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
1.
2.
3.
4.
5.
6.
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