Radial and bilateral symmetry
Radicle
Radioactive dating
Radula
Reabsorbtion
Receptor
Recessive
Recombinant DNA
Red blood cell
Reflex
Reflex arc
Reforestation
Rejection
Relative dating
Replication
Repressor
Reproductive isolation
Reproductive system
Respiration
Respiratory system
Resting potential
Restriction enzyme
Retrovirus
Rheumatic fever
Rheumatoid arthritis
Rhizoid
Rhizome
Root cap
Roundworm
Rumen