Chapter 30

Question 1

Seed plants have come to dominate the terrestrial landscape over the last

Answer 1

several hundred million years​

Over 400,000 species of seed plants today​

Evolved from spore-bearing plants known as progymnosperms.​

Success attributed to evolution of seed​

Protects and provides food for embryo.​

Allow embryos to pause development and growth and germinate after a harsh winter or dry season has passed​

Question 2

Seeds and the Embryo

Answer 2

Embryo protected by integument​

An extra layer or two of sporophyte tissue.​

Hardens into seed coat.​

Megasporangium divides meiotically inside ovule to produce haploid megaspore​

Megaspore divides by mitosis to produce a female gametophyte carrying the female gamete, an egg​

Also contain food supply for embryo

Question 3

Two kinds of gametophytes

Answer 3

Male gametophytes​

Pollen grains.​

Carried to female gametophyte by wind or a pollinator.​

No need for water.​

Female gametophytes​

Develop within an ovule.​

Enclosed within diploid sporophyte tissue in angiosperms.​

Ovule and protective tissue are the ovary.​

The ovary develops into fruit.

Question 4

Gymnosperms

Answer 4

Plants with “naked seeds”​

Encompass four of the five lineages of seed plants​

Coniferophytes.​

Cycadophytes.​

Gnetophytes.​

Ginkgophytes.​

All have ovule exposed on a scale​

All lack flowers and fruits of the fifth lineage, angiosperms

Question 5

Conifers (phylum Coniferophyta)

Answer 5

Most familiar gymnosperm phylum​

Pines, spruces, firs, cedars, and others​

Coastal redwood – Tallest living vascular plant.​

Bristlecone pine – Oldest living tree.​

Found in colder temperate and sometimes drier regions of the world​

Conifers are sources of important products​

Timber, paper, resin, and taxol (anti-cancer

Question 6

Pines

Answer 6

More than 100 species, all in the Northern hemisphere​

Produce tough needlelike leaves in clusters​

Leaves have thick cuticle and recessed stomata to minimize water loss​

Leaves have canals with resin to deter insect and fungal attacks​

Wood lacks some of the more rigid cell types found in other trees, which is why they are sometimes referred to as “soft” wood

Question 7

Pine reproduction

Answer 7

Male gametophytes (pollen grains)​

Develop from microspores in male cones by meiosis.​

Female pine cones form on the upper branches of the same tree​

Female cones are larger and have woody scales.​

Two ovules develop on each scale.​

Each contains a megasporangium that is known as the nucellus.

Question 8

Female Pine Cones

Answer 8

The nucellus is surrounded by the integument​

Micropyle: small opening at end of integument.​

Seed coat forms from a layer of integument.​

One megaspore mother cell within each megasporangium forms four megaspores via meiosis​

3 megaspores break down.​

1 slowly develops into a female gametophyte via mitosis.

Question 9

Female Gametophyte

Answer 9

At maturity, the female gametophyte may consist of thousands of cells​

Female gametophyte has 2 to 6 archegonia at the micropylar end​

Each archegonium has a single large egg

Three mitotic divisions of the megaspore nucleus produces 8 haploid nuclei in 2 groups of 4​

2 nuclei (1 from each group of 4) migrate toward center.​

Cell wall forms around the polar nuclei to form the central cell.​

Cell closest to the micropyle becomes the egg.​

2 other cells in that group become synergids.​

Antipodals are the 3 cells at other end – they have no apparent function.​

Integuments become the seed coat​

The 8 haploid nuclei in 7 cells make up the female gametophyte​

Also known as the embryo sac

Question 10

Conifer Pollination

Answer 10

Female cones usually take two or more seasons to mature​

During the first spring, pollen grains drift down between open scales​

Pollen grains drawn down into micropyle.​

Scales close.

Question 11

Conifer Fertilization

Answer 11

A year later, female gametophyte matures​

Pollen tube is digesting its way through nucellus​

Mature male gametophyte has 2 sperm.​

15 months after pollination, pollen tube reaches archegonium and discharges contents​

One sperm unites with egg = zygote.​

Other sperm degenerates.

Question 12

Cycads (phylum Cycadophyta)

Answer 12

Slow-growing gymnosperms of tropical and subtropical regions​

Sporophytes of most 250 known species resemble palm trees​

Individuals make either pollen-bearing or ovule-bearing cones, not both​

Female cones are huge (up to 45 kg)​

Sperm is formed in pollen tube but released within ovule to swim to archegonium

Question 13

Gnetophytes (phylum Gnetophyta)

Answer 13

Only gymnosperms with vessels in their xylem​

Contain 65 species in three (unusual) genera​

Welwitschia.​

Ephedra.​

Gnetum.

Question 14

Ginkgophytes

Answer 14

Only one living species remains​

Ginkgo biloba.​

Flagellated sperm​

Dioecious​

Male and female reproductive structures form on different trees.

Question 15

Angiosperms

Answer 15

Flowering plants​

Ovules are enclosed in diploid tissue at the time of pollination​

Carpel, a modified leaf that encapsulates seeds, develops into fruit

Question 16

Angiosperm Abundance

Answer 16

Today there are some 300,000 species of flowering plants​

The emergence of angiosperms changed the terrain of Earth​

Previously dominated by ferns, cycads, and conifers.​

Unique angiosperm features aided abundance​

Flower production, insect pollination, broad leaves with thick veins.

Question 17

Angiosperm origins are a mystery

Answer 17

Oldest known angiosperm in the fossil record is Archaefructus​

At least 125 million years old.​

Unlikely to have been the first angiosperm.​

Multiseeded carpels (fruits) and stamens​

Lack sepals and petals.

Question 18

Closest living relative to the original angiosperm is Amborella

Answer 18

Horizontal gene transfer explains the presence of moss mitochondrial genes in the genome of Amborella

Question 19

Flowers House Gametophytes

Answer 19

Flowers are modified stems bearing modified leaves.​

Originate as primordium that develops into a bud at the end of a stalk called a pedicel.​

Pedicel expands at the tip to form a receptacle, to which other parts attach.​

Flower parts are organized in circles called whorls.

Question 20

Flower Whorls

Answer 20

Outermost whorl – sepals​

Second whorl – petals​

Third whorl – stamens (androecium)​

Pollen is the male gametophyte.​

Each stamen has a pollen-bearing anther and a filament (stalk).​

Innermost whorl – gynoecium​

Consists of one or more carpels.​

House the female gametophyte.

Question 21

The Carpel

Answer 21

Carpel has 3 major regions​

Ovary – swollen base containing ovules.​

Later develops into a fruit.​

Stigma – tip where pollen lands.​

Style – neck or stalk connecting stigma and ovary

Question 22

Ovule

Answer 22

A single diploid megaspore mother cell in ovule undergoes meiosis to produce 4 haploid megaspores.​

3 disappear.​

Nucleus of remaining megaspore divides mitotically to form female gametophyte

Question 23

Pollen Production

Answer 23

Pollen production occurs in the anthers​

It is similar but less complex than female gametophyte formation.​

Diploid microspore mother cells undergo meiosis to produce four haploid microspores.​

All four at first remain together as a tetrad​

The nucleus of each one divides once by mitosis​

Binucleate microspores become pollen grains.

Question 24

Pollination

Answer 24

Mechanical transfer of pollen from anther to stigma​

May or may not be followed by fertilization​

If the stigma is receptive, pollen grains develop a pollen tube that is guided to the embryo sac​

One of the two pollen grain cells lags behind​

This generative cell divides to produce two sperm cells.​

No flagella on sperm.

Question 25

Double Fertilization and Seed Production

Answer 25

Double fertilization​

One sperm unites with egg to form the diploid zygote.​

New sporophyte.​

Other sperm unites with the two polar nuclei to form the triploid endosperm.​

Provides nutrients to embryo.​

Seed may remain dormant for many years​

Germinate when conditions are favorable.

Question 26

Seeds

Answer 26

In many angiosperms, development of the embryo is arrested soon after meristems and cotyledons differentiate​

Integuments develop into a relatively impermeable seed coat​

Encloses the seed with its dormant embryo and stored food

Question 27

How Seeds Protect Embryos

Answer 27

They maintain dormancy under unfavorable conditions​

They protect the young plant when it is most vulnerable​

They provide food for the embryo until it can produce its own food​

They facilitate dispersal of the embryo

Question 28

Dessication of a Seed

Answer 28

Once a seed coat forms, most of the embryo’s metabolic activities cease​

A mature seed contains only about 5 to 20% water​

Under these conditions, the seed and embryonic plant are very stable​

Germination cannot take place until water and oxygen reach the embryo​

Seeds of some plants have been known to remain viable for thousands of years

Question 29

Germination

Answer 29

Specific adaptations ensure that seeds will germinate only under appropriate conditions​

Some seeds lie within tough cones that do not open until exposed to fire.​

Some germinate only when inhibitory chemicals leach from their seed coats,​

Others must pass through the intestines of birds or mammals to weaken the seed coat before germinating

Question 30

Fruits

Answer 30

Most simply defined as mature ovaries (carpels)​

During seed formation, the flower ovary begins to develop into fruit​

It is possible for fruits to develop without seed development​

Bananas are propagated asexually.

Question 31

Fruit Structure

Answer 31

The ovary wall is termed the pericarp​

3 layers: exocarp, mesocarp, and endocarp.​

Their fate determines the fruit type.​

Fruits contain 3 genotypes in 1 package​

Fruits and seed coat from prior sporophyte generation.​

Embryo represents next sporophyte generation.​

The endosperm is a transient, triploid product of fertilization

Question 32

Fruit Dispersal

Answer 32

Occurs through a wide array of methods​

Ingestion and transportation by birds or other vertebrates.​

Hitching a ride with hooked spines on birds and mammals.​

Burial in caches by herbivores.​

Blowing in the wind.​

Floating and drifting on water.