30. In ecosystems, the rhizobium bacteria are associated with _______ that fix ________.
A. Leguminous plants; nitrogen
B. Conifers; nitrogen
C. CAM plants; carbon at nights
D. Hydrophytes; carbon at daytime
A. Leguminous plants; nitrogen
To answer this question, we need to understand the association between rhizobium bacteria and the type of plants they are associated with, as well as what substance they fix.
To begin, rhizobium bacteria are known for their symbiotic relationship with certain types of plants. These bacteria form nodules on the roots of plants, leading to a mutually beneficial association.
Now, let's evaluate each option to determine the correct answer:
A. Leguminous plants; nitrogen
Leguminous plants, such as peas, beans, and clovers, are commonly associated with rhizobium bacteria. These bacteria have the ability to fix atmospheric nitrogen into a form that can be utilized by the plants. This allows leguminous plants to obtain nitrogen, an essential nutrient, from the air.
B. Conifers; nitrogen
Conifers, which include trees like pines, firs, and spruces, do not form a symbiotic relationship with rhizobium bacteria. Instead, they have specialized structures called resin canals and mycorrhizal associations to help them obtain nutrients. Therefore, option B is not correct.
C. CAM plants; carbon at nights
CAM (Crassulacean Acid Metabolism) plants, such as cacti and succulents, have a unique way of photosynthesis where they open their stomata at night to take in carbon dioxide. However, there is no direct association between rhizobium bacteria and CAM plants. Therefore, option C is also not correct.
D. Hydrophytes; carbon at daytime
Hydrophytes are plants that grow in aquatic or waterlogged environments. There is no specific association between rhizobium bacteria and hydrophytes. Moreover, the fixation of carbon dioxide during the daytime is common to most plants through the process of photosynthesis, unrelated to rhizobium bacteria. Thus, option D is not correct.
Based on the information provided, the correct answer is option A: Leguminous plants; nitrogen. Rhizobium bacteria are associated with leguminous plants and are responsible for fixing atmospheric nitrogen, enabling these plants to acquire an essential nutrient.