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Cell Division Notes Key Concepts: Introduction (1) How do multicellular objects like humans and trees grow so big? Cells will increase in size slightly but increase greatly in number. (2) If all life on earth begins as a single cell, how do some of them become complex multicellular organisms? A single cell grows and then divides, forming two cells. Then two cells grow and divide forming four, and so on. Terminology CELL CYCLE – The regular sequence of growth and division that cells undergo. DAUGHTER CELLS – The two new cells that are formed at the end of cell division. THREE STAGES OF CELL DIVISON Stage 1: Interphase (the period before cell division) Growing – The cell reaches its full size and makes sure it has everything it needs inside. (new organelles are made if necessary) Copying DNA – An exact copy of DNA is made in a process called replication. Preparing for Division – Structures needed for cell division are produced. (Ex. centrioles) Stage 2: Mitosis (one nucleus divides to create two) (It’s all about the chromosomes!) Phase 1: Prophase – Chromosomes and spindle fibers form; nuclear (envelope) membrane breaks down. Phase 2: Metaphase – Chromosomes line up across the center and attach to a spindle fiber. Phase 3: Anaphase – Centromeres split; chromatids separate and move to opposite ends. Phase 4: Telophase – Chromosomes stretch out; new nuclear (envelope) membrane forms around the chromosomes. Stage 3: Cytokinesis (completes the process of cell division) Animal Cells – Cell pinches in two; each daughter cell has same number of identical chromosomes. Plant Cells – A cell plate forms across the middle of the cell; the cell plate gradually develops into two new cell membranes between the daughter cells; new cell walls will form around the cell membranes. Illustrating Cell Division * Draw what an animal cell would look like in each of the stages of cell division. Be sure to include key cell parts in your sketches. 1 & 2: Interphase & Late Interphase 3: Mitosis – Prophase 4: Mitosis – Metaphase 5: Mitosis – Anaphase 6: Mitosis – Telophase 7: Cytokinesis Key Concepts: Conclusion (1) Cell division is also known as the CELL CYCLE. Explain why the word “CYCLE” is appropriate to use to describe the process of cell division. The cell cycle (cell division) doesn’t end. The cycle starts over when the cell divides (after cytokinesis). (2) During cellular reproduction, a cell must divide in order to multiply. Explain this statement. A cell going through the cell cycle divides (splits) causing the number of cells to increase (multiply) in number. One cell becomes two, two becomes 4, 4 becomes 8, etc.