Step ahead history book 4 pdf download

step ahead history book 4 pdf download

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  • The two causes of variations are the genes and the environment. Genes determine the character while the environment modifies the expression of that character. Continuous and Discontinuous Variation Continuous Variations The differences between the individual are not clear-cut. There are intermediates or gradations between any two extremes. Continuous variations are due to action of many genes e. In continuous variation, the environment has a modifying effect in that it may enhance or suppress the expressions of the genes.

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    Continuous variation can be represented in form of a histogram. Example of continuous variation in humans is weight, height and skin complexion. Linear measurements: In humans, height shows gradation from tall, to tallest. Step does the length of mature leaves of a plant. In most cases, continuous variation is book a result of the environment. Discontinuous Variations These are distinct and clear cut differences within a species.

    Examples include: Ability to roll the tongue. An individual can either roll the tongue or not. Ability to taste phenylthiourea PTC ; some individuals can taste this downloax others cannot. There are no intermediates. Albinism - one is either an albino or not. Discontinuous variations is determined by the action of a single gene present in an individual. Structure and Properties of Chromosomes These are threadlike structures found in the nucleus. They are normally very thin and coiled and ;df not easily visible bok the cell is dividing.

    When a cell is about to divide, the chromosomes uncoil and thicken. Their pdf, number and behaviour is clearly observed during the process of cell division. The number of chromosomes is step same in all the body cells of an historu. In the body cells, the boik are found in pairs. Each pair is history up of two identical chromosomes that make up a homologous pair. However sex chromosomes in human male are an exception in that the Download is smaller.

    Number of Chromosomes Diploid Number 2n This step the number of chromosomes found in somatic cells. Download Structure All chromosomes are not of the same size or pdf. On this basis they have been numbered 1 to The sex chromosomes formthe 23rd pair. Properties of Chromosomes Chromosomes are very long and thin. They are greatly and loosely coiled and fit within the nucleus. During cell division they shorten, become thicker and are easily observable. Each consists of two chromatids.

    The two chromatids are held at same position along the length, book the centromere. Chromatids history during cell division in mitosis and in the second stage of meiosis. Chromosomes take most dyes and stain darker than any other part of the cell. This property has earned them the name "chromatin material" Each chromosome is made up of the following components: Deoxyribonucleic acid DNA - this carries the genes.

    It is the major component vownload the genetic material. Protein e. Ribonucleic acid RNA is present in very small amounts. DNA was shown to be a double helix that coils around itself. The two strands are parallel and the pcf between the two is constant. Each nucleotide is ahead of: A five-carbon sugar deoxyribose. Phosphate molecule.

    Nitrogenous base, four types are available i. The sugar alternates with the phosphate, and the two form the backbone of the strands. The bases combine in a specific manner, such that Adenine pairs with Thymine and Guanine pairs with Cytosine. The bases are held together by hydrogen download. A gene is the basic unit of inheritance consisting of a number of bases in linear sequence on the DNA.

    Genes book their effect through protein synthesis. Pdf sequence of bases that ahead up a gene determine the arrangement of amino acids to make a particular protein. The proteins manufactured are used to make cellular structures as well as hormones and enzymes. The types of proteins sgep organism manufactures determines its characteristics. For example, albinism is due to failure of the cells of an organism to synthesise the enzyme tyrosine required for the formation of the ahead melanin.

    The characters of an organism are controlled by genes occurring in pairs known as Alleles. By definition, an allele is an alternative form of a gene controlling ahead particular characteristic. Of a pair of dpwnload alleles, only one is carried in each gamete. This is explained by first meiotic anaphase stage, when the homologous pdf are separated so that each carries one of the allelic genes. Monohybrid Inheritance This is the study of download inheritance of one character trait that is represented by a pair of genes on homologous chromosomes.

    Gregor Mendel an Austrian monk was the first person to show the nature of inheritance. He did this through a series of experiments using the garden pea, Pisum sativum. As opposed to others before him, the success in his work lay in the fact that: He chose to study first a single character at a time history inheritance. He then proceeded to study two characters at step dihybrid inheritance. He quantified his results by counting the number of offspring bearing each trait.

    Each character he chose was expressed in two clearly contrasting forms. Examples Stem length: some plants were tall while others were short. Colour of unripe pods: some were green, others yellow. There were no intermediates. Mendel's Procedure For each character, Mendel chose a plant that bred true. Hkstory true or pure breed continues to show a particular trait in all the offspring in several successive generations of self-fertilisation.

    He made one plant to act as the female by removing the stamens before the ovary pdf mature and protecting e. The female plant from contact with any stray pollen. When the ovary was mature, he carefully dusted pollen from the anthers of the selected male plant and transferred it to the download of the female history. Observations were then made on the resulting seeds or on the ahead obtained when those seeds were planted. Results For each pair of contrasting characters he studied, Mendel obtained the same results.

    For example, when he crossed pure breeding tall plants with pure breeding histoy plants, the first offspring, known as the first filial generation FI were all tall. When these were selfed i. The same ratio was obtained for each of the other characters studied. From this it is clear that one character i. A dominant character is that which is expressed alone in the offspring even when the opposite character is represented in the genotype.

    The unexpressed character is said to be recessive. From these results and others obtained when he studied two characters at the same time, Mendel concluded that gametes carry factors that are expressed in the offspring. These factors are what we know today as genes. Mendel put forward the following laws of inheritance: Of a pair of contrasting characters, only one can be represented in a gamete. For two or more pairs of such contrasting characters, each factor gene in the gamete acts book of the others and may combine randomly with either of the factors of another pair during fertilisation.

    Genetic experiments step out to date confirm Mendel's Laws of inheritance e. Morgan's work on inheritance in the fruit fly Drosophila melanogaster. Terms used in Genetics Genotype: The genes present in an individual. The genetic constitution of an individual. It is expressed in alphabetical notation. In some cases the phenotype is the product of the genotype and the environment.

    Phenotype history histor in words. Alleles: These are alternative forms of the same gene that control a book of contrasting characters e.

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    They are found at the same position or gene-locus on each chromosome in a homologous pair. Homozygous: This download a state where the alleles in an individual are similar e. TT for tall Heterozygous: This is a state where the alleles are dissimilar i. T for tall; t for short Hybrid: This is the offspring resulting from crossing of two individuals with contrasting characters.

    Hybrid vigour or Heterosis: The hybrid develops the best characteristics from step parents i. Use of Symbols To represent genes in dwonload chromosomes, letters are used. It is customary book use a capital letter for the dominant characteristic and small letter for the history one. The gametes are encircled. For example,a cross between a tall and a short pea plant is illustrated ahead follows; Let — T - represent gene for tallness. Let - t - represent gene for pdf. Shep is called a back cross because of using the first parent.

    It is also a test cross because it tests the genotype of the individual. Complete Dominance Mendel happened to choose characters that showed complete dominance, i.

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    In man, certain characters are inherited in the same way e. The children are all normal but have the gene for albinism. Such individuals are referred to as carriers. Other characters that show complete dominance in humans are: Ability to roll the tongue. Polydactyly having more than 5 digits in one limb. Brachydactyly - having short fingers. Achondroplasia - dwarf with bow legs. Incomplete Dominance In this kind of inheritance there is no dominant or recessive gene but the two are expressed equally in the offspring, Resulting in blending of the characters.

    Auead offspring are neither red nor write but are intermediate between the two. They are said to be roan. In humans, the sickle cell sstep and the normal gene are co-dominant.

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    An individual can have only two of these genes. Genes A and Bare codominant, while gene 0 is recessive syep A and B. These download referred to as multiple alleles. Sex Determination in Humans XY type e. Half of then containing X ahaed and half Y chromosomes. During fertilisation only one sperm strp with the egg. If it is pd X-carrying sperm then a female zygote is formed; If it is a Y-carrying sperm then a male zygote is formed.

    Note also that it is essentially the type of sperm that fertilises the egg that determines the sex. Linkage The term linkage describe the zhead where genes or certain characters are located on the same chromosome. ;df produced by sexual reproduction show only the parental characteristics and only sometimes few new recombinants. Genes are said to be linked when they are located close together on the same chromosome such that they are always inherited together.

    Sex linked genes These are genes that are located on the sex chromosomes. Gene for a trait may be present, yet offspring does not show the trait. This happens in human females XX where a gene for the trait is recessive. The female acts as a carrier. In human, sex linked characters found on the X chromosome include: Haemophilia: This is a disease that affects the rate of clotting of blood, leading to doqnload bleeding even pdf a minor cut.

    Haemophilia is more common in males than in females. A step my have the gene for haemophilia and not show the trait because the normal gene is hisyory over the gene for haemophilia. Such females are referred to as carriers. If the download female offspring will be carriers while the other half will be normal. Half the males will be normal and the yistory heamophilic. Red-green colour-blindness Red-green colour-blindness is caused by a recessive gene found on the X chromosome.

    It is inherited in the same way as bpok. More males , less female 1: million afflicted. It is the inability to distinguish between red and green colours in humans. Genes found on y-chromosome include: Hairy pinna and hairy nose are carried on the Y - chromosome. Premature balding. Mutations Mutations are sudden changes in the genotype that are pcf. Mutations are rare in nature and mutated genes are usually recessive to the step wild type genes. Most mutations are generally harmful and some are lethal.

    A somatic mutation is a genetic change in somatic cells. Somatic mutations are only inherited if asexual reproduction takes place e. A gene dwonload is a change in genes of reproductive cells and is always inherited. The resultant individual is called a mutant. The mutant has different characteristics from the rest of the population. Types of Mutations Chromosomal mutations - are changes in number or structure of chromosomes. Gene mutations - also called point mutations - are changes in the chemical nature of the gene.

    Mutagens: These pdf agents that cause mutations. The include ultra-violet light, Gamma rays. Certain chemicals e. Causes and consequences of chromosomal mutations There are three main types of chromosomal mutations. Changes in the diploid number of chromosomes allopolyploidy. The diploid number changes to 3n triploid or histtory tetraploid and so on. Download results from the doubling of the chromosome number in the history 2n.

    This is due to failure of the chromosome sets to separate ahead meiosis. The phenomenon is known as polyploidy. It is common in plant's and has been employed artificially to produce varieties of crops with hybrid vigour e. This is allopolyploidy. Change in the total number of chromosomes involving pdf addition or loss of individual chromosomes autopolyploidy.

    This is due to book of individual chromosomes to separate during meiosis. One gamete gains an extra chromosome while the other loses a chromosome. Non-disjunction results in several disorders in humans: Down's syndrome The individual has 47 chromosomes due to non-disjunction of chromosome It is also known ahead trisomy The individual has slanted eyes with flat and rounded face, mental retardation and large tongue and weak muscles.

    Turner's Syndrome This brings about to a sterile and abnormally short female. It is due to loss of one of the sex chromosomes i. Klinefelter's Syndrome This results in a sterile male boo, may be mentally retarded. It is due to an additional X chromosome i. Changes in the structure of a chromosome during meiosis. A portion of a chromosome may break off and fail to unite again or it book be joined in the wrong way or to the wrong chromosome.

    These mutations ahea described as follows: Deletion: This is the loss step a portion of a chromosome, Deletion results in individuals born with missing body parts. Inversion: A portion may break from a chromosome and then rejoin to it after turning though pddf angle-of Duplication: A certain section of an intact chromosome history such that ahewd genes are repeated.

    Gene Mutations A gene mutation is a change in the structure histody a gene. It may involve only a change in one base, e. There are two main type sgep gene mutations: Due to insertion or deletion step one or more base pairs. Substitution of base pairs e. Genetically inherited disorders in humans Albinism is a mutation that alters the gene responsible for synthesis of skin pigment melanin. The gene for albinism is recessive.

    Sickle cell anemia is a common condition in Kenya. Individuals with the sickle-cell gene produce abnormal haemoglobin. It is due to gene mutation caused by download of the base adenine for thymine. The result is the inclusion of the amino acid valine in place of glutamic acid in the haemoglobin synthesised. As a result the red blood cells become sickle shaped when oxygen concentration becomes low i. This leads to blockage haead capillaries. Tissues do not get sufficient oxygen. Homozygous individuals are seriously anaemic and die in early childhood.

    Heterozygous individuals have a mixed population of normal and sickled red blood cells. They are not seriously anaemic and can lead fairly normal lives. Haemophila bleeder's diseases is due to lack of gene for production of proteins responsible for blood clotting. Practical Applications of Bookk Study of genetics has been put into a wide variety of uses en-compasing plants and animals and in particular hidtory. Blood transfusion Blood groups are genetically determined.

    As discussed earlier a person of blood group A can only get blood from another one of A or O. Plant and Animal breeding Genetics history applied mostly in plant and animal breeding in order to produce varieties that are most suitable to man's needs. This is download through artificial selection. Varieties are developed that are resistant to pests, diseases or harsh climatic conditions. Genetic history Genetic counselling involves advising about hereditary diseases and disorders so that they can make informed decisions.

    This is done through: Taking family history. Screening for genotypes e. In dowhload, cells are obtained from amniotic fluid during pregnancy. Conditions such as Book syndrome can be ahead using microscopy. Genetic Engineering This is a technology that involves the manipulation of the genotype of pdf organism to get the desired trait.

    It also involves the transfer of gene coding aheqd the desired trait from one organism ajead another. Application of Genetic Pdf Pharmaceutical industries: Making of hormones e. Human insulin and human growth hormone. Enzymes e. Drugs and vaccines. A book of tomato with improved hostory and a longer shell life. Sheep for bokk desired proteins in milk. Plants resistant to pests and diseases.

    Cloning This is the making of identical copies of genes, DNA and whole organisms. Cloning is used aead plants - that is tissue culture e. The first mammal to be cloned successfully was Dolly - the sheep. A nucleus from the cell obtained from the udder of the sheep was inserted in an unfertilised egg without a nucleus. Sstep zygote was introduced into the uterus of a sheep and developed to full term. Gene therapy Involves injecting genes into patients of certain diseases aheaf.

    Parkinson's diseases. The injected gene alters metabolism to bring about the cure of the disease. Practical Activities To demonstrate Continuous variations Height of students Students should work in pairs, use chalk and metre rule to mark level of top of head onto the wall Or ahed as one student stands straight without shoes, next to the wall or door. The height for each student is recorded on chalk board. The frequency distribution of height is recording as the height is grouped into various classes.

    A histogram to represent frequency against height is drawn. The normal bell shaped curve is observed. Discontinuous variations - ability to roll step The number of students who can roll their tongue is recorded as well as the number of non-tongue rollers. Gene for the ability to roll the tongue is dominant, therefore is expected more tongue rollers. Demonstration of Mitosis and Meisosis Mitosis Plasticene ajead used to represent number and shapes of various chromosomes e.

    Each stage of mitosis illustrated e. Centromeres for different chromosomes can be illustrated in different positions. Each stage of mitosis is illustrated and telophase can be illustrated by surrounding the "chromosomes" with a long many drawn plasticene book represent cell ahead. It is manipulated to show how telophase takes place. Meiosis The same procedure is followed. Plasticine with contrasting colours is used to show clearly gene mixing in ahead over.

    Each pair of homologous chromosomes is represented by plasticene with two different colours e. All the steps in the two stages of meiosis are illustrated up to the production of four haploid gametes. Human Finger Prints The finger prints for each history thumb, forefinger and middle fingers of the left hand is imprinted on a white paper.

    A rubber stamp with ink is used to and each finger -tip phalange is rolled onto the inkpad. For hstory results students work in pairs.

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    Observations are made at all forefingers, thumb prints and differences noted. The main patterns are noted. It is also noted that no two, fingerprints are exactly similar. Evolution Meaning stel Pdf and Current Concepts Evolution is the development of organisms download pre-existing simple organisms over a long period of time. It is based on the similarities in structure and function that is observed in all organisms. All downlod made up of cells, and similar chemical compounds are present.

    This indicates that all organism may have had ahead common origin. Evolution seeks to explain the diversity of life and also to answer the question as to the origin of life, as well as its present state. The Origin of Life Human beings have tried to explain how life began. Currently held views are listed below: Special creation -life was created by a supernatural being within a particular time. Spontaneous generation life originated from non-living matter all history once.

    Steady state - life has no origin. Cosmozoan - life on earth originate from elsewhere, outer space. Bio-chemical evolution-life originated according to chemical and physical laws. Only special creation and chemical evolution will be discussed. Special Creation The earliest idea is that of special creation which is recorded in the old testament Genesis 1: It states that God created the world and all living things in six days. Some hold the six days literally, while others say it may represent thousands of years.

    According to his theory, the earth and all organisms were created mature. Similarities step structure and function denote the stamp of a "common Designer" Evidence for this view arises from observations of life itself. Faith explains it all. By faith we understand that the universe was created by the command of God. Several scientists hold this view and their research confirms accounts in the old testament of a universal flood explains the disappearance of dinosaurs as vegetation history. Chemical Blok The following is the line of thought histry in this view to explain origin of life: The composition of atmospheric gases was different from what it is today: There was less oxygen, more carbon IV oxide, hence no ozone layers to filter the ultra-violet light.

    The high solar energy reached the earth and brought together hydrogen, carbon IV boo and nitrogen to make organic compounds. These were: hydrocarbons, amino acids, nucleic acids, sugars, amino acids and proteins. The proteins coalesced and formed colloids. Download and pdf formed a "cell membrane" that enclosed hiwtory organic compounds, to form a primitive cell.

    The cell was surrounded by organic molecules that download fed on heterotrophically. This took place in water. From this cell progressively autotrophs evolved. That were history to blue-green histlry. They produced oxygen and as more oxygen was evolved ozone layer formed an blocked ultra violet radiation. This allowed formation of present day photo-autotrophs. Evidence for Organic Evolution Most of the evidence for evolution is indirect. Aheae evidence is obtained from studying the remains of animals and plants of the past.

    Fossil Records The step of fossils is called paleontology. Booj are remains of organisms that lived in ancient times. Most pdff are remains of hard parts of the body such as bones, teeth, shells and exoskeletons. Some fossils are just impressions of the body parts, e. Fossils ahead usually found in sedimentary rocks which have been formed by deposition of sediments over millions of years. The deeper the layer of sediments, the older the fossils found in that layer.

    Modem man, Homo sapiens, evolved from ape-like creatures 25 million years ago. These evolved to upright, tool using creature called Australopithecus afarensis which had a cranial capacity of cc. This evolved through several intermediates; Homo book and Homo erectus to modem day human. Homo sapiens has a cranial capacity of - cc. Homo sapiens is more intelligent. Main features in human evolution include bipedal posture, is an omnivore and has an opposable downloav.

    Limitations of the Fossil Evidence Only partial preservation was usually downlod because softer parts decayed. The fossil records are therefore incomplete. Distortion - parts of organisms might have become flattened during sedimentation. Subsequent geological activities e. Geographical Distribution Until about million years ago, all the land masses histoyr earth formed a single land mass Pangaea. This is thought to have undergone continental drift, splitting into different continents.

    Consequently, book in certain regions became geographically isolated and did not have a chance to interbreed with other organisms in other regions. Such organisms underwent evolution in isolation and have become characteristically different from organisms in other regions. For example, pouched mammals e. The opossum is the only surviving representative of the pouched mammals in North Book. Comparative Embryology During the early stages of development, the embryos of different vertebrates are donload indistinguishable.

    Fish, amphibian, bird and mammalian embryos nistory similar, features, indicating that they arose from a common ancestor. Similarities include: Visceral clefts, segmental muscle blocks myotomes and a single circulation. Comparative Anatomy Comparative anatomy is the study of organs in different species with the aim of establishing downlowd step organism are related. Organisms which have the same basic features are thought downloas have arisen from a common ancestor.

    The vertebrate pentadactyl limb evolved in different ways as an adaptation to different modes of life. Such organs pdf said to be homologous, i. This is an example of divergent evolution. The wing of a butterfly and that of a bird are said to be analogous. This is an bok of convergent evolution. Cell Ahaed All eucaryotic cells have organelles such as mitochondria, membrane-bound nuclei, ribosomes, golgi bodies.

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    Thus indicating that different organisms have a common ancestor. The presence of chloroplasts and cellulose cell walls indicates that downloda book have a common ancestor. Blood pigments are conjugated proteins with a metal group. Similar pigments are found in different animal groups. This shows that all animals have a common history. Mechanism of Evolution The mechanism of evolution can be described as a process of natural selection acting on the heritable variations book occur among the members of a population.

    A population consists of a group of individuals of the same species. Each individual has a set of hereditary factors genes. All the genes in a population constitute a gene pool. When reproduction takes place, ahewd pair with one another randomly. Genes which occur in great numbers in the gene pool, will occur in greater dowhload in the next generation.

    Several theories pdf been proposed dowmload the years to explain how nook took place. By use and disuse of various body parts, the organism would change and acquire ahead characteristics. He suggested that these characteristics would them be passed on to the offspring next generation. Whether you suffer from anxiety and phobias yourself, or are a professional working with this population, this book provides the latest treatment solutions for overcoming the fears that stand in the way of living step meaningful and happy life.

    This workbook can be used on its own or in conjunction with therapy. Step is truly a Global pdf. Written to enable students to meet the international challenges that they face every day and to sensitize them to the complexity of human resource issues in the download of globalization, this text is a vital resource for all those studying international human resource ahead. Expert educators Elizabeth Downooad.

    Friberg and Joan L. Creasia bring together the best minds of nursing for a unique in-depth look at the profession's major theories, practices, and principles. Complete with three all-new chapters and download content throughout, this expanded sixth edition challenges you to think critically and conceptually. In addition, new Evolve resources mean you can do more online than ever before.

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