Cells & Cell Division

THREE main jobs of cell division… 1.Growth: Cells divide once they have grown large enough Example. Cells grow & divide in multicellular organisms

2.Repair: Old, dead or damaged cells replaced through cell division Example. Bark cells divide to produce new bark tissue

3.Reproduction: Usually used by unicellular organisms to make new individuals Example. Bacteria divide  2 identical bacteria

A Quick Review of Science 8! 1. Nucleus: Contains cell’s genetic info (DNA); controls cell functions 2. Nuclear Membrane: Allows materials in/out of the nucleus 3. Chromosomes: Made of DNA; in nucleus Chromosomes are made up of DNA. Almost all humans cells 23 pairs of chromosomes

What does DNA look like? What is it’s job in a cell? DNA looks like a twisted ladder (double helix) It contains genes… these are instructions for making proteins for the cell

4. Cytoplasm: Gel-like substance supporting organelles 5 4. Cytoplasm: Gel-like substance supporting organelles 5. Microtubules: Tiny tubes in cytoplasm; allow movement of organelles 6. Centrioles: Used during cell division

7. Ribosomes: Site of protein synthesis Ribosomes can be free in the cytoplasm or attached to the rough endoplasmic reticulum (ER). This ER is needed to make and transport proteins for the cell. ER that doesn’t have ribosomes on it is called smooth ER. It is needed to make and transport fats.

How are the nucleus and nucleolus different? 8. Nucleolus: contains RNA for making ribosomes Once assembled, ribosomes move from the nucleus to the cytoplasm Differences: Nucleus contains DNA and nucleolus contains RNA

Which organelles are present ONLY in plant cells and not animal cells? Cell wall Chloroplasts Water vacuole