sat2课程辅导——生物专业学术单词分享

　　今天考而思学习小助手为大家带来sat2课程的生物专业的学术单词分享

　　Mutagen(诱变剂)：Any agent that induces genetic mutation. Examples： certain chemical substances， ultraviolet，light， radioactivity.

　　Mutation(突变)： A permanent inheritable alteration in the DNA sequence or content of a cell. Mycelium(菌丝体)： The filamentous mass that makes up a mold. Composed of hyphae.

　　narrow spectrum(窄谱)： Denotes drugs that are selective and limited in their effects. For example， they inhibit either gram-negative or gram-positive bacteria， but not both.

　　negative stain(负染色)：A staining technique that renders the background opaque or colored and leaves the object unstained so that it is outlined as a colorless area

　　nitrogen fixation(固氮)：A process occurring in certain bacteria in which atmospheric Na gas is converted to a form (NH^ usable by plants.

　　Nucleocapsid(核衣壳)： In viruses， the close physical combination of the nucleic acid with its protective covering.

　　Nucleoid(拟核)：The basophilic nuclear region or nuclear body that contains the bacterial chromosome.

　　Nutrient(营养物质)：Any chemical substance that must be provided to a cell for normal metabolism and growth. Macronutrients are required in large amounts， and micronutrients in small amounts.

　　Obligate(专性的)： Without alternative; restricted to a particular characteristic. Example： An obligate parasite survives and grows only in a host; an obligate aerobe must have oxygen to grow; an obligate anaerobe is destroyed by oxygen.

　　Parasite(寄生)： An organism that lives on or within another organism (the host)， from which it obtains nutrients and enjoys protection. The parasite produces some degree of harm in the host indirectly by donation of preformed immune substances (antibodies) produced in the body of another Individual.

　　Pasteurization(巴斯德消毒)： Heat treatment of perishable fluids such as milk， fruit juices， or wine to destroy heat-sensitive vegetative cells， followed by rapid chilling to inhibit growth of survivors and germination of spores. It prevents infection and spoilage.

　　Pathogen(病原体)：Any agent， usually a virus， bacterium， fungus， protozoan， or helminth， that causes disease.

　　Saprophytes(腐生型) Organisms that obtain their nutrients from decaying plants and animals. Saprophytes are important in recycling organic material.

　　Pathogenidty(致病性)：The capacity of microbes to cause disease.

　　Pathology(病原学)：The structural and physiological effects of disease on the body.

　　passive transport(被动扩散)Diffusion across a plasma membrane in which the cell expends no energy.

　　Penicillins(青霉素)：A large group of naturally occurring and synthetic antibiotics produced by penicillium mold and active against the cell wall of bacteria.

　　Peptidoglycan(肽聚糖)： A network of polysaccharide chains cross-linked by short peptides that forms the rigid part of bacterial cell walls. Gram-negative bacteria have a smaller amount of this rigid structure than do gram-positive bacteria.

　　Plasmids(质粒)Self-replicating， circular DNA molecules found in bacterial cells; often used as vectors in recombinant DNA technology. Small circles of double-stranded DNA found in some bacteria. Plasmids can carry from four to 20 genes. Plasmids are a commonly used vector in recombinant DNA studies.

　　periplasmic space(周质空间)：The region between the cell wall and cell membrane of the cell envelopes of gram-negative bacteria.

　　Phage(噬菌体)：A bacteriophage; a virus that specifically parasitizes bacteria.

　　Phenotype(表型)： The observable characteristics of an organism produced by the interaction between its genetic potential (genotype) and the environment.

　　Photoautotroph(光能自养菌)： An organism that utilizes light fa-ils energy and carbon dioxide chiefly for its' carbon needs.

　　Pilus(性丝) Projection from surface of a bacterial cell (F+) that can donate genetic material to another (F-)。

　　prokaryote cell(原核细胞)： A small， simple cell lacking a true nucleus， a nuclear envelope， and membrane-enclosed organelles

　　prophage(前噬菌体)：A lysogenized bacteriophage; a phage that is latently incorporated into the host chromosome instead of undergoing， viral replication and lysis. prophylactic Any device， method， or substance used to prevent disease.

　　Protoplast(原生质体)：A bacterial cell whose cell wall is completely kicking and that is vulnerable to osmotic lysis.

　　Pseudohypha(假菌丝)：A chain of easily separated， spherical to sausage-shaped yeast cells partitioned by constrictions rather than by septa.

　　Psychrophile(嗜冷菌)：A microorganism that thrives at low temperature (0°-20°C)， with a temperature optimum of 0°-15°C.

　　respiratory chain(呼吸链)：In cellular respiration， a series of electron-carrying molecules that transfers energy-rich electrons and protons to molecular oxygen. In transit， energy is extracted and conserved in the form of ATP.

　　reverse transcriptase(逆转录酶)：The enzyme possessed by retroviruses that carries out the reversion of RNA to DNA—a form of reverse transcription.

　　SCP(单细胞蛋白)：Abbreviation for single-cell protein， a euphemistic expression for microbial protein intended for human and animal consumption……

　　selective media(选择培养基)： Nutrient media designed to favor the growth of certain microbes and to inhibit.

　　Serotyping(血清型)：The subdivision of a species or subspecies into an immunologic type， based upon antigenic characteristics.

　　sexual reproduction(有性繁殖)A system of reproduction in which two haploid sex cells fuse to produce a diploid zygote.

　　Spheroplast(球形体)： A gram-negative cell whose peptidoglycan， when digested by lysozyme，

　　remains intact but is osmotically vulnerable

　　spike(刺突)：A receptor on the surface of certain enveloped viruses that facilitates specific attachment to the host cell.

　　Spirillum(螺菌)：A type of bacterial cell with a rigid spiral shape and external flagella.

　　Spirochete(螺旋体)：A coiled， spiral-shaped bacterium that has endoflagella and flexes as it moves.

　　Sporangium(孢囊)：A fungal cell in which asexual spores are formed by multiple cell cleavage. Sterilization(灭菌)：Any process that completely removes or destroys all viable microorganisms， including viruses， from an object or habitat. Material so treated is sterile.

　　Strain(菌株)：In microbiology， a set of descendants cloned from a common ancestor that retain the original characteristics. Any deviation from the original is a different strain.

　　subcellular vaccine(亚单位疫苗)： A vaccine against isolated microbial antigens rather than against the entire organism.

　　superoxide ion(超氧离子)： A toxic radical form oxygen metabolism

　　suppressor T cell(抑制T细胞)：A class of T cells that inhibits the actions of B cells and other T cells.

　　temperate phage(温和噬菌体)：A bacteriophage that enters into a less virulent state by becoming incorporated into the host genome as a prophage instead of in the vegetative or lytic form that eventually destroys the cell.

　　thermal death point(致死温度)：The lowest temperature that achieves sterilization in a given quantity of broth culture upon a 10-minute exposure. Examples：55°C for Escherichia coil. 60°C for

　　Mycobaaerium tuberculosis， and 120°C for spores.

　　thermal death time( 热致死时间)：The least time required to kill all cells of a culture at a specified temperature.

　　Therrnophlle(嗜热菌)：A microorganism that thrives at a temperature of 50°C or higher.

　　T lymphocyte (T cell)：A white blood cell that is processed in the thymus gland and is involved in cell-mediated immunity.

　　Toxoid(类毒素)：A toxin that has been rendered nontoxic but is still capable of eliciting the formation of protective antitoxin antibodies; used in vaccines.

　　Transduction(转导)：The transfer of genetic material from one bacterium to another by means of a bacteriophage vector.

　　Transformation(转化)：In microbial genetics， the transfer of genetic material contained in "naked" DNA fragments from a donor cell to a competent recipient cell.

　　Transposon(转座)：A DNA segment with an insertion sequence at each end， enabling it to migrate to another plasmid， to the bacterial chromosome， or to a bacteriophage.

　　Vaccine(免疫法)：Originally used in reference to inoculation with the cowpox or vaccinia virus to protect against smallpox. In general， the term now pertains to injection of whole microbes (killed or attenuated)， toxoids， or parts of microbes as a prevention or cure for disease.

　　Virold(类病毒)：An infectious agent that， unlike a virion， lacks a capsid and consists of a closed circular RNA molecule. Although known viroids are all plant pathogens， it is conceivable that animal versions exist.

　　Zygospore(接合孢子)：A thick-walled sexual spore produced by the zygomycete fungi. It develops from the union of two hyphae， each bearing nuclei of opposite mating types.

　　A

　　abiotic

　　Nonliving materials in the environment—such as elements, sunlight, and soil—that influence and are influenced by living (biotic) entities on the planet.

　　acetylcholine

　　A neurotransmitter released by neurons to excite an action potential or trigger a muscle to contract.

　　acids

　　Hydrogen ion (H+) donors. Acids are very important in the chemical reactions of life because they are highly reactive. Acids have pH values below 7. They are the opposite of bases.

　　actin

　　Protein filaments that, along with myosin, allow muscles to contract.

　　active site

　　The part of an enzyme that interacts with, or binds to, a substrate.

　　active transport

　　The movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration. Because active transport involves moving the molecule against the natural flow of the concentration gradient, the process requires energy.

　　adaptive radiation

　　The evolutionary process by which ancestral forms of an organism are diversified through adaptation to new environments.

　　adenosine triphosphate (ATP)

　　The energy storage molecule for the cell. ATP consists of an adenosine molecule bonded to three phosphate groups. Each phosphate bond contains energy; by breaking these bonds, the cell can get the energy it needs for chemical reactions. Cells build ATP during cell respiration, using the raw material of glucose.

　　adrenal glands

　　Two glands, the adrenal cortex and adrenal medulla, located on the kidney.

　　aerobic respiration

　　A form of cell respiration requiring oxygen (as opposed to anaerobic respiration, which does not need oxygen). Aerobic respiration is much more efficient than anaerobic respiration; it produces 36 ATP for every molecule of glucose. Aerobic respiration proceeds in three stages: glycolysis, the Krebs cycle, and the electron transport chain.

　　allele

　　A specific form or possible version of a gene having multiple versions. Alleles may be dominant or recessive.

　　allelic frequency

　　The frequency with which a particular allele for a certain characteristic appears among all possible alleles for that characteristic in a population.

　　alternation of generations

　　The fluctuation between the diploid (sporophyte) and haploid (gametophyte) life stages that occur in plants.

　　amino acid

　　The monomer of a protein. A central carbon attached to an amino group (–NH2), a carboxyl group (–COOH), and a hydrogen atom (–H). The fourth group is variable and defines the amino acid’s chemical identity.

　　anaerobic respiration

　　A form of cell respiration that does not use oxygen (as opposed to aerobic cell respiration). Anaerobic respiration is less efficient than the aerobic variety and produces just 2 ATP per molecule of glucose. Anaerobic respiration has two stages: glycolysis and fermentation.

　　analogous trait

　　A trait that is morphologically and functionally similar to that of a different species but that arose from a distinct, ancestral condition.

　　anaphase

　　The stage of mitosis in which sister chromosomes are separated and pulled to opposite ends of the cell by microtubules; the fourth stage of the first meiotic division (meiosis I), during which maternal and paternal homologous pairs are separated on microtubules; the fourth stage of the second meiotic division (meiosis II), during which either maternal or paternal sister chromatids are separated on microtubules.

　　angiosperm

　　A vascular flowering plant in which seeds are enclosed inside protective ovaries, such as fruit or flowers. Angiosperms can be monocots or dicots.

　　anther

　　Pollen-producing structure at the top of the stamen, the male reproductive organ of flowers.

　　anticodon

　　The sequence of three nucleotides on tRNA that pairs with a codon of mRNA at the A site of a ribosome during translation.

　　antigen

　　A protein coat on the surface of red blood cells; a red blood cell may have a protein coat of type A, B, or AB. If the cell has no antigens, it is called type O. The presence of a foreign antigen in a body will cause blood to clot.

　　aorta

　　The largest artery in the body; carries oxygenated blood from the left ventricle of the heart.

　　aphotic zone

　　Literally, zone without light. The aphotic zone is part of the marine pelagic zone and begins 600 feet below the surface of the ocean. Only chemosynthetic organisms, scavengers, and predators are able to survive in this habitat.

　　artery

　　Vessel that carries blood away from the heart and has thick, elastic, muscular walls that can dilate or contract to control blood pressure within the vessels. Blood in arteries is oxygenated, with the exception of the blood in the pulmonary artery.

　　autonomic nervous system

　　The involuntary half of the peripheral nervous system. The autonomic nervous system is in two antagonistic parts: the sympathetic and parasympathetic nervous systems. Their interactions control smooth and cardiac muscle, glands, and organs and processes such as heartbeat, the movements of the digestive tract, and the contraction of the bladder.

　　autosome

　　Any chromosome that is not a sex chromosome. Humans have 44 autosomes, in 22 homologous pairs. The two sex chromosomes are the twenty-third pair of chromosomes.

　　autotroph

　　An organism that can produce the organic molecules and energy necessary for life through the processes of photosynthesis or chemosynthesis. Autotrophs do not rely on other organisms for food. In a food web, autotrophs are producers.

　　auxin

　　One in a class of plant hormones that stimulates (among other things) cell elongation, secondary tissue growth, and fruit development.

　　B

　　base

　　An ion or compound that removes H+ ions from solution. Often bases are substances that release hydroxide ions (OH–). Bases have pH values above 7. They are the opposite of acids.

　　bile

　　An emulsifier of fats secreted by the liver and stored in the gallbladder for release in the small intestine.

　　binary fission

　　Asexual reproduction found in prokaryotes in which a cell divides into two equal daughter cells by a nonmitotic process.

　　biomass

　　The amount of living matter in a given ecosystem. Because only 10 percent of energy is transferred between trophic levels, the biomass of lower trophic levels is greater than the biomass of subsequent trophic levels: biomass of producers > biomass of primary consumers > biomass of secondary consumers > biomass of tertiary consumers.

　　biome

　　A particular geographic area with a common climate and characteristic plant and animal life. There are six major terrestrial biomes and two aquatic biomes. The six terrestrial biomes are tropical rain forest, savanna, desert, temperate deciduous forest, taiga, and tundra. The two aquatic biomes are marine and freshwater. Each biome is characterized by specific climax communities.

　　blood

　　The liquid that carries nutrients and oxygen to the cells and carries carbon dioxide and nitrogenous wastes away. The liquid fluid of blood is called plasma. Red blood cells contain hemoglobin, an iron-containing protein that binds oxygen. White blood cells fight disease. Platelets clot to prevent extreme blood loss resulting from injury.

　　bone

　　Rigid structures composed of living cells rooted in a matrix of calcium, phosphate salts, and collagen fibers. Bones are the primary component of most vertebrate skeletons.

　　brain

　　The center of the central nervous system. The brain coordinates the processes of the body. It is composed of various distinct regions, all of which have different functions, including the cerebrum, cerebellum, medulla oblongata, and hypothalamus.

　　bryophyte

　　A lower terrestrial plant (often a moss or liverwort) that lacks a vascular system and is dependent on environmental moisture for reproductive and nutritive functions.

　　budding

　　Asexual reproductive process in which a small portion of the cell membrane and cytoplasm receive a nucleus and pinch off from the parent cell.

　　buffer

　　Solutions that resist change in pH even when acids and bases are added.

　　bulb

　　Roughly spherical underground bud containing additional buds that can develop asexually into new plants.

　　C

　　Calvin cycle

　　Light-independent phase of photosynthesis, where carbon dioxide is fixed to a three-carbon compound used to form glucose. ATP and NADH are consumed in this cycle. Also called the Calvin-Benson cycle or the dark reactions.

　　capillary

　　Tiny blood vessels able to branch through the body and deliver oxygen and nutrients to every cell.

　　carbon

　　The central element of life. Carbon has the ability to form bonds with up to four other elements or molecules at the same time.

　　carrying capacity

　　The maximum number of individuals in a population that can be sustained in a given environment. As populations become increasingly concentrated, competition for food and space, predation, and disease all determine carrying capacity.

　　cartilage

　　A firm but flexible substance, found in regions of vertebrate skeletons, such as the ribs, that need to bend.

　　cell

　　The smallest unit of life, consisting of a solution of organic molecules enclosed by a plasma membrane.

　　cell cycle

　　A process in which cells reproduce. First the cell replicates its DNA and then divides into two daughter cells. The two main phases of the cell cycle are interphase and mitosis.

　　cell membrane

　　The phospholipid bilayer that surrounds all cells, regulating the passage of molecules in and out of the cell.

　　cellular respiration

　　The process in which the cell burns glucose to create ATP with the aid of oxygen. Cells have two different methods of turning food into usable fuel: aerobic respiration and anaerobic respiration.

　　cell theory

　　The doctrine that every living organism is composed of cells and that all cells come only from other preexisting cells.

　　cell wall

　　A rigid structure that surrounds the outer membrane of some cells and helps maintain their shape. In plants the cell wall contains cellulose; in fungi it contains chitin; in prokaryotes it typically contains peptidoglycan.

　　cellulose

　　A complex carbohydrate that constitutes the cell walls of plants and protist molds.

　　central nervous system (CNS)

　　The brain and the spinal cord. The CNS acts as the central command center of the body. Mostly made up of interneurons.

　　centriole

　　A structure in the cell that plays an important role in cell replication. During prophase, the centrioles migrate to the poles of the cell and form the mitotic spindle, which allows the chromosomes to be organized and split when the cell divides.

　　cerebellum

　　Part of the brain. Makes sure that movements are coordinated and balanced.

　　cerebrum

　　Part of the brain. Controls all voluntary movement, sensory perception, speech, memory, and creative thought.

　　chemical cycles

　　The cycles in which inorganic elements move through the biotic and abiotic aspects of an ecosystem. The two most important chemical cycles are the carbon and nitrogen cycles.

　　chemosynthesis

　　Synthesizing organic compounds by energy derived from chemical reactions rather than from the energy of the sun. Chemosynthetic organisms are autotrophs.

　　chitin

　　A rough polysaccharide that constitutes the cell wall of fungi and exoskeleton of arthropods.

　　chlorophyll

　　A pigment located within a chloroplast that absorbs light in plant cells, helping to convert light energy into biological energy through the process of photosynthesis.

　　chloroplast

　　A double-membrane-bound organelle that contains chlorophyll and is found in plant cells. Chloroplasts are responsible for mediating photosynthesis.

　　chromatin

　　The stringy web of genetic material and histone proteins found in the nucleus of eukaryotic cells. During cell division, each strand of DNA coils to form a chromosome.

　　chromosome

　　A physical structure composed of a single long strand of DNA (and associated proteins), containing along its length many genes. The human genome consists of 46 chromosomes contained within the nucleus of each cell.

　　cilia

　　Short, hairlike projections found on eukaryotic cells that can help the cell move or can sweep food particles toward the mouth.

　　circadian rhythms

　　Behavior cycles that depend on time of day.

　　circulatory system

　　System of organs and blood that brings nutrients and oxygen to cells and carries away wastes. In higher vertebrates, the system has a pulmonary and systemic circuit. The pulmonary circuit carries blood to the lungs to be oxygenated, while the systemic circuit carries oxygenated blood to the body. Vertebrates have a closed circulatory system, while arthropods have an open system.

　　citric acid cycle

　　See Krebs cycle.

　　climax community

　　A combination of plant and animal forms that dominate mature ecological communities. Climax communities are unique and shaped by various factors, including temperature, rainfall, and soil acidity.

　　codominance

　　A phenomenon in which two alleles of the same gene are fully expressed in the phenotype when both are present in a heterozygote. Blood type is an example of codominance.

　　codon

　　A three-nucleotide sequence in a DNA or mRNA molecule. Each codon specifies a single amino acid.

　　coenzyme

　　A compound that regulates activity by binding to an enzyme to tell it when to catalyze a reaction.

　　cold-blooded

　　Animals that are unable to retain heat produced by metabolic activities. Also known as ectothermic. The metabolism of cold-blooded animals is greatly influenced by climate and temperature.

　　community

　　The many populations that interact in a given geographical locale constitute ecological communities. Communities exhibit particular interactions such as competition, symbiosis, predation, and food relationships. They also undergo ecological succession.

　　competition

　　The struggle for survival between organisms or populations that use similar resources and occupy similar niches. Interspecific competition refers to competition between populations that may drive a population out of a community or push it to evolve a different niche to reduce competition. Intraspecific competition refers to competition between individuals of the same species.

　　consumer

　　Consumers are heterotrophic organisms within the food web of a community. In the trophic levels of the food chain, primary consumers consume producers, secondary consumers consume primary consumers, and tertiary consumers consume secondary consumers.

　　contractile vacuole

　　An organelle often found in protozoa that pumps excess water out of the cell to keep the cell from bursting in a hypotonic environment (like freshwater).

　　corpus luteum

　　After releasing its ovum (ovulation), the follicle becomes the corpus luteum, which produces progesterone for the continued buildup of the uterine wall.

　　crossing-over

　　The exchange of genetic information between homologous chromosomes during meiosis I. Crossing-over can disrupt the normal linkage between genes on the same chromosome.

　　cytokinesis

　　The final part of mitosis, in which a cell with duplicated contents splits into two independent cells.

　　cytoplasm

　　The entire content of the cell outside the nucleus, including the membrane-bound organelles and the cytosol.

　　cytoskeleton

　　A system of protein filaments found throughout the cytoplasm of eukaryotic cells, which provides structural support for the cell. The cytoskeleton also helps with the movement of organelles within the cell. It is composed of microfilaments and microtubules.

　　cytosol

　　The main component of the cytoplasm. It is a grayish, gel-like liquid containing the nucleus, organelles, and cytoskeleton.

　　D

　　Darwin, Charles

　　English naturalist (1809–1882) who proposed the modern theory of evolution through natural selection. Darwin traveled aboard the HMS Beagle to the Galápagos Islands, where his revolutionary observations took shape.

　　decomposer

　　Organisms that consume waste products and dead organic material and constitute part of the food web, which also includes producers and consumers. Also called saprophytes. Decomposers liberate inorganic elements such as nitrogen and carbon and allow those elements to move back into their respective chemical cycles. Examples of decomposers are bacteria and fungi.

　　dehydration synthesis

　　A common biochemical reaction in which a new compound is formed by the joining of two compounds to release water. Occurs in the synthesis of polysaccharides and polypeptides. The reverse of hydrolysis.

　　deoxyribonucleic acid (DNA)

　　A type of nucleic acid polymer built from sugar-phosphate backbones and nitrogenous bases. DNA’s sugar, deoxyribose, has one fewer oxygen atom than ribose, found in RNA. The nitrogenous bases adenine, cytosine, guanine, and thymine are used in DNA.

　　dicot

　　A flowering plant (angiosperm) that possesses two cotyledons during embryonic development. Usually has taproots, flower parts in multiples of fours and fives, and branching veins in leaves.

　　diffusion

　　The transport or natural drift of molecules traveling from an area of higher concentration to an area of lower concentration. Diffusion does not require outside energy from the cell.

　　digestive system

　　The system of organs that converts food to usable nutrients through mechanical and chemical breakdown. Important components of the system are the alimentary canal, glands, esophagus, stomach, small intestine, large intestine, and rectum.

　　diploid number

　　The total number of chromosomes present in a somatic cell. The diploid number is twice the haploid number. In humans, the diploid number is 46.

　　disaccharide

　　A sugar compound consisting of two carbohydrate monomers.

　　dominant

　　Refers to an allele that controls the phenotype even when a different allele is also present, as in a heterozygote. Can also refer to the trait or phenotype produced by a dominant allele. Also known as Mendel’s law of dominance, based on Gregor Mendel’s observations that when two purebred individuals with different forms of the same trait are mated, only one of the two forms appears in the first generation of offspring. Mendel called the apparent form dominant and the suppressed form recessive.

　　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.