Text of Chapter 4: Reproduction of Organisms Life Science 7th grade
Chapter 4: Reproduction of Organisms Life Science 7th grade
Inquiry Do you think ALL living things have two parents? What might happen if the penguins (on the chapter cover photo) did not reproduce? Why do you think living things reproduce?
Bell work Ch4. L1 Sexual reproduction: reproduction in which the genetic materials from two different cells combine, producing an offspring. Egg: female sex cell that forms in the ovary. Sperm: male sex cell that forms in the testis. Fertilization: the process during which an egg cell and a sperm cell join together to form a new cell. Zygote: The new cell that is formed as a result of fertilization. Diploid cell: Cells that have pairs of chromosomes Homologous chromosomes: pairs of chromosomes that have genes for the same trait arranged in the same order Haploid cell: Cells that only have one chromosome from each pair Meiosis: The process by which one diploid cell divides to make four haploid cells
Launch Lab (work in pairs) Each pair gets one male parent and one female parent bag Without looking in the bag, select three beads from each bag. Record bead colors from each bag The six beads you pulled represent one offspring (x4) Put beads back in respective bags after each offspring Offspring #1Offspring #2Offspring #3Offspring #4 Male bag Female bag 1- How are the offspring similar? How are they different? 2- Why were there differences between offspring? Are differences beneficial? Why or why not?
What is sexual reproduction? Reproduction in which the genetic materials from two different cells combine, producing an offspring. Those cells are called sex cells Sex cells form in reproductive organs What are sex cells in humans and where do they form?
Sex cells Egg Female sex cell Forms in ovary Sperm Male sex cell Forms in testis
Fertilization An egg cell and a sperm cell join together This forms a new cell Zygote= new cell that forms from fertilization Develops into an organism What process is responsible for the development of a zygote into an organism?
Diploid cells Cells that have pairs of chromosomes Similar chromosomes occur in pairs This happens in body cells Diploid cells are produced via mitosis Video
Chromosomes Homologous chromosomes: pairs of chromosomes that have genes for the same trait arranged in the same order One from mom, one from dad make up a pair *****NOT IDENTICAL= DIFFERENT FROM SISTER CHROMATIDS.****** Video DO YOU THINK A MORE COMPLICATED ORGANISM HAS MORE CHROMOSOMES THAN A SIMPLER ORGANISM?
How many chromosomes? Human body cells have 23 pairs of chromosomes= 46 total chromosomes Number of chromosomes does NOT correlate with how complicated an organism is Dog has 78, Fern has 1,260 chromosomes
Haploid cells Cells that only have one chromosome from each pair (in humans have 23 total, not 46 total) Sex cells are haploid Haploid cells are produced via meiosis ONE STEP UP: WHY do you think sex cells are haploid?
Meiosis overview Many similarities to mitosis Mitosis+cytokinesis= one division of nucleus + one division of cytoplasm End result= Two diploid cells Meiosis= TWO divisions of nucleus and TWO divisions of cytoplasm End result= FOUR haploid cells Happens in two phases- meiosis I and meiosis II Video
Meiosis - phases Interphase- EXACTLY THE SAME AS IN MITOSIS. Period of growth and replication. Chromosomes are duplicated and each duplicated chromosome has two sister chromatids joined at the centromere. This only happens once
Meiosis I - phases Prophase I: chromosomes condense, homologous chromosomes form pairs. Nuclear envelope breaks apart, nucleolus disappears.
Meiosis I - phases Metaphase I: Homologous chromosomes line up along the middle of the cell. Spindle fiber attaches to centromere.
Meiosis I - phases Anaphase I: Chromosomes pairs (homologous chromosomes) are pulled apart. SISTER CHROMATIDS STAY TOGETHER.
Meiosis I - phases Telophase I: Nuclear membrane reappears around PAIRS of chromosomes, nucleolus reappears. Cytoplasm divides through cytokinesis. Two daughter cells form.
Meiosis II - phases NO SECOND INTERPHASE. Daughter cells from meiosis I immediately undergo meiosis II Prophase II: Because no replication, chromosomes stayed as thick sister chromatids Nuclear envelope breaks down Nucleolus disappears.
Meiosis II - phases Metaphase II: Sister chromatids line up along the middle of the cell Spindle attaches to centromere.
Meiosis II - phases Anaphase II: Sister chromatids pulled apart and move toward opposite ends of the cell
Meiosis II - phases Telophase II: Nuclear membrane forms around chromosomes cytoplasm divides via cytokinesis. Result= four haploid cells.
Meiosis summary Interphase Cell growth and replication. Sister chromatids attached at centromere. Prophase I Homologous chromosomes form pairs, nuclear membrane breaks apart, nucleolus disappears Metaphase I Homologous chromosomes line up in center of cell, spindle fiber attaches to each chromosome Anaphase I Homologous chromosomes pulled apart towards opposite ends of the cell. SISTER CHROMATIDS stay together. Telophase I Nuclear membrane forms around sister chromatids, cytokinesis divides cytoplasm. Two daughter cells formed. Prophase II Nuclear membrane breaks apart, nucleolus disappears. Metaphase II Sister chromatids line up along metaphase plate, spindle fiber attaches to centromere. Anaphase II Sister chromatids pulled apart towards opposite ends of cell. Telophase II Nuclear envelope reappears around individual chromosomes, nucleolus reappears. Cytokinesis divides cell. End Result: FOUR haploid cells
Why is meiosis important? Maintains diploid cells When haploid cells join (via fertilization) they make a diploid cell= zygote. Zygote then divides via mitosis to make the organism Creates haploid cells Maintains correct number of chromosomes in sex cells so when they join, they form a zygote with the correct number of chromosomes
Mitosis vs Meiosis (table p.122) CharacteristicMeiosisMitosis and Cell division Number of chromosomes in parent cell Diploid Type of parent cellReproductiveBody Number of divisions of nucleus 21 Number of daughter cells produced 42 Chromosome number in daughter cells HaploidDiploid FunctionForms sperm and egg cell Growth, cell repair, some kinds of reproduction
Advantages of sexual reproduction Genetic variation Inherit different genes from parents compared to siblings Occurs in all organisms that reproduce sexually Includes plants Selective breeding Choose the traits you like (breed individuals with those traits) and over time those can become dominant Video
Disadvantages of sexual reproduction Takes time and energy Search for mate can be problematic Expose to predators, disease or harsh environments Limitations Gestational period (pregnancy) Cant get pregnant while already pregnant, have to wait for one to finish before can start another one ONE STEP UP: Can you think of a way some organisms overcome the gestational limitation?
HOMEWORK Ch4 L.1 Vocabulary words on flash cards Memorize for quiz Lesson review questions p.126 #1-10 Outline lesson 1 Quiz lesson 1
Meiosis lab p.138 Lets recreate mitosis and meiosis using pool noodles 8 volunteers to be chromosomes Each person gets one 8 volunteers to be nuclear envelope Surrounds chromosomes 8 volunteers to be spindle 8 volunteers to be narrators/puppeteers
Bell Work Ch4 L.2 Asexual reproduction: the process by which one parent organism produces offspring WITHOUT meiosis and fertilization Fission: cell division in prokaryotes that forms two genetically identical cells Budding: the process by which a new organism grows by mitosis and cell division on the body of its parent. Regeneration: occurs when an offspring grows from a piece of its parent Vegetative reproduction: a form of asexual reproduction in which offspring grow form a part of a parent plant Cloning: a type of asexual reproduction performed in a laboratory that produces identical individuals from a cell or from a cluster of cells taken from a multicellular organism
Yeast launch lab p.129 I warmed water to 34C (93F) I added 5g yeast and 5g sugar What does the mixture look like initially? After 5 minutes? Drop of solution onto slide (cover with cover slip) Draw what you see under microscope. Evidence of reproduction? TURN THIS IN
What is asexual reproduction? One parent organism produces offspring WITHOUT meiosis and fertilization. Inherit all DNA from one parent What are some advantages/disadvantages of reproducing this way? Mold: a type of fungus that can reproduce sexually OR asexually. (fuzzy stuff on old food) Bacteria, protists, plants and some animals can