The Life Cycles of Animals

Transcription

1 Chapter The Life Cycles of Animals Hey, look at the eggs in this nest! Some baby birds have hatched! All baby frogs have tails. The tail disappears as the frog becomes an adult. Baby frogs look quite different from their parents! Mom, look! A frog with a tail. How strange! Baby animals grow into adults. Adult animals have young. Why and how do animals reproduce? Did you know that the young of some animals do not look like their parents?

2 Biology What s In This Chapter? Reproduction are a result of can have Life cycles of animals can have Three stages Four stages What Will I Learn? 2 I will:. Know why and how animals reproduce. 2. Understand that plants and animals have different life cycles. 3. Observe and compare the life cycles of different animals. 4. Know that the characteristics of parents are passed down to their young.

3 How Do Animals Reproduce? The Life Cycles of Animals Chapter All living things will grow old and die eventually. Living things reproduce to ensure the continuity of their own kind. Animals reproduce by laying eggs or giving birth to young alive. Birds, reptiles, amphibians, insects and most fish reproduce by laying eggs. The young develops in the egg until it is ready to be hatched. Cross Link! Recall what you have learnt about how different groups of animals reproduce in Grade 3 Chapter 2: Sorting Living Things. Egg Egg Snakes and frogs lay eggs. Most mammals, such as humans, give birth to their young alive. Baby sheep Baby seal Sheep and seals give birth to their young alive. 3

4 Biology Ama ing Facts! Rabbits can give birth to nearly 00 babies a year! Rabbits have many young to ensure that at least some young will survive to become adults. In this way, there are always adults to reproduce so that their kind would not die out. Kit Newborn rabbits are called kits. The kits only open their eyes after about 0 days. Although female mammals do not lay eggs, they produce eggs too. The eggs remain inside their bodies. The egg develops into a young in the female s body until it is ready to be born. The young grows up and can then reproduce as well. A life cycle is made up of all the stages of an animal s life. These stages include the animal entering the world, undergoing changes and growth, as well as reproduction. Different animals go through different stages of development in their life cycles. Some animals, such as reptiles, birds, amphibians and some insects and fish, go through a three-stage life cycle. Other animals, such as some insects, go through a four-stage life cycle. Discover More! The life cycles of plants start from seeds or spores, not eggs. The life cycles of plants are different from the life cycles of animals. You will find out more about the life cycle of plants in Grade 5 Chapter : The Life Cycle of Plants. Seed >> Workbook Activity Activity : Ways of Reproduction A plant growing from a seed 4

5 What Are the Life Cycles of Some Animals? The Life Cycles of Animals Chapter Life cycles with three stages Some animals, such as chickens, cockroaches and frogs, have three stages in their life cycles. The three stages are the egg, the young and the adult. The young of some of these animals look different from the adults. Egg During the egg stage, the chick develops inside the egg. The eggshell protects the developing chick. The egg yolk provides the developing chick with food. Life cycle of a chicken Young The chick hatches after about three weeks. The chick looks like its parent. The chick grows to become a chicken. Inside an egg Developing chick Egg yolk Adult A hen (adult female chicken) usually lays one egg each day. Discover More! Newborn chicks have a hard lump on their beaks, called an egg tooth. The chick uses its egg tooth to break the shell of its egg. The egg tooth usually falls off within a day after the chick hatches. Watch a video of a chick using its egg tooth to break its shell at Internet Link.. Egg tooth 5

6 Biology Egg The eggs are stored in an egg case in the parent s body until the parent finds a suitable place for its young to hatch. Life cycle of a cockroach Egg case Adult The adult has a pair of wings that allows it to fly. An adult female cockroach can lay up to 50 eggs at a time. The eggs are laid in an egg case. Young The young is called a nymph. The nymph looks like the adult, except that it has no wings and is smaller in size. It moults a few times. That is, the nymph sheds its old skin so that its body can grow bigger. The nymph grows to become an adult cockroach. 6 A grasshopper The life cycle of a grasshopper is similar to the life cycle of a cockroach.

7 Egg Each egg hatches into a little tadpole. Life cycle of a frog The Life Cycles of Animals Chapter Young The tadpole looks very different from the adult. It can only live in water. The tadpole undergoes metamorphosis, a great change of appearance. As the tadpole develops into an adult, its back legs appear first, followed by its front legs. The tail also shrinks. Adult Frogs can live on land and in water. An adult female frog lays a few hundred eggs at a time in the water. Back and front legs appearing Shrinking tail Developing tadpole Ama ing Facts! As the body of a tadpole changes, so does its diet! Adult frogs have a very different diet from their young. Most tadpoles feed on water plants. Some can also feed on tiny living things in the water. Frogs feed on insects. Housefly Frogs eat insects such as flies. 7

8 Biology Life cycles with four stages Some animals, such as mealworm beetles, butterflies and mosquitoes, have four stages in their life cycles. The four stages are the egg, the larva (plural: larvae), the pupa (plural: pupae) and the adult. The young of these animals look different from the adults. They undergo metamorphosis. Life cycle of a mealworm beetle Egg The eggs are tiny and white or cream in colour. Larva The larva is called a mealworm. It moults many times as it grows. Adult The adult emerges from the pupa as a mealworm beetle. It will stay still as its wings unfold and dry. The female mealworm beetle is now ready to make and lay eggs. Pupa The larva becomes a pupa. The pupa does not feed. The pupa undergoes metamorphosis. >> Workbook Activity Activity 2: My Mealworm Pet! 8

9 Egg The female butterfly lays tiny eggs on the leaves and stems of plants. Life cycle of a butterfly Egg The Life Cycles of Animals Larva The egg hatches into a larva called a caterpillar. The caterpillar eats many leaves and grows quickly. It moults a few times. Chapter Adult The adult butterfly emerges from its cocoon. The female adult butterfly lays 0 00 eggs at a time. Ama ing Facts! Cocoon The life cycle of parasitic wasps depends on other animals such as caterpillars. A female parasitic wasp lays its eggs inside a caterpillar. When the wasp larvae hatch, they chew through the caterpillar s skin from the inside. Then, they spin cocoons around themselves as they become pupae. The caterpillar will carry the pupae until they emerge as adult wasps. Learn more about parasitic wasps at Internet Link.3. Caterpillar Pupae A caterpillar carrying many pupae on it Pupa The larva builds a cocoon around itself. A cocoon is a casing to protect the pupa. The pupa does not feed or move. The pupa undergoes metamorphosis inside the cocoon. Discover More! Watch the movie and try out the interactive games at Internet Link.2 to learn more about the life cycles of frogs, butterflies and birds. Next, do an Internet search to find out more about the life cycle of a snake. Find out: How many stages are there in the life cycle of a snake? Does the young of a snake undergo moulting? How is the young of a snake different from its parent? 9

10 Biology Life cycle of a mosquito Egg The eggs are laid in a cluster on the surface of still water. Breathing tube Larva The larva is called a wriggler. It can only live in water. It breathes air from the water surface through a breathing tube. The wriggler moults a few times. Adult When the adult mosquito emerges, it spreads out its wings to dry them. A female adult mosquito lays up to a few hundred eggs at a time in the water. Pupa The pupa lives in the water. It is comma-shaped. The pupa does not feed, but it can dive below the water surface to escape danger. It undergoes metamorphosis. >> Workbook Activity Activity 3: Complete My Life Cycle! Activity 4: Animal Life Cycles Discover More! Go to Internet Link.4 to find out more about the life cycle of a mosquito. Adult mosquitoes have different diets from their young. Female adult mosquitoes suck blood, while male adult mosquitoes feed on plant juices. What do wrigglers feed on? Do an Internet search to find out. Like mosquitoes, bedbugs are pests that affect humans. Do an Internet search to find out more about their life cycle and ways to get rid of them. 0

11 Experimen Tim e! t The Life Cycles of Animals Observing, Comparing, Inferring Chapter Let s observe how the young of a frog changes in appearance as it grows into an adult. Ask a parent to try this with you. Materials: Tadpoles Large plastic container Small rocks or gravel Large rock or piece of wood Aquatic plants (eg hydrilla) Dechlorinated water Fish flakes Frog Tadpole Step Put a large rock or piece of wood in the container. Cover the bottom with small rocks or gravel. Fill the container with dechlorinated water (you can use tap water that has been left in the Sun for a few days). The large rock or piece of wood should be only partly submerged. Plant a few aquatic plants. Step 2 Put a few tadpoles into the container. Feed the tadpoles with fish flakes. Step 3 Observe how the appearance of the tadpoles changes over a few weeks. (Start feeding the tadpoles with small insects once they start developing legs.) State how the tadpoles appearance has changed. Build Your Skills! Observing, Comparing Compare the life cycles of a chicken and a butterfly. Complete the table below. How are they similar or different? Chicken Butterfly Does its life cycle start from an egg? How many stages are there in its life cycle? Does the young look like its parent? Does the young undergo moulting?

12 Biology Why Do Young Grow Up to Look Like Their Parents? Some young look like their parents. A cockroach and its young I look just like my parent! I don t look like my parent at all! Other young look different from their parents. A frog and its young The young of all animals will eventually grow up to look like their parents. Why do you think this is so? The answer is in the genes! Most animals have two parents. Genes are passed down from parents to their young. Genes contain information that determines the physical characteristics or traits that we have. The passing down of traits is known as heredity. 2

13 Here are some traits that can be passed down for humans. The Life Cycles of Animals Chapter Hair colour Eye colour Nose shape Skin color This mother and her daughter both have black hair, black eyes, fair skin and the same nose shape. Double eyelid Dimple This father and his daughter both have dimples and double eyelids. Do you have double eyelids? What about your friends? Not everybody has double eyelids. Only those who have inherited this trait have double eyelids. 3

14 Biology Just like humans, animals inherit traits from their parents. The young of the ladybird have red body coverings with black spots, just like their parents. Large ears Black spots on red body covering Trunks The young of the elephant has a trunk and large ears, just like its parent. Spines Young Hedgehog The young of the hedgehog has spines on its back, just like its parent. 4 Do you notice that you do not look exactly like either of your parents? This is because we inherit genes from both our parents. For example, if only one of your parents has dimples, you may or may not have dimples. It all depends on whose set of genes you inherit for a particular trait. We inherit a mixture of traits from both our parents.

15 The Life Cycles of Animals Chapter Discover More! Some diseases can be passed down from parents to their young. One example is haemophilia. For people with this disease, their blood cannot clot easily. Thus, when people with haemophilia are injured, it is hard for them to stop bleeding. Some traits are not inherited from our parents, such as the length of our hair, length of our nails and scars. Do an Internet search to find out other traits that are not inherited from our parents. Someone with haemophilia will bleed for a long time from injuries. Ama ing Facts! Our fingerprints and iris patterns are unique. The basic pattern of our fingerprints and colour of our eyes are determined by our genes. However, the pattern of our irises and the fine details of our fingerprints are formed randomly when we are developing in our mothers bodies. This is why fingerprint scanners and iris scanners are able to identify people based on their fingerprints and iris patterns! Fingerprint Compare your fingerprint with a friend s. How are they different? Iris The coloured part of your eye is called the iris. The iris can be made up of more than one colour. >> Workbook Activity Activity 5: My Family Tree Activity 6: How Similar Am I to My Parents? Talk It Out Can you remember what these new words mean? Pair up with a friend and test each other on these words! cocoon gene heredity larva life cycle metamorphosis moult nymph pupa trait 5

16 Biology Map It Out Animals can reproduce by laying eggs or giving birth to young alive. Living things reproduce to ensure the continuity of their own kind. Traits are passed down from parents to their young through genes. Reproduction Some young look like their parents, but some young look different from their parents. All young will grow into adults that look like their parents. such as Animals that give birth to young alive Most mammals can have are a result of Life cycles of animals can have Three stages can have which are Egg, larva, pupa and adult Four stages such as in Mealworm beetles, butterflies and mosquitoes like Humans, sheep and sealions which are Egg, young and adult such as in Chickens, cockroaches and frogs 6

17 Work It Out The Life Cycles of Animals Chapter Let s work out the following question together! Study the graph below. It shows how long each stage in the life cycle of Insect X lasts. Observing, Inferring Days Duration of the stages in the life cycle of Insect X Egg Larva Pupa Adult Stages a. How many stages are there in the life cycle of Insect X? [ mark] Four stages b. How many days would Insect X take to hatch from the egg? [ mark] Four days c. What does each bar represent? [ mark] Each bar represents the duration of each stage of Insect X s life cycle. d. How many days would Insect X take to become an adult after the egg is hatched? [ mark] 24 days What stages does the young of Insect X have to undergo before it becomes an adult? 7

18 Biology Work Environmental literacy Making use of the silkworm s life cycle You have learnt in Grade 3 that silk comes from silkworms. But why do silkworms make silk in the first place? The silkworm is actually a caterpillar, not a worm. Like butterfly larva, silkworms build cocoons to protect themselves during the pupa stage. Inside the cocoon, the pupa transforms into an adult moth. Silkworms Silkworm spinning its cocoon Silk is the material that silkworms use to make their cocoons. Using the silk excreted from their salivary glands, each silkworm spins a single thread of silk around and around itself! The silk will eventually harden into a cocoon. Silkworm moth To get silk, silkworm farmers first boil the cocoons to kill the pupae inside. If the pupae were allowed to grow and emerge as adults from the cocoons, they would break the cocoons in the process. Soaking the cocoons in water also softens them and loosens the threads. The silk threads can now be removed for spinning into silk. Boiling cocoons Scientists are now engineering silkworms in laboratories to produce silk with enhanced qualities. The silkworms are given some spider proteins, which allows them to produce stronger, tougher and more elastic silk. Gathering silk threads from cocoons This improved silk could be used to make medical sutures, artificial ligaments and even parachutes! Who would have thought the humble silkworm had such a useful life cycle? 8