1.
Human development (biology)
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Human development is the process of growing to maturity. In biological terms, this entails growth from a zygote to an adult human being. Fertilization occurs when the sperm enters the ovums membrane. The genetical material of the sperm and egg that combine to form a cell, called a zygote. The germinal stage refers to the time from fertilization, through the development of the early embryo, the germinal stage is over at about 10 days of gestation. The zygote contains a full complement of genetic material and develops into the embryo, briefly, embryonic developments have four stages, the morula stage, the bastula stage, the gastrula stage, and the neurula stage. Prior to implantation, the remains in a protein shell, the zona pellucida. A week after fertilization the embryo still has not grown in size and this induces a decidual reaction, wherein the uterine cells proliferate and surround the embryo thus causing it to become embedded within the uterine tissue. The embryo, meanwhile, proliferates and develops both into embryonic and extra-embryonic tissue, the forming the fetal membranes and the placenta. In humans, the embryo is referred to as a fetus in the stages of prenatal development. The transition from embryo to fetus is arbitrarily defined as occurring 8 weeks after fertilization, in comparison to the embryo, the fetus has more recognizable external features and a set of progressively developing internal organs. A nearly identical process occurs in other species, auxology Child development Developmental biology Embryogenesis Life-history theory
2.
Human embryogenesis
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Human embryogenesis is the process of cell division and cellular differentiation of the embryo that occurs during the early stages of development. In biological terms, human development entails growth from a zygote to an adult human being. Fertilisation occurs when the cell successfully enters and fuses with an egg cell. The genetic material of the sperm and egg then combine to form a single cell called a zygote, embryogenesis covers the first eight weeks of development, at the beginning of the ninth week the embryo is termed a fetus. Human embryology is the study of development during the first eight weeks after fertilisation. The normal period of gestation is nine months or 38 weeks, the germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus. The germinal stage takes around 10 days, during this stage, the zygote begins to divide, in a process called cleavage. A blastocyst is then formed and implanted in the uterus, embryogenesis continues with the next stage of gastrulation, when the three germ layers of the embryo form in a process called histogenesis, and the processes of neurulation and organogenesis follow. In comparison to the embryo, the fetus has more recognizable external features, the entire process of embryogenesis involves coordinated spatial and temporal changes in gene expression, cell growth and cellular differentiation. A nearly identical process occurs in species, especially among chordates. Fertilization takes place when the spermatozoon has entered the ovum. This usually takes place in the ampulla of one of the fallopian tubes, the 46 chromosomes undergo changes prior to the mitotic division which leads to the formation of the embryo having two cells. Successful fertilization is enabled by three processes, which act as controls to ensure species-specificity. The first is that of chemotaxis which directs the movement of the sperm towards the ovum, secondly there is an adhesive compatibility between the sperm and the egg. The entry of the sperm causes calcium to be released which blocks entry to other sperm cells, a parallel reaction takes place in the ovum called the zona reaction. This sees the release of granules that release enzymes which digest sperm receptor proteins. The granules also fuse with the membrane and modify the zona pellucida in such a way as to prevent further sperm entry. The beginning of the process is marked when the zygote divides through mitosis into two cells
3.
Fetus
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A fetus is a stage in the prenatal development of viviparous organisms. In human development, a fetus or foetus is a human between the embryonic state and birth. The fetal stage of development tends to be taken as beginning at the age of eleven weeks. In biological terms, however, prenatal development is a continuum, the use of the term fetus generally implies that an embryo has developed to the point of being recognizable as a human, this is the point usually taken to be the ninth week after fertilization. A fetus is also characterized by the presence of all the body organs, though they will not yet be fully developed and functional. The word fetus is from the Latin fētus, the British, Irish, and Commonwealth spelling is foetus, which has been in use since at least 1594. It arose as a hypercorrection based on an incorrect etymology that may have originated with an error by Isidore of Seville in AD620 and this spelling is the most common in most Commonwealth nations, except in the medical literature, where fetus is used. The etymologically accurate original spelling fetus is used in Canada and the United States, in addition, fetus is now the standard English spelling throughout the world in medical journals. The spelling faetus was used historically, in humans, the fetal stage commences at the beginning of the ninth week. At the start of the stage, the fetus is typically about 30 millimetres in length from crown to rump. The head makes up half of the fetus size. Breathing-like movement of the fetus is necessary for stimulation of lung development, the heart, hands, feet, brain and other organs are present, but are only at the beginning of development and have minimal operation. The genitalia of the starts to form and placenta becomes fully functional during week 9. At this point in development, uncontrolled movements and twitches occur as muscles, the brain, and pathways begin to develop. A woman pregnant for the first time, typically feels fetal movements at about 21 weeks, whereas a woman who has given birth at least once, by the end of the fifth month, the fetus is about 20 cm long. The amount of body fat rapidly increases, thalamic brain connections, which mediate sensory input, form. Bones are fully developed, but are soft and pliable. Iron, calcium, and phosphorus become more abundant, fingernails reach the end of the fingertips
4.
Infant
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An infant is the more formal or specialised synonym for baby, the very young offspring of a human or other animal. A newborn is, in use, an infant who is only hours, days. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth, the term applies to premature, full term, and postmature infants, before birth, the term fetus is used. The term infant is typically applied to children under one year of age, however, definitions may vary. When a human child learns to walk, the toddler may be used instead. In British English, infant is a term that can be applied to children aged between four and seven. As a legal term, infancy continues from birth until age 18, a newborns shoulders and hips are wide, the abdomen protrudes slightly, and the arms and legs are relatively long with respect to the rest of their body. In first world nations, the total body length of newborns are 35. 6–50.8 cm. The Apgar score is a measure of a transition from the uterus during the first minutes after birth. In developed countries, the birth weight of a full-term newborn is approximately 3.4 kg. After the first week, healthy term neonates should gain 10–20 grams/day, a newborns head is very large in proportion to the body, and the cranium is enormous relative to his or her face. While the adult human skull is one seventh of the total body length. Normal head circumference for an infant is 33–36 cm at birth. At birth, many regions of the skull have not yet been converted to bone. The two largest are the anterior fontanel, located at the top front portion of the head, and the smaller triangular-shaped posterior fontanel. Later in the life, these bones will fuse together in a natural process. A protein called noggin is responsible for the delay in an infants skull fusion, during labour and birth, the infants skull changes shape to fit through the birth canal, sometimes causing the child to be born with a misshapen or elongated head. It will usually return to normal on its own within a few days or weeks, special exercises sometimes advised by physicians may assist the process
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Toddler
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A toddler is a child 12 to 36 months old. The toddler years are a time of great cognitive, emotional and social development, the word is derived from to toddle, which means to walk unsteadily, like a child of this age. Toddler development can be broken down into a number of interrelated areas, there is reasonable consensus about what these include, Physical, growth or an increase in size. Gross motor, the control of muscles which enable walking, running, jumping and climbing. Fine motor, the ability to control small muscles, enabling the toddler to feed themselves, draw, vision, the ability to see near and far and interpret what is seen. Hearing and speech, the ability to hear and receive information and listen, social, the ability to interact with the world through playing with others, taking turns and fantasy play. Although it is useful to chart defined periods of development, it is necessary to recognize that development exists on a continuum. There is a range of what may be considered normal development. Talking is the milestone of which parents are typically aware. A toddlers first word most often occurs around 12 months, the child will then continue to steadily add to his or her vocabulary until around the age of 18 months when language increases rapidly. He or she may learn as many as 7–9 new words a day, around this time, toddlers generally know about 50 words. At 21 months is when toddlers begin to incorporate two word phrases into their vocabulary, such as I go, mama give, and baby play, before going to sleep they often engage in a monologue called crib talk in which they practice conversational skills. At this age, children are becoming very proficient at conveying their wants, there are several other important milestones that are achieved in this time period that parents tend not to emphasize as much as walking and talking. Gaining the ability to point at whatever it is the child wants you to see shows huge psychological gains in a toddler and this generally happens before a childs first birthday. This age is sometimes referred to as the twos, because of the temper tantrums for which they are famous. This stage can begin as early as nine months old depending on the child, toddlers tend to have temper tantrums because they have such strong emotions but do not know how to express themselves the way that older children and adults do. They also throw tantrums to let know that they are free. The toddler is discovering that they are a separate being from their parent and are testing their boundaries in learning the way the world around them works and this time between the ages of two and five when they are reaching for independence repeats itself during adolescence
6.
Child
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Biologically, a child is a human being between the stages of birth and puberty. The legal definition of child generally refers to a minor, otherwise known as a younger than the age of majority. There are many issues that affect children, such as childhood education, bullying, child poverty, dysfunctional families, child labor, hunger. Children can be raised by parents, by fosterers, guardians or partially raised in a day care center. The United Nations Convention on the Rights of the Child defines child as a human being below the age of 18 years unless under the law applicable to the child and this is ratified by 192 of 194 member countries. Biologically, a child is generally anyone between birth and puberty, some English definitions of the word child include the fetus. In many cultures, a child is considered an adult after undergoing a rite of passage, recognition of childhood as a state different from adulthood began to emerge in the 16th and 17th centuries. Society began to relate to the not as a miniature adult but as a person of a lower level of maturity needing adult protection, love. This change can be traced in paintings, In the Middle Ages, in the 16th century, images of children began to acquire a distinct childlike appearance. From the late 17th century onwards, children were playing with toys. Every child goes through stages of social development. An infant or very young child will play alone happily, if another child wanders onto the scene, he or she may be physically attacked or pushed out of the way. Next, the child can play with another child, gradually learning to share, eventually, the group grows larger, to three or four children. By the time a child enters kindergarten, he or she can join in. Children with ADHD and learning disabilities may need help to develop social skills. The impulsive characteristics of an ADHD child may lead to poor peer relationships, children with poor attention spans may not tune into social cues in their environment, making it difficult for them to learn social skills through experience. The age at which children are considered responsible for their society-bound actions has changed over time. In Roman times, children were regarded as not culpable for crimes, in the 19th century, children younger than seven years old were believed incapable of crime
7.
Preadolescence
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Preadolescence, also known as pre-teen or tween, is a stage of human development following early childhood and preceding adolescence. It commonly ends with the beginning of puberty, but may also be defined as ending with the start of the teenage years, for example, dictionary definitions generally designate it as 10–13 years. Preadolescence can bring its own challenges and anxieties, being prepubescent is not the same thing as being preadolescent. Instead, prepubescent is a term for boys and girls who have not developed secondary sex characteristics, preadolescence may also be defined as the period from 9 to 14 years. The point at which a child becomes an adolescent is defined by the onset of puberty or by the beginning of the teenage stage, adolescence is also viewed as ending with the teenage stage. However, in individuals, puberty begins in the preadolescence years. Studies indicate that the onset of puberty has been one year earlier with each generation since the 1950s, one can also distinguish middle childhood and preadolescence – middle childhood from approximately 5–8 years, as opposed to the time children are generally considered to reach preadolescence. While known as preadolescent in psychology, the terms preteen, preteenager or tween are common in everyday use, a preteen or preteenager is a person 12 and under. Generally, the term is restricted to close to reaching age 12. Tween is an American neologism and marketing term for preteen, which is a blend of between and teen, people within this age range are variously described as tweens, preadolescents, tweenies, preteens, pubescents, junior highers or tweenagers. In this context, the word is either a shortened version of between or a portmanteau of teen and twenty, and in either case has no connection to teens, preteens or the American marketing niche. Preadolescent children in fact have a different view of the world from younger children in many significant ways, typically, theirs is a more realistic view of life than the intense, fantasy-oriented world of earliest childhood. Preadolescents have more mature, sensible, realistic thoughts and actions and they will often have developed a sense of intentionality. The wish and capacity to have an impact, and to act upon that with persistence and this can include more realistic job expectations. Preadolescents may well view human relationships differently, alongside that, they may begin to develop a sense of self-identity, and to have increased feelings of independence, may feel an individual, no longer just one of the family. A different view on morality can emerge, and the child will also show more cooperativeness. The ability to balance ones own needs with those of others in group activities, preadolescents may still suffer tantrums at the age of 13, sometimes leading to rash decisions regarding risky actions. Such decisions may in rare cases result in situations such as accidental death
8.
Adolescence
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Adolescence is a transitional stage of physical and psychological development that generally occurs during the period from puberty to legal adulthood. Adolescence is usually associated with the years, but its physical, psychological or cultural expressions may begin earlier. For example, puberty now typically begins during preadolescence, particularly in females, physical growth, and cognitive development can extend into the early twenties. Thus age provides only a marker of adolescence, and scholars have found it difficult to agree upon a precise definition of adolescence. A thorough understanding of adolescence in society depends on information from various perspectives, including psychology, biology, history, sociology, education, and anthropology. Within all of these perspectives, adolescence is viewed as a period between childhood and adulthood, whose cultural purpose is the preparation of children for adult roles. It is a period of transitions involving education, training, employment and unemployment. The end of adolescence and the beginning of adulthood varies by country, Adolescence is usually accompanied by an increased independence allowed by the parents or legal guardians, including less supervision as compared to preadolescence. Major pubertal and biological changes include changes to the sex organs, height, weight, cognitive advances encompass both increment in knowledge and in the ability to think abstractly and to reason more effectively. The study of adolescent development often involves interdisciplinary collaborations, for example, researchers in neuroscience or bio-behavioral health might focus on pubertal changes in brain structure and its effects on cognition or social relations. Sociologists interested in adolescence might focus on the acquisition of social roles, developmental psychologists might focus on changes in relations with parents and peers as a function of school structure and pubertal status. Some scientists have questioned the universality of adolescence as a developmental phase, puberty is a period of several years in which rapid physical growth and psychological changes occur, culminating in sexual maturity. The average age of onset of puberty is at 11 for girls and 12 for boys, every persons individual timetable for puberty is influenced primarily by heredity, although environmental factors, such as diet and exercise, also exert some influences. These factors can contribute to precocious and delayed puberty. Some of the most significant parts of pubertal development involve distinctive physiological changes in height, weight, body composition. These changes are largely influenced by hormonal activity, puberty occurs through a long process and begins with a surge in hormone production, which in turn causes a number of physical changes. It is the stage of life characterized by the appearance and development of sex characteristics. This is triggered by the pituitary gland, which secretes a surge of hormonal agents into the blood stream, initiating a chain reaction to occur
9.
Adult
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Biologically, an adult is a human or other organism that has reached sexual maturity. In human context, the term adult additionally has meanings associated with social and legal concepts, in contrast to a minor, a legal adult is a person who has attained the age of majority and is therefore regarded as independent, self-sufficient, and responsible. Human adulthood encompasses psychological adult development, conversely, one may legally be an adult but possess none of the maturity and responsibility that may define an adult character. In different cultures there are events that relate passing from being a child to becoming an adult or coming of age. This often encompasses the passing a series of tests to demonstrate that a person is prepared for adulthood, or reaching a specified age, most modern societies determine legal adulthood based on reaching a legally specified age without requiring a demonstration of physical maturity or preparation for adulthood. Historically and cross-culturally, adulthood has been determined primarily by the start of puberty, in the past, a person usually moved from the status of child directly to the status of adult, often with this shift being marked by some type of coming-of-age test or ceremony. After the social construct of adolescence was created, adulthood split into two forms, biological adulthood and social adulthood, thus, there are now two primary forms of adults, biological adults and social adults. Depending on the context, adult can indicate either definition, thus, the base definition of the word adult is the period beginning at puberty. Puberty generally begins around 10 or 11 years of age for girls and 11 or 12 years of age for boys, legally, adulthood means that one can engage in a contract. One can distinguish the legality of acts of a person, or of enabling a young person to carry out that act, by selling, renting out, showing, permitting entrance, allowing participation. There may be distinction between commercially and socially enabling, sometimes there is the requirement of supervision by a legal guardian, or just by an adult. Sometimes there is no requirement, but rather a recommendation, with regard to films with violence, etc. Some cultures in Africa define adulthood at age 13, according to Jewish tradition, adulthood is reached at age 13 for Jewish boys and girls, they are expected to demonstrate preparation for adulthood by learning the Torah and other Jewish practices. The Christian Bible and Jewish scripture contain no age requirement for adulthood or marrying, which includes engaging in sexual activity. The 1983 Code of Canon Law states, A man before he has completed his year of age
10.
Human fertilization
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Human fertilization is the union of a human egg and sperm, usually occurring in the ampulla of the fallopian tube. The result of union is the production of a zygote cell, or fertilized egg. Scientists discovered the dynamics of human fertilization in the nineteenth century, the process of fertilization involves a sperm fusing with an ovum. The most common sequence begins with ejaculation during copulation, follows with ovulation, various exceptions to this sequence are possible, including artificial insemination, in vitro fertilization, external ejaculation without copulation, or copulation shortly after ovulation. Upon encountering the secondary oocyte, the acrosome of the sperm produces enzymes which allow it to burrow through the outer coat of the egg. The sperm plasma then fuses with the plasma membrane, the sperm head disconnects from its flagellum. In vitro fertilization is a process by which egg cells are fertilized by sperm outside the womb, the sperm binds through the corona radiata, a layer of follicle cells on the outside of the secondary oocyte. Fertilization occurs when the nucleus of both a sperm and an egg fuse to form a cell, known as zygote. The successful fusion of forms a new organism. Where the spermatozoon is about to pierce, the yolk is drawn out into a conical elevation, once the spermatozoon has entered, the peripheral portion of the yolk changes into a membrane, the perivitelline membrane, which prevents the passage of additional spermatozoa. At the beginning of the process, the sperm undergoes a series of changes, after binding to the corona radiata the sperm reaches the zona pellucida, which is an extra-cellular matrix of glycoproteins. A special complementary molecule on the surface of the sperm binds to a ZP3 glycoprotein in the zona pellucida. This binding triggers the acrosome to burst, releasing enzymes that help the sperm get through the zona pellucida, some sperm cells consume their acrosome prematurely on the surface of the egg cell, facilitating the penetration by other sperm cells. As a population, sperm cells have on average 50% genome similarity so the premature acrosomal reactions aid fertilization by a member of the same cohort and it may be regarded as a mechanism of kin selection. Recent studies have shown that the egg is not passive during this process, once the sperm cells find their way past the zona pellucida, the cortical reaction occurs. Cortical granules inside the secondary oocyte fuse with the membrane of the cell. This prevents fertilization of an egg by more than one sperm, the cortical reaction and acrosome reaction are both essential to ensure that only one sperm will fertilize an egg. The oocyte now undergoes its second meiotic division producing the haploid ovum, the sperm nucleus then fuses with the ovum, enabling fusion of their genetic material
11.
Language acquisition
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Language acquisition is the process by which humans acquire the capacity to perceive and comprehend language, as well as to produce and use words and sentences to communicate. Language acquisition is one of the human traits, because non-humans do not communicate by using language. Language acquisition usually refers to first-language acquisition, which studies infants acquisition of their native language and this is distinguished from second-language acquisition, which deals with the acquisition of additional languages. The capacity to use language requires one to acquire a range of tools including phonology, morphology, syntax, semantics. Language can be vocalized as in speech, or manual as in sign, human language capacity is represented in the brain. Even though human language capacity is finite, one can say and understand a number of sentences. Evidence suggests that individual has three recursive mechanisms that allow sentences to go indeterminately. These three mechanisms are, relativization, complementation and coordination, some early observation-based ideas about language acquisition were proposed by Plato, who felt that word-meaning mapping in some form was innate. In a more modern context, empiricists, like Thomas Hobbes and John Locke, proponents of behaviorism argued that language may be learned through a form of operant conditioning. In B. F. Skinners Verbal Behaviour, he suggested that the use of a sign, such as a word or lexical unit, given a certain stimulus. Some empiricist theories of language include the statistical learning theory. Charles F. Hockett of language acquisition, relational frame theory, functionalist linguistics, social interactionist theory, Skinners behaviourist idea was strongly attacked by Noam Chomsky in a review article in 1959, calling it largely mythology and a serious delusion. Arguments against Skinners idea of language acquisition through operant conditioning include the fact that children often ignore language corrections from adults. Instead, children follow a pattern of using an irregular form of a word correctly, making errors later on. For example, a child may learn the word gave. Eventually, the child will go back to learning the correct word. The pattern is difficult to attribute to Skinners idea of operant conditioning as the way that children acquire language. Chomsky argued that if language were solely acquired through behavioral conditioning, children would not likely learn the use of a word
12.
Puberty
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Puberty is the process of physical changes through which a childs body matures into an adult body capable of sexual reproduction. It is initiated by signals from the brain to the gonads, the ovaries in a girl. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when a body has been developed. Until the maturation of their capabilities, the pre-pubertal physical differences between boys and girls are the external sex organs. On average, girls begin puberty around ages 10–11, boys around ages 11–12, girls usually complete puberty around ages 15–17, while boys usually complete puberty around ages 16–17. In the 21st century, the age at which children, especially girls, reach puberty is lower compared to the 19th century. Puberty which starts earlier than usual is known as precocious puberty, Puberty which starts later than usual is known as delayed puberty. Two of the most significant differences between puberty in girls and puberty in boys are the age at which it begins, and the sex steroids involved, the testosterones. Although there is a range of normal ages, girls typically begin the process of puberty at age 10 or 11. Girls usually complete puberty by ages 15–17, while boys usually complete puberty by ages 16–17, girls attain reproductive maturity about four years after the first physical changes of puberty appear. In contrast, boys accelerate more slowly but continue to grow for about six years after the first visible pubertal changes, any increase in height beyond the post-pubertal age is uncommon. For boys, an androgen called testosterone is the sex hormone. While testosterone is produced, all changes are characterized as virilization. The conversion of testosterone to estradiol depends on the amount of body fat, the male growth spurt also begins later, accelerates more slowly, and lasts longer before the epiphyses fuse. Although boys are on average 2 centimetres shorter than girls before puberty begins, the hormone that dominates female development is an estrogen called estradiol. While estradiol promotes growth of the breasts and uterus, it is also the principal hormone driving the growth spurt and epiphyseal maturation. Estradiol levels rise earlier and reach higher levels in women than in men, the hormonal maturation of females is considerably more complicated than in boys
13.
Death
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Death is the cessation of all biological functions that sustain a living organism. Bodies of living organisms begin to decompose shortly after death, other concerns include fear of death, necrophobia, anxiety, sorrow, grief, emotional pain, depression, sympathy, compassion, solitude, or saudade. The potential for an afterlife is of concern for some humans, the word death comes from Old English deað, which in turn comes from Proto-Germanic *dauthuz. This comes from the Proto-Indo-European stem *dheu- meaning the Process, act, when a person has died, it is also said they have passed away, passed on, expired, or are gone, among numerous other socially accepted, religiously specific, slang, and irreverent terms. Bereft of life, the person is then a corpse, cadaver, a body, a set of remains, and when all flesh has rotted away. The terms carrion and carcass can also be used, though more often connote the remains of non-human animals. As a polite reference to a person, it has become common practice to use the participle form of decease, as in the deceased. The ashes left after a cremation are sometimes referred to by the neologism cremains, senescence refers to a scenario when a living being is able to survive all calamities, but eventually dies due to causes relating to old age. Almost all animals who survive external hazards to their biological functioning eventually die from biological aging, some organisms experience negligible senescence, even exhibiting biological immortality. These include the jellyfish Turritopsis dohrnii, the hydra, and the planarian, unnatural causes of death include suicide and homicide. From all causes, roughly 150,000 people die around the world each day, physiological death is now seen as a process, more than an event, conditions once considered indicative of death are now reversible. Where in the process a dividing line is drawn between life and death depends on factors beyond the presence or absence of vital signs, in general, clinical death is neither necessary nor sufficient for a determination of legal death. A patient with working heart and lungs determined to be dead can be pronounced legally dead without clinical death occurring. As scientific knowledge and medicine advance, formulating a precise definition of death becomes more difficult. The concept of death is a key to understanding of the phenomenon. There are many approaches to the concept. For example, brain death, as practiced in medical science, One of the challenges in defining death is in distinguishing it from life. As a point in time, death would seem to refer to the moment at which life ends, determining when death has occurred requires drawing precise conceptual boundaries between life and death
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Developmental psychology
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Developmental psychology is the scientific study of how and why human beings change over the course of their life. Originally concerned with infants and children, the field has expanded to include adolescence, adult development, aging, and this field examines change across three major dimensions, physical development, cognitive development, and socioemotional development. Developmental psychology examines the influences of nature and nurture on the process of human development, many researchers are interested in the interaction between personal characteristics, the individuals behavior and environmental factors, including social context and the built environment. Ongoing debates include biological essentialism vs. neuroplasticity and stages of development vs. dynamic systems of development, influential developmental psychologists from the 20th century include Urie Bronfenbrenner, Erik Erikson, Sigmund Freud, Jean Piaget, Barbara Rogoff, Esther Thelen, and Lev Vygotsky. Watson and Jean-Jacques Rousseau are typically cited as providing the foundations for modern developmental psychology, in the mid-18th century Jean Jacques Rousseau described three stages of development, infants, puer and adolescence in Emile, Or, On Education. Rousseaus ideas were taken up strongly by educators at the time, stanley Hall, who attempted to correlate ages of childhood with previous ages of mankind. James Mark Baldwin who wrote essays on topics that included Imitation, A Chapter in the Natural History of Consciousness and Mental Development in the Child, Baldwin was heavily involved in the theory of developmental psychology. Sigmund Freud, whose concepts were developmental, had a significant impact on public perceptions, Sigmund Freud believed that we all had a conscious, preconscious, and unconscious level. In the conscious we are aware of our mental process, the preconscious involves information that, though not currently in our thoughts, can be brought into consciousness. Lastly, the unconscious includes mental processes we are unaware of and he believed there is tension between the conscious and unconscious, because the conscious tries to hold back what the unconscious tries to express. To explain this he developed three personality structures, the id, ego, and superego, the id, the most primitive of the three, functions according to the pleasure principle, seek pleasure and avoid pain. The superego plays the critical and moralizing role, and the ego is the organized, based on this, he proposed five universal stages of development, that each are characterized by the erogenous zone that is the source of the childs psychosexual energy. The first is the stage, which occurs from birth to 12 months of age. During the oral stage the libido is centered in a babys mouth, the baby is able to suck. The second is the stage, from one to three years of age. During the anal stage, the child defecates from the anus, the third is the phallic stage, which occurs from three to five years of age. During the phallic stage, the child is aware of their sexual organs, the fourth is the latency stage, which occurs from age five until puberty. During the latency stage, the sexual interests are repressed
15.
Positive youth development
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PYD is used in scientific literature and by practitioners who work with youth to refer to programs designed to optimize developmental progress. PYD differs from other approaches to youth in that it rejects an emphasis on trying to correct what is wrong with childrens behavior or development, programs and practitioners seek to empathize with, educate, and engage children in productive activities. While not particularly common in use yet, PYD has been used across the world to address social divisions, such as gender, Positive youth development originated from ecological systems theory to focus on the strengths of adolescence. It is also similar conceptually with the principles of positive psychology, the major catalyst for the development of positive youth development came as a response to the negative and punitive methods of the traditional youth development approach. Another aspect of the traditional approach lies in that many professionals, specific evidence of this problem-centered model is present across professional fields that deal with young people. Many connections can also be made to the current U. S. criminal justice model that favors punishment as opposed to prevention, encouraging the positive development of adolescents can help to lessen the likelihood of such problems arising by easing a healthy transition into adulthood. Or as solely a means of avoiding risky behaviors, rather than grounding its developmental approach in the presence of adversity, risk or challenge, a PYD approach considers the potential and capacity of each individual young person. Lerner and colleagues write, The goal of the youth development perspective is to promote positive outcomes. This idea is in contrast to a perspective that focuses on punishment, Positive youth development is both a vision, an ideology and a new vocabulary for engaging with youth development. Its tenets can be organized into the 5 Cs which are, competence, confidence, connection, character, when these 5 Cs are present, the 6th C of contribution is realized. This cultural sensitivity reflects the influence of Bronfenbrenners ecological systems theory, the University of Minnesotas Keys to Quality Youth Development summarizes eight key elements of programs that successfully promote youth development. Physical activity-based programs like Girls on the Run are being increasingly utilized around the world for their ability to encourage psychological, emotional, and social development for youth. Girls on the Run enhances this type of physical activity program by specifically targeting youth in an effort to reduce the gendered view of a male-dominated sports arena. Girls on the Run is a non-profit organization begun in 1996 that distributes a 12-week training program to help prepare for a 5k running competition. This particular program is available to 3rd through 5th grade female students throughout the United States. Another example of youth development principles being utilized to target youth gender inequities can be seen in that of a participatory diagramming approach in Kibera. This community development effort enabled participants to feel safe discussing their concerns regarding gender inequities in the community with the dominant male group and this approach also enabled youth to voice their needs and identify potential solutions related to topics like HIV/AIDS and family violence. Positive youth development can be used to combat negative stereotypes surrounding youth of minority groups in the U. S
16.
Adult development
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Adult development encompasses the changes that occur in biological, psychological, and interphonal domains of human life from the end of adolescence until the end of ones life. These changes may be gradual or rapid, and can reflect positive, negative, changes occur at the cellular level and are partially explained by biological theories of adult development and aging. Biological changes influence psychological and interpersonal/social developmental changes, which are described by stage theories of human development. Stage theories typically focus on “age-appropriate” developmental tasks to be achieved at each stage, erik Erikson and Carl Jung proposed stage theories of human development that encompass the entire life span, and emphasized the potential for positive change very late in life. The concept of adulthood has legal and socio-cultural definitions, the legal definition of an adult is a person who has reached the age at which they are considered responsible for their own actions, and therefore legally accountable for them. This is referred to as the age of majority, which is age 18 in most cultures and this may or may not coincide with the legal definition. Jeanne Louise Calment exemplifies successful aging as the longest living person and her long life can be attributed to her genetics and her active lifestyle and optimistic attitude. She enjoyed many hobbies and physical activities and believed that laughter contributed to her longevity and she poured olive oil on all of her food and skin, which she believed also contributed to her long life and youthful appearance. Changes in adulthood have been described by a number of theories and metatheories, Life span development is an overarching framework that considers individual development from conception to old age. The framework considers the accumulation of developmental gains and losses. According to this theory, life span development has multiple trajectories and causes, individual variation is a hallmark of this theory – not all individuals develop and age at the same rate and in the same manner. Erik Erikson developed stages of ego development that extended through childhood, adolescence and he was trained in psychoanalysis and was highly influenced by Freud, but unlike Freud, Erikson believed that social interaction is very important to the individuals psychosocial development. His stage theory consists of 8 stages in life from birth to old age, during each stage, one developmental task is dominant, but may be carried forward into later stages as well. According to Erikson, individuals may experience tension when advancing to new stages of development and it offers a standard method of examining the universal pattern of development. The archaic stage is characterized by consciousness, while the monarchic stage represents the beginning of logical. Youth, Maturing sexuality, growing consciousness, and a realization that the days of childhood are gone forever. People strive to gain independence, find a mate, and raise a family, middle Life, The realization that you will not live forever creates tension. If you desperately try to cling to youth, you will fail in the process of self-realization, Jung believed that in midlife, one confronts ones shadow
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Attachment theory
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Attachment theory is a psychological model that attempts to describe the dynamics of long-term and short-term interpersonal relationships between humans. However, attachment theory is not formulated as a theory of relationships. It addresses only a specific facet, how human beings respond within relationships when hurt, separated from loved ones, essentially all infants become attached if provided any caregiver, but there are individual differences in the quality of the relationships. Fathers or any other individuals, are likely to become principal attachment figures if they provide most of the child care. In the presence of a sensitive and responsive caregiver, the infant will use the caregiver as a base from which to explore. It should be recognized that even sensitive caregivers get it right only about 50 percent of the time and their communications are either out of synch, or mismatched. There are times when parents feel tired or distracted, the telephone rings or there is breakfast to prepare. In other words, attuned interactions rupture quite frequently, but the hallmark of a sensitive caregiver is that the ruptures are managed and repaired. Attachments between infants and caregivers form even if this caregiver is not sensitive and responsive in social interactions with them, infants cannot exit unpredictable or insensitive caregiving relationships. Instead they must manage themselves as best they can within such relationships, early patterns of attachment, in turn, shape — but do not determine — the individuals expectations in later relationships. Four different attachment classifications have been identified in children, secure attachment, anxious-ambivalent attachment, anxious-avoidant attachment, and disorganized attachment. Attachment theory has become the dominant theory used today in the study of infant and toddler behavior and in the fields of infant mental health, treatment of children, and related fields. Secure attachment is when children feel they can rely on their caregivers to attend to their needs of proximity, emotional support and it is considered to be the best attachment style. Anxious-ambivalent attachment is when the infant feels separation anxiety when separated from the caregiver, anxious-avoidant attachment is when the infant avoids their parents. Disorganized attachment is when there is a lack of attachment behavior, in the 1980s, the theory was extended to attachment in adults. Attachment applies to adults when adults feel close attachment to their parents, within attachment theory, attachment means a biological instinct in which proximity to an attachment figure is sought when the child senses or perceives threat or discomfort. Attachment behaviour anticipates a response by the attachment figure which will remove threat or discomfort. Such bonds may be reciprocal between two adults, but between a child and a caregiver these bonds are based on the childs need for safety, security and protection, paramount in infancy, in the most complex organisms, instinctive behaviors may be goal-corrected with continual on-course adjustments
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Ecological systems theory
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Ecological systems theory, also called development in context or human ecology theory, identifies five environmental systems with which an individual interacts. This theory provides the framework from which community psychologists study the relationships with individuals contexts within communities, Ecological systems theory was developed by Urie Bronfenbrenner. Microsystem, Refers to the institutions and groups that most immediately and directly impact the development including, family, school, religious institutions, neighborhood. For example, a parents or childs experience at home may be influenced by the other parents experiences at work, the parent might receive a promotion that requires more travel, which might increase conflict with the other parent and change patterns of interaction with the child. Macrosystem, Describes the culture in which individuals live, cultural contexts include developing and industrialized countries, socioeconomic status, poverty, and ethnicity. A child, his or her parent, his or her school, members of a cultural group share a common identity, heritage, and values. The macrosystem evolves over time, because each generation may change the macrosystem. Chronosystem, The patterning of environmental events and transitions over the life course, for example, divorces are one transition. Researchers have found that the effects of divorce on children often peak in the first year after the divorce. By two years after the divorce, family interaction is less chaotic and more stable, an example of sociohistorical circumstances is the increase in opportunities for women to pursue a career during the last thirty years. The persons own biology may be considered part of the microsystem, per this theoretical construction, each system contains roles, norms and rules which may shape psychological development. For example, an inner-city family faces many challenges which an affluent family in a gated community does not, the inner-city family is more likely to experience environmental hardships, like crime and squalor. On the other hand, the family is more likely to lack the nurturing support of extended family. Bronfenbrenner has identified Soviet developmental psychologist Lev Vygotsky and German-born psychologist Kurt Lewin as important influences on his theory, there are many different theories related to human development. The ecological theory emphasizes environmental factors as playing the role to development. Bioecological model Ecosystem Ecosystem ecology Systems ecology Systems psychology Theoretical ecology Urie Bronfenbrenner, the Ecology of Human Development, Experiments by Nature and Design. ISBN 0-674-22457-4 Dede Paquette & John Ryan, Bronfenbrenner’s Ecological Systems Theory Woodside, Arch G. Caldwell, Marylouise, Spurr, Ray. Advancing Ecological Systems Theory in Lifestyle, Leisure, and Travel Research, marlowe E. Trance, Kerstin O. Flores
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Psychosexual development
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Each stage – the oral, the anal, the phallic, the latent, and the genital – is characterized by the erogenous zone that is the source of the libidinal drive. He argued that adult neurosis often is rooted in childhood sexuality, sexual infantilism, in pursuing and satisfying his or her libido, the child might experience failure and thus might associate anxiety with the given erogenous zone. e. The tendency to place objects in the mouth, the id dominates, because neither the ego nor the super ego is yet fully developed, and, since the infant has no personality, every action is based upon the pleasure principle. Nonetheless, the ego is forming during the oral stage, two factors contribute to its formation, in developing a body image, he or she is discrete from the external world. Weaning is the key experience in the oral stage of psychosexual development. In the case of too little gratification, the infant might become passive upon learning that gratification is not forthcoming, the style of parenting influences the resolution of the id–ego conflict, which can be either gradual and psychologically uneventful, or which can be sudden and psychologically traumatic. If the child obeys the id, and the yield, he or she might develop a self-indulgent personality characterized by personal slovenliness. If the parents respond to that, the child must comply, but might develop a sense of self, because it was the parents will, and not the childs ego. The third stage of development is the phallic stage, spanning the ages of three to six years, wherein the childs genitalia are his or her primary erogenous zone. In the phallic stage, a boys decisive psychosexual experience is the Oedipus complex and this psychological complex derives from the 5th-century BC Greek mythologic character Oedipus, who unwittingly killed his father, Laius, and sexually possessed his mother, Jocasta. Analogously, in the stage, a girls decisive psychosexual experience is the Electra complex. The boy focuses his libido upon his mother, and focuses jealousy, Electra, Whereas boys develop castration anxiety, girls develop penis envy that is rooted in anatomic fact, without a penis, she cannot sexually possess mother, as the infantile id demands. As a result, the girl redirects her desire for sexual union upon father, thus, moreover, after the phallic stage, the girls psychosexual development includes transferring her primary erogenous zone from the infantile clitoris to the adult vagina. Freud thus considered a girls Oedipal conflict to be more intense than that of a boy, resulting, potentially. Psychologic defense, In both sexes, defense mechanisms provide transitory resolutions of the conflict between the drives of the Id and the drives of the Ego. The first defense mechanism is repression, the blocking of memories, emotional impulses, in a boy, a phallic-stage fixation might lead him to become an aggressive, over-ambitious, vain man. The genital stage affords the person the ability to confront and resolve his or her remaining psychosexual childhood conflicts, as in the phallic stage, the genital stage is centered upon the genitalia, but the sexuality is consensual and adult, rather than solitary and infantile. Hence, the stage proved controversial, for being based upon clinical observations of the Oedipus complex
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Piaget's theory of cognitive development
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Piagets theory of cognitive development is a comprehensive theory about the nature and development of human intelligence. It was first created by the Swiss developmental psychologist Jean Piaget, the theory deals with the nature of knowledge itself and how humans gradually come to acquire, construct, and use it. Piagets theory is known as a developmental stage theory. To Piaget, cognitive development was a reorganization of mental processes resulting from biological maturation. Moreover, Piaget claimed that development is at the center of the human organism. Piagets earlier work received the greatest attention, child-centered classrooms and open education are direct applications of Piagets views. Despite its huge success, Piagets theory has some limitations that Piaget recognized himself, for example, Piaget noted that reality is a dynamic system of continuous change and, as such, is defined in reference to the two conditions that define dynamic systems. Specifically, he argued that reality involves transformations and states, transformations refer to all manners of changes that a thing or person can undergo. States refer to the conditions or the appearances in which things or persons can be found between transformations, for example, there might be changes in shape or form, in size, or in placement or location in space and time. Thus, Piaget argued, if human intelligence is to be adaptive, operative intelligence is the active aspect of intelligence. It involves all actions, overt or covert, undertaken in order to follow, recover, figurative intelligence is the more or less static aspect of intelligence, involving all means of representation used to retain in mind the states that intervene between transformations. That is, it involves perception, imitation, mental imagery, drawing, at any time, operative intelligence frames how the world is understood and it changes if understanding is not successful. Piaget stated that this process of understanding and change involves two basic functions, assimilation and accommodation, through his study of the field of education, Piaget focused on two processes, which he named assimilation and accommodation. To Piaget, assimilation meant integrating external elements into structures of lives or environments, assimilation is how humans perceive and adapt to new information. It is the process of fitting new information into pre-existing cognitive schemas, assimilation in which new experiences are reinterpreted to fit into, or assimilate with, old ideas. It occurs when humans are faced with new or unfamiliar information, in contrast, accommodation is the process of taking new information in ones environment and altering pre-existing schemas in order to fit in the new information. This happens when the schema does not work, and needs to be changed to deal with a new object or situation. Accommodation is imperative because it is how people will continue to interpret new concepts, schemas, frameworks, Piagets understanding was that assimilation and accommodation cannot exist without the other
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Sperm
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Sperm is the male reproductive cell and is derived from the Greek word sperma. In the types of reproduction known as anisogamy and its subtype oogamy. A uniflagellar sperm cell that is motile is referred to as a spermatozoon, Sperm cells cannot divide and have a limited life span, but after fusion with egg cells during fertilization, a new organism begins developing, starting as a totipotent zygote. The human sperm cell is haploid, so that its 23 chromosomes can join the 23 chromosomes of the egg to form a diploid cell. In mammals, sperm develops in the testicles and is released from the penis, the mammalian sperm cell consists of a head, neck, a midpiece and a tail. The head contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an acrosome, the neck contains the sperm centriole. The midpiece has a central core with many mitochondria spiralled around it, used for ATP production for the journey through the female cervix, uterus. The tail or flagellum executes the lashing movements that propel the spermatocyte, although semen contains millions of sperm, the egg will admit only one. The other ones will die and be absorbed. The spermatozoa of animals are produced through spermatogenesis inside the gonads via meiotic division. The initial spermatozoon process takes around 70 days to complete, the spermatid stage is where the sperm develops the familiar tail. The next stage where it becomes fully mature takes around 60 days when it is called a spermatozoan, Sperm cells are carried out of the male body in a fluid known as semen. Human sperm cells can survive within the reproductive tract for more than 5 days post coitus. Semen is produced in the vesicles, prostate gland and urethral glands. In 2016 scientists at Nanjing Medical University claimed they had produced cells resembling mouse spermatids artificially from stem cells and they injected these spermatids into mouse eggs and produced pups. Sperm quantity and quality are the parameters in semen quality. Thus, in humans, it is a measure of fertility in a man, the genetic quality of sperm, as well as its volume and motility, all typically decrease with age. Human sperm cells are vulnerable to free radical attack and the generation of oxidative DNA damage
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Embryo
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An embryo is an early stage of development of a multicellular diploid eukaryotic organism. In general, in organisms that reproduce sexually, an embryo develops from a zygote, the zygote possesses half the DNA of each of its two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism, the result of this process is an embryo. First attested in English in the mid-14c, the word embryon derives from Medieval Latin embryo, itself from Greek ἔμβρυον, lit. Young one, which is the neuter of ἔμβρυος, lit, growing in, from ἐν, in and βρύω, swell, be full, the proper Latinized form of the Greek term would be embryum. In animals, the development of the zygote into an embryo proceeds through specific stages of blastula, gastrula. The blastula stage typically features a fluid-filled cavity, the blastocoel, surrounded by a sphere or sheet of cells, in a placental mammal, an ovum is fertilized in a fallopian tube through which it travels into the uterus. An embryo is called a fetus at an advanced stage of development. In humans, this is from the week of gestation. During gastrulation the cells of the blastula undergo coordinated processes of cell division, invasion, in triploblastic organisms, the three germ layers are called endoderm, ectoderm, and mesoderm. The position and arrangement of the layers are highly species-specific, however. For example, in neurogenesis, a subpopulation of cells is set aside to become the brain, spinal cord. Modern developmental biology is extensively probing the molecular basis for every type of organogenesis, including angiogenesis, chondrogenesis, myogenesis, osteogenesis, and many others. In botany, a plant embryo is part of a seed, consisting of precursor tissues for the leaves, stem. Once the embryo begins to germinate — grow out from the seed — it is called a seedling, bryophytes and ferns also produce an embryo, but do not produce seeds. In these plants, the embryo begins its existence attached to the inside of the archegonium on a parental gametophyte from which the egg cell was generated, the structure and development of the rest of the embryo varies by group of plants. Once the embryo has expanded beyond the enclosing archegonium, it is no longer termed an embryo, embryos are used in various fields of research and in techniques of assisted reproductive technology. An egg may be fertilized in vitro and the embryo may be frozen for later use
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Birth
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Birth, also known as parturition, is the act or process of bearing or bringing forth offspring. In some species the offspring is precocial and can move around almost immediately after birth but in others it is altricial, in marsupials, the fetus is born at a very immature stage after a short gestational period and develops further in its mothers wombs pouch. It is not only humans and mammals give birth. Some reptiles, amphibians, fish and invertebrates carry their young inside them. Some of these are ovoviviparous, with the eggs being hatched inside the mothers body, in these large animals, the birth process is similar to that of a human, though in most the offspring is precocial. This means that it is born in an advanced state than a human baby and is able to stand, walk. In the case of whales, dolphins and porpoises, the calf is normally born tail first which minimises the risk of drowning. The mother encourages the newborn calf to rise to the surface of the water to breathe, most smaller mammals have multiple births, producing litters of young which may number twelve or more. In these animals, each fetus is surrounded by its own amniotic sac and has a separate placenta and this separates from the wall of the uterus during labor and the fetus works its way towards the birth canal. Humans usually produce a single offspring at a time, the mothers body is prepared for birth by hormones produced by the pituitary gland, the ovary and the placenta. The total gestation period from fertilization to birth is normally about 38 weeks, the normal process of childbirth takes several hours and has three stages. The first stage starts with a series of contractions of the muscular walls of the uterus. The active phase of the first stage starts when the cervix is dilated more than about 4 cm in diameter and is when the contractions become stronger, the head of the baby is pushed against the cervix, which gradually dilates until is fully dilated at 10 cm diameter. At some time, the sac bursts and the amniotic fluid escapes. In stage three, which begins after the birth of the baby, further contractions expel the placenta, amniotic sac, enormous changes take place in the newborns circulation to enable breathing in air. The umbilical vein, umbilical arteries, ductus venosus and ductus arteriosus are not needed for life in air, birthing in cattle is typical of a larger mammal. A cow goes through three stages of labor during normal delivery of a calf, during stage one, the animal seeks a quiet place away from the rest of the herd. Hormone changes cause soft tissues of the canal to relax as the mothers body prepares for birth
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Childhood
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Childhood is the age span ranging from birth to adolescence. According to Piagets theory of development, childhood consists of two stages, preoperational stage and concrete operational stage. In developmental psychology, childhood is divided up into the stages of toddlerhood, early childhood, middle childhood. Various childhood factors could affect a persons attitude formation, the concept of childhood emerged during the 17th and 18th centuries, particularly through the educational theories of the philosopher John Locke and the growth of books for and about children. Previous to this point, children were seen as incomplete versions of adults. The term childhood is non-specific and can imply a range of years in human development. Developmentally and biologically, it refers to the period between infancy and adulthood, in common terms, childhood is considered to start from birth. Some consider childhood as a concept of play and innocence which ends at adolescence, in the legal systems of many countries, there is an age of majority when childhood officially ends and a person legally becomes an adult. The age ranges anywhere from 15 to 21, with 18 being the most common, Early childhood follows the infancy stage and begins with toddlerhood when the child begins speaking or taking steps independently. While toddlerhood ends around age three when the child becomes less dependent on assistance for basic needs, early childhood continues approximately through years seven or eight. According to the National Association for the Education of Young Children, at this stage children are learning through observing, experimenting and communicating with others. Adults supervise and support the development process of the child, which then lead to the childs autonomy. Also during this stage, an emotional bond is created between the child and the care providers. The children also start to begin kindergarten at this age to start their social lives, Middle childhood begins at around age seven or eight, approximating primary school age. It ends around puberty, which marks the beginning of adolescence. In this period, children are attending school, thus developing socially and mentally and they are at a stage where they make new friends and gain new skills, which will enable them to become more independent and enhance their individuality. However, because of reasons, that adolescents arent kids its most acceptable to call this age late childhood rather than middle childhood. Adolescence is usually determined by the onset of puberty, however, puberty may also begin in preadolescence
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Prenatal development
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Prenatal development is the process in which an embryo and later fetus develops during gestation. Prenatal development starts with fertilization the first stage in embryogenesis which continues in development until birth. In human pregnancy, prenatal development, also known as development, is the development of the embryo following fertilization. By the end of the week of gestational age the embryo has acquired its basic form and is referred to as a fetus. The next period is that of development where many organs become fully developed. This fetal period is described both topically and chronologically with major occurrences being listed by gestational age, in other animals the very early stages of embryogenesis are the same as those in humans. In later stages, development across all taxa of animals and the length of gestation vary, the perinatal period is around the time of birth. In developed countries and at facilities where expert neonatal care is available, in many developing countries, the starting point of this period is considered 28 completed weeks of gestation. In ICD-10, a classification list by the WHO, there is a particular chapter relating to certain conditions originating in the perinatal period. The antepartum period is equivalent to prenatal. Practically, however, antepartum usually refers to the period between the 24th/26th week of age until birth, for example in antepartum hemorrhage. When semen is released into the vagina, the travel through the cervix and body of the uterus. Fertilization of the egg cell, usually takes place in one of the Fallopian tubes, many sperm are released with the possibility of just one sperm cell managing to adhere to and enter the thick protective shell-like layer surrounding the ovum. The first sperm that penetrates fully into the egg donates its genetic material, the egg then polarizes, repelling any additional sperm. The resulting combination is called a zygote, a new and genetically unique organism, the term conception refers variably to either fertilization or to formation of the conceptus after its implantation in the uterus, and this terminology is controversial. Prior to fertilization, each ovum, as a gamete, contains half of the material that will fuse with the male gamete. The ovum only carries the X female sex chromosome whilst the sperm carries a single sex chromosome of either an X or a male Y chromosome. The resulting human zygote is similar to the majority of cells because it contains two copies of the genome in a diploid set of chromosomes
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Embryogenesis
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Embryogenesis is the process by which the embryo forms and develops. In mammals, the term refers chiefly to early stages of development, whereas the terms fetus. Embryogenesis starts with the fertilization of the egg cell by a sperm cell, once fertilized, the ovum is referred to as a zygote, a single diploid cell. The zygote undergoes mitotic divisions with no significant growth and cellular differentiation, the egg cell is generally asymmetric, having an animal pole and a vegetal pole. It is covered with protective envelopes, with different layers, the first envelope - the one in contact with the membrane of the egg - is made of glycoproteins and is known as the vitelline membrane. Different taxa show different cellular and acellular envelopes englobing the vitelline membrane, fertilization is the fusion of gametes to produce a new organism. In animals, the process involves a sperm fusing with an ovum, depending on the animal species, the process can occur within the body of the female in internal fertilisation, or outside in the case of external fertilisation. The fertilized egg cell is known as the zygote, cell division with no significant growth, producing a cluster of cells that is the same size as the original zygote, is called cleavage. At least four initial cell divisions occur, resulting in a ball of at least sixteen cells called the morula. The different cells derived from cleavage, up to the stage, are called blastomeres. Depending mostly on the amount of yolk in the egg, the cleavage can be holoblastic or meroblastic, on the other hand, meroblastic cleavage occurs in animals whose eggs have more yolk, i. e. birds and reptiles. Because cleavage is impeded in the pole, there is a very uneven distribution and size of cells, being more numerous. In holoblastic eggs the first cleavage always occurs along the axis of the egg. Fluid collects between the trophoblast and the part of the inner cell-mass, and thus the morula is converted into a vesicle. After the 7th cleavage has produced 128 cells, the embryo is called a blastula, the blastula is usually a spherical layer of cells surrounding a fluid-filled or yolk-filled cavity. Mammals at this form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula. The blastocyst must not be confused with the blastula, even though they are similar in structure, their cells have different fates. On the deep surface of the cell mass, a layer of flattened cells, called the endoderm, is differentiated and quickly assumes the form of a small sac
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Fertilisation
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The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms the haploid male gamete combines with two polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation. In 1784, Spallanzani established the need of interaction between the females ovum and males sperm to form a zygote, oscar Hertwig, in Germany, described the fusion of nuclei of spermatozoa and of ova from sea urchin. In flowering plants there are two sperm from each pollen grain, in seed plants, after pollination, a pollen grain germinates, and a pollen tube grows and penetrates the ovule through a tiny pore called a micropyle. The sperm are transferred from the pollen through the pollen tube, bryophyte is a traditional name used to refer to all embryophytes that do not have true vascular tissue and are therefore called non-vascular plants. Some bryophytes do have specialised tissues for the transport of water, however, since these do not contain lignin, a fern is a member of a group of roughly 12,000 species of vascular plants that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular and they have stems and leaves, like other vascular plants. Most ferns have what are called fiddleheads that expand into fronds, the gymnosperms are a group of seed-producing plants that includes conifers, Cycads, Ginkgo, and Gnetales. The term gymnosperm comes from the Greek composite word γυμνόσπερμος, meaning naked seeds and their naked condition stands in contrast to the seeds and ovules of flowering plants, which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, often modified to form cones, the pollen tube does not directly reach the ovary in a straight line. It travels near the skin of the style and curls to the bottom of the ovary, then near the receptacle, it breaks through the ovule through the micropyle, after being fertilised, the ovary starts to swell and develop into the fruit. With multi-seeded fruits, multiple grains of pollen are necessary for syngamy with each ovule, the growth of the pollen tube is controlled by the vegetative cytoplasm. The sperms are interconnected and dimorphic, the one, in a number of plants, is also linked to the tube nucleus and the interconnected sperm. Double fertilisation is the process in angiosperms in which two sperm from each pollen tube fertilise two cells in a gametophyte that is inside an ovule. After the pollen tube enters the gametophyte, the tube nucleus disintegrates. This is the point when fertilisation actually occurs, pollination and fertilisation are two separate processes, the nucleus of the other sperm cell fuses with two haploid polar nuclei in the centre of the gametophyte. This triploid cell divides through mitosis and forms the endosperm, a nutrient-rich tissue, the two central-cell maternal nuclei that contribute to the endosperm arise by mitosis from the single meiotic product that also gave rise to the egg. Therefore, maternal contribution to the constitution of the triploid endosperm is double that of the embryo
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Zygote
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A zygote, is an eukaryotic cell formed by a fertilization event between two gametes. The zygotes genome is a combination of the DNA in each gamete, in multicellular organisms, the zygote is the earliest developmental stage. In single-celled organisms, the zygote can divide asexually by mitosis to produce identical offspring, oscar Hertwig and Richard Hertwig made some of the first discoveries on animal zygote formation. In fungi, the fusion of haploid cells is called karyogamy. The result of karyogamy is a diploid cell called a zygote or zygospore and this cell may then enter meiosis or mitosis depending on the life cycle of the species. In plants, the zygote may be polyploid if fertilization occurs between meiotically unreduced gametes, in land plants, the zygote is formed within a chamber called the archegonium. In seedless plants, the archegonium is usually flask-shaped, with a long hollow neck through which the cell enters. As the zygote divides and grows, it does so inside the archegonium, in human fertilization, a release ovum and a haploid sperm cell —combine to form a single 2n diploid cell called the zygote. The other product of meiosis is the polar body with only chromosomes. In the fertilized daughter, DNA is then replicated in the two separate pronuclei derived from the sperm and ovum, making the zygotes chromosome number temporarily 4n diploid. After approximately 30 hours from the time of fertilization, fusion of the pronuclei, between the stages of fertilization and implantation, the developing human is a preimplantation conceptus. However, the National Institute of Health has made the determination that the classification of pre-implantation embryo is still correct. After fertilization, the travels down the oviduct towards the uterus while continuing to divide mitotically without actually increasing in size. After four divisions, the conceptus consists of 16 blastomeres, through the processes of compaction, cell division, and blastulation, the conceptus takes the form of the blastocyst by the fifth day of development, just as it approaches the site of implantation. When the blastocyst hatches from the zona pellucida, it can implant in the lining of the uterus. The human zygote has been edited in experiments designed to cure inherited diseases. In the amoeba, reproduction occurs by division of the parent cell
. PMID 21110899.
