Chapter 30

• Overview: Feeding the World

Plant Diversity II: The
Evolution of Seed Plants

• Seeds changed the course of plant evolution
– Enabling their bearers to become the dominant producers in most terrestrial ecosystems

PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece

Lectures by Chris Romero

Figure 30.1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Advantages of Reduced Gametophytes
• Concept 30.1: The reduced gametophytes of seed plants are protected in ovules and pollen grains • The gametophytes of seed plants
– Develop within the walls of spores retained within tissues of the parent sporophyte

• In addition to seeds, the following are common to all seed plants
– Reduced gametophytes
– Heterospory
– Ovules
– Pollen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Heterospory: The Rule Among Seed Plants
• Gametophyte/sporophyte relationships
Sporophyte
(2n)

Sporophyte
(2n)

Gametophyte
(n)

(a) Sporophyte dependent on gametophyte
(mosses and other bryophytes). Gametophyte
(n)

small, independent gametophyte (ferns and other seedless vascular plants).

Microscopic male gametophytes (n) inside these parts of flowers
(dependent)

Figure 30.2a–c

– Which produce megaspores that give rise to female gametophytes

(b) Large sporophyte and

Microscopic female gametophytes (n) in ovulate cones
(dependent)

Microscopic male gametophytes (n) in pollen cones
(dependent)

• Seed plants evolved from plants that had megasporangia Sporophyte (2n)
(independent)

Microscopic female gametophytes (n) inside these parts of flowers
(dependent)

• Seed plants evolved from plants that had microsporangia – Which produce microspores that give rise to male gametophytes

Sporophyte (2n), the flowering plant
(independent)

(c) Reduced gametophyte dependent on sporophyte
(seed plants: gymnosperms and angiosperms).

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

1

Ovules and Production of Eggs

Pollen and Production of Sperm

• An ovule consists of

• Microspores develop into pollen grains

– A megasporangium, megaspore, and protective integuments
Integument
Spore wall

Megasporangium
(2n)

– Which contain the male gametophytes of plants • Pollination
– Is the transfer of pollen to the part of a seed plant containing the ovules

Megaspore (n)

Figure 30.3a

(a) Unfertilized ovule. In this sectional view through the ovule of a pine (a gymnosperm), a fleshy megasporangium is surrounded by a protective layer of tissue called an integument. (Angiosperms have two integuments.) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• If a pollen grain germinates
– It gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule Female gametophyte (n)

– Eliminated the water requirement for fertilization Egg nucleus (n)

Spore wall

Male gametophyte
(within germinating pollen grain) (n)

Discharged sperm nucleus (n)
Micropyle

Figure 30.3b

• Pollen, which can be dispersed by air or animals Pollen grain (n)

(b) Fertilized ovule. A megaspore develops into a multicellular female gametophyte. The micropyle, the only opening through the integument, allows entry of a pollen grain. The pollen grain contains a male gametophyte, which develops a pollen tube that discharges sperm.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Evolutionary Advantage of Seeds
• A seed
– Develops from the whole ovule
– Is a sporophyte embryo, along with its food supply, packaged in a protective coat
Seed coat