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 #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?

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

• Video

Meiosis summaryInterphase 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)Characteristic Meiosis Mitosis and Cell

division

Number of chromosomes in parent cell

Diploid Diploid

Type of parent cell Reproductive Body

Number of divisions of nucleus

2 1

Number of daughter cells produced

4 2

Chromosome number in daughter cells

Haploid Diploid

Function Forms 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)

• 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?

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

• 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

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 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

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?

Types of asexual reproduction

• Fission: cell division in prokaryotes that forms two genetically identical cells.

1. Prokaryote’s DNA is copied 2. Each copy attaches to cell

membrane3. Cell elongates, pulling

copies of DNA apart4. Cell membrane pinches

inward along middle of the cell

5. Cell splits and forms two new identical offspring

• Example: E.coli

Types of asexual reproduction

• Mitotic cell division: used by unicellular eukaryotes– Organism produces

two offspring through mitosis and cell division

• Example: amoeba

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).

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)

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

Types of asexual reproduction• Vegetative reproduction: a

form of asexual reproduction in which offspring grow form a part of a parent plant.

1. Parent plant can grow long stems called stolons

2. If a stolon touches the ground, it forms roots.

3. Once roots are down, a new plant can grow.

4. If stolon is broken from parent plant, the new plant can survive on its own.

– Example: strawberries, raspberries and potatoes.

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.

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

Advantages of asexual reproduction

• Don’t need a mate

• Rapidly produce a large number of offspring

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

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.141-145 (all)– You MUST write the entire question and answer

down for credit. Only answers will NOT be accepted.