Sexual Reproduction 6.2

Objectives By the end of the lesson you should be able to: Describe the 4 conditions necessary for embryonic development Compare and contrast internal vs external fertilization Describe the process of plant pollination

Sexual Reproduction Overview Requires a male gamete (sperm) to fertilize the female gamete (egg) The first cell that forms is called a zygote The zygote grows (by mitosis) into an embryo

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

Embryonic Development Requirements Enough nutrients Temperature must be warm enough so proteins and enzymes will function properly Sufficient moisture so embryo doesn’t dry out Protected from predators and environmental factors (ex. UV radiation)

Types of Fertilization External: egg and sperm meet outside the bodies of the parents Internal: egg and sperm meet inside the body of the female

External Fertilization Common in marine/aquatic animals (i.e. salmon, sea urchins) Advantages: Very little energy required Large number of offspring are produced Little competition for food because so spread out Problems: Not all eggs get fertilized Environmental hazards (ex. Storms) Eggs are eaten by predators Few survive to adulthood

External Fertilization

Internal Fertilization Common in higher animals (ex. Whales, humans) 100 million sperm can be deposited, only 100 will reach the egg and only 1 will fertilize it After the egg has been fertilized it changes its electric charge which prevents any other sperm from entering the egg

Internal Fertilization Advantages: Embryo is protected from predators inside the womb Offspring are typically protected for months or years after birth Disadvantages: Requires more energy Produce fewer offspring Requires more time

Life cycle of Animals

Pollination Pollination is the transfer of the male gametes (pollen) to the female gametes (ova)

Pollination Process Anther produces pollen Pollen lands on stigma Pollen tube grows down to ovule Sperm is delivered to egg Fertilization occurs Zygote grows into embryo which is protected and nourished by seed

Pollen Transport Pollinators are attracted by coloured petals (ex. Bees, butterflies, bats) Wind Fruit Seed Transport Birds and Animals

Embryonic Development

Embryonic Development Embryonic development is the early development of an organism - in humans, it is the first two months after fertilization Stages 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, and have the ability to develop into any kind of cell See pages 216 - 217

Embryonic Development 3-4 weeks embryo is known as a gastrula develops 3layers: ectoderm (skin, nerves), mesoderm (muscles, bones), and endoderm (lungs, liver, digestive system lining) “more blasting gas” See pages 216 - 217

Gastrula Video

Fetal Development The cell layers now differentiate into the organs and tissues of a baby - this is divided into 3 trimesters. First Trimester (0-12 weeks) Organ systems begin to develop and 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. See pages 218 - 219

Sexual Reproduction: Advantages and Disadvantages See page 220