JEDIDIAH BRANDON

Biology 1544

Oct 16th, MMXII

Creatures of the Sun

What is life? Where did we come from? What are we made of? These questions and

many others like them have been being asked for thousands of years and the basic harmonies of

the life forms around us has been observed for just as long. The process of figuring out how and

why has been a journey taken by many great minds but it seems the answer of what the

beginning catalyst for these harmonies has never been in question. Most prehistoric peoples such

as the Aztecs, Egyptians, and Celts made it their first Idol and worshipped it, intensely. We call

this giver of all and bringer of light, the Sun.

In our cycle of life and energy on this planet, everything begins with the Sun. A massive

ball of mostly Hydrogen and Helium going through a constant process of nuclear fusion in

which the Hydrogen is converted into other elements and is protruded from the surface in the

form of light and radiation. It speeds across our solar system at 186,000mps and slams into our

planet’s atmosphere, every day. Before the ‘Blue Planet’ was blue, it was red and black with fire

and poisonous gases spewing from our highly active crust. Even within this chaotic habitat,

bacteria and other organelles were able to exist and prosper with the use of the available

resources such as minerals, gases, and most of all, sunlight to grow and adapt. The first

Cyanobacteria were able to take the abundantly available CO2 and the visible light from the sun

and produce their own food in the form of sugar molecules through the process of

photosynthesis. As important as these sugars will become in the development of organisms that

was soon to follow, the most important byproduct of this process is the H2O that was released

into our atmosphere thus creating an oxygen rich environment for the following species to

flourish in. In the later paragraphs, I hope to explain how the suns energy is the key ingredient to

all organism and how it is cycled through all living things through the food chain.

Feeding off the Sun

Since I was a child, I always associated a lot of colors with plants and flowers. But one

color that was always prominent was the color green. As a child I remember asking, “Why is

grass green?” It would take until Jr High before I would receive an answer other than, “It just is.”

To uncover the answer of why plants are green, you also uncover the answers behind

photosynthesis. Let’s picture a tree for a second. What is the overall basic structure? You have

the roots which are positioned at the bottom and are in charge of pulling the essential water and

mineral’s from the ground and piping them upward through the root structure and to its

destination at the top of the tree were leaves reside. The leaf’s construction is specifically

designed for the production of sugars to fuel the trees growth and reproduction. When the visible

spectrum of the suns light hits the leaf, it passes through the cuticle and epidermis until it makes

contact with the mesophyll. The mesophyll is a network of cells and within these cells is a large

number of chloroplast. Chloroplasts are the power house of the plant and are where the process

of photosynthesis takes place. Inside the chloroplast are stacks of disk shaped objects called

thylakoids which possess pigment molecules called chlorophyll. When the sunlight hits the

pigment, it absorbs the red and blue light but reflects the green light back, which is why your eye

perceives it as green. Because the chlorophyll is arranged in clusters of photosystems, they’re

able to work together to abstract the photons from the sun and excite electrons to a higher

energy. With the chlorophyll molecules excited, they pass the high energy electron along the

photosystem until it hits a key chlorophyll molecule. Here it finds its way to membrane bound

protein and is transfer to the accepter molecule where it begins its process as the main element in

the light-dependent reaction. Here is where the suns energy is used to make food.

Making Sugar like Willy Wonka

Now that the photon has taken its long but short journey through the light-dependent

reactions which involved traveling from the sun, being captured by the chlorophyll within the

plant, and using it to make ATP and NADPH, It’s time to switch to the chemical process side of

photosynthesis and make some sugar, or as I like to call it, the ‘Dark Side’. In the light-

independent reaction, aka The Calvin cycle, The ATP and NADPH are released out of the

thylakoid and into the stroma of the chloroplast. Here it reacts in a chemical process brought on

by enzymes located there and begins the conversion of CO2 to organic molecules like glucose.

These molecules are used to power the plant in its efforts to obtain water and sunlight and to

reproduce. After a little understanding of this process, you can start to see how the flesh of a

plant can be substantial in fueling many different species thus sustaining a vast ecosystem.

Passing the Energy Up the Chain

In the opening paragraph, I used a tree as an example. But photosynthesis is used by all

plants to make food. Like a blade of grass in a cow pasture. It uses the same cycles as the tree to

make sugars. And not only is the ATP and NADPH used by the grass to grow and reproduce, but

is also used by the cow in the pasture to create energy. Let’s discuss a little on how this transfer

happens. First we need to break down the organic molecules to retrieve the ATP that was

produced during photosynthesis. Animals do this by a process called cellular respiration which

involves stripping the excited electrons away from chemical bonds and using them to make our

own ATP. The loss of an electron is called oxidation and the gain of one is called reduction. The

first stage of this process is called glycolysis and is a series of reactions. Two phosphates are

added to the ends of the glucose molecule and then is split into two sugar phosphates. After this

they are again split into two pyruvates. When this happens, a high-energy hydrogen is obtained

as NADH and two ATP molecules are formed. Now that we have two pyruvates made, we need

to convert them into our own ATP. We do this by Oxidative Respiration in our mitochondria. It

harvests the energy from the pyruvate in two steps: First oxidize the pyruvate to make acetyl-

CoA, then oxidizing the acetyl-CoA in the Citric Acid cycle. After one of the three carbons is

separated from the pyruvate, it travels to one of the biggest enzyme complexes to dehydrogenase.

In this process, a hydrogen and electrons are removed from the pyruvate and donated to NAD+

to form NADH. The two carbon fragments left after removing the CO2 is joined to coenzyme A

forming the compound acetyl-CoA and is either stored in fat synthesis if the cell has plenty of

ATP or put through the Citric Acid cycle if ATP is immediately needed. The next step in

Oxidative respiration is forming our ATP from acetyl-CoA that we made earlier. We do this in a

process called the Citric Acid cycle or the ‘Krebs Cycle’ which takes place in the mitochondria.

First acetyl-CoA enters and joins with four carbon molecule. Two carbons are removed as CO2

and their electrons are donated to NAD+, leaving a four-carbon molecule and producing an

ATP.. Then more electrons are extracted and form NADH and FADH2. The starting material is

regenerated. This entire process is carried out in the mitochondria. The NADH and FADH2

molecules contain gained hydrogen’s and electrons. They carry their electrons to the inner

mitochondrial membrane and transfer them to the electron transport chain. And here, at the cell

membrane, is where our journey ends. We made our way from the center of the sun, through

space, to our planet where its collected by plants, absorbed by the chloroplasts using chlorophyll

and made into sugars. Then ingested by animals and converted to usable ATP to full our cells.

With such a complicated process of using the rays of the sun to provide all life on earth, it’s easy

to see how the ancient civilizations of the past found the need to worship it.