(c) McGraw Hill Ryerson 2007 6.2 Sexual Reproduction (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Sexual reproduction brings non-identical gametes together to form a new organism. Advantage: Offspring are genetically different from parents so may be better suited to survive new diseases, environmental changes, or threats. (c) McGraw Hill Ryerson 2007 See pages 204 - 206

(c) McGraw Hill Ryerson 2007 Three stages: Mating - process by which gametes are bought together at same place & same time Fertilization - process by which egg & sperm join to form a new organism Development - process by which an organism develops from zygote to embryo to fetus (c) McGraw Hill Ryerson 2007

Methods of Fertilization Two types: External or Internal Fertilization Note: To produce a successfully developing embryo, certain conditions must be met: Embryo must have enough nutrients. Temperature must not be too cold or too hot. There must be enough moisture so the embryo does not dry out. Embryo must be protected from predators & environmental elements that could potentially harm it. See page 207

External Fertilization In external fertilization, sperm & egg join outside parents Advantages Very little energy required to mate Large numbers of offspring produced Offspring can be spread widely in the environment so less competition between each other & parents Disadvantages Many gametes will not survive Many eggs will not be fertilized Must be in a moist/wet environment Offspring are often not protected by parents, so many of them die Frog Eggs - GNU Free Doc Photo See pages 208 - 209 (c) McGraw Hill Ryerson 2007

Internal Fertilization In internal fertilization, sperm and egg join inside parents & embryo is nourished inside mother Advantages Embryo is protected Can reproduce in dry environments Offspring more likely to survive, as many species will protect their them while they mature Disadvantages Much more energy required to find mate Fewer zygotes produced, resulting in less offspring More energy required to raise and care for offspring (c) McGraw Hill Ryerson 2007 See pages 210 - 211

(c) McGraw Hill Ryerson 2007 Pollination See pages 212 - 214 Sexual reproduction in many types of plant Internal fertilization pollen (male gametes) from the male reproductive part is transferred to the female reproductive part Pollen can be carried by wind, water, or organisms. (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 In Flowering Plants The flower contains male & female reproductive structures The stamen (male reproductive organ) produces pollen which transfers to the stigma (female reproductive organ) A pollen tube forms to deliver the sperm cells to egg cells Egg cells are contained within ovules within an ovary Zygote develops into an embryo which is nourished by food stored within the seed (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 In Conifers Cones contain male & female reproductive structures Pollen from male cones is carried by wind to female cones (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Stages of Development Stage 1 –Germinal Period End of the first week - ball of cells called morula By end of second week it is a hollow ball called a blastula Cells at this stage are stem cells, & have the ability to develop into any kind of cell (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 In humans, first 12-14 days From fertilization (zygote) to morula to blastula implantation (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

Stage 2 – Embryotic Period Embryonic development = early development of an organism in humans, implantation to 8 weeks “critical stage” Vulnerable to outside influences Probability of structural defects are at their greatest 18 days See pages 216 - 217 (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 In this stage, a gastrula forms 3 germ layers: ectoderm (skin, nerves) mesoderm (muscles, bones) endoderm (lungs, liver, digestive system lining) The cell layers now differentiate into the organs and tissues of a baby 3rd week: head, blood vessels, brain 4th week: heart begins to beat 5-8 weeks: hands, feet, fingers, & toes develop; kidney & liver function, bones (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Stage 3 – Fetal Period In humans, 9 weeks to birth Continued development Weight gain Facial features Active movement Rapid rate of growth Brain development See pages 218 - 219 (c) McGraw Hill Ryerson 2007

The cell layers now differentiate into the organs & tissues of a baby This is divided into 3 trimesters: First Trimester (0-12 weeks) Organ systems begin to develop & form. Bone cells form. Second Trimester (12-24 weeks) Rapid growth from 12-16 weeks. Third Trimester (24+ weeks) Continued growth, especially of brain. Fat begins to deposit at 32 weeks to keep baby warm at birth.

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Take the Section 6.2 Quiz (c) McGraw Hill Ryerson 2007