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In this article, we will discuss sexual reproduction in plants. We will also discuss the functions of sepals, petals, anthers, stigmas, and ovaries along with pollination and fertilization. But before discussing sexual reproduction in plants, first, let us recall the reproduction and its types in plants.
Types of Reproduction in Plants
Plants reproduce either asexually or sexually.
Sexual Reproduction
- Sexual reproduction in plants occurs when a pollen grain from the male part of the flower undergoes fusion with the ovule from the female part of the flower.
- Plants depend on the wind or insects to move their pollen to different parts. Two parents are needed
- In sexual reproduction, two parents are required and the offspring produced is genetically different from its parents.
Some advantages of sexual reproduction are:
- It brings variations into a population
- The species have the capacity to adapt to new environments
- There is a low probability of a disease affecting all individuals in a population.
Some disadvantages of sexual reproduction are given below:
- It is impossible for an isolated individual
- Time and energy are required to fetch a mate
Asexual Reproduction
- Few plants have the capacity to reproduce asexually by growing runners.
- Unlike sexual reproduction, a single parent is needed in asexual reproduction.
- The offspring produced by asexual reproduction are genetically identical to their parents. For instance, the production of spores by fungi, formation of tubers in potatoes, bulbs in daffodils, and reproduction in bacteria are examples of asexual reproduction.
- Gardeners can produce several genetically identical plants with desirable features by cloning plants.
Some advantages of asexual reproduction are:
- There is a quick increase in the population
- Can exploit the desired habitat rapidly
Some disadvantages of asexual reproduction are:
- Unlike sexual reproduction, asexual reproduction produces identical offspring which means there is no variation in a population
- The species may be suitable for a single habitat only
- There is a greater probability of diseases affecting all individuals in a population because of no genetic variation.
So far we have discussed the differences between sexual and asexual reproduction, their benefits, and bottlenecks in detail. In the next section of the article, we will only focus on sexual reproduction in plants.
Sexual Reproduction in Plants
For sexual reproduction in plants, a male gamete, i.e. the pollen from one flower should come in contact with the female gamete, i.e. the ovule of another flower. Plants cannot move from one place to another like humans, animals, and insects. Hence, they depend on the insects and wind for sexual reproduction.
Flowers
Flowers play a critical role in the sexual reproduction of plants by producing male sex cells known as pollen grains and female sex cells that are contained in ovules. For sexual reproduction to occur, both these cells must meet. This process is referred to as pollination.
A flower has many parts and each part plays its role in sexual reproduction. Different parts of the flower and their respective functions are listed below.
- Sepal: The primary function of the sepal is to protect the unopened, i.e. developing flower.
- Petals: Petals have bright colours to attract insects.
- Stamen: It refers to the male part of the flower. It consists of an anther that is attached to the filament.
- Anther: Anther is a part of the flower that produces male sex cells known as pollen.
- Stigma: It refers to the top of the female part of the flower that plays a role in the collection of pollen grains.
- Ovary: It is the part of the flower that produces female sex cells that are contained in ovules.
- Carpel: The female parts of the flower are collectively known as carpel.
There are two types of flowers:
- Insect pollinated flowers
- Wind pollinated flowers
Insect-pollinated Flowers
- Insect-pollinated flowers have bright-coloured petals and sweet-smelling nectar so that insects can be attracted to the reproductive parts of the plants.
- As the insects sit on the flower to collect its nectar, the pollen grains attach to the insects from the anther of the flower.
- When insects travel to another flower, these pollen grains are transferred to the stigma that contains a sticky surface for catching pollen grains.
Wind-pollinated Flowers
- The wind-pollinated flower relies on wind for pollination, therefore, they do not tend to look as pleasant and attractive as insect-pollinated flowers.
- Examples of insect-pollinated flowers include wheat and grasses.
- In these flowers, each anther is connected to the long stamen which swings about in the wind.
- The pollen grains of these flowers are tiny and light. Hence, a gust of wind can easily move these pollens away so that they can land on the stigma of another flower
- The long and feathery features of the stigmas give them a large surface area so that they can catch pollens easily.
Fertilization
The process of fertilization is explained below in detail.
- As the pollen grain reaches the stigma of the flower, the pollen tube grows down the length of the style.
When a pollen grain lands on a stigma, a pollen tube grows down the length of the style with the assistance of digestive enzymes.
As a result, a tunnel is created through the style which enables pollen to pass through so that it can reach the ovary.
At a tiny opening known as micropyle, the pollen tube penetrates the ovule (egg) so that nucleus of the pollen can fuse with the nucleus of the ovule during fertilization.
The following things happen after fertilization:
- The ovules transform into the seeds
- The ovary transforms into the fruit
To provide energy to the seedling, the seeds have a large store of food. This is because seedling is still in the development stage and cannot photosynthesize to produce their food.
Germination
Germination refers to the process that is controlled by the enzymes and in which the seed starts to develop into a new plant. The factors needed for successful germination include water, warmth, and oxygen.
There are three parts of the seed:
- Embryo: The young root and shoot that will develop into an adult plant
- Food store: starch for use of the young plant until it can make its food
- Seed coat: a protective outer covering of the seed.
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