When we were at the pond, I found some frogspawn. Why are the frog eggs soft but the chicken eggs are hard? I thought eggs had hard shells that can crack and break?
Our puppies looked similar to the mother dog but the tadpoles I found in the pond did not look like frogs at all. I wonder why?
Our puppies are a year old now and look very similar to the adult dogs - will they still change a lot? When will I know that they are adult dogs?
This term, we studied many of the different plants and animals on Earth and their interdependence in different habitats. In this section we are going to finish our study of plants and animals, and look specifically at their life cycles.
Introducing this topic
Play the song, Circle of Life, from the Disney classic, The Lion King. Discuss at length the words and meaning of this song as it pertains to our interdependence on each other and the circle of life that we are part of. It is available on: http://www.youtube.com/watch?v=vX07j9SDFcc.
This topic LIFE CYCLES has a very strong emphasis on the growth and development of plants and animals, to show that all living things need to grow and develop which is a theme carried through from Gr. 4. This textbook treats these topics therefore as a focus on GROWTH and DEVELOPMENT and not on individual plants and animals per se. Teachers are encouraged to follow a similar route to develop the underlying concepts and to draw learners' attention to the similarities between living organisms that grow and develop.
Teachers are encouraged to display as many different reading materials, including books, posters, print-outs, etc. showing animal and plant life cycles, and to refer to these often during the course of this section.
Growth and development
Introducing this topic
Show learners a plant and the seed that it has grown from - if necessary buy a seedling from a nursery or grow your own seeds a few weeks before this lesson.
Ask learners to describe how the seed changed from the seed-form to the plant-form and ask them to explain how the seed that seemed not to be living could come alive. (This is revision of Gr. 4 work on living and non-living things.)
Remind them that under the right conditions something that seemed non-living can come alive again - the seed needed water and heat to come alive.
Ask them whether the plant will stop growing once it has reached the present size and discuss their ideas about plant growth (a really good opportunity to assess existing knowledge of this topic.)
Plants and animals grow and develop throughout their lives
All plants and animals need to make new plants or they will become extinct (no longer exist on Earth). The adult plant or animal needs to reproduce offspring that will grow over time into a new adult that will reproduce offspring of its own. We call this a life cycle. It is a cycle because when a new plant or animal is made the cycle begins again.
A plant or animal can die anywhere in its life cycle - at birth, as a young or old plant or animal. Let's take a closer look at the life cycle of flowering plants.
When will you stop growing? Discuss this with a friend and then share your ideas with the class.
This question is meant to make learners think about growth and development in their own lives before requiring them to apply this knowledge to other plants and animals.
Plant life cycles
In flowering plants, the life cycle begins when a seed germinates. Look at the diagram showing the seed after it has germinated.
The stages of plant germination and growth.
The seed germinates when a small root (radicle) and stem start to grow out of the seed. This grows into a young plant.
A very young plant just after it has germinated and begun to grow.
The germinates, grows and develops into a seedling. In time the seedling grows and matures into a young adult plant that is bigger. The young adult plant continues to grow until it becomes a mature adult plant. The adult plant can reproduce using flowers that produce seeds. The plant reaches maturity when it makes flowers.
Look at the three different pictures below. What do you think the insects in these pictures are doing?
The flowers produce pollen. Insects carry the pollen from one flower to the next. This is called pollination.
The pollen fertilises the ovules in the flower.
The fertilised ovules now develop into seeds.
The seeds are then dispersed and start to grow in a new place.
Seeds can be dispersed in different ways.
Different methods for seed dispersal.
Why does a plant need to disperse its seeds?
Teachers are encouraged to discuss this question with the class. Point out that new plants will be in competition with the parent plant for resources like water, soil, sunlight, etc and therefore the seeds need to go far away to find their own resources. Also, the parent plant wants to ensure the survival of the species and therefore sends seeds to different places in order to minimise the risk that all the seeds will be lost if something happens to them in one location.
Look at the pictures showing ways in which seeds are dispersed. Discuss these four ways and explain how you think the seeds are adapted in each method to be the most efficient.
The seeds dispersed by animals are either tasty so that birds and squirrels eat them, such as berries and nuts, or they have burrs so that they stick to the fur of animals. Seeds which are dispersed by the wind are light and have features which enable them to "fly" in the wind, such as wings. Seeds can be dispersed by explosion when the seed pods burst open and spray the seeds out. Seeds can be dispersed by water if the seeds drop into a river for example and are carried downstream. These seeds also need to be light and must float.
When a seed lands in soil it can start to germinate. The cycle begins again.
About 5 - 6 weeks before this activity plant some cherry tomato seeds in a large container or in a sunny spot in the school garden. They grow very easily when given enough water and light and can provide the perfect example for this activity. Also, the learners can eat the cherry tomatoes that are harvested! Large tomatoes will take very long to ripen but can also work here. Remember to stake the tomato plants (for a VERY simple stake you can use any sort of stick, just stick it into the ground near the plant and tie the plant's biggest stems to this).
The life cycle of a tomato plant
MATERIALS:
Tomato plants in your classroom or in the garden
The seeds of these tomato plants
Some ripe tomatoes similar to the ones growing in your class.
Picture below of the life cycle of tomato plants
Consider halving the class / breaking into groups. One group can do the observation of the tomato plant while the other group does the drawing of the tomato with the teacher's assistance.
INSTRUCTIONS:
The life cycle of a tomato plant.
Study the life cycle of a tomato plant. List the developmental stages of a tomato plant starting at the seeds - you can use the illustration above to help you.
Carefully study the tomato fruit that is on display in your class. Do you see where the little stem is connected? Can you see any leaves around it?
Draw the tomato fruit in the space below. Remember to make a scientific drawing using the correct way of labelling that you learnt in Gr. 4.
In Grade 4, a lot of time was spent teaching learners to make scientific drawings. The teacher must go through this / revise this carefully. Perhaps make a poster and display this in class. The labeling must be done scientifically:
the drawing must have a heading (printed in pen)
labeling lines must be in pencil
labeling lines must be drawn using a ruler
labeling lines must be parallel to the top / bottom of the page
labeling lines must touch the part of the drawing being labeled
labeling lines must end the same distance from the drawing (i.e. the labels must be in a vertical line underneath each other)
labels must be printed in pen
The correct labels must be used in the correct place.
Carefully examine the tomato seeds from the seed packet. Your teacher will cut open the tomato fruit. Compare the seeds from the fresh fruit with those from the seed packet. Write this comparison in the space below.
The fresh tomato seeds looked:
The seeds from the seed packet looked:
Look at the tomato plant in your class. Find the following plant structures on the plant and describe each of these in the space next to it. Then make a sketch in the space provided of each plant structure:
Describe the plant structure
Sketch the plant structure.
Stem
Leaves
Flowers
Teachers guide only:Extension Activity - Learning about life cycles
MATERIALS:
Flower (like a petunia, for instance)
Sharp blade or knife (be very very careful with this as it might cut you!)
Magnifying glass
INSTRUCTIONS
Gently remove the green leaves at the base of the flower. You can use your fingers for this. These are the sepals which protect the flower bud.
Carefully remove the colourful petals of the flower. Also use your fingers here.
Remove all the parts that you find inside and sort them into groups. Remember to work carefully because the parts are fragile.
Carefully dissect (cut) the pistil from the sticky top stigma down to the bottom ovary.
Use a magnifying glass to see the ovule in the ovary.
In the space below, make a scientific drawing of the different flower parts that you discovered inside the flower. Remember to follow the scientific method for making scientific drawings using the correct labelling, headings and a sharp pencil.
Animal life cycles
All animals need to reproduce or they will become extinct. In this section we will learn more about the life cycles of animals.
Life cycle of a frog
The reason for doing this activity is to let learners experience the different stages in a frog's life cycle. This activity is placed here to allow teachers to demonstrate the different stages as work progresses through this section in the workbook.
MATERIALS:
aglass aquarium, a large glass or plastic container, or a 5 litre ice-cream tub
chlorine free water
water plants (if available)
some large rocks that will stick out the surface of the water
fish flakes
NB: Tadpoles are VERY sensitive to chlorine and need fresh water regularly. Change the water REGULARLY (every day or two) by pouring half of the used water out and replacing it with fresh water. Do not add tap water directly to the remaining water. Boil the tap water and let it stand for 24 hrs before adding it to the tadpoles' water. Alternatively, buy de-chlorinating tablets but even then let the replacement water stand for 24 hrs before the water change. Here is an easy step-by-step guide to keeping tadpoles: http://allaboutfrogs.org/info/tadpoles/
INSTRUCTIONS:
Prepare the habitat for the tadpoles using the materials above.
Collect a few tadpoles from a local stream in a sealable container and bring them to school.
Carefully place the tadpoles in the water habitat you prepared for them.
Change the water at least every second day.
Feed the tadpoles with fish flakes.
As a class, keep a diary of the tadpoles' growth and development over the next few weeks on large pieces of paper or something similar.
Date
Description of your observations
Sketch of your observations
Stages in an animal life cycle
Most animals like fish, reptiles, birds and mammals have a simple life cycle. We can identify different stages in such a simple life cycle:
Gestation - before birth
Growth and development
Maturation
Reproduction
The gestation stage in an animal's life is the time before the embryo (young animal) is bor Animals produce young in different ways:
Born alive: some animals grow inside the womb of the mother animal and are then born alive.
Hatched from eggs: the mother animal lays eggs and the embryo develops inside the egg before it hatches.
Hatched from eggs inside the mother animal's body and are then born alive: the embryo develops within an egg inside the mother animal's body. The eggs can hatch just before or just after birth.
Gestation - in a human the baby grows in the mother's womb and is then born. In a chicken, the mother lays an egg and the embryo develops in the egg before hatching.
After the animal is born or hatched, they grow and change.
Some animals undergo a simple change. Puppies, for example, look similar to adult dogs.
In dogs, the puppy looks similar to the adult dog.
Other animals (mostly amphibians and insects) look very different to the adult animal when they hatch. They go through very big changes in their life cycles. This change is called a metamorphosis. Look at the stages of metamorphosis of a monarch butterfly below.
AMonarch caterpillar eats and grows.
The caterpillar gets ready to make a pupa.
Inside the pupa the caterpillar is changing into a butterfly.
The adult butterfly emerges from the pupa.
Observing fruit flies reproduce
MATERIALS:
clear plastic bottle
sharp knife
ripe fruit
INSTRUCTIONS:
Cut the top part off a clear plastic bottle.
Put ripe fruit in the bottle. (Be careful - if the fruit is too watery, the flies will die.)
Put the top upside down in the bottle as if this is a funnel. look at the picture below
Setup for this activity.
Keep a diary of all that you see happening inside the bottle over the next 2 - 3 weeks. Provide a short description and a neat sketch (not a scientific drawing). Keep your daily diary in the space provided below:
Date
Description of your observations
Sketch of your observations
Fruit-flies can smell ripe fruit and come from a long distance to find it. The females lay eggs on the fruit. When the eggs of the fruit-fly hatches, little worms like larvae hatch. The larvae eats as much as it can and grows quickly. It turns into a pupa. The pupa has a hard case or chrysalis. Inside the chrysalis the pupa undergoes tremendous changes. After four days, the case breaks open and a fly with wings comes out. The activity might not work and you might not get fruit flies hatching. In that case, explain to the learners that the flies did not smell the fruit and did not come. Refer to the diagram below to continue the activity.
After keeping the fruit fly diary, carefully study the following diagram of the fruit fly's life cycle. Write a sentence or two explaining what is happening at each stage of the fruit fly's life cycle.
The fruit fly life cycle.
Label the stage:
Describe the stage:
A
B
C
D
Once a young animal matures into an adult, it is ready to produce its own offspring. Mature females produce egg cells and mature males produce sperm cells. When they mate, the male sperm cells fertilise the female egg cells. This produces an embryo and the life cycle begins all over again.
Fertilisation is when a male sperm cell enters the female egg cell.
An animal can die at any stage in its life cycle. Various things can cause death to the animal.
In your group, discuss a number of possible causes of death of animals and write them below.
Causes include: old age, illness, environmental conditions such as drought or flooding, being eaten by predators or hunted by humans, death due to human causes, like poisoning or destroying the environment or through pollution.
The Frog Life Cycle
You should have been watching and observing the tadpoles develop into frogs over the past while. This activity is to reinforce what you have observed. If you were not able to actually watch tadpoles develop in class, then just use the following activity to show how tadpoles change into frogs.
INSTRUCTIONS:
Hopefully you were able to see some tadpoles develop into frogs.
Let's revise the stages of a frog's life cycle.
Look at the life cycle of the frog in the illustration below.
Describe the various stages in the life cycle of this frog in the table below.
The frog life cycle.
Description of this stage:
Gestation stage
Larva stage
Young adult stage
Adult stage
Answers:
Description of this stage:
Gestation stage
Frog embryos develop inside the eggs and then tadpoles hatch from this.
Larva stage
The tadpole has a tail and gills; it looks like a fish; after some time it grows hind legs, front legs and the tail shrinks.
Young adult stage
The young adult doesn't have a tail anymore and the front and hind legs develop fully.
Adult stage
The frog matures and can reproduce.
All living things carry out the life process of growth and development. This is part of their life cycle.
A life cycle describes the stages and processes that take place as a plant or animals grows and develops.
A life cycle also describes how one generation of a plant or animal reproduces to make new plants or animals that will make many more generations.
Death can occur at any stage in the life cycle.
Explain what it means when we say that a plant or animal has a life cycle.
Plants and animals grow and develop throughout their lives and a life cycle describes the stages and processes that take place as a plant and animal grows and develops from embryo to mature reproducing adult.
Explain the 4 stages in the life cycle of a flowering plant - think for example of a tomato or bean plant.
seeds - germinate to form little plants - little plants grow and develop - plants mature and make flowers - flowers are pollinated and form little tomatoes - tomatoes make seeds
Plants use their brightly coloured petals and their scent to attract animals. Why do they need to attract animals?
Plants need these animals to spread their pollen and receive pollen from other flowers.
Plants pollinated by the wind are much less attractive than plants that have to attract birds and insects. Why do you think this is?
The wind does not choose which plant to pollinate and pollinates all the plants therefore the plants only have to make their pollen available to the wind to disperse.
When plants disperse their seeds by means of water, what important features do these seeds need to have?
The seeds need to be watertight.
Why do animals and plants reproduce?
If they do not reproduce they will become extinct.
Use the following words in the to complete these sentences. Write the sentences out in full:
egg-laying
umbilical cord
born alive
external
life cycle
A _____ describes how reproduction takes place and shows the way in which a plant or animal changes as it grows.
A chicken and snake embryo has an _____ type of gestation.
A puppy or kitten are _____ from the wombs of the female animal.
While in the womb the embryo of a cow or horse receives nourishment through the _____ that is attached to the mother's body.
A(life cycle) describes how reproduction takes place and shows the way in which a plant or animal changes as it grows.
A chicken and snake embryo has an (egg-laying) type of gestation.
A puppy or kitten are (born alive) from the wombs of the female animal.
While in the womb the embryo of a cow or horse receives nourishment through the (umbilical cord) that is attached to the mother's body.
The life cycle of a dog
Order the pictures above into the correct order that it takes place in. Write numbers 1 - 4 in the order that the pictures should be.
Describe the different stages in the life cycle of a cat and the processes that take place in the space below. You may use illustrations to enhance your work but these will not be assessed.
Gestation: the kittens develop inside the womb of the female cat
Growth and Development: once the kittens are born alive, they are blind and suckle from the mother cat. After about 6 weeks they leave the mother cat and grow and develop on their own.
Maturation: The kitten grows and matures. It changes but the basic body shape remains the same.
Adult reproduction: The cat matures and can reproduce.
When does an animal die?
An animal can die at any time during its life cycle.
Why do you think certain plant species declined in areas where specific animals have been poached, like chimpanzees, orangutans or hornbills, parrots and other exotic birds?
These animals spread the plants' seeds and if they are removed the seeds cannot often germinate or grow and develop as needed.
What possible dangers do crop sprays, pesticides and pollution hold for plants and animals?
This question is meant to engage learners and requires them to display their understanding of the negative human impact on the environment. Learners' answers will vary but needs to display this understanding.
