18. The Second Law of Biology: The Law of Equivalence

all living organisms consist of membrane-encased cells. Enveloping membranes allow physical separation between the living and the non-living worlds. Viruses, plasmids, transposons, prions, and other selfish, biological entities are not alive. They cannot “self” reproduce. They are dependent on a living cell for this purpose. By definition, they therefore, are not alive. A corollary of the Second Law is that the cell is the only structure that can grow and divide independently of another life form. A second corollary of the Second Law is that all life is programmed by genetic instructions. Genetic instructions are required for cell division, morphogenesis, and differentiation. From single-celled prokaryotic organisms to normal or cancerous tissues in multicellular animals and plants,

genetic instructions are required for the maintenance of life.

19. The Third Law of Biology: The Law of Diversity

all living organisms arose in an evolutionary process. This law correctly predicts the relatedness of all living organisms on Earth. It explains all of their programmed similarities and differences. Natural selection occurs at organismal (phenotypic) and molecular (genotypic) levels. Organisms can live, reproduce, and die. If they die without reproducing, their genes are usually removed from the gene pool, although exceptions exist. At the molecular level, genes and their encoding proteins can evolve “selfishly,” and these can combine with other selfish genes to form selfish operons, genetic units and functional parasitic elements such as viruses.

20. The Fourth Law of Biology: The Law of Reproduction

Reproduction  is the biological process by which new individual organisms – "offspring" – are produced from their "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. There are two forms of reproduction: asexual and sexual.

21. Life can be studied as a hierarchical systems

The structure of living organisms including those of entire populations and ecosystems is organized in a hierarchical fashion that allows a systematic exploration of the question ‘What is life?’. In the biological sciences, the following hierarchical levels are recognized:

Level- Ecosystem- Community- Population- Organism- Organ system- Organ- Tissue- Cell- Macromolecule - Molecule

22. The chemistry of life

Biochemistry is the study of the basic molecules used by living things. Nucleic acids, proteins, lipids (fats), and carbohydrates all perform specific functions within and between cells that allow organisms to survive. Biochemists seek to understand how these substances are formed, what purposes they serve, and how they might be used elsewhere to make medicines or other products.

23. Mendelian genetics and patterns of inheritance

Gregor Mendel crossed various pure lines of garden peas and, by following their hybrid progeny, observed that traits are inherited as alternate states of independent units of inheritance or genes (which Mendel called “factors”), and that these units come in pairs. Each unit of inheritance can have alternate states (alleles) that segregate at meiosis, with each gamete receiving only one allele (the principle of segregation, Mendel's first law); different alleles assort independently in the gametes (the principle of independent assortment, Mendel's second law). Different alleles can exert different phenotypic effects; broadly speaking, most genes are either dominant or recessive.