Electron transport, Chemiosmosis and the Photosystems

Last time, i talked about photosynthesis, and pigments. I'm just admitting it now, I forgot to mention/explain one thing, so I am explaining it here instead. Pigments are compounds that absorb light, and in the thylakoid membrane there are the chlorophylls a and b. However, there are more compounds, including carotenoids. Carotenoids don't absorb yellow, orange or brown. In fall, many plants lose their chlorophylls, but keep their carotenoids, making the leaves take on many different colors. Why is this important? Well, the chlorophylls and carotenoids are grouped together in clusters within the thylakoid membrane. Each cluster is referred to as a photo system. there are types of Photosystem, Photosystem 1 and Photosystem 2. Although similar in terms of the pigments each contains, they have very different roles in the light reaction process. The light reactions begin with absorbing light. By absorbing light, the pigment molecules aquire some of the energy carried by light waves. Within each photosystem, the aquired energy is quickly passed to other pigment molecules until it reaches a specific pair if chlorophyll a molecules. Now, I can explain this in five steps. Step 1: The light energy forces electrons to have a higher energy level in the two chlorophyll a molecules in photosystem 2. These electrons are said to be 'excited' Step 2: The excited now have enough energy to leave the chlorophyll a molecules. Since they have lost electrons, the chlorophyll a molecules have now undergone an oxidation reaction. Step 3: The electrons are now passed along a series of molecules called an electron transport chain. However, along the way, they lose most of the energy gained from sunlight. This energy is used to move protons into the thykaloid. Step 4:As light excites the electrons in photosystem 2, it does the same in photosystem 1. It specifically excites the electrons in the chlorophyll a molecules. The electrons move away from that pair, and continue being passed along until they reach a primary electron acceptor. The electrons from photosystem 2 replace the ones lost in photosystem 1 Step 5: Electrons from photosystem 1 travel along an electron transport chain, and at the end of the chain, they combine with NADP+ and H+ to make NADPH. Finally, we are at chemiosmosis. This is derived from greek, chemia meaning alchemy and osmosis meaning pushing. Why bring this up? Well, alchemy was meant to be able to turn lead to gold, which is a little unrelated, or is it? The driving chemical energy of photosynthesis is ATP. ATP is produced by glucose. Comparison; "lead" glucose is turned into the "Gold" or ATP. Chemiosmosis relies on the concentration gradient of protons across the thylakoid membrane. I cant remember if I included this or not last time, but when water is broken down inside the thylakoid, some protons are produced. This makes up for some of the protons used, but not all of them. The others are brought in from the stroma. The energy required to due so is gained from the excited electrons from photosystem 2. See? It all ties into itself. Oh, wait there's more to chemiosmosis. The protons brought in from the stroma are used to build a higher and higher concentration gradient. Now, the concentration gradient of protons represents potential energy. ATP harnesses this potential energy into chemical energy. NADPH uses some of the protons too, and together, ATP and NADPH provide energy for the second set of reactions in photosynthesis. So, this is all a very detailed explanation of the first set of photosynthesis. It is called the light cycle too sometimes, because it harnesses energy from light. The second cycle is called the dark cycle, or, more commonly, the Calvin cycle. This will be explained further in the next post. Sorry for so many posts on photosynthesis, but the process is very long and very complicated. Also, it is probably important for the survival of every species of the planet, but let's not get ahead of ourselves

Photosynthesis

Organisms can be classified based on how they obtain energy. There are autotrophs, organisms that manufacture their own energy, and heterotrophs, organisms that can't make their own energy. Animals, like humans, can't obtain their energy on their own, so they eat autotrpohs or heterotrophs that eat autotrophs. Confusing? Yeah, a little. Think of it like this, we eat steak, which comes from cows. But cows don't eat other cows, they eat grass. Grass is an autotroph, thus the food chain cycle is shown. But, how does a plant like grass obtain its energy? Plants get their energy through a process called photosynthesis. Photosynthesis involves a complex series of chemical reactions, even using a by product of a previous reaction. A plant releases oxygen as a byproduct in an early reaction, but need it in a later one. Back on topic, photosynthesis uses light as its fuel. A plant absorbs sunlight through chloroplasts. The light reactions take place in the thylakoids. To clear things up, the chloroplasts have a membrane surrounding three things. These are the thylakoids, grana and stroma. Thylakoids stack to form a grana, and is surrounded by a solution called the stroma. Moving on, plants are often picky with the light they absorb. As you probably know, the visible light spectrum includes red, orange, yellow, green, blue, indigo and violet. But, why are plants green most of the time? A part of the chloroplast is the chlorophyll. There are several types , but the two important ones are chlorophyll a and chlorophyll b. These are pigments, basically a compound that absorbs light. Chlorophyll a absorbs red to yellow light in the color spectrum, while chlorophyll b absorbs blue to violet light. This is why plants typically appear green. This is only the first stage in the entire process, but I'll get to electron transfer, chemiosmosis, and the different photo systems in my next post.

The Discovery of Cells

Cells are covered in many of the textbooks given to students in middle school and high school. But, who was it that discovered cells? The first observation of cells is attributed to an English scientist named Robert Hooke. He used a microscope to examine a thin slice of cork in 1665. He noticed that the cells appeared in "little boxes". You and me know that plant cells are the "little boxes" Hooke observed, but Robert was the first person to see them. He looked at carrots, ferns, and the stems of elder trees, and all of them displayed a similar formation of cells. Pattern? He was looking only at plant cells. The first person to observe living cells was a Dutch microscope maker named Anton van Leeuwenhoek. After 150 years, scientists began to organize the observations begun by Hooke and van Leeuwenhoek. They formed the cell theory. The theory has three parts: 1. All living things are composed of one or more cells. 2. Cells are the basic units of structure and function in an organism and 3. Cells only come from the reproduction of existing cells. The evidence to support this theory was provided by a trio of German scientists. In 1838, the botanist Matthias Schleiden concluded that all plants are made of cells. A year later, zoologist Theodor Schwann made the same conclusion about animals. Finally, in 1855, a physician named Rudolf Virchow reasoned that cells only come from existing ones. Over the years, modern scientists have gathered a lot of additional information that strongly supports the cell theory.

Bernoulli 's Principles

Often, I see birds flying. Then, sometime later, I see a plane flying. Birds are light weight, have hollow bones and have to flap or use updrafts to fly. Planes, are huge metal things that have engines and literally, weigh tons. So how does a plane fly? Bernoulli was a scientist who observed that with any fluid, an increase in velocity equaled a decrease in pressure. It applies in actual fluids, like water, and with gas, like what we inhale and exhale. The airplanes wings are shaped so air has to cycle around it, creating low pressure above the wing and high pressure beneath it. That helps the plane to fly. There are always four forces acting on a plane. The planes weight, thrust, drag, and lift. The thrust has to be greater than the drag for it to go forward. For it to go upwards as well, it has to have greater lift than its weight. One of pilots worst enemies is gravity since it always wants to pull down the plane from 5000 feet up. Anyways, planes couldn't fly if they had  a square shaped body. Why? The air wouldn't be able to circulate around it. Bernoulli said that the increase in velocity, for planes its mostly speed instead of direction, meant a decrease in pressure. http://www.centennialofflight.gov/essay/Dictionary/bernoulli/DI9.htm 

Fluids and Pressure

Pressure is simply how much force is applied to one area. Say, you have a cat laying on you lap and you petting it. The cat gets bored and walks away. The amount of pressure went from a large area, its body since it was laying down, to a small area, its paws. Pressure, like speed, acceleration, and momentum, can be increased or decreased. If you wanted to increase pressure on an object, you would either decrease the area you are applying it to, or increase the amount of force you are using. How are fluids related to this? Well, fluids, like everything one this planet, are made up of particles to small to see without a microscope. Water, for example, is made up of two hydrogen particles and one oxygen particle. They aren't as densely packed as a solid object, which is rigid (a good example is a tree. Try moving a full grown one without any tools). Since they are so loosely put together, its motion is random. The particles bounce into each other, away from each other, and go pretty much everywhere. If an object was dropped into a fluid, the object would be acted upon equally from all sides, constantly. Pressure is everywhere, especially in air (duh). At sea level, the air pressures roughly 2.2 pounds of pressure per square centimeter of your body. You wont notice though, since its pressuring equally from all sides. If you have ever gone in a plane, as you get higher in elevation, your ears pop. That's from the air pressure. The higher you get, the more air pressure there is. There is a lower density of breathable air as well, which is why you are in the plane and not outside it. I realize that air isn't related much to fluids, but water(or any other fluid) is a lot denser than air. Similar to the way that the pressure goes up as you get higher in the air, the pressure gets higher the farther down you go. If you went down 3300 feet without any equipment, your lungs would collapse and you would die. Its impossible to get that far down without equipment though, well, unless you were dead. Still, pressure gets higher when the elevation goes up, and gets higher the farther you go down in water.
http://www.school-for-champions.com/science/fluid_pressure.htm link

Density and the Titanic

Density is what makes something float or sink. The Titanic was thought to be unsinkable, until it hit an iceberg, and sank. The Titanic was made so if one level filled with water, it would still float. When the iceberg scraped the sides of the ship, it made holes on several levels. When the water flooded in, the Titanic had the same amount of space as it did before, but the water made it denser.  The water flooded in and first it tilted, then was verticle, then it was too much weight the ship could bear so it broke in half and sank. If the iceberg hadn't hit so many levels, it could have maybe survived with the thousands of people on it. Most icebergs are bigger under the surface. Often, the visible part is only a fraction of the size, thus the expression, the tip of the iceberg. The lower section of the iceberg is completely invisible, so the captain didn't know were it was. It was dark and he couldn't  see the iceberg until he almost collided with it. He tried to steer it away, but the lower decks got hit and let the water in. The water flooding in made it too dense to float. So, it sank, and took hundreds of people to the depths of the Atlantic ocean because there simply wasn't enough life boats.

Density

A heavy wooden block floats in water but a much lighter stone sinks. Why? Well, the stone is denser than the wood. The molecules that compose them are closer together in the stone than in the rock. Think of it like a storage container. One is packed with stuff when the other has a smaller amount of stuff shoved in. The one with more stuff is the exact same size as the one with less stuff, but weighs more. Why? Density. The stuff is much more densely packed into that unit. Density is mass per unit of volume. A stone weighs less than the wood, but is more dense, so it sinks. The wooden block is heavier but is less dense. http://www.physics.ucla.edu/k-6connection/Mass,w,d.htm