Plant Processes
Chapter 12
M.Elizabeth
MLK JHS
2005-2006
Review
• What are the two types of reproduction?
• What is the name of the plant female reproductive
organ?
• What is the name of the plant male reproductive
organ?
• What is the purpose of reproduction?
• What are the two gases involved in photosynthesis?
• Where does photosynthesis occur in a plant cell?
• What is the name of the pigment which absorbs
light energy?
12.1 The Reproduction of Flowering Plants
• How does fertilization occur
– Sperm cells produced in the stamen must be
able to reach eggs in the pistil.
– Sperm cells within pollen grains move down
the pollen tube which the plant has produced,
and into the ovary.
– Fertilization occurs when a sperm cell fuses
with an egg cell.
A seed is born
Flower Anatomy
From Flower to Fruit
• After fertilization the following takes place:
– the fertilized egg within the ovule develops into
a seed.
– The ovary surrounding the ovule develops into a
fruit.
– The fruit swells and ripens while holding and
protecting the developing seeds.
– The seeds represent the next generation once
germinated and looking like a plant.
Seeds Become New Plants
• Once a seed is fully developed, the seeds
stop developing and become DORMANT.
– When seeds are dormant they are inactive and
the seeds metabolism stops.
– Dormant seeds can survive long periods of
drought or freezing temperature.
• Once a seed is in an environment with
water, oxygen, and a suitable temperature
(ideally about 27C or 80.6F) the seed
germinates or sprouts.
Seed Germination
Andrew Syred
http://www.visions-of-science.co.uk/winners2004/win-04.htm.
Asexual Reproduction
• Parts of a plant are used to create a new
plant without forming flowers or seeds;
• Examples:
– Strawberry runners
– Potato Tubers
– Geranium slips
Don’t eat green potatoes.
Potatoes belong to the
nightshade family, and most
green portions of plants in this
family contain an alkaloid
poison called solanine.
12.2 The Ins and Outs of Making Food
• Photosynthesis – light to sugar
– Occurs in plant cell chloroplasts
– Chloroplast contain chlorophyll, a green pigment
that absorbs light energy.
– Chlorophyll is green because in the light
spectrum green is not absorbed, it is reflected.
– The overall reaction involves multiple steps:
6 CO2 + 6 H2O
C6H12O6 + 6O2
Gas exchanges occurs through leaf stomata
(stoma, singular). Transpiration is the
movement of water through the stoma.
What are the
two gasses
involved in
photosynthesis?
12.3 Plant Responses to the
Environment
• Response to Stimuli
– Anything that causes a reaction in an
organism, organ system, organ, tissue, or
cell is a stimulus.
• Tropism - Plants growth in respond to a
stimulus either:
– positively/towards the stimulus or
– negatively/away from the stimulus:
Tropic Responses
– Light = phototropism
•Stems are positively phototropic
–moving towards the light stimulus
•Roots are negatively phototropic
–moving away from the light
stimulus
– Gravity = gravitropism
•Stems are negatively gravitropic
•roots are positively gravitropic.
Current ideas about Phototrophism
• Cells produce a hormone called an auxin,
indole-3-acetic acid (IAA) while growing
• Unequal distribution of auxin causes the
bending in phototropism by affecting the
cell length of plant cells
– High concentration the cells become longer
– Low concentrations the cells become shorter
Phototropic Effect
Adaptive Value of Phototropisms
• Roots growing down and/or away from light
are more likely to find the soil, water, and
minerals they need.
• Stems growing up and toward the light will
be able to expose their leaves so that
photosynthesis can occur.
What is the adaptive value of gravitropism?
• Think – Pair – Share
Seasonal Responses
Length of Day
• The length of day changes over a season.
• Days are longer in the summer than in the
winter.
• The difference between day and night
length is an important stimulus for many
plants.
• Length of day is a stimulus that
determines when some plants will
reproduce.
Poinsettia
Seasonal Changes in Leaves
• All trees lose their leaves
• Evergreens and Deciduous Trees
– Evergreen trees shed their needle leaves a little
at a time
– Deciduous trees lose their leaves at the same
time each year.
•Usually in the fall and winter
•Tropics or areas near the Equator have only
wet and dry seasons so the deciduous trees
shed leaves before the dry season begins.
Prickly Pear Cactus
• Desert plants live with extremes in
temperature, water availability and solar
radiation by adapting physically rather than
behaviorally.
• Most desert plant adaptations seem to be
geared towards minimizing water loss; a
difficult task since plants must "breathe" in
order to photosynthesize, losing body water
to the atmosphere in the process..
Different Desert Adaptations:
• In their effort to survive in a hostile environment,
desert plants have three adaptations types that have
developed.
• Morphological - related to the form and structure of
the plant
• Physiological - related to the biological function of the
plant. Such features may include:
· Accumulate water
· Self-pruning
· Plant chemically shifts temperature
• Behavioral - where the plant can survive
Remember plants cannot move
· Grow where there is more water
· Cracks in the sandstone - where water accumulates
Morphological features
•
•
•
•
•
•
•
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Fuzzy or hairy leaf surface
Waxy leaves
Shiny, reflective leaves
Small leaves
Deep tap roots
Extensive surface roots
Thicker leaves
Leaf orientation such that minimizes the area exposed to
midday heat
• Spines instead of leaves
• Thicker leaves
• Grow in shade or self-shade
12.4 Plant Growth
• All living things grow. A plant’s growth is
affected by its
• Genes: sequences of DNA that code for a
particular trait. Heredity the passing of traits
from one generation to the next.
• Hormones: are chemical messengers that
carry information from one part of an
organism to another, produced in small
quantities when genes are expressed.
• Environment: determines behavior and
appearance.
Plant Hormones
•
A plant hormone is produced in a part of a plant,
then moves through the plant to cause a response in
all parts of the plant it contacts.
• Five classes of have been identified:
1. Auxin – growth stimulator,
2. Cytokinin – growth stimulator
3. Gibberellin – growth stimulator
4. Abscisic acid – growth inhibitor, promote dormancy,
and help the plant withstand stressful conditions.
5. Ethylene - growth inhibitors or "aging stimulators".
A gas produced and involved in fruit ripening.
How Hormones Work
• Generally they work by affecting cell division,
elongation and differentiation (telling the cell
what DNA sequences should be expressed).
• Effects of the chemicals vary depending on
target area, developmental stage, hormone
concentration, and interactions with other
hormones.
• At the cellular level, the hormones result in
gene expression, effects on enzymes, or
modifications of cell membrane properties.
Review
1. Which of the following statements is NOT true
of flowering plants?
a. Fertilization takes place within the flower.
b. They produce seeds in fruit.
c. They use flowers to reproduce asexually.
d. They are the largest group of plants in the
world.
2. Flowers can have both male and female
reproductive structures. True or False?
Review
3. The ovule becomes a _____________after
fertilization.
4. A fruit, which protects and holds the seeds,
develops from the __________ of a flower.
5. Green light is reflected by chlorophyll. True or
False?
6.During photosynthesis, light energy is used to split
water into __________ and ____________
7. Sugar is broken down by plant cells for energy
during cellular respiration. True or False?
Review
8. Transpiration is the loss of water vapor from
leaves. True or False?
9. When a tropism is _________, a plant will grow
toward the stimulus. (positive or negative)
10. A plant’s traits are determined by heredity.
True or False?
11. After seeds develop fully, and before they
sprout, they may become ______________.
(deciduous or dormant)
Review
12. During________________, energy from
sunlight is used to make sugar.
(photosynthesis or phototropism)
13. The loss of water through stomata is called
_______________.(transpiration or tropism)
14. A change in plant growth in response to the
direction of light is called_______________.
(gravitropism or phototropism)
15. Plants that have leaves year-round are
______________. (deciduous or evergreen)
Review
16. Plants that seasonally lose their leaves are
_____________.(deciduous or evergreen)
17. Plant cells need carbon dioxide for
a. cellular respiration. b. phototropism.
c. fertilization.
d. photosynthesis.
18. When chlorophyll breaks down,
a. pollination occurs.
b. other pigments become visible.
c. red pigments disappear.
d. photosynthesis occurs.
Phototropism
• Early in the history of science, Darwin kept birds.
To provide the birds with vitamins in those days,
one needed to grow sprouts. A common species
was Phalaris or canary grass!
• Darwin noted that the first leaf (coleoptile) of
canary grass was very sensitive and responsive to
light. He sprouted the seeds in flats and fed the
mature seedlings to the birds. But before they made
green leaves, the white first leaf (coleoptile)
appeared and grew toward the light coming from
the nearby window.
• Darwin was very curious about this and did a few
experiments.