E–H
11.1 A–D
 
11.2 E–H
 
11.3 I–L
 
 
11.4 M–P
 
11.5 Q–T
 
11.6 U–Z
 
E–H
E
ear
Sensory organ capable of detecting sound.
ecological succession
The progression of plant life and attendant animal life in a given geographic location, from pioneer plant to climax community.
ecology
The study of the interactions and relationships of populations with each other and their abiotic environments.
ecosystem
A community of organisms and its abiotic environment.
ectotherm
See cold-blooded.
egg
The female gamete in sexual reproduction; also called an ovum.
electron microscope
An instrument that uses an electron beam to form clear and highly magnified images of microscopic structures. Electron microscopes cannot take pictures of living organisms.
electron transport chain
The final stage of aerobic respiration. The electron transport chain establishes an electrochemical gradient across the inner mitochondrial membrane that powers the synthesis of ATP in oxidative phosphorylation.
embryo
Before birth, the maturing cells that will grow into a fully formed organism.
endocrine system
Control system of the body that functions by releasing hormones into the bloodstream.
endocytosis
Process by which liquids or small solid particles are taken into a cell in the form of small vesicles that are produced through the invagination of the cell membrane.
endoplasmic reticulum
A network of membrane-bound tubes and sacs in the cytoplasm. The endoplasmic reticulum is a major site of protein and lipid synthesis.
endoskeleton
An interior skeleton found in vertebrates made of bone and cartilage.
endotherm
See warm-blooded.
energy pyramid
Energy in a community can be depicted as a pyramid of food or biomass. The availability of food, biomass, and energy from the trophic level of producers up through each subsequent level on the food web is approximately 10 percent of that available in the previous trophic level.
enzymes
Biological catalysts made from proteins. Enzymes have attachment locations for substrates called active sites.
estrogen
Hormone that stimulates the growth of the uterine lining during pregnancy and that develops and maintains the female secondary sex characteristics, such as the development of mammary glands, a narrower waist and wider hips, axillary and pubic hair, and a higher-pitched voice.
eukaryote
An organism whose cells have membrane-bound intracellular organelles, including a nucleus containing multiple chromosomes. Eukaryotes, unlike prokaryotes, can undergo sexual reproduction via meiosis. Compared to prokaryotes, eukaryotes are more complex and arose later in evolutionary history. Protists, fungi, plants, and animals are all eukaryotic organisms.
excretory system
The organ system that filters blood and removes nitrogenous wastes from the body in the form of urea or uric acid. In humans, the two kidneys are the vital organs of blood filtration. In annelids, nephridia fill the filtering role; Malpighian tubules do the same in arthropods. In humans, other important structures of the system are the ureters, the urinary bladder, and the urethra.
exocytosis
Process by which molecules are secreted from the cell. Exocytosis occurs when a vesicle fuses with the cell membrane and releases its contents to the outside.
exoskeleton
A rigid, chitinous protective structure that surrounds the bodies of arthropods and provides support.
eye
Sensory organ capable of detecting light.
F
F1 generation
The first generation of offspring from a cross between two varieties or individuals. In Mendel’s experiments, all the F1 offspring were heterozygous hybrids with a dominant phenotype.
F2 generation
The second generation of offspring in a breeding experiment; the offspring from a mating between two F1 hybrids. In Mendel’s monohybrid experiments, the ratio of dominant to recessive phenotypes in the F2 generation was 3:1.
facilitated diffusion
Diffusion of molecules that cannot pass through the cell membrane independently, but rather through permeable protein channels embedded in the membrane. Facilitated diffusion does not require outside energy.
FADH2
A molecule that stores energy for harvest by the electron transport chain.
Fallopian tube
Duct that connects the ovaries with the uterus; the passage through which the ovulated egg travels from the ovaries to the uterus.
fermentation
The second stage of anaerobic respiration, which produces the NAD+ necessary for glycolysis. There are two types of fermentation: alcoholic fermentation and lactic acid fermentation. Yeast engage in alcoholic fermentation, while muscle cells lacking oxygen produce lactic acid.
fetus
The name given to an embryo after it has developed organs.
flagellum
A whiplike structure projecting from the surface of some cells and single-celled organisms; coordinated waving of the flagellum allows the organism to swim. Prokaryotic flagella are made of a single helical chain of flagellin proteins; eukaryotic flagella are made of multiple chains of microtubule proteins.
fluid-mosaic model
Theory describing the cell membrane as a dynamic structure with proteins floating, yet partially embedded, in a sea of phospholipids.
food chain
A linear relationship of predators and prey.
food web
Many connected food chains that exhibit the relationships of all predators to all prey constitute a food web.
fossil record
The grouping of fossilized remains according to relative and absolute age.
G
gallbladder
An organ that stores the bile produced by the liver and releases it to the small intestine during digestion.
gamete
A haploid sex cell (either an egg or sperm cell); male and female gametes join during fertilization to create a diploid zygote. Gametes are created out of germ cells and are passed down to offspring.
gametophyte
A haploid plant or plant structure that produces haploid gametes through mitosis.
ganglion
A simple cluster of nerve cells that acts as a coordinating center. In more sophisticated organisms, ganglia evolved into a brain and spinal cord.
gene
The fundamental unit of heredity, composed of a stretch of DNA. In general, a single gene encodes the information needed to produce one kind of protein. Each gene resides in a specific spot on a chromosome.
gene flow
The movement of genes, within a population or between populations, through mating.
genetic code
The series of codons that make up an organism’s DNA.
genotype
The entire set of specific alleles present in an organism or cell: the genetic information that (together with the environment) defines the phenotype. Often refers only to the alleles controlling a particular trait of interest.
germ cell
Cells that lead to the production of gametes. Produced by meiosis.
glucose
A monosaccharide with the chemical formula C6H12O6. Used as the raw material for cellular respiration.
glycolysis
The first step of aerobic and anaerobic respiration. Glycolysis produces ATP while converting glucose to pyruvate, which is the raw material for the rest of aerobic respiration.
Golgi apparatus
A series of membrane-bound sacs in the eukaryotic cytoplasm. The Golgi apparatus takes proteins produced by the endoplasmic reticulum and packages and secretes them to various destinations inside and outside of the cell.
gonads
Sex organs that produce gametes. The gonads also release sex hormones, such as testosterone, estrogen, and progesterone. In humans, the male gonads are the testes; in females, the ovaries.
grafting
An artificial form of vegetative propagation in which parts of two young plants are joined together, first by artificial means and then by tissue regeneration.
Gram staining
A process by which components of bacterial cell walls are bound to Gram’s stain. Depending on the amount of peptidoglycan in their cell walls, bacteria stain differently and are classified as Gram-negative or Gram-positive.
guard cells
Epidermal plant cells found in pairs surrounding the stomata of leaves. By increasing or decreasing their size, guard cells regulate gas exchange by opening and closing individual stoma.
gymnosperm
A vascular nonflowering plant (commonly known as a conifer) in which seeds are “naked”—collected in a cone and not protected by an ovary. The dispersion of their spermatozoids often relies on wind.
H
haploid number
The number of homologous pairs in a cell. Equal to half the diploid number. Gametes, cells that are passed on to offspring, contain the haploid number of chromosomes. In humans, the haploid number is 23.
heart
The muscular organ that pumps blood through the circulatory system. Mammals and birds have a four-chambered heart, with a left atrium and ventricle and a right atrium and ventricle. The right half of the heart receives deoxygenated blood from the body and pumps it to the lungs, while the left half receives oxygenated blood from the lungs and pumps it to the body.
heredity
The genetic transmission of traits from parents to offspring, so that offspring resemble their parents. Traits transmitted this way are called hereditary traits.
heterotrophs
Organisms that can only get the organic molecules and energy necessary for life through the consumption of other organic matter. In the food web, all consumers and decomposers are heterotrophs. Heterotrophs can be herbivores, carnivores, or omnivores.
heterozygous
A situation in which an individual (heterozygote) possesses two dissimilar alleles for the same gene. The opposite is homozygous.
homologous chromosomes
Chromosomes containing the same series of genes; they may or may not carry the same alleles. Humans receive one set of 23 paternal chromosomes from their male parent and another set of 23 maternal chromosomes from their female parent. Each set matches up to the other for a total of 23 different pairs of homologous chromosomes. During meiosis, homologous pairs line up and are separated. In males, the X and Y chromosomes act as a homologous pair, although they are only partially homologous.
homologous trait
A trait found in different species that are morphologically and functionally similar and that comes from the same ancestral condition. A whale’s fin and a human’s arm are homologous structures.
homozygous
A situation in which an individual (homozygote) has the exact same allele on both homologous chromosomes. Mating of two individuals with the same homozygous genotype will produce only offspring with that same identical genotype. The two identical alleles may be dominant or recessive (e.g., RR or rr). The opposite of homozygous is heterozygous.
hormones
A chemical messenger that can be made of either peptides or lipids. Secreted by glands in one part of the body, hormones affect glands or organs in another part.
hybrid
A genetic mixture; the offspring of two genetically different parents. Hybrids are usually heterozygous for a variety of genes.
hydrogen bond
A weak bond between hydrogen and a set of other elements, including oxygen. Hydrogen bonds are a subset of dipole-dipole interactions.
hydrolysis
A common biochemical reaction in which the bond between two molecules is split by the addition of a water molecule. Hydrolysis is the process that breaks down polymers and dimers. The reverse is dehydration synthesis.
hydrophilic
Having an affinity for water; usually polar molecules. For the SAT II Biology, this is principally important in relation to the phospholipid bilayer.
hydrophobic
Having a reluctance to mix with water; usually nonpolar molecules. The fatty acids that form the interior pocket between the two layers of the cell membrane are hydrophobic.
hydrostatic skeleton
A fluid skeleton in many soft-bodied invertebrates, including annelids, that allows an organism to change shape but not volume.
hypertonic
A situation in which the concentration of solutes in a solution is higher than what it contains. For example, a sodium solution of 10 percent would be hypertonic to an animal cell (with a sodium concentration of about 0.9 percent), causing water to leave the cell by osmosis.
hypothalamus
Part of the brain responsible for temperature regulation, controlling hunger and thirst, and managing water balance. It also helps generate emotion.
hypotonic
A situation in which the concentration of solutes in a solution is lower than what an organism contains. An example is a paramecium in pond water: the organism has more solutes than its environment, so water flows into the cell by osmosis. Paramecia have evolved contractile vacuoles to keep from exploding.
Help | Feedback | Make a request | Report an error