Biology – Science 206
Energy, Metabolism, and Cells –
Photosynthesis & Cellular Respiration
John Carter
August 11, 2013

1. Explain how photosynthesis and respiration are linked in order to provide you with energy from the food you eat.

Photosynthesis can be defined as the process that living organisms such as plants use to translate the sun’s energy into chemical energy. Once the plant has translated the sun’s energy into chemical energy it then releases that energy and makes it readily available to other living things (Vermaas, 2007).
Aerobic respiration can be defined as nutrients being converted into useful energy. Respiration allows cells to use the energy stored during the photosynthesis process. It’s the chemical reaction that breaks down the glucose and changes it into a larger amount of Adenosine Triphosphate which is also called ATP (Board, 2012).
Plants use sunlight to make ATP for its energy source by creating a series of chemical reactions by producing oxygen as a waste product. Next, animals and human beings eat these plants. The nutrients digested by animals and human beings reverse the process by using the ATP as a source of energy. Our cells use the nutrients from the plants and convert the nutrients in a process that uses oxygen (Board, 2012). Once our bodies have used all the nutrients will be need from those plants our bodies as well as animals release carbon dioxide as waste.
Photosynthesis and respiration are both means of converting one state of energy into another more useful state of energy at a cellular level (Vermaas, 2007). Although photosynthesis and aerobic respiration both convert energy, their processes are opposite one another. In photosynthesis, plants use the water, sun’s energy, and carbon dioxide to generate sugar compounds and oxygen. In aerobic respiration cells use the sugar compounds that are used in the photosynthesis process to release water, carbon dioxide and energy (Board, 2012). Plants use photosynthesis to convert energy, while animals and human beings use aerobic respiration, such as carbon dioxide and oxygen to energy. 2. In the absence of oxygen some cells and organisms can use glycolysis coupled to fermentation to produce energy from the sugar created by photosynthesis.
Fermentation is the process that changes sugar into acids, alcohol or gases. Fermentation is the most common form of anaerobic respiration, which occurs when oxygen is not present during the time when sugars are changed into acid, alcohol or gases.
When oxygen is not present, pyruvate, which is end product of glucoses, does not go into the tribcarboxylic acid also known as TCA cycle. In the anaerobic respiration process the pyruvate is forced to go into easier pathways (Board, 2012). In human beings when there is no oxygen present while energy is being changed there is often a buildup of lactic acid. The process of no oxygen being present during the conversion of energy is called anaerobic respiration.
Once there is a buildup of lactic acid in human beings, our bodies react by giving symptoms such as headaches, muscle aches, and muscle fatigue. These symptoms usually occur after a long period of exercising. If there is a lactic acid buildup in the body after a long jog, it is caused when the is unable to get rid of the lactic acid fast enough. The human body uses aerobic acid to produce the energy needed to exercise and lactic acid is the waste product of that converted energy (Board, 2012).
In other living organisms such as plants, the anaerobic respiration process produces a waste product of ethanol or what is known as drinking alcohol instead of lactic acid. Yeast is an example of an organism that produces ethanol (Helmenstine, 2012).
The major difference between aerobic respiration and anaerobic respiration is while aerobic respiration continues to produce energy cycle after cycle or continuously, anaerobic respiration does not. Once the waste or the end product is produced during the anaerobic respiration cycle, is ceases to produce energy (Board, 2012).

3. Cells use enzymes as biological catalysts to increase or accelerate the rate of reactions, such as those in photosynthesis or glycolysis. This allows reactions to occur under conditions that sustain life.
Enzymes are the molecules that are responsible for controlling all internal cellular responses. Enzymes are protein molecules that act as biological catalyst, meaning they increase the rate of chemical reactions in cells without being used. Enzymes are considered to be the “workhorses” of a cell, because of its function in the cell, and because the enzyme is controlled by cell (Board, 2012).
Enzymes will catalyst a reaction by two different methods. The two types of enzyme controlled reactions degradation and synthesis. Degradation which is a catabolic reaction happens when an enzyme breaks down large molecules into smaller molecules (Board, 2012). An example of degradation is during the human digestive process. During digestion food is broken down in smaller parts and passed through the large and small intestines.
Synthesis which is an anabolic reaction occurs when the enzyme builds up larger molecules from smaller ones for example photosynthesis.
The three main steps of the cycle of enzyme-substrate interactions are when the enzyme and substrate come together, when the enzyme-substrate complex is formed, and when the enzyme and product are left. When the enzyme and substrate come together it takes place at what is known as the “active site.” Because the enzymes are typically larger than the substrates that they attach to, is causes the newly formed complex to have a “groove or unique pocket” which causes the complex to have more of a three dimensional shape (Board, 2012). At the end of the cycle of enzyme-substrate only the enzyme and the product are left. For example, when enzymes are added hydrogen peroxide creates water and oxygen.

References
Board, E. (2012). Biology. (1 ed.). Words of Wisdom. Retrieved July 27, 2013, from http://wow.coursesmart.com/9781934920602/firstsection
Helmenstine, A. (2012). What is Fermentation?, About.com Chemistry. Retrieved August 10, 2013, from http://chemistry.about.com/od/lecturenoteslab1/f/What-Is-Fermentation.htm Vermass, W. (2007). An Introduction to Photosynthesis and Its Applications. Center for the Study of
Early Events in Photosynthesis, Retrieved August 10, 2013, from
http://bioenergy.asu.edu/photosyn/education/photointro.html