NCERT Class 7 Science Chapter 12: Reproduction in Plants YouTube Lecture Ha ndouts

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NCERT Class 7 Science Chapter 12: Reproduction in Plants

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BRAIN TEASERS

  • How does the cottony growth on bread develop?

  • Ovules develop into ___

  • How are castor seeds dispersed?

  • What are the types of asexual reproduction in plants with examples?

LET’S BEGIN!!

Reproduction: Production of new individuals from their parents

  • Asexual Reproduction – new plants without seeds

  • Sexual reproduction – new plants from seeds

Types of Asexual Reproduction

Vegetative Propagation

  • By root, leaves, stem and buds

  • By Branch – rose or champa “bud in axil”

  • Axil – point of attachment of leaf at node of leaves that develop into shoot – called vegetative buds

  • Bud – short stem with immature overlapping of buds

  • Potato – eye (scars) – also in turmeric and ginger

  • Bryophyllum (sprout leaf plant) – buds in margins of leaves; in moist soil each bud can give rise to new plant

  • Roots can give rise to plants – sweet potato and dahlia

  • Detached plant grows into new plant – Cactus

  • Benefits – takes less time to grow; are exact copies; bear fruit and flowers earlier than seeds

  • Vegetative Reproduction – sugarcane, potato, rose

Budding

  • Asexual reproduction, with single parent new plants are produced without seeds

  • Yeast – single celled organism

  • Develops by small bulb like projection – budding

  • Bud later detaches from the main cell and matures – chain of bud

Fragmentation

  • Algae – in presence of water and nutrients grow

  • Break

  • Continues over larger area in shorter period of time

    Spore Formation

    • Cottony growth on bread is molds (fungus) and develop from spores

    • Spore float in air – are light and cover long distances

    • Covered with hard protective coat to withstand unfavorable conditions – high temperature and low humidity

    • Can survive for long time

    • When conditions are favorable – germinate and develop into new plant

    • Same goes for mosses and ferns

Sexual Reproduction

  • Male – stamens

  • Pollen grains are found in anther

  • Female – pistils (stigma, style and ovary)

  • Female gamete or egg is formed in ovule

  • Ovary contains one or more ovules

  • Fusion of gametes is fertilization

  • Zygote (fusion of male and female gamete) grows into embryo which is enclosed in seeds

  • Ovules develop into seeds (contains embryo in protective seed coat)

  • Ovary develops into fruits (fleshy like mango or orange or hard like almond or walnut)

  • Female reproductive part where pollen grains germinate – stigma

  • Unisexual flower – have either stamen or pistil (corn, papaya, cucumber)

  • Bisexual flower – have both stamen and pistil (mustard, rose, petunia)

Pollination

  • Self-pollination (within plant)

  • Cross pollination (across plant)

Seed Dispersal

  • Seed dispersal helps the plants to

  • Prevent overcrowding

  • Avoid competition for sunlight, water and minerals

  • Invade new habitats

  • Dispersal by air - Winged seeds – drumstick, maple, light seeds of grass, hairy seeds of aak (madar), hairy fruit of sunflower

  • Dispersal by Water - Coconut fruit has spongy fibers, which helps it to float in water.

  • Dispersal by animals – spiny seeds with hooks attach to animals – Xanthium, Urena

  • Dispersal when fruit burst with jerk – castor, balsam – seeds are scattered far from the parents

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