How Do Organisms Reproduce Class 10 16v5

How do organisms reproduce? What is reproduction? The production of new organisms from the existing organisms of the same species is known as reproduction. Significance of reproduction: 1. Continuation of life 2. Continuation of species 3. Replacement of dead or killed individuals in the population 4. Maintaining the population characteristics 5. Maintaining variations in the population 6. Transfer of variations to the next generation Basic feature of reproduction is replication of DNA that is creation of DNA copy by biochemical reactions. Species: a group of organisms having similar features that can freely interbreed and produce fertile off springs DNA: Deoxy Ribo Nucleic Acid. DNA contains hereditary material in the form of different gene codes for different proteins. Different proteins give different body designs. When two copies of DNA are made they separate by cell division resulting in two cells.(Mitosis) Cause of variations during reproduction: Biochemical reactions responsible for DNA copying are not absolutely reliable. Changes in these reactions bring variations in generations.

Consequence of too drastic variations is that the new born cell will die. Significance of variations: If variations are suitable to changes in the environment, the organism / species will survive. Asexual reproduction:

Reproduction with the help of a single parent, in which gametes are not involved is called asexual reproduction. 1. Fission: In unicellular organisms single parent divides itself in to two or more daughter cells. Binary fission: single parent cell divides in to two daughter cells- Amoeba Binary fission occurs in definite orientation in relation to its structure-Leishmania Multiple fission: single parent cell divides in to many daughter cells- malarial parasite (plasmodium)

2.

Fragmentation: In simple multi cellular organisms body breaks up in to many pieces and each piece grows in to a new individual- Spirogyra.

3.

Regeneration: The process by which a fully differentiated organism somehow cut or broken up in to pieces, each piece grow in to a separate individual (complete organism). Example- Hydra, planaria. Regeneration is carried out by specialized cells. These cells proliferate and make large number of cells. From this mass of cells different cells undergo changes to become various type of cells and tissues (differentiation). These changes take place in an organized sequence leading to development of the organism. Regeneration is not the same as reproduction as most of the organisms do not undergo this process and it is unreliable to depend upon being cut up to form new individuals.

4.

Budding: A small bulb like projection arise from the body due to repeated cell division at a specific site known as Bud. These buds develop in to the new individuals. They become independent at maturity and detach from the parent --Hydra, yeast.

5. Vegetative propagation: Propagation of plants using vegetative parts like roots, leaves, stems etc. Natural method: Root- sweet potato; stem-potato, sugarcane; leaves- Bryophyllum etc. Artificial method: Artificial method is useful in propagating Banana, Rose, Orange, and Jasmine etc. as they have lost the capacity to produce viable seeds. The methods of artificial propagation are 1. Grafting 2. Layering 3. Cutting 4. Tissue culture.

Advantages of vegetative propagation: 1. Cheaper, easier and faster method of propagation 2. Characters of the parent plant are preserved 3. Better quality plants can be maintained 4.

Many seedless varieties of grapes, banana, oranges are produced by this method.

5. Plants produced are genetically similar to the parent plant Limitations of vegetative propagation: 1. Off springs are the exact copies of the parents. 2. No genetic variation will be found. There is no scope for evolution of new species or varieties. 3.

They are not able to cope up with the changes of environmental conditions and have less chance to survive.

6. Spore formation: ( Fungi, Pteridophytes) Sporangia arise from hyphae. In these sporangia, spores will develop. These spores are covered by thick walls that protect them until they begin to grow in to a new individual. (Rhizopus, Ferns)

Sexual reproduction: • It involves two individuals. • DNA copying mechanism creates variations which are useful for ensuring survival of the species. Significance:

1. The DNA of the new individual is equally contributed by both the parents. 2.

The DNA content does not double in the new individual because the gametes have the quantity of DNA as compared to body cells (Meiosis- haploid).

3.

Gametes are reproductive cells (sex cells). In animals- male gamete-sperm; female gamete-ovum: in plants-male sex cell is pollen grain and the female sex cell is ovule. Zygote: Zygote is the single celled body obtained by the fusion of male and female gametes. Fertilisation: The process of fusion of male and female gametes (sex cells) to form zygote is called fertilisation.

Sexual reproduction in flowering plants: Flowers are the reproductive parts of the plant. Some flowers are unisexual. Eg. Papaya, Watermelon. These flowers have only one type of sex organs. Bisexual flowers: Hibiscus, Mustard. These flowers have both sex organs. Sepals and petals are non reproductive organs ( non essential parts )of the flower where as stamens and carpel are reproductive parts (essential parts) of the flower. Pollination: The process of transfer of pollen grains from the anthers to the stigma is known as pollination. It is of two types. Self pollination: The transfer of pollen grains from anther to the stigma of the same flower. Cross pollination: Transfer of pollen grains from anther to stigma of another flower of the same species.

Agents of pollination: wind, water, animals, Insects etc. Fertilisation: after pollination pollen grains germinate and pollen tube forms. This tube grows towards the ovules which is present in the ovary. The male gamete fuses with the female gamete and forms a zygote. Changes after fertilisation: Ovary changes in to a fruit, Ovules in to seeds. Sepals, petals, stamens, and style will fall off. Sepals may persist in some plants like Brinjal, Datura etc. Seed contains a future plant that is embryo, which develops in to a seedling under appropriate conditions.(germination) Future shoot is plumule and future root is radicle. Cotyledons contain reserve food for the baby plant. Reproduction in humans: In there is sexual mode of reproduction. Puberty: period during which a male and a female attains sexual maturity. In males sexual maturity is attained at the age of 13 to 14 years and in females at the age of 10 to 12 years. Testes and ovaries produce gametes and also secrete hormones. Testes- testosterone Ovary- estrogen, progesterone Changes common in both boys and girls (during adolescence) 1. Growth of thick hair in armpits and genital areas. 2. Oily skin and appearance of pimples.

Changes in boys: 1.

Growth of thick facial hair

2. Voice begins to crack and development of deep voice. 3. Development of male sex organs completely (penis). Changes in girls: 1. Breast size begins to increase 2. Darkening of nipple skin. 3. Start of menstruation process. Male reproductive system: 1. A pair of testes.  Produce sperms and testosterone  Located outside the body in a sac like structure called scrotum because sperm formation requires low temperature than the body temperature. 2. Vas deferens: A tube arises from each testis, s urethra, urethra opens through penis. Penis is common age for both semen and urine. 3. Prostate glands: Secrete liquids used for both the nutrition of sperms and lubrication. 4. Seminal vesicle: Secrete fluids for nourishment of sperms. 5. Sperms:

They are tiny bodies and contain genetic material in the head region. The long tail region helps to move towards the female gamete. Female reproductive system: Female germ cells are eggs (ova). These are made in the ovaries. 1. Ovaries: Produce female sex hormones and ovum, present inside the abdominal cavity. 2. Fallopian tubes: A pair of long tubes carries ova from ovary to uterus. Fertilisation takes place in oviduct. 3. Uterus : It is a hollow muscular elastic muscular elastic bag like structure where zygote is implanted. 4. Vagina: It is a birth canal through which uterus opens. 5. Cervix : Opening of uterus to the vagina 6. Placenta : It is a nourishing tissue around the foetus through which exchange of gases, food, and waste materials takes place between mother and foetus (embryo). 7. Implantation: Close attachment of embryo with walls of uterus. Period of human pregnancy is 9 months (gestation period).

Menstruation: At the time of ovulation, the uterus develops a thick tissue rich in blood capillaries to receive the embryo. Thus the lining becomes thick and spongy, which is required for the nourishment of the embryo. If the fertilisation doesn’t occur, the lining of the uterus slowly breaks and comes out through vagina as blood and mucus. This is known as menstruation and this cycle takes place every month and it lasts for 3 to 5 days. Reproductive health: STD: Diseases which are spread by sexual with an infected person is called sexually transmitted diseases. E.g. Syphilis, gonorrhea are bacterial diseases. AIDS and warts are viral diseases. AIDS= Acquired immuno Deficiency Syndrome. HIV= Human Immuno deficiency Virus.

Birth control: Family planning can be done using birth control measures that can be done by preventing pregnancy. Contraception: The prevention of pregnancy in women by preventing fertilisation is called contraception. Birth control methods can be divided in to 4 categories. Barrier methods: condoms in males, cervical caps for females Chemical methods: oral pills (hormonal) are used to prevent ovulation, since they change the hormonal balance, they can cause side effects. IUCD= Intra Uterine Contraceptive Devices. – Copper- T, and Loop

Surgical methods: 1.

Vasectomy: portion of vas deferens is cut and removed to block sperms.

2.

Tubectomy: a portion of fallopian tube is cut and removed to bock ovum. Surgical methods are safe in long run Surgery can also be done for removal of pregnancy (MTP – medical termination of pregnancy).

MTP is being used for illegal sex selective abortion of female fetuses.

Sex ratio: Number of females for 1000 males. Female child sex ratio is declining due to female feticide after using ultra sound ( pre natal sex determination ).