Biology - An Illustrated Guide to Science (794127), страница 35
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It stores chemical substances neededfor life and is the site of important metabolic reactions.decomposer An organism that breaks down deadorganic material.dehiscence The process of splitting open to releasereproductive structures.dendrite The branched filament of a nerve cell thatreceives impulses from other nerve cells and passesthem on to the cell body.dentine The calcified tissue that makes up the bulk of atooth.deoxyribosenucleic acid (DNA) The molecule thatholds the genetic code.diaphragm A sheet of muscle lying over the liver andstomach and under the lungs.diastole The phase of the heartbeat when the heartmuscle relaxes and the heart fills with blood.dicotyledons Plants with two seed leaves (cotyledons) inthe embryo.diffusion The spreading of gases or liquids caused byrandom movement of their molecules.digestion The mechanical and chemical breakdown offoods into nutrients an animal can absorb.diploid The number of chromosomes of a normal cell.discontinuous variation Variation that does not have aspectrum of types, e.g., being able to roll your tongueor not.DNA See deoxyribosenucleic acid.dominant In genetics, the allele that masks anotherallele.double circulation A circulatory system where the bloodpasses through the heart twice—once for the body andonce for the lungs.Down syndrome A genetic condition in which an extrachromosome causes a number of significant mental andphysical problems.
It is caused by an extra copy of all orpart of chromosome 21.eardrum The thin membrane at the junction of themiddle and outer ear.ectoplasm The gel-like outer cytoplasm of the cellfound close to the plasma membrane.egg The female gamete.electron transfer chain A series of enzymes that cantransfer energy from excited electrons into ATP.embryo The early stages that develop from the fertilizedegg.embryo sac The structure in the ovule of a floweringplant containing the female nuclei that will fuse withnuclei from the pollen grain to form the zygote.endocrine gland A gland that secretes hormonesdirectly into the blood.endocytosis The engulfing of materials by a cell.endodermis In plants, the innermost layer of cells thatseparates the cortex of the root from the pericycle.endoplasmic reticulum The network of plasmamembranes running throughout the cytoplasm.
It isinvolved in the synthesis, storage, and transport of cellproducts.endosperm The food storage tissue found in the seedsof flowering plants.enzyme A protein found in living organisms that speedsup the rate of a chemical reaction.enzyme-coenzyme complex The giant molecule formedby an enzyme and coenzyme.epidermis The outer, protective layer of cells in animalsand plants.epididymis The part of the testis that stores sperm.epithelium A sheet of tissue that covers the internalsurfaces of the body.eustachian tube A tube connecting the middle ear andthe back of the throat to equalize pressure on bothsides of the eardrum.© Diagram Visual Information Ltd.KEY WORDS200KEY WORDS© Diagram Visual Information Ltd.exocytosis The release of intracellular materials to theoutside of the cell via vacuoles or vesicles.exoskeleton The hard skeleton on the outside of thebody.factor VIII A blood protein required for clotting that ismissing in people suffering from hemophilia.fallopian tube The tube leading from the ovaries to theuterus.fatty acid An acid with long hydrocarbon chain (roughly30–40 carbon atoms) that is the major component ofnatural fats and oils.feces The waste and indigestible food that passes out ofthe gut through the anus.fertilization The fusion of gametes from two sexes toproduce the zygote.fetus The developing young in the uterus before birth.fission Splitting of a cell or organism into two or moredaughters.food chain A simple diagram showing feedingrelationships between some plants and animals.food web A diagram showing how all of the food chainsin an area link together.fossil record The evidence from studies of the fossilsfor a particular line of evolution.fruit A structure developed from the swollen wall of theovary that helps the dispersal and survival of seeds.gamete A mature male or female reproductive cell.
Itcontains half the number of chromosomes of normalbody cells. At fertilization, male and female gametesfuse to form a zygote.gametophyte In plants, the generation that producesgametes.gaseous exchange The movement of gases—usuallycarbon dioxide and oxygen—across an exchangemembrane.gastrodermis The inner body layer in Cnidaria.gene A length of DNA that determines inheritedcharacteristics.generative nucleus The nucleus in the pollen grain thateventually fuses with the egg nucleus in the ovule.genotype The genetic composition of an organism.germ cell A cell involved in sexual reproduction.
Alsocalled a gamete.germination In plants, the first stages of growth of aseed or spore.gill The respiratory organ of most aquatic animals thatbreathe water to obtain oxygen.glomerulus A mass of capillaries at the entry of a kidneytubule. Blood plasma is filtered out of the blood in theglomerulus into the tubule.glucose The most widely distributed six-carbon sugar inanimals and plants.
It is the energy source inrespiration.glycerol A small alcohol with three OH groups. Itcombines with fatty acids to form fats and oils.glycogen A polysaccharide used in animals to storeenergy.glycolysis The breakdown of six-carbon sugars to three-carbon sugars in the cytoplasm.glycosidic bond A bond formed betweenmonosaccharides by a condensation reaction.Golgi body An organelle involved in assembling andstoring metabolic substances.granum A chlorophyll-rich membrane structure presentin chloroplasts.guard cell A cell that changes shape to open or close astoma in a leaf.gut The long tube that starts at the mouth and leads tothe anus. It includes the large and small intestine and issometimes called the digestive tract.haploid Having half the number of chromosomesnormally found in the cells of an organism.hemoglobin A protein found in red blood cells inmammals.
It reacts reversibly with oxygen.hepatic portal vein The vein carrying blood from thegut to the liver.herbivore An animal that only eats plants.hermaphrodite An organism with both male and femalesexual organs.heterozygous An organism having two different allelesfor an inherited trait.homologous chromosome Chromosomes that pair upduring meiosis. They have the same genes but may havedifferent alleles so are not identical.homozygous An organism having two identical allelesfor an inherited trait.host The organism that supports the parasite.hypothalamus A small organ at the base of the brainthat coordinates visceral functions.impermeable Material that it is not easily penetrated.incisor A chisel-shaped tooth at the front of the mouthused for cutting and biting.inhibitor A chemical that slows down the speed of achemical reaction.insertion In genetics, the process by which a base isadded to a sequence of DNA.insulin The hormone secreted by the pancreas thatcontrols the blood glucose level.intercostal muscle A muscle between the ribs.interphase The period between cell divisions.intestine The region of the alimentary canal betweenthe stomach and anus or cloaca where nutrients aredigested and absorbed and feces produced.invertebrate An animal without a backbone.karyotype The number and types of chromosomescharacteristic of a species.keratin A structural protein found in hair and nails.kidney The organ responsible for filtering and excretingliquid wastes and maintaining the composition of theblood.Krebs cycle Sometimes called the tricarboxylic acidcycle, it occurs in the matrix of mitochondria andinvolves the break down of three-carbon sugars intocarbon dioxide and hydrogen ions.201larva An immature form of an animal that has adifferent structure and way of life from the adult.lateral line A pressure-sensitive sense organ runningalong the sides of a fish or larval amphibian.lenticel A small raised pore in the epidermis of the stemor bark of a plant with gaps between cells that permitgaseous exchange.life cycle The successive stages organisms go throughfrom birth to death.light-dependent reaction The first stage inphotosynthesis that converts light energy into chemicalenergy.light-independent reaction The reduction of carbondioxide to glucose in photosynthesis using energycaptured during the light-dependent reaction.lignin A complex polymer in the cell wall of plants thatgives them strength and rigidity.lipid An organic molecule, insoluble in water, that isformed by the reaction of a fatty acid with glycerol.
It isthe chief component of fats, oils, and phospholipids inthe body.liver The large gland opening into the gut that hasmultiple functions and plays an important role inmetabolism.lung The respiratory organ of air-breathing vertebratesacross which carbon dioxide and oxygen diffuse.lymph vessel A vessel that transports lymph fluid.lymphatic system The complete system of lymphvessels and nodes that conduct lymph from tissues tothe circulatory system.lysosome A membrane-bound organelle containing amixture of powerful enzymes that are capable ofbreaking down many substances.Malpighian layer The layer of cells at the base of theepidermis.
The epidermal cells all originate from celldivision in the Malpighian layer.mammary gland A milk producing gland in femalemammals.matrix (1) The material in which another substance isembedded. (2) The central space of the mitochondrion.maxilliped One of a pair of appendages in crustaceansand centipedes that manipulate food prior to ingestion.medulla oblongata The part of the brain near thejunction with the spinal cord that controls involuntarybody functions such as breathing.meiosis A specialized form of cell division that producescells carrying half the usual number of chromosomes.These cells, called gametes, are used in sexualreproduction.mesoglea The layer between the outer and inner layerin cnidarian bodies.mesosome The infolding of the plasma membrane intothe main body of the cell in some bacteria.messenger RNA (mRNA) The RNA molecule thattransfers the genetic code for a protein from the DNA inthe nucleus to a ribosome in the cytoplasm, where itserves as the template for the synthesis of that protein.metabolism The range of living processes within anorganism that provides for its needs.metamorphosis A large change in the shape of the bodyduring growth.metaphase A stage in mitosis when the nuclearmembrane breaks down and the spindle begins to form.metaphase II The second metaphase in meiosis.micropyle In plants, the pore in the ovule throughwhich the pollen tube enters before fertilization.mitochondrion A membrane organelle, sometimes calledthe powerhouse of the cell, that produces the cell’senergy in the form of ATP.mitosis The process of cell division that gives rise tocells genetically identical to the parent cells.molar A large tooth at the back of the mouth used tocrush food.molecule The smallest naturally occurring unit of anelement.molting The loss of the outer body surface (feathers,fur, skin, exoskeleton) and its replacement by a newone.monocotyledon A plant with a single seed leaf(cotyledon).monosaccharide A simple sugar with only one ring unitin its molecule, e.g., glucose.
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