CHAPTER 6 SECTION 3 ANIMAL REPRODUCTION AND FERTILIZATION

HOW DO ANIMALS REPRODUCE?? All animals undergo either asexual or sexual reproduction to make more of their own kind or species. Asexual Reproduction- 1. Fragmentation- where a new organism grows from a fragment of the parent (ex. Chop a worm in half and a whole new worm may form from the pieces) 2. Budding- where a new organism identical to parent grows out of the parent and breaks off.

SEXUAL REPRODUCTION Joining of 2 sex cells – male sperm cell and female egg cell Both carry DNA that determines physical characteristics such as size and color. During sexual reproduction, sex cells of two parent organisms join together to produce a new organism that has DNA that differs from its parents.

COMPARING ASEXUAL AND SEXUAL REPRODUCTION Asexual ReproductionSexual Reproduction Advantage Disadvantage One parent can quickly produce many identical offspring The offspring may have characteristics that help them survive changes in the environment The offspring have the same DNA as parents and may not survive changes in the environment Parents must find a mate and development of offspring takes a longer time

REPRODUCTIVE CYCLES Several water invertebrates (spineless organisms) such as sponges and cnidarians have life cycles that alternate between asexual and sexual reproduction. Sponges- reproduce asexually through budding and sexually (sponge can produce both sperm and egg cells) Cnidarians (ex. Jellyfish) alternate between 2 body forms (polyp and medusa). When in polyp stage, they reproduce asexually. When is medusa stage, they reproduce sexually.

QUESTIONS What are the 2 types of reproduction? A. sexual reproduction and asexual reproduction How do the offspring of asexual reproduction compare to the parent? A. They are identical because they have the same DNA What are 2 sex cells called? A. sperm and egg What is the joining of these 2 sex cells called? A. Fertilization

What do these cells contribute to the new organism? A. DNA How does the DNA of the offspring compare to that of the parents? A. It is a combination of DNA, so the offspring is not identical to either Why is sexual reproduction important for adaptation? A. produces new combinations which increases variation in the population Why do you think budding happens in simpler organisms? A. they have few body structures to duplicate, so a bud is not difficult to produce

How do sperm get from one sponge to another? A. They are released into water and swim In the cnidarian, which body form reproduces sexually? A. medusa Which body form reproduces asexually? A. polyp

HOW DO EXTERNAL AND INTERNAL FERTILIZATION DIFFER? External fertilization occurs outside the female’s body. Female releases eggs into the water and then the male releases sperm nearby. Internal fertilization occurs inside the female’s body. The male releases sperm directly into the female’s body where the eggs are located. Most invertebrates and many fish, amphibians, reptiles and birds lay eggs outside the parent’s body. Offspring continue to develop inside the eggs. For most mammals fertilized eggs develop inside the female animal. The female gives birth to live young. The length of time between fertilization and birth is called the gestation period.

QUESTIONS What is external fertilization? A. joining of an egg and sperm outside the body Why does external fertilization usually take place in water? A. keep eggs and sperm from drying out What are some organisms that have external fertilization? A. Fishes, amphibians, and aquatic invertebrates In which animals does internal fertilization take place? A. most invertebrates, many fishes, amphibians, reptiles, birds and mammals How is reproduction in mammals different from reproduction by most other groups of animals? A. in mammals, fertilized egg develops inside the body of the female