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In this lesson, we will review different facets of science to show how integrating knowledge gained from different types of science can enable a more meaningful and complete understanding of our universe. We will use surface area, volume, and mass as a way to integrate physics and biology.
We have reviewed one of the more important ideas in biology: The evolutionary process. The theory developed by Charles Darwin and Alfred Russel Wallace.
The relationships between surface area, volume, and mass are an integral aspect of the physical properties of all biological systems. A primary law of how organisms relate to their environment has a lot to do with their size, surface area, and mass. Examples are; the limits of certain body types, organs, and cells. The table below shows how the volume of an object increases relative to surface area and length. The table also shows that as the length of a side increases the surface area increases as the square, and the volume increases as the cube of the linear dimension.
| Side Length, Surface Area, and Volume of a Cube | |||
|---|---|---|---|
| Side length (units) |
Surface area : face (square units) |
Surface area : solid (square units) |
Volume (cubic units) |
| 1 | 1 | 6 | 1 |
| 2 | 4 | 24 | 8 |
| 3 | 9 | 54 | 27 |
| 4 | 16 | 96 | 64 |
| 5 | 25 | 150 | 125 |
To extrapolate, if the length increases by a factor of three, the volume will increase 27 times. In biological systems, this becomes important to the physics of how and why natural selection acts on certain characteristics. In very simple terms, it really is all about surface area.
Let us assume there is a mutation in a population of insects that affects body size by a factor of two. If one of these double-sized insects stepped on a scale, how much more would the mutated animal weigh that the non-mutated version? Assume that volume and mass are directly proportional.
The correct answer is D. We know that when a linear dimension of an object doubles, its volume increases by the cube. Since the cube of two is eight, the mutated animal would weigh eight times as much as the non-mutated animal. Decreasing the ratio of surface area to volume by making the object larger, enables living organisms to accrue certain benefits, like being able to maintain a constant body temperature with less calorie investment than smaller organisms. Their larger volume contains more heat and the rate at which they lose heat is proportionate to their relatively smaller surface area. Hence, they are able to keep warm more easily than physically smaller animals. Think of how and why surface area to volume ratios can be integral aspects of the development of organ systems, like our digestive, reproductive, respiratory, and circulatory systems. Think of why there are limits to the sizes of organisms. Could this also be related?
The obvious integration of geology and biology is the remains of organisms that have died, but left clues about their characteristics in behind. Paleontologists have used fossil records to determine how organisms have changed over time through evolution. Paleontologists study fossils and make comparisons to extant organisms (living today).
Fossils are usually formed in sediments whose lowest (oldest) sediments are deposited first with newer layers laid down on top of the older layers. Thus, fossils located in lower layers of rock are considered to be older than fossil layers closer to the surface. The rocks in which fossils are formed (or the fossils themselves) usually contain carbon-14, a slightly radioactive element that decays over time into a more stable isotope, carbon-12. Scientists measure the ratio of these two isotopes to determine how old the rock is where the fossil is found.
Since organisms have limited lifetimes, they must reproduce in order to continue the species. Most animals and plants reproduce sexually. Sexual reproduction is the process in which an offspring develops from the fusion of two gametes (a male’s sperm cell and a female’s egg cell). The gametes contain the characteristics of each parent and when they fuse, they pass certain traits such as size, shape, color, or ability to fight disease onto the offspring. Each offspring resulting from sexual reproduction exhibits a combination of characteristics from both parents. Each gamete is haploid, meaning that the gamete contains half the number of chromosomes as the parent. This division of genetic material to be passed on is mediated by the process of meiosis. During meiosis, the chromosome pairs separate and are distributed to different daughter cells. The resulting gametes have half as many chromosomes as the other cells in the organism. When gametes combine, each contributes half the normal number of chromosomes, thus each offspring receives the normal number of chromosomes — half from each parent.
Some organisms reproduce asexually as well as sexually. Asexual reproduction is the process in which a single organism produces an offspring identical to itself. There are many examples in nature when organisms reproduce asexually. Sometimes environmental factors may be important in determining when an organism reproduces asexually. At other times, when an organism has enough energy, it may reproduce sexually. The ability to reproduce sexually is thought to add variability, and the potential for selection to affect traits can help organisms adapt to their environment faster. This could mean the difference between survival and extinction.
Selective breeding is the process of selecting organisms with desirable traits to be parents of the next generation. As farmers and animal domesticators, humans have excelled at selecting both crop plants and animals (for food and work) through time. Excellent examples are the sweet potato, corn, rice, cows, chickens, and pigs. Two common selective breeding techniques that have been used to mold better plants and animals are inbreeding and hybridization.
Inbreeding involves crossing two individuals that have similar characteristics and/or may be closely related. For example, suppose a male and a female chicken are plump and have grown to maturity very quickly. The male and female chickens are inbred and their offspring will probably have the same desirable traits. Inbred organisms have alleles that are very similar to their parents and are genetically very similar to each other and their parents. Because of this similarity, inbreeding increases the probability that organisms will inherit alleles that lead to genetic disorders such as hip problems common with many breeds of dogs. This is called inbreeding depression and is one of the deleterious aspects of inbreeding.
Hybridization involves crossing two genetically different individuals. The resulting offspring is intended to have the desirable traits of both parents. For example, a farmer may cross corn that produces many kernels per cob with corn that is drought resistant, with the goal of growing drought-resistant corn that also produces numerous kernels per cob. Although this is an excellent idea in theory, there are often complications that prevent getting only the best characteristics from each parent.
Genetic engineering is not necessarily a high-tech laboratory activity. As mentioned above, humans have been genetically engineering both plants and animals for centuries in the process of selective breeding and artificially selecting specific traits they deemed important and beneficial. Today, however, we are getting much better at selecting the exact properties we want plants and animals to have. Scientists have developed other powerful techniques for producing organisms with desirable traits, where genes from one organism are transferred into the DNA of another organism. In addition to producing new plants and animals, genetic engineering can produce medicines and improve food crop quality and yield.
Another interesting and very promising new technology involving genetic engineering is bioremediation. In a non-polluted environment, microorganisms are constantly at work breaking down organic matter. If an organic pollutant such as oil has contaminated this environment, some of the microorganisms would die, while others capable of eating the organic pollution would survive. Bioremediation works by providing these pollution-eating organisms with fertilizer, oxygen, and other conditions that encourage their rapid growth. These organisms would then be able to break down the organic pollutant at a correspondingly faster rate. In fact, bioremediation is often used to help clean up oil spills. Because it harnesses the power of living organisms to help solve environmental problems, it has become extremely valuable as tool for environmental protection.
Bioremediation provides a technique for cleaning up pollution by enhancing the same biodegradation processes that occur in nature. Depending on the site and its contaminants, bioremediation may be safer and less expensive than alternative solutions such as burning or burying the pollutants. It also has the advantage of treating the contamination in place so that large quantities of soil, sediment or water do not have to be dug up or pumped out of the ground for treatment.
The process of selecting organisms with desirable traits to be parents of the next generation is called?
The correct answer is A. Selective Breeding is the process of selecting organisms with desirable traits to be parents of the next generation. Sexual reproduction is the process in which an offspring organism develops when two sex cells (a male’s sperm cell and a female’s egg cell), meiosis is the process of dividing the genetic material of an organism into a haploid gamete, and inbreeding is the crossing two related individuals that have similar characteristics.
Heredity is the passing of physical characteristics from parents to offspring. In the mid-nineteenth century (at the same time as Wallace and Darwin’s theory of evolution), Gregor Mendel wondered why different pea plants had different characteristics, such as how tall they grew or why some had different color seeds. Mendel observed that sometimes pea plants had the same traits as their parents and sometimes they did not. Mendel experimented with over 28,000 pea plants to understand the process of heredity, which ultimately laid the foundation for the study of genetics. Mendel developed a method by which he could cross-pollinate pea plants that had different traits. In one experiment, Mendel crossed purebred tall plants with purebred short plants, and found that all offspring of the first generation were tall — that the shortness trait seemed to disappear.
Today, we use the word gene for the factors that control a trait. We also use the word allele for different forms of a gene. The gene that controls the height in the pea plants, for example, has one allele for tall plants (T) and one allele for short plants (t). Mendel’s discovery of genes and alleles changed scientist’s ideas about heredity. Before Mendel, most people thought the traits of an individual were simply a blend of the parent’s characteristics (i.e., if a tall plant were crossed with a short plant, that the offspring would all have medium height). Mendel’s experiments showed that parent’s traits do not simply blend in the offspring; instead, traits are determined by individual, separate alleles inherited from each parent.
Unfortunately, none of Mendel’s conclusions were realized as such important breakthroughs at the time. Gregor Mendel never knew how important his discoveries would be to a new synthesis of evolutionary theory that was developed well after Wallace and Darwin shared their views with the world. Fortunately for us, however, the modern synthesis of evolutionary theory has withstood the tests of time, innumerable experiments, and was strengthened by the integration of this new knowledge about the units of heritability.