Lesson 24: Life Cycles
Life cycles connect development and reproduction across generations. Comparisons among organisms introduce different stages, sexual and asexual reproduction, and the fact that not every individual reproduces.
Key Ideas
- Reproduction is how living things produce new living things. Not every individual reproduces.
- Sexual reproduction joins reproductive cells, such as sperm and egg. In asexual reproduction, a living thing produces young without those cells joining.
- Parents and their young belong to different generations. Several generations can be alive at the same time.
- A life cycle connects growth, development, and reproduction. Different kinds of living things have different life cycles.
- Nonliving things can change or go through repeating patterns, but they do not reproduce as living things do.
Vocabulary
- Reproduction: The process of producing new living things.
- Fertilization: The joining of a sperm cell and an egg cell during sexual reproduction.
- Egg: A large reproductive cell that can join with a sperm cell during fertilization.
- Generation: One step in a family line, such as parents and then their young.
- Life Cycle: The stages of growth and reproduction that connect one generation to the next.
Discussion Questions
- Why do scientists use the word “reproduction” instead of just talking about having babies? How do sexual and asexual reproduction both produce new organisms?
- What makes something a life cycle? How is a life cycle different from simply getting older or changing?
- If a species stopped reproducing, what would eventually happen to that species? Why?
- How is the next generation connected to the generation before it? Can you think of examples where the offspring look or behave differently from their parents?
- Nonliving things can change and have cycles. What distinguishes those cycles from biological development and reproduction?