Big Idea 1

2. Adaptation of an Animal: An adaptation of an animal is a change in an animal's structure or function in order to promote its survival and reproduction. This Ctenosaura defensor (club-tailed iguana) is armored with a spiky tail so that it can defend itself against predators. 

3. Adaptation of a Plant: An adaptation of a plant is an alteration in a plant's structure or function such that it can better survive, reproduce, and thrive in its environment. The seeds of this Sago Palm are extremely poisonous to animals if ingested because they contain high levels of the toxin cycasin, which can lead to liver failure. This adaptation promotes the success of the plant's reproduction. 

4. Amniotic Egg: An amniotic egg is a terrestrially adapted, watertight egg that consists of a hard shell that protects it from the environment, a food source (yolk), and a series of membranes that contributes to its self-sufficiency. Amniotic eggs are characteristic of all modern reptiles, birds, and oviparous mammals, and these three classes are called amniotes. A chicken egg is thus an amniotic egg because it consists of a shell for protection and to prevent drying, a yolk sac that provides food for the embryo, a chorion that allows for the exchange of gases but retains water, an amnion that encases the embryo within which there is amniotic fluid, and an allantois that functions in waste removal. 

6. Angiosperm: An angiosperm, or flowering plant, is a plant in which the ovules are enclosed within a leaflike organ called a carpel at the time of pollination. Because this camellia plant produces flowers and encased ovules, it is an angiosperm. 

8. Arachnid: An arachnid is an invertebrate and type of arthropod with four pairs of segmented legs, a body formed of two parts, and no antennae. They are distinguished from insects, which only possess six legs. This large and hairy tarantula, of which about nine hundred species have been discovered, is an arachnid because it is a spider, one of the many types of organisms classified as arachnids.

10. Arthropod: Arthropods, including all crustaceans, insects, and spiders, are invertebrates that have exoskeletons, segmentation, and jointed appendages. These mealworms are the larval forms of mealworm beetles, which are insects in the phylum Arthropoda. The adult form of these mealworms exhibits a segmented body, jointed appendages, and an exoskeleton. 

11. Artificial Selection: Artificial selection refers to human interference in the the breeding of plants and animals in order to produce offspring with desirable traits. My dog is a "maltichon," or a cross between a Maltese and a Bichon Frise. He has the smooth, white hair of a Maltese and the kind, playful temperament of a Bichon Frise. He is a result of artificial selection.

12. Bilateral Symmetry: Bilateral symmetry is the equal arrangement of an organism on either side of a plane, or central line. This leaf from a geranium plant exhibits bilateral symmetry because the left side of the leaf can be exactly folded onto the ride side of the leaf.

21. Gastropod: Gastropods are mollusks, such as snails or slugs, characteristic of a coiled shell or none at all, a ventral muscular foot for movement, and a distinct head bearing sensory organs. Many thousands of species of gastropods, ranging from ones that live in terrestrial environments to others that live in marine habitats, have been discovered. This sea snail is in the class Gastropoda because it possesses a univalve shell, sensory organs, and a foot for locomotion.

22. Genetic Variation: Genetic variation refers to dissimilarities in alleles of genes (and thus phenotypes) among individuals of a population. This variation is brought about by the changes in the chemical structure of genes in a population overtime, making the descendants differ from their ancestors. Four different genes and many different alleles contribute to the determination of eyes color within the human population, giving rise to much genetic variation. 

24. Gymnosperm Cone: Gymnosperms, as opposed to angiosperms, are plants that produce unenclosed ovules not within an ovary. The ovules of gymnosperms often develop on modified leaves known as cones, such as the one from a pine tree pictured above. These larger female cones, possessing the unenclosed ovules, grow towards the lower end of a gymnosperm, while the male pollen cones are smaller and grow closer to the top of the gymnosperm. This makes it easier for the pollen to drift down and fertilize the ovules on the female cones. 

25. Gymnosperm Leaf: Gymnosperms are vascular plants that produce unenclosed, or "naked," ovules. Christmas trees, like the one pictured, are typically a type of gymnosperm known as a conifer. More specifically, this gymnosperm is a fir tree. The tree's leaves, which are simple and needlelike, are often modified into cones for reproduction purposes. Moreover, as compared to the leaves of deciduous plants, most gymnosperms have leaves that are retained for more than one growing season.

26. Homologous Structures: Homologous structures are structures in different species that have developed from a common ancestor. The arm of a primate, such as a chimpanzee, and the wings of bird, such as the plain-colored amazon, are homologous because they are made of similar bones and thus must have a common evolutionary origin; however, they do not perform the same function in the different organisms. 

28. Modified Leaf of a Plant: A modified leaf of a plant is a change in a leaf's structure such that it performs other functions that just photosynthesis. The leaves of this Desert Spoon shrub have been altered into thin, sharp, and pointy leaves in order to dissuade herbivory and its own consumption. 

29. Modified Root of a Plant: Modified roots of plants are roots that have changed their structures in order to carry out specific functions as an adaptation to the environment. The roots of carrots have been modified in order to store starch because underground, where the roots grow, is a great place to secure energy and resources, away from predators and consumers. 

30. Modified Stem of a Plant: A modified stem is a stem that has been transformed such that it performs a specialized function. Normal stems transport nutrients and water and are used for support; however, because this stem of a rose plant has portions that are altered into thorns for defense, it is considered a modified stem.

37. Radial Symmetry (Animal): Radial symmetry is symmetry about a central point, around which radiating segments are equally arranged. Sea anemones exhibit radial symmetry because they only have tops and bottoms rather than left and right sides. Moreover, dividing a sea anemone along any central axis will produce two equal halves. 

39. Tetrapod: A tetrapod is a vertebrate with four limbs, or any vertebrate that had four-legged ancestors. All amphibians, reptiles, birds, and mammals, are tetrapods, and thus this four-legged giraffe is a tetrapod. 

40. Unicellular Organism: A unicellular organism is simply an organism that consists of one cell. They carry out all of their functions in this single cell. Yeasts, which are able to convert sugar into alcohol and carbon dioxide through fermentation, are fungi that consist of single cells. 

41. Vestigial Structure: A vestigial structure is a structure that was at one time useful for a species but has lost its apparent function overtime. The wings of an emu are vestigial structures because emus are unable to fly and thus do not use their wings for a particular purpose.