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GLE 6 – Compare the life cycles of a variety of organisms, including non-flowering and flowering plants, reptiles, birds, amphibians, and mammals. GLE 14 – Differentiate between sexual and asexual reproduction. How Do Animals Reproduce? Animals undergo either asexual or sexual reproduction to make more of their own kind or species. Asexual Reproduction Budding In this form of asexual reproduction, an offspring grows out of the body of the parent. Hydras exhibit this type of reproduction. Asexual Reproduction Regeneration In regeneration, if a piece of a parent is detached, it can grow and develop into a completely new individual. Echinoderms and worms exhibit this type of reproduction. Sexual Reproduction The sex cells of two parent organisms join together to produce a new organism that has DNA that differs from both parents. All vertebrate classes (fish, amphibians, reptiles, birds, and mammals) and most invertebrates reproduce sexually. Some worms, mollusks, and fish may produce both eggs and sperm. Individuals of these species will usually fertilize the eggs of another individual. Asexual vs. Sexual Asexual Reproduction Advantage - One parent can quickly produce many identical offspring. Disadvantage - The offspring have the same DNA as the parent and may not survive changes in the environment. Sexual Reproduction Advantage - The offspring may have characteristics that help them survive changes in the environment. Disadvantage - Parents must find a mate, and the development of offspring takes a longer time. Sponges Reproductive Cycle – Sponges have life cycles that alternate between asexual and sexual reproduction. They reproduce asexually through budding. A sponge produces both sperm cells and egg cells. A larva develops after a sponge egg is fertilized. Cnidarians Reproductive Cycle – Cnidarians alternate between two body forms: a polyp that looks like an upright vase and a medusa that looks like an open umbrella. Some polyps reproduce asexually by budding or by pulling apart. Adult medusas reproduce sexually by releasing sperm and eggs into the water. How Do External and Internal Fertilization Differ? External Fertilization The joining of an egg and a sperm outside the female’s body Occurs outside the body for many fish, amphibians, and aquatic invertebrates Takes place in water to prevent the eggs and sperm from drying out Female releases eggs into the water Male releases the sperm nearby Internal Fertilization The joining of an egg and a sperm inside of the female’s body Occurs in most invertebrates, many fish, amphibians, reptiles, birds, and mammals Many fish, amphibians, reptiles, and birds lay fertilized eggs outside the parent’s body and the offspring continue to develop inside the eggs In mammals, the fertilized egg develops inside the female. The length of time between fertilization and birth is the gestation period. Development and Growth Where Do Embryos Develop? The growing offspring, or embryo, may develop inside or outside of the parent’s body. Egg-Laying Animals Most animals without backbones (including worms and insects) lay eggs. Many fish, reptiles, and birds lay eggs too. A few mammals lay eggs too. Egglaying mammals are called monotremes. The duck-billed platypus and four species of anteaters lay eggs. The contents of the egg provide nutrients for the developing embryo. The eggs of land vertebrates are called amniotic eggs. Amniotic eggs have a shell which allows the offspring to grow and develop without drying out. Egg-Retaining Animals In some fish, amphibians, and reptiles, an embryo develops inside an egg that is kept inside the parent’s body. The embryo gets its nutrients from the yolk, just like in the egg-laying animals. The parent’s body provides extra protection for the eggs. The egg hatches either before or after being released from the parents body. Sharks, guppies, and garter snakes retain their eggs. Placental Mammals In most mammals, the embryo develops inside the mother’s body until its body systems can function on their own. The mother provides the embryo with everything it needs during development through an organ called the placenta. Blood carrying food and oxygen from the mother flow to the placenta and then to the embryo. Blood carrying wastes and carbon dioxide from the embryo flow to the placenta and then to the mother. The mother’s blood does not mix with the embryo’s blood. How Do Young Animals Develop? Young animals undergo changes in their bodies between birth and maturity, when they are able to reproduce. Crustaceans Three stages: egg, larvae, adult Most crustaceans begin their lives as tiny, swimming larvae. The larvae do not resemble the adult. Through metamorphosis, larvae change into adults. Insects – See handout. Complete Metamorphosis Incomplete Metamorphosis Four Stages: egg, larva, Three stages: egg, pupa, adult nymph, and adult Amphibians The term “amphibian” means double life - one life in the water and one life on land. Adult frogs reproduce sexually. Eggs are fertilized outside of the female’s body. A tadpole (larva) hatches from an egg, lives in water, and breathes with gills. Legs develop. Tail shortens and lungs develop. Tail is absorbed and development is complete. Adult frog breathes with lungs and can live on land. How Do Animals Care for Their Young? Most amphibians and reptiles do not provide parental care, while birds and mammals typically care for their offspring. No Parental Care Most fish, amphibians, and reptiles do not care for their offspring Reptiles will bury their eggs for protection. When their offspring hatch they will be in an area that provides shelter and food. Fish and amphibian eggs are not protected by a shell and they are not hidden from predators. The offspring must be able to care for themselves from the time birth. Most of the offspring is eaten by predators. Parental Care Birds Mammals Most bird species lay their eggs in a nest and keep the eggs warm until they hatch. Some hatchlings can move around and find food right after they hatch. Other hatchlings are helpless and must be fed by their parent. Parent birds feed and care for their young until they are able to take care of themselves. Young mammals are usually quite helpless for a long time after they are born. One or both parents may continue to care for their offspring until the young animals are independent.