1. Sexual Reproduction
6.2

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

3. 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

4. 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

5. 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)

6. 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

7. 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

8. External Fertilization

9. 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

10. 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

11. Life cycle of Animals

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

13. 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

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

15. Embryonic Development

16. 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

17. 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

18. Gastrula
Video

19. 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 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

20. Sexual Reproduction: Advantages and Disadvantages
See page 220