Cell Division The Importance of Cell Division Cell division allows organisms to carry out three necessary functions: REPRODUCE GROW REPAIR DAMAGE FERTILIZATION: You started life as a single cell, but today your body is made of trillions of cells. Cell division allowed you to grow into the person you are today.
Cell Division for Reproduction The ability to reproduce is a characteristic of all living things. 1. Asexual Reproduction aka cloning One parent cell produces 2 identical daughter cells
Cell Division for Reproduction 2. Sexual Reproduction Two half cells (gametes) from different parents combine to form one complete cell Each half cell contains half of the genetic information of the parent it came from Gametes are produced by meiosis
Cell Division for Growth Multicellular organisms grow by increasing their number of cells Nutrients enter cells and move between cells by crossing the cell membrane The movement of these chemicals occurs by diffusion.
Diffusion DIFFUSION is the movement of nutrients (particles) from an area of high concentration to an area of low concentration
Diffusion Example Example: a drop of food dye in a glass of water
Osmosis OSMOSIS involves the movement of water. Osmosis is when water crosses a membrane to the side where the solution is more concentrated. The end result is that both sides of the membrane have the same concentration. Diffusion and osmosis occur much more efficiently across many small cells as opposed to one large cell.
Osmosis
Egg Osmosis Demo
Chemical Reaction of Egg Shell
Cell Division for Repair Every day your body sheds millions of dead skin cells, which are replaced by new ones Every red blood cell in your body is replaced about every 120 days Every cut and blister needs new cells to fill the gaps All organisms need to repair themselves to stay alive
The Cell Cycle
The Cell Cycle As eukaryotic cells grow and divide, they move through three distinct stages known as THE CELL CYCLE. The three stages of the cell cycle are: Interphase Mitosis Cytokinesis. Stage Cellular Processes Occurring 1. Interphase Normal growth 1. Mitosis 2. Cytokinesis Cell division
The Cell Cycle The length of one cell cycle varies, depending on the cell type and growth conditions. Embryonic cells divide very rapidly. Some cells, like adult nerve cells and cardiomyocytes (heart cells), never divide at all.
Interphase Stages of the Cell Cycle Cells are usually in interphase. DNA is in extremely long, thin strands (not visible under microscope) DNA strands duplicate in preparation for cell division; organelles also duplicate
Stages of the Cell Cycle Cell Division occurs in two stages: 1. Mitosis division of the contents of the nucleus 2. Cytokinesis division of everything else (cytoplasm, membrane, all organelles)
Cell Cycle - Mitosis Mitosis occurs in four phases: Prophase, Metaphase, Anaphase, and Telophase (PMAT) Use this acronym to help you remember the stages of mitosis. Let us examine each of these stages more in depth
Prophase (pro = before ) Long strands of DNA condense and become visible under microscope as chromosomes Each chromosome consists of two identical strands (=chromatids) which are held together by a centromere Nucleus dissolves, contents spill into cytoplasm
Metaphase (meta = middle ) Chromosomes line up along middle of cell
Anaphase Centromeres split and sister chromatids separate Chromatids are actually pulled apart/moved around by specialized structures called spindle fibres
Telophase (telo = end ) DNA stretches back out, becoming invisible under microscope New nucleus forms cells appear to have two nuclei during this stage
Cytokinesis Cytoplasm divides producing two identical daughter cells Membrane is pinched off in centre (in plants, a new cell wall also forms at this stage) Interphase begins again!
Checkpoints in the Cell Cycle Cells do not divide at a constant rate. Special molecules monitor cellular conditions to determine if a division is necessary or not. A cell will remain in interphase and not divide under any of the following conditions Surrounding cells send signals telling them not to divide Low nutrients DNA damage DNA not replicated
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HOMEWORK Hand in homework from last lesson Read pages 40-43 and take notes Answer questions #1-6 Prepare for quiz on tuesday for the cell organelles and cell cycle (mitosis)