Dichotomous Keys in Taxonomy

Animals

• Multicellular organisms that can be divided into two main groups: vertebrates and invertebrates

Vertebrates

• Phylum Chordata
• Include mammals, birds, reptiles, amphibians, and fish
• Have a backbone

Invertebrates

• No backbone
• Include many groups, such as arthropods, insects, crustaceans, arachnids, and myriapods

Mammals

• Habitat: land and water
• Physical features: hair or fur for insulation, constant internal body temperature
• Fertilization: internal, with eggs fertilized by sperm inside the female's body
• Give birth to live young, which develop inside the mother's body supported by a placenta
• Young are fed on milk by mammary glands
• Some species display extensive parental behavior

Birds

• Habitat: almost every environment and across every continent
• Physical features: feathers, wings, well-developed circulatory system, modified bones
• Fertilization: internal, with eggs fertilized by sperm inside the female's body
• Lay hard-shelled eggs, which develop outside the parent's body
• Significant parental behavior to protect the eggs and young

Reptiles

• Habitat: marine, freshwater, and dry desserts
• Physical features: thick, dry scaly skin, varies with environmental temperature
• Fertilization: internal, with eggs fertilized by sperm inside the female's body
• Lay eggs, which are protected by leathery shells
• Young develop outside the parent's body

Amphibians

• Habitat: spend part of their life in water and part on land
• Physical features: two pairs of legs, gills and tails in tadpoles
• Body temperature: cold-blooded, relies on the environment to maintain body temperature
• Fertilization: external, with males shedding sperm over eggs released by the female
• Young develop from eggs

Fish

• Habitat: marine, freshwater, and river water bodies
• Physical features: streamlined body, fins and tail, swim bladder, scales, operculum
• Body temperature: cold-blooded, relies on the environment to maintain body temperature
• Fertilization: external, with males shedding sperm over eggs released by the female
• Young hatch from eggs and fend for themselves

Ferns

• Physical features: broad, divided leaves called fronds
• Grow as clumps of fronds from the ground
• Some species have a thick trunk
• Method of reproduction: release spores into the air from spore cases under the leaves

Flowering Plants

• Physical features: central stem, side branches, leaves, roots
• Method of reproduction: depends on flowers, male gametes in pollen grain, female gamete in ovule
• Fertilization results in seeds, which are produced in fruits that aid in dispersal or protection

Monocotyledons vs Dicotyledons

• Monocotyledons: single cotyledon, long strap-leaves, parallel veins
• Dicotyledons: two cotyledons, broad leaves, branching veins

Fungi

• Physical features: single-celled or multicelled, hyphae, no chlorophyll
• Obtain nutrients through saprotrophic nutrition, secreting digestive enzymes outside the cells

Prokaryotes

• Physical features: single-celled, microscopic, cells smaller than plants and animals
• No nucleus, genetic material lies free in the cytoplasm
• Examples: bacteria like Salmonella and Mycobacterium

Insects

• Physical features: three body regions, six jointed legs, pair of wings, exoskeleton made of chitin
• Head has sense organs: compound eyes, antennae, chemical detectors
• Some insects have complex social structure with intricate behavior patterns

Protoctists

• Physical features: single-celled, microscopic, eukaryotes
• Have features of animal and plant cells
• Examples: various single-celled organisms