Internal Fertilization:
1. Location: Occurs within the female’s reproductive tract.
2. Process: Sperm fertilizes the egg inside the female’s body.
3. Common in: Mammals, reptiles, birds, and certain fish.
4. Advantages: Provides protection and a controlled environment for embryo development.
5. Parental Care: Often involves parental care for offspring after birth/hatching.

External Fertilization:
1. Location: Occurs outside the bodies of both sexes, often in water.
2. Process: Eggs and sperm meet in the external environment.
3. Common in: Aquatic organisms like fish, amphibians, and many invertebrates.
4. Challenges: Exposes gametes to environmental risks like predation and unfavorable conditions.
5. Parental Care: Generally limited or absent; offspring survival relies on external factors.

These distinctions highlight how different reproductive strategies suit the needs and environments of various organisms, whether terrestrial or aquatic.