The biology puzzle.

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Across
  1. 6. Blood to heart
  2. 7. attack Damage of coronary arteries
  3. 9. molecules that have the same molecular formula but different structures
  4. 10. bond Bond formed when one or more electrons are transferred from one atom to another
  5. 12. Atom that has a positive or negative charge
  6. 13. Negatively charged particle; located outside the atomic nucleus
  7. 14. the fact or quality of being diverse; difference
  8. 15. a chemical subunit that serves as a building block of a polymer
  9. 17. the differences within a species
  10. 20. a chain of amino acids linked by peptide bonds
  11. 21. helix the form assumed by DNA in living cells, referring to its two adjacent polynucleotide strands wound into a spiral shape
  12. 24. Damage of arteries in brains
  13. 25. Substance consisting entirely of one type of atom
Down
  1. 1. the condition of the constant state of being of organism on earth
  2. 2. ability of an organism to survive and reproduce in its environment
  3. 3. Substance formed by the chemical combination of two or more elements in definite proportions
  4. 4. Smallest unit of most compounds
  5. 5. Basic unit of matter
  6. 8. the study of embryos
  7. 9. Tissue swelling
  8. 11. disappearance of a species from all parts of its geographical range
  9. 16. organism in its early stage of development
  10. 18. steroids synthetic variants of testosterone
  11. 19. formation of new species
  12. 22. Cells Multi-potent cells that can replenish blood cell populations
  13. 23. pool is the set of all genes, or genetic information, in any population, usually of a particular species.