Reproduction and Modification in plants

We know already that flowering plants have root,stem and leaves.They are called vegetative organs.Flowers,fruits and seeds in a plant are called reproductive organs.In earlier classes we have seen that new plants can be grown from seeds.In this lesson,we are going to know how a flower changes itself into a fruit,and the modifications of root,stem and leaves of a plant.

Reproduction

We can see from this activity that watermelon plant is produced from that seeds.potato plant is not from seed,but from the steam Tuber (Vegetative part).seed is not only the source for new generation,even vegetative part of a plant can be used to produce a new plant.The process by which plants and animals produce young ones and increase their number is known as ‘reproduction’. Drumstick tree can be grown from both seeds and stem cuttings.When plants are reproduced from the seeds we call that process as sexual reproduction.All other ways of reproduction without seed are called as asexual reproduction.

Sexual reproduction

Seed is produced from a flower by the process of pollination and fertilization.This is known as sexual reproduction.To understand how seeds are formed in a flower, first we need to understand parts of a flower.

Parts of a flower

Let us compare few buds and opened flowers of Hibiscus and Datura.Observe bud and opened flower of Hibiscus and Datura.we can tabulate the characteristics of Hibiscus and Datura flowers as below.

In a bud ,we can see a green colour,leaf like structure which cover the whole bud or flower.Each of these green leaf like structure present as an outermost layer is called as sepal.This outer most ring of sepals is known as Calyx.Petals are the largest part of flowers.They are often attractive, brightly coloured, sometimes sweet scented and attract the insects.The ring of petals together is called corolla.

Inside corolla,in Hibiscus,we can observe a long tube on which many stamens are arranged.But,in Datura we can see only five stalked structures,stamens.This ring or whorl of a flower is called androecium.Each stamens consists of two parts-a stalk called filament and a lobe called anther.If you touch these lobes in a mature flower,we can get a powdery substance called pollen grains

Inside androecium whorl,we can find a female reproductive part of the flower, called gynoecium.You will find this part with a swollen bottom part.

This is a ovary.Seeds are produced in this part.On top of the ovary there is a slender tube like structure called style.The top most striky tip of the style is stigma.Pollen grains are received by the stigma.This is the fourth whorl of a flower.

Types of flowers

Flowers can be divided into two types.They are explained below.

Complete Flower

If all the four whorls-calyx,corolla,stamens and pistil are present,then it is called as complete flower.complete flowers are bisexual flowers.

Incomplete Flower

If any of these four whorls is missing,then it is called as incomplete flower.Incomplete flowers are unisexual flowers.There are two types of Unisexual flowers,male flowers and female flower.The flower with androecium and without gynoecium is called as male flower and the one with gynoecium and without androecium is known as female flowers.

Pollination

We know that flowers of pumpkin are unisexual-that is some flowers are male while many are female flowers.We can easily identify the male and female flower of pumpkin,even before the buds bloom.To understand how a flower develops into fruit,let us perform an experiment on pumpkin plant.The process by which pollen grains reach stigma is called as pollination.The flower that receives pollen grains is called pollinated flower while the one that did not receive pollen grains is called as unpollinated flower.In the above experiment we transferred the pollen grains from male flower to the female flower. This is called as an artificial pollination.However ,in nature there are many ways in which pollen grains reach the stigma of the flower and it is called as natural pollination.
In some plants like grasses, pollen grains are light.Staments shed pollen grains,and are carried by wind to other flower.Insects ,birds are also agents of pollination.Bees, butterflies and variety of birds hover around flowers. They help to carry pollen from one flower to another.Pollen grains stick to their legs,wings or abdomen when they move from one flower to another.This is called as cross pollination.when you shake,pollen grains fall.Thus,when wind shakes the flower or when a butterfly agitates the flower,pollen grains could fall into the sigma of the same flower.Some plants that have both the male and female parts within a single flower (bisexual) pollinate by this means.This is called as self pollination

Beans(Fabaceae) and tomatoes (Solanaceae) commonly self-pollinate.Even though,for example,tomato self pollinate,they need the help of the insects to create vibrations within the flowers that will effectively loosen the pollen.Paddy is mostly self pollinating using just gentle wind as the pollinating agent.The agents that are helping in pollination are called as pollinators.In many plants,pollens have to come from some other flowers.This is obvious in case of plants which have distinct male and female flowers like pumpkin.In some flowers the gynoecium matures first before the androecium shed pollens.Such as apples,plums, strawberries, pumpkins use insects for cross-pollination.

Fertilization

During pollination,pollen grains reach stigma.What happens to them after this? substance produced on the stigma causes the pollen grain to germinate.During the germination a tube develops from the pollen grain which carries male gametes and ultimately reaches female inside the ovary through the style.Male gamete fuses with the female gamete to form zygote .This process is known as fertilization.Where is this female gamete located? Inside the ovary,small rounded structures,ovules are present.In these ovules, female gamete is present.To know more about this,we should cut ovary of a flower in longitudinal and transverse ways.cut a ovary of a flower both vertically and horizontally.Observe the ovules.compare the ovary and ovules from few different flowers.Are there one or more ovules? Can you see any connection between the number of ovules in the ovary number of seeds in each fruit?

Collect some fruits like tomato,brinjal, lady’s finger(vegetable),mango,peas and custard apple and observe.You can see some green part above brinjal and lady’s finger.what are they?
Compare mango, custard apple and peas.All these are single fruits but custard apple has many small parts in it,each with a seed .Mango has a single seed and pea has many seeds.what do you understand from the above observations?
♦ A green part above fruit of brinjal and lady’s finger are sepals of a flower.In some plants,after fertilization,sepal will not fall from fruit and remain or persist with fruit.
♦️ Custard apple is made up of many fruits, aggregated together.Each fruit part is thin, membranous with some granule like, which is edible.
♦️ In mango the outer skin and middle pulpy are edible and sweet .The inner most part is with single seed.
♦️ In pea the fruit is not fleshy,but forms a convering pouch for many seeds.

In all the above fruits, Ovary,a lower most swollen part of pistil develops into a fleshy fruit.Ovules present inside the ovary gets transformed into a seed.

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