The Nature of Life

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• 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.

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• 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.

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• 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.

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• 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).

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• 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.
  H2, CH4).
• - Ionic bonds form when electrons are
  completely removed removed from one atom (ve
  ion) and transferred to another atom (-ve ion)
  (e.g. NaCl -----gt 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.

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• 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 ------------------gt H2O 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.

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• 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.

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• 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

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• Four important classes of polymers
• 1. Carbohydrates molecules composed of C, H,
  O in a ratio (CH2O)n.
• Examples - Monosaccharides (glucose,
  fructose)
• - Disacchardis (sucrose)
• - Polysaccharides (starch, cellulose)

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2. Lipids fatty or oily substances that are
insoluble in water - Fats Oils saturated,
unsaturated - Waxes - Phospholipids
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3. Proteins, Polypeptides, and Amino Acids -
proteins are composed of amino acids - amino
acids 20 essential amino acids, each contains
an amino group NH2, 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

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• 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

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