BC Science 9: p

Sexual Reproduction  Sexual reproduction brings non-identical gametes together to form a new organism – it occurs in three stages: 1.Mating – the process by which gametes are brought together at the same place and same time. 2.Fertilization – the process by which egg and sperm join to form a zygote (ie. a new organism). 3.Development – the process by which an embryo develops as an organism.

Fertilization Requirements  In order for fertilization to produce a successful developing embryo, certain conditions must be met: 1.Embryo must have enough nutrients. 2.Temperature must not be too cold or too hot. 3.There must be enough moisture so that the embryo does not dry out. 4.Embryo must be protected from predators and items in the environment that can potentially harm it.

External Fertilization  In external fertilization, sperm and egg join outside of the body.  Advantages: Very little energy required to mate. Large numbers of offspring produced. Offspring can be spread widely in the environment (ie. less competition between each other and parents).  Disadvantages: Many gametes will not survive. Many eggs will not be fertilized. Offspring are often not protected by parents, so many of them die.

Internal Fertilization  In internal fertilization, sperm and egg join inside the parents and the embryo is nourished inside the mother.  Advantages: Embryo is protected from predators. Offspring more likely to survive due to protection.  Disadvantages: More energy required to find a mate. Fewer zygotes produced, resulting in less offspring. More energy required to raise and care for offspring.

Pollination  Most plants transfer male gametes as pollen.  Pollen can be carried by wind or by other organisms (eg. bees).

Embryonic Development  Embryonic development is the early development of an organism (eg. the first 2 months in humans).  The stages include: A ball of cells called a morula by the end of the first week. Morula becomes hollow by the end of the second week and becomes a blastula. In the next stage, the embryo is known as a gastrula and develops three distinct layers. 1. Ectoderm (Outside) 2. Mesoderm (Middle) 3. Endoderm (Inside)

Embryonic Development

Fetal Development  The cell layers now differentiate into the organs and tissues of the baby.  Fetal development is divided into three trimesters.  First Trimester (0-12 weeks) Organ systems and bones begin to form.  Second Trimester (12-24 weeks) Rapid growth and movement begin.  Third Trimester (24+ weeks) Continued growth, especially of the brain. Fat begins to deposit at 32 weeks to keep the baby warm at birth.

Advantages and Disadvantages of Sexual Reproduction