AY Honors/Marsupials/Answer Key
1. Distinguish:
a. Mammal from other animals.
The mammals are the class of vertebrate animals characterized by the presence of mammary glands, which in females produce milk for the nourishment of young.
b. Placentals, marsupials and monotremes from one another.
- Placentals
- The placentals are distinguished from other mammals in that the fetus is nourished during pregnancy via a placenta.
- Marsupials
- Marsupials are mammals in which the female typically has a pouch (called the marsupium) in which it rears its young through early infancy. They differ from placental mammals in their reproductive traits.
- Monotremes
- Monotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals.
2. Understand how marsupials are classified into families and describe, in a general way, the habits of these families.
3. Describe the distribution, habitat (ie. type of country they live in), diet breeding behavior, as well as any other interesting information of twelve different groups of marsupials and monotremes.
4. Be able to explain the difference between marsupial reproduction and that in true mammals (ie. placentals).
The pregnant female marsupial develops a kind of yolk sack in her womb which delivers nutrients to the embryo. The embryo is born at a very early stage of development (at about 4-5 weeks), upon which it crawls up its mother's belly and attaches itself to a nipple (which is located inside the pouch). It remains attached to the nipple for a number of weeks. The offspring later passes through a stage where it temporarily leaves the pouch, returning for warmth and nourishment.
The placenta is a temporary organ composed of two parts, one of which is part of the fetus, the other part of the mother. It is implanted in the wall of the uterus, where it receives nutrients and oxygen from the mother's blood and passes out waste. This interface forms a barrier, the placental barrier, which filters out some substances which could harm the fetus.
