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Class 10th Science

Sexual Reproduction in Plants : Science Notes for Class 10 Biology

SEXUAL REPRODUCTION

  • In a population variations are useful for survival of a population.
  • Sexual mode of reproduction allows individuals to have more variations to be generated.
  • Generation of variations in DNA copying mechanism of asexual mode is fairly slow
  • Each new variation is made in a DNA copy that already has variations accumulated from previous generations.
  • Combining variations from two or more individuals would thus create new combinations of variants.
  • Each combination would be novel, since it would involve two different individuals.
  • For each new cell to not have twice the amount of DNA that previous generation have, special lineages of cells in specialised organs have only half the number of chromosomes and DNA as compared to other cells.
  • Two individuals combining during sexual reproduction, result in re-establishment of the number of chromosomes and DNA content in new generation.
  • Motile germ cell is called male gamete and germ-cell containing food is called female-gamete

Sexual reproduction in flowers

  • Flower can be termed as the sexual organ of a plant.
  • All the parts of a flower are arranged around an axis.
    1. Sepals: Green leaf like structure.
    2. Petals: Colourful structures, which add attraction to a flower. This attraction is not only having ornamental value, but a more important role in facilitating reproduction. Insects and birds, attracted by the colour, help transfer pollen grains or male gametes from male flower to female flower. This helps in pollination.
    3. Male Reproductive Organ of Plant: Androecium
  • The flower of a plant contains tube like structures called stamen.
  • At the top of stamen is a chambered structure called Androecium.
  • Androecium is responsible for the production of male gamete also called pollen grains.
    4. Female Reproductive Organ of Plant:
  • GynoeciumUsually at the centre of a flower you can notice Gynoecium.
  • Gynoecium is pitcher shaped structure with a long tube protruding out of it.
  • The gynoecium produces female gamete also called eggs.

Difference between Unisexual and Bisexual Plants

Unisexual Bisexual
  • A flower containing either stamen or carpel is unisexual e.g.watermelon
  • Flower containing both stamen and carpel are bisexual e.g hibiscus
  • Stamen is the male-reproductive part producing pollen which is yellowish in color.

 

  • Stamens and carpels are the reproductive parts of a flower.
  • Carpel is present in the centre of the flower and is the female reproductive part.
  • Carpel is made up of three parts , the swollen part is ovary , the middle elongated part is style and the terminal part is sticky and called stigma.
  • The ovary contains ovule which has an egg cell, the male gamete fuses with the female gamete present in ovule.

Pollination In flower

  • Pollination is the transfer of pollen from a male part of a plant to a female part of a plant, later enabling fertilisation and the production of seeds.
  • The pollen needs to be transferred from stamen to the stigma.
  • If the transfer of pollen occurs in the same flower it is self-pollination, if the transfers occurs in a different flower it is called cross-pollination
  •  Cross pollination can be facilitated by insects, birds, animals, air or water.
  • A tube growing out of the pollen grain and travels through the style to reach the ovary helps the landed pollen grain to reach female-germ cell.

Zygote Formation in Plant Reproduction

  • Once pollen grains enter the androecium, one of them enters the egg to fertilize it to form a zygote.
  • Seeds are the zygote or embryo of the plant.
  • To survive and to germinate,  seeds need source of food.
  • In all seeds there is abundance of food.
  • That is why for our daily need we depend on so many seeds like rice, wheat, groundnut for food.
  • During germination the food in the cotyledon is used to grow a new plant.
  • Once green leaves come out, they take care of further food production
  • After fertilization the zygote develops several times to form an embryo within the ovule.
  • The ovule develops a tough coat and is gradually converted into a seed
  • The seeds contain the embryo which develops into a seedling under proper conditions, this is known as germination

 

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Categories
Class 10th Science

How do Organism Reproduce:Class 10th Science Notes on Biology

Reproduction 

  • Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.
  • Reproduction at its basic level involves creation of the copy of DNA
  • DNA present in the chromosome of the cell is the information source for making proteins.
  • If the information is changed, different proteins will be made, and would lead to altered body designs.
  • The two DNA’s need to be separated, for the copy of DNA to have an organised cellular structure, DNA copying is accompanied by creation of additional cell apparatus.
  • Since no bio-chemical reaction is absolutely reliable, therefore the copying of DNA will have some variations each time.
  • DNA copies generated will be similar to each other and not identical.
  • Some of the variations may even be drastic enough for the new DNA generated not would not be able to work with the cellular apparatus and would eventually lead to death of the new cell.
  • The consistency of DNA copying during reproduction is important for maintenance of body design features that allow the organism to use a particular niche .
  • Reproduction is linked to stability of population of species.

IMPORTANCE OF VARIATION in Reproduction 

  • Population of organisms fill well-defined places or niches in the ecosystem, using their ability to reproduce.
  • Variation in DNA copying can ensure the survival of some individuals among a population, in case of changes in a particular niche in which the population is suited to survive in.
  • Variation is useful for survival of species over time.

ASEXUAL REPRODUCTION

  • Asexual reproduction:A sexual reproduction involves production of Offsprings by single parents.
  • There is no involvement of specialized gamete cell .
  • Offspring are genetically identical to their parents

Types of  Asexual Reproduction 

FISSION

  • In unicellular organisms, fission is the mode of reproduction used to create new individuals.
  • In simple unicellular organisms fission can take place in any plane, such as in amoeba.
  • In organisms showing somewhat more organisation of body, it occurs in a definite orientation in relation to the structure, for example leishmania having a whip-like structure present in one end.
  • Some single-celled organisms simply divide into many daughter cells simultaneously using multiple fission, for example plasmodium.
  • Yeast can put out small buds that separate and grow further

FRAGMENTATION

  • Multicellular organisms with simpler body design use fragmentation as a method of reproduction, for example in spirogyra, which breaks up into smaller pieces upon maturation.
  • These fragments grow into new individuals.
  • Not all multicellular organisms can use cell by cell division for reproduction as they are not simply a random collection of cells, and have organised body designs and structures,
  • In multicellular organisms reproduction via a single cell-type which is capable of growing, proliferating and making other cell types under right circumstances.

REGENERATION

  • Many fully differentiated organisms have the ability to give rise to new individuals from their body parts.
  • For example , if hydra or planaria is cut or broken into any number of pieces each piece grows into a complete organism this is known as regeneration
  • It is not the same as reproduction, since organisms would not depend on being cut up to be able to reproduce.

Budding

  • Organisms such as hydra use regenerative cells for reproduction in process of budding.
  • In hydra a bud develops as an outgrowth due to repeated cell division at one specific site
  • These buds develop into tiny individuals and detach themselves from parent body when fully mature.
Budding In Hydra
Budding In Hydra

Vegetative propagation

  • There are many plants in which parts like roots, stems and leaves can develop into new plants in appropriate conditions, this property is used in vegetative propagation method such as layering or grafting
  • Plants raised by vegetative propagation can bear fruits and flowers earlier than those reproduced by seeds.
  • Plants raised by vegetative propagation are genetically similar enough to the parent plant to have all its characteristics.

Spore formation

  • In rhizopus tiny blob-on-a-stick structures called sporangia containing spores that can develop into new rhizopus are involved in reproduction.
  • The spores have thick walls that protect them until they come into contact of another moist surface and being to grow.
Spore formation in rhizopus
Spore formation in rhizopus

Read the NCERT Solution On Reproduction here