RADIAL SYMMETRY: An animal's body plan that can be divided along any plane, though a central axis, into roughly equal halves.
REACTANT: What you feed into a chemical reaction
RECESSIVE ALLELE: Recessive alleles are always represented by a lowercase letter. Recessive alleles are weaker than dominant alleles, and can only be expressed when two recessive alleles are paired together.
RECOMBINANT DNA: DNA made by combining DNA fragments from different organisms.
REDI, Francesco: The scientist who discovered the theory of biogenesis, which says that life can only come from living things. He did this through his meat and maggot experiment.
REFLEX: A simple, automatic response in an animal that involves no conscious control.
RELATIVE AGE: Whether the rock or fossil is older or younger than something else
RELATIVE DATING: When scientists compare the age of a rock or fossil to something else.
RELIABLE: An experiment is reliable if you (the scientist) get the same result each time you do the experiment.
REPLICATION: Describes DNA making a copy of itself. It must do this before a cell can divide.
REPRODUCTION: Making offspring (babies). This is one of the five characteristics of life.
RESERVOIRS: Areas (usually lakes) where water can be stored until it is treated and distributed for use
RESOLUTION: How clear an image is. The resolution of a microscope is changed using the course and fine adjustment knobs
RESPIRATION: See cellular respiration
RESTRICTION ENZYME: DNA-cutting enzymes. DNA scissors
RIBONUCLEIC ACID: See RNA
RIBOSE: The sugar (carbohydrate) found in RNA.
RIBOSOME: The place where proteins are made in the cell. The site of protein synthesis.
RNA (RIBONUCLEIC ACID): RNA is a nucleic acid that is composed of nucleotides. RNA contains four types of nitrogen bases called adenine, uracil, guanine and cytosine. RNA contains a sugar called ribose. RNA is the molecule that carries DNA's instructions from the nucleus to the ribosome (mRNA), and then helps build proteins at the ribosome (tRNA) in a process called protein synthesis.
rRNA (RIBOSOMAL RNA): RNA that makes up the ribosome
RUN-OFF: Water that does not seep (soak) into the ground, but flows over the land