4 Reproduction of Animals Why do animals reproduce

4. Reproduction of Animals Why do animals reproduce? Here is the life story of Mimi. Let us see what stages she has experienced. 1 2 Mimi was born. One-month old 5 6 Mimi gave birth. 4 3 Three-month old 7 Mimi became older. One year old Mimi finally died.

4. Reproduction of Animals Why do animals reproduce? Let us see what stages Gigi, the bird, has experienced. 1 Laying eggs 2 3 6 5 4 Become adult Growth Birth Old stage Death

4. Reproduction of Animals Why do animals reproduce? How do animals change at different stages of life？ Birth Newborn animals are small in size. Growth Animals mature. They become bigger and stronger.

4. Reproduction of Animals Why do animals reproduce? How do animals change at different stages of life？ Old age Animals become weaker and are easier to get sick. Death As the animals’ health gets worse, their body functions begin to fail and finally they die.

4. Reproduction of Animals Why do animals reproduce? How do animals make their species continue 延續 ? By reproduction. 繁衍 birth old age and growth _____ All animals experience the stages of ________, death Animals ______ reproduce to ensure their species do not extinct (絕種). ____.

4. Reproduction of Animals What similar characteristics特徵do the kitten and its mother have? The kitten looks almost the same as its mother. E. g. Both of them have whiskers鬚 and paws. 爪

4. Reproduction of Animals Do other animals have their parents’ characteristics? Yes Red-crowned crane丹頂鶴 and its young

4. Reproduction of Animals Do other animals have their parents’ characteristics? Yes A woman and her child

4. Reproduction of Animals If animals cannot pass on their characteristics to their offsprings, 後代 what will happen? The characteristics enable 確保animals to survive in their living environment. If their offsprings do not have such characteristics, it is hard for them to survive and their species will become extinct eventually. Animals can / cannot pass on their characteristics to their offsprings.

4. Reproduction of Animals How do animals reproduce? Viviparous animals (胎生動物) Sperm ovum testis 睪丸 ovary 卵巢 Mature sex organs produce sperms精子 and ova卵子. After mating交配, the sperm combines with the ovum to form a fertilised egg. 受精卵 The fertilised egg develops into an embryo胎兒in the mother’s womb. 子宮

4. Reproduction of Animals How do animals reproduce? The foetus 胎兒gets nutrients 營養from its mother. When the foetus is fully developed, the mother gives birth to the baby.

4. Reproduction of Animals How do animals reproduce? What is child of viviparous animal 胎生動物feed on? Its mother’s milk. 母乳 List three examples of viviparous animals. Cats, dogs, sheep etc. The embryo胚胎 of viviparous animal develops inside / outside the mother’s body. The mother gives birth to the young.

4. Reproduction of Animals How do animals reproduce? Oviparous animals (卵生動物) Ovary Testicle A cock 公雞 mates with a hen. The sperm of the cock combines with the hen’s ovum. The hen lays fertilised eggs. 產下受精卵

4. Reproduction of Animals How do animals reproduce? The chicken hatches out. 出生 The embryo胚胎 gets nutrients營養 from the egg. The embryo grows into a chicken 小雞

4. Reproduction of Animals Can you list more oviparous animals 卵生動物 ? Butterfly 蝴蝶 Fish 魚

4. Reproduction of Animals Can you list more oviparous animals 卵生動物 ? Snake 蛇 The fertilised egg of oviparous animal develops inside / outside the mother’s body.

4. Reproduction of Animals Changing in form 形態 Growth of moths 蛾的生長過程 Fertilised eggs Mating After mating, the male’s sperm combines with the female’s ovum to form a fertilised egg. Adult 成蟲 Larva 幼蟲 Pupa 蛹 There are 4 stages in the life cycle of a moth. The form has completely changed. This is called “complete metamorphosis”. 完全變態

4. Reproduction of Animals Changing in form Growth of Frogs 蛙的生長過程 Tadpole 蝌蚪 Mating During mating, the male frog sits on the female’s back. The female frog releases ova into the water, and the male frog releases sperms. The sperms and the eggs combine in the water. Fertilised eggs 受精卵 Tadpoles do not have legs but they have tails.

4. Reproduction of Animals Front legs are formed 長出前腳 Hind legs are formed 長出後腳 Adult 蛙 Some animals go through big changes when growing up.

4. Reproduction of Animals The life cycle of a mosquito

4. Reproduction of Animals

4. Reproduction of Animals The life cycle of a grasshopper

4. Reproduction of Animals The life cycle of a cockroach

4. Reproduction of Animals Complete metamorphosis 完全變態 Incomplete metamorphosis 不完全變態