Organisms and biological classification

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Across
  1. 3. a protein that protects cells from a virus
  2. 4. anything that causes a reaction in a organism
  3. 6. there are _ levels in the classification hierarchy
  4. 7. a plant cell, like a seed, that can make a new plant
Down
  1. 1. invertebrates that have a hard outer shell
  2. 2. the study of naming and classifying organisms
  3. 3. the ability to resist infection again
  4. 5. strand of DNA enclosed in a protein coat