1. Chapter 4: Reproduction of Organisms
Life Science
7th grade

2. 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?

3. 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

4. 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 #1
Offspring #2
Offspring #3
Offspring #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?

5. 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?

6. Sex cells Egg Sperm Female sex cell Forms in ovary Male sex cell
Forms in testis

7. 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?

8. Diploid cells Cells that have pairs of chromosomes Video
Similar chromosomes occur in pairs
This happens in body cells
Diploid cells are produced via mitosis
Video

9. 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?

10. 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
Human on top, dog on bototm.

11. 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?

12. 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

13. 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

14. Meiosis I - phases
Prophase I: chromosomes condense, homologous chromosomes form pairs. Nuclear envelope breaks apart, nucleolus disappears.

15. Meiosis I - phases
Metaphase I: Homologous chromosomes line up along the middle of the cell. Spindle fiber attaches to centromere.

16. Meiosis I - phases
Anaphase I: Chromosomes pairs (homologous chromosomes) are pulled apart. SISTER CHROMATIDS STAY TOGETHER.

17. Meiosis I - phases
Telophase I: Nuclear membrane reappears around PAIRS of chromosomes, nucleolus reappears. Cytoplasm divides through cytokinesis. Two daughter cells form.

18. 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.

19. Meiosis II - phases Metaphase II:
Sister chromatids line up along the middle of the cell
Spindle attaches to centromere.

20. Meiosis II - phases
Anaphase II: Sister chromatids pulled apart and move toward opposite ends of the cell

21. Meiosis II - phases Telophase II: Result= four haploid cells.
Nuclear membrane forms around chromosomes
cytoplasm divides via cytokinesis.
Result= four haploid cells.

22. Meiosis
Video

23. Meiosis summary Interphase Prophase I Metaphase I Anaphase I
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

24. 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

25. Mitosis vs Meiosis (table p.122)
Characteristic
Meiosis
Mitosis and Cell division
Number of chromosomes in parent cell
Diploid
Type of parent cell
Reproductive
Body
Number of divisions of nucleus 2 1
Number of daughter cells produced 4
Chromosome number in daughter cells
Haploid
Function
Forms sperm and egg cell
Growth, cell repair, some kinds of reproduction

26. 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

27. 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)
Can’t 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?

28. 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

29. Meiosis lab p.138
Let’s 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

30. 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

31. Yeast launch lab p.129 I warmed water to 34˚C (93˚F)
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

32. 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 reproduce asexually
ONE STEP UP: How do parent/daughter cells compare to each other in asexual reproduction?

33. Types of asexual reproduction
Fission: cell division in prokaryotes that forms two genetically identical cells.
Prokaryote’s DNA is copied
Each copy attaches to cell membrane
Cell elongates, pulling copies of DNA apart
Cell membrane pinches inward along middle of the cell
Cell splits and forms two new identical offspring
Example: E.coli

34. Types of asexual reproduction
Mitotic cell division: used by unicellular eukaryotes
Organism produces two offspring through mitosis and cell division
Example: amoeba

35. Types of asexual reproduction
Budding: a new organism grows by mitosis and cell division on the body of its parent.
Bud is genetically identical to parent
When bud gets big enough, it can break off from parent
Example: hydra (multicellular organism), yeast (unicellular organism).
Genus of small, simple, fresh-water animals that possess radial symmetry

36. Types of asexual reproduction
Animal regeneration: occurs when an offspring grows from a piece of its parent. (varies greatly among animals)
Producing new organisms: each new organism is identical to starting organism
Example: planarian (can cut in half and each half makes a new organism), sea star (can cut an arm and if it contains part of central disk and conditions are right, that arm will make a whole new star)

37. Types of asexual reproduction
Animal regeneration cont’d
Producing new parts: regeneration
Common in animals. Humans can regenerate skin or liver, some animals can regenerate limbs.
THIS IS NOT CONSIDERED ASEXUAL REPRODUCTION BECAUSE IT DOES NOT PRODUCE A NEW ORGANISM

38. Types of asexual reproduction
Vegetative reproduction: a form of asexual reproduction in which offspring grow form a part of a parent plant.
Parent plant can grow long stems called stolons
If a stolon touches the ground, it forms roots.
Once roots are down, a new plant can grow.
If stolon is broken from parent plant, the new plant can survive on its own.
Example: strawberries, raspberries and potatoes.

39. Types of asexual reproduction
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.

40. Types of asexual reproduction
Plant cloning: do via tissue culture.
Use cells from meristem to grow new plants in lab
Animal cloning (Example: sheep)
Take cell from sheep 1, take unfertilized egg from sheep 2
Remove DNA from unfertilized egg (it’s an empty egg now)
Fuse cell from sheep 1 with empty egg from sheep 2
Cell develops into embryo in laboratory
Implant embryo into sheep 2
Sheep 2 gives birth to clone of sheep 1
Video

41. Advantages of asexual reproduction
Don’t need a mate
Rapidly produce a large number of offspring

42. Disadvantages of asexual reproduction
Genetically identical to parent= little variation within a population
Variation can give better chance of survival
Mutations
Harmful mutations will be passed on to all offspring

43. HOMEWORK Ch4 L.2 Vocabulary wordsß on flash cards
Memorize for quiz
Lesson review questions p.137 #1-9
Outline lesson 2
Quiz lesson 2
OPTIONAL: Extra credit (due on test day) p (all)
You MUST write the entire question and answer down for credit. Only answers will NOT be accepted.