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UNIT 5: Plants: Anatomy, Growth, and Function
Chapter 13: Plants: Uses, Form, and
Function
Chapter 14: Plants: Reproduction,
Growth, and Sustainability
How do plants grow and reproduce?
14: Plants: Reproduction, Growth, Sustainability
Seeds are the embryos of the next generation of plants. By saving
and exchanging seeds produced by plants with desirable traits,
farmers and gardeners ensure the plants’ genetic continuation.
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability
Plants reproduce by both asexual and sexual reproduction. Sexual
reproduction is by sporic reproduction (alternation of generations).
Haploid gametophyte cells (1n) produce gametes, while diploid
(2n) sporophyte cells produce spores. Male and female gametes
unite to form the sporophyte that continues the life cycle.
14.1 Plant Reproduction
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
All plants have a life cycle
involving alternation of
generations. The cycle varies
among species. The variation
is mostly due to the type of
structure that releases the
spores.
Seedless plants include vascular ferns and non-vascular mosses.
Fertilization requires the sperm to swim from the male
gametophyte to the egg in the female gametophyte. Thus, water
must be present, and the sperm must have a flagellum.
In non-vascular plants, the gametophyte
is the dominant generation. In
vascular plants, the sporophyte
is the dominant generation.
Sexual Reproduction in Seedless Plants
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
Peat, or sphagnum, moss commonly
grows in boggy areas. Its antibacterial and
absorbent properties led to its historic use
by some Aboriginal peoples as dressing
for wounds.
Seed plants include gymnosperms and angiosperms. The
gametophytes are not free-living. The male gametophyte, called
a microspore, develops into a pollen grain and sperm.
The female gametophyte, called a macrospore, develops into an
egg cell. In order for pollination to occur, the male
gametophyte must be transferred to the female reproductive
structure.
Sexual Reproduction in Seed Plants
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
During pollination, the pollen grain develops a pollen tube to
reach the egg. Sperm develop in the tube and travel to the
egg. The zygote becomes an embryo with a small amount of
food protected by a tough seed coat. The seeds remain in the
female structure until maturity when they are released. Seeds
grow into sporophytes.
Sexual Reproduction in Gymnosperms
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
Angiosperm sexual reproduction involves the flower organ. Flowers
have:• sepals – protect the flower bud
• petals – attract pollinators
Pollination takes place on the stigma. Female gametophytes develop
in the ovules, where eggs are formed.
Sexual Reproduction in Angiosperms
UNIT 5 Section 14.1Chapter 14: Plants: Reproduction, Growth, and Sustainability
• stamens – male reproductive structure
• pistils – female reproductive structure
• Complete flowers have sepals, petals, stamens, and one or
more pistils (roses, tulips).
• Incomplete flowers are missing one or more flower parts
(grasses, wild ginger).
• Perfect flowers have both pistils and stamens on each flower.
• Imperfect monoecious plants have pistils and stamens found
on separate flowers on same plant (corn, oaks).
• Imperfect dioecious plants have pistils and stamens found on
different plants (willow, ginkgo).
Variations Among Flowers
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
Continued…
• Petal number can distinguish monocots from dicots:
o multiple of four or five: dicot (meadow beauty)
o multiple of three: monocot (trillium)
Variations Among Flowers
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
The meadow beauty (A) and sulfur cinquefoil (B) are
dicots. The trillium (C) is a monocot.
• Self-pollination: Plants pollinate themselves or another flower on
the same plant. This can lead to loss of genetic variation and
species vulnerability.
• Cross-pollination: Plants receive pollen from another plant,
ensuring genetic diversity.
• Animal Pollination: Insects and other small animals move from
flower to flower collecting nectar and moving pollen. Bright,
sweet-smelling flowers attract these pollinators.
• Wind Pollination: Some plants lack colourful reproductive organs
but produce large quantities of light pollen grains to increase the
chances of pollen landing on a receptive reproductive organ.
Pollination Mechanisms
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
As a pollen tube grows to
reach the ovule, the male
gametophyte performs
mitosis to create two
sperm cells. One fuses
with the egg, the other
fuses with the polar nuclei,
forming a triploid (3n) cell
that divides into nutrient-
rich endosperm tissue.
Follow the illustration for
the complete life cycle of a
peach.
Life Cycle of Flowering Plants
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
The zygote (2n) is a sporophyte that divides to produce a
monocot or dicot embryo with a 3n endosperm. The outside
layers of the ovule form a protective cover called the seed
coat. As the ovule develops into a seed, changes occur in the
ovary wall that lead to the formation of a fruit. The fruit may
also be made from other flower parts.
Seed and Fruit Development
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
Seeds of monocots
differ in structure
and function from
those of dicots.
Seed Dispersal
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
If the seed lands in a location with sufficient resources, it can
develop into a seedling. If there are not enough resources, the seed
may lose water slowly and enter dormancy for many, many years.
Seeds of
different species
are adapted to
be dispersed in
different ways.
The survival rate of a species is increased when seeds are dispersed
away from the parent plant(s) to reduce competition for resources.
Fruits attract animals and can be transported great distances, aiding
wide dispersal.
Water, animals, and wind are means of dispersal.
Germination is the resumption of growth after dormancy. The seed
absorbs water, and the seed coat breaks. The stored food supports
the growth of the embryo. The radicle emerges first and becomes
roots. The hypocotyl then emerges as an early stem. It may have
the cotyledons and the embryonic leaves on it. Monocots leave their
cotyledon below ground.
Seed Germination
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
Photosynthesis begins when chloroplast-containing cells emerge.
Asexual reproduction (cloning) can be an advantage when plants
are well-adapted to their environment. Farmers and gardeners
have studied and perfected techniques of artificial propagation
that involve asexual reproduction from a plant’s roots, stems, or
leaves (vegetative propagation).
How does this method of reproduction affect genetic
diversity? Justify your answer.
Asexual Reproduction
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
• split the plant into two or more; each piece contains roots
and shoots
• simple and inexpensive way to propagate or thin out plants
• examples: bulbs (tulips), plants with more than one stem
(peonies, hostas)
Asexual Reproduction: Division (splitting)
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
• shoot or root part is cut and
joined to the vascular
cambium of another
• allows combination of
characteristics of two
varieties of plants; helps
repair damaged trees;
quickens fruit production
• examples: fruit trees (apple),
nut trees (almond),
grapevines
Asexual Reproduction: Grafting
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
• a part of a leaf or entire leaf is cut and placed in growth
medium (water, soil, or vermiculite) so that meristem cells
can grow shoots and roots
• faster than propagating from seed; can be done out of
season
• examples: African violets, snake plants, aloe vera
Asexual Reproduction: Leaf Cutting
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
• A stem or shoot tip is cut and
placed in growth medium to
grow roots from meristem cells
• Faster than propagating from
seed; can be done out of season
• examples: herbs (basil),
gymnosperm and angiosperm
trees (pine, willow), flowering
bushes (roses), grapevines
Asexual Reproduction: Stem Cutting
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
• A root is cut and placed in a growth medium in the same
orientation as the original plant; meristem cells form a new
root and shoot system
• can be done when plant is in spring or autumn dormancy
• examples: trilliums, mint, irises
Asexual Reproduction: Root Cutting
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
• A long, vine-type stem is bent to touch the ground, slightly cut
to promote growth of roots, and buried until a plant develops
that can be cut from the parent to grow independently
• Large clone produced quickly; water and nutrients from parent
will support rooting process
• examples: honeysuckle, willow, hydrangea
Asexual Reproduction: Simple Layering
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
• A strip of outer bark is removed from
a woody stem; moist sphagnum moss
is packed around the wound and
plastic-wrapped until roots develop;
the rooted stem can then be cut from
the parent plant and planted
• Large woody plant clone produced
quickly
• examples: tropical plants (rubber
trees), lilacs, magnolias, fruit and nut
trees
Asexual Reproduction: Air Layering
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
• A cell or small piece of tissue is placed in a sterile nutrient
medium that promotes shoot and root growth; a tiny plantlet
develops
• Can be used to produce millions of plantlets for genetic
modification
• examples: most ferns,
gymnosperms, angiosperms
Asexual Reproduction: Cell Culturing
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
Summary of Plant Reproduction
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.1
Section 14.1 Review
UNIT 5 Section 14.1Chapter 14: Plants: Reproduction, Growth, and Sustainability
Plant hormones are chemical compounds. They:
14.2 Plant Growth and Development
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.2
• play a role in determining cellular differentiation and gene
expression in any cell as a plant grows from shoot and root
apical meristem
• regulate the differentiation of plant cells, plant growth, and the
plant’s response to a given stimulus (gravity, light, touch)
• act as chemical signals between cells and tissues
• include auxins, cytokinins, gibberellins, ethylene, and abscisic
acid
Stimulatory hormones:
Stimulatory vs. Inhibitory Hormones
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.2
• include auxins, cytokinins, and gibberellins
• can stimulate cell division, cell differentiation, early flowering
and cell elongation that develops into apical dominance (growth
is upward with little lateral growth)
• used in industry to increase fruit and cluster size
• examples: indoleacetic acid (auxin)
Continued…
(A) Auxin stimulates apical
meristem growth and inhibits
the growth of side branches.
(B) Removing the apical
meristem decreases the
amount of auxin. As a result,
side branches grow.
Inhibitory hormones:
Stimulatory vs. Inhibitory Hormones
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.2
• include ethylene and abscisic acid
• can inhibit growth by weakening cell walls, promoting
breakdown of starch, blocking stimulatory hormones and blocking
the intake of carbon dioxide
• commercial use: In order to protect fruit in transit, it is shipped
long distances in an unripened state; ethylene gas is then used to
ripen it when it reaches its market.
Bananas and other fruits ripen due to ethylene.
Plant Hormones Summary
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.2
Plants can respond to a stimulus and grow toward it, or they can
perform a simple nastic response, which is a movement of the
plant that is reversible, repeatable, and does not include growth.
An example of a nastic response is the opening and closing of
flower petals as light conditions change.
Plant Responses to Environmental Stimuli
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.2
Nastic movements in the leaves of this sensitive plant (Mimosa pudica)
are caused by changes in water pressure in the leaf cells. When the
stimulus ends, the leaves return to their original orientation.
Tropic responses are growth responses to external stimulation
coming from one direction in the environment. They include:
Phototropism
• a growth response to light produced by an unequal distribution
of auxin. More auxin on the side with less light causes those cells
to elongate and bend the plant toward the light.
Gravitropism
• a “positive” growth response of the roots downward or a
“negative” growth response of stems upward
Thigmotropism
Tropic Responses
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.2
• a growth response to mechanical
(contact) stimuli
What tropism(s) are evident here?
A plant’s ability to grow is affected by:
• sunlight
• carbon dioxide
• water
• soil pH
• macro- and micronutrients
(dissolved in water)
Each plant species grows best within a narrow pH
range. Plants that thrive in acid soil include pine,
blueberry, and potatoes. Plants that thrive in alkaline
soil include lawn grass, beans, pears, and lettuce.
Macronutrients are nutrients that are needed in
amounts greater than 1% of a plant’s dry weight and
include nitrogen, potassium, calcium, magnesium,
phosphorus, and sulfur. Micronutrients are needed in
amounts less than 1% of a plant’s dry weight.
Other Plant Growth Factors
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.2
Nutrients
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.2
14.2 Review
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.2
14.3 Succession and Sustainability
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.3
In addition to the other human and ecosystem services plants
provide, they also play a role in establishing and developing
communities. This is called ecological succession.
Ecological succession is the change in an ecosystem when
one community replaces another; it results from changes in
abiotic and biotic factors.
Events that change the structure of a biological community and
sometimes destroy all actively growing organisms are called
ecological disturbances. They include:
• forest fires
• floods
Within months of most disturbances, new vegetation sprouts and
animals repopulate until, over time, the area is again thick with
growth. Ecologists believe that disturbances, both large and small,
are the norm rather than the exception in communities.
Understanding how disturbances help and hinder plant and animal
species is critical for the preservation of natural communities.
Ecological Disturbances
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.3
• volcanic eruptions
• retreating glaciers
Primary Succession
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.3
Primary succession is the establishment of a community in
an area after an ecological disturbance has left exposed rock
that does not have any topsoil.
Often, liverworts are the first species (pioneer species) to
colonize a barren area. With other organisms, such as
bacteria, algae, and lichens, they form a pioneer community
that can survive in harsh conditions.
What traits do these pioneer species have in common
that make them suited to living in barren areas?
Primary Succession
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.3
As pioneer species continue to grow in a barren area, early
organisms die and begin to form soil. As soil accumulates,
nutrient and moisture content builds and pH changes. This allows
larger species to grow in the area.
Scientists measured changes in the nitrogen content and the number
of plant species during primary succession in Glacier Bay, Alaska.
Primary Succession
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.3
The area continues to change as larger plants move in. Many early
species are vascular and non-vascular seed species; their seeds have
dispersed and germinated quickly. They compete for space and light.
Successive surviving species colonize the area. Different types of
plants provide habitat for different birds and animals. Changes
continually occur until a stable climax community of plants and
animals forms.
It will remain
stable until a
major
disturbance
occurs.
Secondary Succession
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.3
Secondary succession is the recolonization of an
area after an ecological disturbance that has left the
soil intact. It also includes changes in the
composition and number of species over time.
Biodiversity and Ecosystem Resilience
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.3
Research has shown that ecosystems (climax
communities) with high diversity are better able to
withstand disease, competition from invasive
species, and extreme weather events.
Maintaining sustainable
and diverse natural and
human-made ecosystems
is critical to the health of
the biosphere.
14.3 Review
UNIT 5 Chapter 14: Plants: Reproduction, Growth, and Sustainability Section 14.3
UNIT 5 STSE Feature
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