ACADEMIC YEAR 2020-21
NOTES
CH: 2 Reproduction in flowering plants
GRADE: 8 SUBJECT: BIOLOGY
Reproduction in flowering plants
• In flowering plants reproduction is performed by means of flower. The flower is usually the most
conspicuous part of a plant
First whorl – sepals are the outermost (outer covering) parts of the flower forming a whorl of
tiny green leaf- like structures. In the bud condition, they enclose the inner parts of the flower
• Green sepals collectively form a ring called calyx
Second whorl - petals form the second inner whorl arranged next to sepals
• Petals are usually white or large bright coloured and make the flower attractive
• Petals produce scent that attracts insects to pollinate their flowers
• Petals are collectively forming a ring called corolla. Corolla form a circle or a tube
Third whorl- (Male parts) the next third whorl, inner to the petals, consists of delicate, filament
like structure called stamens
• Each stamen is formed of a long narrow thread like filament and broad lobed sac like anther
(pollen producing organ) is found at its tip. These stamens collectively named androecium
Fourth whorl- (female parts) carpels are fourth innermost part of the flower (these may also be
called pistils)
• The carpel consists of a swollen ovary at the base containing one or more ovules, a narrow
slender tube called the style in the middle and a terminal expanded surface called stigma at the
top to receive the pollen
• Several fused carpels collectively called gynoecium
There are two types of flowers
• 1. Insect pollinated flower
• 2. Wind pollinated flowers
The pollen:
• The stamens of a flower are the male organs.
• The anthers of the stamens produce fine powdery material called pollen which consists of
particles called pollen grains. It is often yellow
• The male gametes (male sex cells) are inside the pollen grains which are made in the anther
• The mature pollen grain is a cell with double wall- the outer exine and the inner intine
• Its nucleus is already divided in to a tube nucleus and a generative (male) nucleus
The ovule:
• Female gametes (egg cell) are inside the ovule, in the ovary.
• Ovule is destined to become seed and the ovary to become fruit
• Each ovule has one or two protective coverings called integuments.
• These integuments leave a small opening the micropyle at one end (for entry of pollen tube)
Pollination:
• The transfer of pollen grains from the male part of the plant (anther of stamen) to the female
part of the plant (stigma)
• Most plants produce flowers that have both male and female reproductive parts (stamens and
carpels) is called the bisexual or hermaphrodite flower
Kinds of pollination:
Self-pollination:
• The transfer of pollen grains from the anther of a flower to the stigma of the same flower, or a
different flower on the same plant
Advantage: There is no wastage of pollen grains
Disadvantage:
• It does not yield new varieties.
• Continued self-pollination, generation after generation, may leads to weakening of the variety
of the plant species.
Cross pollination:
• The transfer of pollen grains from the anther of a flower to the stigma of a flower on a different
plant of the same species
• If the pollen lands on the stigma of a different species of plant, the pollen grain usually dies
Advantage: the offspring are healthier and new varieties may be produced
Disadvantage: during pollination there will be a lot of wastage of pollen
After the fertilization: Ovule becomes seed and Ovary becomes fruit
Seed dispersal:
• The process by which seeds are carried away from the parent plant is called dispersal of seeds
• It is very important that the seeds are thrown far away from the parent plant
• If they fall under the same plant all seedling will grow close together and will compete with one
another for food, water, space and sunlight
