carbon dioxide. Please sit in your seats and fasten your seatbelts, because we are about to enter the cell. (Once cell is entered) Now, we are about to enter the chloroplast, the organelle that is responsible for photosynthesis within the cell. (Enter chloroplast).

The first part of photosynthesis is the Light Dependent reaction. This takes place in the grana, structures within the chloroplast. If you look to the left, you can see it. It looks like a stack of coins. Each “coin” in the grana is called a thylakoid. In Photosystem II, the first part of the light dependent reaction, chlorophyll, the light capturing pigment within the chloroplast, captures energy from the sun’s rays. Chlorophyll is what makes the leaves of plants and trees green. The energy is used to energize electrons in the electron transport chain, which is located in the thylakoid. These electrons come from H2O. The water is broken down into electrons, which go into the electron transport chain, oxygen, which is released as waste, and hydrogen, which is pumped through the thylakoid membrane for later use. Next comes Photosystem I, the second part of the light dependent reaction. Try not to get confused, just remember that photosystem II comes before photosystem I. In this phase, the energized electrons in the electron transport chain are used to turn NAD+ into NADPH, an energy molecule much like ATP. Next, the hydrogen molecules that were pumped into the thylakoid now diffuse through a protein channel in the thylakoid membrane, turning ADP into ATP. This process is called ATP synthase. The ATP and NADPH that were produced now go to the second stage of photosynthesis, the light independent reaction.

(Move away from the thylakoid and go to the stroma where the calvin cycle is taking place). The light independent reaction uses the energy made in the light dependent reactions to make sugars, specifically glucose. When you eat your salad, you are eating the sugars made by these plants. The light independent reaction takes place in the stroma, which is the liquid inside of the chloroplast. Think of the stroma as the cytoplasm of the chloroplast. All around us, something called the Calvin Cycle is happening. The Calvin Cycle uses CO2 molecules. The ATP and NADPH molecules that we saw being made before is now used to rearrange the carbon molecules, and after two cycles of this, a high energy carbon molecule, glucose, is made. The ADP and NAD+ is sent back to the light dependent reaction to be made into ATP and NADPH again.

Through these processes, plants make energy. In the Winter, they use their stored energy to survive through the winter, only to start once again in the Spring. With only water, sunlight, and carbon dioxide, these plants survive. I hope that all of you leave this tour filled with an understanding of the world around us. As you leave the ship, you will see a box for donations, and tips are much appreciated. Once again, my name is Ernie, and I hope that you all have a wonderful day.