Parasite: Cuscuta

Explanation:

Parasitism is a type of symbiotic relationship in which one organism benefits at the expense of another organism, known as the host. The parasite depends on the host for its survival, often causing harm or damage to the host in the process.

Out of the given options, the correct answer is option B, Cuscuta, which is commonly known as dodder.

What is Cuscuta (Dodder)?

Cuscuta is a parasitic plant that belongs to the family Convolvulaceae. It is often referred to as dodder or love vine. These plants lack chlorophyll and are unable to produce their own food through photosynthesis. Instead, they rely entirely on other plants for nutrients and water.

How does Cuscuta Parasitize?

1. Attachment: Cuscuta has thin, twining stems that wrap around the stems, branches, or leaves of other plants. It establishes physical contact with the host plant.

2. Penetration: Once attached, Cuscuta produces specialized structures called haustoria that penetrate the host plant's tissues. These haustoria tap into the host's vascular system, allowing the parasite to extract water, nutrients, and carbohydrates from the host.

3. Damage to the Host: As Cuscuta extracts nutrients from the host, it weakens the host plant and may eventually cause its death. The parasite competes with the host for resources, depriving it of essential nutrients and water.

4. Reproduction: Cuscuta produces small, white or yellow flowers that are pollinated by insects. After pollination, it forms seeds that can be dispersed to new areas, allowing the parasite to spread and find new hosts.

Other Options:

- a) Lichen: Lichen is not a parasite. It is a mutualistic association between a fungus and an alga or cyanobacteria.

- c) Pitcher Plant: Pitcher plants are carnivorous plants that obtain nutrients by trapping and digesting insects. They are not parasites as they do not rely on other plants for their survival.

- d) Rhizobium: Rhizobium is a type of nitrogen-fixing bacteria that forms a mutualistic relationship with leguminous plants. It helps the plants obtain nitrogen by converting atmospheric nitrogen into a usable form. It is not a parasite.

In Conclusion:

Among the given options, Cuscuta (dodder) is the only parasite. It depends on other plants for its nutrients and water, attaching itself to the host plant and extracting resources through haustoria. It causes harm to the host plant by competing for resources and weakening it.