fault -- n. (v.) A fracture, or large crack, in the Earth's crust where one side moves up/down/sideways relative to the other; fault block- n. pieces of crust that have slipped into or alongside a fault; fault zone- n. an area with multiple faults.
fertilization -- The process by which an egg is made capable of generating offspring. It is often synonymous with syngamy.
flagellin -- protein which is the primary component of prokaryotic flagella.
flagellum -- n. Hair-like structure attached to a cell, used for locomotion in many protists and prokaryotes. The prokaryotic flagellum differs from the eukaryotic flagellum in that the prokaryotic flagellum is a solid unit composed primarily of the protein flagellin, while the eukaryotic flagellum is composed of several protein strands bound by a membrane, and does not contain flagellin. The eukaryotic flagellum is sometimes referred to as an undulipodium.
floodplain -- n. The flat area on either side of an active river channel that can be covered in water when the river is in flood. When the channel is breached, sediment-laden waters spread across the floodplain. When the waters recede, a layer of sediment is left behind. When the floodplain is not covered with water, it commonly supports vegetation and soil formation.
flower -- Collection of reproductive structures found in flowering plants. More info?
focus -- The initial point within the Earth that ruptures in an earthquake, directly below the epicenter.
fold -- Bent rock strata.
food chain/food web -- All the interactions of predator and prey, included along with the exchange of nutrients into and out of the soil. These interactions connect the various members of an ecosystem, and describe how energy passes from one organism to another.
fruit -- In flowering plants, the structure which encloses the seeds. True fruits develop from the ovary wall, such as bananas and tomatoes, though not all fruits are edible, such as the dry pods of milkweed or the winged fruits of the maple.
frustule -- The mineral "skeleton" of a diatom or other unicellular organism.
fucoxanthin -- yellowish-brown pigment found in some members of the Chromista, including kelps and diatoms.