42 L5-Animal life cycles

Oxford Read and Discover level 5 Animal Life Cycles by Rachel Bladon

牛津阅读和发现第5级动物生命周期由雷切尔·布莱登

Introduction Animals grow and change during their life. To produce young, some animals have babies, and others lay eggs. These young animals then grow up and produce young, too. This journey from being born to producing young is called a life cycle. Animal life cycles are amazing. How do male birds find a mate? How big is a baby kangaroo when it's born? How does a crocodile carry her babies? What does a tadpole grow into? Discover! Now read and discover more about some amazing animal life cycles!

动物一生都在成长和变化。 为了生儿育女，有些动物要生孩子，有些动物要下蛋。 然后这些幼小的动物长大并生育后代。 从出生到生育后代的这段旅程被称为生命周期。 动物的生命周期是惊人的。 雄鸟是如何找到配偶的? 小袋鼠出生时有多大? 鳄鱼是怎么带孩子的? 蝌蚪长成了什么? 发现!现在阅读和发现更多关于一些惊人的动物生命周期!

Chapter 1 Life Cycles There are millions of different species of animal in the world. Some animals, like the blue whale, are very big. Others are so small that we almost can't see them. These animals all have very different life cycles. Animal Groups Scientists put animals into groups. The animals in each group are the same in many ways, and they often have very similar life cycles. The two biggest animal groups are invertebrates and vertebrates. Invertebrates are animals that have no backbone. More than 95% of the animal species in the world are invertebrates, and most of them are very small. There are many different groups of invertebrates. The biggest group is called arthropods. Insects, spiders, and animals like crabs that have a hard shell, are all arthropods. Animals that have a backbone are called vertebrates. Only a few percent of the animals in the world are vertebrates, and most of them are much bigger than invertebrates. Because of this, we see vertebrates more often than invertebrates. Scientists put vertebrates into five big groups they are called fish, amphibians, reptiles, birds, and mammals.

世界上有数百万种不同的动物。 有些动物，比如蓝鲸，非常大。 还有一些很小，我们几乎看不见它们。 这些动物都有非常不同的生命周期。 科学家把动物分成不同的组。 每一组动物在很多方面都是相同的，它们的生命周期也非常相似。 两个最大的动物群体是无脊椎动物和脊椎动物。 无脊椎动物是没有脊椎的动物。 世界上95%以上的动物都是无脊椎动物，而且大多数都很小。 无脊椎动物有许多不同的类群。 最大的一类是节肢动物。 昆虫、蜘蛛和螃蟹等有硬壳的动物都是节肢动物。 有脊骨的动物叫做脊椎动物。 世界上只有百分之几的动物是脊椎动物，而且大多数动物都比无脊椎动物大得多。 正因为如此，我们看到脊椎动物比无脊椎动物更多。 科学家把脊椎动物分为五大类，分别是鱼类、两栖动物、爬行动物、鸟类和哺乳动物。

Staying Alive All animals need to find food to stay alive. Some animals are carnivores. This means that they eat other animals. Herbivores eat plants, and omnivores eat plants and animals. There are many dangers for animals. They have to keep safe from predators— animals that hunt and eat other animals. People hunt birds and other animals. People also cut down trees and build houses and roads on land. When they do this, animals lose their homes and their food. Many animals also become sick or die because of pollution of the land, oceans, rivers, and air. Life is very dangerous for animals. Many animals die before they are old enough to produce young. Discover! Different animals live for different amounts of time. A Galapagos tortoise can live for 150 years, but an adult mayfly usually lives for just a few hours. Breeding Most species of animal have males and females. Males produce sperm, and females produce eggs. Baby animals are made when sperm from the male joins together with an egg from the female. This is called fertilization. Some animals give birth to baby animals. Other animals, like reptiles and birds, lay eggs. Their babies hatch— they break the egg open and come out. Most reptiles and birds care for their babies. Most insects and fish do not care for their eggs or their babies. All mammals care for their babies and feed them milk. Some big mammals stay with their babies for many years.

所有的动物都需要寻找食物来维持生命。 有些动物是食肉动物。 这意味着它们吃其他动物。 食草动物吃植物，杂食动物吃植物和动物。 对动物来说有很多危险。 它们必须远离捕食者——捕食其他动物的动物。 人们捕猎鸟类和其他动物。 人们还砍伐树木，在陆地上建造房屋和道路。 当他们这样做的时候，动物就会失去家园和食物。 许多动物也因为土地、海洋、河流和空气的污染而生病或死亡。 生活对动物来说是非常危险的。 许多动物还没到能生育后代的年龄就死了。 发现!不同的动物寿命不同。 一只加拉帕戈斯龟可以活150年，但一只成年蜉蝣通常只能活几个小时。 大多数动物都有雄性和雌性。 雄性产生精子，雌性产生卵子。 小动物是由雄性的精子和雌性的卵子结合而成的。 这叫做受精。 有些动物生小动物。 其他动物，如爬行动物和鸟类，也会产卵。 他们的孩子孵化-他们打破鸡蛋和出来。 大多数爬行动物和鸟类都会照顾它们的宝宝。 大多数昆虫和鱼类不关心它们的卵或幼崽。 所有哺乳动物都照顾自己的孩子，给他们喂奶。 一些大型哺乳动物会和它们的孩子呆在一起很多年。

Chapter 2 Insects Insects are small animals like butterflies, beetles, flies, bees, and ants. There are more than a million species of insect in the world. Many insects change in amazing ways during their life. Larvae and Nymphs Almost all insects start their life in an egg. The young insect grows inside the egg and then it hatches. Some baby insects, like bees, look very different from their parents. These baby insects are called larvae. Other baby insects, like locusts, look more like their parents. These baby insects are called nymphs. Larvae and nymphs are very small when they hatch. Growing Up A young insect eats a lot of food and grows very quickly. It has a hard cover, called an exoskeleton. When the exoskeleton is too small for the young insect, it breaks open and comes off. A new exoskeleton grows under the old one. This is called molting. Some insects grow wings that get bigger every time they molt. After the insect molts for the last time, it becomes an adult that can fly and produce young. This is called incomplete metamorphosis. Most insects change by complete metamorphosis. When the larva is ready to change into an adult, its exoskeleton comes off. Under the exoskeleton there's a pupa— it's like a closed case. Inside the pupa, an amazing change happens. The larva changes into an adult that looks completely different!

昆虫是一种小动物，像蝴蝶、甲虫、苍蝇、蜜蜂和蚂蚁。 世界上有一百多万种昆虫。 许多昆虫在其一生中以惊人的方式发生变化。 几乎所有的昆虫都是从卵中开始它们的生命。 小昆虫在卵内生长，然后孵化。 有些昆虫宝宝，比如蜜蜂，看起来和它们的父母很不一样。 这些小昆虫被称为幼虫。 其他的小昆虫，比如蝗虫，看起来更像它们的父母。 这些小昆虫被称为若虫。 幼虫和若虫孵化时非常小。 小昆虫吃很多食物，长得很快。 它有一个坚硬的外壳，叫做外骨骼。 当外骨骼对幼小的昆虫来说太小时，它就会破裂并脱落。 旧外骨骼下面长出了新的外骨骼。 这叫做蜕皮。有些昆虫的翅膀每次蜕皮都会变大。 在昆虫最后一次蜕皮后，它就变成了可以飞行和生育后代的成虫。 这被称为不完全变态。 大多数昆虫是通过完全变态来改变的。 当幼虫准备变成成虫时，它的外骨骼会脱落。 在外骨骼下面有一个蛹——它就像一个封闭的盒子。 蛹内部发生了惊人的变化。 幼虫变成了看起来完全不同的成虫!