No, but there is kelp and seaweed.
The above answer is sort of correct. Mangrove trees will go to seed in rivers and sea coast lines. They live part of their lives completely underwater, but will grow out of the water quickly. I am not sure how long they can live completely underwater.
Plants absorb water and nutrients through their roots.
No, onions are not an example of plants with modified roots. Onions have a bulb which is a modified stem, not modified roots. Examples of plants with modified roots include carrot and radish.
No, not all plants possess roots. Some plants, like mosses and ferns, do not have true roots but instead have structures that serve a similar function.
The roots of plants predominantly grow downward, towards the soil.
All flowering plants have leaves, as well as most non-flowering plants (ferns, gymnosperms etc.).
Dugongs and manatees eat fleshy roots and leafs from underwater plants.
Roots don't have roots, plants have roots.
what would happen to plants nutrition if plants did not have roots
Water used in photosynthesis by plants is made available by roots. That is why roots of plants are important to photosynthesis in terrestrial plants. Aqatic plants absorb water from their free surface, hence role of roots in these plants is limited.
The plants that have fine roots : Kangkong etc.....
Not all plants have roots (eg phytoplankton) and while some plants do grow form their roots (eg grasses), most plants do not grow from their roots but from their apical growing tip.
Roots are an incredibly important element to a great many plants. These plants depend on the roots to suck up water.
They have cellular adaptations that make it possible for them to get the chemicals they need underwater. Besides trace nutrients that they obtain from soil around their roots, the main needs of a plant is water (H2O, which they are surrounded by) and carbon dioxide (CO2, which readily dissolves in water). The biggest issue for underwater plants is light, so the deeper and less clear the water, the more challenging it is for plant life to exist.
Plants roots
The roots.
There are many things a plants roots do for an ecosystem. Plants roots help prevent erosion of soil for example.
Plants absorb water and nutrients through their roots.