Plants with Seeds

Chapter 22-4, 22-5

Seed plants

There are two groups of seed plants:

1) Gymnosperms ~ seeds are found on the surfaces of cones

2) Angiosperms ~ seeds are within a layer of tissue that protects the seed

Adaptations of Seed Plants Unlike mosses and ferns, seed

plants do not require water for fertilization of gametes

ADAPTATIONS that allow seed plants to reproduce without water: 1) flowers or cones 2) transfer of sperm by pollination 3) protection of embryos in seeds

Adaptation #1:Cones and Flowers

Cones and flowers are sporophyte structures in which the gametophytes of seed plants grow

Cones = seed-bearing structures of gymnosperms

Flowers = seed-bearing structures of angiosperms

Adaptation #2:

Pollen

In seed plants, the male gametophyte is contained in a pollen grain

The pollen grain is carried to the female reproductive structure by wind, insects or small animals pollination

Pollination

Pollination can occur through biotic and abiotic means (wind, water, birds, insects, etc…)

Morphological characteristics of flowers attract specific pollinators

Insects – the Great Pollinators

Conventional spectrum

What bees see

Bats as Pollinators

Adaptation #3:

Seeds Seed = embryo of the

plant (diploid) Seed has a seed

coat (protective covering) and food supply that gives nutrients to the embryo

The embryo develops from the zygote after fertilization

Development of SeedsDevelopment of Seeds

Function of seed structures:Function of seed structures: Endosperm Nutrition for embryoEndosperm Nutrition for embryo Endosperm Cotyledon(s)Endosperm Cotyledon(s) Cotyledons Nutrition for embryoCotyledons Nutrition for embryo

*Endosperm = food storage tissue

*Cotyledons = first leaf or pair of leaves produced by the embryo of a seed plant

Overall, what is the function of Overall, what is the function of a seed?a seed?

Protects young embryoProtects young embryo

Provides nutrition for the Provides nutrition for the developing embryodeveloping embryo

Allows dispersal of the embryo Allows dispersal of the embryo over time & spaceover time & space

Seed to SeedlingSeed to Seedling

Fruits Fruit. Mature ovary of

the a flower that protects dormant seeds and aids their dispersal

Seeds are the product of pollination

Seeds are located within fruits

There are many different types of fruits

Fruit Types

Seed Dispersal Seeds are highly

adapted to dispersal

Examples of morphological characteristics would be buoyancy in fruits (coconut) and “wings” (maple seeds)

While others are simply blowing in the wind….

Some seeds are dispersed as a result of being eaten and mingling with feces….

GYMNOSPERMS: Non-Flowering Seed Producers

Transition from Ferns to Land Transition from Ferns to Land PlantsPlants

Medullosa – the seed fernMedullosa – the seed fern

Gymnosperms began to dominate landscapes as climates became drier at the end of the Paleozoic era 245 mya

Gymnosperms appear in the fossil record much earlier than flowering plants, and they:

1. Lack enclosed chambers in which seeds develop.2. Are grouped into four divisions: 3. Cycadophyta, Ginkgophyta, Gnetophyta and Coniferophyta.

GYMNOSPERMS:

Plants with seeds that are not enclosed within a fruit, derive their name from the Greek words gymnos (naked) and sperma (seed). In this plant group, the seeds are produced on the open surface of a scale. Unlike flowering plants, the gymnosperms do not form true flowers or fruits. There are four divisions of gymnosperms.

Examples of gymnosperms include cycads, ginkgo, conifers and gnetops.

Kingdom  Plantae - PlantsSubkingdom  Tracheobionta -- Vascular plants

Superdivision  Spermatophyta - Seed plantsDivision  Cycadophyta - Cycads

Class  CycadopsidaOrder  Cycadales

Family  Cycadaceae Genus Cycas- cycads

Evolutionary advancements of Gymnosperms over the ferns and allies:

1. Seeds

2. Lack of dependence on water for fertilization (air-borne pollen)

3. Progressively more dominant sporophyte

4. Life Cycle

a. In the gymnosperms and the flowering plants, the sporophyte generation is dominant with the gametophyte contained in and dependent on the sporophyte.

5. Vascular System

a. They do have a well-developed vascular system of xylem and phloem and have true roots, stems, and leaves.

b. The vascular tissues are significantly more efficient and effective than the vascular systems of the seedless plants such as the ferns.

c. Gymnosperms are usually woody plants. The xylem form the wood if a tree and the phloem tissues are part of the bark (along with cork). The formation of wood from secondary growth is the reason that some sporophytes can reach such large sizes.

CycadophytaClass CycadopsidaOrder CycadalesCycadaceaeCycas sp.

The Gymnosperms

The Cycad – a fernlike gymnosperm.Note the cone, or strobilus

Male cones of Male cones of Pinus nigraPinus nigra

•Unlike the seedless vascular plants, conifers are more prevalent in cooler regions and in desert habitats.

• leaf curled to reduce water loss

• evolved cold hardiness

Female cones of Female cones of Pinus nigraPinus nigra

Gnetophyta

With angiosperm-like broad leaves, but still retaining cones,

the Gnetophytes are another very close link to the Angiosperms

The Gymnosperms

Ephedra viridis Female cones

Welwitschia mirabilis growing in the desert

All bear cones, with naked seeds,

which is an adaptation over the ferns, that

produced spores

More More Gnetophytes!Gnetophytes!

Ginkgophyta

Ginkgo biloba

The link between gymnosperms and

angiosperms (note the fleshy seed)

Angiosperms Phylum Anthophyta

Replaced Gymnosperms as the dominant plant type during the Cretaceous Period 60 million years ago

Produce flowers, fruits, and seeds

Flowers and Fruits Flowers:

Are unique reproductive organs of angiosperms

Contain ovaries which surround and protect the seeds

Thus “angiosperm” = “enclosed seed”

Fruits: A wall of tissue surrounding

the seed Used to attract animals

dispersal of seeds

Can you guess what this is?

The largest seed is produced by the coco de mer, or "double coconut palm", Lodoicea maldivica. The entire fruit may weigh up to 23 kilograms (50 pounds) and usually contains a single seed

Flower Morphology

Monocot Monocot vs.vs. Dicot Seeds Dicot Seeds

CornCorn BeanBean

Seed coatSeed coat

Stored foodStored food(Endosperm)(Endosperm)

EmbryoEmbryoplantplant

Monocot SeedsMonocot Seeds

Monocot Monocot seeds have:seeds have:

EndospermEndosperm One One

cotyledoncotyledon

seed coatseed coat

endospermendosperm

cotyledoncotyledon

coleoptilecoleoptile

radicleradicle

Dicot SeedsDicot Seeds

Dicot seeds have:Dicot seeds have:

No endosperm No endosperm at maturityat maturity

Two cotyledonsTwo cotyledons

Seed coatSeed coat

First leavesFirst leaves

Early rootEarly root

CotyledonCotyledon

Organization of primary tissues in a young dicot stem (eg. Bean)

The primary tissues of a young monocot stem (eg. Corn)

Primary tissues of a young dicot root

Cross-section through a monocot root

General Angiosperm Life Cycle

Plant life spans Annual: flower plants that complete a

life cycle within one growing season Marigolds, pansies, wheat, cucumbers

Biennials: life cycle complete in two years (flowers in second year) Parsley, celery, foxglove

Perennials: flowering plants that live for more than two years (most have woody stems) Asparagus, grasses, palm trees, maple trees

Understanding Concepts, page 575

Questions 13-24