Download How Do Flowering Plants Reproduce?

2.2 Explore
2.2 Explore
How Do Flowering
Plants Reproduce?
petals
stigma
When you built the Reeze-ots, you noticed a
lot of variety across different Reeze-ots. The
variety, you know, came from the ways pairs
of traits show themselves. However, you
might not know how organisms get the
traits they have.
carpel
(pistil)
style
ovary
Mammals reproduce sexually and so do flowering plants. Their flowers play
a role in reproduction. Rice plants are flowering plants; they reproduce
sexually. Reproduction in flowering plants includes two processes:
pollination and fertilization. Pollination is delivery of pollen, a structure
that carries the male cells, to the female part of a plant, its ovary. The male
cells inside the pollen contain the male traits.
After pollination, fertilization takes place. A cell from inside the pollen fuses
with a cell from the ovary, which contains the female traits. This fusion takes
place inside the ovary, the plant structure that makes female cells.
The processes of pollination and fertilization result in seed formation. A seed
receives both male and female traits. When planted, each seed can grow a
new plant. The new plant will show features that are in the pairs of traits in
the seed.
PBIS_GEN_SE_LS2_2013.indd 45
stamen
filament
In living things, traits often come from an
organism’s parents. Some organisms have two
sepals
parents and some (like rice and many other
plants) have only one parent. When organisms
reproduce sexually, the female parent and the
male parent (or the female and male parts of the same organism) each
contribute one half of the trait description (one of the letters that represent
the trait). The offspring (child) of that reproduction shows the trait that
goes with the combination contributed by the parents or parent. For
example, if a mother Reeze-ot contributes an H for height and the father
Reeze-ot contributes an h for height, the Reeze-ot offspring will be three
marshmallows high, corresponding to the Hh combination.
GEN 45
anther
ovule
receptacle
reproduce
sexually (sexual
reproduction):
reproduction
that combines
in the offspring
the female and
male traits of the
parents or parent.
offspring: the
descendants of a
person, animal,
or plant.
pollination: the
delivery of pollen
to the female part
of the plant.
fertilization: the
fusion of the cell
that contains the
male traits with the
cell that contains
the female traits.
pollen: a structure
in flowering plants
that has cells that
contain the male
traits.
ovary: the part
of the plant that
makes the cells
containing the
female traits.
GENETICS
5/31/13 1:59:13 PM
Learning Set 2 • How Are Traits Passed Down From Generation to Generation?
Materials
The Female Parts of a Flower
• tweezers
The female part of the plant is the carpel. The carpel includes the stigma,
a tube-like style, and an ovary. The ovary contains ovules (egg cells) that
contain the female traits. Fertilized ovules develop into seeds. In some flowers,
the parts of the carpel are fused together. The female part of the plant is
called the pistil in these plants.
• invisible tape
The Male Parts of a Flower
carpel: the female
part of flowers.
The male part of the flower is called the stamen. It includes the anthers,
where pollen (which contains sperm cells) is produced. Sperm cells contain
the male traits. A filament, a very delicate, thread-like structure, attaches the
anther to the base of the flower. Each flower has several anthers arranged
around the carpel.
• newspapers or
paper towels
• a flower
• hand lens
stigma: the top
part of the carpel
where the pollen is
deposited.
style: the slender,
tube-like part of
the carpel.
ovule (egg
cells): a tiny,
egg-like structure
in flowering plants
that contains
the female traits
and develops
into a seed after
fertilization.
pistil: the female
reproductive organ
of a flower; may
be made up of a
single carpel or of
two or more fused
carpels.
stamen: the male
part of the flower.
anther: the
structure on the
stamen of flowers
where pollen
and sperm are
produced.
The Outer Covering of a Flower
Flowers have an outer covering to protect their male and female parts. The
outer protective covering includes the petals and the sepals. These parts
are also used to attract insects and birds that help pollinate flowers. All of a
flower’s parts are attached to the receptacle at the base of the flower.
Not all flowers look the same. Some flowers have both male and female
parts. Other flowers have only the male part or only the female part.
Flowers also have different numbers of sepals and petals.
Procedure: Observe the Reproductive Structures
of a Flower
You will receive a flower to dissect. You will identify the male and female
parts of the plant. As you do that, you should think about the role of each
of these parts in reproduction and the passing on of traits.
Working with your group, spread newspapers or paper towels on the desk.
Place the flower on the paper.
1. Observe the structure of the flower. Identify and count the sepals and
petals. Keep in mind that the sepals and petals vary from flower to
flower. The number, color, and shape of the sepals and petals in your
flower may look different from the drawing on the previous page
showing the parts of a flower. Record the number, color, and shape of
the sepals and petals in your flower.
GEN 46
Project-Based Inquiry Science
PBIS_GEN_SE_LS2_2013.indd 46
5/31/13 1:59:13 PM
2.2 Explore
2. Use the tweezers to detach all the petals from one side of your flower
to expose its internal structure. On a piece of paper, draw the inside of
your flower. Label the parts you can identify.
3. Remove a stamen. Use your magnifying glass to inspect the stamen.
Can you find the pollen? Draw and describe what it looks like.
4. Use your magnifying glass to look at the end of the pistil. This is the
stigma. Rub a stamen onto the stigma and, using the magnifying glass,
observe it again. Record your observations.
5. Use the scissors or your fingernails to open the ovary. Use the
magnifying glass to locate and count the ovules inside. Draw a diagram
of the inside of the ovary.
Stop and Think
1. On your diagram, identify the parts of your plant that are used in
pollination.
2. On your diagram, identify the parts of your plant that are used in
fertilization.
3. Describe the process through which pollination and fertilization work to
pass on traits.
More on Pollination
You might wonder how flowers become pollinated. Some plants become
pollinated when a bird, insect, or the wind transports pollen from the
male part of one plant to the ovary of another plant. This is called crosspollination. In other types of plants, the male part of the plant pollinates
the female part of the same plant. In these plants, the male and female
parts are close enough to each other so that pollen is easily transferred
from the male part of the plant to the ovary of the same plant when the
wind blows gently. This is called self-pollination.
sperm cells:
structures that
contain the male
chromosomes.
petal: a flower’s
outer protective
covering, usually
colored. Used also
to attract insects
and animals for
pollination.
sepal: a flower’s
outer protective
covering, usually
green.
receptacle: the
main stem of a
flower.
cross-pollination:
the transfer of
pollen on one plant
to the female part
of another plant.
self-pollination:
the transfer of
pollen on one plant
to the female part
of the same plant.
Rice uses self-pollination for reproduction. Pollen is transferred from the
stamen to the pistil of one flower. The seeds and plants produced by selfpollinating plants inherit their traits from only one parent. Therefore, new
plants produced through self-pollination are more similar to the parent
plant than plants produced through cross-pollination are to their parent
plants.
GEN 47
PBIS_GEN_SE_LS2_2013.indd 47
GENETICS
5/31/13 1:59:13 PM
Learning Set 2 • How Are Traits Passed Down From Generation to Generation?
One disadvantage of self-pollination is that the new
plants are very similar to one another. If new diseases
or pests are introduced or enviromental changes occur,
plants with less variety of traits have less chance of
survival than plants produced through cross-pollination,
which have a greater variety of traits. In rice, crosspollination is difficult, because the pollen grain lives for
only a few minutes.
Bees help transfer
pollen in plants that
cross-pollinate. They
deliver the pollen,
which contains the
first flower’s male
traits, to the second
flower’s female part.
Update the Project Board
You can now add your new knowledge from your explorations of plant
reproduction to the Project Board. Record information about plant
reproduction in the What are we learning? column of the Project Board. As
you do this, remember that you must support your science knowledge with
evidence. Put evidence from your reading and investigation in the What is
our evidence? column. You may have new questions about reproduction and
how plants grow from seeds. Add any new questions you might have or ideas
for investigations to the What do we need to investigate? column. Add to the
What do we think we know? column all the information you think you now
know about how traits are passed on through reproduction.
What’s the Point?
You dissected a flower to learn about the reproductive parts of a flowering
plant. The ovary is the structure where the egg cells containing the female
traits are produced. The anthers on the stamen are the structures where
the sperm cells containing the male traits are produced. Pollen, which
contains sperm cells, and ovules, which are egg cells, are both necessary for
reproduction in flowering plants. The sperm cell and egg cell fuse together
during fertilization to produce a seed.
The mixing of traits from the male cells and traits from the female cells
produces variety in traits in the next generation. Cross-pollination occurs
when the pollen of one plant is transferred to the female part of another
plant. Self-pollination occurs when the pollen on one plant is transferred to
the female part of the same plant. Self-pollinating plants have less variation
in traits than those that produce offspring through cross-fertilization. Rice is
a self-pollinating plant. In rice, cross-pollination is difficult, because the pollen
lives only for a few minutes.
GEN 48
Project-Based Inquiry Science
PBIS_GEN_SE_LS2_2013.indd 48
5/31/13 1:59:13 PM