Chapter 2 The Nature of Life Attributes of Living Organisms Composition and Structure: cell is the basic unit of life; prokarotes; eukaryotes; cytoplasm; DNA; plant cells have cell wall. Growth: increase in mass and volume and results from the production of new cells. Reproduction Response to Stimuli: Plants respond to wounding by forming a callose first then forms callus. Plants respond in different ways to environmental stimuli such heat, salinity, drought and flooding. Metabolism: All the biochemical reactions taking place in a living body. Cells have primary and secondary metabolism.

Movement: cytoplasm movement is known as cyclosis or cytoplasmic streaming. Complexity of Organization: Cells of living organisms are made of biomolecules that are arranged in a variety of ways that differs from one species to another. This organization is genetically determined.

Chemical and Physical Basis of Life A. The Elements: Units of Matter Matter is “stuff of the universe” Matter exists in three forms: solid, liquid and gas Matter has three characteristics: it occupies space, it has mass and is composed of elements (92 natural and 19 artificial) The atom is the smallest subdivision of an element. It is composed of a nucleus (protons + neutrons) and electrons. Atomic number = number of protons Atomic mass = number of protons and neurons Electrons exist in atomic orbitals around the nucleus Isotopes exist for atoms when the number of neutrons exceed the number of protons in the nucleus. The atom becomes unstable and splits to smaller parts releasing radioactivity.

B. Molecules: Combinations of Elements Compound is formed when two or more atoms unite in a definite ratio by chemical bonds. Molecule is the smallest independently existing particle of a compound or element. In living cells, chemical reactions between molecules are controlled by organic catalysts called enzymes. A water molecule has one side that has a slightly negative charge while the other side has a slightly positive charge (Polar Molecule). Due to its polarity, water molecules form a cohesive network and leads to the capillary movement of water in fine tubes (xylem of plants). The attraction between the hydrogen atoms of water and other negatively charged molecules causes adhesion (-ve cellulose in xylem tubes of plants).

C. Bonds and Ions Electrons can be lost, gained or shared between different atoms, forming bonds, so that the outermost orbital contains 8 electrons. Three type of chemical bonds are important in living organisms - Covalent bonds form when two atoms share a pair of electrons between their outermost orbits. Sometimes more than two atoms are held together by covalent bonds. Every pair of electrons shared is a single covalent bond (e.g. H 2, CH 4 ). - Ionic bonds form when electrons are completely removed removed from one atom (+ve ion) and transferred to another atom (-ve ion) (e.g. NaCl -----> Na + + Cl - ). - Hydrogen bonds form due to the attraction of a positively charged hydrogen atom in a polar molecule and a negatively charged atom (such as O or N) in another polar molecule. Hydrogen bonds are very abundant in biomolecules (DNA, proteins) and only have 7%-10% of the energy in a covalent bond.

D. Acids, Bases, and Salts Acids: release positively hydrogen (H + ) ions when dissolved in water. Bases: release negatively charged hydroxyl (OH - ) ions when dissolved in water. Salts: when an acid and a base are mixed, the H + ions of the acid bond with the OH - ions of the base forming water and the remaining ions bond together forming a salt. HCl + NaOH > H 2 O + NaCl pH is the hydrogen (H + ) ions concentration of solution (ranges from 0 -14). Pure water has a pH of 7.0 Acids have a pH below 7 and alkalines have a pH above 7.

E. Energy: definition: is the ability to do work. First Law of Thermodynamics: Energy is constant; it cannot be increased or diminished, but it can be converted from one form to another. - Energy has different forms: chemical, electrical, heat and light. Second Law of Thermodynamic: When energy is converted from one form to another form, the amount of useful energy remaining is always less than before. - Energy in motion is kinetic energy - Energy is storage form is potential energy Electrons have varying amounts of potential energy. The closer to the nucleus the electron is the less potential energy it carries.

E. Chemical components of Protoplasm: Organic molecules contain C while inorganic molecules no C. Macromolecules - biological macromolecules are polymers - polymers are composed of identical, smaller molecules called monomers - bonding of molecules occurs by dehydration synthesis - polymers broken down into monomers by reverse reaction called hydrolysis

Four important classes of polymers 1. Carbohydrates: molecules composed of C, H, & O in a ratio (CH 2 O) n. Examples: - Monosaccharides (glucose, fructose) -Disacchardis (sucrose) - Polysaccharides (starch, cellulose)

2. Lipids: fatty or oily substances that are insoluble in water - Fats & Oils: saturated, unsaturated - Waxes - Phospholipids

3. Proteins, Polypeptides, and Amino Acids - proteins are composed of amino acids - amino acids: 20 essential amino acids, each contains an amino group NH 2, carboxyl group COOH, and a side chain R which is different for each of the twenty different essential amino acids. - polypeptides are two or more amino acids bonded together by a peptide bond - structural organization of peptides (proteins) - primary - secondary - tertiary - quaternary

Enzymes: - are large complex proteins - a special type of RNA can function as an enzyme (Ribozyme) - all enzymes are organic catalysts that have lower energy of activation - enzyme names end in -ase, e.g. maltase

4. Nucleic Acids: - are complex polymers consisting of repeating subunits called nucleotides - Types - DNA (deoxyribonucleic acid) - RNA (ribonucleic acid)