BIO153H5 Chapter Notes - Chapter 30: Dicotyledon, Gas Exchange, Heterospory

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5 Feb 2013

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Key Concepts
The green plants include both the green algae and the land plants
Green algae are an important source of oxygen and provide food for aquatic organisms; land plants
hold soil and water in place, build soil, moderate extreme temperatures and winds, and provide
food for other organisms
Land plants were the first multicellular organisms that could live with most of their tissues
exposed to the air. A series of key adaptations allowed them to survive on land. In terms of total
mass, plants dominate today’s terrestrial environments
Once plants were able to grow on land, a sequence of important evolutionary changes made it
possible for them to reproduce efficiently even in extremely dry environments
The green plants dominate terrestrial and freshwater habitats
Comprise two major types of organisms: the green algae and the land plants
Green algae are important photosynthetic organisms in aquatic habitats (lakes, pond and other
freshwater settings)
Land plants are the key photosynthesizes in terrestrial environments
They are the closet living relative to land plants and form a monophyletic groups with them
The transition from aquatic to terrestrial life occurred when land plants evolved from green algae
30.1 Why Do Biologists Study the Green Plants?
Agriculture, forestry and horticulture are among the mot important endeavors supported by
biological science
Biologists study plants not only because they are captivating organisms but also because they keep
us alive
Plants Provide Ecosystem Services
An ecosystem consists of all the organisms in a particular area, along with physical components of
the environment, such as the atmosphere, precipitation, surface water, sunlight, soil and nutrients
Plants provide ecosystem services because they add to the quality of the atmosphere, surface
water, solid and other physical components of an ecosystem
Plants alter the landscape in ways that benefit other organism:
o They produce oxygen via oxygenic photosynthesis
o They build soil by providing food for decomposers
o They hold soil and prevent nutrients from being lost by erosion by wind and water
o They moderate the local climate by providing shade, reducing the impact of winds that dry
out landscapes or make them colder
Perhaps the most important ecosystem service provided by plants involves food
They are the dominant primary producers in terrestrial ecosystems and provide the base of the
food chain in the vast majority of terrestrial habitats
Plants are eaten by herbivores which are eaten by carnivores which eaten by omnivores
organisms that eat both plant and animals
Omnivores feed at several different levels in the terrestrial food chain
Green plants are the key to the carbon cycle on the continents
Plants Provide Humans with Food, Fuel, Building Materials and Medicines
Plants provide most of our food supply as well as a significant percentage of the fuel, fibres,
building materials and medicines that we use
Agricultural research began with the initial domestication of crop plants
Artificial selection for plants with certain properties can lead to dramatic changes in plant
Humans have relied on plant-based fuels such as wood and coal
Plants are a key source of drugs
30.2 How Do Biologists Study Green Plants?
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Notes From Reading
To understand how green plants originated and diversified, biologists use three tools:
o They compare the fundamental morphological features of various green algae and green
o They analyze the fossil record of the lineage
o They assess similarities and difference in DNA sequences from homologous genes to
estimate phylogenetic trees
Analyzing Morphological Traits
Green algae have long been hypothesized to be closely related to plants on the basis of several key
morphological traits
The green algae include species that are unicellular, colonial or multicellular and that live in
marine or freshwater habitats
Based on morphology, the most important phyla of plants are groups into three categories:
nonvascular plants, seedless vascular plants and seed plants
Nonvascular plants lack vascular tissue specialized groups of cells that conduct water or
dissolved nutrients from one part of the plant body to another
Seedless vascular plants have well-developed vascular tissue but do not make seeds
A seed consists of an embryo and a store of nutritive tissue, surrounded by a tough protective
Seed plants have vascular tissue and make seeds
Within the seed plants, gymnosperms produce seeds that do not develop in an enclosed structure
In the flowering plants or angiosperms, seeds develop inside a protective structure called a
Using the Fossil Record
The fossil record for green algae began 700-725 million years ago
The fossil record for land plants began 475 million years ago
The fossil record for plants is massive and is broken up into five segments, each of which
encompasses a major event in the diversification of land plants
According to the fossil record, the green algae first, followed y the nonvascular plants, seedless
vascular plants and seed plants
Evaluating Molecule Phylogenies
The phylogenetic tree has several important points
1. Land plants probably evolved from green algae
2. The green algal group called Charales is the sister group to land plants meaning that
Charales are the closet living relative
3. The green plants are monophyletic, meaning that a single common ancestor gae rise to all of
the green algae and land plants
4. The green algae group is paraphyletic; the land plants are monophyletic
5. The nonvascular plants are the most basal groups among land plants
6. Morphological simplicity of the whisk ferns is probably a derived trait, meaning that complex
structures have been lost in this lineage
7. Seeds and flowers evolved only once
30.3 What Themes Occur in the Diversification of Green Plants?
The story of land plants is the story of adaptations that allowed photosynthetic organisms to move
from aquatic to terrestrial environments
The Transition of Land, I: How Did Plants Adapt to Dry Conditions?
Plants had to adapt to conditions in which only a portion of their tissues are wet
The adaptation of the water problem arose in two steps
o Prevention of water loss from cells
o Transportation of water from tissues with access to water to tissues without access
Preventing Water Loss: Cuticle and Stomata
Cuticle is a waxy, watertight sealant that gives plants the ability to survive in dry environments
Gas exchange is accomplished by stomata, which have a pore that opens and closes as the guard
cells change shape
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