Taxonomy and Evolution

The sequence of bases along the DNA molecule may be compared between species. If the base sequences are similar then the species are closely related. For example, there is a 1.2 percent difference between the DNA of humans and that of chimpanzees, and a 1.4 percent differences between humans and gorillas, making the chimpanzee a closer relative to humans than the gorilla. Humans and orangutans share 97.6 percent of their DNA, but this does not match the 98.8 percent shared by chimpanzee and human.

Evolution is the process of gradual change by which the characteristics of living organization are altered from generation to generation the changes in given organism eventually become so great that it can no longer be regarded as the same species. Fossil records show that such replacement of one species by a more advanced one has been taking place for many millions of years, and that most species have survived for only about ten million years. The idea that living things have all evolved from simple ancestors was first put forward by the ancient Greeks, but until Charles Darwin and Alfred Russel Wallace published their work on natural selection no one could give satisfactory explanation.

Darwin and Wallace noticed that plants and animals produce large numbers of offspring and that there is a struggle for existence among the progeny- competition to find food and avoid predators as well as a struggle against adverse environmental factors. They also realized that the progeny vary, and reasoned that only those most suited to their surroundings would survive. The progressive improvement shown throughout evolution is thus brought about by natural selection of the best in each generation.

Human Chromosomes and DNA Fingerprinting

Every human body cell, except for sperm and egg cells, contain 46 chromosomes.  These contain around 100000 genes that between them determine all of an individual’s characteristics, from hair colour to potential height. Sperm and egg cells each contain 23 chromosomes. When they fuse during fertilization, the chromosome number is restored to 46, or 23 pairs of chromosomes. Thus everybody cell nucleus contains 23 paternal chromosomes paired up with 23 maternal chromosomes. 

 DNA fingerprinting, also known as genetic finger printing this process is used to reveal the genetic identity of an individual. The arrangement of bases within his or her DNA is unique to that individual, just as his or her fingerprints are; the only exceptions are identical twins, who share the same DNA. A tissue sample, usually of blood, is taken from the person and DNA molecules are then cut into small pieces and separated. By adding a radioactive probe, and using an X-ray film, a banded strip is produced, unique to its owner. The more closely two people are related, the greater the similarity between the pattern of bands. Genetic fingerprinting was used to confirm the human remains found in Russia were those of the Romanovs, the Russian royal family, by comparing DNA fingerprints from the remains with those of the Romanovs’  living relatives. Genetic fingerprinting is similarly used to prove paternity. In criminal cases such as rape, DNA extracted from the perpetrator’s semen or other body fluids can be used to confirm his identity.

DNA

Deoxyribonucleic acid or DNA is the nucleic acid, containing the sugar deoxyribose, which forms the materials of which the chromosomes and genes of organisms are composed. It carries the blueprint for construction of all the cells of an organism and all instructions that control their activities, and which enables these instructions to be passed on from one generation to the next. DNA is found in all living organisms except certain viruses which contain RNA (ribonucleic acid), a closely related nucleic acid.

In eukaryotic ells- which make up the majority of organisms- DNA is found in the membrane bound sphere called the nucleus. Here, it forms chromosomes, normally long threads (but in cells that are about to divide chromosomes form separate X shapes as they duplicate themselves). Within the chromosomes DNA is tightly packed in coils and super coils. Once unraveled, DNA can be seen to consist of two long strands wound around each other in spiral structure or double helix, like a twisted ladder. The rungs of this ladder are made up of different bases. A rung is formed when adenine from one DNA strand binds with thymine on the other. The arrangement of bases along the double helix constitutes the genetic code, which controls production of the protein molecules that facilitate all cell activities, including metabolism and construction.

Classification of Plants and Animals

Every different kind of organism called a species, and closely related species are grouped together into genera (the singular of with is genus). Each species has a two part scientific name, composed of its generic name and its species name. For example, the house fly, which belongs to the genus Musca, is scientifically known as Musca domestica. Where a number of members of the genus Musca are mentioned, later examples may be abbreviated to, for instance, M. domestica. By convention the genus name begins with a capital letter.

Related genera are grouped into families, related families are grouped into Orders, Orders are grouped into classes, and classes are grouped into phyla. The latter are the largest divisions of each kingdom. Family names in the animal kingdom always end in  …idea, while  plant families always end in  ..aceae.

Viruses

Viruses are on the borderline of living and non living things and do not fit into the five kingdoms of the living world. They are much smaller than bacteria and each consists simply of a lump of DNA inside a protein envelope.

There are many different kinds of viruses and they all produce disease in plants and animals by invading living cells and interfering with their normal functions. The viruses can be converted to a crystalline form, in which they can survive for a very long time, but they cannot grow or reproduce on their own. They need the help of the host cells for this. The virus DNA takes control of the cell nucleus and instructs it to make more virus mater. The new virus particles then escape from the host cell and rapidly infect other cells. Human diseases caused by viruses include the common cold, measles, polio and aids

Animal and Plant Cells

All living things are made of cells and part from those of the bacteria the cells all have much the same internal structure, although their external appearance varies enormously according to the jobs they have to do. A variety of animal cells are shown on the right below. There are several hundred different kinds of cells in the human body, and the total number of cells may exceed ten trillion. Most of them are obviously extremely small, and it is only recently that powerful microscopes have revealed their detailed structure. The nucleus the most conspicuous of the internal structures or organelles is the cell’s control center. It is bounded by the nuclear membrane and it contains the chromosomes that carry all the hereditary material. The nucleus produces the ribosomes, which themselves are responsible for the formation of the cell’s proteins. This takes place on the surface of the endoplasmic reticulum, which is a network of flattened and connected to the nuclear membrane and spreading throughout the cell.

The Kingdom Protoctista

This kingdom contains all single celled organisms in which there is a distinct nucleus enclosed in a membrane, and in which there are also other discrete organelles, such as mitochondria and endoplasmic reticula. It includes all those microscopic organisms, such as amoeba and paramecium that were once regarded as single celled animals and placed in the phylum Protozoa. It also includes the slime moulds. The large sea weeds that is also included in the Protoctista because, although they are multi cellular organisms, their cells are all alike and not easily differentiable from single celled algae.

The sea weeds include species with fronds many meters long and made up of millions of cells, but they are included with the single celled organisms in the Protoctita because their cells are all more or less alike. Some biologists regard the seaweeds as assemblages of cells rather than true multi cellular organisms. There are three major groups or phyla- the green sea weeds (Chlorophyta), the brown sea weeds (phaeophyta) and the red sea weeds (Rhodophyta). All contains chlorophyll and make their food by photosynthesis, but the brown and red seaweeds contain other pigments that mask the chlorophyll. They have a variety of reproductive strategies.