Note 9 |standard 12|Sexual reproduction in flowering plants| agents of Pollination | notes| NCERT| Biology

 Sexual reproduction in flowering plants (New syllabus chapter 1 / old syllabus Chapter 2)

Agents of Pollination|reproduction in flowering plants|short notes| NCERT| standard 12| Biology

Note 9

Agents of pollination

2 types of agents are used by plants for pollination:

> 1) Biotic: 

--> animals and insects 

--> these agents are used by majority of plants

--> flowers need to attract animals and insects for pollination - hence, flowers are colorful, attractive and nectar-producing 

> 2) Abiotic:

--> wind and water

--> used by small portion of plants

--> here, flowers produce large numbers lf pollen grains compared to the number of ovules available - because pollen grain landing on stigma (by abiotic pollination) is a chance factor

--> flowers are not very colorful & do not produce nectar - because no need to attract animals or insects

>> Abiotic agents

> Wind pollination:

-> more common abiotic pollinating agent

-> pollen grains are be light and sticky - so that they can be transported in wind currents

-> Stamens are well exposed - so that pollen grains get easily dispersed into wind currents 

-> Stigma- large and feathery - so that pollen grains from wind current can be trapped easily

-> Flowers - 

----> single ovule in each ovary

----> numerous flowers packed into one inflorescence

-> example - 

-----> corn cob - its tassles are stigma and style - they wave in the wind to trap pollen grains

-----> Grass - wind pollination is common in here

Wind pollinated flower

> Water pollination

-> quiet rare in flowering plants

-> limited to approximately 30 genera - mostly monocotyledons

-> in lower plants, like Algae, Bryophytes and Pteridophytes, water is essential for the transport of male gamete. 

-> distribution of these lower plants is limited - because of requirement of water for male gamete transfer and fertilization. 

-> pollen grains of water-pollinated species - has mucilagenous covering  - that protect the pollen from wetting

-> Not all aquatic plants are water-pollinated. 

-> in majority of aquatic plants, like water hyacinth and water lily, flowers emerge above the water surface and pollination occur by insects or wind - in similar fashion to terrestrial plants

-> examples:

----> Hydrila

----> Vallisneria

---------> here, female flowers reach the surface of water by it's long stalk

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

---------> male flowers are released on the surface of water

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

---------> male flowers get carried away by water currents passively (without spending energy/in the direction of water flow)

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

---------> some of the male flowers would reach to female flowers and stigma

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

---------> pollination and fertilization occurs 

Vallisneria (water-pollination)

----> Sea grasses (Zostera)

---------> pollen grains of many such species are long, ribbon like and they are carried passively inside water 

--------> female flowers remain submerged inside water

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

--------> pollen grains are released inside water

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

---------> some pollen grains reach stigma and perform pollination

>> Biotic agents

> Range of animals as pollinating agent: bees, butterflies, flies, beetles, wasps, ants, moths, birds (sun birds & humming birds), bats

> Bees are dominant biotic pollinating agents

> Larger animals also seen as pollinators: primates (Lemurs), arboreal (tree-dwelling) rodents, reptiles (gecko lizards & garden lizards)

> Flowers of animal pollinated plants are specifically adopted for a particular species of animal

> Flowers - 

---> large, colorful, fragrant and rich in nectar

---> if flower size is small - flowers are clustered into inflorescence - so that they are easily detectable

> Animals attract to flowers by color and/or fragrance

> Flowers pollinated by flies & beetles - secret foul odors - to attract them

Insect pollinated flower

> To make animal visit keep visiting - flowers have to give rewards to them

> Usual floral rewards - nectars & pollen grains

---> Animals visitors come to flower to get rewards

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

---> animal come in contact with anther and stigma

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

---> animal body gets covered with pollen grains while fetching the rewards - because pollen grains of animal pollinated flowers are sticky in nature

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

---> animal with pollen grains on their body come in contact with stigma

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

---> pollination occurs

> Floral rewards can also be - providing safe space for laying eggs

---> example: eggs layed in flowers - tallest (6 feet heighted flower) Amorphophallus

---> example: Moth and Yucca

-------> Moth lays egg in the locule of ovary

-------> Yucca flower gets pollinated by moth

-------> As seeds start developing - moth larvae come out

-------> both cannot complete their life cycle without each other

> Pollen / nectar robber :

---> animals or insects that may consume pollen but do not bring about pollination - they're called as pollen / nectar robber

Thank you for reading!!

Happy learning!

Manish Mevada

Urvi Bhanushali