Reproduction in Plants

1. THE MISSION

An environmental disaster has occurred and an acidic rain has killed all forms of flora on the planet you reside in. You are a researcher and you are well aware of modes of reproduction in various types of plants and hence you plan on making your planet green again. You with the help of three gatekeepers from your planet who are storing the limited seeds carefully but humans from another planet have come into your planet to destroy all the seeds so that the process of reproduction and growth will not happen in your planet and that all organisms in your planet will perish and the humans from other planet can occupy your planet. The gamer has to strategically prevent the destruction of the seeds with state of the art equipment which will immobilise the humans and trap them to take them for punishment. The second step to the game involves using both Asexual and Sexual mode of reproduction depending on the plant by segregation. The player has to prevent any form of error in segregation of plants and a detailed plan on how the particular plan will reproduce should be taught to the gatekeeper so that they can have a close watch. In the game, if the gatekeepers do not constantly observe and record the progress of the mode of reproduction for the plant and show the result of multiplication within 30 minutes to the ministers of your planet. If the gatekeepers don’t observe correctly and report you will be sent out of the planet and you will lose.

2. CONCEPTS

Reproduction allows living organisms to continue to live on the earth from one generation to the other.

1. Modes of reproduction in plants

Most plants have roots, stems and leaves. These are called the vegetative parts of a plant. After a certain period of growth, most plants bear flowers. You may have seen the mango trees flowering in spring. It is these flowers that give rise to juicy mango fruit we enjoy in summer. We eat the fruits and usually discard the seeds. Seeds germinate and form new plants.

So, what is the function of flowers in plants? The flowers perform the function of reproduction in plants. Flowers are the reproductive parts of a plant. A flower may have either the male part or the female part or both male and female parts. There are several ways by which plants produce their offspring. These are categorised into two types:

1. Asexual reproduction
2. Sexual reproduction

In asexual reproduction plants can give rise to new plants without seeds, whereas in sexual reproduction, new plants are obtained from seeds.

1. Asexual reproduction

In asexual reproduction new plants are obtained without production of seeds or spores.

Vegetative Propagation: It is a type of asexual reproduction in which new plants are produced from roots, stems, leaves and buds. Since reproduction is through the vegetative parts of the plant, it is known as vegetative propagation.

Fragmentation, budding, spore formation and vegetative propagation are some of the different type of asexual reproduction.

• Fragmentation: In this method the body of the parent organism breaks into ‘fragments’ and each fragment can grow to function as a new individual. For example; Algae like Oscillatoria and Spirogyra are reproduced by fragmentation.
• Budding: Some simple organisms reproduce by producing small outgrowths from their body. These outgrowths,called Buds. The buds gradually grow and get detached from the parent cell and form a new organism. For example, Yeast.
• Spore formation: Spores are tiny, spherical unicellular bodies protected by a thick wall to withstand unfavorable conditions When the conditions are favorable, these spores germinate into new individuals. Mosses, ferns, fungi, etc. reproduce by this method.
• Vegetative propagation from root: Some plants like sweet potato and dahlia have swollen roots without any shape. These roots are called tuberous roots. These roots have small buds which give rise to a new plant when they are planted into the soil.
• Vegetative propagation from leaves: Plants like Bryophyllum produce buds from the margin of the leaves. These buds drop off from the leaves and fix themselves to the ground and later grow into new plants.
• Vegetative propagation by artificial means:
  • Cutting: Plants such as rose, cactus and bougainvillea can be propagated through cutting from their stem. The cut stem is planted in moist soil, which eventually developed roots and shoots and grows into a new plant.
  • Grafting: Grafting involves two plants of the same species. A bud or a stem cutting from one plant called scion is inserted into a groove of a second plant called stock which is rooted to the ground. The stock and scion join together to form one plant. Varieties of fruit bearing trees developed by grafting.
  • Layering: In plants such as Jasmine and grapevine, the lower branch of the plant is bent down and covered with moist soil after removing a ring of bark from the stem. After a few weeks, new roots develop and the plant is separated from the mother plant

Advantages of vegetative propagation:

• Vegetative propagation is very useful for plant growers as they can get large quantities of new plants in a short time
• The newly reproduced plant has the exact characters as that of their parent plant
• Fruit without seed, disease and drought resistant plants can be produced using these methods
• It is easy to produce new varieties of plants with the required characteristics
• Vegetative plants grow faster than the plants grown from seeds and need less attention during early stages of growth.

1. Sexual reproduction

In sexual reproduction, in male cell (gamete) produced by the male part of the flower fuses with the female cell (gamete) produced by the female part of the flower. The fusion of the male and female gametes known as fertilization, leads to the formation of a single cell called the zygote. This cell divides and re-divides and slowly gives rise to a new individual. Flower is the reproductive part of flowering plants. A typical flower has four parts- sepals, petals, stamens and a carpel.

• Sepals: Sepals are green and they protect the other part of a flower before it blooms
• Petals: Petals are either colored or white and are seen as the flower blooms. They usually attract insects. The sepals and petals do not directly take part in reproduction
• Stamen: Stamen is the male part of the flower, that has a long filament with an elongated sac-like structure at its tip called the anther. Anthers produce pollen grains
• Pistil: The pistil or carpel is the female reproductive organ of the flower. The carpel has a stalk-like style with a sticky tape called the stigma and a swollen base, called the ovary. Ovaries contain one or more ovules. Ovules contain the egg cells, the female gamete of the plant.

Reproduction in plants happens through pollination:

The transfer of pollen grains from the anther to the stigma of the same kind of flower is called pollination. Pollination is of two types:

• Self-pollination: When the pollen grain of a flower pollinates the stigma of the same or stigma of another flower of the same plant, this process is called self-pollination
• Cross pollination: Pollinating agents is cross pollination. Birds insects, bats and wind carry pollen Grain from flower to flower. Flowers of these plants have special features that attract their pollinating agents. Different plants have different pollinating agents
  1. Fertilization

When a pollen grain falls on the stigma of a flower of the same kind, it develops a long tube called Pollen tube. The Pollen tube grows downwards through the style towards the ovary. The male gametes are inside the pollen tube. Once inside the ovary, it enters the ovule. The male gamete fuses with the female gamete and forms zygote. The process of fusion of the male and female gamete is known as fertilization. The fertilized cell is known as the zygote. The ovule develops into a seed and the ovary into the fruit after fertilization.

1. What are seeds?

A The fertilized egg begins to divide inside the ovule and develops into an embryo. The ovule develops into a seed. The embryo has a radical and plumule. It is attached to one or two cotyledons. Upon germination the radicle will develop into the root system, while the plumule will develop into the shoot system. The cotyledon has a store of food which is used by the seedling.

• Fertilization by Seed dispersal: Once the seeds dry, they get dispersed. Seed dispersal in the scattering of seeds over a large area by various means. The different means of seed dispersal are wind, water, animals and explosion of fruits. Different means of seed dispersal help the plants as it helps the seeds to reach a suitable medium for germination, far away from the parent plant.
• Fertilization by the wind: Some plants like drumsticks and maple have winged seeds, which are carried by the wind. The seeds of other plants, like milkweed silk cotton and Devil’s tree have tufts of hair which help them ride on the wind.
• Fertilization by water: Seeds that are dispersed by water have a spongy coat or a layer of fibre that make them light. This properly helps them to float on water. The flowing water then carries them too far off places for example coconut

Fertilization by animals: Birds, monkeys and other animals eat the fruit of many plants and throw away the seeds. Some plants have fruit or seeds with hooks, bristles, or spines. These get attached to the fur of animals or to our clothes. They are carried a long way before they fall off or are brushed off. By exploding fruits: The fruits of the rubber tree, balsam, lady finger, and night jasmine explode when they ripen. The sudden bursting of the fruit scatters the seeds away from the parent plant.