1. Double fertilisation in plants is?
Double fertilisation is a distinguished process in angiosperms where two sperm cells fertilise two different cells in the ovule, which gives rise to a zygote and endosperm.
2. How does double fertilisation take place in angiosperms?
It takes place through the formation of a pollen tube that delivers two sperm cells into the ovule. The two sperm cells fertilise the egg cell and central cell, respectively.
3. Why is double fertilisation important in plants?
To ensure proper resource allocation, it must allow the endosperm to develop only after the egg is fertilised for it to become nourishment for the developing embryo.
4. What are the processes of double fertilisation?
They are pollination, pollen tube growth, and entry of sperm cells into the ovule, followed by the fusion of the sperm cells with the egg cell and central cell respectively.
5. What is the function of endosperm in double fertilisation?
Endosperm nourishes the developing embryo and provides nutrients for the growth of the seed to enhance its development.
6. What would happen if only one sperm cell reached the embryo sac?
If only one sperm cell reached the embryo sac, it would likely fertilize the egg cell, forming a zygote. However, without the second fertilization event, the endosperm would not form properly. This would result in a seed with an embryo but little or no nutritive tissue, significantly reducing its chances of successful development and germination.
7. How does the chemical composition of the endosperm differ from that of the embryo?
The endosperm typically has a higher concentration of storage compounds such as starches, proteins, and oils compared to the embryo. This is because the endosperm's primary function is to provide nutrition for the developing embryo and, in many species, for the germinating seedling.
8. What is the evolutionary advantage of having triploid endosperm?
The triploid nature of the endosperm provides an evolutionary advantage by allowing for increased gene expression and rapid growth. This results in a more efficient production of nutrients for the developing embryo, potentially leading to larger seeds and more successful offspring.
9. How does double fertilization differ from fertilization in gymnosperms?
Double fertilization is unique to angiosperms and involves two fusion events. In gymnosperms, only one fertilization event occurs, where a single sperm cell fuses with the egg cell. Gymnosperms also lack the formation of triploid endosperm.
10. How does the process of double fertilization ensure seed viability?
Double fertilization ensures seed viability by simultaneously initiating the development of both the embryo (future plant) and the endosperm (nutritive tissue). This coordinated development provides the embryo with a reliable food source, increasing the chances of successful seed germination and seedling establishment.
11. What is double fertilization in angiosperms?
Double fertilization is a unique reproductive process in flowering plants (angiosperms) where two separate fusion events occur. One sperm cell fuses with the egg cell to form the zygote, while the other sperm cell fuses with two polar nuclei to form the endosperm. This process ensures the development of both the embryo and its nutritive tissue.
12. How does the process of double fertilization in angiosperms compare to fertilization in animals?
While both involve the fusion of male and female gametes, double fertilization in angiosperms is unique because:
13. How does the concept of double fertilization challenge the idea of alternation of generations in plants?
Double fertilization challenges the traditional concept of alternation of generations because it involves the formation of a triploid tissue (endosperm) that doesn't fit neatly into either the gametophyte or sporophyte generation. This unique feature of angiosperms represents an evolutionary innovation in plant reproduction.
14. How does double fertilization contribute to the success of angiosperms as a group?
Double fertilization contributes to the success of angiosperms by:
15. What is the role of calcium ions in the process of double fertilization?
Calcium ions play several important roles in double fertilization:
16. What is the fate of each sperm cell during double fertilization?
During double fertilization, one sperm cell fuses with the egg cell to form the zygote, which will develop into the embryo. The other sperm cell fuses with the two polar nuclei in the central cell to form the triploid endosperm nucleus, which will develop into the nutritive tissue for the embryo.
17. How does the pollen tube deliver sperm cells to the ovule?
The pollen tube grows through the style of the pistil, guided by chemical signals from the female tissues. It enters the ovule through the micropyle and releases the two sperm cells into the embryo sac, where fertilization occurs.
18. What role does the pollen tube play in ensuring the success of double fertilization?
The pollen tube plays a crucial role in the success of double fertilization by:
19. How does pollination relate to double fertilization?
Pollination is a prerequisite for double fertilization. It involves the transfer of pollen grains (containing sperm cells) from the anther to the stigma of a flower. After pollination, the pollen grain germinates and forms a pollen tube, which delivers the sperm cells to the ovule where double fertilization occurs.
20. What is the significance of the micropyle in double fertilization?
The micropyle is a small opening in the ovule through which the pollen tube enters to reach the embryo sac. It plays a crucial role in guiding the pollen tube to the correct location for sperm cell delivery, ensuring that double fertilization can occur efficiently and accurately.
21. How many male gametes (sperm cells) are involved in double fertilization?
Two male gametes (sperm cells) are involved in double fertilization. These sperm cells are produced by the pollen grain and delivered to the ovule through the pollen tube.
22. What structures within the ovule are involved in double fertilization?
The key structures within the ovule involved in double fertilization are the embryo sac (female gametophyte), which contains the egg cell and two polar nuclei, and the micropyle, through which the pollen tube enters to deliver the sperm cells.
23. What is the difference between syngamy and triple fusion in double fertilization?
In double fertilization, syngamy refers to the fusion of one sperm cell with the egg cell to form the zygote. Triple fusion, on the other hand, involves the fusion of the other sperm cell with the two polar nuclei to form the primary endosperm nucleus. Both processes are essential components of double fertilization.
24. How does the timing of the two fusion events in double fertilization compare?
The two fusion events in double fertilization typically occur almost simultaneously. This synchronization ensures the coordinated development of both the embryo and its nutritive tissue, the endosperm.
25. What role do synergid cells play in the process of double fertilization?
Synergid cells play crucial roles in attracting and guiding the pollen tube to the embryo sac. They also assist in the release of sperm cells from the pollen tube and may help facilitate the movement of sperm cells to the egg and central cell for fertilization.
26. Why is double fertilization considered a defining characteristic of angiosperms?
Double fertilization is considered a defining characteristic of angiosperms because it is unique to this group of plants. It allows for the simultaneous development of both the embryo and the endosperm, which provides nutrition for the developing embryo. This efficient reproductive strategy has contributed to the evolutionary success of flowering plants.
27. How does the formation of triploid endosperm benefit the developing embryo?
The triploid endosperm serves as a nutritive tissue for the developing embryo. Its higher ploidy level allows for increased gene expression and rapid growth, providing a rich source of nutrients to support embryo development and early seedling growth.
28. What is the significance of the second fertilization event in angiosperms?
The second fertilization event, which forms the endosperm, is significant because it provides a dedicated nutritive tissue for the developing embryo. This allows for more efficient seed development and contributes to the reproductive success of angiosperms.
29. How does double fertilization contribute to genetic diversity in angiosperms?
Double fertilization contributes to genetic diversity by combining genetic material from both parents in two different ways: in the zygote (which becomes the embryo) and in the endosperm. This allows for various combinations of parental traits in both the offspring and its nutritive tissue.
30. What is the ploidy level of the zygote formed after fertilization?
The zygote formed after fertilization is diploid (2n). It results from the fusion of a haploid (n) sperm cell with a haploid (n) egg cell, restoring the diploid chromosome number characteristic of the species.
31. What is the ploidy level of the endosperm formed after double fertilization?
The endosperm formed after double fertilization is triploid (3n). It results from the fusion of one haploid (n) sperm cell with two haploid (n) polar nuclei, creating a tissue with three sets of chromosomes.
32. What happens to the other cells in the embryo sac during double fertilization?
During double fertilization, the egg cell and central cell (containing polar nuclei) are directly involved in fusion events. The other cells in the embryo sac, including the synergids and antipodal cells, typically degenerate or play supporting roles in the fertilization process.
33. How does the process of double fertilization differ in plants with different types of embryo sacs?
While the basic process of double fertilization is similar across angiosperms, there can be variations in plants with different types of embryo sacs. For example, in some plants with bisporic or tetrasporic embryo sacs, the number and arrangement of nuclei may differ, but the fundamental process of two separate fusion events still occurs.
34. How does double fertilization differ between monocots and dicots?
The basic process of double fertilization is the same in both monocots and dicots. However, there can be differences in the subsequent development of the endosperm. In many dicots, the endosperm is consumed by the developing embryo, while in monocots, it often persists as a major component of the mature seed.
35. What factors can prevent successful double fertilization?
Several factors can prevent successful double fertilization, including: pollen incompatibility, failure of pollen tube growth, inability of sperm cells to reach the embryo sac, defects in gamete formation, and environmental stresses such as extreme temperatures or drought.
36. What are some common misconceptions about double fertilization?
Common misconceptions about double fertilization include:
37. How does the structure of the pollen grain relate to its function in double fertilization?
The pollen grain's structure is adapted for its role in double fertilization:
38. How does double fertilization affect the development of fruit in angiosperms?
Double fertilization initiates seed development, which in turn stimulates fruit development. The hormones produced by the developing seeds, particularly the endosperm, trigger the ovary to develop into a fruit. This coordination ensures that fruits develop alongside viable seeds.
39. How does double fertilization contribute to seed coat formation?
While double fertilization doesn't directly form the seed coat, it initiates the process. The fertilization events trigger the development of the seed, including signals that stimulate the ovule integuments to develop into the seed coat. This coordination ensures that the seed coat develops alongside the embryo and endosperm.
40. What happens to the pollen tube after it delivers the sperm cells?
After delivering the sperm cells, the pollen tube typically degenerates. Its contents may be absorbed by the surrounding tissues of the ovule or embryo sac, potentially providing additional nutrients for the developing seed.
41. How does self-incompatibility in some plant species affect double fertilization?
Self-incompatibility is a mechanism that prevents self-fertilization in some plant species. It can affect double fertilization by preventing pollen tube growth or sperm cell release in genetically similar individuals. This ensures genetic diversity but can also prevent double fertilization if compatible mates are not available.
42. What is the fate of the central cell if double fertilization fails to occur?
If double fertilization fails to occur, the central cell typically degenerates along with the other structures in the embryo sac. In some cases, it may develop into a nutritive tissue without fertilization (autonomous endosperm), but this is relatively rare and usually does not support full seed development.
43. What is the significance of the fact that one pollen grain can fertilize only one ovule?
The fact that one pollen grain can fertilize only one ovule ensures a 1:1 ratio between pollen grains and potential seeds. This promotes genetic diversity by allowing multiple pollen donors to contribute to seed formation within a single flower or plant. It also makes pollination a more precise and efficient process.
44. What is the relationship between double fertilization and seed dormancy?
While double fertilization doesn't directly cause seed dormancy, it sets the stage for it. The fertilization events trigger seed development, including the formation of the seed coat and the accumulation of storage compounds in the endosperm. These structures and compounds can contribute to seed dormancy mechanisms, which are important for seed survival and timely germination.
45. How does the process of double fertilization differ in plants with different pollination mechanisms?
The process of double fertilization itself doesn't differ significantly based on pollination mechanisms. However, the way pollen is delivered to the stigma can affect the timing and efficiency of the process. For example, wind-pollinated plants may produce more pollen to ensure successful pollination, while plants pollinated by specific insects may have more precise pollen delivery mechanisms.
46. What role do plant hormones play in the process of double fertilization?
Plant hormones play several roles in double fertilization:
47. How does the nutritional status of the parent plant affect double fertilization?
The nutritional status of the parent plant can affect double fertilization in several ways:
48. What is the significance of the fact that the endosperm often has a different ploidy level than the embryo?
The different ploidy level of the endosperm (triploid) compared to the embryo (diploid) is significant because:
49. How does double fertilization relate to the concept of genetic imprinting?
Double fertilization is closely related to genetic imprinting, particularly in the endosperm. The triploid nature of the endosperm, with two maternal and one paternal genome copies, allows for complex patterns of gene expression based on the parent of origin. This imprinting plays crucial roles in seed development and can influence seed size and viability.
50. What are some of the evolutionary precursors to double fertilization in plants?
Evolutionary precursors to double fertilization may have included: