Birds have many bones that are hollow pneumatized with criss-crossing struts or trusses for structural strength. During exhalation bottom , warm air from the lungs returns through the nasal passage and is cooled as it passes over the turbinate surfaces. Genetic pollution from farm forestry using eucalypt species and hybrids: The development of a beak has led to evolution of a specially adapted digestive system. Read More on This Topic. They provided, and continue to provide, power for transport and agriculture, as well as various commodities such as meat , dairy products , wool , and leather. Palestine Sunbirds have somehow overcome the problems of life on liquid diet, so McWhorter et al.
General description and location
A plant that prefaces the Calvin cycle with reactions that incorporate CO 2 into four-carbon compounds, the end-product of which supplies CO 2 for the Calvin cycle. The Calorie with a capital C , usually used to indicate the energy content of food, is a kilocalorie. The second of two major stages in photosynthesis following the light reactions , involving atmospheric CO 2 fixation and reduction of the fixed carbon into carbohydrate. A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions, first discovered in the family Crassulaceae.
Carbon dioxide entering open stomata during the night is converted into organic acids, which release CO 2 for the Calvin cycle during the day, when stomata are closed. A burst of evolutionary origins when most of the major body plans of animals appeared in a relatively brief time in geological history; recorded in the fossil record about to million years ago.
The movement of water or any liquid along a surface; results from the combined effect of cohesion and adhesion. The protein shell that encloses the viral genome; rod-shaped, polyhedral, or more completely shaped.
Worldwide circulation and reutilization of carbon atoms, chiefly due to metabolic processes of living organisms. Inorganic carbon, in the form of carbon dioxide, is incorporated into organic compounds by photosynthetic organisms; when the organic compounds are broken down in respiration, carbon dioxide is released. Large quantities of carbon are "stored" in the seas and the atmosphere, as well as in fossil fuel deposits. The incorporation of carbon from CO 2 into an organic compound by an autotrophic organism a plant, another photosynthetic organism, or a chemoautotrophic bacterium.
A process in which positively charged minerals are made available to a plant when hydrogen ions in the soil displace mineral ions from the clay particles. An ordered sequence of events in the life of a dividing eukaryotic cell, composed of the M, G 1 , S, and G 2 phases.
A cyclically operating set of proteins that triggers and coordinates events in the eukaryotic cell cycle. The type of immunity that functions in defense against fungi, protists, bacteria, and viruses inside host cells and against tissue transplants, with highly specialized cells that circulate in the blood and lymphoid tissue.
A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis. All living things are composed of cells; cells arise only from other cells. No exception has been found to these two principles since they were first proposed well over a century ago. A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists.
In the case of plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid, and is the primary constituent of wood.
The structural and functional divergence of cells as they become specialized during a multicellular organism's development; dependent on the control of gene expression. The most prevalent and efficient catabolic pathway for the production of ATP, in which oxygen is consumed as a reactant along with the organic fuel.
An animal cell usually has a pair of centrioles, which are involved in cell division. Material present in the cytoplasm of all eukaryotic cells and important during cell division; also called microtubule-organizing center. A phenomenon in which species that live together in the same environment tend to diverge in those characteristics that overlap; exemplified by Darwin's finches.
An attraction between two atoms resulting from a sharing of outer-shell elctrons or the presence of opposite charges on the atoms; the bonded atoms gain complete outer electron shells. In a reversible chemical reaction, the point at which the rate of the forward reaction equals the rate of the reverse reaction. The energy released as electrons pass down an electron transport chain is used to establish a proton gradient across an inner membrane of the organelle; when protons subsequently flow down this electrochemical gradient, the potential energy released is captured in the terminal phosphate bonds of ATP.
A receptor that transmits information about the total solute concentration in a solution or about individual kinds of molecules. Applied to autotrophic bacteria that use the energy released by specific inorganic reactions to power their life processes, including the synthesis of organic molecules. A protein-carbohydrate complex secreted by chondrocytes; chondrin and collagen fibers form cartilage. A small sample of the fetal portion of the placenta is removed and analyzed.
When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope. Each chromosome consists of one very long DNA molecule and associated proteins. A dichotomous phylogenetic tree that branches repeatedly, suggesting a classification of organisms based on the time sequence in which evolutionary branches arise. A type of associative learning; the association of a normally irrelevant stimulus with a fixed behavioral response.
The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane; specifically, the succession of rapid cell divisions without growth during early embryonic development that converts the zygote into a ball of cells. The first sign of cleavage in an animal cell; a shallow groove in the cell surface near the old metaphase plate. Also, see gene cloning. An agent used to transfer DNA in genetic engineering, such as a plasmid that moves recombinant DNA from a test tube back into a cell, or a virus that transfers recombinant DNA by infection.
Most vitamins function as coenzymes in important metabolic reactions. Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis. A theory accounting for the upward movement of water in plants.
According to this theory, transpiration of a water molecule results in a negative below 1 atmosphere pressure in the leaf cells, inducing the entrance from the vascular tissue of another water molecule, which, because of the cohesive property of water, pulls with it a chain of water molecules extending up from the cells of the root tip. The process by which plants increase their tolerance to freezing by exposure to low, nonfreezing temperatures.
The location in the kidney where filtrate from renal tubules is collected; the filtrate is now called urine. All the organisms that inhabit a particular area; an assemblage of populations of different species living close enough together for potential interaction. A type of plant cell that is connected to a sieve-tube member by many plasmodesmata and whose nucleus and ribosomes may serve one or more adjacent sieve-tube members.
Interaction between members of the same population or of two or more populations using the same resource, often present in limited supply. The concept that when the populations of two species compete for the same limited resources, one population will use the resources more efficiently and have a reproductive advantage that will eventually lead to the elimination of the other population.
A substance that reduces the activity of an enzyme by entering the active site in place of the substrate whose structure it mimics. A group of at least 20 blood proteins that cooperate with other defense mechanisms; may amplify the inflammatory response, enhance phagocytosis, or directly lyse pathogens; activated by the onset of the immune response or by surface antigens on microorganisms or other foreign cells.
A digestive tube that runs between a mouth and an anus; also called alimentary canal. An incomplete digestive tract has only one opening. A type of multifaceted eye in insects and crustaceans consisting of up to several thousand light-detecting, focusing ommatidia; especially good at detecting movement.
A regular increase of decrease in the intensity or density of a chemical substance. When a gradient exists, the ions or other chemical substances involved tend to move from where they are more concentrated to where they are less concentrated.
A reaction in which two molecules become covalently bonded to each other through the loss of a small molecule, usually water; also called dehydration reaction. A gymnosperm whose reproductive structure is the cone. Conifers include pines, firs, redwoods, and other large trees.
Animal tissue that functions mainly to bind and support other tissues, having a sparse population of cells scattered through an extracellular matrix. A goal-oriented science that seeks to counter the biodiversity crisis, the current rapid decrease in Earth's variety of life.
A heterotroph that derives its energy from living or freshly killed organisms or parts thereof. Primary consumers are herbivores; higher-level consumers are carnivores.
The gradual movement of the Earth's continents that has occurred over hundreds of millions of years. A gradation of small differences in a particular trait, such as height, within a population; occurs in traits that are controlled by a number of genes.
A steroid hormone, produced by the adrenal cortex, that promotes the formation of glucose from protein and fat; also suppresses the inflammatory and immune responses.
The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient. The opposite flow of adjacent fluids that maximizes transfer rates; for example, blood in the gills flows in the opposite direction in which water passes over the gills, maximizing oxygen uptake and carbon dioxide loss. In cells, the linking of endergonic energy-requiring reactions to exergonic energy-releasing reactions that provide enough energy to drive the endergonic reactions forward.
A process by which some species of plants in hot, dry climates take in carbon dioxide during the night, fixing it in organic acids; the carbon dioxide is released during the day and used immediately in the Calvin cycle. The reciprocal exchange of genetic material between nonsister chromatids during synapsis of meiosis I. Cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is a common intracellular signaling molecule second messenger in eukaryotic cells, for example, in vertebrate endocrine cells.
It is also a regulator of some bacterial operons. In the vertebrate immune system, protein factors secreted by macrophages and helper T cells as regulators of neighboring cells. In animal development, substances deposited by the mother in the eggs she produces that regulate the expression of genes affecting the early development of the embryo. A circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells. Movement of Molecules in Solution Closer Look: Concentration Gradient Concept 4: Movement of Molecules and Cells Concept 5: Water Potential Concept 7: Calculating Water Potential Concept 8: Water Potential and Potato Cores Exercise 4: Water Potential Exercise 5: Osmosis Analysis of Results Lab Quiz.
Enzyme Structure Concept 2: Binding Specificity Concept 3: Induced Fit Concept 4: The Cell Cycle Closer Look: Nuclear Division Karyokinesis Closer Look: Cytoplasmic Division Cytokinesis Concept 2: Spore Formation in Sordaria Exercise 1: The Process of Respiration Closer Look: Features and Functions of a Respirometer Exercise 2: How the Respirometer Works Exercise 3: How to Read a Pipette Exercise 4: Assembling the Respirometer Exercise 5: More Information on Germinating Peas Exercise 6: Bacterial Colonies Concept 2: Transformation Procedure Closer Look: Step 1 Closer Look: Step 2 Closer Look: Step 3 Closer Look: Step 4 Closer Look: Step 6 Exercise 2: Transformation Procedure Animation Exercise 3: How Do Restriction Enzymes Work?
Preparing the Gels Exercise 2: Loading the Gel Exercise 3: Filling the Wells Exercise 4: Running the Gel Exercise 6: Parental Generation Exercise 2: A Large Breeding Population Concept 2: Random Mating Concept 3: No Immigration or Emigration Concept 5: No Natural Selection Concept 6: Estimating Allelic Frequency Concept 7: The Hardy-Weinberg Equation Concept 8: Sample Problem 1 Concept 9: Sample Problem 2 Concept Sample Problem 3 Concept Hydrogen Bonding Concept 2: How Do Guard Cells Function?
Guard Cell Function Animation Concept 5: Transpiration and Photosynthesis Concept 6: An Overview of the Experiment Experiment 2: Blood Pressure Concept 2: Understanding Blood Pressure Concept 3: Measuring Blood Pressure Concept 4: The renal arteries arise, one on each side, from the abdominal aorta at a point opposite the upper border of the second lumbar vertebra i.
Close to the renal hilus each artery gives off small branches to the adrenal gland and ureter and then branches into anterior and posterior divisions. The large veins carrying blood from the kidneys usually lie in front of the corresponding arteries and join the inferior vena cava almost at right angles.
The left vein is longer than the right vein because the inferior vena cava lies closer to the right kidney. The kidneys are supplied with sympathetic and parasympathetic nerves of the autonomic nervous system , and the renal nerves contain both afferent and efferent fibres afferent fibres carry nerve impulses to the central nervous system; efferent fibres, from it. A cross section of a kidney reveals the renal sinus and two layers of kidney tissue distinguishable by their texture and colour.
The innermost tissue, called the renal medulla , forms comparatively dark cones, called renal pyramids , with bases outward and apexes projecting, either singly or in groups, into the renal sinus. Each projection of one or more pyramid apexes into the sinus is known as a renal papilla. The bases of these pyramids are irregular, with slender striations extending toward the external kidney surface.
The paler, more granular tissue external to the medulla is the cortex. It arches over the bases of the pyramids and fills gaps between the pyramids. Each group of pyramids that projects into a papilla, together with the portion of cortex that arches over the group, is called a renal lobe.
The renal sinus includes the renal pelvis , a funnel-shaped expansion of the upper end of the ureter, and, reaching into the kidney substances from the wide end of the funnel, two or three extensions of the cavity called the major calyxes.
The major calyxes are divided in turn into four to 12 smaller cuplike cavities, the minor calyxes , into which the renal papillae project.
The renal pelvis serves as the initial reservoir for urine, which flows into the sinus through the urinary collecting tubules, small tubes that open into the sinus at the papillae. The structural units of the kidneys that actually produce urine are the nephrons , of which there are approximately 1,, in each kidney. Each nephron is a long tubule or extremely fine tube that is closed, expanded, and folded into a double-walled cuplike structure at one end. The capsule and glomerulus together constitute a renal corpuscle , also called a malpighian body.
Blood flows into and away from the glomerulus through small arteries arterioles that enter and exit the glomerulus through the open end of the capsule. This opening is called the vascular pole of the corpuscle. The tubules of the nephrons are 30—55 millimetres 1. The corpuscle and the initial portion of each tubule, called the proximal convoluted tubule , lie in the renal cortex.
The tubule descends into a renal pyramid , makes a U-shaped turn, and returns to the cortex at a point near its point of entry into the medulla. This section of the tubule, consisting of the two parallel lengths and the bend between them, is called the loop of Henle or the nephronic loop. After its reentrance into the cortex, the tubule returns to the vascular pole the opening in the cuplike structure of the capsule of its own nephron.
The final portion of the tubule, the distal convoluted tubule , leads from the vascular pole of the corpuscle to a collecting tubule , by way of a short junctional tubule. Several of the collecting tubules join together to form a somewhat wider tubule, which carries the urine to a renal papilla and the renal pelvis. Although all nephrons in the kidney have the same general disposition , there are regional differences, particularly in the length of the loops of Henle.
Glomeruli that lie deep in the renal cortex near the medulla juxtamedullary glomeruli possess long loops of Henle that pass deeply into the medulla, whereas more superficial cortical glomeruli have much shorter loops. Among different animal species the length of the loops varies considerably and affects the ability of the species to concentrate urine above the osmotic concentration of plasma.
The successive sections of the nephron tubule vary in shape and calibre , and these differences, together with differences in the cells that line the sections, are associated with specific functions in the production of urine.
The intrarenal network of blood vessels forms part of the blood-processing apparatus of the kidneys. The anterior and posterior divisions of each renal artery , mentioned earlier, divide into lobar arteries, each of which enters the kidney substance through or near a renal papilla. Each lobar artery gives off two or three branches, called interlobar arteries, which run outward between adjacent renal pyramids.
When these reach the boundary between the cortex and the medulla they split almost at right angles into branches called arcuate arteries that curve along between the cortex and the medulla parallel to the surface of the kidney.
Many arteries, called interlobular arteries , branch off from the arcuate arteries and radiate out through the cortex to end in networks of capillaries in the region just inside the capsule. En route they give off short branches called the afferent arterioles , which carry blood to the glomeruli where they divide into four to eight loops of capillaries in each glomerulus.
Near and before the point where the afferent arteriole enters the glomerulus, its lining layer becomes enlarged and contains secretory granules. This composite structure is called the juxtaglomerular apparatus JGA and is believed to be involved in the secretion of renin see below The role of hormones in renal function.
They are then reconstituted near the point of entry of the afferent arteriole to become the efferent arterioles carrying blood away from the glomeruli. The afferent arterioles are almost twice as thick as the efferent arterioles because they have thicker muscular coats, but the sizes of their channels are almost the same. Throughout most of the cortex the efferent arterioles redivide into a second set of capillaries, which supply blood to the proximal and distal renal tubules.
The efferent glomerular arterioles of juxtaglomerular glomeruli divide into vessels that supply the contiguous tubules and vessels that enter the bases of the renal pyramids. Known as vasa recta, these vessels run toward the apexes of the pyramids in close contact with the loops of Henle.
Like the tubules they make hairpin bends, retrace their path, and empty into arcuate veins that parallel the arcuate arteries. Normally the blood circulating in the cortex is more abundant than that in the medulla amounting to over 90 percent of the total , but in certain conditions, such as those associated with severe trauma or blood loss, cortical vessels may become constricted while the juxtamedullary circulation is preserved. Because the cortical glomeruli and tubules are deprived of blood, the flow of urine is diminished, and in extreme cases may cease.
The renal venules small veins and veins accompany the arterioles and arteries and are referred to by similar names. The venules that lie just beneath the renal capsule , called stellate venules because of their radial arrangement, drain into interlobular venules.
In turn these combine to form the tributaries of the arcuate, interlobar, and lobar veins. Blood from the renal pyramids passes into vessels, called venae rectae, which join the arcuate veins. In the renal sinus the lobar veins unite to form veins corresponding to the main divisions of the renal arteries, and they normally fuse to constitute a single renal vein in or near the renal hilus.
Lymphatic capillaries form a network just inside the renal capsule and another, deeper network between and around the renal blood vessels. Few lymphatic capillaries appear in the actual renal substance, and those present are evidently associated with the connective tissue framework, while the glomeruli contain no lymphatics.
The lymphatic networks inside the capsule and around the renal blood vessels drain into lymphatic channels accompanying the interlobular and arcuate blood vessels. The main lymph channels run alongside the main renal arteries and veins to end in lymph nodes beside the aorta and near the sites of origin of the renal arteries.
The ureters are narrow, thick-walled ducts, about 25—30 centimetres 9. Throughout their course they lie behind the peritoneum, the lining of the abdomen and pelvis, and are attached to it by connective tissue. In both sexes the ureters enter the bladder wall about five centimetres apart, although this distance is increased when the bladder is distended with urine.
The ureters run obliquely through the muscular wall of the bladder for nearly two centimetres before opening into the bladder cavity through narrow apertures.
This oblique course provides a kind of valvular mechanism; when the bladder becomes distended it presses against the part of each ureter that is in the muscular wall of the bladder, and this helps to prevent the flow of urine back into the ureters from the bladder.
The wall of the ureter has three layers, the adventitia, or outer layer; the intermediate, muscular layer; and the lining, made up of mucous membrane. The adventitia consists of fibroelastic connective tissue that merges with the connective tissue behind the peritoneum. The muscular coat is composed of smooth involuntary muscle fibres and, in the upper two-thirds of the ureter, has two layers—an inner layer of fibres arranged longitudinally and an outer layer disposed circularly.
In the lower third of the ureter an additional longitudinal layer appears on the outside of the vessel. As each ureter extends into the bladder wall its circular fibres disappear, but its longitudinal fibres extend almost as far as the mucous membrane lining the bladder.
The mucous membrane lining increases in thickness from the renal pelvis downward. Thus, in the pelvis and the calyxes of the kidney the lining is two to three cells deep; in the ureter, four to five cells thick; and in the bladder, six to eight cells.
The mucous membrane of the ureters is arranged in longitudinal folds, permitting considerable dilation of the channel. There are no true glands in the mucous membrane of the ureter or of the renal pelvis. The chief propelling force for the passage of urine from the kidney to the bladder is produced by peristaltic wavelike movements in the ureter muscles. The urinary bladder is a hollow muscular organ forming the main urinary reservoir. It rests on the anterior part of the pelvic floor see below , behind the symphysis pubis and below the peritoneum.
The symphysis pubis is the joint in the hip bones in the front midline of the body. The shape and size of the bladder vary according to the amount of urine that the organ contains. When empty it is tetrahedral and lies within the pelvis; when distended it becomes ovoid and expands into the lower abdomen.
It has a body, with a fundus, or base; a neck; an apex; and a superior upper and two inferolateral below and to the side surfaces, although these features are not clearly evident except when the bladder is empty or only slightly distended.
The neck of the bladder is the area immediately surrounding the urethral opening; it is the lowest and most fixed part of the organ.
In the male it is firmly attached to the base of the prostate, a gland that encircles the urethra. The superior surface of the bladder is triangular and is covered with peritoneum.
The bladder is supported on the levator ani muscles, which constitute the major part of the floor of the pelvic cavity. The bladder is covered, and to a certain extent supported, by the visceral layer of the pelvic fascia. This fascial layer is a sheet of connective tissue that sheaths the organs, blood vessels, and nerves of the pelvic cavity. The fascia forms, in front and to the side, ligaments, called pubovesical ligaments, that act as a kind of hammock under the inferolateral surfaces and neck of the bladder.
The blood supply of the bladder is derived from the superior, middle, and inferior vesical bladder arteries. The superior vesical artery supplies the dome of the bladder, and one of its branches in males gives off the artery to the ductus deferens , a part of the passageway for sperm.
The middle vesical artery supplies the base of the bladder. The inferior vesical artery supplies the inferolateral surfaces of the bladder and assists in supplying the base of the bladder, the lower end of the ureter, and other adjacent structures.
The nerves to the urinary bladder belong to the sympathetic and the parasympathetic divisions of the autonomic nervous system. The sympathetic nerve fibres come from the hypogastric plexus of nerves that lie in front of the fifth lumbar vertebra.
Sympathetic nerves carry to the central nervous system the sensations associated with distention of the bladder and are believed to be involved in relaxation of the muscular layer of the vesical wall and with contraction of sphincter mechanism that closes the opening into the urethra. The parasympathetic nerves travel to the bladder with pelvic splanchnic nerves from the second through fifth sacral spinal segment.
Parasympathetic nerves are concerned with contraction of the muscular walls of the bladder and with relaxation of its sphincter. Consequently they are actively involved in urination and are sometimes referred to as the emptying, or detrusor, nerves. The bladder wall has a serous coat over its upper surface. This covering is a continuation of the peritoneum that lines the abdominal cavity; it is called serous because it exudes a slight amount of lubricating fluid called serum.
The other layers of the bladder wall are the fascial, muscular, submucous, and mucous coats.