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Across 2. Chemistry. a widely distributed element that forms organic compounds in combination with hydrogen, oxygen, etc., and that occurs in a pure state as diamond and graphite, and in an impure state as charcoal. 5. chemistry , the substance that is added or pollutes the li$uid 6. biology .a plant having its seeds enclosed in an ovary 7. Chemistry. a usually inactive substance that acts as a vehicle for an active substance. 9. biology,the basic physical unit of heredity 10. Biology. a cell, cell product, or organism that is genetically identical to the unit or individual from which it was derived. 13. physics.the meeting of particles or of bodies in which each exerts a force upon the other, causing the exchange of energy or momentum. 14. Chemistry. the reciprocal action of chemical agents upon each other; chemical change. 17. physics.a ray of light 18. physics.the negative terminal of a voltaic cell or battery. 19. physics.a sound heard again near its source after being reflected.

Down 1. Mathematics.the greatest lower bound of two elements in a lattice. 3. Mathematics. nothing expressions, relations, etc. 4. Physics. mass per unit volume. 8. Biochemistry. a purine base, C 5 H 5 N 5 , one of the fundamental components of nucleic acids, as DNA, in which it forms a base pair with thymine, and RNA, in which it pairs with uracil. 11. water containing naturally an unusual amount of calcium carbonate or calcium sulfate. 12. Cell Biology. part of the process of gamete formation, consisting of chromosome conjugation and two cell divisions, in the course of which the diploid chromosome number becomes reduced to the haploid. 13. a quantity assumed to be unchanged throughout a given discussion. 15. biology.the transparent anterior part of the external coat of the eye covering the iris and the pupil and continuous with the sclera. 16. biologyan analogous organ in certain invertebrates, as arachnids or terrestrial gastropods.