Grade 10 Biology Textbook PDF

TEXTBOOK BIOLOGY GRADE 10 CHAPTER 1 INTRODUCTION TO BIOLOGY Learning Outcomes It is expected that students will ƒexplain how the study of biology is important...

TEXTBOOK BIOLOGY GRADE 10 CHAPTER 1 INTRODUCTION TO BIOLOGY Learning Outcomes It is expected that students will ƒexplain how the study of biology is important in daily life ƒidentify the common characteristics of living things ƒknow how living things are classified into three domains andnd six kingdoms ngdoms x 1.1 THE STUDY OF BIOLOGY Biology is the study of living things. A large variety of living things exists on tth the land, in the water and in the air. Living things (organisms) isms) include plants, animals including nisms) inclu Bo humans and other organisms. Thus, biology deals als with the study of all organisms organism that live or have ever lived on the earth. 1.1.1 The Importance of Biology in Everyday veryday Life Biology is very fundamental al and important ant science dealing with w bacteria, protista, fungi, plants and animals including ing humans. Their structures and functions ffu are associated with one another in their respectiveective environments. To a great extent, exte we owe our daily high ext standard of living to biologicalgical advances in two areas: food pr production and disease control.                                 food than did older varieties. arieties. The improvements in the plants, along with better farming BE practices, have greatly atly increased food production. reatly Biological ical research has also improved food foo production by developing controls for fo the disease organisms, pests and weeds that reduce re yields. Biologists must understand the                         7KH'L൵HUHQW)LHOGVRI6WXG\LQ%LRORJ\ 7KH 'L൵HUHQW ൵HUHQW )LHOGV ) RI 6WXG\ 6WX The main branches of biology biolo are: biol Botany Bo : study of plants Zoology Zo : study of animals D Microbiology Micro : study stu of microscopic organisms Some other branches b of biology are: Morphology rphology : study of forms and structures of organisms Anatomy natomy my : study of gross internal structures Histology logy : study of microscopic structures of tissues Cytology : study of cells Physiology : study of living processes or functions of the various parts of organisms Embryology : study of early development of organisms Palaeontology : study of fossils (the remains of organisms that lived millions of years ago; now preserved in rocks) 1 GRADE 10 BIOLOGY TEXTBOOK           Ecology : study of the relationships of organisms to their environments Biodiversity : study of varieties among living organisms Evolution : study of the origin and change in forms of organisms over time Genetics : study of heredity and variations Mycology : study of fungi Protistology : study of protists Phycology : study of algae Virology : study of viruses Bacteriology : study of bacteria Molecular Biology : study of molecules in organisms Biotechnology sms in industrial : study of utilization of living organisms ustrial processes processe Bioinformatics : study of information technology to interpret molecular biology data 1.1.3 Characteristics of Living Things ngs are their cellular structure, me The main characteristics of living things metabolism, n and adaptability. growth, movement, irritability, reproduction Cellular structure prot pro All living things consist of the living substance called protoplasm which forms the basis of cells. These cells contain DNA (deoxyribonucleic ac acid) molecules that carry biological information. Cellss of plants and animals are organize organized into tissues and tissues are ans and systems. These stru in turn organized into organs structures aare responsible for carrying out ses. the various life processes. Metabolism bolism is the sum of the various ppr Metabolism processes that give the organism’s life. The two aspectsts of metabolism are anabolism and an catabolism. The food material is made into ganism in the process of anabolism. a part of the organism an The food material, when broken down, ases ses energy and results in the form releases formation of waste products. This process is termed as atabolism. The important metabol catabolism. metaboli metabolic processes that take place in organisms involve the utilization of food. This includes nutrition, respiration and excretion. Growth Growt The growth of an organism is seen as an increase in size and weight resulting from the use se of food to fur furt further develop structures in the organism. ement Movement ll living All li things show some kinds of movement. This is more obvious in animals since they have organs of movement or locomotion. Movements in plants mainly take place inside the cells although some results from a stimulus such as light. 2 TEXTBOOK BIOLOGY GRADE 10 Irritability Living things respond to stimulus. The stimulus can be any changes in the environment (light, sound, touch, temperature, etc.) which brings about a reaction in an organism due to a sensitivity to the stimulus. Reproduction                    sexual reproduction, reproduction are asexual reproduction and sexual reproduction. In asexual roducti the new individual may be produced by a part of the old one. There is only onee parent organism org needed for asexual reproduction. x Sexual reproduction produces a new individual as a resultt of the fusion of two parental sex cells. These two cells come, one from each individual al of the same species. T The cells are fused to form a single new organism. Adaptability the environment. 1.2 TAXONOMY Y Bo Living organisms are able to adjust and adapt themselves to changes in their and internal environments. Adaptability increases the chances of spec cies. For instance, a change of seasons result in the formation of a new species. ther place where the of food may cause certain birds to migrate to another ery straight and upright to stand abo favourable. A plant may grow very pecies to get enough sunlight to survive enables this plant or plant species sur su seas s sur t species surviving external and can or a shortage th conditions are more above plants around it. This and even to dominate BE                                          1.2.1 Diversity of Organisms Theree are vast numbers of llivin living things in the world. The word ‘biodiversity’ is a   !  !       "   "         species. #            $                nature. It is because, previo previously unknown species are being discovered all the time. D 1.2.2 Taxonomy omy in i tthe Study of Biology  %                        things gs to sort out oou and compare unless they are organized into manageable categories. With          &      '         and make generalizations.      (   &                  )        related, fossils should also be considered in this scheme. 3 GRADE 10 BIOLOGY TEXTBOOK         x giving every organism an agreed name x placing the organism into a group based on the common characteristics it shares with others in the group. 1.2.3 The Importance of Taxonomy illions off known By taxonomy, it is much easier to learn biology as there are millions kno olutionary history of and unknown organisms. Taxonomy can be used to examine the evolutionary organisms and the relationships between organisms. x 1.2.4 Taxonomic Hierarchy *            && &                     +  &              Bo toget to possible in placing similar organisms together. Just as similar species are grouped together into the same genus (plural genera). Similar genera are grouped together into to families fam families.. This approach is extended exten from ivisions and kingdoms. families to orders, then classes, phyla or divisions kingdoms. This is the hierarchical    &                  ,     -         & &         ,     by other taxonomic ranks of divisionion or phylum, class, order, family, genus and species. For examples, Kingdom lantae : Plantae Kingdom King : Animalia BE Division : Magnoliophyta iophyta Phylum Phylu : Chordata Class : Monocotyledons Clas Class : Mammalia er Order : Cyperales O Order : Primates amily Family : Poaceae Family : Hominidae Genuss : Ory Oryza Genus : Homo Species : O. ssativa Species : H. sapiens   &ODVVL¿FDWLRQ  ¿FDWLRQ RI 3ODQWV &ODVVL¿FDWLRQRI3ODQWVDQG$QLPDOV Everyonee must be able abl to identify objects and to relate their observations to other D people. Most people aare fa familiar with some of the common forms of plants and animals..  &&       ,   &   "  ! !" ! "" /       Linnaeus 01232412256&#    &      ndss of plants thousands pl p and animals. He introduced the Binomial System of Nomenclature in    12789    4        name is the genus and the second is the species. The name of the genus is always started with a capital letter and the name of the species is started with a small letter. These two            :    &     human is Homo sapiens and that of paddy plant is Oryza sativa. 4 TEXTBOOK BIOLOGY GRADE 10 1.3 KINGDOMS A Kingdom is a subdivision of a Domain         in one of the six kingdoms. The three domains - Bacteria, Archaea and Eukarya diverged early in the history of life. Subsequently, many new kinds of organisms have evolved. Each of these kingdoms has its own set of characteristics. 1.3.1 Kingdoms of Living Things Organisms are divided into six kingdoms. There are twoo kingdomss within with the acteria and Eubacteria. domains Archaea and Bacteria, namely kingdoms Archaebacteria Eubac Eubacteria. Their differences are based primarily on the metabolism and genetic tic composition of x the organisms. Within the domain Eukarya, there are four kingdoms: doms: Protista, Fungi, Fungi, Plantae and Animalia (Table 1.1 and Figure 1.1). Table 1.1 Characteristics ristics Bo :  11        tics of six kingdoms kingdom        ,  ,     BE Kingdoms Characteristics Examples Diagrams Archaebacteria - imitive Primitive Thermophiles - Livee in extreme environment environm Methanogens - Prokaryo Prokaryote - Unic Unicellular - anaerob anaero Obligate anaerobic Thermophiles Eubacteria - Prokaryote karyote Bacteria - Unicellular Unicellu Cyanobacteria D - Autotrophs A Autot or heterotrophs - Asexual As reproduction by   Bacteria rotista Protista - Eukaryote Amoeba - Unicellular Euglena - Autotrophs or heterotrophs Slime mold - Asexual or sexual Paramecium reproduction Paramecium 5 GRADE 10 BIOLOGY TEXTBOOK Table 1.1 Characteristics of six kingdoms (continued) Kingdoms Characteristics Examples Diagrams Fungi - Eukaryote Yeast - Unicellular or multicellular Rhizopus - Heterotrophs Mushroom - Asexual or sexual reproduction Mushroom hroom Plantae - Eukaryote Algae x - Multicellular Liverworts - Autotrophs Mosses - Vegetative, asexual or Ferns Bo sexual reproduction ifers Conifers Angiosperms Angiosperm Animalia - Eukaryote Earth Earthworms - Multicellular Insects - Heterotrophs Fish ish - Asexual or sexual Birds reproduction Mammals Mammal Viruses Viruses are not included luded in the six kingdoms of living liv organisms. Viruses, although not BE        & &          ( '0:   1;6     )+    )   . ive the functions of acronutrients in plants. 1    7"       1 deficiency.. hich acronutrients prevent constipation ention theirr functionss food   1 ficiency. x. escribe the nutrients that the ani als need to sustain in life.. hat icronutrients are essential for hu an. hat are the acronutrients Ho i portant are they inn a hu an diet 1. hat ill happen to the hu an body if the diet is not balanced alanced ocus on o Bo nutrient deficiencies. 11. escribe the structures and functions of teeth in hu aan. 12. hy are foods needed to be digested ted 1. here do che ical digestion and ndd absorption of food occur in the hhu an digestive tract 1. nu erate the factors hich aintain a healthy digestive sy sys syste. 1. plain so e of the co o on sy pto s and diseases of alfunctioning digestive syste. BE D 62 TEXTBOOK BIOLOGY GRADE 10 Concept ap x Bo BE D 63 GRADE 10 BIOLOGY TEXTBOOK CHAPTER 5 CONTINUATION OF LIFE Learning Outcomes It is expected that students will ƒexplain the types of reproduction in plants and animals ƒdescribe the formation and role of gametes ƒexplain how chromosomes behave during reproduction ƒidentify the steps in the processes of mitosis and meiosis and x nd comparee the two processes ƒexplain the role of chromosomes and genes in the inheritance heritance of characteristics and on the continuation of life 5.1 REPRODUCTION Bo The production of new organisms fromom m the existing organisms of tthe sam called reproduction. Reproduction is essential of reproduction ensures continuation of life on earth. 5.1.1 Reproduction in Fungi and Plants Two main types of reproduction found in fungi and plants reproductions. same species is earth. The process ential for survival of species on ear pla are asexual and sexual pl BE Asexual reproduction on in cyanobacteria, fungi and plants ion pl p A new individual produced from a single parent without involving the sex cell (gamete) is called alled asexual reproduction. Asexual reproduction may occur through binary or multiple fission, ission, budding, fragmentation, spore spor formation and vegetative propagation. spo Fission When the parent organism rre reaches its maximum growth, it splits to form two new etc. (Figure 5.1) organisms. e.g., Cyanobacteria, eet D Figure 5.1 Asexual reproduction in Cyanobacteria by binary fission Figu Figur Budding In budding, a small part of a body of the parent organism grows out as a bud which then detaches and becomes a new organism. e.g., Yeast (Figure 5.2) 64 TEXTBOOK BIOLOGY GRADE 10 Figure 5.2 Asexual reproduction in yeast by budding Fragmentation The breaking up of the body of simple multicellular cellular organism rganism into two or more mo fragments, each fragment subsequently grows to form rm a new complete mplete organism. e.g., Spirogyra       Figure 5.3 Asexual sexual al reproduction reprodu in Spirogyra ra by b fragmentation Spore formation The parent plant produces microscopic reproductive oduces many microscopi re units called spores inside the spore sac. When bursts, then the spores spread into air. When hen the spore sac (sporangium) burs these spores stand on food or soil, under favorable favorab condition they germinate and produce favora the new plants. lants. e.g., Fern (Figure 5.4) Figure 5.4 Asexual reproduction in Fern by spores Vegetative ativ propagation In vegetative propagation, new plants are obtained from the parts of old plants such as stems, leaves or roots without the help of any reproductive organ. The green grass grows                      propagation. 65 GRADE 10 BIOLOGY TEXTBOOK Similarly, Bryophyllum plants can be reproduced by vegetative propagation by its leaves; gingers grow from the nodes of rhizomes, potato grows from the bud or eye of the tuber (Figure 5.5, 5.6 and 5.7). x Figure 5.5 Vegetative propagation of Bryophyllum um by leaves ginger by rhizome me Artificial methods of vegetative Bo Figure 5.6 Vegetative propagation ation of egetative getative propagation Figure 5.7 Vegetative Vegetativ propagation of potat by tuber potato BE The process off growing many plants from one plant pla by man-made method is called                  1. Cutting: ing:: A small part of root, stem, or leaves ing leav from a plant which is cut with a sharp lea knife ife is called cutting. A cut piece of tthe plant necessary to have some buds on it. e.g., (Figur 5.8)..g., rose, sugarcane, cactus (Figure 2. Layering: Layeringing:: It is a type of vegetative vegetati multiplication in which shoot of parent plant is vege allowed to develop roots while whi it is intact with the plant. After the development of wh enough roots, the shoot is detached from the parent plant to plant in the medium to lead an independent life. lif In layering, rooted branch is called a layer. e.g., rubber, croton (Figure 5.9). D 3. Grafting !! 3 Grafting!     " #    "     without roots) roo are joined together to grow as single plant is called grafting. The new plant has the characteristics of both plants. The cut stem having roots is called stock st and the cut stem of another plant without roots is called scion. e.g., apple, mango, avocado (Figure 5.10). 4. Budding: Budding is a form of grafting most often used commercially. In this procedure, just the axillary buds are grafted onto the stem of another plant. e.g., rose, avocado, plum, citrus (Figure 5.11). 66 TEXTBOOK BIOLOGY GRADE 10 x Figure 5.8 Figure 5.9 Vegetative propagation by cutting Vegetative ative propagation pagation by layering Figure re 5.10 Vegetative propagation ropagation Bo n by grafting Vegetative V Veg Figure 5.11 propagation by budding BE Micropropagation gation (Tissue Culture) Thehe new plants are produced from a ssmall piece of the plant tissue (e.g., branch tip, root tip, p,, leaf portion) in growing medium (agar medium). Sexual exual xual reproduction in plants The production of new plplant from two parent plants by the use of sex cells (gametes) pla   $     $    %   $ "  & " D Fema gamete Female Fertilization ttakes place inside the ovary inside which is the female gamete. One or any ovules are ffound attached to the inner wall of the ovary by means of funicles. many The bobody of the ovule is termed as the nucellus and one or two layers of integuments cover er it. A ppore, left uncovered, at the tip of the ovule, is the micropyle. Embedded in the nucellus is a large oval-shaped embryo sac, containing eight nuclei. Three of these are situated at the micropylar end. The biggest is called the egg cell or the female gamete. The other two are the synergids. At the opposite end are three nuclei, known as the antipodal cells. At the centre of the embryo sac are two polar nuclei (Figure 5.12). 67 GRADE 10 BIOLOGY TEXTBOOK x Figure 5.12 L.S. of ovule Male gamete Bo The formation of male gamete takes place inside the pollen, a more or less rounded structure. It is uninucleate and possesses a two-layered Some weak spots called germ pores may be present nt in the exine. At the time of pollination, the stigma is viscous exi sugar and other compounds. This substance stimulates the pollen grai Just before pollination, the nucleus of the pollen divides into and the generative nucleus. On pollination, the pollen begins to protrudes through the germ nucleus, carried along with m pore of the exine and elongates elo su s ous with a sticky substance sub rou ro -layered wall. The inner wall or the intine is soft and thin. The outer wall or the exine is tough ugh and often provided with spinous outgrowth. grains to germinate. grain containing int two, the tube nucleus in t germinate and the intine to form a pollen tube. The tube ith the generative nucleus at tthe ttip of the pollen tube controls the BE growth of the pollen n tube. The pollenen tube penetr penetrates the stigma and grows down the style until it finally reaches the ovule. vule. By that time, the generative nnucleus has already divided into two male gametes (Figure igure 5.13) 5.13). D Figure 5.13 Germinating pollen grain 68 TEXTBOOK BIOLOGY GRADE 10 Fertilization The pollen tube enters the ovule through the micropyle and it passes through the nucellus to approach the embryo sac. Then the tip of the pollen tube dissolves and the two male gametes are set free into the embryo sac. The tube nucleus disintegrates eventually. One of the two male gametes fuses with the female gamete or egg cell, ell, resulting res in the fertilized egg or oospore. This process is termed as “fertilization”. Thee two polar nuclei          ! "           gamete to form the primary endosperm nucleus. The fusion of three nuclei, i.e. the two polar nuclei and thee male gamete amete is the therefore termed as “triple fusion”. One male gamete fuses with the egg gg cell andd the other with the x two polar nuclei and that is why this process of fertilizationion and triple iple fusion are together known as “double fertilization”. gids direct the During the process of fertilization, the synergids he male gamete towards the Bo rate. The antipodal cells disappe egg cell and the polar nuclei. They then disintegrate. disappear before fertilization (Figure 5.14). BE Figure 5.14 L.S. of tth the ovule showing the process of fertilization Changes after fertilization  '     (                  "     # ! D        # #                   The develop into seeds and the ovary as a whole changes to form a fruit. The embryo he ovules develo sac enlarges and the fertilized egg grows and gives rise to an embryo. At the same time, the primary maryry endosperm endo end nucleus divides repeatedly to form the endosperm which stores food material ial for f the growing embryo. The integuments become the seed coats. 69 GRADE 10 BIOLOGY TEXTBOOK 5.1.2 Reproduction in Animals Two types of reproduction, asexual and sexual, are found among the animals. Asexual means ‘without sex’ and this method of reproduction does not involve gametes (sex cells). In sexual reproduction, gametes from male and female combine to form an embryo which then grows into a young organism. Asexual reproduction in animals  $  )                $       fragmentation, budding or parthenogenesis. Some protists such as Amoeba moeba reproduce by   "                  % %    x insects such as bees reproduce by parthenogenesis. Hydra is a small animal, imal, 5-10 mm long, which lives in ponds attached to pondweed. Hydra has an asexual method of reproduction called budding. But Hydra can also reproduce sexually by gametess (Figure 5.15). Figure 5.15 Asexual reproduction starts dividing rapidly and Bo duction by budding in Hydra (a) a ggroup of cells on the column ndd produces a bulge (b) the bulge b grows g and develops tentacles (c) BE the daughter Hydra pulls itself off the parent and (d) th the daughter becomes an independent animal Sexual reproduction oduction in animals Sexual exual production of sex cells. These sex cells are called xual reproduction involves the pro gametes tes and they reproductive organs called testes (in male) and ovaries (in ey are made in reproduct reprodu female). that produces the gametes is called meiosis. In sexual ale). The process of cell division tth reproduction, the male and female ggametes come together and fuse (fertilization), i.e. their together to form a single cell called a zygote. The zygote or cytoplasm and nuclei join toge toget embryo then grows into a new individual (Figure 5.16). D Figure 5.16 Fertilization and development of embryo and young in sexual reproduction of an animal 70 TEXTBOOK BIOLOGY GRADE 10 Sexual reproduction in humans In humans, like in other mammals, an ovum from a female (a woman) is fertilized by a sperm from a male (a man), after sexual intercourse. This produces an embryo in the woman’s uterus. After 270 days of conception which is about nine months, an embryo grows into a foetus and then a baby is born. Female ure 5.17 and Table The female reproductive organs and parts are shown in Figure Tabl 5.1. x Figure 5.17 Bo.17 The female reproductive system in human (side view) Table 5.1 Functions off parts of the female reproductive reprodu system in humans BE Parts Functions Ovary - Contains follicles in which wh ova (eggs) are produced Funnel of oviduct oviduc - Directs an ovum (egg) (eg from the ovary into the oviduct (e - Carries an ovum o to the uterus, with propulsion provided by tiny Oviduct viduct cilia in the wall; w also the site of fertilization Uterus - Where the tth foetus develops Cervix - A ring rin of muscle, separating the vagina from the uterus ri D - Receives R the male penis during sexual intercourse; Vagina Vagin sperm are deposited here: serves also as a birth canal Urethra - Carries urine from the bladder Vestibule tibule - Area guarding the urethral and vaginal openings 71 GRADE 10 BIOLOGY TEXTBOOK Male The male reproductive organs and parts are shown in Figure 5.18 and Table 5.2. Figure 5.18 The male reproductive ve system in human (side view) Testis Parts Epididymis Sperm duct - A mass B Table 5.2 Functions of parts of the male reproductive - Male gonad ad that produces pr ctive system in humans Functions unctions sperm ss of tubes in which sperm are stored - Muscular uscular tube that links passage store link the testis to the assage of semen containing sperm t urethra to allow the BE Seminal vesicle **'& '&            Prostate gland **'& '& ' &           Scrotum - A sac that holds the testes teste outside the body, keeping them cooler than the body temperature temper Urethra - Passes semen containing ccont sperm through the penis; also carries urine from the bladder Penis - Can become becom firm, to insert into the vagina of the female during sexual exual intercourse in to transfer sperm D Fertilization Fertiliz Immediately after aaft mating or copulation (sexual intercourse), the sperm swim up the he uterus the mucus lining to the oviducts (fallopian tubes). If there is an egg, one terus through th of the he sperm erm may fuse with it to form a zygote. The process in which an egg unites with a sperm is termed terme as fertilization. Implantation The zygote divides continuously into a ball of cells called embryo. The embryo moves towards the uterus, becomes attached to the wall and is surrounded by the uterus lining. This process is termed implantation. 72 TEXTBOOK BIOLOGY GRADE 10 Gestation period The period between fertilization and birth is called gestation period and it takes about nine months in humans. During this period, the following new structures are developed to keep the embryo alive and healthy.      Placenta *   * +        nic blood capillary uterine wall (maternal tissue). The villi consist of maternal and embryonic cap capill $     "     "#   $     antibodies to the embryo and metabolic wastes from the embryo. The placenta nta also secretes se hormones. acenta. The Umbilical cord - connects the embryo’s body to the placenta. he two umbilical arteries                        ! !     deoxygenated blood and excretory wastes from the embryo mbryo to the placenta. The vein ca carries oxygenated blood and dissolved nutrients from the placenta to the embryo embryo. Amnion - * +        " " "  "   &      & & & $PQLRWLFÀXLGallows the embryoyo freedom of movement ovement during gr gro growth and cushions it against knocks and mechanicall injury ((Figure 5.19). Figure 5.1 5.19 Developing foetus in human uterus Birth Bi The embryo mbryo eventually eve develops into a foetus, with recognizable human features. At the end of gestation gestati period, the muscular uterine walls begin to contract. This is termed gesta  ! labour! as labour labour      &!$  thee foetus etus now called a baby, passes through the vagina, then out of the mother’s body. This is termed med bbirth. rmed Lactation and maternal care Lactation is the process of producing milk in the mother’s breasts, for feeding the baby. Breastfeeding is one of the maternal care activities. 73 GRADE 10 BIOLOGY TEXTBOOK Menstrual cycle Ovulation occurs once in about every 28 days in woman. If the egg is not fertilized within 36 hours, it dies and the uterus lining breaks down slowly. The dead egg together with the uterus lining, mucus and some blood are discharged through the vagina. This period of bleeding is termed as menstruation. Ovulation does not occur during pregnancy.. Therefore, Ther menstruation ceases once a woman is pregnant until after the baby is born. 5.2 INHERITANCE eneration to generation. Inheritance is the transmission of genetic information from generation generati Plants and animals inherited certain characteristics such as plantnt height, fruit ruit colour, seed x racteristicss is called shape, skin colour and eye colour. The inheritance of such characteristics call heredity. heredity redit.   ,         #!         how heredity works is genetics. Chromosome Structure of chromosome Bo 5.2.1 Nature of Chromosomes, Genes and DNA agee of DNA Chromosome is an organized package A found in nucleus of two chromatids, joined at one point called a centromere.. Each rson’s characteristics. The other genes, coding for the person’s nes are segments in the same order. Genes ot chr egments of DNA (Figure 5.20). 5 o the cell. Each chromosome is madee up of DNA and proteins. It can be seen at the time of cell division. Each chromosome hass certain characteristics when it is re ready to divide. It becomes Ea chromatid is a string of chromatid carries the same genes BE ody (somatic) cell nucleus contains 23 pairs of chromosomes. These are A human body     -               ( appearances.. This arrangement is calle called a karyo kary karyotype (Figure 5.21). D Figure 5.20 Nature of chromosomes, genes and DNA 74 TEXTBOOK BIOLOGY GRADE 10 Figure 5.21 Human karyotype x Number of chromosomes There is a fixed number of chromosomes in each cell ll of the same species. In human body cells, each contains 46 chromosomes, mouse cell contains 40, wheat contains conta Bo 42 and garden pea contains 14. The number of chromosomes in a species is the same sa in all of its body cells. There are 46 chromosomes nerve cell, es in each of liver cells, in every nne skin cell and so on in humans. The chromosomes osomes are always in pairs, called homologous chromosomes such as two long ones, twoo short ones and two medium ones because one of each pair comes from the male gametee and one from the female gamete. gamete In humans, there are 46 chromosomes in each cell which chromosome from the mother and h are inherited as 23 chromosomes another 23 from the father. Genes The gene is the he basic physical and functional func uunit of heredity. It is a length of DNA which      .   . .           BE               Gene locus  /                   Allele lele forms of a gene. In a diploid cell, there are usually two alleles One of the alternative form locus of a pair of homologous chromosomes. occupying the same gene locu Deoxyribonucleic aacid (D(DNA) D DNA is the chemical ch substance found in the chromosomes of the nucleus of a cell. NA is the basis oof inheritance in all organisms. DNA Structure ture of DNA ructure A molecule of DNA is made from two strands of nucleotides. Each nucleotide contains a nitrogenous base which is either adenine (A) or thymine (T) or cytosine (C) or guanine (G), a sugar molecule and a phosphate group (Figure 5.22). 75 GRADE 10 BIOLOGY TEXTBOOK In the two strands of DNA, nucleotides with adenine are always paired to opposite nucleotides with thymine and nucleotides with guanine to that of cytosine. Adenine and thymine are complementary bases, as are also cytosine and guanine. Complementary bases  "  "    !   " $  !  + "  * rule. DNA can replicate itself, so replication is able to pass genetic information n fro from one     $ genetic code (Figure 5.23). x Bo BE Figure. 5.22 A nucleotide of DNA Figure Figur 5.23 The structure of DNA 5.2.2 Cellularr Reproduction Cellular llular reproduction is a process by which w cells duplicate their contents and then divides to produce two similar cells. It is es essential to growth and development of cells. Cell lll division   /    *$           Cell division consists of four st stages, prophase, metaphase, anaphase and telophase. The sta        0  +       D "    "     %+    " are two distinct types of o cell division; a vegetative cell division where each daughter cell is genetically netically identical to the parent cell i.e., same number of chromosomes (mitosis) and a cally identica reproductive ductive cell division where the number of chromosomes in the daughter cell is reduced tive cel by half too pro produce haploid gametes (meiosis). Types of cell division !" #     +      76 TEXTBOOK BIOLOGY GRADE 10 Mitosis Mitosis is a process that creates a nearly exact copy of the parental cells. The mitotic cell division involves mitosis and cytokinesis. Mitosis is the division of the nucleus and results into two identical daughter nuclei. Cytokinesis is the division of the cytoplasm into ge two cells. After mitosis and cytokinesis, two diploid daughter cells which are genetically identical to the diploid parent cells (Figure 5.24). Meiosis    1 #                 $  $ osis I is thee first cell division, cells. It consists of two stages: Meiosis I and Meiosis II. Meiosis x results into two haploid cells and meiosis II is the secondd cell division, ision, results into four ction division haploid cells. This type of cell division is called reduction ision because they cont contain half the number of chromosomes of the diploid parent nt cells (Figure ure 5.25). 5 Bo BE Figure 5.24 Mi Mitosis Mit Figure 5.25 Meiosis D Importance of mitosis mito Mitosis produces prod pro two daughter cells with the same identical genetic components (chromosomes) romosomes) aas the parent cell. Mitosis is important to regulate the cell growth, development andd repair pair in multicellular m organisms. Importance of meiosis Meiotic cell division produces four haploid sex cells from existing diploid cell and therefore it creates genetic variation. Meiosis is nature’s way of keeping the chromosome number constant from generation to generation. 77 GRADE 10 BIOLOGY TEXTBOOK Table 5.3 Mitosis versus meiosis Facts Mitosis Meiosis Type of reproduction - Asexual - Sexual Occurs in - All eukaryotes - Humans, animals, plants, fungi Genetically - Identical to parent cell   *2#    Function - Cellular reproduction, general iversity through - Genetic diversity rough growth, repair of the body and tion sexual reproduction clone production x Chromosome number - Remain the same as in parent nt cell - Reduce by half of parent cell Creates - New cells other than sex cells ells only: female egg - Sex cells Bo cel cells or male sperm cells 5.2.3 The Role of Cellular Reproduction in Multicellular Organisms ular In multicellular organisms, the cellularlar reproduction (cell division) divisio is important im for the following purposes. ematic tissues of multicellular plant 1. Growth – The cells in meristematic plants divide throughout life for growth in length and girth, while growth in anim animal cells increases in number by mitotic cell ll division. divisi 2. Healing of wounds – In both plants and animals, cells ddivide to heal the wounds. It is an occasional event vent by mitosis. 3. Reproduction – Sex cells lls of both plants and animals anim an divide meiotically during the BE reproductiveve age. 4. Stem cells lls – In animals, after mitotic cell ddivision, some cells become specialized but some ome become stem cells which are able a to divide for continuous growth of the animals. nimals. imals. But specialized cells cease tot divide. 5.2.4 The Role of Chromosomes an and Genes in Inheritance Heredity is the transfer or passing p of characteristics genetically from the parents to  #  The genetic information is carried within chromosomes. The chromosomes are found etic informatio D in the nucleus of a cell. cell Long Lo coiled molecules of DNA make up chromosomes. The genes aree contained in the DNDNA. They are the units of heredity and are responsible for inheritance. DNA %       $       2#      # # !           # e.g., thee height heigh of a person or the facial features such as nose or jawline are all controlled  #  The inheritance of characteristics in an organism is contributed equally by the mother and father. The mother and father provide equal amounts of genetic material to their #!    "           other that comes from the father. 78 TEXTBOOK BIOLOGY GRADE 10 Most of the genes have more than two variations, they are called alleles. e.g., there  "            ! #           " #      3  #   " #         "!     and a recessive trait. The dominant trait comes from an allele of the gene that decidess the trait in the presence of the other recessive allele of the identical gene. The trait that does not ge get to express itself is called the recessive trait. Genetics nherited characteristics, Genetics is the study of heredity and variations of inherited cs, and the way that characters are passed on from one generation too the next. Character anism A distinctive inherited feature of an organism Trait  2#      Variation       4   #  "  "         Dominant trait xpressed pressed in an organism, suppressing The trait is expressed suppressin the recessive trait. The dominant suppr sing ing capital letters. trait is denoted using rait Recessive trait The trait stays suppressed or cannot be expressed in the presence of the dominant trait. The ssive ve trait is denoted using small recessive smal lett letters. Dominant alle allele Ann allele carries the dom dominant trait and is expressed in the phenotype of the organism. For example, the dominant ttrait tall is represented by T. Reces Recessive allele An allele cca carries the recessive trait and is only expressed as the phenotype of the organism anism in the absence of the dominant allele. For example, the recessive trait short or arf is repr dwarf repre represented by t. type Genotype  !         #    #    present in a gene. That is TT or Tt for tall genotypes, tt for short or dwarf genotype. 79 GRADE 10 BIOLOGY TEXTBOOK henotype  !                   ! "        " " & "    omo ygote An individual contains only one allele of the allelic pair. Alleles that form the homo ygous allelic pair are the same (e.g., TT). A homo ygote producess only one ind of gamete. etero ygote x lelic pair. Alleles that form the An individual contains one of each member of the allelic   (   # Tt'  (     # + # +   gamete.  ure reeding plants generation. ure line animals Bo !     "  *  (   individuals of pure line with same atterns of inheritance The breeding e periments ents are carried     # carri outt to study #      # ating se ually between the homo ygous individuals (male anda female) produces me genetic identity for many generations. genera gener stu the inheritance of characteristics BE in se ually reproducing cing plants and animals. There is a general pattern for describing the ucing results of e periments. iments. At fertili ation, male gamete gamet fuses with female gamete to produce game #   %"  % "              ym ols   by using sym               cross. D 80 TEXTBOOK BIOLOGY GRADE 10 For e ample onohybrid crosses et T tall allele and t dwarf or short allele for height The capital letter is used for dominant allele and small letter is used for recessive allele. Tall T and dwarf t are alleles for pea plant height. x A cross between a homo ygous tall (TT) and a homo ygous dwarf (tt) parents x A cross between a hetero ygous gous tall (Tt) (Tt) and a hetero tero ygous tall ta t (Tt) parents from F  ! !      %     #  in the 3 ratio rati but each fertili ation is random so that the ratio may vary. In theory, a cross rat  " "   (      #    5   5!         # "  height (tall) is 3 or 5 and recessive (dwarf) is or 25. 81 GRADE 10 BIOLOGY TEXTBOOK Revie uestions. numerate the types of ase ual reproduction in plants and e plain any two with appropriate diagrams. 2. Define the term vegetative propagation with e amples. diagra 3. plain how the bud grafting is carried out in plants with a suitable diagram.. hat happens to the pollen grain before and after pollination 5. Describe the process after pollination in plants. 67  #        . tate the parts and functions of female reproductive system stem in human. man. x roductive system. Describe the parts with related functions in male reproductive ystem of human.. ow many chromosomes would be in the nucleus leus of (a) human muscle cell Bo (b) a mouse idney cell (c) human s in cell (d) human sperm cell. ow many chromosomes would ld be present in (a) a mouse sperm cell (b) a mouse ovum heredit. hat is the basic unit of heredity onents of a nu 2. hat are the components nucleotide enous bases in DN 3. Name the nitrogenous DNA.. DNA e ists ass a double heli. Name the bbase pai pairs that hold the double heli together. BE 5. ow many any stages are involved in mitosis pare the meiotic and mitotic cell ddi. Compare divisions with diagrams. ompare the signif. Compare signif icance of mitosis versus meiosis. significance      58 %     " #  # #     "!   is controlled ntrolled by one pair of gen genes. Tall is dominant over dwarf. Choose the suitable letters for the gene pair. D 82 TEXTBOOK BIOLOGY GRADE 10 Concept map x Bo BE D 83