Introduction
Let's have a look at our daily food intake. From breakfast cereals and fruits to the chapatis and vegetables we eat in our diet comes from plants. Thus, plants are the primary source of food for human beings.
But have you ever wondered how these plants produce grains like wheat, rice or the delicious fruits and vegetables we eat?
The answer to this question is very simple, it is all a result of sexual reproduction in plants. Let us understand the mechanism of sexual reproduction in plants and it's fruitful result.
How Do Plants Reproduce Sexually?
Flower are the structural units that favour sexual reproduction in plants. A flower has the following parts-
Sepals- they are green coloured and are distinctively seen when the flower is in bud stage.
Petals- the beautiful coloured part of flowers.
Androecium - it is the male reproductive part and is composed of the anther (contains male gametes) and filament.
Gynoecium - it is the female reproductive part and comprises stigma, style and ovary (contains female gametes).
Some plants may have both male and female flowers on the same plant and are referred to as monoecious whereas some plants have male and female flowers on different plants and are referred to as dioecious.
Mechanism of Sexual Reproduction
Sexual reproduction involves the fusion of male and female gametes. For this event to occur firstly the male and female gametes must be brought to the vicinity, which is achieved by pollination.
Pollination: Pollination is the transfer of pollen grains (containing male gametes) from another to the stigma of flowers. This process is aided by various biotic (living organisms such as bees, wasps, ants, animals, and human beings) and abiotic factors (non-living factors such as wind, water).
Plants have evolved various mechanisms to favour pollination.
Anemophily - pollination by wind. The tassels of maize are evolved to capture pollen in wind. This type of pollination is common in cereal crops, grasses etc.
Hydrophily - pollination by water. Pollen grains are carried away by water currents and cause pollination in aquatic as well as many terrestrial plants.
Zoophily - pollination by animals and insects. The pollen gets adhered to the body of insects and animals and is transported from one place to another.
After pollination, the pollen grains on reaching the stigma of flowers germinate and give rise to pollen tubes that penetrate stigma and grow inside style to reach the ovary. This leads to the next step fertilization.
Fertilization - It involves the fusion of male and female gametes. The pollen tube on reaching the ovary releases 2 male gametes which then enter the ovary through micropyle opening and fuse with female gametes in the embryo sac. This results in the formation of zygote.
How Does Sexual Reproduction Benefit Humans?
The zygote formed as a result of fertilization develops into a seed and the ovary develops into fruit both of which are important products for human beings. Wheat, Rice, Maize etc. are all seeds developed from the zygote and the fruits and vegetables we eat are ripened ovaries. Thus we are fortunate that plants reproduce sexually.
FAQs on Are We Not Lucky that Plants Reproduce Sexually?
1. Why is sexual reproduction in plants considered beneficial for agriculture and biodiversity?
Sexual reproduction in plants is highly beneficial because it leads to genetic variation among offspring. This variation is crucial for several reasons:
- Adaptation: It allows plant populations to adapt to changing environmental conditions, such as new diseases or climate shifts.
- Hybrid Vigor: The combination of different genes can result in stronger, more resilient offspring (hybrid vigor), which is beneficial in agriculture for creating high-yield and disease-resistant crops.
- Evolution: It is the primary driver of evolution, creating new traits and contributing to the rich biodiversity we see in the plant kingdom.
2. What is the main difference between pollination and fertilisation in flowering plants?
While often confused, pollination and fertilisation are two distinct stages. Pollination is the physical process of transferring pollen grains from the anther (male part) to the stigma (female part) of a flower. In contrast, fertilisation is the biological process that occurs after successful pollination, where the male gametes from the pollen grain fuse with the female gametes inside the ovule to form a zygote.
3. What is double fertilisation and why is it a unique characteristic of angiosperms (flowering plants)?
Double fertilisation is a complex process unique to flowering plants. It involves two separate fusion events within the embryo sac:
- Syngamy: One male gamete fuses with the egg cell to form the zygote (2n), which develops into the embryo.
- Triple Fusion: The second male gamete fuses with the two polar nuclei in the central cell to form the Primary Endosperm Nucleus (PEN) (3n), which develops into the endosperm, a nutritive tissue for the embryo.
This dual process ensures that the food-storing tissue (endosperm) only develops when an embryo is successfully formed, making it a highly efficient reproductive strategy.
4. What are the key components of a mature embryo sac in a flowering plant?
A typical mature embryo sac, as per the CBSE/NCERT syllabus for 2025-26, is a 7-celled, 8-nucleate structure. It contains:
- The Egg Apparatus: Located at the micropylar end, it consists of one egg cell and two synergids which guide the pollen tube.
- The Central Cell: The largest cell, containing two polar nuclei that fuse with a male gamete.
- Antipodal Cells: Three cells located at the chalazal end, which generally degenerate after fertilisation.
5. How does pollen-pistil interaction prevent fertilisation by the wrong type of pollen?
Pollen-pistil interaction is a crucial compatibility check. The surface of the stigma has specialised proteins and chemicals that can recognise the pollen grain. If the pollen is of the correct species (compatible), the pistil accepts it and promotes pollen tube growth. If it is from a different species or from the same plant in cases of self-incompatibility, the pistil rejects the pollen, preventing its germination or inhibiting the growth of the pollen tube. This ensures successful reproduction with a suitable partner.
6. What would happen if double fertilisation did not occur in a flowering plant?
If double fertilisation failed, the entire process of seed development would halt. Without syngamy (the first fertilisation), the egg cell would not be fertilised, and no embryo would form. Similarly, without triple fusion (the second fertilisation), the Primary Endosperm Nucleus would not be created, meaning the nutritive endosperm tissue would not develop. Consequently, a viable seed containing both an embryo and its food supply could not be formed.
7. Do all plants reproduce sexually, or are there other methods?
Not all plants rely solely on sexual reproduction. Many plants are capable of asexual reproduction, also known as vegetative propagation. In this method, a new plant grows from a part of the parent plant, such as a stem, leaf, or root, without the fusion of gametes. For example, potatoes can grow from tubers and Bryophyllum can grow from leaf notches. This method produces genetically identical offspring, which is different from the genetic variation created by sexual reproduction.
8. What is the functional difference between the endosperm and the embryo within a seed?
The embryo and endosperm have distinct but complementary roles within a seed. The embryo is the miniature, dormant plant itself, containing the precursor structures for the future root (radicle), shoot (plumule), and seed leaves (cotyledons). The endosperm, on the other hand, is not part of the baby plant but serves as its dedicated food source. It provides the necessary nourishment for the embryo during germination until it can perform photosynthesis on its own.
