NATURAL SELECTION: The mechanism for change (evolution) within populations. Natural selection happens when organisms with the best variations (genes) survive and pass on these variations to the next generation. Natural selection favors the most fit organisms for the environment.
NEUTRAL: A substance with a pH of 7 is neutral. Water is the only substance with a truly neutral pH.
NEUTRON: The part of an atom with no charge (neutral). The neutron(s) are located in the middle of an atom.
NICHE: The ROLE an organism plays. For example, a mosquito's role is that it is a heterotrophic flying parasite.
NITRATES: A form of nitrogen that can be found in water. They can be introduced into the water supply through sewage and fertilizers. Excess (too many) nitrates can cause eutrophication.
NITROGEN BASE: There are five types of nitrogen bases that are found in nucleic acids (DNA & RNA)
1) Adenine
2) Thymine
3) Guanine
4) Cytosine
5) Uracil
1) Adenine
2) Thymine
3) Guanine
4) Cytosine
5) Uracil
NOBLE GASSES: Group 8A. Nonmetals. 8 valence electrons (a complete outer shell) (except for Helium, which has 2). No reactivity.
NONDISJUNCTION: A condition caused by chromosomes not separating correctly during meiosis & mitosis. This can lead to Trisomy 21.
NON-POLAR: Having no charge. Example: lipids
NUCLEAR ENVELOPE: The membrane that surrounds the nucleus. It is also called the nuclear membrane.
NUCLEAR MEMBRANE: See nuclear envelope
NUCLEIC ACIDS: A large molecule, or polymer, made of nucleotide monomers. Nucleic acids are used for heredity. Examples of nucleic acids are DNA and RNA.
NUCLEOTIDE: The building block (monomer) of nucleic acids (DNA and RNA) Nucleotides are composed of a phosphate, sugar, and a nitrogen base.
NUCLEUS: The nucleus is like the brain of the cell. It controls all the cell's activities. DNA is found in the nucleus.