Growth by cell division occurs ___ in plants and ___ in animals

The correct option is "continuously, only up to a certain age".

Let us understand the process of growth and cell division in both plants and animals step-by-step:
1. Growth in Plants: Plants possess localized regions of active cell division called meristems (such as apical, lateral, and intercalary meristems). Due to the continuous activity of these meristems, plants exhibit indeterminate growth, meaning they continue to grow and divide their cells continuously throughout their life span.
2. Growth in Animals: Unlike plants, animals exhibit determinate growth. Cell division occurs only up to a certain age to reach a characteristic adult size. After reaching maturity, cell division in animals is primarily restricted to replacing lost, damaged, or dead cells rather than contributing to overall body growth.
3. Conclusion: Therefore, growth by cell division occurs continuously in plants and only up to a certain age in animals.