Aerobic cellular respiration and oxygenic photosynthesis are two cellular proces

Question

Aerobic cellular respiration and oxygenic photosynthesis are two cellular processes that evolved in a similar matter. Define and describe the two processes and describe how the processes are related (for example: products, reactants, biochemical pathways). Finally, provide evidence to show that oxygenic photosynthesis evolved before aerobic cellular respiration.

Description of cellular respiration (5 points); Description of photosynthesis (5 points); Comparison of cellular respiration and photosynthesis (5 points); Evolution of oxygenic photosynthesis before aerobic cellular respiration (5 points)

Abbreviations you can use - ATP, NAD+, NADH, FAD, FADH2, NADP, NADPH

Abbreviations you CANNOT use - CO2, O2, H2O - write these out

NOTE: This covers chapters 8,9, 10. Chapter 25 has extra information about the evolution of photosynthesis

There are no proper nouns except the Calvin cycle, so the only capitalization should occur at th beginning of the sentence.

Explanation / Answer

Photosynthesis, a chemical process, is part of a larger process known as plant metabolism. This process occurs in sunlight, at which point plants create stores of energy and their own food. This takes place in the plant cells that contain chlorophyll, the pigment within plant leaves that give them their green color. The chlorophyll absorbs light energy and uses it to create sugars (carbohydrates) from water (H2O) and carbon dioxide (CO2). Oxygen is created by this chemical reaction and is then released into the atmosphere.

Photosynthesis is a two step process:

The light dependent reactions convert light energy from the Sun into chemical energy (ATP).
The light independent reactions use the chemical energy to synthesise organic compounds (e.g. carbohydrates).


Step 1: Light Dependent Reactions

Light is absorbed by chlorophyll, which releases energised electrons that are used to produce ATP (chemical energy).
The electrons are donated to carrier molecules (NADP+), which is used (along with ATP) in the light independent reactions.
The electrons lost from the chlorophyll are replaced by water, which is split (photolysis) to produce oxygen and hydrogen.
The light dependent reactions occur in the intermembrane space of membranous discs called thylakoids.


Step 2: Light Independent Reactions

ATP and hydrogen / electrons (carried by NADPH) are transferred to the site of the light independent reactions.
The hydrogen / electrons are combined with carbon dioxide to form complex organic compounds (e.g. carbohydrates).
The ATP provides the required energy to power these anabolic reactions and fix the carbon molecules together.
The light independent reactions occur within the fluid-filled interior of the chloroplast called the stroma.

Cellular respiration is a process in which water and carbon dioxide are produced through the break down of chemical bonds of glucose or the oxidizing of food molecules. Energy is released during cellular respiration and is captured as Adenosine Triphosphate (ATP) and then utilized by different cell activities that consume energy. Aerobic respiration and glycolysis are the two main steps responsible for completely breaking down glucose into water and carbon dioxide.

Cellular respiration occurs in both eukaryotic and prokaryotic cells. It has three main stages glycolysis, the citric acid cycle and electron transport chain.

Glycolysis
Glycolysis is the anaerobic catabolic reaction of glucose.
Glycolysis occurs in almost all cells.
This pathway takes place with or without the presence of oxygen.
Aerobic conditions produce pyruvate and anaerobic conditions produce lactate as the end products of glycolysis.
In the eukaryotic cells, glycolysis occurs in the cytosol.
Glycolysis a process where a molecule of glucose is converted into two molecules of pyruvic acid.
There are ten intermediate compounds in this process and there are ten enzymes are needed for the process of glycolysis.
Two energy rich ATP molecules are required to start the process of glycolysis.
At the end, the process yields a pyruvate molecule, four molecules of ATP are made and two NADP molecules.
Both ATP and NADP molecules are energy-rich and are used in other cell reactions.
The cells which use oxygen, the pyruvate is passed on to the second process known as the Kreb's cycle by which more ATP molecules are produced.

Citric Acid Cycle
Citirc acid cycle is also known as the Krebs cycle and the tricarboxylic acid cycle.
In the presence of oxygen, the pyruvate produced at the end of glycolysis is converted to acetyl-CoA.
In the presence of oxygen the mitochondria will undergo aerobic respiration which leads to Krebs cycle.
In the absence of oxygen fermentation of the pyruvate molecule will occur.
When acteyl-CoA is produced, this molecule enters the citric acid cycle, which takes place in the mitochondrial matrix.
This molecule gets oxidized to CO2 and reduced NAD to NADH.
NADH is then again used in the electron transport chain to produce more ATP in oxidative phosphorylation.
The TCA cycle is a process with 8 steps and involves different enzymes and co-enzymes.
The net energy gain from a single citric acid cycle is 3 NADH, 1 FADH2 and 1 GTP. The GTP is subsequently used to produce ATP.


Electron Transport Chain
The electron transport system is found in the mitochondria and chloroplast of eukaryotic organisms and is seen in the plasma membrane of prokaryotes.
This pathway consists of series of carrier molecules which pass electrons from a high energy molecule to the final low energy electron acceptor molecule.
Energy released during this process of oxidation and reduction produces ATP.
The NADH and FADH2 molecules bring electrons to the electron transport system.
This system contains membrane-bound electron carriers that pass electrons from one to another.
When a carrier molecule reduces another molecule, the energy that is released is used to pump hydrogen ions across the membrane into the intermembrane space.
The remaining energy is used to reduce the next carrier molecule.
As a result of this, hydrogen ions become concentrated in the intermembrane space.
The ATP synthase enzyme uses the energy of this gradient to produce ATP.
In the electron transport system, NADH and FADH2 are oxidized and the energy released in this process is used to produce ATP.

Comparison of cellular respiration and photosynthesis

Photosynthesis and cell respiration both involve the production of chemical energy (ATP).

In photosynthesis, ATP is produced via light energy (photophosphorylation) and used to make organic molecules
In cell respiration, ATP is produced by breaking down organic molecules (oxidative phosphorylation).

In both cases, the production of ATP involves an electron transport chain and chemiosmosis.

In photosynthesis, electrons are donated by chlorophyll and protons accumulate within the lumen of the thylakoid.
In cell respiration, electrons are donated by hydrogen carriers and protons accumulate in the intermembrane space.

EVOLUTION OF OXYGENIC PHOTOSYNTHESIS

The most widely discussed yet poorly understood event in the evolution of photosynthesis is the invention of the ability to use water as an electron donor, producing O2 as a waste product and giving rise to oxygenic photosynthesis. The production of O2 and its subsequent accumulation in the atmosphere forever changed the Earth and permitted the development of advanced life that utilized the O2 during aerobic respiration. Several lines of geochemical evidence indicate that free O2 began to accumulate in the atmosphere by 2.4 billion years ago, although the ability to do oxygenic photosynthesis probably began somewhat earlier. In order for O2 to accumulate, it is necessary that both the biological machinery needed to produce it has evolved, but also the reduced carbon produced must be buried by geological processes, which are controlled by geological processes such as plate tectonics and the buildup of continents. So the buildup of O2 in the atmosphere represents a coming together of the biology that gives rise to O2 production and the geology that permits O2 to accumulate.

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