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Reproduction- P.

posted Jan 27, 2015, 10:05 PM by Ranmini Perera   [ updated Sep 2, 2017, 11:19 AM by Upali Salpadoru ]

Why do Plants have flowers?

They have tender petals, attractive colour and design, along with a pleasant smell. Some even store a drop of sweet nectar.  

All this effort is merely to attract the pollinators. Bees, butterflies and a few other creatures positively respond.

What do the plants get from Bees and Butterflies?

Fig.1 Dressing up for reproduction.

Reproduction or the proliferation and the continuation of a species is the primary concern of every organism. It is possible for most plants to multiply by vegetative propagation. There are a few short comings in this method. Cloned varieties are true to the original but these lack variety or differentiation. Genetic variation is an essential factor for natural selection.
Parts of a Flower
A flower normally has the following parts in the form of whorls attached to the peduncle.( flower stalk)
1.    Calyx     There are a few green sepals joined to form a cup shaped structure which houses the other parts of the flower during the bud stage.
2.    Corolla  -  Sepals -  Consist of several petals of pleasing shades, soft and tender
3.    Androecium - Stamens-  Several long filaments hoisting up the  anther lobes at the end.
4.    Gynoecium - Pistil – Formed formed from  carpels (modified leaves to form the ovary) in which the female gametes called the egg cells develop. The stigma, the sticky and the broader terminus is designed to receive the pollen grains. The part between the stigma and the ovary is called the stylus.

Fig.2 Parts of a normal dicot flower.


 Mathematics of Flowers

Dicot flowers know the 5 times table.

Monocot flowers know the 3 times table.

Dicots have 5 or 10 petals and the same number of stamens.

Monocots have 3 0r 6 petals and a similar number of stamens.

 Fig.3   A section of a dicot flower. 

Purpose of Flowerin

The purpose of flowering is to produce seeds, which will give rise to a progeny which would be slightly different from the mother plant. In higher plants (angiosperms) this  is achieved during the flowering stage.  Flowers produce sex cells called gametes. The antherlobes in the stamen produce pollen by reduction division. (meiosis)    The ovaries produce egg cells called ovules by the same kind of division.  These gametes will have half the number of chromosomes as that of the parent plant. During fertilization the chromosomes of these two  gametes fuse and produce a zygote. This becomes the seed.
Fig. 4    Life cycle of a flowering plant.

The sections with a touch of blue are included in the diploid stage, which is also called the sporophyte. Pollen grains and the ovules, marked in red consist of the Haploid stage, which is also called the gemetophyte stage. They are produced as a result of meiosis. 

Life cycle of a Non flowering Plant - Fern

Take a mature fern leaf and place it on your hand . Press hard. You will get an imprint with a kind of dust. These are the  spores from the under surface of the leaf.  They are  formed in the sporangia. When they get blown off and settle down in a moist field they grow into a heart shaped structure called a ‘thallus’.  When this matures it produces the gametes by meiosis. The male gametes which are called sperms swim to meet a parent thallus with a mature egg cell and fuses with it. Thus a zygote is produced. The new fern plant grows from this zygote.


  Fig 5  Life cycle of a Fern.

In the diagram the diploid stage is shown by blue while the haploid stage is in red.


Fig.5  Adapted for Pollination by a bee.

            1.0   Name the numbers.