Across
- 6. a cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter.
- 9. a contracting mass of gas that represents an early stage in the formation of a star, before nucleosynthesis has begun.
- 11. the process whereby organisms better adapted to their environment tend to survive and produce more offspring. The theory of its action was first fully expounded by Charles Darwin and is now believed to be the main process that brings about evolution.
- 13. an organism consisting of a cell or cells in which the genetic material is DNA in the form of chromosomes contained within a distinct nucleus. Eukaryotes include all living organisms other than the eubacteria and archaebacteria.
- 15. deoxyribonucleic acid, a self-replicating material present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information.
Down
- 1. a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
- 2. resulting from or showing the effect of the mutation.
- 3. a supernova that is classified as having hydrogen lines in its spectra that are made by the explosion of a very large star.
- 4. an explosion that results from the collapse of a white dwarf.
- 5. any of a class of nitrogenous organic compounds that consist of large molecules composed of one or more long chains of amino acids and are an essential part of all living organisms, especially as structural components of body tissues such as muscle, hair, collagen, etc., and as enzymes and antibodies.
- 7. a planet that orbits a star outside the solar system.
- 8. a microscopic single-celled organism that has neither a distinct nucleus with a membrane nor other specialized organelles. Prokaryotes include the bacteria and cyanobacteria.
- 10. a simple organic compound containing both a carboxyl (—COOH) and an amino (—NH2) group.
- 12. a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.
- 14. ribonucleic acid, a nucleic acid present in all living cells. Its principal role is to act as a messenger carrying instructions from DNA for controlling the synthesis of proteins, although in some viruses RNA rather than DNA carries the genetic information.