Monoculture, 155
Monohybrid cross, 317
Monomers, 46
Monophyletic group, 516
Montreal Protocol, 175
Mountain ranges, 116
Mouthparts, 785–786
Mullis, Kary, 423
Multicellular organisms, 527–528
Multiple alleles, 320
Multipotent cells, 295
Muscle contraction, 930–932
Muscle fibers, 929
Muscular systems
Museum guide, 559
Mutagens, 375
Mutant, 420
Mutualistic symbionts, 783
Mycelium, 619
Mycorrhizae, 624–625
Myelin sheath, 897
Myocardium, 949
Myofibrils, 930
Myoglobin, 933
Myosin, 930
Nails, human, 937
National Institute of Drug Abuse (NIDA), 905
Natural resources. See Resources, natural
Natural selection, 460–464. See also Evolution
Navigation, 813
Nematodes, 755
Neogene Period, 563
Nephridia, 797
Nephrons, 884
Nephrostomes, 797
Nerve impulses, 897–900
Nerve nets, 810
Nerves, 897
Nervous system, human, 896–908
Nervous tissue, 863
Neuromuscular junction, 931
Neurotransmitters, 900
Neurulation, 997
Neutrons, 34–35
Niches, 99–100
Nicotinamide adenine dinucleotide (NAD+), 255
Nicotinamide adenine dinucleotide phosphate (NADP+), 232–233, 235–237
Nitrogen cycle, 84
Nitrogenous bases, 344–345
Nitrogenous waste, 794–795
Nodes of plant stem, 675
Nondisjunction, 401
Nonpoint source pollution, 160
Nonrenewable resources, 157
Nonsteroid hormones, 980
Norepinephrine, 983
Northwestern coniferous forests, 114
Nose, 963
Notochord, 731
Nucleolus, 197
Nutrient cycles, 82–86
Nymphs, 823
Obesity, 874
Observation
Occipital lobe, 903
Occupation of organism, 100
Oceans, 120–121. See also Aquatic ecosystems
Oken, Lorenz, 191
Omnivores, 71
1000 Genomes Project, 409
On the Origin of Species, 460
Oomycetes, 608
Open circulatory systems, 791
Operant conditioning, 843
Operator (O), 378
Operon, 377–378
Opposable thumb, 767
Optic lobes, 811
Optic nerve, 913
Order, 513