Draw the diagram showing the germination of pollen on stigma and label the following parts
(i) Stigma
(ii) Pollen tube
Hint: Pollination and fertilization are the two key stages of sexual reproduction in flowering plants. Pollen grains, either from a different plant or occasionally from the same plant, land on the flower’s stigma and begin to germinate, creating a pollen tube.
Complete answer:
Here is a diagram illustrating pollen germination on the stigma:
In this illustration, the elongated, tubular structure symbolizes the pollen tube. The stigma, located at the upper part of the pistil, is where pollen grains adhere after pollination.
Additional Information: The germination of a pollen grain starts when it lands on the stigma. In flowering plants, the stigma is connected to the ovary by a hollow structure known as the style. On the stigma, the pollen grain absorbs water and nutrients, triggering the growth of a slender pollen tube. This tube extends down through the style, reaching the ovary. The tube cell then expands and emerges from the pollen grain through a germ pore to form the pollen tube. The tube nucleus moves to the tip of the pollen tube, followed by the generative cell, which divides to create two male gametes. In the process of double fertilization, one male gamete joins with the egg cell, while the other fuses with the two supportive nuclei within the ovule. The fusion of the egg and one male gamete leads to embryo development, while the fusion of the second male gamete with the accessory nuclei begins endosperm formation. Eventually, the ovule develops into a seed.
Note: The transfer of a pollen grain to the stigma of the pistil is called pollination, and it occurs with the help of either biotic or abiotic agents. Biotic agents include animals like insects, birds, bats, as well as mammals and even humans. This step is crucial for fertilization to happen.