Explain the Discovery of Evolution Science

(Originally posted on SoYouWanna)

Overview

Crediting a single person with the discovery of evolution would prove a great disservice to the many scientists and naturalists whose work contributed to our still changing understanding of the evolutionary process. Although Charles Darwin published one of the first treatises on the theory of evolution by natural selection, the idea that organisms change through time was introduced long before Darwin started his work.

Buffon

Georges-Louis Leclerc, Comte de Buffon, was an 18th-century naturalist whose career centered around creating an encyclopedia entitled “Histoire Naturelle,” intended to contain everything known about the natural world in that age. In writing his encyclopedia, Buffon attempted to explain the facts that he accumulated using far-reaching theories about the Earth and its inhabitants. Buffon argued that life originated in the hot oceans of the early Earth, already divided into a number of distinct types. Buffon’s theories accounted for the geographical distribution of similar species around the world by theorizing that the supply of organic molecules that could be used to create new individuals changed as a species migrated, thus changing the species’ “internal mould.” Although no single idea of Buffon’s has withstood the test of time, his theories foreshadowed some of the most important advances in the natural sciences that were to come in the decades to follow his death in 1788.

Lamarck

Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, a French naturalist, proposed a fully developed theory of evolution in 1801. Lamarck argued that changes in use of an organ would result in morphological changes in that organ, which could build up through an organism’s lifetime and be passed on to its offspring. Lamarck also proposed that nature drove organisms upward from simple forms to increasingly complex ones. Although Charles Darwin did not accept this arrow of complexity guiding the history of life, Lamarck and Darwin used many of the same lines of evidence, such as vestigial organs and artificial selection, to support their different theories. Lamarckian evolution was highly regarded throughout the 1800s until it was discarded with the discovery of genes.

Malthus

Despite the fact that Thomas Malthus was a political economist, not a biologist, his most famous work, “An Essay on the Principle of Population As It Affects the Future Improvement of Society,” served as an inspiration for both Alfred Wallace’s and Charles Darwin’s theories of evolution by natural selection. In his essay, Malthus looked at humans as a group of individuals all subject to the same basic laws of behavior. He used the same principles an ecologist would use to study plants or animals, pointing out the fact that the same forces of fertility and starvation that shaped plants and animals also shaped the human species.

Wallace and Darwin

In the middle of the 19th century a British biologist named Alfred Russel Wallace and the well-known naturalist Charles Robert Darwin independently conceived of the process of evolution by natural selection. When both scientists read Malthus’s “Essay on the Principle of Population” it occurred to them that the population pressures of fertilization and starvation could endow organisms with traits adapted to survival in a specific environment, giving those organisms a reproductive advantage. In 1858 Wallace, who had been supplying Darwin with birds from South America and Asia, sent Darwin his theory on evolution, hoping Darwin could help him publish the work. Wallace’s theory nearly replicated the theory that Darwin had been working on since the 1830s. In 1858 both Wallace and Darwin presented their papers to a meeting of the Linnaean Society, and Darwin published the seminal “On the Origin of Species by Natural Selection” in 1859.

Mendel

Although heredity provides the raw material for natural selection, the exact method of heredity remained a mystery throughout the 19th century. As Darwin was working on “On the Origin of Species” in the 1850s, a monk named Gregor Mendel was researching heredity in a monastery pea garden. Mendel bred thousands of pea plants and recorded how traits such as pea color, pea texture, and flower color were passed on to the offspring of each generation; he eventually discovered what geneticists now call alleles. Mendel abandoned his experiments in the 1860s after his findings failed to pick up steam in the scientific community. It wasn’t until 15 years after Mendel’s death in 1884 that scientists finally realized that Mendel had uncovered the secret of heredity in living organisms, solidifying evolutionary theory’s place in biology textbooks.

References:
University of California Museum of Paleontology Understanding Evolution: Georges-Louis Leclerc, Comte de Buffon
Understanding Evolution: Jean Baptiste Lamarck
Understanding Evolution: Thomas Malthus
Understanding Evolution: Charles Darwin & Alfred Russel Wallace
Understanding Evolution: Gregor Mendel
Understanding Evolution: The History of Evolutionary Thought

How to Graph Data Sets With Polynomials

(Originally posted on eHow)

Overview

Polynomials are algebraic expressions consisting of terms in the form ax^n where the exponent “n” is a non-negative number and the coefficient “a” is a real number. The degree of a polynomial is determined by the largest exponent applied to the variable “x.” The first quadratic equations, polynomial equations of the second degree, were being solved by the Babylonians in 400 BC. Today, polynomials are used to encode functions for solving problems in biology, chemistry, physics, and various social sciences including economics.

Instructions

Step 1: Determine the degree of the polynomial being graphed. A polynomial in the form P(x) = ax^n + ax^(n-1) + ax^(n-2) + … is a degree n polynomial. For example, the polynomial P(x) = x^2 + 2x^3 + x — 1 has a degree of 3, the largest exponent of the variable x in the equation.

Step 2: Use the degree of the polynomial to determine the general shape of the graph. A polynomial of even degree with a positive coefficient will increase infinitely at both ends of the graph. A polynomial of even degree with a negative coefficient will decrease infinitely at both ends of the graph. A polynomial of odd degree with a positive coefficient will increase infinitely to the right and decrease infinitely to the left. A polynomial of odd degree with a negative coefficient will decrease infinitely to the right and increase infinitely to the left.

Step 3: Factor the polynomial and solve for all zeroes of the equation. The zeroes of the equation represent where the graph will touch the x axis. Plot the zeroes with a point on the graph.

Step 4: Determine the y intercept of the polynomial by plugging 0 into the equation for x. Plot the y intercept on the graph

Step 5: Plug various numbers into the polynomial for the variable x. The more points you find the more accurate your graph will be. Plot at least one point at each end of the graph and one point between each pair of zeroes found in Step 4.

Step 6: Connect the points you have plotted with a smooth line.

Tips & Warnings:

Note that ^ stands for superscript. For example, 5^2 would be 5 to the second power, or 5 squared, or 25.

References:
University of Tennessee Math Archives: Polynomials
Lamar University: Graphing Polynomials
Lamar University: Polynomials
University of Hawaii: A Brief History of Solving Polynomial Equations

The Major Pathways & Reactions of Cellular Respiration

(Originally posted on eHow)

Overview

Cellular respiration is the biochemical process by which cells release energy from the chemical bonds of glucose to provide the energy needed for the critical functions of life. All living cells perform either aerobic respiration, in the presence of oxygen, or anaerobic respiration, in the absence of oxygen. Both aerobic respiration and anaerobic fermentation start with the same first step, glycolysis, which splits the 6-carbon glucose molecule into two 3-carbon pyruvic acid molecules.

Glycolysis

Glycolysis, the one metabolic pathway found in all living organisms, occurs in the cytoplasm of a cell and does not require oxygen to take place. Each of the 10 steps of glycolysis is catalyzed by an enzyme specific to that reaction. Initially two molecules of ATP, the cellular energy currency, are used to activate a molecule of glucose for glycolysis, but the entire process results in a net gain of two ATP molecules. The biochemical pathways of glycolysis also lead to the reduction of two molecules of NAD+ resulting in two molecules of NADH, which can be used to create ATP in later steps of cellular respiration.

Anaerobic Respiration

When oxygen is not present, a cell must bypass the much more lucrative aerobic respiration pathways and instead rely on anaerobic respiration for the cell’s energy. Under great exertion, when oxygen levels are low, human muscle cells undergo a particular form of anaerobic respiration called lactic acid fermentation. In lactic acid fermentation the pyruvate molecules produced by glycolysis are broken down into waste products that can be removed from the cell. This is done in order to oxidize the NADH molecules produced by glycolysis so the resulting NAD+ molecules can perform glycolysis again and produce more energy. The waste product of lactic acid fermentation, lactic acid, is what makes your muscles feel sore the day after exercising.

Kreb’s Cycle

When oxygen is present, the pyruvate produced by glycolysis enters the mitochondrion of the cell where it is converted to acetyl CoA, producing two more molecules of NADH per glucose molecule. The acetyl CoA then enters the Krebs Cycle, also called the citrus acid cycle, where it is broken down to produce four carbon dioxide molecules, two ATP, six NADH and two FADH2 molecules, which can be used later in respiration to produce more ATP energy.

Electron Transport Reactions

The electron transport system is a chain of electron carriers located in the inner membrane of the mitochondrion of eukaryotes. The NADH and FADH2 molecules produced in the previous steps of cellular respiration deliver electrons to the electron transport system. As each electron is transferred from carrier to carrier in the electron transport chain, some energy is released and hydrogen ions are pumped into the intermembrane space of the mitochondrion. Oxygen is the final acceptor of the electron resulting in the formation of water. For the energy produced by each molecule of NADH that delivers an electron, about three ATP can be formed; for each molecule of FADH2, about two ATP can be formed.

ATP

The action of the electron transport chain results in the formation of a hydrogen ion gradient across the inner membrane of the mitochondrion. The concentrated hydrogen ions located in the intermembrane space contain energy much like that of a hydroelectric dam. As the hydrogen ions move from the intermembrane space back to the matrix of the mitochondrion, they must pass through the enzyme ATP synthase. The energy of the hydrogen ions moving through the ATP synthase enzyme results in the production of ATP.

References:
Georgia State University: Cellular Respiration
University of Cincinnati Biology: Cellular Respiration and Fermentation
The State University of New York: Cellular Respiration
Earlham College: Cellular Respiration

What is the job of mRNA?

(Originally posted on Answerbag)

Overview

Ribonucleic acid, or RNA, consists of multiple nucleic acid subunits similar to those which form DNA. There are many types of RNA, each responsible for critical functions of the cell. Messenger RNA, typically abbreviated mRNA, serves as the messenger which tells the ribosomes what proteins to make and when.

Transcription

Transcription consists of the synthesis of RNA from a DNA template. The enzyme RNA polymerase binds to particular sights on the DNA strand and synthesizes a complimentary strand of mRNA.

Base Pairs

RNA and DNA are both polymers of nucleotide subunits with one of four base groups. DNA and RNA both use cytosine, guanine, and thymine. However, RNA utilizes the base uracil while DNA uses thymine. The strands are called complimentary because there are specific geometric requirements in the formation of bonds between the strands of RNA and DNA.

Translation

Translation is the process by which information encoded in mRNA guides the construction of a polypeptide chain. Translation involves three types of RNA: messenger RNA, transfer RNA, and ribosomal RNA.

Ribosomes

Ribosomes are the enzymes which catalyze the process of translation. The ribosome recognizes a start signal on the mRNA and assembles there before going down the line translating the mRNA into a protein three base pairs at a time.

Codons

Codons are sequences of three nucleotide monomers on an mRNA strand. Each codon encodes a specific amino acid added to the protein chain. While each codon only encodes for a single amino acid, most amino acids are encoded for by more than one codon.

Sources:
Arizona State University: DNA, RNA and Protein Synthesis
Portland State University: Transcription
Elmhurst College: DNA Double Helix
University of Wisconsin La Crosse Bioweb: Translation
University of Washington: Translation Study Guide

More Information:
The University of Utah Learn Genetics: Transcribe and Translate a Gene

Embryological development processes: Grasshopper testis, frog blastulas, and chicken hearts.

(Originally Posted on _____. Why not?)

Grasshopper Testis

Cross section of grasshopper testis.

The testis of the grasshopper consist of a series of lobes that contain cells in varying stages of spermatogenesis. In each testicular lobe can be found many smaller compartments, known as testicular cysts. As the sperm cells develop they travel from the apical end of the testicular lobe to the basal end. At the apical end, the cells are grouped into presumptive germ cells known as spermatogonia. These cells undergo mitosis and give rise to all of the remaining germ cells in the testis. Moving from the spermatogonia in the apical end of the testis to the vas deferens at the opposite end of the testis, the cells mature as a group inside the testicular cysts. All the cells in one testicular cyst are in the same stage of development.

Frog Blastula

Blastula stage frog embryo.

Each animal, whether frog, human, earthworm, or dog, passes through similar stages of development. Fertilization (the fusion of genetic material from two gametes) starts the life cycle and stimulates the egg to begin development. The stages of development between fertilization and hatching are known as embryogenesis; and although there is an incredible variety of embryogenic types, most patterns are variations on five fundamental processes:

1. Cleavage
2. Gastrulation
3. Organogenesis
4. Gametogenesis
5. Metamorphosis

Cleavage consists of a series of extremely fast mitotic divisions immediately after fertilization. During cleavage the volume of cytoplasm does not grow, cells merely divide the enormous volume of zygote cytoplasm into many smaller cells called blastomeres. The amount and distribution of yolk in each cell determines the rate of cleavage and the relative size of the blastomeres. The large, yolk-rich vegetal pole cells (macromeres) divide slowly compared to the smaller, relatively low yolk animal pole cells (micromeres) causing the vegetal pole cells to become progressively larger. The micromeres of the animal pole stain darker than the macromeres of the vegetal pole due to the higher concentration of organelles in the cytoplasm. Throughout this process, a fluid-filled cavity important for allowing cell movements during gastrulation (blastocoel) forms in the animal hemisphere of the blastula.

Chicken Embryos

“It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.”
-Lewis Wolpert

Whole mount of a chick embryo after 24 hours of development.

During gastrulation, cell movements result in a massive reorganization of the embryo and the differentiation of the three embryonic germ layers. The ectoderm will develop into organs such as the skin, the nervous system, and the lens of the eye. The endoderm develops into the inner linings of the digestive tract, the linings of the respiratory passages, and many glands such as the liver and pancreas. The mesoderm forms the somites, the notochord, and the mesenchyme, which give rise to the muscles, circulatory and excretory systems of the body. In amniote embryos, a structure known as the primitive streak organizes the process of gastrulation and, thus, lays the foundation of the embryonic body plan.

By 24 hours time many structures have already formed in the chicken embryo. The neural fold can be seen, which is formed of ectodermal tissue and will eventually close to form the neural tube (the precursor to the brain cavity and spinal cord). Also, the somites flanking the soon-to-be neural tube are developing and will ultimately form parts of the skeletal and muscular systems. Hensen’s node (a.ka. the primitive knot) is the anterior most portion of the primitive streak. It is the site of involution in chick gastrulation works in the same way as the dorsal lip of the blastopore in amphibian development.

Serial cross sections of a chicken embryo after 48 hours of development.

The heart of the chicken embryo develops from the fusion of paired precardiac mesodermal tubes located on either side of the developing foregut. After about 25 to 30 hours of incubation, the paired heart vesicles begin to fuse at the anterior end and continue to fuse posteriorly forming a single continuous tube. After this fusion is complete, the heart tube has four distinct regions that can be identified from anterior to posterior:

1. conotruncus
2. ventricle
3. atrium
4. sinus venosus

After 24 hours of development the heart tube is nearly straight and blood flows anteriorly from the sinus venosus to the conotruncus. After 33 hours the heart develops a distinct “S” shape with the ventricle bulging dramatically to the right. This is the start of cardiac looping, which, when completed, will produce the basic configuration of the mature heart. By 48 hours, the heart has folded upon itself, forming a single loop. This moves the sinus venosus and atrium to a position anterior and dorsal to the ventricle and the conotruncus. The ventricle has become U-shaped and in the medial ventral position and blood now flows posteriorly and then makes a sharp turn to flow anteriorly. In the 72-hour chick the heart has just two chambers, but the atrium and ventricle have started to expand. The atrium will eventually join the sinus venosus and divide into the two atrial chambers, and the ventricle will also divide into two chambers resulting in the adult four-chambered heart.

(All images by Bryan Perkins)