We will start off the unit by learning about cell division. Sound familiar?? If you recall, we first learned about cell division way back in the Bacteria and Viruses Unit when we discussed how bacteria reproduce through a process called binary fission. Cell division occurs in all living things, from uni to multicellular. Cell division enables unicellular organisms (like bacteria and protists) to reproduce, while helping multicellular organisms (like humans) to grow, develop and repair themselves.
Before a cell divides, it must first make sure that each daughter cell will be identical to itself - it does this by making a duplicate copy of its genetic material, DNA. DNA (short for deoxyribonucleic acid) is a chemical that contains all the information needed for an organism's growth and functioning. It is comprised of two strands of molecules that twist around one another, like a twisted ladder. The two strands are connected in the center by chemical rungs. We call this structure a double helix.
DNA is located within the nuclei of eukaryotic cells. Most of the time, DNA looks like loose strands. However, before the cell divides, DNA wraps itself around proteins and forms structures called chromosomes. The chromosome is made of two identical structures called chromatids that are held together in the middle by a centromere. Humans have 46 chromosomes in each of their non-reproductive cells - a number that is consistent throughout the human species. Other species have different chromosomal numbers - fruit flies have 8 chromosomes, dogs have 78 and cats have 38.
Additionally, the DNA is very well wrapped around the chromosome's protein core - if you stretch out a single strand of DNA, it measures approximately 2 meters! Even cooler - some sources state that if you line up all of the DNA in all of the cells in your body end-to-end, it can reach from Earth to the Sun and back - 70 times!
All of this is very important for the development of any organism - unicellular organisms reproduce by cell division and therefore need to ensure that their offspring have the same genetic information as themselves. Cell division is very important to you, as a multicellular organism, as well. Each one of us started out as a single fertilized egg cell. Through cell division after cell division, we became multicellular. Cell division enables you to grow - the bigger you get, the more cells you have, to the point where an adult human can have about 100 trillion cells! From one to 100 trillion....amazing!
This week, we will also be sitting for state testing in Language Arts and Math. There is no science component for the 7th grade (though there is one in 8th grade). Testing will take place in the morning, and the afternoons will have an altered schedule so that every class meets at least twice during the week. The schedule is as follows:
- Tuesday: testing until 11:28, periods 3, 4, 5, 6
- Wednesday: testing until 11:48, periods 3, 4, 2, 1
- Thursday: testing until 10:48, periods 3, 4, 5, 6
- Friday: testing until 10:48, periods 3, 4, 2, 1
During the test week, don't forget to stick to these basic guidelines:
- Get plenty of rest the night before (be in bed way before 10pm!).
- Eat a nourishing breakfast the morning of the test.
- Arrive to school on time!
- Read the directions carefully, paying close attention to what the question is asking you to do.
- Stay relaxed and do the best that you can.