Chapter 39 Study Guide
Angiosperm Reproduction 
Overview
•	__________   reproduction is not the sole means by which flowering plants reproduce.
•	Many species can also reproduce  __________  , creating offspring that are genetically identical to them.
•	The propagation of flowering plants by sexual and asexual reproduction forms the basis of agriculture.
•	For 10,000 years, plant breeders have altered the traits of a few hundred angiosperm species by artificial selection, transforming them into today’s crops.
A. Sexual Reproduction
1. Sporophyte and gametophyte generations alternate in the life cycles of plants.
•	The life cycles of angiosperms and other plants are characterized by an  __________   of  __________  , in which haploid (n) and diploid (2n) generations take turns producing each other.
•	The diploid plant, the  __________  , produces haploid spores by meiosis.
•	These spores divide by mitosis, giving rise to multicellular male and female haploid plants—the  __________  .
•	The gametophytes produce gametes— __________   and  __________  .
•	Fertilization results in diploid  __________  , which divide by mitosis to form new sporophytes.
•	In angiosperms, the sporophyte is the dominant  __________  , the conspicuous plant we see.
•	Over the course of seed plant evolution, gametophytes became reduced in  __________   and  __________   on their sporophyte parents.
•	Angiosperm gametophytes are the most reduced of all plants, consisting of only a few cells.
•	In angiosperms, the sporophyte produces a unique reproductive structure, the  __________  .
•	Male and female gametophytes develop within the  __________   and  __________  , respectively, of a sporophyte flower.
•	__________   by wind, water, or animals brings a male gametophyte (pollen grain) to a female gametophyte contained in an ovule embedded in the ovary of a flower.
•	Union of gametes (__________  ) takes place within the ovary.
•	Ovules develop into  __________  , while the ovary itself develops into the  __________   around the seed.

2. Flowers are specialized shoots bearing the reproductive organs of the angiosperm sporophyte.
•	Flowers, the reproductive shoots of the angiosperm sporophyte, are typically composed of four whorls of highly modified leaves called floral organs, which are separated by very short internodes.
•	Unlike the indeterminate growth of vegetative shoots, flowers are  __________   shoots in that they cease growing once the flower and fruit are formed.
•	The four kinds of floral organs are the  __________  , __________  , __________  , and __________  .
•	Their site of attachment to the stem is the  __________  .
•	Sepals and petals are sterile.
•	__________  , which enclose and protect the floral bud before it opens, are usually green and more leaflike in appearance than the other floral organs.
•	In many angiosperms, the  __________   are brightly colored and advertise the flower to insects and other pollinators.
•	Stamens and carpels are the male and female reproductive organs, respectively.
•	A  __________  consists of a stalk (the  __________  ) and a terminal  __________   containing chambers called pollen sacs.
•	The pollen sacs produce  __________  .
•	A  __________   has an  __________   at the base and a slender neck, the  __________  .
•	At the top of the style is a sticky structure called the  __________   that serves as a landing platform for pollen.
•	Within the ovary are one or more  __________  .
•	Some flowers have a single carpel.
•	In others, several carpels are fused into a single structure, producing an ovary with two or more chambers, each containing one or more ovules.
•	The anthers and the ovules bear  __________  , where spores are produced by  __________   and where gametophytes later develop.
•	The male gametophytes are sperm-producing structures called  __________   __________  , which form within the pollen sacs of anthers.
•	The female gametophytes are egg-producing structures called  __________   __________  , which form within the ovules in ovaries.
•	__________   is the transfer of pollen from an anther to a stigma.
•	It begins the process by which the male and female gametophytes are brought together so their  __________   can unite.
•	Pollination occurs when pollen released from  __________   is carried by wind, water, or animals to land on a  __________  .
•	Each pollen grain produces a  __________   __________  , which grows down into the ovary via the  __________   and discharges  __________  into the embryo sac, fertilizing the  __________  .
•	The zygote gives rise to an  __________  .
•	The ovule develops into a  __________  , and the entire ovary develops into a  __________   containing one or more seeds.
•	Fruits carried by wind, water, or animals disperse seeds away from the source plant where the seed  __________  .
•	Numerous floral variations have evolved during the 130 million years of angiosperm history.
•	Plant biologists distinguish between  __________   flowers, those having all four organs, and  __________   flowers, those lacking one or more of the four floral parts.
•	A  __________   flower is equipped with both stamens and carpels.
•	All complete and many incomplete flowers are bisexual.
•	A  __________   flower is missing either stamens (therefore, a carpellate flower) or carpels (therefore, a staminate flower).
•	A  __________   plant has staminate and carpellate flowers at separate locations on the same individual plant.
•	For example, maize and other corn varieties have ears derived from clusters of carpellate flowers, while the tassels consist of staminate flowers.
•	A  __________   species has staminate flowers and carpellate flowers on separate plants.
•	For example, date palms have carpellate individuals that produce dates and staminate individuals that produce pollen.
•	In addition to these differences based on the presence of floral organs, flowers vary in size, shape, and color.
•	Much of this diversity represents adaptations of flowers to different animal  __________  .
•	The presence of animals in the environment has been a key factor in angiosperm evolution.
3. Male and female gametophytes develop within anthers and ovaries, respectively; pollination brings them together.
•	The male gametophyte begins its development within the  __________   (pollen sacs) of the anther.
•	Within the sporangia are microsporocytes, each of which will form four haploid  __________   through  __________  .
•	Each microspore can give rise to a haploid  __________  gametophyte.
•	A microspore divides once by  __________   and produces a generative cell and a tube cell.
•	The  __________   cell will eventually form sperm.
•	During maturation of the male gametophyte, the generative cell passes into the  __________   cell.
•	The tube cell, enclosing the generative cell, produces the  __________   tube, which delivers  __________   to the  __________  .
•	This is a pollen grain, an immature  __________   gametophyte.
•	This two-celled structure is encased in a thick, ornate, distinctive, and resistant wall.
•	A pollen grain becomes a mature gametophyte when the generative cell divides by  __________   to form two  __________   cells.
•	In most species, this occurs after the pollen grain lands on the stigma of the carpel and the pollen tube begins to form.
•	The pollen tube grows through the long  __________   of the carpel and into the  __________  , where it releases the sperm cells in the vicinity of the  __________   __________  .
•	__________  , each containing a single sporangium, form within the chambers of the ovary.
•	One cell in the sporangium of each ovule, the megasporocyte, grows and then goes through __________  , producing four haploid  __________  .
•	In many angiosperms, only one megaspore  __________  .
•	This megaspore divides by  __________   three times without  __________  , forming  one cell with eight haploid nuclei.
•	Membranes partition this mass into a multicellular  __________   gametophyte—the embryo sac.
•	Three cells sit at one end of the embryo sac: two  __________   cells flanking the  __________  cell.
•	The synergids function in the attraction and guidance of the pollen tube.
•	At the other end of the egg sac are three  __________   cells of unknown function.
•	The other two nuclei, the  __________   nuclei, share the cytoplasm of the large central cell of the embryo sac.
•	The ovule now consists of the embryo sac and the surrounding  __________  , layers of protective tissue from the sporophyte that will eventually develop into the  __________   coat.
•	__________  , which brings male and female gametophytes together, is the first step in the chain of events that leads to fertilization.
•	Some plants, such as grasses and many trees, release large quantities of pollen on the  __________   to compensate for the randomness of this dispersal mechanism.
•	At certain times of the year, the air is loaded with pollen, as anyone plagued by pollen allergies can attest.
•	Some aquatic plants rely on  __________   to disperse pollen.
•	Most angiosperms interact with  __________   or other animals that transfer pollen directly between flowers.
4. Plants have various mechanisms that prevent self-fertilization.
•	Some flowers self-fertilize or “self,” but most angiosperms have mechanisms that make this difficult or impossible.
•	The various barriers that prevent self-fertilization contribute to genetic  __________   by ensuring that sperm and eggs come from different parents.
•	Dioecious plants cannot self-fertilize because they are  __________  .
•	In plants with bisexual flowers, a variety of mechanisms may prevent self-fertilization.
•	For example, in some species  __________   and  __________   mature at different times.
•	Alternatively, they may be arranged in such a way that it is mechanically unlikely that an animal pollinator could transfer pollen from the anthers to the stigma of the same flower.
•	The most common anti-selfing mechanism is  __________  - __________  , the ability of a plant to reject its own pollen and that of closely related individuals.
•	If a pollen grain from an anther happens to land on a stigma of a flower on the same plant, a biochemical block prevents the pollen from completing its development and fertilizing an egg.
•	The self-incompatibility systems in plant are analogous to the immune response of animals.
•	Both are based on the ability of organisms to distinguish “self” from “nonself.”
•	The key difference is that the animal immune system rejects nonself, but self-incompatibility in plants is a rejection of  __________  .
•	Recognition of “self” pollen is based on genes for self-incompatibility, called S-genes, with dozens of different alleles in a population.
•	If a pollen grain and the carpel’s stigma have matching alleles at the S-locus, then the pollen grain  __________   to initiate or complete the formation of a pollen tube.
•	Because the pollen grain is haploid, it will be recognized as “self” if its one S-allele matches either of the two S-alleles of the  __________   stigma.
•	Although self-incompatibility genes are all referred to as S-loci, such genes have evolved independently in various plant families.
•	As a consequence, self-recognition blocks pollen tube growth by different molecular mechanisms.
•	In some cases, the block occurs in the pollen grain itself, called  __________   self-incompatibility.
•	In some species, self-recognition leads to enzymatic destruction of RNA within the rudimentary pollen tube.
•	RNases are present in the style of the carpel, and they can enter the pollen tube and attack its RNA only if the pollen is of a “self” type.
•	In other cases, the block is a response by the cells of the carpel’s stigma, called  __________   self-incompatibility.
•	In some species, self-recognition activates a signal transduction pathway in epidermal cells that prevents germination of the pollen grain.
•	Germination may be prevented when cells of the stigma take up additional water, preventing the stigma from hydrating the relatively dry pollen.
•	Basic research on self-incompatibility may lead to agricultural applications.
•	Many agricultural plants are self-compatible.
•	Plant breeders sometimes hybridize different varieties of a crop plant to combine the best traits of the varieties and counter the loss of vigor that can result from excessive inbreeding.
•	To maximize hybrid seed production, breeders currently prevent self-fertilization by laboriously removing anthers from the parent plants that provide the seeds or by developing male sterile plants.
•	Eventually, it may be possible to impose self-incompatibility on species that are normally self-compatible.
5. Double fertilization gives rise to the zygote and endosperm.
•	After landing on a receptive stigma, the pollen grain absorbs moisture and germinates, producing a pollen tube that extends down the style toward the ovary.
•	The nucleus of the generative cell divides by mitosis to produce two  __________  , the male gametes.
•	The germinated pollen grain contains the mature  __________   gametophyte.
•	Directed by a chemical attractant, possibly calcium, the tip of the pollen tube enters the ovary, probes through the  __________   (a gap in the integuments of the ovule), and discharges  __________   sperm within the embryo sac.
•	Both sperm fuse with nuclei in the embryo sac.
•	One sperm fertilizes the egg to form the  __________  .
•	The other sperm combines with the two  __________   nuclei to form a triploid nucleus in the central cell.
•	This large cell will give rise to the  __________  , a food-storing tissue of the seed.
•	The union of two sperm cells with different nuclei of the embryo sac is termed  __________   __________  .
•	Double fertilization ensures that the endosperm will develop only in ovules where the egg has been fertilized.
•	This prevents angiosperms from squandering nutrients.
•	Normally nonreproductive tissues surrounding the embryo have prevented researchers from visualizing fertilization in plants, but recently, scientists have been able to isolate sperm cells and eggs and observe fertilization in vitro.
•	The first cellular event after gamete fusion is an increase in cytoplasmic Ca2+ levels, which also occurs during animal gamete fusion.
•	In another similarity to animals, plants establish a block to polyspermy, the fertilization of an egg by more than one sperm cell.
•	In plants, this may be through deposition of  __________   __________   material that mechanically impedes sperm.
•	In maize, this barrier is established within 45 seconds after the initial sperm fusion with the egg.
6. The ovule develops into a __________   containing an embryo and a supply of nutrients.
•	After double fertilization, the  __________   develops into a seed, and the  __________   develops into a fruit enclosing the seed(s).
•	As the embryo develops, the seed stockpiles proteins, oils, and starch.
•	Initially, these nutrients are stored in the  __________  .
•	Later in seed development in many species, the storage function is taken over by the swelling storage leaves (__________  ) of the embryo itself.
•	Endosperm development usually precedes embryo development.
•	After double fertilization, the triploid  __________   of the ovule’s central cell divides, forming a multinucleate “supercell” having a milky consistency.
•	It becomes multicellular when cytokinesis partitions the  __________   between nuclei.
•	Cell walls form, and the endosperm becomes solid.
•	Coconut “milk” is an example of liquid endosperm and coconut “meat” is an example of solid endosperm.
•	The endosperm is rich in nutrients, which it provides to the developing embryo.
•	In most monocots and some dicots, the endosperm also stores nutrients that can be used by the  __________   after germination.
•	In many dicots, the food reserves of the endosperm are completely exported to the cotyledons before the seed completes its development, and consequently the mature seed lacks  __________  .
•	The first mitotic division of the zygote is transverse, splitting the fertilized egg into a  __________   cell and a  __________   cell.
•	The terminal cell gives rise to most of the  __________  .
•	The basal cell continues to divide transversely, producing a thread of cells, the  __________  , which anchors the embryo to its parent.
•	The suspensor functions in the transfer of  __________   to the embryo from the parent.
•	The terminal cell divides several times and forms a spherical  __________   attached to the suspensor.
•	__________   begin to form as bumps on the proembryo.
•	A eudicot, with its  __________  cotyledons, is heart-shaped at this stage.
•	Only  __________   cotyledon develops in monocots.
•	After the cotyledons appear, the embryo elongates.
•	Cradled between cotyledons is the embryonic shoot apex with the apical  __________   of the embryonic shoot.
•	At the opposite end of the embryo axis is the apex of the embryonic root, also with a apical  __________  .
•	After the seed germinates, the apical meristems at the tips of the  __________   and  __________   sustain primary growth as long as the plant lives.
•	During the last stages of maturation, a seed  __________   until its water content is only about 5–15% of its weight.
•	The embryo stops growing and becomes  __________   until the seed germinates.
•	The embryo and its food supply are enclosed by a protective  __________   __________   formed by the integuments of the ovule.
•	In the seed of a common bean, the embryo consists of an elongate structure, the embryonic axis, attached to fleshy cotyledons.
•	Below the point at which the fleshy cotyledons are attached, the embryonic axis is called the  __________  ; above it is the  __________  .
•	At the tip of the epicotyl is the plumule, consisting of the shoot tip with a pair of miniature leaves.
•	The hypocotyl terminates in the  __________  , or embryonic root.
•	While the cotyledons of the common bean supply food to the developing embryo, the seeds of some dicots, such as castor beans, retain their food supply in the  __________   and have cotyledons that are very thin.
•	The  __________   will absorb nutrients from the endosperm and transfer them to the embryo when the seed germinates.
•	The embryo of a monocot has a single  __________  .
•	Members of the grass family, including maize and wheat, have a specialized cotyledon called a  __________  .
•	The scutellum is very thin, with a large surface area pressed against the endosperm, from which the scutellum absorbs  __________   during germination.
•	The embryo of a grass seed is enclosed by two sheathes, a  __________  , which covers the young root, and a  __________  , which covers the young shoot.
7. The ovary develops into a fruit adapted for  __________   dispersal.
•	As the seeds are developing from ovules, the ovary of the flower is developing into a  __________  , which protects the enclosed seeds and aids in their dispersal by wind or animals.
•	Fertilization triggers hormonal changes that cause the  __________   to begin its transformation into a fruit.
•	If a flower has not been pollinated, fruit usually does not develop, and the entire flower withers and falls away.
•	The wall of the ovary becomes the  __________  , the thickened wall of the fruit, while other parts of the flower wither and are shed.
•	In some angiosperms, other floral parts contribute to the fruit.
•	In apples, the fleshy part of the fruit is derived mainly from the swollen  __________  , while the core of the apple fruit develops from the  __________  .
•	Fruits are classified into several types, depending on their developmental origin.
•	A typical fruit is derived from a single carpel or several fused carpels and is called a  __________   fruit.
•	Some simpler fruits are fleshy, like a peach, while others are dry, like a pea pod.
•	An  __________   fruit results from a single flower that has more than one carpel, each forming a small fruit.
•	The fruitlets are clustered together on a single receptacle, like a raspberry.
•	A  __________   fruit develops from an inflorescence, a group of flowers tightly clustered together.
•	When the walls of the ovaries thicken, they fuse together and form one fruit, as in a pineapple.
•	The fruit usually ripens about the same time as its seeds are completing their development.
•	For a  __________   fruit such as a soybean pod, ripening is a little more than senescence of the fruit tissues, which allows the fruit to open and release the seeds.
•	The ripening of  __________   fruits is more elaborate, its steps controlled by the complex interactions of hormones.
•	Ripening results in an edible fruit that serves as an enticement to the animals that help spread the seeds.
•	The “pulp” of the fruit becomes softer as a result of enzymes digesting components of the cell walls.
•	Color changes from  __________   to red, orange, or yellow.
•	The fruit becomes sweeter as organic acids or starch molecules are converted to  __________  .
8. Evolutionary adaptations of seed germination contribute to seedling survival.
•	As a seed matures, it  __________   and enters a  __________   phase, a condition of extremely low metabolic rate and a suspension of growth and development.
•	Conditions required to break dormancy and resume growth and development vary between species.
•	Some seeds germinate as soon as they are in a suitable  __________  .
•	Others remain dormant until some specific environmental  __________  causes them to break dormancy.
•	Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling.
•	For example, seeds of many desert plants germinate only after a substantial  __________  , ensuring enough water to complete development.
•	Where natural fires are common, many seeds require intense  __________   to break dormancy, allowing them to take advantage of new opportunities and open space.
•	Where winters are harsh, seeds may require extended exposure to  __________  .
•	Small seeds such as lettuce require  __________   for germination and break dormancy only if they are buried near the surface.
•	Other seeds require a chemical attack or  __________   abrasion as they pass through an animal’s digestive tract before they can germinate.
•	The length of time that a dormant seed remains viable and capable of germinating varies from a few days to decades or longer.
•	It depends on the species and on  __________   conditions.
•	Most seeds are durable enough to last for a year or two until conditions are favorable for  __________  .
•	Thus, the soil has a pool of  __________   seeds that may have accumulated for several years.
•	This is one reason vegetation reappears so rapidly after a fire, drought, flood, or some other environmental disruption.
•	Germination of seeds depends on  __________  , the uptake of water due to the low water potential of the dry seed.
•	This causes the expanding seed to rupture its  __________  coat and triggers  __________   changes in the embryo that enable it to resume growth.
•	Enzymes begin digesting the  __________   materials of endosperm or cotyledons, and the nutrients are transferred to the growing regions of the  __________  .
•	The first organ to emerge from the germinating seed is the radicle, the embryonic  __________  .
•	Next, the  __________   tip must break through the soil surface.
•	In garden beans and many other dicots, a  __________   forms in the hypocotyl, and growth pushes it aboveground.
•	Stimulated by light, the  __________   straightens, raising the cotyledons and  __________  .
•	As it rises into the air, the epicotyl spreads its first foliage  __________   (true leaves).
•	These foliage leaves expand, become  __________  , and begin making food by photosynthesis.
•	After the cotyledons have transferred all their  __________   to the developing plant, they shrivel and fall off the seedling.
•	Corn and other grasses, which are monocots, use a different method for breaking ground when they germinate.
•	The  __________  , the sheath enclosing and protecting the embryonic shoot, pushes upward through the soil and into the air.
•	The shoot tip then grows straight up through the  __________   provided by the tubular coleoptile.
•	The tough seed gives rise to a fragile  __________   that will be exposed to predators, parasites, wind, and other hazards.
•	Because only a small fraction of seedlings endure long enough to become parents, plants must produce enormous  __________   of seeds to compensate for low individual  __________  .
•	This provides ample genetic variation for natural  __________   to screen.
•	However, flowering and fruiting in sexual reproduction is an expensive way of plant propagation in terms of the  __________   consumed.
B. Asexual Reproduction
1. Many plants clone themselves by  __________   reproduction.
•	Many plants  __________   themselves by asexual reproduction.
•	Many plants are capable of both sexual and asexual reproduction, and each offers advantages in certain situations.
•	When reproducing  __________  , a plant passes on all of its genes to its offspring.
•	When reproducing  __________  , it passes on only half of its genes.
•	If a plant is superbly suited to a stable environment, asexual reproduction has advantages.
•	A plant can clone many  __________   of itself rapidly.
•	If the environmental conditions remain stable, the clones will be well suited to the  __________  .
•	The offspring are not as frail as the seedlings produced by  __________   reproduction in seed plants.
•	They are usually mature  __________  
•	 fragments of the parent plant.
•	In  __________   environments, where evolving pathogens and other variables affect survival and reproductive success, sexual reproduction can be advantageous because it generates  __________   in offspring.
•	In contrast, the genotypic  __________   of asexually produced plants puts them at great risk of local extinction if there is a catastrophic  __________   change, such as a new strain of disease.
•	Seeds produced by  __________   reproduction can disperse to new locations and wait for favorable growing conditions.
•	Seed dormancy allows growth to be  __________   until hostile environmental conditions are reversed.
•	Asexual reproduction is an extension of the capacity of plants for indeterminate growth.
•	Meristematic tissues with dividing undifferentiated cells can sustain or renew growth  __________  .
•	Parenchyma cells throughout the plant can divide and differentiate into various types of specialized cells.
•	Detached  __________   of some plants can develop into whole offspring.
•	In fragmentation, a parent plant separates into parts that re-form into  __________   plants.
•	A variation of this occurs in some dicots, in which the root system of a single parent gives rise to many  __________   shoots that become separate root systems, forming a clone.
•	A ring of creosote bushes in the Mojave Desert of California is believed to be at least 12,000 years old.
•	A different method of asexual reproduction, called  __________  , is found in dandelions and some other plants.
•	These produce seed without their flowers being  __________  .
•	A diploid cell in the ovule gives rise to the embryo, and the ovules mature into  __________  .
•	These seeds are dispersed by the  __________  .
•	This combines  __________   reproduction and seed  __________  .