Science High School Reviewer | Grade 4 Science | Life Science | Kingdoms of Life | Lesson 7: How Seed Plants Reproduce

Grasses, trees, and other seed plants grow from
seeds. A seed is a plant that is not fully formed.
The coating of a seed protects the plant inside.
There are about 250,000 species of seed plants.
How could you classify all of them? What would
you look for?
Comparing Seeds and Structures
Seeds come in all shapes and sizes. You can
use those differences to classify seed plants. A
watermelon has many flat, slippery seeds. A
peach has just one seed, or pit, that is hard and
round. A cherry seed is smaller and smoother.
Plants that make seeds also have roots, stems,
and leaves. These parts can be very different
among plants. They can also help you classify
seed plants. Coconuts are giant seeds that come
from certain palm trees. The trees are tall and
sturdy, with woody stems. Watermelons and
grapes grow on vines.

Flowers and Cones
We can also classify seed plants
by where they store seeds. Most
seed plants have flowers that bear
fruit. The fleshy tissue of the fruit
protects the seeds inside.

Have you ever seen a pinecone?
Pinecones come from conifers
(KON•uh•furz). A conifer is a seed
plant that has no flowers or fruit.
If they have no fruit, where do
conifers store their seeds? Pine trees
and other conifers bear seeds on the
surface of cones. Every conifer has
male and female cones. The male
cones are smaller than the females.
The male cones produce a yellow
powder called pollen. A gust of wind
can blow pollen grains from a male
cone to a female. If the pollen lands
on a female cone, the seeds develop
there.

How do seeds form?

Think about a delicate red rose or a colorful tulip.
Flowers may look pretty or smell nice, yet they do not
make food for a plant. What is the job of a flower?

Reproduction
You know that all living things can make more of
their kind. Reproduction (ree•pruh•DUK•shuhn) is how
living things make offspring.

***

Parts of Flowers
One way that scientists classify plants is by how they make
new plants, or reproduce. When plants are classified in this
way, they are put into one of two groups. Plants in one group
make seeds. Flowering plants and conifers are in this group.

Most flowers have four main parts. The part that you can see
easily is the petals. Petals are often colorful. They are different
shapes and sizes. They protect the parts of the flower that make
seeds. They attract bees, butterflies, birds, and other living things.
The small, green leaves below the petals are sepals. They
cover and protect the flower as it grows inside the bud. As the
bud opens and the flower spreads its petals, the sepals are
pushed apart.
If you look at the center of the flower in the photos, you can
see small, knoblike structures. These structures are part of the
pistil. The smaller stalks surrounding the pistil are stamens.
The anthers are at the tips of the stamens. The anthers make
tiny grains of pollen. Sperm cells in pollen combine with the
flower’s eggs to make seeds.

Pollen on the Move
In order for a seed to form, pollen has to get
from a stamen to a pistil. Animals play a big
part in making this happen.
Flowers make a sweet liquid called nectar.
This is a tasty food for bats, bees, butterflies,
and birds. These and other animals move from
flower to flower in search of nectar. The colors of
the petals and the flower’s scent attract animals
and guide them to the nectar deep inside the
flower. As the animal feeds, pollen from the
stamens rubs off onto its body. The pollen may
then rub off onto the pistil of the next flower
the animal visits. This movement of pollen from
stamen to pistil is called pollination.
Once a pollen grain lands on a pistil, a thin
tube grows from the pollen down through the
pistil. This pollen tube reaches the thick bottom
part of the pistil called the ovary. Inside the
ovary are egg cells. Sperm cells from the pollen
travel down the pollen tube into the ovary.
There the sperm cell and egg cell combine
in a process called fertilization.

***

Flowering plants use flowers to reproduce. Like
cones, flowers have male and female parts. The male
part is the stamen, which includes the anther. The
anther makes pollen that has male sex cells. The
female part of a flower is the pistil, which includes
the ovary (OH•vuh•ree). The pistil makes female sex
cells, or eggs. The ovary stores the eggs. To reproduce,
flowering plants combine male and female sex cells.
How do those cells join together?

Pollination
A gust of wind can blow pollen
from an anther to a pistil. More
often, plants rely on birds, insects,
or other pollinators. Pollinators are
animals that carry pollen from one
flower to another. For instance, bees
suck up nectar—a sugary liquid inside
a flower. If the bee touches an anther,
pollen sticks to its body and legs. At
the next flower, the pollen falls from
the bee to the pistil. The process of
moving pollen is called pollination.
Fertilization
The next step in seed formation
is to move pollen to the ovary. The
pistil grows a long tube for the
pollen to travel. Inside the ovary, the
male sex cell combines with an egg.
Fertilization occurs when the male
sex cell joins with the female sex
cell. Fertilization is the process that
forms a seed.