Cells & Cell Division An informative presentation by your wacky science teacher! LG4: Explain basic principles of HEREDITY, including CELL DIVISION (MITOSIS & MEIOSIS).
A Question.. What do you, an ant, and an oak tree have in common (talk to a partner)?
An Answer. Yes, you are all living things but more importantly You are all made of trillions of cells! AND you all started out as a single cell!
Cell Theory In the 1830 s Theodor Schwann & Matthias Schleiden proposed Cell Theory
Cell Theory states 1. All living things are made of cells. 2. Cells are the basic unit and function of all living things. 3. Living cells only come from other living cells. How do you become a multicellular organism if you started out as just ONE cell (talk to a partner)?
Cell Division Zygote Through cell division, a single cell becomes two cells. Those two cells divide into four. Time for math how many cells would you have after 6 divisions?
How Many? You would have 64 cells!
Cell Division Cells multiply by dividing! Answer (talk to your neighbor): How does your drawing show that cell division can cause organisms to grow larger in size? Is there a limit to how large a cell can be? Why or why not?
Consider. What are the purposes of cell division? GRR! Growth/Regrowth Repair Reproduction (Hint: This is important!)
Growth How tall were you when you were 5? How tall were you last year? How tall are you now? Did your cells get bigger? Discuss with a neighbor what happened
Growth While individuals grow in size, a larger organism has MORE CELLS than a smaller organism There are limits on how big a cell can get. What do you think is the main reason why cells only get to be a certain size?
Regrowth When an organism is fully grown, some cells die off and need to be replaced.
Regrowth As cells age and die, they need to be replaced. In the human body: There are about 200 different types of cells (remember the pictures?). Every minute or so, your skin loses about 40,000 cells! In contrast, your brain cells need to last a very long time!
Specialization We know that cells divide in order to make bigger organisms. However, if cell division were the only process occurring in cells, all multicellular organisms would end up as spheres of identical cells.
Specialization As the cell grows, more processes are needed for it to function, so its demand for instructions increases. However, the amount DNA (instructions) remains constant. The instructions will determine what type of cell it becomes. During development, cells become specialized to perform particular functions. Name specialized cells in the human body
In Other Words. Cells get instructions from DNA about what type of cell it will become and what will be its function!
Cell Types Some cells might become layered skin cells, while others might become long, thin nerve cells. Nerve Cells Cheek Cells Red Blood Cells Bone Cells
One purpose of cell division Growth/Regrowth Next reason
Repair Have you gotten a paper cut recently? Have you broken a bone in your arm or leg?
Repair The body repairs injuries like these by means of cell division. For example. When your skin is cut, skin cells on either side of the cut make new cells to heal the wound.
One purpose of cell division Repair Next reason
Reproduction In order for organisms to reproduce, reproduction (sex cells meiosis) must occur Reproductive cell division produces sex cells with ½ the genetic information from each parent (humans 23 from mom / 23 from dad)
Summary Cells are the main components of all living things The purpose for cell division: Regrowth Repair Reproduction
Cell Cycle
Mitosis in Words Interphase Cytokinesis Cell membrane pinches in two; each daughter cell has same number of identical chromosomes. Telophase Chromosomes stretch out; new nuclear envelope forms around chromosomes. Cell grows, makes a copy of DNA. (90% of cell s life is spent here!) The Cell Cycle Anaphase Prophase Chromosomes and spindle fibers form; nuclear envelope breaks down. Metaphase Chromosomes line up across the center and attach to a spindle fiber. Centromeres split; chromatids separate and move to opposite ends.
Length of the Cell Cycle
Mitosis
One More Look at Mitosis
Meiosis ( my-o-my! Sex Cells!) The process by which the number of chromosomes is reduced by half to form sex cells (sperm and egg) Chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many chromosomes as the other cells in the organism.
Meiosis Requires two divisions of the nucleus Meiosis I- (Just like mitosis) Meiosis II- two daughter cells go through a second division of the nucleus. (during this process, there is no chromosome replication) Meiosis II (after Meiosis I which is Mitosis)
The difference between Mitosis and Meiosis Mi T osis ( T is for TWIN!) One division of the nucleus = 2 cells Used for growth and repair Creates exact T win of cell (diploid cells) Meiosis ( MY-OH-MY! SEX CELLS!) Two divisions of the nucleus (mitosis, THEN meosis = 4 sex cells cells) Used for sexual reproduction Creates cells with ½ genetic material (haploid cells) in humans, 23 chromosomes from each parent = new human with 46
Cancer is Uncontrolled Mitosis: Mitosis must be controlled, otherwise growth will occur without limit (cancer) Mutations in control proteins can cause cancer
Cancer Cells What is it? Cancer is a disease in which cells grow and divide uncontrollably, damaging the parts of the body around them. It is caused by a mutation that causes uncontrolled mitosis.
Cancer cells are held together.
Mutations A mutation (from Latin word that means change) is any change in a gene or chromosome. Can cause a cell to produce an incorrect protein during protein synthesis. As a result, the organism s trait, or phenotype, may be different from what it normally would have been.
Results of Mutations If a mutation occurs in a SEX CELL, the mutation can be passed on to an offspring and affect the offspring s phenotype. If a mutation occurs in a BODY CELL, the mutation will not be passed on to the organism s offspring.
Effects of mutations Introduce change in an organism (genetic variation) Can be harmful (reduces the organism s chance for survival and reproduction) Can be helpful (improve an organism s chance of survival and reproduction) Antibiotic resistance in bacteria Can be neither harmful nor helpful
Rate Yourself! LG4: Understand cells role in living things and heredity. Before this presentation, I was a (scale rating 0-4) because I knew about cells. now, I feel like I am a (scale rating 0-4) because I learned
Don t forget to thank a science teacher today!