1. An endangered species is a type of organism that is threatened by extinction. Species become endangered for two main reasons: loss of habitat and loss of genetic variation. A loss of habitat can happen naturally. Development can eliminate habitat and native species directly.

2. During sexual reproduction in animals, a haploid sperm and unites with a haploid egg cell to form a diploid zygote. After birth or hatching, the animal develops into a mature adult capable of reproduction. Some invertebrates reproduce by self-fertilization, in which an animal's sperm fertilizes its own eggs.

3. Internal fertilization is characterized by sperm fertilizing the egg within the female; the three methods include: oviparity (egg laid outside female body), ovoviparity (egg held within female), and viviparity (development within female followed by live birth).

4. Oviparous and viviparous are such two methods. The main difference between oviparous and viviparous animals is that oviparous animals do not undergo any embryonic development inside the mother whereas viviparous animals develop into a young animal inside the mother. This means oviparous animals lay eggs.

5. They perform a number of elaborate parental care behaviors. And they seem to step it up whenever females are around. This could explain why it's advantageous for males to take care of their eggs: doing so helps them get more chances to mate, and therefore many more offspring.

Answer:

1. An endangered species is a type of organism that is threatened by extinction. Species become endangered for two main reasons: loss of habitat and loss of genetic variation. A loss of habitat can happen naturally. ... Development can eliminate habitat and native species directly.

2. During sexual reproduction in animals, a haploid sperm and unites with a haploid egg cell to form a diploid zygote. ... After birth or hatching, the animal develops into a mature adult capable of reproduction. Some invertebrates reproduce by self-fertilization, in which an animal's sperm fertilizes its own eggs.

3.

4. Oviparous and viviparous are such two methods. The main difference between oviparous and viviparous animals is that oviparous animals do not undergo any embryonic development inside the mother whereas viviparous animals develop into a young animal inside the mother. This means oviparous animals lay eggs.

5.