7th Grade - 1/9/12 Discussion Points

Good discussion yesterday about what makes an animal. To recap there are 5 main characteristics that allow us to call a species an animal.

1. It must be able to move (at some point of its life)

2. It must be able to obtain food, water, and oxygen

3. It must be able to reproduce

4. It must be able to maintain a stable environment within its body - homeostasis

5. It cells lack a cell wall

The second thing we covered in class was the hierarchical structure of an organism. From smallest part to largest an organism's body is arranged...

Cells --> Tissues --> Organs --> Systems --> Organism

From looking at your exit slips, I want to point out that although it is important to obtain water and food, most of you left out the important element of oxygen. THIS IS VERY IMPORTANT FOR ANIMALS OF ALL SIZES because it allows for cellular respiration.

A couple questions that were raised in both classes were whether having a brain or a heart determines animalness.

I did a little research and only those animals that have distinct body cavities possess a brain. So most invertebrates have a cluster of nerve cells that act like a brain but would technically not be brain such as sea sponges and starfish. If you are interested there is more information at http://www.pa.msu.edu/sciencet/ask_st/090893.html.

When it comes to talking about having a beating heart, only those animals that have a circulatory system are in need of a heart. Only the most primitive of animals lack a heart such as jellyfish. Here is some more information if you are interested - http://www.educationalvideos.com/jellyfish-have-no-brains-no-heart-and-no-blood/

The last question that I could not answer was whether or not all animals are multicellular or not. I thought for sure that they would in fact be multicellular but it turns out there used to be a class of protists called protozoa that are now considered animals. These species are unicellular but contain all the characteristics of an animal and have now been reclassified. Some examples of this animal are what we looked at under a microscope before break like the paramecium and amoeba. Here is a link of some cool videos featuring these animals - http://www.mcwdn.org/Animals/protozoavideos.html.