Cell Division Is Bigger Really Better Do bigger
Cell Division
Is Bigger Really Better? Do bigger organisms have bigger cells? � Why can’t cells get very big? ◦ Bigger cells make it difficult to transport needed materials into the cell. (Surface area to volume ratio). ◦ The nucleus can only control a certain amount of cytoplasm. �
Why Do Cells Divide? �Growth. ◦ Increase in size. ◦ Differentiation (specialization). �Repair. ◦ Complete or partial regeneration. ◦ Your skin is replaced every 28 days! �Reproduction. ◦ Making a new organism.
Human Growth �Controlled by human growth hormone. �Produced in pituitary gland in the brain. �What happens if there is a shortage? �Dwarfism.
When Do Cells Divide? �Cell division: splitting a single cell into two cells. �When? Cells divide when they reach their maximum size. 5. 1
The Life of a Cell �Interphase. Growth and preparation. �Replication. ◦ Dividing into two cells. ◦ Mitosis (the nucleus divides). ◦ Cytokinesis (the cytoplasm divides). ◦
Section 10 -2 G 1 phase M phase S phase G 2 phase
Interphase � 90% �G 1 of the time. (gap 1): cell grows and develops. �S (synthesis): chromosomes and nucleus replicate. �G 2 (gap 2): cell makes new organelles for new cell.
DNA in Cell Division �Chromatin: thin, fibrous form of DNA. �Sister chromatids: the chromosomes replicate, condense, and pair up (light microscope). �Centromere: point where sister chromatids attach.
2 Parts to Cell Division � Mitosis: replicating nucleus. � Cytokinesis: cytoplasm divides.
4 Phases of Mitosis Prophase. � Metaphase. � Anaphase. � Telophase. (PMAT) �
Mitosis �Prophase: chromosomes condense. Mitotic spindles form and attach. �Metaphase: chromosomes align. �Anaphase: sister chromatids are pulled apart. �Telophase: chromosomes uncoil, nuclear envelope reappears. Cytokinesis begins.
Mitosis and Cytokinesis Section 10 -2 Spindle forming Centrioles Nuclear envelope Chromatin Interphase Centromere Chromosomes (paired chromatids) Prophase Cytokinesis Spindle Centriole Telophase Nuclear envelope reforming Centriole Individual chromosomes Anaphase Metaphase
Mitosis and Cytokinesis Section 10 -2 Spindle forming Centrioles Nuclear envelope Chromatin Interphase Centromere Chromosomes (paired chromatids) Prophase Cytokinesis Spindle Centriole Telophase Nuclear envelope reforming Centriole Individual chromosomes Anaphase Metaphase
Mitosis and Cytokinesis Section 10 -2 Spindle forming Centrioles Nuclear envelope Chromatin Interphase Centromere Chromosomes (paired chromatids) Prophase Cytokinesis Spindle Centriole Telophase Nuclear envelope reforming Centriole Individual chromosomes Anaphase Metaphase
Mitosis and Cytokinesis Section 10 -2 Spindle forming Centrioles Nuclear envelope Chromatin Interphase Centromere Chromosomes (paired chromatids) Prophase Cytokinesis Spindle Centriole Telophase Nuclear envelope reforming Centriole Individual chromosomes Anaphase Metaphase
Mitosis and Cytokinesis Section 10 -2 Spindle forming Centrioles Nuclear envelope Chromatin Interphase Centromere Chromosomes (paired chromatids) Prophase Cytokinesis Spindle Centriole Telophase Nuclear envelope reforming Centriole Individual chromosomes Anaphase Metaphase
Mitosis and Cytokinesis Section 10 -2 Spindle forming Centrioles Nuclear envelope Chromatin Interphase Centromere Chromosomes (paired chromatids) Prophase Cytokinesis Spindle Centriole Telophase Nuclear envelope reforming Centriole Individual chromosomes Anaphase Metaphase
� � � Interphase: growth, DNA replicated. Prophase: centrioles, mitotic spindle, centromeres. Metaphase: align in center. Anaphase: pulling apart. Telophase: cleavage furrow, daughter cells.
Some Differences Between Plant and Animal Cell Division �Cleavage (plants). furrow (animals) and cell plate 5. 2
Sexual vs. Asexual Reproduction �What’s the difference? �Humans have 46 chromosomes (arranged in 23 pairs). �Ameba = 50. �Worm = 36. �Fern = 1010. �Onion = 16. Do any of these numbers surprise you?
Sexual Reproduction �In sexual reproduction each parent gives a set of its chromosomes to the offspring. �If two humans (46 chromosomes) mate, how many chromosomes will the child have? �In sexual reproduction haploid cells must be combined.
Diploid and Haploid �Diploid: a cell with two complete sets of chromosomes. (2 n) �Haploid: a cell with one complete set of chromosomes. (n)
Haploid Cells �Normal human cells (diploid) have 46 chromosomes. �How many chromosomes do haploid cells have? � 23. �In humans, haploid cells are used for reproduction (sex cells) and are called gametes (eggs, sperm).
Remember This Question �If two humans mate, how many chromosomes will the child have? �In sexual reproduction, only gamete cells are used (i. e. they only have one set of chromosomes). �Human diploid cells have 46, haploid have 23. �Male gamete (23) + female gamete (23). � 23 + 23 = 46 chromosomes! �This keeps the number of chromosomes the same from generation to generation.
How Are Gametes Made? �Haploid cells are created through a process called meiosis. �During meiosis, 1 diploid cell divides into 4 haploid cells.
8 Stages of Meiosis Prophase I � Metaphase I � Anaphase I � Telophase I � Prophase II Metaphase II Anaphase II Telophase II
Meiosis Prophase I: pairs attach. � Metaphase I: lining up. � Anaphase I: pulling apart. � Telophase I: cytokinesis, two haploid cells are formed. �
Figure 11 -15 Meiosis Section 11 -4 Meiosis I
Meiosis, cont. Prophase II: spindle fibers. � Metaphase II: lining up. � Anaphase II: pulling apart. � Telophase II: cytokinesis, four haploid cells are formed. �
Figure 11 -17 Meiosis II Section 11 -4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Telophase II Meiosis II results in four haploid (N) daughter cells.
Comparing Mitosis and Meiosis MITOSIS MEIOSIS Number of chromosomes is half chromosomes the original. remains the same. Cell is genetically New cell is unique. genetically identical to parent. Cell division takes place twice. Cell division takes place only once. 5. 3
Comparing Asexual and Sexual Reproduction ASEXUAL Offspring comes from a single parent (i. e. the cell splits). Offspring is genetically identical to the parent. SEXUAL Offspring comes from combination of two parents (i. e. haploid cells combine). Offspring is genetically unique.
Comparing Sexual and Asexual: Which Way Is Better? �If all of our immune systems were exactly the same, what would happen if a fatal virus attacked? �A change in the environment that destroys one individual (such as the arrival of a new disease) would destroy all the individuals. �Having unique individuals protects a species from extinction through environmental changes. 5. 4
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