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Plant
Processes
Chapter 12
Section 1
The Reproduction of Flowering Plants
 Flowering
plants are the largest & most divers
group of plants in the world.
 Their
success is partly due to their flowers, which
are adaptations for sexual reproduction.
 During
sexual reproduction, an egg is fertilized by
a sperm cell.
 In
flowering plants, fertilization takes place
within the flower & leads to the formation of one
or more seeds within a fruit.
Section 1
How Does Fertilization Occur?
Fertilization For Flowering Plants
 Start of fertilization: When pollen grains are
transported from anthers to stigmas.
 After pollen lands on the stigma, a tube grows
from the pollen grain through the style to the
ovary.
 Sperm cells within pollen grain move down the
pollen tube & into an ovule. Fertilization occurs
as one of the sperm cells fuses with the egg inside
the ovule.
Section 1
From Flower to Fruit
 After
fertilization takes place, the ovule
develops into a seed that contains a tiny,
undeveloped plant.
• The ovary surrounding the ovule develops
into a fruit.
• As the fruit swells & ripens, it holds &
protects the developing seeds.
 Petals & stamens fall away.
Section 1
Seeds Become New Plants
 When
a seed is fully developed
• The young plant inside stops growing
• It may become dormant
 Dormant = alive but temporarily inactive
 When dormant it can survive long periods of
drought or freezing temperatures. Some seeds
need extreme conditions such as cold winters
or forest fires to break their dormancy.
 When planted in an area that has water, oxygen, &
suitable temperatures, it germinates (or begins to
grow)
Section 1
Other Methods
 Many
flowering plants can also reproduce
asexually. Asexual reproduction in plants does not
involve the formation of flowers, seeds, & fruits.
In asexual reproduction, a part of a plant, such as
a stem or root, produces a new plant.
Section 1
Other Methods Examples
 Potato
tubers are underground stems that are
swollen with stored food. The “eyes” of potatoes
are buds that can grow asexually into new plants
 The strawberry plant produces runners, which are
stems that run horizontally along the ground.
Buds along each runner grow into new plants that
root in the ground.
 The kalanchoe plant produces plantlets, tiny
plants along the margins of its leaves. The young
plantlets eventually fall off the mother plant &
root in the soil as separate plants.
Section 2
The Ins & Outs of Making Food
 Plants
do not have lungs, but they need air just
like you.
 Air
is a mixture of oxygen, carbon dioxide, &
other gases.
 Plants
must have carbon dioxide to carry out
photosynthesis, which is the way they make their
own food.
Section 2
What Happens During Photosynthesis?
 Plants
need sunlight to produce food.
 During
photosynthesis, the energy in sunlight is
used to make food in the form of sugar (C6H12O6)
from carbon dioxide (CO2) & water (H2O).
 How
does this happen?
Section 2
Capturing Light Energy
 Plant
cells have organelles called chloroplasts.
• Chloroplasts contain chlorophyll.
Chlorophyll = a green pigment that absorb
light energy.
 Sunlight is a mixture of all the colors of the
rainbow.
• Chlorophyll absorbs most of the colors in light,
but not green. Plants look green because
chlorophyll reflects green light.
Section 2
Making Sugar
The light energy absorbed by chlorophyll is used to
split water (H2O) into hydrogen (H) & oxygen (O).
The hydrogen is then combined with carbon
dioxide (CO2) from the air surrounding the plant to
make sugar (C6H12O6). Oxygen is given off as a
byproduct. There process of photosynthesis is
summarized in the following chemical equation:
6CO2 + 6H2O
light energy
C6H12O6 + 6O2
Section 2
Making Sugar Cont.
 The
energy stored in food molecules is used by
plant cells to carry out their life processes. Within
each living cell, sugar & other food molecules are
broken down in a process call cellular respiration.
 Cellular
respiration = coverts the energy stored
in food into a form of energy that cells can use.
 During
this process, the plant uses oxygen &
releases carbon dioxide & water.
Section 2
Gas Exchange
= a waxy layer that doesn’t allow gases or
water to pass through. It covers all aboveground
plant surfaces.
 Stomata = an opening in the leaf’s epidermis &
cuticle. Each stoma is surrounded by two guard
cells, which act like double doors opening &
closing the gap.
 Transpiration = when water vaper exits the leaf
through the stomata
 cuticle
Section 3
Plant Tropisms
Tropism = growth in response to stimulus (can be
positive [plant grows towards stimulus] or negative
[plant grows away from the stimulus)
light – Phototropism = a change in the
growth of a plant that is caused by light. (positive)
 Sensing
 Which
Way is Up? Gravitropism = when the
growth of a plant changes direction in response to
the direction of gravity. (the plant negative while
the roots are positive)
Section 3
As Different as Night & Day
 As
autumn & winter approach, the days get
shorter & nights get longer. The opposite happens
when spring & summer approach. This difference
in the length of day & night is an important
environmental stimulus for many plants.
 Short-day
plants: plants that bloom in autumn.
Poinsettias, ragweed, & chrysanthemums
 Long-day
plants: plants that bloom in spring or
early summer. Clover, spinach & lettuce
Section 3
Seasonal Changes in Leaves
 Evergreen
= have leaves adapted to survive
throughout the year.
 Deciduous
= lose all their leaves at the same time
each year. Having bare branches during the winter
or dry season reduces the water lost by
transpiration.
 As
autumn approaches, chlorophyll, the green
pigment used in photosynthesis, breaks down. As
chlorophyll is lost from leaves, other pigments are
revealed. (like red, yellow, or orange)
Section 4
Plant Growth
Heredity
 A plant’s traits, such as heart-shaped leaves or red
flowers, are determined mainly by the plant’s
genes, or its DNA.
Environment
 A plant’s behavior & appearance can be affected
by the plant's environment.
 The amount of daylight, darkness, water, and the
kind of soil are just a few of many environmental
factors that can affect the plant’s growth.
Section 4
Plant Hormones
Heredity & environment affect a plant’s production
of hormones.
 Hormones
= chemical messengers that carry
information from one part of an organism to
another. They are produced in small amounts, but
they have a strong effect on the organism.
– a hormone produced in shoot tips, has
many effects on plant growth. (phototropism)
 Auxin
– affects plant growth. (makes the
plant grow tall & bear more fruit)
 Gibberellin