Podcast
Questions and Answers
What is the initial cell type that undergoes meiosis to form microspores in the anther?
During the development of the embryo sac, how many times does the surviving megaspore nucleus undergo mitosis without cytokinesis?
What is the primary function of the tube cell in the pollen grain?
What structures do the two polar nuclei in the embryo sac eventually combine with a sperm cell to form?
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Which of the following correctly describes the two main fertilization processes that occur after pollination?
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Which structure in the ovule is responsible for becoming the seed coat after fertilization?
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How many functional microspores are formed from one microsporocyte during meiosis?
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What is the role of the synergid cells in the embryo sac?
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Study Notes
Pollen Grain Development
- Anther contains four microsporangia, each hosting numerous diploid microsporocytes
- Each microsporocyte undergoes meiosis, resulting in four haploid microspores, collectively known as a tetrad
- Each microspore undergoes mitosis, forming an immature pollen grain (male gametophyte) with one generative cell and one tube cell
- During pollination, the pollen grain arrives on the stigma
- The generative cell divides mitotically, producing two sperm cells (male gametes)
- The tube cell extends a pollen tube to deliver the sperm cells to the egg
Ovule Development
- Ovule contains a single megasporangium, housing a large diploid megasporocyte
- The megasporocyte undergoes meiosis, generating four haploid megaspores
- Usually, three megaspores degenerate, leaving one surviving megaspore
- This surviving megaspore undergoes three mitotic divisions without cytokinesis, forming the embryo sac (female gametophyte)
- The embryo sac contains eight haploid nuclei arranged with four at each end
- Two nuclei migrate to the center, forming polar nuclei
- Three nuclei at the chalaza end become antipodal cells, whose function is not fully understood
- At the micropyle end, one nucleus becomes the egg cell, and two others become synergid cells, vital for attracting and guiding the pollen tube
Double Fertilization
- After pollination, the pollen grain germinates on the stigma, absorbing moisture and extending a pollen tube through the style to the ovary
- The pollen tube grows towards the micropyle, guided by synergid cells
- The tube nucleus degenerates
- The pollen tube releases two sperm cells into the embryo sac
- The first fertilization occurs when one sperm cell fuses with the egg cell, forming a diploid zygote
- The second fertilization takes place when the other sperm cell combines with the two polar nuclei, resulting in a triploid endosperm
- The zygote develops into the embryo
- The endosperm functions as the food storage tissue for the growing embryo
- The ovule, including the embryo sac, develops into a seed
- The integuments transform into the testa (seed coat)
- The ovary matures into a fruit, providing protection for the seed
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Description
Explore the intricate processes of pollen grain and ovule development in flowering plants. This quiz covers key concepts such as microsporangia, meiosis, and gametophyte formation. Test your knowledge on how these reproductive structures contribute to plant fertilization.
