Reproduction and Development of Flowering Plants
(bee keeper) ©Liu Jin/AFP/Getty Images; (bee): ©Stephen Dalton/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-1
Most angiosperms reproduce sexually
Section 24.1
Flowers are the sex organs of angiosperms. This bee is gathering pollen that might deliver sperm to the next flower it visits.
©Stephen Dalton/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-2
Angiosperms seeds develop from fertilized egg cells
Section 24.1
This cedar waxwing is carrying a seed, which developed from a fertilized egg cell.
Figure 24.11
(a): ©Rod Planck/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-3
Sexual reproduction results in genetically unique offspring
Section 24.1
Flowers and seeds are produced by angiosperms that
sexually reproduce, yielding genetically unique offspring
with traits derived from two parents.
Figure 24.11
©Stephen Dalton/Science Source
(a): ©Rod Planck/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-4
Some angiosperms reproduce asexually
Section 24.1
Some species of angiosperms also reproduce asexually, forming new individuals by mitotic division.
Figure 24.1
(a): ©Steven P. Lynch RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-5
Asexual reproduction produces clones
Section 24.1
Offspring produced asexually are genetically identical
to each other and to their parents.
Figure 24.1
(a): ©Steven P. Lynch RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-6
Some angiosperms can reproduce sexually or asexually
Section 24.1
These aspen trees can reproduce either asexually, as suckers grow from roots, or sexually via seeds.
Figure 24.1
(a): ©Steven P. Lynch RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-7
An example of asexual reproduction
Section 24.1
Similarly, the leaves of this kalanchoe plant produce genetically identical plantlets.
Figure 24.1
(b): ©Steven P. Lynch RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-8
Advantages of asexual and sexual reproduction
Section 24.1
Asexual reproduction is advantageous when conditions are stable and plants are well-adapted to their surroundings.
Sexual reproduction produces variable offspring,
increasing reproductive success in a changing world.
Figures 24.1 24.11
(b): ©Steven P. Lynch RF
(a): ©Rod Planck/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-9
Angiosperm sex: Flowers, fruits, and seeds
Section 24.2
The angiosperm life cycle is an alternation of generations with multicellular diploid and haploid stages.
Figure 24.3
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-10
Alternation of generations
Section 24.2
This diagram is an overview of the angiosperm life cycle.
Let’s start with the flower.
Figure 24.4
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-11
Angiosperm sex: Flowers
Section 24.2
The first step in angiosperm reproduction is the formation of flowers on the mature sporophyte.
Figure 24.5
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-12
Angiosperm flower structures
Section 24.2
A typical flower has four whorls of structures, all of which are modified leaves.
Figure 24.5
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-13
Angiosperm flower structures: Calyx
Section 24.2
The outer whorl is the calyx. It consists of sepals, which enclose and protect the inner floral parts.
Figure 24.5
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-14
Angiosperm flower structures: Corolla
Section 24.2
The second whorl is the corolla, which is made of petals.
Figure 24.5
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-15
Angiosperm flower structures: Stamen
Section 24.2
The third whorl is the male reproductive parts. Stamens are filaments with pollen-producing anthers on top.
Figure 24.5
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-16
Angiosperm flower structures: Carpel
Section 24.2
The fourth whorl is the female reproductive parts. A carpel includes:
-the ovary, which encloses one or more ovules.
-a stalklike style. The top of the style, called the stigma, receives pollen.
Figure 24.5
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-17
Inside the flower: Meiosis
Section 24.2
Inside the flower, meiosis produces haploid spores that develop into gametophytes.
Figure 24.3
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-18
Inside the flower: Microspores and megaspores
Section 24.2
Anthers produce microspores, which divide into male gametophytes (pollen grains).
Ovules produce megaspores, which divide into female gametophytes (embryo sacs).
Figure 24.4
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-19
Modes of pollen dispersal: Wind
Section 24.2
Some flowers release pollen grains in the wind.
Figure 24.6
©Dr. Jeremy Burgess/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-20
Modes of pollen dispersal: Animals
Section 24.2
Other flowers attract animal pollinators, which unwittingly carry pollen between plants.
Figure 24.6
(a): ©Corbis RF; (b): ©MedioImages/Getty Images RF;
(c): ©Merlin D. Tuttle/Bat Conservation International/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-21
Plant and pollinator: A mutualistic relationship
Section 24.2
Often, the pollinator benefits from its association with plants—animals use plants for food, shelter, or a mating ground.
Figure 24.6
(a): ©Corbis RF; (b): ©MedioImages/Getty Images RF;
(c): ©Merlin D. Tuttle/Bat Conservation International/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-22
Angiosperm sex: Pollination
Section 24.2
If a pollen grain lands on a receptive stigma, pollination occurs.
Figure 24.4
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-23
Angiosperm sex: Pollen tube
Section 24.2
When the pollen grain germinates, a pollen tube begins to grow toward the ovule.
Figure 24.7
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-24
Angiosperm sex: Two sperm nuclei
Section 24.2
Two sperm nuclei travel through the pollen tube to the ovule.
Figure 24.7
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-25
Angiosperm sex: Fertilization
Section 24.2
The stage is now set for fertilization.
Figure 24.3
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-26
Angiosperm sex: Double fertilization
Section 24.2
In double fertilization, these sperm nuclei fertilize the egg and the two polar nuclei.
Figure 24.7
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-27
Angiosperm sex: Triploid endosperm
Section 24.2
Double fertilization results in a diploid zygote and triploid endosperm nucleus.
Figure 24.7
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-28
Angiosperm sex: Seeds
Section 24.2
After fertilization, the seed starts to develop.
A seed consists of an embryo, endosperm, and seed coat.
Figure 24.4
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-29
Seeds contain an embryo
Section 24.2
The zygote develops from a single cell into an embryo.
Figure 24.8
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-30
Seeds contain cotyledons
Section 24.2
Cotyledons are the embryo’s “seed leaves.” Embryonic shoots and roots also form.
Figure 24.8
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-31
Endosperm feeds the embryo
Section 24.2
Endosperm cells divide rapidly and nourish the embryo.
Figure 24.9
(a): ©Steven P. Lynch/McGraw-Hill Education
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-32
The seed coat
Section 24.2
The seed coat is a tough outer layer that protects
the embryo from damage, dehydration, and predators.
Figure 24.9
(b): ©Steven P. Lynch RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-33
Angiosperm sex: Fruits
Section 24.2
At the same time, a fruit develops from the ovary enclosing the developing seed(s).
Figure 24.4
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-34
Fruit formation
Section 24.2
These photos show how the fruit forms.
After pollination, the flower loses its petals.
Figure 24.10
Pollination occurs.
Petals are shed.
Fruit protects and disperses seeds.
Ovary and receptacle swell as seeds develop.
(all): ©Brent Seabrook
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-35
Hormones and fruit formation
Section 24.2
A developing seed releases hormones that trigger
fruit formation. The ovary swells.
Figure 24.10
Pollination occurs.
Petals are shed.
Fruit protects and disperses seeds.
Ovary and receptacle swell as seeds develop.
(all): ©Brent Seabrook
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-36
There are many types of fruit
Section 24.2
Fruits come in many forms.
Table 24.1
TABLE 24.1 Types of Fruits: A Summary
Fruit Type
Characteristics
Example(s)
Simple
©Ingram Publishing/�Alamy RF
Derived from one flower with one carpel
Olive, cherry, peach, plum, coconut, grape, tomato, pepper, eggplant, apple, pear
Aggregate
©Corbis RF
Derived from one flower with many separate carpels
Blackberry,�strawberry, raspberry, magnolia
Multiple
©Ingram Publishing/�Alamy RF
Derived from tightly clustered flowers whose ovaries fuse as the fruit develops
Pineapple, fig
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-37
The function of fruit
Section 24.2
Fruits protect and disperse seeds.
Seeds carried away from parent plants decrease the
chance of competition among parents, offspring, and siblings.
Figure 24.11
(a): ©Rod Planck/Science Source; (b): ©Barry Barker/McGraw-Hill Education; (C) ©Scott Camazine/Science Source; (d): ©Ingram Publishing/SuperStock RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-38
When does fruit ripen?
Section 24.2
Unripe fruits, which contain immature seeds, are usually distasteful. Ripe fruits are tasty; mature seeds are deposited in droppings.
Figure 24.11
(a): ©Rod Planck/Science Source; (b): ©Barry Barker/McGraw-Hill Education; (C) ©Scott Camazine/Science Source; (d): ©Ingram Publishing/SuperStock RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-39
Prickly fruits
Section 24.2
Prickly fruits stick to feathers or fur.
Figure 24.11
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-40
Flying and floating fruit
Section 24.2
Some fruits catch the wind with tufts of fluff.
Still others float in water currents.
Figure 24.11
(a): ©Rod Planck/Science Source; (b): ©Barry Barker/McGraw-Hill Education; (C) ©Scott Camazine/Science Source; (d): ©Ingram Publishing/SuperStock RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-41
24.2 Mastering concepts
How does pollen move from one flower to another, and why is this process essential for sexual reproduction?
(bee keeper): ©Liu Jin/AFP/Getty Images; (bee): ©Stephen Dalton/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-42
Plant growth begins with seed germination
Section 24.3
How does the embryo continue developing into a mature sporophyte?
Figure 24.3
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-43
Seed germination
Section 24.3
Figure 24.12
(b): ©Ed Reschke/Photolibrary/Getty Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-44
Seed germination: Rupturing the seed coat
Section 24.3
Figure 24.12
(b): ©Ed Reschke/Photolibrary/Getty Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-45
Seed germination: Endosperm fuels the growth of the embryo
Section 24.3
Figure 24.12
(b): ©Ed Reschke/Photolibrary/Getty Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-46
Plant growth before photosynthesis
Section 24.3
At first, the only energy source is fuel stored in the endosperm.
Figure 24.12
(b): ©Ed Reschke/Photolibrary/Getty Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-47
Photosynthesis takes over
Section 24.3
After the shoot emerges from the ground and the first leaves unfold, photosynthesis begins.
Figure 24.12
(b): ©Ed Reschke/Photolibrary/Getty Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-48
Seed germination in monocots and dicots
Section 24.3
Monocots and eudicots, two groups of plants, have slightly different development patterns.
Figure 24.12
Monocot development
Eudicot development
(a): ©Dwight Kuhn; (b): ©Ed Reschke/Photolibrary/Getty Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-49
Hormones regulate plant growth
Section 24.4
Chemicals called hormones travel between cells and regulate many aspects of plant growth.
Figure 24.14
©Nigel Cattlin/Alamy
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-50
Five hormones regulate most plant growth
Section 24.4
Five hormones cue many of the major changes in plant growth and development:
Figure 24.14
©Nigel Cattlin/Alamy
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-51
Hormones regulate plant growth: Auxin
Section 24.4
Auxins control plant responses to light and gravity, promote elongation of cells in a stem, and suppress the growth of lateral buds.
Figure 24.14
©Nigel Cattlin/Alamy
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-52
Hormones regulate plant growth: Cytokinins
Section 24.4
Cytokinins stimulate cell division in many plant parts, delay shedding of leaves, and stimulate growth of lateral buds.
Figure 24.14
©Nigel Cattlin/Alamy
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-53
Apical dominance
Section 24.4
Auxins are primarily released from the shoot tip, and cytokinins are primarily released from the roots.
The counteracting effect of these hormones is called apical dominance.
Figure 24.14
©Nigel Cattlin/Alamy
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-54
The role of auxin
Section 24.4
If the shoot tip is in place, auxins suppress the growth of lateral buds.
Figure 24.14
Apical dominance
©Nigel Cattlin/Alamy
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-55
The role of cytokinins
Section 24.4
Removing the shoot tip reduces the auxin concentration. Cytokinins stimulate cell division in lateral buds.
The plant’s growth becomes bushier.
Figure 24.14
Apical dominance
©Nigel Cattlin/Alamy
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-56
Hormones regulate plant growth: Gibberellins
Section 24.4
Gibberellins also stimulate shoot elongation. Farmers use these hormones to stimulate stem elongation and fruit growth.
Figure 24.15
©Custom medical Stock Photo/Newscom
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-57
Hormones regulate plant growth: Ethylene
Section 24.4
Ethylene hastens fruit ripening and stimulates shedding of leaves, flowers, and fruits.
Figure 24.16
©Kent Knudson/PhotoLink/Getty Images RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-58
The effects of ethylene
Section 24.4
Ethylene is the hormone responsible for the changes in texture, softening, color, and other processes involved in ripening. Ethylene gas is used commercially to ripen tomatoes. If the tomatoes on the left were exposed to ethylene, they would turn red.
Figure 24.16
©Kent Knudson/PhotoLink/Getty Images RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-59
Hormones regulate plant growth: Abscisic acid
Section 24.4
Abscisic acid inhibits shoot growth, maintains seed dormancy, and stimulates closure of stomata.
Figure 24.30
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-60
A summary of hormones and plant growth
Section 24.4
This table summarizes how hormones affect plant germination and development.
Table 24.2
TABLE 24.2 The “Classic Five” Plant Hormones: A Summary
Class | Synthesis Site(s) | Mode of Transport | Selected Actions |
Auxins | Shoot apical meristem, developing leaves and fruits | Diffusion between parenchyma cells associated with vascular tissue |
|
Cytokinins | Root apical meristem | In xylem |
|
Gibberellins | Young shoot, developing seeds | In xylem and phloem |
|
Ethylene | All parts, especially under stress, aging, or ripening | Diffusion of gas |
|
Abscisic acid | Mature leaves, especially in plants under drought or freezing stress | In xylem and phloem |
|
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-61
Light is a powerful influence on plant life
Section 24.5
Many plants grow toward light.
Figure 24.17
©Martin Shields/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-62
Phototropism
Section 24.5
Phototropism is a plant’s tendency to grow toward or away from light. How does this process occur?
Figure 24.17
©Martin Shields/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-63
Light and auxin
Section 24.5
The hormone auxin has a role in phototropism. As auxin molecules migrate away from light, they accumulate on the shaded side of a stem.
Figs. 24.17, 24.18
©Martin Shields/Science Source
Auxins stimulate proteins in cell membrane to pump protons out of cytoplasm into the cell wall.
High acidity in cell wall loosens bonds between cellulose fibers.
Cell elongates as water moves in by osmosis and turgor pressure stretches the weakened cell wall.
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-64
Auxin and phototropism
Section 24.5
Auxin binds to proton pumps, which transport hydrogen ions out of the cell. As the acidity in the cell wall increases, the bonds between cellulose fibers loosen.
Figure 24.18
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-65
Auxin and phototropism, continued
Section 24.5
Water enters cells on the shaded side of the stem by osmosis. Since the cell wall is less rigid, inflowing water causes the cells elongate.
Figure 24.18
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-66
The effect of phototropism
Section 24.5
Elongation of these cells causes the stem to bend toward the light.
Figs. 24.17, 24.18
©Martin Shields/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-67
Light and phytochrome
Section 24.5
Light also regulates seed germination, daily rhythms, and flowering by means of a photoreceptor in plants called phytochrome.
Figure 24.19
Translation produces proteins controlling seed germination, flowering, etc.
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-68
Phytochrome
Section 24.5
Phytochrome transforms to its active form when�it absorbs red light.
Figure 24.19
Translation produces proteins controlling seed germination, flowering, etc.
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-69
The effects of phytochrome
Section 24.5
Phytochrome helps plants sense day length. Plants flower when periods of darkness meet certain thresholds.
Figure 24.22
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-70
Phytochrome and flowering
Section 24.5
The dominant form of phytochrome determines whether flowering will occur. In this experiment, the last flash of light determines the prevalent form of phytochrome.
Figure 24.23
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-71
Plants respond to gravity and touch
Section 24.6
Gravity is another important environmental cue.
Figure 24.25
©Mariëlle Hoefnagels/McGraw-Hill Education
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-72
Gravitropism
Section 24.6
Gravitropism is directional growth in response to gravity. Shoots always grow upward.
Figure 24.25
©Mariëlle Hoefnagels/McGraw-Hill Education
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-73
Gravitropism and statoliths
Section 24.6
Roots always grow downward. Statoliths sink to the bottom of cells and therefore might help plants detect gravity.
Figure 24.24
(a): ©Martin Shields/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-74
Thigmotropism
Section 24.6
Plants also respond to touch, a reaction called thigmotropism.
Figure 24.25
©Mariëlle Hoefnagels/McGraw-Hill Education
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-75
An example of thigmotropism
Section 24.6
Specialized epidermal cells detect contact with an object, which stimulates the tendril to bend.
Figure 24.25
©Mariëlle Hoefnagels/McGraw-Hill Education
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-76
Plant parts die or become dormant
Section 24.7
During senescence, metabolism changes from synthesis to breakdown.
Figure 24.26
©Steven P. Lynch RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-77
Senescence
Section 24.7
Senescence also occurs in plants that survive for multiple growing seasons (perennial plants).
Figure 24.26
©Steven P. Lynch RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-78
An example of senescence
Section 24.7
Each year, deciduous trees loose their leaves.
Figure 24.26
©Steven P. Lynch RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-79
Ethylene and senescence
Section 24.7
Influenced by a high level of ethylene, the leaf separates from the tree at the abscission zone.
Figure 24.26
©Steven P. Lynch RF
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-80
Dormancy
Section 24.7
During the winter, some plants enter a seasonal state of dormancy, during which metabolism slows down.
Figure 24.27
©L. West/Science Source
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-81
Investigating life: �A red hot chili pepper paradox
Section 24.7
Why would natural selection favor spicy chili peppers, when one of the main function of fruits is seed dispersal?
Figure 24.28
©Sierra Vista Herald, Jonathon Shacat/AP Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-82
Investigating life: �A red hot chili pepper paradox —�who eats spicy food?
Section 24.7
Mammals, but not birds, avoid the spicy chemical in pungent chili peppers.
Figs. 24.28, 24.29
©Sierra Vista Herald, Jonathon Shacat/AP Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-83
Investigating life: �A red hot chili pepper paradox—�why think about digestion?
Section 24.7
Chili seeds eaten by mice and pack rats are destroyed, but they pass through birds intact.
Figs. 24.28, 24.29
©Sierra Vista Herald, Jonathon Shacat/AP Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-84
Investigating Life:�A red hot chili pepper paradox —�seed destroyers vs seed dispersers
Section 24.7
Natural selection favors adaptations that deter seed-destroyers but not beneficial dispersers.
Figs. 24.28, 24.29
©Sierra Vista Herald, Jonathon Shacat/AP Images
© McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution without the prior written consent of McGraw-Hill Education.
24-85