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Cell Reproduction

Cell Reproduction. Chapter 4 Notes. Why is cell division important?. Many celled organisms grow because cell division increases the number of cells they have. One-celled organisms reproduce using cell division. The Cell Cycle. Like organisms have life cycles, cells have life cycles.

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Cell Reproduction

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  1. Cell Reproduction Chapter 4 Notes

  2. Why is cell division important? • Many celled organisms grow because cell division increases the number of cells they have. • One-celled organisms reproduce using cell division.

  3. The Cell Cycle • Like organisms have life cycles, cells have life cycles. • It is a series of events that takes place from one cell division to the next. • The time it takes to complete the cycle is not the same for all organisms or all cells in an organism. • Most of the time, a cell is in interphase. (Inter=between) (Between cell divisions). It is a period of growth and development. After that, cell division begins. • Study Figure 2 on page 97.

  4. Mitosis • PART of cell division—the nucleus divides into two. • The two new nuclei will be identical because everything duplicates (copies) before it separates (during interphase). The chromosomes thicken into coils called chromatids and they attach to their pair at a spot called a centromere. • Steps of mitosis: (PMAT) • prophase – nuclear membrane breaks down, chromatid pairs are visible, centrioles move to opposite ends of the cell • metaphase – the pairs of chromatids line up at the center of the cell, centromere is attached to centriole by spindle fibers • anaphase – centromere divides, spindle fibers shorten and chromatids begin to move to opposite ends of the cell (now they are called chromosomes again) • telophase – new nucleus forms, chromosomes uncoil

  5. Cell Division • After mitosis, the cytoplasm divides and two new cells are created. • In animal cells, the cytoplasm pinches in (like a balloon with a string tied around it). • In plant cells, a cell plate forms and new cell walls grow on each side. • After the cytoplasm divides, the cell enters interphase again, the period of growth and development.

  6. Asexual Reproduction • Some organisms with eukaryotic cells can reproduce asexually by using cell division. • All cells will be genetically identical to the parent cell because of the duplication of the nucleus that happens in mitosis. • Bacteria do not have a nucleus, so they can’t use mitosis/cell division to reproduce asexually. They use fission. • Budding – new organism growing from the body of a parent organism • Regeneration – process that uses cell division to replace lost body parts

  7. Body Cells vs. Sex Cells • Two types of cells in your body—body cells and sex cells. (ALL cells except sex cells (sperm and egg) are body cells.) • Body cells – chromosomes are in pairs (diploid). Humans have 23 pairs (46 chromosomes). • Sex cells – have half the number of chromosomes as body cells (one from each pair). (23 for humans.)

  8. Sexual Reproduction • Two sex cells come together—sperm (male) and egg (female). • The sperm cell enters the egg cell in a process called fertilization. • The resulting cell is called a zygote.

  9. Meiosis • Meiosis is the process used to create haploid cells so that sexual reproduction can take place. • Sex cells have half so that when they combine with another sex cell, which also has half, the result will be “whole.” [If two diploid cells combined, the offspring would have double the amount of chromosomes.] • During meiosis, the nucleus divides twice (Meiosis I and Meiosis II). • Study diagrams and descriptions on pages 106-107.

  10. DNA (deoxyribonucleic acid) • Contains information that an organism needs to grow and function • Has a structure that resembles a twisted ladder • sides are made up of sugar-phosphate molecules • rungs are made up of nitrogen bases (remember this later for nitrogen cycle) • To duplicate itself, it unwinds, separates its sides, and then forms new sides.

  11. Genes • Genes—sections of DNA on a chromosome (pieces of code) [Ex: like a slice is part of a loaf] • Contain instructions for making specific proteins • RNA carries codes for making proteins from the nucleus to the ribosomes in the cytoplasm • Messenger RNA (mRNA), Ribosomal RNA (rRNA), Transfer RNA (tRNA) • Cells use only the genes that direct the making of proteins needed by that cell (like a character in a play only reads the lines in the script for them)

  12. Mutations • Any permanent change in the DNA sequence of a cell’s gene or chromosome. • can change the traits of the organism • can be caused by outside factors like X-rays, sunlight, and some chemicals • Can be passed to offspring only if mutation is passed to a sperm or egg cell.

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