Plant Diversity I: How Plants Colonized Land CH. 29

From which organisms did plants evolve?

Plants evolved from green algae.

How many plant species exist?

There are approximately 325,000 plant species.

What are the key traits shared between plants and algae?

Plants are multicellular, eukaryotic, and photosynthetic autotrophs with cell walls made of cellulose and chloroplasts containing chlorophylls a and b.

Which algae are the closest relatives of plants?

Charophytes (green algae) are the closest relatives of plants.

What distinctive trait do charophytes share with plants?

Charophytes have cellulose-synthesizing membrane proteins arranged in rings.

What is sporopollenin?

Sporopollenin is a durable polymer that covers exposed zygotes, preventing them from drying out.

What benefits did the move to land provide for plants?

Benefits included unfiltered sunlight, more CO2, and nutrient-rich soil.

What challenges did plants face when moving to land?

Challenges included scarcity of water and lack of structural support against gravity.

What are the four key derived traits of plants absent in charophytes?

Alternation of generations, multicellular dependent embryos, walled spores produced in sporangia, and special meristems.

What is the function of the cuticle in plants?

The cuticle is a waxy covering that reduces water loss.

What are stomata and their role in plants?

Stomata are pores that allow gas exchange (CO2 and O2) and support photosynthesis.

What is alternation of generations in plants?

It is the process where the life cycle alternates between two generations: gametophytes (haploid) and sporophytes (diploid).

What is the role of the female gametophyte in plant reproduction?

The female gametophyte retains and protects the diploid embryo, providing nutrients through placental transfer cells.

What are sporangia?

Sporangia are multicellular organs in the sporophyte stage that produce spores.

What is the significance of apical meristems in plants?

Apical meristems are regions of continuous cell division at the tips of roots and shoots, allowing for growth and resource acquisition.

What role did mycorrhizal fungi play in early plant evolution?

Mycorrhizal fungi formed symbiotic associations with early plants, aiding nutrient uptake and helping them colonize land.

When did the first plant spores appear in the fossil record?

Spores from early plants appear in fossils dating back to 470 million years ago.

What distinguishes vascular plants from nonvascular plants?

Vascular plants have a complex vascular tissue system for transporting water and nutrients, while nonvascular plants do not.

What is vascular tissue?

Vascular tissue consists of cells joined into tubes that transport water and nutrients throughout the plant body.

What is the significance of the first plant fossils dating to 420 million years ago?

These fossils indicate the diversification of early land plants.

What adaptations allowed plants to thrive on land despite challenges?

Plants diversified through adaptations such as the development of cuticles, stomata, and vascular tissues.

What are embryophytes?

Plants are called embryophytes due to the dependency of the embryo on the parental gametophyte.

What are the three types of nonvascular plants?

Liverworts, mosses, and hornworts

What are seedless vascular plants?

Plants that have vascular tissue but lack seeds.

What are the two clades of seedless vascular plants?

Lycophytes and Monilophytes.

What do lycophytes include?

Club mosses and their relatives.

What do monilophytes include?

Ferns, horsetails, whisk ferns, and their relatives.

What is a seed?

An embryo packaged with a supply of nutrients inside a protective coat.

What are the two groups of seed plants?

Gymnosperms and Angiosperms.

What are gymnosperms?

Seed plants with 'naked seeds' that are not enclosed in chambers, such as conifers.

What are angiosperms?

Flowering plants whose seeds develop inside chambers that originate within flowers.

What dominates the life cycle of nonvascular plants?

Gametophytes.

What are the three phyla of bryophytes?

Liverworts (phylum Hepatophyta), mosses (phylum Bryophyta), and hornworts (phylum Anthocerophyta).

What is the dominant stage of the life cycle in bryophytes?

Haploid gametophytes.

What are rhizoids?

Root-like structures that anchor gametophytes to the substrate.

What are archegonia?

Female gametangia that produce a single non-motile egg.

What are antheridia?

Male gametangia that produce many motile sperm.

What is required for sperm to reach the egg in bryophytes?

Water.

What does the sporophyte consist of?

Foot, seta, and sporangium.

What is the function of the foot in bryophyte sporophytes?

It absorbs nutrients from the gametophyte.

What is the purpose of the sporangium?

It produces spores by meiosis.

What is the peristome?

The structure located on the upper part of the capsule that opens and disperses spores when conditions are dry.

How do moss and hornwort sporophytes differ from liverworts?

Mosses and hornworts have larger and more complex sporophytes.

What unique feature do hornwort sporophytes have?

A cuticle.

What are hornworts?

Hornworts are plants in the phylum Anthocerophyta characterized by long, tapered sporophytes that can grow up to 5 cm tall.

What is a unique feature of hornwort sporophytes?

Hornwort sporophytes lack a seta and consist only of a sporangium.

How do hornworts release their spores?

Spores are released when the horn splits open.

What are the characteristics of hornwort gametophytes?

Hornwort gametophytes are 1-2 cm in diameter, grow horizontally, and have multiple sporophytes attached.

Why are hornworts important in ecology?

They are among the first species to colonize open areas with moist soils due to their symbiotic relationship with nitrogen-fixing cyanobacteria.

What is the height range of moss gametophytes?

Moss gametophytes range from 1 mm to 60 cm in height, but are usually less than 15 cm tall.

What is the visibility of moss sporophytes?

Moss sporophytes are usually visible to the naked eye.

How do mosses adapt to various environments?

Mosses can survive in cold or dry areas by losing most of their body water and rehydrating when moisture is available.

What role did bryophytes play in plant evolution?

Bryophytes were the main vegetation for the first 100 million years of plant evolution.

What allowed vascular plants to grow taller?

The development of vascular tissue allowed plants to grow taller.

What are the two types of vascular tissue in plants?

Xylem and phloem.

What is the function of xylem?

Xylem conducts most of the water and minerals from the roots.

What are tracheids?

Tracheids are tube-shaped cells in xylem that carry water and minerals up from the roots.

What is the function of phloem?

Phloem transports sugars, amino acids, and other organic products throughout the plant.

What are roots in vascular plants responsible for?

Roots absorb water and nutrients from the soil and anchor vascular plants to the ground.

What are microphylls?

Microphylls are small, often spine-shaped leaves with a single vein, found only in lycophytes.

What are megaphylls?

Megaphylls are larger leaves with a highly branched vascular system, found in all other plant groups.

What are sporophylls?

Sporophylls are modified leaves that bear sporangia.

What is the difference between homosporous and heterosporous plants?

Homosporous plants produce one type of spore, while heterosporous plants produce two types of spores (mega and micro).

What are the characteristics of fern sporophytes?

Fern sporophytes have large megasporophylls (fronds) divided into leaflets.

What is unique about horsetail sporophytes?

Horsetail sporophytes have jointed stems with rings of small leaves or branches.

What is the significance of seedless vascular plants in Earth's history?

They contributed to a large drop in CO2, causing global cooling and glacier formation during the Devonian and Carboniferous periods.