Cell Division presented by Betsy Sanford 7 th

Cell Division presented by Betsy Sanford 7 th Grade Life Science Lost Mountain Middle School

Cell Division l l All organisms are made of cells. Eukaryotic organisms start out with only one single cell and develop into multi-cellular organisms. Cells divide to form new cells. That’s how we grow and develop. To grow and develop, an organism’s cells must go through a process called the cell cycle.

The Cell Cycle l The cell cycle has three parts – – – l Interphase Mitosis Cytokinesis Interphase, the time when… – – – DNA gets copied two sets of chromosomes form happens in the nucleus

The Cell Cycle l Mitosis is the time when the two copies of DNA get separated into two new nuclei – – Prophase – nucleus disappears, spindle fibers appear Metaphase – chromosomes are attached to spindle fibers and line up in the center of the cell Anaphase – the chromosomes split apart Telophase – a new nucleus appears around each set of chromosomes

The Cell Cycle l l Cytokinesis is the end of the cell cycle. It is the time when the cells splits into two new cells The two cells separate. The two new cells formed contain exactly the same DNA as the original cell.

The Cell Cycle l l All cells except sex cells complete this process. This process starts with a single cell. Two new cells are produced in this process. In humans, there are 46 chromosomes (DNA strands) in all cells except the sex cells.

The Cell Cycle l l l The original cell has 46 chromosomes in humans. The two new cells both have 46 chromosomes as well. Once the process starts, many cells will continue dividing at the same time for rapid growth and development of the organisms.

Cell Division Animation

Mnemonic – Create your own memory sentence for the cell cycle. l Example – Interphase = Intelligent – Prophase = People – Metaphase = Meet – Anaphase = At – Telophase & Cytokinesis= Three o’Clock

Review Questions 1. 2. 3. 4. 5. What does the smaller circle represent? nucleus How many cells does Mitosis start with in humans? 1 How many chromosomes does Mitosis start with in humans? 46 How many cells are present at the end of Mitosis? 2 How many cells at the end of Mitosis? 2

Review Questions l l What is cell division? Include a list of steps seen in the cell cycle. – interphase, mitosis (prophase, metaphase, anaphase, telophase), & cytokinesis Why do living things need cell division? Include at least 3 specific reasons. – repair damage (ex. : new skin under a scab) – replace worn out cells (red bloods cells get replaced every 120 days because they get worn out from continuous use; they are being pumped around the body carrying oxygen constantly)