About Plant Biology

Chapter 1

Why Study Plant Biology?

• Show interrelationships between plants and other fields of study

• Prepare for careers in plant biology

• Gain fundamental knowledge for upper division plant biology courses

• Share expertise gained with nonbotanists

What is a Plant?

• An organism that is green and photosynthetic

• Additional characteristics– Cell wall composed of cellulose– Multicellular body– Can control water loss– Have strengthening tissues– Can reproduce by means of microscopic,

drought-resistant spores

Ecologic Services

• Sources of food, fabric, shelter, medicine

• Produce atmospheric oxygen and organic nitrogen

• Build new land

• Inhibit erosion

• Control atmospheric temperature

• Decompose and cycle essential mineral nutrients

Importance of Plants to Human Civilizations

• Trees for lumber to make warships

• Fuel to smelt metals, cure pottery, generate power and heat

• Sources of wealth– spices

• Sources of industrial products– Rubber– oil

Natural Plant Losses

• Plant losses occurring at a faster rate than ever before

• Factors include– Agriculture– Urbanization– Overgrazing– Pollution– Extinction

Environmental Laws

• Described in 1961 by plant biologist Barry Commoner

• Laws becoming more true every day

• Four “environmental laws”– Everything is connected to everything else.– Everything must go somewhere.– Nature knows best.– There is no such thing as a free lunch.

Scientific Method

• Codefined and promoted in 17th century by Rene Decartes and Francis Bacon

• Steps involved in scientific method– Make observations– Ask questions– Make educated guesses about possible answers– Base predictions on the guesses– Devise ways to test predictions– Draw conclusions

Scientific Method

• Hypothesis – “educated guess” based on observations and questioning

• Predicted result occurs – hypothesis is most likely correct

• Individuals using scientific method should be objective and unbiased

Scientific MethodOriginal Hypothesis Devise method to

test hypothesisAnalyze results

Results support

hypothesis

Results support

hypothesis but suggest minor refinements

Results are so unexpected that

they do not support original hypothesis and require a new

hypothesis

Results do not support original

hypothesis but fall within range that

could be expected if original

hypothesis is slightly modified

Retest using minor

refinements of process

Test using slightly modified

hypothesis

Test new hypotheses

Studying Plants From Different Perspectives

• Plant genetics – study of plant heredity• Plant systematics – study of plant evolution and

classification• Plant ecology – study of how the environment

affects plant organisms• Plant anatomy – study of a plant’s internal

structure• Plant morphology – study of how a plant

develops from a single cell into its diverse tissues and organs

Study Plants from Taxonomic Classification

• Microbiology – study of bacteria

• Mycology – study of fungi

• Phycology – study of algae

• Bryology – study of mosses

Interrelationships Among Several Plant Biology Disciplines

GenesGenetics

Evolution

Taxonomy & Systematics

METABOLISMPhysiology

ENVIRONMENTEcology

Paleoecology

Biogeography

TAXONOMIC GROUPS

DEVELOPMENT

STRUCTUREPhycology

Microbiology

Mycology

Bryology

Morphology

Anatomy

PLANT

Plant Classification

• Taxonomy

• Linnaean system– Easy to use – Based on idea that species never changed – Grouped organisms according to arbitrary

similarities– Fails to meet needs of modern biologists

Linnaean Taxa

Taxa Ending

Kingdom

Division -phyta

Class -opsida

Order -ales

Family -aceae

Genus No standard ending

Species No standard ending

Plant Classification

Whittaker’s Five Kingdoms

• Developed in 1969 by Robert Whittaker

• Each kingdom assumed to be monophyletic group of species

• Molecular biology techniques– Cladistics– Show five kingdom system also does not

recognize evolutionary groups

Whittaker’s Five KingdomsKingdom Description

MoneraIncluded bacteria

FungiIncluded molds, mildews, rusts, smuts, and mushrooms

ProtistaIncluded simple organisms, some were photosynthetic, mostly aquatic organisms called algae

PlantaeIncluded more complex photosynthetic organisms that typically grew on land

AnimaliaIncluded typically motile, multicellular, nonphotosynthetic organisms

Plant Classification

Cladistics

• Based on evolutionary groups

• Compare DNA base pair sequences of organisms to determine relatedness

• Obtain percent similarity between organisms

Plant Classification

• Clades – evolutionary groups

• Cladogram = phylogenetic tree– Branching diagram– Emphasizes shared features from common

ancestor– Future discoveries may require modifications

of cladogram

Plant Classification

• Domain– Neutral term– Groups of organisms as large or larger than a

kingdom– Monophyletic

• Three domains based on cladistics– Eukarya– Bacteria– Archaea

Domain Eukarya

• Made up of Whittaker’s plant, animal, and fungal kingdoms

• Eukaryotic cells– Membrane-bounded organelles

• Linear chromosomes

• Protists – Not monophyletic– Controversy over where to place organisms

Domain Bacteria

• Organisms originally were placed in Whittaker’s Kingdom Monera

• Microscopic

• Prokaryotic cells– No membrane-bounded organelles– Circular chromosome

• Sexual reproduction unknown

• Found in every habitat on Earth

Domain Bacteria

Beneficial aspects

• Decomposers

• Some carry on photosynthesis– Cyanobacteria or blue-green algae

• Nitrogen fixation– Convert inorganic N2 into ammonium for plant

use– Cyanobacteria

Domain Bacteria

Detrimental effects

• Pathogens – cause diseases

• Human diseases– Botulism, bubonic plague, cholera, syphilis,

tetanus, tuberculosis

• Plant diseases

Domain Archaea

• Organisms originally were placed in Whittaker’s Kingdom Monera

• Prokaryotic

• Different cell structure and chemistry than organisms in Domain Bacteria

Domain Archaea

Divided into three groups based on habitat• Bacteria of sulfur-rich anaerobic hot

springs and deep ocean hydrothermal vents

• Bacteria of anaerobic swamps and termite intestines

• Bacteria of extremely saline waters– Extreme halophiles– Photosynthetic – pigment bacteriorhodopsin

Three Domains

Domain Cell Type Description

Eukarya EukaryoticMembrane bounded organelles, linear chromosomes

Archaea ProkaryoticFound in extreme environments, cell structure and differ from members of Domain Bacteria

Bacteria ProkaryoticOrdinary bacteria, found in every habitat on earth, play major role as decomposers

Kingdom Fungi

• Eukaryotic cells

• Typically microscopic and filamentous

• Rigid cell wall made of chitin

• Reproduce sexually in a variety of complex life cycles and spores

• Widely distributed throughout world – mainly terrestrial

Kingdom Fungi

Economic importance

• Decomposers

• Form associations with roots of plants

• Important foods for animals and humans– Mushrooms, morels

• Decomposing action of yeast– Flavored cheeses, leavened bread, alcoholic

beverages

Economic importance

• Production of antibiotics– Penicillium

• Pathogens– Invade both plant and animal tissue– Cause illnesses– Reduce crop yields

Kingdom Fungi

Kingdom Protista

• Eukaryotic cells

• Reproduce both sexually and asexually

• Catch-all group– Photosynthetic organisms – algae– Nonphotosynthetic organisms – slime molds,

foraminiferans, protozoans

Kingdom Protista

Algae

• Arrangements – Single cells, clusters, filaments, sheets, three-

dimensional packets of cells

• Photosynthetic

• Float in uppermost layers of all oceans and lakes

Kingdom Protista

• Phytoplankton– “grasses of the sea”– Microscopic algae– Form base of natural food chain– Produce 50% of all oxygen in atmosphere

Kingdom Plantae

• Included all organisms informally called plants

• Bodies more complex than bacteria, fungi, or protists

• Eukaryotic

• Unique biochemical traits of plants– Cell walls composed of cellulose– Accumulate starch as carbohydrate storage

product– Special types of chlorophylls and other

pigments

Kingdom Plantae

Kingdom Plantae

Ecologic and economic importance of plants

• Form base of terrestrial food chains

• Principal human crops

• Provide building materials, clothing, cordage, medicines, and beverages

Challenge for 21st Century

While the human population increases, the major challenge of retaining natural biological diversity and developing a sustainable use of the world’s forests, grasslands, and cropland remains. As you study plant biology, think of the ways that you can contribute to this challenge.