Notes And Study Material for Exam Papers

Meiosis or reduction division is complicated type of cell division occurring in the reproduction of germ cells at the time of gametic formation. In animals it occurs during gametes formation. Every species has definite number of chromosomes and that this number remains constant in its somatic cells, generation after generation. To keep the number constant the chromosome number in gametes is reduced to half. When male and female gametes and their nuclei fuse, normal number of chromosomes characteristic of each species is restored. The somatic or vegetative cells having the complete number of chromosomes are called diploid (2n). While gametes containing half of the original number of chromosomes are called haploid (n) or monoploid. The events of Meiosis: Meiosis consists of two successive divisions of mother cells. First division is reduction division, during which the chromosome number (2n) in both daughter cells is reduced to half (n), the second division is simple mitotic div...

During life cycle of most animals some diploid cells undergo meiosis and haploid gametes form in a process called gametogenesis. The testes of the male, produces sperms and is called spermatogenesis, in the ovaries of female, the production of oval (eggs) is called oogenesis. Spermatogenesis: Spermatogenesis produces mature sperm as follows: (1)        Spermatogenesis begins in unspecialized germ cells called spermatogomia (singular spermatogonium). The spermatogonium enlarges and becomes primary spermatocyte. (2)        A primary spermatocyte undergoes meiosis (meiotic division I) and produces two smaller secondary spermatocytes). (3)        Both secondary spermatocytes undergo second meiotic division (meiotic division II) to form spermatids each primary spermatocyte gives rise to four spermatids, each with the haploid number of chromosomes. (4)  ...

Animal Systematics: The goal of animal systematics is to arrange animals into group, that reflect evolutionary relationship. Monophyletic group: When groups include single ancestral species and all of its descendents such a group is called monophyletic group, in searching out monophyletic groups, taxonomists look for animal attributes called characters that indicate relatedness. Character: A character is virtually anything that has a genetic basis and can be measured from an anatomical feature to a sequence of nitrogenous bases in DNA or RNA. Polyphyletic groups: They have members that can be traced to separate ancestors. Since each group should have single ancestor, a polyphyletic group reflects insufficient knowledge of the group. Paraphyletic group: It includes some, but not all, members of a lineage. Paraphyletic groups result when knowledge of the group is insufficient. Evolutionary Systematics: It is the oldest of three approaches. It is also called tra...

In 1969, Whittaker described a system of classification that distinguished between kingdom according to cellular organization and mode of nutrition. According to this system members of kingdom monera are bacteria and cyanobacteria. They are prokaryotes members of kingdom protista are eukaryotic and consist of single cells or colonies of cells. Members of kingdom plantae are eukaryotic, multi-cellular and photosynthetic. Plants have walled cells and are usually non motile. Members of kingdom fungi are also eukaryotic and multi-cellular. They also have walled cells and are usually non motile. Fungi are decomposers. Members of kingdom animalia are eukaryotic and multi-cellular and they usually feed by ingesting other organisms or parts of other organisms. Their cells lack walls and they are usually motile. For the first two billion years of life on the earth, living forms were prokaryotic microbes. Molecular studies of variations in base sequences of ribosomal RNA from more than ...

Invertebrate Coelomic fluid and hemolymph: Some animals like Echinoderms, Annelids and Sipunculans are coelomic fluid as Supplementary or sole circulatory system. Coelomic fluid may be identified in composition to interstitial fluids or may differ particularly with respect to specific proteins and cells. Coelomic fluid transports gases, nutrients and waste products. It also functions in certain invertebrates (annelids) as a hydrostatic skeleton. Hemolymph is circulatory fluid of animals with an open circulatory system. Most Arthropods, Ascidians and many Molluscs have hemolymph. In these animals heart pumps hemolymph at low pressure through vessels to tissue spaces (hemocoel) and sinuses. Generally hemolymph volume is high and the circulation slow. In the process of movement, essential gases, nutrients and wastes are transported. Many times hemolymph has no circulatory functions. In insects, hemolymph pressure assists in molting of old cuticle and in inflation of the wings....

Biochemistry of Hormones or Chemical nature of hormones: Most hormones are proteins (Polypeptides) derivates of amino acids (amines) or steroids. A few are fatty acid derivates e.g. most invertebrate neurosecretary cells produce polypeptides called neuropeptides. Hormones that the vertebrate pancreas secretes are proteins; those that the thyroid gland secretes are amines. The ovaries, testes and cortex of adrenal glands secrete steroids. Hormones are effective in small amount. Only few molecules of hormone may be enough to produce a dramatic response in a target cell. In target cell hormones help to control biochemical reactions in three ways: (i) A hormone can increase the rate at which other substances enter or leave the cell. (ii) It can stimulate a target cell to synthesize enzymes, proteins or other substances. (iii) It can prompt a target cell to activate or suppress existing cellular enzymes. Hormones are not changed by reaction they regulate. Lobes of pituitary glands (...

Depolarization and Re-polarization: When a stimulus is appeared to a point along the resting plasma membrane the permeability to Na + ions causes the temperature to go from -70mV toward 0. This loss in membrane polarity is called depolarization. When depolarization reaches certain level, special Na + channels (voltage gated) that are sensitive to changes in membrane potential quickly open and more Na+ ions can rush to the inside of the neuron. Re-polarization: Shortly after Na + ions move into the cell, Na + ions rapidly diffuse outward. The movement of K + ions out of the cell builds up positive charge outside the cell again and membrane becomes re-polarized. Hormone and its effect on target cells: A hormone specialized chemical messenger that an endocrine gland produces and secretes. Hormones circulate through body fluid and affect the metabolic activity of target cells in a specific way. Target cells has receptors to which chemical messenger either selectively bind ...

Propioreceptors: Propio = self. Propioreceptors commonly called “stretch receptors” are internal sense organs that respond to mechanically induced changes caused by stretching, compression, bending or tension. These receptors give an annual information about the movement of its body parts and their position relative to each other. Proprioreceptors have been most thoroughly studied in arthropods where they are associated with appendage, joints and body extensor muscles. In these animals the sensory neurons involved in proprioreception are associated with and attached to some part of the body that is stretched. These parts may be specialized muscle cells, elastic connective tissue fibres or various membranes that span joints. As these structures change shape, sensory nerve endings of the attached nerves distort accordingly and initiate a generator potential. Tactilereceptors and Thermoreceptors: Tactilereceptors: Tactile = touch. Tactilereceptors are derived from modification...

Baroreceptors and chemoreceptors: baros = weight + receptor. Baroreceptors sense changes in pressure. Responses to pressure changes have been identified in ocean dwelling copepod crustaceans, ctenophores, jelly-fish medusa and squids. Some intertidal crustaceans coordinate migratory activity with daily tidal movement possibly in response to pressure changes accompanying water depth changes. Chemoreceptors: They pertain to chemistry and respond to chemicals. Protozoa have chemical sense. They respond with avoidance behaviour to acid, alkali and salt stimuli. Chemoreceptors of may aquatic invertebrates are located in pits or depression through which water carrying the specific chemicals may be circulated. In arthropods chemoreceptors are on antennae, mouthparts and legs in the form of hollow hairs containing chemo sensory neusons. The types of chemicals which invertebrates respond are closely associated with their life styles as humidity detection, pH assessment, prey tracking, f...

Skeletal muscle contraction: Electron microscopy and biochemical analysis show that in muscle fibres cell bends are due to the placement of muscle protein action and myosin with myofibrils. Myosin occurs as thick filaments and actin as thin filaments. The lightest region of a myofibril contains only actin whereas the darkest region contains both. The functional (contractile) unit of a myofibril is sarcomere each of which extends from one Z line to another z line. The actin filaments attach to the Z lines whereas myosin filaments do not. When a sarcomere contracts the actin filament slide pas the myosin filaments as they approach one another. This process shortens the sarcomere. The combined decreases in length of the individual sarcomeres account for contraction of the whole muscle fibres and in turn, the whole muscle. A ratchet mechanism between two filament types produces the actual contraction. Myosin contains globular projections that attach to actin as specific active ...

Sudoriferous and Sebaceous glands in Mammals: Sudoriferous glands: Sudor = sweat. They are also called sweat glands and are distributed over most of the human body surface. These glands secrete sweat by a process called perspiration. Perspiration helps to regulate body temperature and maintain homeostasis, largely by the cooling effect of evaporation. In some mammals curtain sweat glands also produce pheromones (it is a chemical that an animal secretes and that communicates with other members of the same species to elicit certain behavioural responses). Sebaceous glands: They are oil glands. They are simple glands connected to hair follicles in the dermis. They lubricate and protect by secreting sebum. Sebum is a permeability barrier, an emollient (skin softening agent) and a protective agent against micro organisms. Sebum can also act as pheromone. Hydrostatic skeleton: Skeleton of invertebrates is a core of liquid (water or a body fluid such as blood) surrounded by a ...

Integumentary system of Protozoa: Some protozoa have only a plasma membrane for external covering. This membrane is structurally and chemically identical to the plasma membrane of multicellular organisms. In protozoa plasma membrane has large surface area relative to body volume so that gas exchange and removal of soluble wastes occur by diffusion. This large surface area also facilitates the uptake of dissolved nutrients from surrounding fluids. Paramecium has thick protein coat called pellicle outside the plasma membrane. This pellicle is protective and is a semi rigid structure that transmits force of cilia or flagella to entire body of Protozoa as it moves. Cuticle and tegument in invertebrates: Some invertebrates like rotifers have cuticles that are thin and elastic. In crustaceans, archanids, insects, cuticles are thick and rigid and support the body. Such cuticles consist of chitin and proteins in rigid plates that a flexible membrane links together. Cuticles retard gr...

Development in terrestrial environments: Reptiles, Aves and mammals develop on land and required protection from desiccation which is provided by extra embryonic membranes. Longer developmental periods of these animals reflect their lack of independent larval stages. Avian embryology: Egg: The yellow portion of the chicken egg is single cell produce in chicken ovary. This egg is released into the oviduct where fertilization may occur. Following fertilization, membranes and fluids collect around the egg. A vitelline membrane covers the surface of true egg. The ‘white’ consists of water and a protein called albumen. This watery environment protects the egg from mechanical damage and drying. Albumen is a source of nutrients and is eventually consumed during development.  Two denser strands of albumen (called chalazas) attach to the inside of the shell and to the egg and suspend the egg in the centre of watery albumen. The shell is made up of calcium carbonate impregnated...

Amphibian embryology: Most amphibians lay eggs in watery environments and the eggs are fertilized as the female releases them. Frog eggs have a pigmented animal pole. Because the vegetal pole is heavily laden with yolk, the eggs rotate in their jelly coats so that the less dense, darky pigmented animal pole is oriented up. This rather simple series of events has interesting adaptive significance. Amphibian eggs develop with little parental care. The pigmentation helps camouflage developing embryos from predators. When viewed from below, the light colour of the vegetal end of floating eggs blends with the sky above. When viewed from above the dark colour of the animal end blends with the bottom of the pond, lake or stream. The dark pigment of the animal pole also absorbs heat from the sun and the warming promote development. Cleavages/Morula: The first longitudinal cleavage begins at the animal pole and divides the grey crescent in half, because of the large amount of yolk in ...

The eggs of echinoderms have relatively little yolk and the yolk is evenly distributed throughout the egg. Morula: Cleavages and holoblastic and result in smaller blastomeres. In just few hours the morula is produced. As cell division continuous, cells pull away from the interior of the embryo. A fluid filled cavity the blastocoel forms and the cells form single layer around the cavity. The embryo is now a hollow sphere called blastula. In sea urchins development through the blastula stages takes place within the fertilization membrane. When the cells of the blastula develop cilia, the blastula breaks out of the fertilization membrane and begins to swim. Late in the blastula stage, groups of cells break free of the animal and of the embryo and position themselves within the blastocoel. These cells called primary mesenchyme will form skeletal elements (spicules) of the embryo. FIG will be attached, photo copy Gastrulation: First sign of gastrulation is the imagination of...

The fusion of acrosonal and egg membranes is the beginning of egg activation. Egg activation is a series of biochemical changes in the egg that ensures the completion of fertilization and initiates embryonic development. Biologists have extensively studies of events and some of the findings of egg activation in echinoderms that work are discussed here. Membrane events: Some of the earliest changes in the zygote at the plasma membrane and in the outer region of the cell cytoplasm (called cortex). These early changes ensure fertilization by only single sperm. Single sperm fertilization is important because multiple fertilization usually results in genetic imbalances and a nonviable embryo. After contract by sperm, microvilli from the plasma membrane of the ovum wrap around single sperm. Contraction of micro filaments in egg’s cytoplasm then draws the sperm into the egg. Second series of events defends against multiple fertilization within milliseconds of penetration by a ...

Human female do not undergo a seasonal oestrous cycle as lower mammals do, instead one egg is released from an ovary about once every 28 days. This is often called ovarian cycle. This correlated with certain uterine changes which occur to prepare it for a possible pregnancy; this often is called uterine cycle. This monthly egg maturation and uterine preparation is collectively menstrual cycle (often called menses, month). Menstruation begins around the age of thirteen and stops menopause around the age of fifty. Menstrual cycle is the preparation of uterus for a possible pregnancy. The menstrual cycle is controlled by hormones and completes every 28 days. It occurs in four distinct phases (i) Menstruation or M phase (ii) follicle or f phase (iii) ovulation or O phase (iv) Corpus luteum or L phase. Menstruation: Menstruation is the onset of bleeding that is discharge of blood and discarded tissue of the uterus through vagina. Menstruation takes place when the body becomes aware ...

Events: The development of human being can be divided into prenatal (before birth) and postnatal (after birth) periods. During prenatal period the developing individual begins life as a zygote, then becomes a ball of cells called morulla and eventually becomes a blastocyst that implants in the endometrium. From two weeks after fertilization until the end of eighth week of its existence, the individual is called an embryo. From nine weeks until birth it is fetus. During or after birth it is called a newborn. Pregnancy is divided into three month periods called trimesters. First Trimester: After fertilization usually in the upper third of the uterine tube, the zygote goes through several cleavages as it moves down the tube. It eventually becomes a solid ball of cells called morulla and by fourth day, it develops into 50 to 120 cell blastula stage called a blastocyst. The next stage of development occurs when the blastocyst adheres to the uterine wall and implants. During ...

Human female organs: Females produce gametes (eggs or ova) after fertilization, they also nourish, carry and protect developing embryo. After the offspring is born, the mother may nurse it for a time. Female reproductive system consists of number of structures with specialized functions: (1) Two ovaries produce eggs and the female sex hormones estrogen and progesterone. (2) Two uterine tubes, one from each ovary carry eggs from the ovary to the uterus. Fertilization occurs in upper third of a uterine tube. (3) If fertilization occurs the uterus receives blatocyst and houses the developing embryo. (4) Vagina receives semen from the penis during sexual intercourse. It is the exist point for menstrual flow and is the canal through which body passes from uterus during child birth. (5) External genital organs have protective functions and a play role in sexual arousal. (6) Mammary glands contained in paired breasts produce milk for new born baby. Hormonal regulatio...