Chapter Summary

1. Activities of living organisms originate in cells. Structure and growth are among the attributes of living organisms. Growth has been described as an increase in volume; it results primarily from the production of new cells. Variations in form may be inherited or result from response to the environment.

2. Reproduction involves offspring that are always similar in form to their parents; if reproduction ceases, the organism becomes extinct. Plants generally respond to stimuli more slowly and in a different fashion from animals.

3. All living organisms exhibit metabolic activities, including respiration, digestion, assimilation, production of new cytoplasm, and, in green organisms, photosynthesis; they also all exhibit movement. Cyclosis is the streaming motion of cytoplasm within living cells. Living organisms have a much more complex structure than nonliving objects and are adapted to their individual environments.

4. The basic "stuff of the universe" is called matter, which occurs in solid, liquid, or gaseous form. It is composed of elements, of which the smallest stable subdivision is an atom. Atomic nuclei contain positively charged protons and uncharged neutrons; the nuclei are surrounded by much larger orbitals of whirling, negatively charged electrons. Isotopes are forms of elements that have slight variations in the number of neutrons in their atoms.

5. The combining capacities of atoms or ions are called valence. Atoms can bond to other atoms, and those of most elements do not exist independently; compounds are substances composed of two or more elements combined in a definite ratio by chemical bonds; molecules are the smallest independently existing particles. In a covalent bond, pairs of electrons link two or more atomic nuclei; nitrogen and/or oxygen atoms of one molecule may form weak hydrogen bonds with hydrogen atoms of other molecules. If a molecule loses or gains electrons, it becomes an ion, which may form an ionic bond with another ion.

6. Water molecules are polar because they are asymmetrical in shape. Water molecules cohere to each other and adhere to other molecules.

7. Acids release positively charged hydrogen ions when dissolved in water. Bases release negatively charged hydroxyl ions when dissolved in water. The pH scale is used to measure degrees of acidity or alkalinity. Salts and water are formed when acids and bases are mixed.

8. Energy can be defined as "ability to produce a change in motion or matter" or as "ability to do work." Its forms include chemical, electrical, heat, light, kinetic, and potential. The farther away from the nucleus an electron is, the greater the amount of energy required to keep it there.

9. Cells are composed of carbon, hydrogen, oxygen, and nitrogen, with a little phosphorus and potassium, plus small amounts of other elements. A plant may convert the simple molecules or ions it recycles or absorbs from the soil to very large, complex molecules. Organic molecules are usually large polymers that have a "backbone" of carbon atoms.

10. Carbohydrates contain carbon, hydrogen, and oxygen in a ratio of 1C:2H:1O. Carbohydrates occur as monosaccharides (simple sugars) and disaccharides (two simple sugars joined together). Polysaccharides may consist of many simple sugars condensed together; others are more complex. Simple sugars, when they are attached to one another, each give up a molecule of water, forming starch. Hydrolysis involves restoring a water molecule to each simple sugar when starch is broken down during digestion.

11. Lipids (e.g., fats, oils, and waxes), which are insoluble in water, consist of a unit of glycerol or other alcohol with three fatty acids attached. They contain carbon, hydrogen, and oxygen, with proportionately much less oxygen than is found in carbohydrates. Saturated fats have hydrogen atoms attached to every available attachment point of their carbon atoms; if there are very few places for hydrogen atoms to attach, the fat is said to be polyunsaturated. Phospholipids have a phosphate group replacing one fatty acid.

12. Proteins are usually large molecules composed of subunits called amino acids. Each amino acid has an amino group (-NH2) and a carboxyl group (-COOH); these groups bond amino acids together, forming polypeptide chains; the bonds are called peptide bonds. Enzymes are large protein molecules that function as organic catalysts. Their names end in -ase. Some have important industrial uses.

13. There are two nucleic acids (DNA and RNA) associated primarily with cell nuclei. DNA and RNA molecules consist of chains of nucleotides. Four kinds of nucleotides, each with a unique nitrogenous base, occur in DNA. Helical coils of DNA contain coded information determining the nature and proportions of substances in cells and the ultimate form and structure of the organism. RNA has a different sugar and nucleotide.