The number of species that are known and described range between ______________________. Fill in the blanks with the correct option from the following.

The correct answer is 1.7 to 1.8 million.

Step-by-Step Explanation:

1. Understanding Biodiversity: Biodiversity refers to the immense variety of life forms existing on Earth, encompassing all organisms ranging from microscopic bacteria and fungi to massive plants and animals.

2. Scientific Estimates and Records: According to established scientific studies and taxonomical records (such as those compiled in standard biological references like NCERT), the total number of species that have been formally discovered, studied, named, and described by science falls in the range of approximately 1.7 to 1.8 million.

3. Composition of the Described Species: Out of this documented total, the majority are animals (accounting for over 70%, with insects being the most species-rich group), followed by plants (including algae, fungi, bryophytes, pteridophytes, gymnosperms, and angiosperms) which make up about 22%.

4. Matching with the Options: Comparing the documented range of 1.7 to 1.8 million species with the provided choices:
- "1.4 to 1.5 million" (Incorrect)
- "1.6 to 1.7 million" (Incorrect)
- "1.7 to 1.8 million" (Correct)
- "1.9 to 2 million" (Incorrect)