Across
- 4. the part of a cell where respiration releases energy
- 9. a type of variation with distinct categories such as blood group
- 11. a nerve cell that carries messages as electrical signals
- 12. the building block of DNA made of a sugar phosphate and base
- 13. a change in the environment that causes a response
- 16. differences between individuals of the same species
- 18. an enzyme filled part at the tip of a sperm that helps it break into an egg
Down
- 1. a small cell structure where proteins are made
- 2. a fatty layer around an axon that speeds up nerve impulses
- 3. a weak bond that holds the two DNA strands together between bases
- 5. the part of a microscope that magnifies the specimen
- 6. a cell with half the usual number of chromosomes such as a sperm or egg
- 7. a long fibre that carries electrical impulses away from the neurone cell body
- 8. the twisted ladder shape of the DNA molecule
- 10. a change in the DNA sequence that can create new alleles
- 14. how many times larger an image is compared to the real object
- 15. the scientist who proposed the theory of evolution by natural selection
- 17. the preserved remains or traces of ancient organisms found in rock