THE “EVOLUTION” OF SEED PLANTSPacket #71

Chapters 29, 30 & 38

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THE “EVOLUTION” OF PLANT ORGANS

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“EVOLUTION” OF ROOTS

The “evolution” of roots allowed plants to become anchored and helped enable them to absorb water and nutrients from the soil

Roots allow the shoot system to grow taller and contain lignified vascular tissue.

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“EVOLUTION” OF LEAVES

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Leaves increase the surface area of vascular plants.

Leaves can be classified as microphylls or megaphylls All lycophytes (club mosses)

have small, usually spine-shaped leaves with a single vein

Microphylls Leaves of other “modern”

vascular plants are known as megaphylls

The larger sized leaves are possible due to the highly branched vascular system which supports greater photosynthetic activity.

See Pages 584-586

Chapter 29

Figure 29.13

Page 586

THE EVOLUTION OF SEED

The evolution of seed facilitated reproduction on land Plants that produce seeds may be placed into two

categories Gymnosperms Angiosperms

A seed consists of a plant embryo packaged with a food supply in a protective coat

The first vascular plant, according to the theory of evolution, originated about 360 MYBP in the Devonian Period. Those seeds were not enclosed in any special

chambers. These plants evolved into the gymnosperms

“The Naked Seeds”

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THE EVOLUTION OF FLOWERS

According to the theory of evolution, flowers evolved in the Cretaceous Period about 130 MYBP Led to further plant diversity

A flower is a complex structure that bears seeds within a protective chamber called an ovary.

Most “modern day” flowering plants are known as angiosperms.

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APICAL MERISTEMS

Recall, plants cannot move. The elongation of their shoots and roots

maximizes their exposure to environmental resources.

Growth occurs throughout the life of the plant via cell division in the apical meristematic tissue found at the tips of roots and shoots. Cells produced by meristematic tissue can

differentiate into various plant tissues.

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INTRODUCTION TO THE SEED AND SEED BEARING PLANTS

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INTRODUCTION TO SEED BEARING PLANTS Seed plants are vascular plants that produce

seeds. After fertilization in seed plants, an ovule

(megasporangium) and its enclosed structures develop into a seed

Earliest fossilized seeds are gymnosperms. 360 MYBP

Seed plants dominate modern landscapes and are a large component of plant diversity.

Seed bearing plants have important reproductive adaptations: - Continued reproduction of the gametophyte The advent of the seed The evolution of pollen

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INTRODUCTION II

The gametophytes of seed plants are even smaller than those of the seedless vascular plant and are protected in the ovules and pollen grains,

Miniature female gametophytes develop from spores that are retained within the parental sporophyte.

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COMPARISON OF SEEDS VS. SPORES

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Seeds are the primary means of reproduction and dispersal of flowering plants.

Seeds are reproductively superior to spores. Embryonic

development is further advanced in seeds

Seeds contain an abundant food supply

Each seed has a protective coat.

SEEDS, DISPERSAL & ADAPTATION

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Seed dispersal becomes important in adaptations

Seed is a resistant structure that is multicellular and complex.

Seed consists of a sporophyte embryo packaged with food in a protective coat

Seeds can be dispersed by wind, water and animals.

SEED BEARING PLANTS

All seed bearing plants are heterosporousThese plants have different types of

sporangia that produce two types of spores. Megasporangium Microsporangium

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HETEROSPOROUS SPORE PRODUCTION

Megasporangia Produce megaspores

*Retained in the parent sporophyte

Formed within the megasporangium

Enveloped with tissue called integumens

*Entire structure is called the ovule

Microsporangia Produce microspores

Develop into male (sperm containing) gametophytes.

The development of pollen reduced the need for water for fertilization.

Mega. vs. Micro. Diagram on Page 586

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MEGASPORES

Develop into female (egg containing) gametophytes. In the female gametophyte, there is the

production of one or more egg cells If egg is fertilized by sperm, the zygote develops into a

sporophyte embryo The ovule, that contains the fertilized egg, develops

into a seed. Seed may be viable for days, months or years.

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MICROSPORES

Microspores develop into pollen grains Pollen grains mature to become the

gametophytes of seed plants

The most common gymnosperms, and all angiosperms sperm, lack flagella.

Pollen can be transferred by wind and animals.

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POLLINATION

The transfer of pollen to ovules Self Pollination Cross Pollination

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REVIEW

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REVIEW

Students List potential examination questions and/or here,

and on following slides, based on the packet.

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