Download AP Biology Notes Outline Plant Diversity II: The Evolution of Seed

AP Biology Notes Outline
Plant Diversity II: The Evolution of Seed Plants
Chapter 30
FIGURE 30.2 – EVOLUTION OF SEED PLANTS: Seed plants are VASCULAR plants that produce seeds.
Seeds changed the course of plant evolution enabling their bearers to become the dominant producers in most
terrestrial ecosystems. The two clades of seed plants are gymnosperms (cone-bearers) and angiosperms
(flowering plants).
FIGURE 30.2 – KNOW IT! - Important trends in seed-plant evolution:
1. Reduction of gametophyte continued with the evolution of seed plants.
2. Seeds became an important means of dispersing offspring.
3. Pollen eliminated the liquid-water requirement for fertilization.
Seed: embryo of plant that is wrapped in a protective covering and surrounded by a food supply.
The two clades of seed plants are gymnosperms and angiosperms:
• Gymnosperms – “naked seed” plants – most ancient of seed plants; produce cones with seeds. They
have various modifications for dryness including needle-shaped leaves, thick waxy cuticles, and
stomates located in stomatal crypts to further reduce water loss.
• Conifers, Cycads, Ginkos, Gnetophytes
•
Angiosperms – covered seed plants - these produce flowers….then fruits that have the seeds inside –
fruits provide seed protection and better guarantees seed dispersal when eaten by animals.
Angiosperms are further divided into monocots and dicots:
• Grasses. Flowering trees and shrubs, All flowers
FIGURE 30.3 – FROM OVULE TO SEED: A seed, which is derived from a fertilized ovule, consists of a
sporophyte embryo packaged along with a food supply within a seed coat.
Ovules and the production of eggs (Figure 30.3):
• An ovule consists of a megasporangium, megaspore, and protective integuments
– A fleshy megasporangium is surrounded by protective layers of tissue called integument.
– A megaspore develops into a multicellular female gametophyte (egg). The micropyle, the only
opening through the integument, allows entry of the pollen grain.
– The pollen grain contains a male gametophyte, which develops a pollen tube that discharges
sperm.
– Fertilization initiates the transformation of the ovule into a seed, which consists of a sporophyte
embryo, a food supply, and a protective seed coat derived from the integument.
AP Biology Notes Outline
Plant Diversity II: The Evolution of Seed Plants
Chapter 30
Pollen and the production of sperm:
• Microspores develop into pollen grains which contain the male gametophytes (sperm) of plants
– Pollination is the transfer of pollen to the part of a seed plant containing the ovules
– If a pollen grain germinates it gives rise to a pollen tube that discharges two sperm into the
female gametophyte within the ovule
SEED PLANT CHARACTERISTICS:
In addition to seeds, the following are common to all seed plants – REVIEW CHART ON TEXT PAGE 634:
• Reduced gametophytes (egg and sperm are protected in ovules and pollen grains)
• Heterospory (plants in which the sporophyte produces two kinds of spores that develop into either male
or female gametophytes)
• Ovules (structure that develops in the plant ovary and contains the female gametophyte)
• Pollen (structure that contains immature male gametophyte)
Evolutionary advantage of seeds:
• further dispersal of offspring
• protection an nourishment for developing embryo
Evolutionary advantage of reduced gametophytes:
• The gametophytes of seed plants develop within the walls of spores retained within tissues of the parent
sporophyte
• Because of this, the delicate female gametophytes do not have to cope with many environmental stresses
– The gametophyte and the embryo produced after fertilization are sheltered from drought and UV
radiation by their enclosure in the moist reproductive tissues of the parental sporophyte
generation.
– This arrangement also makes it possible for the gametophytes to obtain nutrients from their
parents.
Heterospory: Heterosporous plants are those in which the sporophyte produces two kinds of spores that
develop into either male of female gametophytes:
• Seed plants evolved from plants that had megasporangia
– Which produce megaspores that give rise to female gametophytes
• Seed plants evolved from plants that had microsporangia
– Which produce microspores that give rise to male gametophytes
Evolutionary advantage of pollen:
• Pollen, which can be dispersed by air or animals eliminated the water requirement for fertilization
– Can be carried away by wind or animals after their release from the microsporangium
• In seed plants, the use of resistant, far-traveling, airborne pollen to bring gametes together is a terrestrial
adaptation that led to even greater success and diversity of plants on land., as opposed to bryophytes and
pterophytes which have flagellated sperm that must swim through a film of water to reach egg cells in
archegonia.
AP Biology Notes Outline
Plant Diversity II: The Evolution of Seed Plants
Chapter 30
FIGURE 30.5 – GYMNOSPERMS (CONE-BEARERS): Gymnosperms bear their seeds “naked” on the scales
of cones.
The gymnosperms include four plant phyla:
• Cycadophyta, Gingkophyta, Gnetophyta, Coniferophyta
Figure 30.6 – The life-cycle of a pine tree demonstrates the key reproductive adaptations of seed plants. Key
features of the gymnosperm life cycle include:
• Dominance of the sporophyte generation, the pine tree
• The development of seeds from fertilized ovules
• The role of pollen in transferring sperm to ovules
Female pine cones are the large, ‘normal’ cones – ovulate cone. Male pine cones are the clusters of small,
worm-like structures at the tips of the branches – pollen cone. Pollination is WIND DEPENDENT!
FIGURE 30.7 thru 30.18 – ANGIOSPERMS (FLOWERING PLANTS): The two clades of angiosperms,
monocots and dicots, include the vast majority of plants. The flower is the defining reproductive adaptation of
angiosperms.
The key adaptation in the evolution of angiosperms is flowers and fruits. Angiosperm means “enclosed seed”.
• Flowers attract pollinators, which makes spreading seeds more efficient than the wind pollination of
most gymnosperms
• Flowers contain ovaries, which surround and protect the seeds
– After pollination, the ovary develops into a fruit, which protects the seed and aids dispersal
– Fruit is a thick wall of tissue and another reason why angiosperms are successful – the fruit
attracts herbivores – which eat the fruit and then spread the seeds
FIGURE 30.7 & 30.8 – FLOWERS AND FRUITS: A flower is an angiosperm structure specialized for sexual
reproduction. A fruit is a mature ovary.
Flowers are specialized shoot with modified
leaves:
•
•
•
•
Sepals, which enclose the flower
Petals, which are brightly colored and attract
pollinators
Stamens, which produce pollen
Carpels, which produce ovules
Evolutionary advantages of seeds & fruit:
•
•
In many angiosperms, insects and other
animals transfer pollen from one flower to
female sex organs on another flower, which
makes pollination less random than the winddependent pollination of most gymnosperms.
Fruits are mature ovaries. As seeds develop
from ovules after fertilization, the wall of the
ovary thickens. Fruits protect dormant seeds
and aid in their dispersal.
AP Biology Notes Outline
Plant Diversity II: The Evolution of Seed Plants
Chapter 30
Figure 30.10 - Angiosperm Life Cycle – KNOW IT!:
• In the angiosperm life cycle double fertilization occurs when a pollen tube discharges two sperm into
the female gametophyte within an ovule
– One sperm fertilizes the egg, while the other combines with two nuclei in the center cell of the
female gametophyte and initiates development of food-storing endosperm
• The endosperm nourishes the developing embryo
Figure 35.13 - Angiosperm Diversity:
• The two main groups of angiosperms are monocots and dicots. These are named for the number of
cotyledons (seed leaves) present on the embryo of the plant. Monocots have one cotyledon (seed leaves)
and dicots have two cotyledons.
1. If you cannot find time to read the chapter, then MAKE SURE you find time to read pages 181-184 in your
AP Test Prep Series book.
2. Text book figures that you MUST KNOW and BE ABLE TO EXPLAIN – 30.2, 30.3, 30.6 (sort of), 30.7,
30.8, 30.9, 30.13, Derived Traits Table on page 634.