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Basic event in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA
DNA copying is accompanied by the creation of an additional cellular apparatus
A cell divides to give rise to 2 cells – these are similar and not identical (it will have some variation at all times)
Multi-cellular organisms with simple structure
Spirogyra, simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals
Specialised cells are organised as tissues, and tissues are organised into organs, which then have to be placed at definite positions in the body. In such a carefully organised situation, cell-by-cell division would be impractical.
Hydra, Starfish and Planaria can be cut into any number of pieces and each piece grows into a complete organism. Regeneration is carried out by specialised cells. These cells proliferate and make large numbers of cells
Hydra, In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.
Pollination, fertilization, embryo & Seedling
Length of pollen tube depends on pollen grain on upper surface of stigma and ovule
Zygote is the first cell of the next generation. It divides to form embryo
Parts of a flower – sepals, petals, stamens and pistil
Stamens and pistil are the reproductive parts of a flower which contain the germ-cells
unisexual (papaya, watermelon) when it contains either stamens or pistil or bisexual (Hibiscus, mustard) when it contains both stamens and pistil. Stamen is the male reproductive part and it produces pollen grains that are yellowish in colour
Pistil is present in the centre of a flower and is the female reproductive part. It is made of three parts – ovary (ovules with egg cells), style and stigma
The male germ-cell produced by pollen grain fuses with the female gamete present in the ovule. This fusion of the germ-cells or fertilisation gives us the zygote which is capable of growing into a new plant. Thus the pollen needs to be transferred from the stamen to the stigma. If this transfer of pollen occurs in the same flower, it is referred to as self-pollination. On the other hand, if the pollen is transferred from one flower to another, it is known as crosspollination.
After fertilisation, the zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is gradually converted into a seed. The ovary grows rapidly and ripens to form a fruit.
The seed contains the future plant or embryo which develops into a seedling under appropriate conditions. This process is known as germination
Radicle future root & plumule is future shoot
The formation of germ-cells or sperms takes place in the testes. These are located outside the abdominal cavity in scrotum because sperm formation requires a lower temperature than the normal body temperature
Testes secrete testosterone – changes in puberty and appearance
The sperms formed are delivered through the vas deferens which unites with a tube coming from the urinary bladder. The urethra thus forms a common passage for both the sperms and urine.
The female germ-cells or eggs are made in the ovaries.
Ovary (production of egg)
Oviduct (site of fertilisation)
Uterus (site of implantation)
Vagina (entry of the sperms
0:00 NCERT Class 10 Science Chapter 8: Organisms’ Reproduction
0:44 Why Do Organisms Reproduce
2:04 DNA Copies
6:41 Asexual Reproduction
6:52 Unicellular Organisms
11:41 Multicellular Organisms
16:15 Vegetative Reproduction
17:25 Tissue Culture
19:17 Sexual Reproduction
27:14 Flowering Plants and Human Beings
32:16 Reproductive Health
#science #organismsreproduction #whydooraganismsreproduce #dnacopies #variations #asexualreproduction #unicellularorganisms #cloning #fission #multicellularorganisms #vegetativereproduction #tissueculture #sexualreproduction #floweringplantsandhumanbeings #reproductivehealth #examrace
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