the angiosperms: an introductions to flowering plants

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

BIOLOGYA GUIDE TO THE NATURAL WORLD

FOURTH EDITION

DAVID KROGH

The Angiosperms:An Introductions to Flowering Plants

Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.

24.1 The Importance of Plants


The Importance of Plants

• Plants are vital to many types of living things on Earth.

• The photosynthesis they carry out indirectly feeds many other life-forms.



• The oxygen plants produce as a by-product of photosynthesis is vital to many organisms.

• The lumber and paper that trees provide is important to human beings.



• Plants act as an anchoring environmental force by preventing soil erosion and absorbing carbon dioxide and pollutants.


The Four Types of Plants

• There are four principal varieties of plants:– Bryophytes, represented by mosses.– Seedless vascular plants, represented by ferns.– Gymnosperms, represented by coniferous

(evergreen) trees.– Angiosperms, or flowering plants.

• Of the four varieties, angiosperms are by far the most dominant on Earth.


24.2 The Structure of Flowering Plants


Structure of Flowering Plants

• Plants live in two worlds, above the ground and below it.

• Their anatomy can be conceptualized as consisting of the aboveground shoots and the below-ground roots.


Structure of Flowering Plants

• Roots absorb water and nutrients, anchor the plant, and often act as nutrient storage sites.

• Shoots include the plant’s leaves, stems, and flowers.

• Leaves serve as the primary sites of photosynthesis in most plants.


Shoots: Leaves, Stems, and Flowers

• Leaves have a profusion of tiny pores, called stomata, that open and close in response to the presence or absence of light.

• In this way, the stomata control the flow of carbon dioxide into the plant and the flow of oxygen and water vapor out of the plant.



• Stems give structure to plants and act as storage sites for food reserves.



• Flowers are the reproductive structures of plants, with most flowers containing both male and female reproductive parts.



• The male reproductive structure, called a stamen, consists of a slender filament topped by an anther.

• The anther’s chambers contain the cells that will develop into sperm-containing pollen grains.



• The female reproductive structure, the carpel, is composed of:– A stigma, on which pollen grains are deposited– A tube called a style, which raises the stigma to

such a height that it can catch pollen– And a structure called an ovary, where fertilization

of the female egg and early development of the resulting embryo take place.


24.3 Basic Functions in Flowering Plants


Reproduction in Angiosperms

• Pollen grains develop from cells called microspores located inside the plant’s anthers.

• At maturity, each pollen grain consists of two sperm cells, one tube cell, and an outer coat.



• Plant eggs develop from a cell called a megaspore within the plant’s ovary.

• When a pollen grain from one plant lands on the stigma of a second plant, the pollen grain germinates, developing a pollen tube that grows down through the second plant’s style.



• Sperm cells from the pollen grain travel through the pollen tube.

• One of the sperm cells reaches the egg in the ovary of the second plant and fertilizes it.



• Once it is fertilized by the sperm cell, the egg (or zygote) develops into an embryo that eventually will be surrounded by a tough outer covering.



• The combination of embryo, its food supply, and the outer covering is called a seed.

• A seed is capable of being planted in the ground and growing into a new generation of plant.



• Angiosperms can be defined as plants whose seeds are surrounded by a layer of tissue called fruit.

• Fruit is the mature ovary of a flowering plant



• Plants can reproduce asexually through such means as grafting.

• This is known as vegetative reproduction.


Fluid Transport

• Fluid transport in plants is handled through two kinds of tissue:– xylem, through which water and dissolved minerals

flow; and– phloem, through which the food the plant produces

flows, along with hormones and other compounds.


Fluid Transport

• Xylem is composed of two types of fluid-conducting cells—vessel elements and tracheids.

• Phloem is composed of cells called sieve elements and their related companion cells.


Hormones

• Plant hormones regulate plant growth and development and integrate the functioning of various plant structures.


Hormones

• Many fruits ripen under the influence of the plant hormone ethylene.

• The hormone IAA is important in controlling plant growth.


Growth

• Plants do not grow vertically throughout their length.

• Instead, they grow almost entirely at the tips of both their roots and shoots.


Growth

• Some plants, such as trees, thicken through lateral or “secondary” growth.

• The growth of most plants is indeterminate, meaning it can go on indefinitely.


Defense

• Plants have formidable defenses, both structural (such as cactus spines) and chemical (such as antifungal compounds).


Cooperative Relationships

• Plants enter into cooperative relationships with other organisms.

• Most plant roots are linked to underground fungal extensions called hyphae.



• The hyphae bring added water and nutrients to the plant and the photosynthesis the plant performs brings food to the fungi.

• The combined root–hyphae associations are known as mycorrhizae.



• Some plants form cooperative relationships with nitrogen-fixing bacteria.

• The bacteria take in atmospheric nitrogen and transform it into a form the plants can use.

• The plants provide the bacteria with nutrients.


Leaves, Reproduction, and Fluid Transport

PLAYPLAY Animation 24.1: Leaves, Reproduction, and Fluid Transport


24.4 Responding to External Signals


Gravitropism

• With gravitropism, plants are able to sense their orientation with respect to the Earth and direct the growth of their roots and shoots accordingly— roots into the Earth, shoots toward the sky.


Phototropism

• Plants will bend toward a source of light through the process of phototropism, meaning a curvature of shoots in response to light.


Thigmotropism

• Thigmotropism is defined as the growth of a plant in response to touch.

• Some plants can climb upward on other objects by making contact with them and then encircling them in growth.


Differential Growth

• Differential growth on one side of the root or stem makes possible phototropism, gravitropism, and thigmotropism.


Responding to Seasons

• In temperate climates, deciduous trees exhibit a coordinated, seasonal loss of leaves and enter into a state of dormancy, existing on stored nutrient reserves in colder months.



• Plants can sense the passage of seasons and time their metabolic and reproductive activities accordingly.

• One mechanism that assists in this process is photoperiodism, which is the ability of a plant to respond to changes it is experiencing in the daily duration of darkness relative to light.



• Some plants that exhibit photoperiodism are long-night plants, meaning those whose flowering comes only with an increased amount of darkness—in late summer or early fall.



• Others are short-night plants, meaning those whose flowering comes only with a decreased amount of darkness—in early to midsummer.


Phototropism

PLAYPLAY Animation 24.2: Phototropism

the angiosperms: an introductions to flowering plants

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