General Biology 101



General Biology 101

Chapter Outlines

Starr & Taggert

10th edition

Chapter 23

Introduction – Pioneers in a New World

It is thought that plants first colonized the land around 700 million years ago. There are fossils of these first pioneers. Today cyanobacteria (photosynthetic prokaryotes) and green algae grow as mats in near-shore waters and freshwater streams, similar areas to what ancestral forms of all modern plants may have first colonized.

Plants are multi-celled photoautotrophs, containing the pigments chlorophyll a and b, similar to the green algae that they share a common ancestor with.

There are currently 295,000 species of known plants.

Section 23.1 Trends in Plant Evolution

Types of plants:

➢ Vascular – those that have internal conducting tissues.

➢ Bryophytes – nonvascular including mosses and liverworts.

➢ Seedless vascular – including horsetails and ferns.

➢ Gymnosperms – cone bearing seed plants

➢ Angiosperms – flowering plants

Characteristics of land plants

Root systems – for absorbing water and anchoring the plant in place.

Shoot systems – energy producing leaves that absorb sunlight and undergo photosynthesis.

Special features:

Lignin – organic compound in cell walls that gives support to stems.

Vascular tissues within stems

Xylem – conducts water and dissolved ions and minerals.

Phloem – distributes sugars made during photosynthesis.

Cuticle – waxy covering on leaves and stems that conserves water.

Stomata – openings in the leaves that allow passage of gases and water vapor.

Life Cycles

Gametophyte – gamete producing phase in a plant’s life cycle. Haploid. Dominant form in bryophytes.

Sporophytes – a multi-celled, diploid plant body that gives rise to spores. They are the dominant form in most land plants. By mitosis spores produce gametophytes.

Advantage of a dominant sporophyte was fertilization and dispersal of new/next generation timed with environmental conditions.

Pollen grains in seed bearing plants contain spores that when mature become the male gametophyte. Pollen helped plants colonize dryer areas on land.

The female gametophyte is associated with the seed bearing tissues e.g. flowers or cones that get pollinated and produce seeds containing the embryo that will start the next generation of plants.

Section 23.2

The Bryophytes

18,600 species

Include:

Mosses * most common

Liverworts

Hornworts

Characteristics:

Nonvascular plants

Grow in moist habitats

Short – less than 20 cm i.e. 8 inches tall

Rhizoids – which are absorptive structures that attach gametophytes to soil.

Land plant derived structures include:

➢ Cuticle

➢ Cellular jacket around reproductive structures around the shoot tip of the gametophyte

➢ Gametophyte stage dominant and don’t get nutrients from the sporophyte.

Peat mosses grow very fast and in some parts of the world are used for a fuel source.

Peat is high in acids which hamper the growth of bacterial and fungal decomposers.

Peat bogs – accumulations of compressed, moist peat. Communities in peat bogs include acid loving plants like cranberries and blueberries.

Liverworts are also gametophytes which can reproduce sexually (with separate male and female plants) as well as asexually in gemma cups.

Section 23.3

Existing Seedless Vascular Plants

Seedless Vascular plants differ from bryophytes in that:

1) Sporophyte does not stay attached to the gametophyte

2) Has true vascular tissues

3) Sporophyte is the more dominant and longer lived portion of the life cycle.

Most reside in wet, humid places.

Flagellated sperm swim to the eggs

I. Lycophytes: Club mosses (found from the Arctic to the tropics). Aka ground pines

- Spores form in hollow chambers in the leaves. Chamber called the sporangium. Spores form via meiosis.

- Strobilus- a cluster of spore producing structures.

II. Whisk Ferns (Psilophyta)

- Have rhizomes which are short, branched, horizontal absorptive stems that grow underground.

- All have vascular tissues i.e. xylem and phloem.

- Sporophtyes have no roots.

III. Horsetails (Sphenophyta)

- Very primitive plant that has been around for the past 300 million years.

- Commonly found along streams and roadsides

- Free-living gametophyte (very small).

- Reinforced stems have silica within them (makes for sandpaper like texture to the plant).

IV. Ferns (Pterophyta)

- Largest and most diverse group of vascular, seedless plants.

- Have vascularized rhizomes, give rise to roots and leaves.

- Young leaves are called fronds. (coiled initially and then unfold).

- On the underside there are typically brown dots called sori, containing a cluster of sporangia. At dispersal the sporangia snap open and catapult the spores out into the nearby environment (usually when it is moist – like after a rain).

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