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2.2 Sexual Reproduction in Animals

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1 2.2 Sexual Reproduction in Animals
Sperm (23) zygote (46) embryo (46)  Egg (23) adult An embryo is a fertilized egg during early development.

2 Successful sexual reproduction requires:
both male and female gametes must arrive in the same place at the same time for fertilization. The zygote must receive adequate food, moisture, warmth, and protection to develop.

3 Mating in the Animal Kingdom
mating is timed for offspring to be born at times with the best chance for survival elk, deer, etc. once a year grunion mate at full or new moon. Honeybee’s mate once in a lifetime Desert Toads only after a rainfall.

4 Fertilization In a warm, moist environment ONLY for sperm to swim, and for fertilization to result. May be INTERNAL or EXTERNAL.

5 External Fertilization
Most water-dwelling animals. Non-moving animals - (ex. Anemones) release large numbers of eggs and sperm into water. Eggs and sperm meet by chance. Zygotes form larvae which swim and feed themselves. Swimming animals – (fish) Females lay eggs in suitable spot. Males release sperm onto the egg cluster. This is called spawning. Sockeye Salmon Video -- National Geographic

6 Internal Fertilization
Animals on land (& aquatic mammals) use this method. Sperm is transferred directly to the female.

7 Reptiles Male transfers sperm into female’s cloaca (where urinary, reproductive and digestive ducts lead). Eggs have enough food to feed the embryo until hatching. No care for young.

8 Sperm entering the egg

9 Birds Males and females have a cloaca.
Close body contact allows for sperm to transfer. Parents shelter, protect, and feed the young.

10 Insects Internal fertilization Incomplete Metamorphosis
Eggs hatch into nymphs (no wings) nymph sheds exoskeleton for growth (moulting) nymph develops into winged adult

11 Complete metamorphosis
Offspring look completely different Cacoon/crysallis Egg larva caterpillar moth pupa or butterfly (cocoon)


13 The cost of reproduction
The male empid fly offers his larger partner the gift of a smaller insect to avoid being eaten after mating. The male praying mantis shows up empty handed and the larger female often eats the smaller male after mating (starting with the head).

14 Mammals Internal fertilization
embryo develops inside mother for protection and nourishment (Placenta and umbilical cord) mother produces milk and parents care for young.

15 Marsupials Kangaroos, Opossums give birth very early in development
Young must crawl into pouch and attach to a nipple for food for several months while they develop.

16 Hermaphrodites Have both male and female reproductive organs on each individual. Includes flatworms (planaria), and earthworms. Each hermaphrodite injects sperm into the other’s reproductive pore.

17 Assignment HowStuffWorks Videos "Fertilization and
Sexual Reproduction: Part I" Questions on page 59 # 1 – 7 Sexual Reproduction Handout (Manitoba Fisheries) “Fish Net” Scavenger Hunt – Group Activity

18 Page The fundamental cycle that allows all animals to reproduce sexually is: Meiosis produces gametes Fertilization (male gamete combines with female gamete) Zygote produced embryo Embryo develops through mitosis into mature offspring – cycle repeats

19 Sexual Reproduction Questions
Fertilization External fertilization takes place outside the organisms body Internal fertilization sperm are transported into the oviducts of the female Amphibians and most fish use external fertilization

20 The disadvantages of external fertilization are:
Only one parent to care for offspring Parent usually disappears – no care for eggs Less genetic variability in organisms of same species Internal fertilization is necessary because there is no aquatic environment and fewer eggs are produced (therefore more parental care is provided)

21 The purpose of the amniotic egg is to provide a “life raft” for water animals
The chicken’s egg white provides an artificial pond for the developing embryo Amniotic egg must be fertilized internally so that the sperm can enter the egg before the shell forms A placental mammal is an animal that keeps the embryo inside their bodies in a specialized area called the womb/uterus.

22 Care for young because they have fewer to ensure survival.
All embryos develop in a “pond.” The embryo develops in a bag filled with amniotic fluid – this breaks just before birth.

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