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Table of Contents
Chapter: Plant Processes
Section 1: Photosynthesis and
Respiration
Section 2: Plant Responses
Photosynthesis and Respiration
1
Taking in Raw Materials
• Food is one of the raw materials you need to
grow. Oxygen is another.
• Your cells use oxygen
to help release energy
from the food that you
eat.
• “Does a tree need to
eat? Does it use
oxygen? How does it
get rid of wastes?”
Photosynthesis and Respiration
1
Movement of Materials in Plants
• Plants make their own foods using the raw
materials water, carbon dioxide, and
inorganic chemicals in the soil.
• Plants also produce waste products.
• Most of the water used by plants is taken in
through roots. Water moves into root cells
and then up through the plant to where it is
used.
Photosynthesis and Respiration
1
Movement of Materials in Plants
• Leaves, instead of lungs, are where most gas
exchange occurs in plants.
• Carbon dioxide,
oxygen, and water
vapor exit and
enter the plant
through openings
in the leaf.
Photosynthesis and Respiration
1
Leaf Structure and Function
• A leaf is made up of many different layers.
• The outer cell layer of the leaf is the
epidermis. A waxy cuticle that helps keep the
leaf from drying out covers the epidermis.
Photosynthesis and Respiration
1
Leaf Structure and Function
• If you examine the epidermis under a
microscope, you will see that it contains
many small openings.
• These openings, called stomata (stoh Mah
tuh) (singular, stoma), act as doorways for
raw materials such as carbon dioxide, water
vapor, and waste gases to enter and exit the
leaf.
Photosynthesis and Respiration
1
Leaf Structure and Function
• Stomata also are found on the stems of many
plants.
• More than 90 percent of the water plants take
in through their roots is lost through the
stomata.
Photosynthesis and Respiration
1
Leaf Structure and Function
• Two cells
called guard
cells surround
each stoma
and control
its size.
• As water moves into the guard cells, they
swell and bend apart, opening a stoma.
• When guard cells lose water, they deflate and
close the stoma.
Photosynthesis and Respiration
1
Leaf Structure and Function
• Stomata usually are open during the day,
when most plants need to take in raw
materials to make food.
• They usually are closed at night when food
making slows down. Stomata also close
when a plant is losing too much water.
Photosynthesis and Respiration
1
Leaf Structure and Function
• Inside the leaf
are two layers
of cells, the
spongy layer
and the
palisade layer.
• Carbon dioxide and water vapor fill the spaces
of the spongy layer.
• Most of the plant’s food is made in the
palisade layer.
Photosynthesis and Respiration
1
Chloroplasts and Plant Pigments
• Most leaves look green because some of their
cells contain so many chloroplasts.
• Chloroplasts are green because they contain a
green pigment called chlorophyll (KLOR uh
fihl).
Photosynthesis and Respiration
1
Chloroplasts and Plant Pigments
• A pigment is a substance that reflects a
particular part of the visible spectrum and
absorbs the rest.
• When you see
a green leaf,
you are seeing
green light
energy
reflected from
chlorophyll.
Photosynthesis and Respiration
1
Chloroplasts and Plant Pigments
• In fall, the chlorophyll in some leaves breaks
down and the leaves change color as other
pigments become visible.
Photosynthesis and Respiration
1
Chloroplasts and Plant Pigments
• Pigments, especially chlorophyll, are important
to plants because the light energy that they
absorb is used to make food.
Photosynthesis and Respiration
1
Chloroplasts and Plant Pigments
• For plants, this food-making
processphotosynthesishappens in the
chloroplasts.
Photosynthesis and Respiration
1
The Food-Making Process
• Photosynthesis (foh toh SIHN thuh suhs)
is the process during which a plant’s
chlorophyll traps light energy and sugars
are produced.
• Pigments, especially chlorophyll, are
important to plants because the light
energy that they absorb is used to make
food.
Photosynthesis and Respiration
1
The Food-Making Process
• For example,
photosynthesis occurs
only in a carrot plant’s
lacy green leaves.
• Excess sugar produced
in the leaves is stored in
the familiar orange root
that you and many
animals eat.
Photosynthesis and Respiration
1
The Food-Making Process
• Besides light, plants also need the raw
materials carbon dioxide and water for
photosynthesis.
• The overall chemical equation for
photosynthesis is shown.
Photosynthesis and Respiration
1
Light-Dependent Reactions
• During light-dependent reactions, chlorophyll
and other pigments trap light energy that
eventually will be stored in sugar molecules.
• Light energy causes water molecules, which
were taken up by the roots, to split into
oxygen and hydrogen.
Photosynthesis and Respiration
1
Light-Dependent Reactions
• The oxygen leaves the plant through the
stomata.
• Hydrogen produced when water is split is
used in photosynthesis reactions that occur
when there is no light.
Photosynthesis and Respiration
1
Light-Independent Reactions
• Reactions that don’t need light are called the
light-independent reactions of photosynthesis.
• The light energy trapped during the lightdependent reactions is used to combine
carbon dioxide and hydrogen to make sugars.
• One important sugar that is made is glucose.
The chemical bonds that hold glucose and
other sugars together are stored energy.
Photosynthesis and Respiration
1
Light-Independent Reactions
Photosynthesis and Respiration
1
Light-Independent Reactions
• What happens to the oxygen and glucose
that were made during photosynthesis?
• Most of the oxygen from photosynthesis
is a waste product and is released through
stomata.
• Glucose is the main form of food for plant
cells.
• A plant usually produces more glucose than
it can use. Excess glucose is stored in plants
as other sugars and starches.
Photosynthesis and Respiration
1
Light-Independent Reactions
• Glucose also is the basis of a plant’s structure.
• Cellulose, an important part of plant cell
walls, is made from glucose.
• Leaves, stems, and roots are made of
cellulose and other substances produced
using glucose.
• The products of photosynthesis are used for
plant growth.
Photosynthesis and Respiration
1
Importance of Photosynthesis
• Organisms that carry on photosynthesis
provide food directly or indirectly for nearly
all the other organisms on Earth.
Photosynthesis and Respiration
1
Importance of Photosynthesis
• Photosynthetic organisms use carbon dioxide
and release oxygen. This removes carbon
dioxide from the atmosphere and adds oxygen
to it.
Photosynthesis and Respiration
1
The Breakdown of Food
• Respiration is a series of chemical reactions
that breaks down food molecules and releases
energy. Respiration occurs in cells of most
organisms.
Photosynthesis and Respiration
1
The Breakdown of Food
• Respiration that uses oxygen to break down
food chemically is called aerobic respiration.
• In plants and many organisms that have one or
more cells, a nucleus, and other organelles,
aerobic respiration occurs in the mitochondria
(singular, mitochondrion). The overall
chemical equation for aerobic respiration is
shown.
Photosynthesis and Respiration
1
Aerobic Respiration
• Aerobic respiration takes place in the
mitochondria of plant cells.
Photosynthesis and Respiration
1
Aerobic Respiration
Photosynthesis and Respiration
1
Importance of Respiration
• Respiration changes food energy into a form
all cells can use. This energy drives the life
processes of almost all organisms on Earth.
• The waste product carbon dioxide is also
important.
• Aerobic respiration returns carbon dioxide
to the atmosphere, where it can be used
again by plants and some other organisms
for photosynthesis.
Photosynthesis and Respiration
1
Comparison of Photosynthesis
and Respiration
• You can see that aerobic respiration is almost
the reverse of photosynthesis.
Section Check
1
Question 1
This diagram shows that plants take in raw
materials through their roots and leaves and get
rid of wastes through _______.
Section Check
1
A. neither their roots nor leaves
B. their leaves only
C. their roots only
D. their roots and leaves also
Section Check
1
Answer
The correct answer is B. Plants take in carbon
dioxide and oxygen through their leaves and
water through their roots. They give off waste
of water vapor, oxygen, and carbon dioxide
through their leaves.
Section Check
1
Question 2
Why are stomata on leaves usually open during
the day but shut at night?
Answer
Because photosynthesis is taking place mostly
during the day, this is the time most plants need
to take in raw materials. During the night, this
process slows down.
Section Check
1
Question 3
What do plants produce during the process of
photosynthesis?
Answer
Plants produce sugars (or glucose) and oxygen.
The sugars produced are used by the plant for
growth and energy. Most of the oxygen is
given off as a waste.
Plant Responses
2
What are plant responses?
• A stimulus is anything in the environment
that causes a response in an organism. The
response often involves movement either
toward the stimulus or away from the
stimulus.
• A stimulus may come from outside (external)
or inside (internal) the organism.
Plant Responses
2
What are plant responses?
• Internal stimuli are usually chemicals
produced by organisms.
• Many of these chemicals are hormones.
Hormones are substances made in one part
of an organism for use somewhere else in
the organism.
Plant Responses
2
What are plant responses?
• Many different
chemicals are known
to act as hormones in
plants.
• Plants respond to
external stimuli such
as touch, light, and
gravity.
Plant Responses
2
What are plant responses?
• Some responses are
rapid. Other plant
responses are slower
because they involve
changes in growth.
Plant Responses
2
Tropisms
• Some responses of a plant to an external
stimuli are called tropisms.
• A tropism (TROH pih zum) can be seen
as movement caused by a change in
growth and can be positive or negative.
• For example, plants might grow toward a
stimulusa positive tropismor away
from a stimulusa negative tropism.
Plant Responses
2
Touch
• One stimulus that can result in a change in a
plant’s growth is touch.
• When some plants touch a solid object, they
respond by growing faster on one side of its
stem than on the other side.
• As a result the stem bends and twists around
any object it touches.
Plant Responses
2
Light
• Light is an important stimulus to plants.
• When a plant responds to light, the cells
on the side of the plant opposite the light
get longer than the cells facing the light.
• Because of this uneven growth, the plant
bends towards the light.
Plant Responses
2
Light
• When a plant grows toward light it is called
a positive response to light, or positive
phototropism.
Plant Responses
2
Gravity
• The downward
growth of plant
roots is a positive
response to
gravity.
• A stem growing
upward is a
negative
response to
gravity.
Plant Responses
2
Plant Hormones
• Hormones control the changes in growth
that result from tropisms and affect other
plant growth.
Plant Responses
2
Ethylene
• Ethylene is produced in cells of ripening
fruit, which stimulates the ripening process.
Plant Responses
2
Ethylene
• Another plant response to ethylene causes
a layer of cells to form between a leaf and
the stem.
• The cell
layer causes
the leaf to
fall from the
stem.
Plant Responses
2
Auxin
• Auxin is a type of
plant hormone that
causes plant stems
and leaves to exhibit
positive response to
light.
Plant Responses
2
Auxin
• When light shines
on a plant from one
side, the auxin
moves to the
shaded side of the
stem where it
causes a change in
growth.
Plant Responses
2
Auxin
• Development of many parts of the plant,
including flowers, roots, and fruit, is
stimulated by auxins.
• Because auxins are so important in plant
development, synthetic auxins have been
developed for use in agriculture.
Plant Responses
2
Gibberellins and Cytokinins
• Gibberellins (jih buh
REH lunz) are chemical
substances that were
isolated first from a
fungus.
• The fungus infects the
stems of plants and
causes them to grow
too tall.
Plant Responses
2
Gibberellins and Cytokinins
• Gibberellins can be
mixed with water and
sprayed on plants and
seeds to stimulate plant
stems to grow and seeds
to germinate.
Plant Responses
2
Gibberellins and Cytokinins
• Cytokinins (si tuh KI nunz) also cause rapid
growth.
• Cytokinins promote growth by causing
faster cell divisions.
• Like ethylene, the effect of cytokinins on
the plant also is controlled by auxin.
Plant Responses
2
Abscisic Acid
• Abscisic acid is the substance that keeps
seeds from sprouting
and buds from
developing during
the winter.
• This plant hormone
also causes stomata to
close and helps plants
respond to water loss
on hot summer days.
Plant Responses
2
Photoperiods
• A plant’s response to the number of hours of
daylight and darkness it receives daily is
photoperiodism (foh toh PIHR ee uh dih
zum).
• The hours of daylight and darkness vary
with the seasons.
• These changes in lengths of daylight and
darkness affect plant growth.
Plant Responses
2
Darkness and Flowers
• Generally,
plants that
require less
than 10 h to
12 h of
darkness to
flower are
called longday plants.
Plant Responses
2
Darkness and Flowers
• Plants that
need 12 or
more hours
of darkness
to flower are
called shortday plants.
Plant Responses
2
Day-Neutral Plants
• Day-neutral plants have no specific
photoperiod, and the flowering process can
begin within a range of hours of darkness.
• In nature,
photoperiodism
affects where
flowering plants can
grow and produce
flowers and fruit.
Plant Responses
2
Day-Neutral Plants
• This table
shows
how day
length
affects
flowering
in all
three
types of
plants.
Section Check
2
Question 1
Which is an example of negative gravitropism?
A. plants coiling around things
B. plants leaning toward a window
C. roots growing downward
D. stems growing upward
Section Check
2
Answer
The correct answer is D. Plants growing
upwards is a positive response to gravity while
roots’ downward growth is a negative response
to gravity.
Section Check
2
Question 2
Which plant hormone
is responsible for the
uneven growth
illustrated in this
diagram?
Section Check
2
A. abscisic acid
B. auxin
C. cytokinins
D. gibberellins
Section Check
2
Answer
The answer is B. The hormone auxin causes
this to occur. Auxin is more concentrated on
the shaded side of the plant and causes the cells
there to elongate. The plant then grows toward
the light.
Section Check
2
Question 3
What are examples of three stimuli that cause
tropisms in plants?
Section Check
2
Answer
Possible answers include: touch, light, gravity,
electricity, temperature, and darkness.
Tropisms are apparent movements of a plant
that are caused by changes in growth. They can
be positive or negative.
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