CBSE CLASS 10 CHAPTER 8 NOTES

 

CHAPTER 8

CBSE SCIENCE
CLASS 10

HOW DO ORGANISMS

REPRODUCE?

 

REPRODUCTION

·        Reproduction – allows perpetuation of species & increase the population of a species

·        Plays an important role in evolution – by transmitting favourable variation – from one generation to another

·        Basic event – creation of DNA – DNA copying accompanied by cell division – giving rise to 2 cells

·        2 main methods of reproduction

·        Asexual reproduction

·        Sexual reproduction

ASEXUAL REPRODUCTION

·        Asexual reproduction – takes place in many ways – depends on the body design of the organisms

·        They are

·        Fission

·        Fragmentation

·        Regeneration

·        Budding

·        Vegetative Propagation

·        Spore formation

FISSION

·        Fission – 2 types

o   Binary fission

o   Multiple fission

BINARY FISSION

·        Division of one cell into two similar daughter cells

·        Nucleus – first divides automatically – followed by the division of cytoplasm

·        Cell finally splits into 2 daughter cells

·        Eg: Amoeba – reproduces through simple binary fission

·        Leishmania – also reproduces through binary fission – occur along a definite orientation – they have whip like structure at one end of their cell

  

 

MULTIPLE FISSION

·        Multiple fission – single organism divide into many daughter cells at the same time

·        Eg: Plasmodium

FRAGMENTATION

·        Multi cellular organisms with simple body structure – breaks into 2 or more small pieces of fragments upon maturation

·        These fragments grows into news individuals

·        Eg: Spirogyra – filamentous algae

FRAGMENTATION IN SPIROGYRA

  

REGENERATION

·        Many fully differentiated organisms – have the ability to rise to new individuals from their body parts

·        If the organism is cut or broken into many pieces – each of these pieces will grow into new individual – known as regeneration

·        Regeneration – carried out by specialised cells that proliferate to make large number of cells

·        These cells then differentiate into various types of cells & tissues

·        Eg: Planaria

·        These changes takes place in an organised sequence called development

·        Regeneration – not the same as reproduction

·        As organisms may not rely on being cut to regenerate

BUDDING

·        A small part of the parent’s body – grows out as a bud

·        The bud – detaches from the parent – grows into a new organism

·        Eg: Hydra – reproduce by budding – using regenerative cell

VEGETATIVE PROPAGATION

·        In vegetative propagation – new plants – obtained from the parts of old plants – stems, roots & leaves – without the help of any reproductive organ

·        2 types of vegetative propagation

·        Natural Vegetative propagation

·        Artificial Vegetative propagation

 

NATURAL VEGETATIVE PROPAGATION

·        In Natural vegetative Propagation – various parts of the plant – stem, roots, leaves – fall on the soil – grow into individual plant

·        Eg: Bryophyllum – buds are produced in the notches of leaf margin – it develops into new plant

ARTIFICIAL VEGETATIVE PROPAGATION

·        Artificial Vegetative propagation – takes place through cutting, layering and grafting – Used in agriculture & horticulture

·        Cutting – Any part of the plant (root, stem or leaf) is cut & buried in moist soil

·        Layering – A branch of a plant is hurried under soil, while it is still attached to the plant – adventitious roots are produced in the branch of the stem – this is called layer – this is then detached from the parent plant

·        Grafting – Two plants of closely related varieties – joined together as one plant

·        Portion of plant that is grafted – scion

·        Plant in which grafting is done – stock

·        This method is used to improve variety of fruits – Mango, apple, pears, citrus, guava, etc.,

CUTTING

LAYERING

GRAFTING

ADVANTAGES OF VEGETATIVE PROPAGATION

·        Only one parent is required – this eliminates the need for special mechanisms

·        Many plants – tide over unfavourable conditions

·        Plants that do not produce seeds – can be propagated

·        Traits / characters of parent plant is observed

SPORE FORMATION

·        Common method of asexual reproduction – in many lower forms of life – bacteria, fungi, etc

·        Spore formation – takes place in Rhizopus (bread mould)

·        Rhizopus – consists of – thread like projections – hyphae

·        Knob like structure – Sporangia – contains spores

·        Spores have thick walls to protect them

·        Spores when come in contact with moist surface – grow into new individual

SEXUAL REPRODUCTION IN FLOWERING PLANTS

·        Sexual reproduction – flowering plants – Phylum Angiosperms

·        Gametes are produced – within flowers

      

·        Flowers – usually bisexual – male & female reproductive parts – present  in same plant

·        Main parts of a flower – sepals, petals, stamens & carpels

·        Stamens & carpels – reproductive parts – contains germ cells

·        Male organ of a flower – stamen – makes male gamete – present in pollen grains

·        Female organ – carpel or pistil – makes female gamete – present in ovules of the plant

·        Ovules – enclosed in carpel

 

POLLINATION

·        Transfer of pollen grains from the anther of a stamen to the stigma of a carpel

·        Pollination – 2 types

·        Self Pollination

·        Cross Pollination

DIFFERENCE BETWEEN SELF & CROSS POLLINATION

FERTILISATION IN PLANTS

·        In plants – pollination is followed by fertilisation

·        Pollen grains deposit on the stigma & form tubes – pollen tubes

·        One pollen tube – grows through the style – reaches the ovary – where ovules are located

·        Inside the ovule – pollen tube releases 2 male gametes – into embryo sac

·        Embryo sac contains egg

·        One male gamete – fuses with egg – fusion called Syngamy

·        Other male gamete – fuses with polar nuclei – Triple fusion

·        Mechanism of 2 fusion – occuring in an embryo sac – called Double fertilization

·        The fusion of the germ cells or fertilization gives us the zygote which is capable of growing into a new plant

POST FERTILISATION CHANGES IN FLOWER

·        Sepals, petals, stigma, style, stamen – degenerate

·        Fertilised egg – embryo (baby plant)

·        Ovary – ripens into fruits

·        Ovules – ripens into seeds

·        Integument of ovule – seed coat

·        Funicle – stalk of the seed

SEEDS

·        Seeds – reproductive unit of plant – grows into a new plant

·        Contains a baby plant / embryo – food for the baby plant

·        Baby plant in the seed – in dormant/inactive stage

·        Seeds – when they get suitable conditions – water, warmth, air & light – new plants grow out

·        Cotyledons – store food, Plumule – shoot, Radicle – root

·        Parents reproduces more plants like itself – by forming seeds through flowers

REPRODUCTION IN HUMAN BEINGS

·        The reproductive organ of human beings – testis (male) & ovary (female) – becomes functional only after attaining maturity

·        In males – sexual maturity – attained at the age of 13 to 14 years

·        In females – 10 to 12 years

·        This is known as the age of puberty

SECONDARY SEXUAL CHARACTERS COMMON IN BOTH BOYS & GIRLS

·        Hair growth in armpits & genital areas between thighs

·        Appearance of thin hair – legs & arms

·        Skin frequently becomes oily & develop pimples

SECONDARY SEXUAL CHARACTERS

 IN BOYS

·        Thick growth of hair in their faces

·        Their voice begin to crack

·        Penis – occasionally becomes enlarged & erect

 

 IN GIRLS

·        The breast size – increase

·        Tips of breast – skin of nipples – dark

·        Girls begin to menstruate

VARIATIONS DURING SEXUAL REPRODUCTION

·        During preparation of DNA copies – hundreds of biochemical reactions occur

·        Few of them form a different product – they are not identical to the original

·        This gives rise to variation

DIFFERENCE BETWEEN SPERM & EGGS IN HUMANS

·        Major difference – genetic difference – sex chromosome of sperm (male gamete) & egg (female gamete) are different

·        Sperm – X and Y chromosome

·        Egg – has only X chromosome

IMPORTANCE OF THE DIFFERENCE

·        The difference in the sperm and egg cells maintains continuity of species generation after generation – by the process of reproduction

MALE REPRODUCTIVE SYSTEM

·        Male reproductive system – consists of testes – formation of sperms (germ cells) takes place

·        Testes – present outside the abdominal cavity – in Scrotum – as sperm formation requires low temperature than normal body temperature

·        Testes – secretes a hormone – Testosterone – that brings changes in appearance of boys – at puberty

·        Sperms – delivered through Vas deferens – which unites the tube from urinary bladder

              

·        Urethra – common passage for both sperms & urine

·        Along the path of vas deferens – prostrate gland & seminal vesicles add their secretions – sperms are in a fluid

·        Prostrate gland – provide secretions – contains chemicals – for mobility of sperm

·        Seminal vesicles – contains fructose, proteins & other chemicals – necessary for nourishing & stimulation of sperms

·        Sperms – tiny bodies – consists mainly genetic materials – a long tail – helps to move towards female germ cells

FEMALE REPRODUCTIVE SYSTEM

·        Eggs (female germ cells) – are made in ovaries

·        Ovary – secretes female hormones – Oestrogen & Progesterone

·        A girl during her birth – have thousands of immature eggs in her ovary

·        On reaching puberty – some of the eggs start maturing

·        One egg is produced every month by one of the ovaries

·        From the ovary – egg is taken to womb by a thin tube – Fallopian tube or oviduct

·        2 oviducts opens into an elastic bag like structure – Uterus

·        Uterus open into the vagina – through cervix

·        During sexual intercourse – sperms enter through the vaginal passage

·        Sperms travel upwards – reach the oviduct – where they may encounter the egg 

·        Fertilisation – takes place & the zygote is formed – is implanted in the uterus

·        Zygote – divides repeatedly to form a mass of cells – called embryo

·        Inner lining of the uterus – thickens every month – Supplied with blood – to nourish the embryo

PLACENTA

·        Embryo – gets nutrition from the mother’s blood – help of a special tissue – Placenta

·        Placenta – disc – embedded in the uterine wall

·        It contains villi – on the embryo side of the tissue

·        On the mother’s side – are blood space that surrounds the villi

·        Villi – provides large surface area – for glucose & oxygen to pass from mother to the embryo

·        Development of the child inside the mother’s body – takes approximately 9 months

·        Child – born as a result of rhythmic contraction of muscles in the uterus

WHAT HAPPENS WHEN THE EGG IS NOT FERTILIZED?

·        If the egg is not fertilized – it lives for one day

·        The uterus lining is no more required

·        Hence it breaks down – gets released in the form of blood & mucous – through vagina

·        This process lasts for 2 to 8 days

·        This cycle occurs every month – Menstruation

 

REPRODUCTIVE HEALTH

·        Reproductive health – aspects of general health – helps a person to lead a normal, safe & satisfying life

·        Sexually transmitted diseases (STDs) – spread by sexual contact – from infected person to a healthy person

·        Common STDs – Gonorrhoea, Syphilis, Trichomiasis, AIDS

CONTRACEPTIVE METHODS

·        Different methods – developed to prevent pregnancy – such as mechanical methods, chemical methods, oral pills or surgical methods

·        Different methods are

·        Condoms – on penis or covering on the vagina – creates a mechanical barrier – sperm doesn’t reach the ovary

·        Changing the hormonal balance – eggs are not released – fertilization does not occur – done by taking pills

·        Loop or Copper–T – placed in the uterus to avoid entry of sperm – avoid pregnancy

·        Either Vas deferens (male) or fallopian tube (female) – blocked which avoids fertilization – done by surgery

·        Surgery – (abortion) – of unwanted pregnancy (for its removal) 

EFFECTS OF CONTRACEPTIVE METHODS TO THE HEALTH

·        Helps in family planning – controls the number of children in a family – reduces the chance of poverty

·         Reduces the chances of transmission of STDs – such as AIDS

·         Birth control methods – plays an important role in the health & prosperity of a family