Download Chapter 13

Chapter 13
Plant Processes
SECTION 1 Reproduction of Flowering Plants
Remember: Flowers are the structure for angiosperms to carry out sexual reproduction.
The main role of the flower is to produce sperm and egg cells for reproduction. How does
it happen?
Recall the male structures of the flower (anthers that produce pollen) and the female
structure (stigma, style and ovary that contains the ovules). If a pollen grain from an
anther lands on the stigma, a pollen tube forms down through the style. The sperm cells
travel down the pollen tube and enter the ovary. Inside the ovary, there are the ovules that
contain the eggs. The sperm travel down the pollen tube and fertilize an egg. The ovules
develop into seeds and the ovary surrounding the ovules develops into a fruit. Example:
A watermelon plant will bloom with flowers. When the pollen is formed, an insect often
serves as a pollinator and transfers the pollen onto the stigma. A pollen tube grows down
through the style and into the ovary. The sperm travel down the pollen tube and fertilize
the egg. The fertilized egg turns into a seed or seeds if more than one egg is fertilized and
the ovary turns into the fruit we call a watermelon.
This is the same process for tomatoes, squash, beans, peas, apples, pears, and any other
flowering plants you may want to write down.
SEEDS
Seeds contain the young plant that is capable of producing more flowers and fruit. When
a seed becomes mature in fruit, the seed becomes dormant. In other words the seed does
not develop any further until conditions are “good” again. Many seeds require cold
temperatures, some require freezing, and some may require extreme heat like a fire to
break their dormant period. When a seed ends up in a suitable location to grow (proper
temperature, moisture and oxygen) it germinates or undergoes germination. Germination
is when the young plant begins to grow. Experiment at home: Take a small bowl with
moist paper towels and line the bottom, place 5-10 dry pinto beans into the bowl and
cover with a few more moist paper towels. Keep the towels moist but not wet. Check the
beans daily, but be careful not to allow them to dry out. As you watch them for 7-10 days
you will see the beans germinate (begin to grow).
There are other methods of reproduction that are asexual. Some plants may send out rootlike structures from the main plant called runners. These runners will form new plants.
Strawberries are an example of a plant that will send out runners to make new plants.
Potatoes can also reproduce asexually. Have you ever seen an “eye” of a potato? You can
cut the potato eye leaving some of the potato flesh with it and plant the eye and a new
potato plant will grow. The new plant will be a clone genetically to the potato the eye was
removed from.
Some other plants may have “pieces” of vegetation fall from the plant that will grow into
a new plant.
The Food Making Process
Plants make food in the form of a sugar (glucose). They do this through photosynthesis.
Plants will take in carbon dioxide and water and capture the light energy from the sun and
produce glucose and oxygen. The formula for photosynthesis should be a review for you.
Formula for photosynthesis:
6CO2 + 6H2O --------light energy C6H12O6 + 6O2
Six Carbon Dioxides + Six Waters captured sunlight energy Yields Glucose + Oxygen
The chemical that enables plants to capture the light energy is chlorophyll. It appears
green because it absorbs all colors of the light spectrum except green light. It reflects the
green light and that is why plants look green to us.
Photosynthesis occurs mainly in the leaves of plants, but some plants also have stems that
contain chlorophyll and photosynthesis can occur here also. The plants can use the
glucose for their energy needs and when they do this they carry out cellular respiration
like we discussed humans and other animals do. When they need to repair structures, they
will use the glucose and oxygen and give off carbon dioxide and water.
RECALL: If we look at the layers of a leaf, we know that the lower epidermis and cuticle
have guard cells that regulate gas exchange into and out of the leaf. This is where carbon
dioxide enters and oxygen and water will leave the plant. If there is more water leaving
the plant than the root system is taking into the plant, the plant will wilt. To prevent total
drying out at times, the guard cells may “close” off the opening. The opening the guard
cells surround is called the stoma (singular) or stomata (plural). When water is lost
through the leaves of plants it is called transpiration.
SECTION 3 Plant Responses to the Environment
Recall: anything that causes a reaction in a tissue is a stimulus. Plants also have stimuli,
which we call tropisms. The two main tropisms are gravitropism and phototropism.
Phototropism is the tendency for plants to grow toward the available sunlight. If you
place a plant near a window, it will “bend” toward the light from the window. It is
bending, but the side away from the light tends to grow a little faster and it appears the
plant bends toward the light. It does grow toward the light.
In gravitropism, the roots of plants grow toward gravity, which is a positive tropism and
the shoot system grows away from the center of gravity and we call this a negative
tropism.
Some plants respond to seasonal changes. Many may change the colors of their leaves
based on the length of the night. Some may flower when the length of day and night fall
into a specific range. Some may flower when the days are longer than the nights (long
day plants like lettuce and clover), and vise versa like poinsettias. During long nights,
their green leaves will turn red, and so individuals that grow them for Christmas sales,
use artificial light and control when the leaves are red.
Recall: Some trees stay green all yearlong, these are evergreen trees. Evergreen trees
include conifers, cedars, spruces, hemlocks and Southern Magnolias in our area. The
trees with leaves that change color in the fall are called deciduous trees because they lose
their leaves during the winter.
As the days get shorter in the fall, the chlorophyll that reflects the green we see begins to
break down and we begin to see the chlorophyll types that reflect reds, yellows, and
scarlet shades. This is considered one of the prettiest times of the year in the southeastern
United States.
So it is not the color of the chlorophyll we see, but the colors that are not absorbed. Your
clothing is the same way. A red shirt is red because it reflects the red wavelength of light
and absorbs all other colors. Structures that are white reflect ALL wavelengths and those
that are black absorb ALL wavelengths.
SECTION 1 STUDY GUIDE
1. The ____________________ contain the male and female reproductive parts of
Angiosperm plants.
2. The _______________________ make the pollen grains which contain the
______________________ cells in Angiosperms.
3. Pollen grains must land on the _______________________ and grow pollen tubes
to allow sperms to enter the ovary of a flower.
4. A sperm cell unites with an _____________________ in order for fertilization to
occur in an angiosperm.
5. The colorful portions of a flower make up the ________________.
6. The _______________________ develops into a fruit and the ______________
develops into seeds.
7. If there are six fertilized ovules in an ovary, how many seeds will form and how
many fruit will develop.
8. When seeds are inactive (not growing), we say they are ____________________.
9. When seeds ______________________ they begin to grow and the young plant
will emerge.
10. Some flowering plants can also reproduce by ______________________
reproduction. An example of this is the eye of a potato.
SECTION 2 STUDY GUIDE
1. _____________________________ is the chemical that captures sunlight energy
in plants for photosynthesis.
2. Explain why we see plants as being green.
3. 6CO2 + 6H2O --------light energy C6H12O6 + 6O2 is the chemical equation for
___________________________________.
4. C6H12O6 is the chemical formula for what sugar? _____________________
5. Organisms that break down C6H12O6 for the use of carrying out life activities are
carrying out ________________________ respiration. This will release carbon
dioxide and water.
6. _______________________ is the process in which plants lose water out their
stoma.
7. The size of stoma in a plant leaf is controlled by the ___________________
____________________ that surround the stoma.
8. When plants grow in response to a stimulus like light or gravity, we say the
stimulus is a _____________________.
9. __________________________ is the growth stimulus that results due to gravity.
10. __________________________ is the growth stimulus plants have in response to
light.
11. The length of ________________ and _________________ often triggers growth
responses in plants.
12. _________________________ have their leaves year round. They may lose some
leaves, but they will be replaced.
13. ___________________________ trees lose their leaves during some portion of
the year. This allows trees to slow transpiration and survive during extreme
periods of the year. Some places the trees may lose their leaves during a drought
and others may lose their leaves during cold temperatures.