Explanation:
Pollination is the transfer of pollen grains from the anther (male reproductive part) to the stigma (female reproductive part) of a flower. This process is essential for the production of seeds and fruits in plants. While some plants can self-pollinate, others require the help of animal vectors such as insects, birds, bats, and even mammals, for successful pollination.

Cucumber and Animal Vectors:
Cucumber is a monoecious plant, which means it has separate male and female flowers on the same plant. However, cucumber plants have incomplete flowers, meaning that they lack certain reproductive structures. As a result, they require the assistance of animal vectors for successful pollination.

The flowers of cucumber plants are large and showy, with bright yellow petals and a distinct odor. These characteristics attract a variety of insects, including bees, flies, and butterflies, which act as pollinators. When these insects visit the cucumber flowers to feed on nectar or pollen, they inadvertently transfer pollen grains from the male flowers to the female flowers, thus facilitating pollination.

In addition to insects, some species of birds may also act as pollinators for cucumber plants. For example, the black-chinned hummingbird is known to visit cucumber flowers in search of nectar, and in doing so, may transfer pollen between flowers.

Other Plants and Animal Vectors:
While cucumber is an example of a plant that requires animal vectors for pollination, there are many other plants that also rely on this process. Some examples include:

- Mulberry: Mulberry trees produce small, inconspicuous flowers that are wind-pollinated. However, when grown for fruit production, they require the assistance of insects, particularly honeybees, for optimal pollination.

- Maize: Maize is a monoecious plant with separate male and female flowers on the same plant. While it is possible for maize to self-pollinate, cross-pollination by wind or animal vectors, such as bees or butterflies, is more efficient.

- Vallisneria: Vallisneria is an aquatic plant that is entirely reliant on underwater pollination. It produces separate male and female flowers that release their pollen and ovules into the water. Once the pollen grains reach a female flower, they must be carried to the stigma by water currents to achieve pollination.

In conclusion, animal vectors play a crucial role in pollination for many plants, including cucumber. Without these pollinators, many plants would struggle to produce seeds and fruits, which are essential for the survival of the species.