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Sexual reproduction
in flowering plants
Experiment 1: sowing the seeds.
Materials
- cotton wool or paper towels
- a glass jar
- 4 broad beans
Work plan
Setting up the experiment
- Take some cotton wool or paper towels,
make it soaking wet and place them in jar as
shown in the figure on the right.
- Take four broad beans and place them, half
way the jar, between the glass and cotton
wool or paper towel.
- Fill the jar with sand so that the paper towel
Figure 1. bean in a jar
is pressed against the glass.
- Make sure they don’t fall down but stay pressed against the glass as shown
in Fig. 1.
- Make sure the cotton wool/paper towels stay wet.
Measurements
- Keep a log book. Keeping a log book is writing down every day, the date,
everything you see about the beans, when they start to germinate, how
long their roots (when the roots are bent, measure them as well as
possible) or their stems are, the number of leaves etc. Write down as many
numbers as possible. Later these results can be used in diagrams.
- In addition, write down every day how much water you gave the beans;
where you placed the jar, in the sun or in the shadow; etc.
- When the plant is 15 cm tall, you make a drawing of one bean plant in
which you label the parts (use internet). Make sure it is a schematic, but
clear drawing. Not just a sketch!
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Report
- After two weeks you finish off your report.
- The report consists of: an introduction, experimental set up (work plan),
results (including diagrams), conclusion, discussion.
Introduction
- In the introduction you write in your own words about what you now know
about the roles of seeds, fruits and flowers etc. in the life cycle of a plant.
Basically, this is what this chapter is about. Therefore, in your introduction
tell me what you know about this chapter (ca. 2 pages of text).
- The scientific question is: “What role does a seed play in the life cycle of a
plant?”
Materials and work plan
- What did you use in your experiment?
- What did you do in your experiment?
Results
- In your results present diagrams made on basis of the numbers in the
logbook.
- Number these diagrams and describe in the accompanying text what the
diagrams are about.
- In class you made some drawings of seeds, fruits and flowers during the
practicals. Include the drawing of the 15 cm tall plant in your experiment.
- Number these drawings as well and write in the accompanying text what
we can see in the drawing.
Discussion
- In this discussion describe the answer to the question “What role does the
seed play in the life cycle of a plant?” Use the diagrams and drawings to
underline and support your story.
- In the discussion refer to the diagrams and drawings.
Conclusion
- In your conclusion simply answer the question. Make sure it is a statement.
- Leave out any discussion here, just answer the question.
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1 Where do new plants come from.
Having read the book about “Jake and the bean stake” Jerome wants to grow
bean plants in his garden himself. So he goes to the shop and buys beans.
First, he puts the beans on wet tissues and waits until the seeds start to grow
little roots. The process of seeds starting to grow little roots is called
germination. Now he digs little, 2 cm deep holes in the garden, puts the
seeds in and covers them with soil. The beans will now start to grow into a
adult bean plant.
Do experiment 1 at home (see previous page).
Take seeds home and set up the experiment there. Read the manual
carefully to avoid forgetting things afterwards (e.g. keep a log book).
Experiment 2: taking a closer look at a seed.
Materials
- Dry beans.
- Soaked beans.
- Drawing paper
Work plan
- Take a seed out of the box Jake bought at the store.
As you can see, the seed is completely dry and can’t be opened easily.
This way seeds can rest for years. If you want to take a look at the
inside, you need to first place it in water for a day so that they can suck
up the water and become soft.
- Take a bean that has been placed in water for a day.
If we take a closer look at the bean (seed) you used at home, we see
that the outside of the seed is brown. This is called the seed coat.
- Remove the seed coat, carefully, so that you can see the inside of the seed.
Once the seed coat has been removed the cotyledons or seed leaves
become apparent (visible). They look like the two halves of a peanut
(pinda). The funny thing is that peanuts are actually the seed leaves of
the peanut seed. The most important part of the seed is between the
seed leaves.
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- Carefully move the seed leaves apart.
Attached to one of the seed leaves you’ll find the young plant (embryo).
- Use a magnifying glass to observe the young plant closely.
One part of the embryo (the scientific name for a young “unborn” plant)
is the young root and the other part that looks like two very small
leaves will later form the first leaves of the new pant. Actually the seed
leaves are part of the embryo as well.
- Make a drawing of the seed and label the parts mentioned above.
Remember the drawing rules. Save the drawing in your notebook for
later use in your report on experiment 1. You can work on your drawing
after the experiment if you think it doesn’t look nice enough for the
report.
2 Seeds and fruit
A seed in the soil brings forth a young plant. In previous chapters we learned
that for growth plants need nutrients. Adult plants make their own nutrients
through photosynthesis. But a seed doesn’t have leaves or chloroplasts. It
isn’t even above the ground. So, where does the young plant get its nutrients
from?
Experiment 3: What’s inside? (demonstration)
- Grind a cotyledon in a mortar and boil it for a minute to open up the cells.
- Then add Benedict’s solution to half of the ground cotyledon and place it
in a 70C water bath for a minute.
- Add iodine to the ground cotyledon and see what colour it turns.
- Also do a negative and a positive test.
questions:
1. What was present in the seed leaves?
2. Which test tubes were the positive tests?
3. Which test tubes were the negative tests?
4. Why do we need to include a positive and a negative test to this
investigation?
5. Where in the seed are the nutrients stored?
6. Where are these nutrients formed, originally?
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Experiment 4: “like peas in a pod”
In this experiment you are going to observe the peas (erwten) as they are in
the pod (peul). The scientific name of the common bean (sperzieboon) is
Phaseolus vulgaris.
Materials
- A pod of Phaseolus vulgaris
- Drawing paper
Work plan
- Open up the pod carefully.
- Make a drawing of the opened pod.
- Take note of the connection between the peas and the pod.
- Make sure to label one part of your drawing with “fruit”?
- Save your drawing for the report.
questions:
7. To what genus does the common
bean belong?
8. In the experiment you noticed the
connection between the peas and the
pod. The same connection can be
seen in a tomato (see Fig. 2).
What is the function of this
Figure 2. cross section of a tomato
connection?
9. Name two nutrients that could be present in the cotyledons?
10. What are the indicators for showing the presence of these substances.
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3 fruits
The pod is the fruit of the common bean plant. This pod is also filled with
nutrients. But are these nutrients meant for the young plant as well, or do
they serve a different purpose? To find out we are going to take a look at a
few fruits below.
Figure 3. several fruits: apple, melon, avocado, egg plant (aubergine).
questions:
11. Where do the nutrients present in the fruits come from?
12. Where do the nutrients present in the fruits in Fig. 3 end up?
13. The production of the nutrients in the fruit costs the plant a lot of energy.
What is the advantage to the plant of putting these nutrients in the fruit?
Generally speaking, plants make fruits to have their seeds dispersed as far
away from the mother plant as possible. Sometimes the plants use animals to
help them disperse the seeds, sometimes they use different paths.
DVD 5 program 1 – dispersal of seeds
dispersal of seeds
Figure 4. dispersal of seeds: dandelion, maple (esdoorn), burdock (klit) and
himalyan balsam or touch-me-not (balsemien of springzaad).
himalyan balsam
question:
14. For each of the pictures below describe how the fruit helps
the plant to disperse the seeds (watch hymalyan balsam).
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4 sexual reproduction
We have seen structures that contain starch before. Tubers contained starch
and used it to grow into a new plant in absence of leaves as well. The starch
stored in tubers came from the parent plant. Seeds are formed the same
way. A mother plant brings glucose through the phloem vessels to the seed
and fills the seed up while it grows.
There is, however, one big difference between a seed and a tuber. The
plant that grows from a tuber is genetically identical to (it has the same
genes/chromosomes as) the parent plant, while the plant that grows from a
seed is only partly the same as the mother plant. The other characteristics
the young plant received from the “father” plant. A seed is the product of
sexual reproduction.
For reproductive purposes, humans produce sperm cells (zaadcellen) and
egg cells. When a man makes love to a woman he brings his sperm to the
egg cell inside the woman. Likewise, plants form similar reproductive cells
(voortplantingscellen). For plants, however, it is not possible to have sexual
intercourse, because for that they would have to be able to move. So, they
can’t bring the male gametes (mannelijke geslachtscellen) to the female to
fertilise (bevruchten) her egg cells. Plants need a different course of action.
They let others bring the pollen grains (that is what we call the plant’s male
gametes) to the female egg cell (those are called egg cells as well in plants
as in animals). The pollen grains are brought to the egg cells in two different
ways. They use the wind or insects.
stamens
Experiment 5: where are the pollen grains formed?
Before we can begin to understand how pollen grains are brought to the egg
cells, we need to take a closer look at the structure that produces pollen
grains and at the one that produces egg cells. Both are located in flowers.
Materials
- A flower
- A magnifying glass
- A drawing paper
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Work plan
- Look at the flower in front of you.
You are given a flower which contains the structure that forms pollen
grains. This structure is called the anther and is a part of the
stamen. In a flower you can recognise the stamen easily because in
most flowers there are many stamens and they consist of a stalk
(steeltje) called the filament with a thick part at the top called the
anther. If you touch the anther some yellow dust may stick to your
finger. This yellow substance are millions of pollen grains.
- Make a drawing of the flower indicating the bold printed words.
- Remove some petals, the coloured leaves surrounding the flower.
- Make a drawing of the flower and label the petals and the stamen,
consisting of an anther and a filament.
5 pollination
If a bee flies into a flower, the pollen grains will
get stuck to the legs and body of the bee. But
why would a bee fly into a flower? The flower
needs to be attractive to the bee, otherwise the
bee will pass the flower when flying by. Some
flowers produce a sweet substance called
Figure 5. pollination by insects
nectar. Insect pollinators smell nice. The
bees smell this scent (geur) and enter the flower. To help the bees find the
flower, the large petals have very distinct colours (duidelijk zichtbare
kleuren). When the bees enter the flower to reach for the nectar they pass
the anthers and touch them. Then the pollen grains will stick to your body or
legs. For this purpose the pollen grains are sticky. The transfer of pollen
grains from the anther to the stigma of a flower of the same species is called
pollination.
In some plants it is only possible to pollinate flowers of another plant (of
the same species). This is called a cross pollinator. If the species allows
flowers of the same plant to be pollinated, it is called a self pollinator.
DVD 5 program 3 - insect pollination
insect pollination (1 and 2)
pollination
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Experiment 6: where are the egg cells formed?
How does the pollen grain reach the egg cell? First we are going to find out
where the egg cell is located.
In the flower in front of you, you can’t see the egg cell itself since it is
much too small. They are actually located in the structure called the carpel.
The carpel is the stalk in the middle of the flower. The stalk that doesn’t
have an anther. Mostly it has a greenish colour with at the top a sticky
substance made of sugar. The top (called the stigma) can have many
shapes. Sometimes it is a round bud, or forked or split three ways. Try to find
out what structure is the carpel.
Figure 6. different shapes of stigma’s
Materials
- A flower
- A magnifying glass
- A drawing paper
Work plan
- Make a drawing and label the petals, carpel and the stigma.
Deep inside the carpel the egg cell is located. So, how does the bee get
the pollen grain inside the carpel? Well, the bee doesn’t. It only leaves
it at the sticky top of the carpel called the stigma. The transfer of the
pollen grains to the stigma is called pollination. The pollen grain needs
to work its way towards the egg cell by itself. Thus, all the bee does is
get the pollen grain from the anther to the stigma. It enters one flower
to collect nectar and picks up the pollen grains. Then it flies to another
flower to collect more nectar and leaves the pollen grains behind on the
stigma. This is how flowers have sexual intercourse.
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Experiment 7: what do wind pollinators look like?
On your table you will find a very small flower of a grass plant. It doesn’t look
like the Lilly you saw before. It is much smaller, doesn’t have large brightly
coloured petals. If fact it doesn’t have petals at all. Take a look at the
stamens. What do you notice?
Materials
- A wind pollinated flower
- A magnifying glass
- A drawing paper
Work plan
- Make a drawing of the grass flower. Label the stamens.
- Find the stigma and draw it.
questions:
15. Both insect and wind pollinators have anthers. The anthers of insect and
wind pollinators have different shapes and have a different location.
Explain the relation between the location of the anther in the flower and
how the flower is pollinated.
16. If the wind picks up the pollen grains from these specially formed anthers,
the stigma of the grass flower must be specialised too.
How is this stigma adapted to its function?
17. Which flower makes more pollen grains, those pollinated by insects or
those pollinated by the wind? Explain your answer.
18. See Fig. 6. Which of the two flowers below is an insect pollinator and
which a wind pollinator? Explain your answer.
Figure 6. two ways of pollination
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DVD 5 program 3 on pollination
wind pollination
6 fertilisation
The pollen grain has landed on the stigma. Here it starts to grow into a very
large tube. This tube reaches all the way to the egg cell that is located inside
the carpel, the part that is called the ovary. The egg cell is surrounded by a
group of cells that will later form the seed coat (the brown outer covering of
the bean in experiment 2). This group of cell are called the ovule.
Once the pollen tube has reached the egg cell the nucleus of the pollen tube
will enter the egg cell. This is called fertilisation. The fertilised egg cell is
called a zygote. The zygote will start to divide many times to form the
embryo and the seed leaves and is covered by the seed coat. This is how the
seed is formed.
When you eat an apple, a tomato or a melon, you have noticed that the
seeds are hidden in a fruit. Even the beans of Jerome or Jake were covered
by a pod (een peul). Where does the fruit come from. The egg cell forms the
embryo and the seed leaves, the ovule results in a seed coat, but what
develops into a fruit? The answer is the ovary. The ovary surrounds the egg
cell and the ovule like the fruit surrounds the seed.
development from a flower into a pod
questions:
19. What consists of cells of the new plant: the ovary, the ovule and/or the
zygote?
20. What is formed from the zygote: the fruit, the sees coat, the seed leaves
and /or the embryo?
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Figure 7. The life cycle of a plant – a summary of this chapter.
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Glossary with ‘sexual reproduction in flowering plants
germination
a seed
the seed coat
cotyledons or seed leaves
embryo
young root
first leaves
fruit
Benedict’s solution
iodine
a negative
a positive test
pod
dispersal of seeds
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sexual reproduction
sperm cells
egg cells
reproductive cells
sexual intercourse
gametes
male gametes
pollen grains
stamen
anther
filament
pollen grains.
petals
pollination
nectar
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insect pollinator
scent
pollination.
cross pollinator
self pollinator.
carpel
stigma
fertilisation
ovary
ovule.
fertilisation
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Sexual reproduction in flowering plants
What you must be able to do:
You need to be able to name all the parts of a flower (find different pictures
of flowers on the internet to practice).
You need to be able to label all the parts of a seed / bean
Name and explain the methods by which a plant can be pollinated. Name the
characteristics of flowers that use each method.
Name and explain the methods of a plant of dispersing seeds. Be able to
recognise this in pictures of fruits.
What develops from the ovule, ovary and egg cell (in a flower)?
Explain how a plant fills the fruits and the seeds leaves with nutrients (story
from leaves to fruit (seed leaves) step by step).
What structures are involved in this process?
What is the advantage of storing nutrients in seeds and of storing nutrients in
fruits?
Explain the sequence of events starting from pollination, growth of a pollen
tube, fertilisation, development of a seed, germination and growth of a new
plant: the life cycle of a plant. Name all the names of the parts of the plant
and the names of the processes that take place.
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