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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