Sexual Reproduction in Flowering Plants - Development of Seed and Formation of Fruit
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Post-fertilization changes: The ovule matures into the seed, and the ovary develops into the fruit. These processes occur simultaneously, triggered by the formation of the zygote () and Primary Endosperm Nucleus ().
Seed Structure: Consists of seed coat(s), cotyledon(s), and an embryo axis. The seed coat is formed from integuments; the outer is the testa and the inner is the tegmen. The micropyle remains as a small pore for the entry of and during germination.
Albuminous vs. Non-albuminous Seeds: Non-albuminous (exalbuminous) seeds have no residual endosperm as it is consumed during embryo development (e.g., Pea, Groundnut). Albuminous seeds retain a part of the endosperm (e.g., Wheat, Maize, Castor).
Perisperm: In some seeds like black pepper and beet, remnants of the nucellus are also persistent. This residual, persistent nucellus is called the perisperm ().
Seed Dormancy: As the seed matures, its water content is reduced to moisture by mass. The metabolic activity of the embryo slows down, entering a state of inactivity called dormancy.
Fruit Development: The wall of the ovary develops into the wall of the fruit called the pericarp. In 'True Fruits', the fruit develops only from the ovary. In 'False Fruits' (e.g., Apple, Strawberry, Cashew), the thalamus also contributes to fruit formation.
Parthenocarpy: Fruits developed without fertilization are called parthenocarpic fruits (e.g., Banana). These are naturally seedless or can be induced through the application of growth hormones.
Advantages of Seeds: They provide better dispersal mechanisms, contain food reserves for the young seedling, and produce new genetic combinations due to sexual reproduction.
📐Formulae
💡Examples
Problem 1:
A plant has a diploid number of chromosomes as . Calculate the number of chromosomes in its endosperm, perisperm, and the cells of the apple fruit flesh.
Solution:
Endosperm = , Perisperm = , Apple flesh = .
Explanation:
- Endosperm is : If , then . Therefore, . 2. Perisperm is persistent nucellus (): chromosomes. 3. Apple flesh is developed from the thalamus (sporophytic tissue, ): chromosomes.
Problem 2:
Explain why apple and cashew are called 'False Fruits'. Which part of the flower forms the edible part in these cases?
Solution:
They are called false fruits because they develop from floral parts other than the ovary, specifically the thalamus.
Explanation:
In most plants, the fruit develops only from the ovary. In apple, pear, and strawberry, the thalamus () grows and forms the fleshy, edible part of the fruit, surrounding the actual fruit (core). In cashew, the edible 'nut' is the true fruit, while the fleshy 'apple' is the modified pedicel/thalamus.