When we compare life cycles, we can use observable characteristics to identify similarities and differences. Observable characteristics include the number of stages and the physical features of the animals — for example, whether the young looks like the adult.
The life cycles of the frog and the grasshopper are similar because both have three stages. However, the life cycles are different because the young of a frog (tadpole) does not look like the adult, but the young of a grasshopper (nymph) looks like the adult.
The life cycles of the frog and the mosquito are similar because the young of both animals do not look like the adults. However, the life cycles are different because the frog has three stages in its life cycle, while the mosquito has four stages.
💡 Life cycles can be compared using two angles: (1) number of stages, and (2) does the young look like the adult? 可以从两个角度比较生命周期：①阶段数量，②幼体是否与成体外形相似。
🔄 Life cycles repeat · 生命周期是循环的
Animals also go through a repeated pattern of change as they grow over time in their life cycles. The stages in a life cycle are repeated. There is no first or last stage — the cycle keeps going.