Key Steps in Seed Formation and Their Biological Roles
The seed is the part of a plant that grows from the ovules after fertilisation. They're contained within the fruit that grows from the fertilised ovary.
Sexual reproduction produces seeds, which contain a young embryo capable of growing into a new plant.
Structure of a Seed
Although the anatomy of seeds from different plants may differ in many ways, the underlying anatomy remains the same. The following are the components of a typical seed:
Tesla
This is the seed's outer coat that serves as a protective barrier for the developing plant inside.
Micropyle
It's a little pore in the testa that's located on the opposite side of the radical's tip. Before active germination, it allows water to enter the embryo.
Hilum
A hilum is a scar created by the stalk that connected the ovule to the ovary wall before it became a seed.
Cotyledon
This includes a lot of starch and serves as a food supply for the developing embryo before germination in some plants; in other plants, and endosperm serves in this role. There is just one cotyledon in monocotyledons, but there are two in dicotyledons.
The cotyledons may remain underground or be dragged above the earth, depending on the kind of germination (epigeous or hypogeous).
Radicle
The embryonic root will eventually develop into the plant's major root. During germination, it is usually the first component of the embryo to emerge from the seed.
Plumule
The embryonic shoot is known as a plumule. It appears as a bud that will give rise to the shoot and the rest of the plant's structures.
Endosperm
In many plants, a distinct component called the endosperm develops for starch storage. It can be found in both maize and wheat.
Function of Seed
The following functions are carried out by the seeds:
They aid in the germination of new plants.
Food reservoirs in the form of cotyledons and endosperm are found in the seeds.
The embryo inside is protected by the seed coat, which is protective.
Importance
The embryo plant is protected by seeds, which allows it to develop once it finds adequate soil.
Seeds are a protective structure that allows a plant embryo to live for a long time before germinating.
Until the embryo's growing conditions are favourable, the seed can remain dormant.
To address the needs of embryos in their early stages of development, food sources for plant embryos are pre-packaged in seeds.
Creatures, wind, birds, and other animals may quickly transport seeds, allowing the plant to populate a broad region. The wind can carry some of them anywhere.
Seeds can survive without water, thus the plant can survive if there is a drought.
Seeds are produced in vast quantities so that plants can reproduce.
FAQs on Seed Formation: Structure, Process & Importance
1. What is a seed and what are its main parts?
A seed is a mature, fertilised ovule that contains an embryonic plant enclosed within a protective outer covering. The three primary parts of a typical seed are:
Seed Coat: The tough, outer protective layer that guards the embryo against mechanical damage and drying out. It develops from the integuments of the ovule.
Embryo: The young, developing plant itself, which consists of a plumule (future shoot), a radicle (future root), and one or two cotyledons (seed leaves).
Endosperm: A nutritive tissue that provides stored food for the embryo during germination. In some seeds, the food is stored in the cotyledons instead.
2. How is a seed formed in flowering plants after double fertilisation?
Following double fertilisation in flowering plants, a series of developmental events leads to seed formation. The diploid zygote undergoes cell division (mitosis) to develop into the embryo. The triploid Primary Endosperm Nucleus (PEN) develops into the endosperm, which serves as a food source. Simultaneously, the integuments of the ovule harden and transform into the protective seed coat. The entire ovule, containing the embryo, endosperm, and seed coat, matures into a seed, while the ovary typically develops into the fruit that encloses it.
3. What is the importance of seed formation for a plant's survival?
Seed formation is critically important for the propagation and survival of plant species. Its key advantages include:
Protection: The hard seed coat protects the dormant embryo from harsh environmental conditions.
Dispersal: Seeds are adapted for dispersal by wind, water, or animals, allowing plants to colonise new areas and avoid competition.
Dormancy: Seeds can remain dormant until conditions are favourable for germination, ensuring a higher chance of seedling survival.
Nourishment: The stored food in the endosperm or cotyledons provides energy for the embryo during its initial growth.
Genetic Variation: As products of sexual reproduction, seeds introduce genetic variation, which is crucial for adaptation.
4. What are the different types of seeds based on the presence of endosperm?
Based on whether the endosperm is retained in the mature seed, seeds are classified into two main types:
Albuminous or Endospermic Seeds: In these seeds, the endosperm is not completely consumed by the embryo during its development and persists in the mature seed. It provides nourishment during germination. Examples include castor, maize, wheat, and barley.
Exalbuminous or Non-Endospermic Seeds: In these seeds, the endosperm is fully consumed by the developing embryo. The food reserves are then stored in the often large and fleshy cotyledons. Examples include pea, gram, bean, and groundnut.
5. What is the difference between a seed and a fruit?
The primary difference between a seed and a fruit lies in their origin and function. A seed develops from a fertilised ovule and contains the embryo that will grow into a new plant. In contrast, a fruit develops from the mature ovary of a flower and its main functions are to protect the seed(s) inside it and to facilitate their dispersal.
6. Why do some seeds remain dormant for long periods before germinating?
Seed dormancy is a survival mechanism that prevents seeds from germinating under unfavourable conditions. This state of suspended growth is crucial for ensuring the seedling emerges when its chances of survival are highest. The reasons for dormancy can be:
An impermeable seed coat that restricts water or oxygen intake.
The presence of chemical inhibitors like abscisic acid within the seed.
The embryo being physiologically immature and needing more time to develop.
Dormancy is broken only when specific environmental cues, such as sufficient water, correct temperature, light, and oxygen levels, are met.
7. What is the significance of double fertilisation in producing a viable seed?
Double fertilisation is a unique process in flowering plants that ensures the efficient formation of a viable seed. It involves two separate fusion events: syngamy (one male gamete fuses with the egg to form the diploid zygote) and triple fusion (the other male gamete fuses with the central cell to form the triploid endosperm). The significance is that the nutritive tissue, the endosperm, is formed only after fertilisation is confirmed. This prevents the plant from wasting valuable resources on nourishing an ovule that has not been successfully fertilised.
8. How does the structure of a seed perfectly align with its function?
A seed's structure is intricately linked to its functions of protection, nourishment, and propagation. The hard seed coat acts as a physical barrier against pests and environmental stress. The endosperm or cotyledons function as a packed lunch, storing essential proteins, starches, and oils to fuel the embryo's growth until it can photosynthesise. The embryo itself contains the rudimentary shoot (plumule) and root (radicle), poised to grow as soon as conditions are right. Finally, the tiny pore called the micropyle serves as a gateway for water absorption, which triggers the entire germination process.
9. Can a seed be formed without fertilisation? What is this process called?
Yes, in some plants, seeds can form without the fusion of gametes through a process known as apomixis. Apomixis is a form of asexual reproduction that mimics sexual reproduction, resulting in the development of a seed. Since there is no fertilisation, the embryo is genetically identical to the parent plant. This phenomenon is an important area of research in agriculture as it allows for the mass production of hybrid seeds with desirable traits without the need for repeated cross-pollination. Examples can be found in some species of grasses and citrus fruits.
