Cell Division 8 th Grade Science

Let’s Review Cells!  What do you know and remember about cells?  What are cells?  What is their function?  Cell  Cell theory  Prokaryote  Eukaryote  Organelle

What’s different about a cell and an atom?  Cell- basic unit of life.  You can’t be considered alive if you are not composed of cells.  Atoms – basic unit of matter, smallest part of an element  Atoms & Cells are two very different things.

What is The Cell Theory? 1. All living things are made up of cells. 2. Cells are the basic units of structure and function in living things. 3. New cells are produced from existing cells.

Remember these?

What does the Nucleus do?  Contains DNA. - DNA: contains the hereditary information.  Controls most cell processes. - Makes proteins…the building blocks of almost everything.

What actually contains the DNA?  Chromatin-  Consists of DNA bound to protein.  Usually spread throughout the nucleus, but during cell division it condenses to form…  Chromosomes-  Contain hereditary genetic information.

How do little elephants grow up to be BIG elephants?

Why do animals shed their skin?

Cell division  In multicellular organisms cell division is needed for three things:  Growth  Reproduction  Repair

Growth  Efficiency of moving materials into the cell  The larger the cell becomes the less efficient it is  The volume of the cell increases faster then its surface area  Cells that grow too large no longer have enough surface area to take in nutrients and remove waste

Growth © Pearson Education, Inc. Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume 1 cm x 1 cm x 6 = 6 cm 2 2 cm x 2 cm x 6 = 24 cm 2 3 cm x 3 cm x 6 = 54 cm 2 1 cm x 1 cm x 1 cm = 1 cm 3 2 cm x 2 cm x 2 cm = 8 cm 3 3 cm x 3 cm x 3 cm = 27 cm 3 6 / 1 = 6 : 1 24 / 8 = 3 : 1 54 / 27 = 2 : 1

Reproduction  Cells divide in order to reproduce themselves.  All cells come from preexisting cells.  Most cells divide by mitosis = making exact copies of themselves  Sex cells divide by meiosis = making copies with ½ the genetic information

Reproduction

Repair  Cells divide to repair tissues upon injury  Cells divide to replace old or damaged cells  When cell division goes wrong, cancer can occur

Repair

First, before a cell can split…  It must copy it’s genetic information.  Each daughter cell then gets a complete copy of that information.

How is genetic info passed on? o Chromosomes carry the cells coded genetic information. o Made up of DNA and proteins.  Human cells have 46 chromosomes.  23 pairs.  Organisms can have different #’s of chromosomes.

Before cell division… Each chromosome is replicated (copied). Each chromosome consists of two identical “sister chromatids.” Attached at the center by a centromere.

Mitosis Cycle Interphase Prophase Metaphase Anaphase Telophase & Cytokinesis

Animated Mitosis Cycle Cell division occurs in a series of stages, or phases.

Mitosis Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis