chapter 38: angiosperm reproduction 1. the life cycle of an angiosperm…

Chapter 38: Angiosperm Reproduction1. The life cycle of an angiosperm….

Figure 38.2 An overview of angiosperm reproduction

Filament

AntherStamen

Anther attip of stamen

Pollen tube

Germinated pollen grain(n) (male gametophyte)on stigma of carpel

Ovary (base of carpel)

Ovule

Embryo sac (n)(female gametophyte)

FERTILIZATIONEgg (n)

Sperm (n)

Petal

Receptacle

Sepal

Stigma

Style

Ovary

Key

Haploid (n)

Diploid (2n)

(a) An idealized flower.

(a) Simplified angiosperm life cycle.See Figure 30.10 for a more detailedversion of the life cycle, including meiosis.

Mature sporophyteplant (2n) withflowers

Seed(developsfrom ovule)

Zygote(2n)

Embryo (2n)(sporophyte)

Simple fruit(develops from ovary)

Germinatingseed

Seed

Carpel

Chapter 38: Angiosperm Reproduction & Biotechnology1. Let’s review the life cycle of an angiosperm….2. Can all plants self-fertilize?

- No- Complete – have all 4 floral parts – sepal, petal, carpel, stamen- Incomplete – lack 1 or more parts- Perfect flowers – have both stamen & carpels- Imperfect flowers – missing either stamen or carpels

- Stamenate – have stamen- Carpellate – have carpel- Monoecious: have stamenate and carpellate flowers on same plant- Dioecious: have stamenate and carpellate flowers on different plants

3. How does pollen (male gametophyte) & the embryo sac (female gametophyte) develop?

Figure 38.4 The development of angiosperm gametophytes (pollen grains and embryo sacs)

Diploid (2n) 10

0 m

3

1

2

Three mitotic divisions of the megaspore form the embryo sac, a multicellular female gametophyte. The ovule now consists of the embryo sac along with the surrounding integuments (protective tissue).

Development of a male gametophyte (pollen grain). Pollen grains developwithin the microsporangia (pollen sacs) of anthers at the tips of the stamens.

(a)

Each one of the microsporangia contains diploid microsporocytes (microspore mother cells).

Each microsporo-cyte divides by meiosis to produce four haploid microspores, each of which develops into a pollen grain.

A pollen grain becomes a mature male gametophyte when its generative nucleus divides and forms two sperm.This usually occurs after a pollen grain lands on the stigma of a carpel and the pollen tube begins to grow. (SeeFigure 38.2b.)

Pollen sac(microsporangium)

Micro-sporocyte

Micro-Spores (4)

Each of 4microspores

Generativecell (wellform 2sperm)

75 m

MaleGametophyte(pollen grain)

Nucleus of tube cell

RagweedPollengrain

KeyTo labels

MITOSIS

MEIOSIS

Ovule

Ovule

Integuments

Embryosac

Mega-sporangium

Mega-sporocyte

Integuments

Micropyle

Survivingmegaspore

AntipodelCells (3)

PolarNuclei (2)

Egg (1)

Synergids (2)

Development of a female gametophyte (embryo sac). The embryo sac developswithin an ovule, itself enclosed by the ovary at the base of a carpel.

(b)

20 m

Within the ovule’smegasporangium is a large diploid cell called the megasporocyte (megasporemother cell).

The megasporo-cyte divides by meiosis and gives rise to four haploid cells, but in most species only one of these survives as the megaspore.

1

2

3

Female gametophyte(embryo sac)

Haploid (n)Diploid (2n)

100

m

Chapter 38: Angiosperm Reproduction & Biotechnology1. Let’s review the life cycle of an angiosperm….2. Can all plants self-fertilize?3. How does pollen (male gametophyte) & the embryo sac (female

gametophyte) develop?4. How can plants prevent self-fertilization?

- Genetic adaptations – “S genes” – self-incompatibility – reject self- Anatomical adaptations – pin & thrum flowers- Temporal adaptations – male & female parts mature at different times

Stigma

AntherWith

pollen

Stigma

Pin flower Thrum flower


gametophyte) develop?4. How can plants prevent self-fertilization?5. How does double fertilization occur & why is this important?

Figure 38.6 Growth of the pollen tube and double fertilization

If a pollen graingerminates, a pollen tube

grows down the styletoward the ovary.

Stigma

The pollen tubedischarges two sperm into

the female gametophyte(embryo sac) within an ovule.

One sperm fertilizesthe egg, forming the zygote.

The other sperm combines withthe two polar nuclei of the embryo

sac’s large central cell, forminga triploid cell that develops into

the nutritive tissue calledendosperm.

1

2

3

Polarnuclei

Egg

Pollen grain

Pollen tube

2 sperm

Style

Ovary

Ovule (containingfemale Gametophyte, orEmbryo sac)

Micropyle

OvulePolar nucleiEgg

Two spermabout to bedischarged

Endosperm nucleus (3n) (2 polar nuclei plus sperm)

Zygote (2n)(egg plus sperm)


gametophyte) develop?4. How can plants prevent self-fertilization?5. How does double fertilization occur & why is this important?6. What happens after fertilization?

- Development of an embryo

Figure 38.7 The development of a eudicot plant embryo

Suspensor

Ovule

Terminal cell

Endospermnucleus

Basal cell

Zygote

Integuments

Zygote

Proembryo

Cotyledons

Shootapex

Rootapex Seed coat

Basal cell

Suspensor

EndospermSuspensor

Figure 38.8 Seed structure

(a) Common garden bean, a eudicot with thick cotyledons. The fleshy cotyledons store food absorbed from the endosperm before the seed germinates.

(b) Castor bean, a eudicot with thin cotyledons. The narrow, membranous cotyledons (shown in edge and flat views) absorb food from the endosperm when the seed germinates.

(c) Maize, a monocot. Like all monocots, maize has only one cotyledon. Maize and other grasses have a large cotyledon called a scutellum. The rudimentary shoot is sheathed in a structure called the coleoptile, and the coleorhiza covers the young root.

Seed coat

Radicle

Epicotyl

Hypocotyl

Cotyledons

Seed coat

Endosperm

Cotyledons

Epicotyl

Hypocotyl

Radicle

Scutellum(cotyledon)

Coleoptile

Coleorhiza

Pericarp fusedwith seed coat

Endosperm

Epicotyl

Hypocotyl

Radicle


gametophyte) develop?4. How can plants prevent self-fertilization?5. How does double fertilization occur & why is this important?6. What happens after fertilization?7. How do fruits develop?

Figure 38.9 Developmental origin of fruits

Simple fruit. A simple fruit develops from a single carpel (or several fused carpels) of one flower (examples: pea, lemon, peanut).

(a) Aggregate fruit. An aggregate fruit develops from many separate carpels of one flower (examples: raspberry, blackberry, strawberry).

(b) Multiple fruit. A multiple fruit develops from many carpels of many flowers (examples: pineapple, fig).

(c)

Pineapple fruitRaspberry fruitPea fruit

Stamen

Carpel(fruitlet) Stigma

Ovary

Raspberry flower

Eachsegmentdevelopsfrom thecarpel ofone flower

Pineapple inflorescence

Stamen

CarpelsFlower

Ovary

StigmaStamen

Ovule

Pea flower

Seed


gametophyte) develop?4. How can plants prevent self-fertilization?5. How does double fertilization occur & why is this important?6. What happens after fertilization?7. How do fruits develop?8. What happens during dormancy? Germination?

--Seed remains dormant until germination is activated by…-heat-light-water-extended cold weather-animal’s digestive juices

Figure 39.11 Gibberellins mobilize nutrients during the germination of grain seeds

2 2 The aleurone responds by synthesizing and secreting digestive enzymes thathydrolyze stored nutrients inthe endosperm. One exampleis -amylase, which hydrolyzesstarch. (A similar enzyme inour saliva helps in digestingbread and other starchy foods.)

Aleurone

Endosperm

Water

Scutellum(cotyledon)

GA

GA

-amylase

Radicle

Sugar

1 After a seedimbibes water, theembryo releasesgibberellin (GA)as a signal to thealeurone, the thinouter layer of theendosperm.

3 Sugars and other nutrients absorbedfrom the endospermby the scutellum (cotyledon) are consumed during growth of the embryo into a seedling.

Figure 38.10 Two common types of seed germination

Foliage leaves

Cotyledon

Hypocotyl

Radicle

Epicotyl

Seed coat

Cotyledon

HypocotylCotyledon

Hypocotyl

Common garden bean. In common garden beans, straightening of a hook in the hypocotyl pulls the cotyledons from the soil.

(a)

Foliage leaves

ColeoptileColeoptile

Radicle

Maize. In maize and other grasses, the shoot grows straight Up through the tube of the coleoptile.

(b)

chapter 38: angiosperm reproduction 1. the life cycle of an angiosperm…

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