Types of cells in 2 celled pollen grains are ________.
Vegetative and Generative
Understanding the 2-Celled Pollen Grain Structure
A pollen grain represents the male gametophyte in seed plants. It develops from a microspore through mitotic divisions. When a microspore divides, it typically forms two cells. This stage is known as the 2-celled stage of the pollen grain.
The two types of cells found in a 2-celled pollen grain are distinct in size, structure, and function:
- Vegetative cell: This is the larger of the two cells. It is also known as the tube cell. The vegetative cell has abundant cytoplasm and a large, irregularly shaped nucleus. Its primary function is to form the pollen tube, which grows through the pistil to reach the ovule.
- Generative cell: This is the smaller cell. It is often spindle-shaped and floats in the cytoplasm of the vegetative cell. The generative cell divides by mitosis to form two male gametes (sperm cells), usually before or during the growth of the pollen tube.
Analyzing the Options
Let's examine the given options in the context of the 2-celled pollen grain structure:
- Central cell and Synergids: These are components of the female gametophyte (embryo sac) found within the ovule, not the pollen grain.
- Antipodals and Megaspore: Antipodal cells are also part of the embryo sac. A megaspore is a cell that develops into the female gametophyte. Neither are components of a typical 2-celled pollen grain.
- Micropylar and Filliform: The micropyle is an opening in the ovule. The filiform apparatus is a structure within the synergids of the embryo sac. Neither are found in a pollen grain.
- Vegetative and Generative: As discussed, the 2-celled pollen grain is characterized by the presence of a large vegetative cell and a smaller generative cell.
Based on the typical structure of a 2-celled pollen grain, the types of cells present are indeed the vegetative cell and the generative cell.
| Feature | Vegetative Cell | Generative Cell |
|---|---|---|
| Size | Larger | Smaller |
| Shape of Nucleus | Large, irregular | Small, often spindle-shaped |
| Cytoplasm | Abundant | Sparse |
| Location | Forms the main body of the pollen grain | Floats within the vegetative cell's cytoplasm |
| Primary Function | Forms the pollen tube | Divides to form male gametes |
Conclusion on Pollen Grain Cells
The question asks about the types of cells in a 2-celled pollen grain. The development of a pollen grain from a microspore involves mitosis, resulting in two distinct cells: the vegetative cell and the generative cell. These are the characteristic components of the pollen grain at this stage.
Revision Table: Key Pollen Grain Concepts
| Term | Description |
|---|---|
| Pollen Grain | Male gametophyte of seed plants. |
| Microspore | Haploid cell that develops into a pollen grain. |
| Vegetative Cell | Larger cell in pollen grain; forms pollen tube. |
| Generative Cell | Smaller cell in pollen grain; divides to form male gametes. |
| Pollen Tube | Tube grown from the vegetative cell carrying male gametes to the ovule. |
| Male Gametes | Sperm cells formed from the generative cell; involved in fertilization. |
Additional Information on Pollen Grain Development
Pollen grain development, or microgametogenesis, starts with a microspore mother cell undergoing meiosis to produce four haploid microspores (forming a tetrad). Each microspore then develops into a pollen grain.
In the initial stage, the microspore undergoes an unequal mitotic division. This division produces two cells of unequal size:
- The larger cell is the vegetative cell (or tube cell).
- The smaller cell is the generative cell.
At the time of pollination, pollen grains are typically shed at either the 2-celled stage or the 3-celled stage. In the 3-celled stage, the generative cell has already divided to form two male gametes before shedding.
The question specifically asks about the 2-celled stage, where the generative cell is still a single cell floating within the vegetative cell.
Therefore, the two cell types in a 2-celled pollen grain are the vegetative cell and the generative cell.
Important Questions from Reproduction in Plants
Sporophyte stage is dominant in which plant group?
Flowers are a fascinating organ of Angiosperms. Flowers are considered the object of aesthetic, ornamental, social and cultural value. Biologically flower is a ________.
In case of flowering plants, after fertilisation, the zygote divides several times to form an embryo within the _______.
The Generative Cell of the pollen grain divides to form -
Pollen grains are generally spherical measuring about _________ in diameter.
