Sexual ReproductionPart 2

Science 9

Name_____________Date______________

Period____

Remember Meiosis?

3 stages of Sexual Reproduction1) Mating: process by which gametes arrive at

the same place at the same time *Requires 2 parents!

2) FertilizationSperm Cell + Egg Cell à Zygote

(haploid) (haploid) (diploid)

3) Development

Advantages of Sexual Reproduction• Results in increased genetic diversity

• Better chance of survival if change in environment

Disadvantages of Sexual Reproduction

• requires energy

• need to find a mate

• whole chromosome mutationsie) Down Syndrome: extra

chromosome #21

Methods of Fertilization

1) External Fertilization: sperm and egg cells join outside of the parents’ bodies

~common in animals and plants that live in water or moist places

Methods of Fertilization

2) Internal Fertilization: sperm and egg cells join inside the body of the female parent

common in birds, mammals, flowering plants, and cone-forming plants

DID YOU KNOW?

• There are Male and Female Plants?• Plants reproduce sexually?• They use internal fertilization too!

Heyyy,How you doin ;)?

Male Female

Internal FertilizationPollination: Form of internal fertilization that

occurs in plants. -Pollen: carries sperm cells in a protective case-Ovules: female plant structure containing egg cells

Read Page 207-211External Fertilization:Advantages Disadvantages

Internal Fertilization:Advantages Disadvantages

- Very little energy required to find a mate- Can produce many offspring at once

- Species can survive environmental disaster- Little competition between parents & offspring for

resources- Maintains genetic variation

- Many gametes will not survive or be fertilized

- Zygotes/embryos unprotected

- Parents do not care for offspring, so few survive to adulthood

- More offspring survive due to embryo protection & parental care

- Requires energy to find a mate

- Fewer zygotes produced than in external fertilization

Sexual Reproduction Part 3: Development

Embryonic Development

• After fertilization, zygote undergoes repeated mitosis

-One Cell (zygote)-2 Cells-4 Cells-8 Cells-Morula: ball of cells by end of 1st week

Embryonic DevelopmentBy the 2nd week, a hollow ball of cells form,

called the blastula.

Embryonic Development• Blastula Stage: embryonic stem cells• Next stage: Gastrula which is made out of

three layers…

Layers of the Gastrula

1) Ectoderm: Outer Layer forms skin and nervous system

2) Mesoderm: Middle layer forms kidneys, muscles, blood vessels, reproductive organs and bones

3) Endoderm: Inner layer forms lungs, liver, and the lining of the digestive system

Ectoderm

Mesoderm

Endoderm

Fetal Development• Differentiation: cell layers form organs and

tissues• Occurs for 38 weeks• Divide this time into 3 trimesters, each 3

months long

Fetal Development• Trimester 1: Developing Organ Systems

– 4 weeks: brain and spinal cord– 8 weeks: bone cells and now called Fetus– 12 weeks: organ systems formed

Fetal Development• Trimester 2: Growth

– Weeks 12-16 rapid growth– Week 20 mother can feel fetus move– Weeks 20-24 slow growth

Fetal DevelopmentTrimester 3: Continued Growth

– Growth in preparation for birth– Brain grows significantly– Week 32: fat deposited under skin