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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
- Veröffentlichungsjahr: 2024
Harvest basic botany knowledge from this abundant book
Botany For Dummies gives you a thorough overview of the fundamentals of botany, but in simple terms that anyone can understand. Great for supplementing your botany coursework or brushing up before an exam, this book covers plant evolution, the structure and function of plant cells, and plant identification. Plus, you'll learn about how plants of different types are changing and adapting in response to changing climates. This new edition goes into more detail on fungi—not technically plants, but no one is holding that against them. Regardless of what brought you to the wonderful world of botany, this book will show you around.
- Get an easy-to-understand introduction to the key concepts in botany
- Read about recent discoveries and theories in the world of plant science
- Understand different families of plants and where they grow
- Improve your grade and pass your exam in your introductory botany course
Get a copy of Botany For Dummies and watch your botany knowledge bloom.
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Table of Contents
Cover
Title Page
Copyright
Introduction
About This Book
Foolish Assumptions
Icons Used in This Book
Beyond the Book
Where to Go from Here
Part 1: Getting Started with Botany Basics
Chapter 1: Exploring Botany
Taking a Close Look at Plant Structure
Figuring Out Plant Functions
Considering Plant Reproduction and Genetics
Exploring the Wide World of Plants
Making Connections Between Plants and People
Chapter 2: Peering at Plant Cells and Tissues
Building Cells from Four Types of Molecules
Entering the World of Cells
Exploring Plant Cells
Combining Cells to Form Tissues
Chapter 3: Vegetative Structures: Stems, Roots, and Leaves
Getting Organized into Plant Organs
Getting Taller with Stems
Digging Deep with Roots
Reaching Out with Leaves
Chapter 4: Reproductive Structures: Spores, Seeds, Cones, Flowers, and Fruits
Reproducing with Spores
Protecting the Offspring with Seeds
Organizing Reproduction in Cones
Finding a Mate with Flowers
Packaging the Seeds in Fruits
Dispersing Fruits and Seeds
Part 2: Discovering Plant Physiology
Chapter 5: Photosynthesis: Making Sugar from Scratch
Rethinking the Role of Soil
Discovering Photosynthesis Fundamentals
Harnessing the Sun: The Light Reactions
Storing Matter and Energy in Sugar: The Light-Independent Reactions
Chapter 6: Cellular Respiration: Making Your Cake and Eating It, Too
Digging into Cellular Respiration Fundamentals
Breaking Down Glucose in Glycolysis
Going Further with the Krebs Cycle
Making Useful Energy: Chemiosmosis and Oxidative Phosphorylation
Chapter 7: Moving Materials through Plants
Shipping and Receiving Materials throughout the Plant
Moving across Membranes
Going with the Flow: Water Transport
Sticky Business: Sugar Transport
Chapter 8: Regulating Plant Growth and Development
Exploring the Cyclical Nature of Plant Life
The Cellular Basis of Plant Growth and Development
Sending Signals with Plant Hormones
Which Way Do I Go?: Plant Movements
What Time Is It?: Sensing the Seasons
Part 3: Making More Plants: Plant Reproduction and Genetics
Chapter 9: Greening the Earth: Plant Reproduction
Reproducing: More Than One Way to Do It
Copying Cells by Mitosis
Reproducing Sexually with Meiosis
Considering Alternation of Generations
Chapter 10: Passing Plant Characteristics to the Next Generation
Tracking the Inheritance of a Single Gene
Tracking the Inheritance of Two Independent Genes
Mixing it Up with Incomplete Dominance
Inheriting Traits through Epigentics
Chapter 11: Changing with the Times: Evolution and Adaptation
Figuring Out the Fundamentals of Evolution
Moving onto the Land
Identifying Important Factors in Plant Evolution
Admiring Plant Adaptations
Part 4: The Wide, Wonderful World of Plants
Chapter 12: The Tree of Life: Showing the Relationships between Living Things
Examining the Branches of the Tree of Life
Organizing Life
Naming the Rose (and Other Living Things)
Chapter 13: Precursors to Plants: Bacteria, Protists, and Algae
Bacteria Can Be Green, Too
The Wild World of Protists
Seaweed: The Plants of the Ocean
Chapter 14: Examining the Forest Floor: Bryophytes and Seedless Vascular Plants
Moving onto the Land
Bryophytes: Nonvascular Plants
Tracheophytes: Vascular Plants
Seedless Vascular Plants
Chapter 15: Their Seeds Are Naked: Gymnosperms
Protecting the Embryo with Seeds
Cycads: Cycadophyta
Ginkgos: Ginkgophyta
Conifers: Coniferophyta (Pinophyta)
Gnetophytes: Gnetophyta
Chapter 16: Say It with Flowers: Angiosperms
Delving into Flowering Plants: Anthophyta
Exploring Angiosperm Diversity
Thinking about Pollination Ecology
Chapter 17: I’m Not a Plant, But I’m a … Fungi
Meet the Neighbors
You’ve Seen Us in Your Kitchen
Morels, Yeast, and Zombie Fungi
Puffballs, Stinkhorns, and Mushrooms
Part 5: Embracing the Synergy of Plants and People
Chapter 18: Exploring the Relationship Between People and Plants
Finding Our Favorites
Making Use of Plant Materials
Discovering the Power of Plant Chemicals
Chapter 19: Foraging, Farming, and Engineering Plants
From Foraging to Farming
Speeding Things Up By Engineering Plants
Trying to Build a Better World
Let’s Talk, Talk, Talk about It: Pros and Cons of Genetic Engineering
Chapter 20: Making Connections with Plant Ecology
Exploring Ecosystems
Interacting with Other Organisms
Part 6: The Part of Tens
Chapter 21: Ten Weirdest Plants
Plants That Eat Insects: Cobra Lily
Plants That Stink: The Corpse Flower
Plants That Move: Galloping Moss
Plants That Mimic Rocks: Stone Plants
Plants That Come Back From the Dead: Resurrection Plant
Plants That Just Look Strange: Welwitschia
Plants That Aren’t Green: Ghost Pipe
Plants That Have Sex with Insects: Australian Tongue Orchid
Plants That Really Know How to Grow: Queen Victoria Water Lily
Plants That Climb: Banyan Tree
Chapter 22: Ten Tips for Improving Your Grade in Botany
Engage Actively During Class
Use Your Lab Time Effectively
Plan Your Study Time
Be Active, Not Passive
Make Up Tricks to Jog Your Memory
Prepare for Different Kinds of Questions
Remember the Supporting Material
Test Yourself Often
Use Your First Test as a Diagnostic Tool
Get Help Sooner Rather Than Later
Index
About the Author
Connect with Dummies
End User License Agreement
List of Tables
Chapter 4
TABLE 4-1 Plant Spores versus Seeds
Chapter 7
TABLE 7-1 Relating Concepts of Water Movement to the Water Potential Equation
Chapter 8
TABLE 8-1 Five Major Groups of Plant Hormones
Chapter 12
TABLE 12-1 A Comparison of the Taxonomy of Several Species
TABLE 12-2 A Dichotomous Key
Chapter 14
TABLE 14-1 A Comparison of Lycophyte Groups
TABLE 14-2 A Comparison of Ferns and Their Allies
List of Illustrations
Chapter 2
FIGURE 2-1: Carbohydrates.
FIGURE 2-2: Amino acids link together to form proteins.
FIGURE 2-3: Structure of a nucleotide (adenosine monophosphate, an RNA nucleoti...
FIGURE 2-4: Polynucleotide chains.
FIGURE 2-5: Saturated and unsaturated bonds in a typical triglyceride.
FIGURE 2-6: Plant cells perform all the functions of life.
FIGURE 2-7: The fluid mosaic model of plasma membranes.
FIGURE 2-8: Structures in a typical plant cell.
FIGURE 2-9: The chloroplast.
FIGURE 2-10: The mitochondrion.
FIGURE 2-11: Plant cell walls and plasmodesmata.
FIGURE 2-12: Meristematic cells.
FIGURE 2-13: Plant meristems.
FIGURE 2-14: Simple plant tissues.
FIGURE 2-15: Types of water conducting cells.
FIGURE 2-16: Components of phloem.
Chapter 3
FIGURE 3-1: External anatomy of a woody stem.
FIGURE 3-2: Internal anatomy of a monocot stem.
FIGURE 3-3: Internal anatomy of an herbaceous dicot stem.
FIGURE 3-4: Internal anatomy of a woody dicot stem.
FIGURE 3-5: Types of specialized stems.
FIGURE 3-6: Types of root systems.
FIGURE 3-7: The internal anatomy of a dicot root.
FIGURE 3-8: Types of specialized roots.
FIGURE 3-9: Internal anatomy of a leaf.
FIGURE 3-10: Some examples of leaf shapes and leaf margins.
FIGURE 3-11: Types of leaves and leaf arrangements.
FIGURE 3-12: Some structures that plants form by modifying their leaves.
Chapter 4
FIGURE 4-1: Structure and germination of a dicot seed.
FIGURE 4-2: Structure and germination of a monocot seed.
FIGURE 4-3: Parts of a typical flower.
FIGURE 4-4: Ovary insertion within a flower.
FIGURE 4-5: Types of inflorescences.
FIGURE 4-6: Regions of a fruit.
FIGURE 4-7: Types of fruits.
FIGURE 4-8: Fruit and seed dispersal.
Chapter 5
FIGURE 5-1: The electromagnetic spectrum.
FIGURE 5-2: Absorption spectra for photosynthetic pigments.
FIGURE 5-3: Oxidation and reduction during photosynthesis.
FIGURE 5-4: The two halves of photosynthesis, the light reactions and the light...
FIGURE 5-5: The light reactions of photosynthesis (noncyclic photophosphorylati...
FIGURE 5-6: The Z scheme (noncyclic photophosphorylation).
FIGURE 5-7: Cyclic photophosphorylation.
FIGURE 5-8: The light-independent reactions, also known as the Calvin cycle.
FIGURE 5-9: CAM photosynthesis.
FIGURE 5-10: photosynthesis.
Chapter 6
FIGURE 6-1: A comparison of the direct burning of sugar with the breakdown of s...
FIGURE 6-2: Oxidation and reduction during cellular respiration.
FIGURE 6-3: An overview of cellular respiration.
FIGURE 6-4: The steps of glycolysis.
FIGURE 6-5: The Krebs cycle.
FIGURE 6-6: The electron transport chain in the inner membrane of the mitochond...
Chapter 7
FIGURE 7-1: Overview of the movement of molecules through plants.
FIGURE 7-2: Diffusion of molecules.
FIGURE 7-3: Transport across membranes.
FIGURE 7-4: Plasmolysis.
FIGURE 7-5: Capillary action.
FIGURE 7-6: The movement of water through a plant.
FIGURE 7-7: The pressure-flow hypothesis explains the movement of sugars throug...
Chapter 8
FIGURE 8-1: Went’s experiments on oat coleoptiles.
FIGURE 8-2: Conversion of phytochrome between its two forms: and .
Chapter 9
FIGURE 9-1: Asexual and sexual reproduction in a strawberry plant.
FIGURE 9-2: The cell cycle.
FIGURE 9-3: The process of mitosis and interphase.
FIGURE 9-4: Cytokinesis in a plant cell.
FIGURE 9-5: The events of meiosis.
FIGURE 9-6: Overview of alternation of generations.
FIGURE 9-7: Alternation of generations with gametophyte dominant (liverwort as ...
FIGURE 9-8: Alternation of generations with sporophyte dominant (fern as exampl...
Chapter 10
FIGURE 10-1: Mendel’s cross between purple- and white-flowered peas.
FIGURE 10-2: A dihybrid cross.
FIGURE 10-3: Independent assortment of homologous chromosomes during meiosis le...
FIGURE 10-4: A Punnett square for incomplete dominance.
Chapter 11
FIGURE 11-1: Natural selection.
FIGURE 11-2: Common strategies plants use to survive desert conditions.
FIGURE 11-3: Adaptations of rainforest plants.
FIGURE 11-4: Adaptations of carnivorous plants.
FIGURE 11-5: Adaptations of aquatic plants.
Chapter 12
FIGURE 12-1: A phylogenetic tree of life based on rRNA genes.
FIGURE 12-2: Reading a phylogenetic tree.
Chapter 13
FIGURE 13-1: Examples of bacteria.
FIGURE 13-2: The serial endosymbiotic theory for the origin of mitochondria and...
FIGURE 13-3: Examples of protists.
FIGURE 13-4: Macroalgae: Seaweeds.
Chapter 14
FIGURE 14-1: Bryophytes and seedless vascular plants.
FIGURE 14-2: Cross-section through a complex, thallose liverwort (
Marchantia)
.
FIGURE 14-3: The life cycle of a moss.
FIGURE 14-4: The life cycle of the club moss
Lycopodium
.
FIGURE 14-5: The life cycle of the spike moss,
Selaginella.
FIGURE 14-6: Life cycle of a horsetail.
FIGURE 14-7: Release of spores from a fern sporangium.
Chapter 15
FIGURE 15-1: A comparison between the seed-bearing structures of gymnosperms an...
FIGURE 15-2: Examples of gymnosperms a. Cycad. b.
Gnetum
. c.
Welwischia
.d.
Gink
...
FIGURE 15-3: A cross-section of a pine needle.
FIGURE 15-4: Life cycle of pine.
Chapter 16
FIGURE 16-1: Angiosperm diversity.
FIGURE 16-2: Primitive versus advanced characteristics in angiosperms.
FIGURE 16-3: Growth of a pollen tube.
FIGURE 16-4: The life cycle of angiosperms.
FIGURE 16-5: Parts of a legume flower. The five petals of this flower have uniq...
FIGURE 16-6: Parts of a spurge flower.
FIGURE 16-7: Parts of a lily flower.
Chapter 17
FIGURE 17-1: How fungi grow.
FIGURE 17-2: Major groups of fungi.
FIGURE 17-3: Life cycle of a zygote fungus (
Mucor
sp.).
FIGURE 17-4: Life cycle of sac fungi (
Pezizales
sp.).
FIGURE 17-5: Life cycle of club fungi.
Chapter 18
FIGURE 18-1: Production of biofuels.
FIGURE 18-2: Paper manufacturing.
FIGURE 18-3: Medicinal plants.
FIGURE 18-4: Poisonous plants.
FIGURE 18-5: Hallucinogenic plants.
Chapter 19
FIGURE 19-1: Origins of agriculture.
FIGURE 19-2: Artificial selection.
FIGURE 19-3: Plant tissue culture.
FIGURE 19-4: Restriction enzymes.
FIGURE 19-5: Inserting a gene of interest into the Ti plasmid.
FIGURE 19-6: Transforming a plant using
Agrobacterium.
FIGURE 19-7: Editing genomes with CRISPR-Cas
.
Chapter 20
FIGURE 20-1: The organization of living things.
FIGURE 20-2: Energy flow in ecosystems shown through a food chain.
FIGURE 20-3: The energy pyramid (trophic pyramid).
FIGURE 20-4: The carbon cycle.
FIGURE 20-5: The greenhouse effect.
FIGURE 20-6: The nitrogen cycle.
Guide
Cover
Table of Contents
Title Page
Copyright
Begin Reading
Index
About the Author
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Botany For Dummies®, 2nd Edition
Published by: John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, www.wiley.com
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Library of Congress Control Number: 2024946963
ISBN 978-1-394-27389-8 (pbk); ISBN 978-1-394-27390-4 (ebk); ISBN 978-1-394-27392-8 (ebk)
Introduction
Everybody’s talking about green these days. Green technology, green energy, green lifestyles. It’s no accident that the word green has come to symbolize a healthy world and sustainable habits. People use the word because it ties into visions of a green and growing world, lush with forests and fields of plants. This book is about the organisms that form the foundation of that green vision — the plants that surround us, support us, and make our world beautiful.
About This Book
Botany For Dummies, 2nd edition, is an introduction to the world of plants and their importance to the rest of life on earth. My goal is to present the concepts of plant biology in a clear and straightforward way, while I help you relate the science to your everyday life. I include lots of pictures of the processes, structures, and life cycles that you’d typically encounter in an introductory course in botany.
Botany is the study of plants, which covers a wide range of subjects, including their structure, function, patterns of inheritance, diversity, and importance to humans. Historically, botany also included the study of microbes and fungi, so I include a little bit about them here, too. I hope you’ll be as surprised and intrigued as I was when I first began to study botany and realized that the seemingly simple world of plants was actually pulsing with life, mystery, and beauty.
Foolish Assumptions
As I wrote this book, I tried to imagine who you might be and what you might need in order to understand botany:
A college biology major studying botany as part of your year-long freshman series.
A college student taking an introductory botany class as a way to fulfill the science requirement for your degree in a nonscience field.
Someone who just wants to know a little bit more about plants — you may be a gardener or a hiker who enjoys the beauty of plants and wants to know a little bit more about how they work.
Icons Used in This Book
The familiar For Dummies icons are used here to help guide you and give you new insights as you read the material.
This bull’s-eye symbol lets you know what you need to do to get to the heart of the matter at hand. These icons mark information that helps you remember the facts being discussed or suggest a way to help you commit it to memory.
This information gives you extra information that isn’t necessary to understand the topic. If you want to take your biology learning to a higher level, incorporate these paragraphs into your reading. If you want just the basics and do not want to be confused by the details, skip them.
This little icon serves to jog your memory. The information spotlighted here is information you should permanently store in your biology file. If you want a quick review of biology, scan through the book reading the remember icons. No need for a chunky yellow highlighter.
This icon alerts you to something that is possibly confusing. This information might be a common misconception shared by lots of people or a technical term that’s used differently in certain situations. When you encounter one of these, slow down and check your understanding to make sure you aren’t falling into a common mistake.
Beyond the Book
In addition to what you’re reading right now, this book also comes with a free, access-anywhere Cheat Sheet that discusses the parts of a flower and the types of plant tissues. To view the Cheat Sheet, simply go to www.dummies.com and type Botany For Dummies Cheat Sheet in the Search box.
Where to Go from Here
Like all For Dummies books, each chapter in Botany For Dummies, 2nd Edition is self-contained, so you can pick up whenever you need it and jump into the topic you are working on. You can start anywhere in the book that you want. If you are reading this book for general interest, you might enjoy starting with the second-to-last part, “Embracing the Synergy of Plants and People.” If you’re taking a college class in botany, you’ll probably want to start at the beginning with the basics on plant cells, tissues, and organs.
I hope you enjoy your journey into the world of plants and find them as amazing and beautiful as I do!
Part 1
Getting Started with Botany Basics
IN THIS PART …
Take a look at the most fundamental structure of plant bodies, the plant cell
Explore the basic organs of the plant body like roots, stems, and leaves
Discover the purpose behind flowers, cones, and fruits
Compare the role of seeds versus spores in plant reproduction
Chapter 1
Exploring Botany
IN THIS CHAPTER
Building plants one cell at a time
Finding out about how plants work
Connecting plants and people
Botany is the study of plants, including plant structure, function, reproduction, diversity, inheritance, and more. Plants may seem like they’re part of the background of your life, when really they’re at the center. The food you eat, the clothes you wear, the materials that make up your home — all these things depend upon plants. Plants remove carbon dioxide from the atmosphere, helping to keep your planet from getting too warm for life as you know it. They provide homes for insects and other animals, filter impurities out of ground water, and help protect shorelines from erosion.
And beyond all these useful things plants do, they’re just cool! Plants have many unique strategies that help them survive in all different kinds of environments. They trap and trick insects, grow in the ground or up in the rainforest canopy, and manage to survive everywhere from the glacial arctic to the hot, dry deserts. They seem so different from people, and yet when you really look at how plants grow and function, you’ll be surprised at how similar they are to you. This chapter offers an overview of the science of botany, giving you a peek into the mysteries of plants.
Taking a Close Look at Plant Structure
You might not think so, but plants are a lot like you. Their bodies are made of cells (that are organized into tissues (see Chapter 2), and these tissues form the familiar plant organs of roots, stems, and leaves (see Chapter 3). Plant cells use the same basic chemistry as your cells, storing information in DNA, using carbohydrates for energy, and putting proteins to work. And your cells and plant cells are both eukaryotic cells, meaning they have a similar structure that includes a nucleus and cellular organelles.
Plants have many ways of reproducing themselves (see Chapter 4). When plants reproduce sexually, they make special reproductive cells called spores. Many familiar plants make a structure that’s even better at starting the next generation — the seed. Seeds protect the plant embryos they carry and nourish them with stored food.
Many familiar plants reproduce sexually by producing showy flowers designed to attract animals to help spread their pollen around. Other flowering plants just dangle their flowers in the wind and let the wind do the work.
Flowers contain the male and female parts of the plant that will participate in sexual reproduction.
Pollen comes from the male part of flowers, carrying and protecting the plant sperm. The female parts of flowers house the ovules that contain the eggs. Pollination occurs when pollen arrives at the female part of the flower. The pollen releases the sperm so that they can fuse with the egg, causing fertilization, and starting the next plant generation. After fertilization in flowering plants, the ovaries within the flowers develop into fruits (see Chapter 4). Some fruits are sweet and fleshy, inviting animals to come eat the fruit and then disperse the seeds. Other fruits are dry and designed to either float on the breeze, hitch a ride on some animal fur, or even explode to release their seeds. Whatever the method, the goal is the same — to find a nice, new home for the embryos inside the seed to grow.
Figuring Out Plant Functions
In addition to being made of cells and having similar chemistry, plants use many of the same strategies that you do to solve life’s challenges. Both you and plants need a source of building material, called matter, to build the cells of your body, and you both need a source of energy so that you can build things and move around. And just like you, plants need to transport food and fluids around their bodies. Finally, you and plants both grow and develop, responding to changes in your environment.
Making and using food
The go-to source of matter and energy for all living things is food. Of course, one big difference between you and a plant is that you have to get your food by eating another organism, whereas plants can make their own.
Plants make their own food through the process of photosynthesis (see Chapter 5). Although the process of photosynthesis is pretty complex, you can get the main idea if you think of it like a recipe. The ingredients are carbon dioxide from the atmosphere and water taken up from the soil. You then follow these directions:
Use light energy from the sun to combine carbon dioxide and water, rearranging the atoms to form sugar and oxygen.
Serve sugar to all parts of the plant that need matter and energy and throw the oxygen gas away.
If you have leftovers, you can combine the sugars into starch to store some for later.
When plants want to use some of the sugar they’ve made to provide themselves with matter and energy, their cells do the same thing that your cells do with food, they break it down in a process called cellular respiration (see Chapter 6). Cellular respiration is a series of chemical reactions that basically unpack food molecules, making the matter and energy available to cells. When cells use cellular respiration to extract all the energy they can from food molecules, they release the waste matter as carbon dioxide and water.
Transporting materials
All the cells of a plant need food to provide them with matter and energy. Plants usually make sugars in their leaves, so they have to ship those sugars from the leaves to the rest of the plant. Likewise, plants take in water through their roots, but they need to get water to the entire plant, especially to the leaves, where it’s needed for photosynthesis. So, just like you have veins and arteries to transport blood around your body, plants have vascular tissue that specializes in the transport of sugar and water (see Chapter 7).
Plants transport dissolved sugars using a special type of tissue called phloem, and they transport water and dissolved minerals using a tissue called xylem.
Phloem transports sugar from the leaves where it’s made through photosynthesis, to all parts of the plant that need it for growth or that will store it as starch for later. Xylem transports water from the roots up through the plant to supply all the cells with the water they need.
Responding to hormones
Yet another similarity between you and plants is that they use hormones to direct their growth and development (see Chapter 8).
Although plants never go through puberty (lucky plants!), they do undergo major developmental changes, such as when a seed switches from being dormant to beginning to grow or when a flowering plant decides it’s the right time of year to start putting on a floral display. Plant hormones also direct responses like helping plants’ shoots grow toward the light and causing plant roots to grow downward toward the pull of gravity.
Considering Plant Reproduction and Genetics
Plants grow like, well … weeds. That’s because weeds are plants. (Okay, now I’m just being silly.) But seriously, plants grow when groups of cells at their tips, called apical meristems, divide in two to produce new cells. The process of cell division that adds new growth is called mitosis (see Chapter 9). Plants do mitosis pretty much the same way your cells do. Woody plants also do mitosis to grow wider, adding girth to tree trunks.
Plants also reproduce sexually, combining sperm and egg to make the next generation of plants. Plant life cycles are more complicated than those of humans (see Chapter 9), but, just like us, they can use a type of cell division called meiosis to produce cells that have half the genetic material of the parents. These cells ultimately give rise to the sperm and egg cells. Sperm and egg cells fuse, bringing together copies of the DNA from the parent plants.
By following the inheritance of traits from one generation to the next through the science of genetics (see Chapter 10), scientists can figure out how plant genes interact with each other to determine the traits of a plant.
Planet Earth is filled with a glorious diversity of plants. Plants can be as tall as the mighty redwood tree or as small as the tip of a pin. They can grow so rapidly that they go from seed to seed in a month, or live for over a thousand years. Because plants moved onto the land over 400 million years ago, they’ve evolved to live in every type of environment (see Chapter 11): Today, plants grow in the deserts, in the rainforests, in the oceans, and up on mountains.
Exploring the Wide World of Plants
Botanists study all the different kinds of plants to understand how each one gets what it needs to survive and reproduce. They also compare the structures and DNA code of plants to figure out the relationships between plant groups and reconstruct how plants evolved (see Chapter 12). They’ve identified the closest relatives to plants (see Chapter 13) and studied how the ancestors of plants had to change in order to survive when they moved from the ocean to the land (see Chapter 14).To survive and reproduce outside of the oceans, plants needed to develop new strategies for managing water, delivering sperm, and protecting embryos.
Some plants developed flowers and fruits, whereas others evolved cones. Some plants learned how to lure insects in to help with pollination, whereas other plants developed ways to trap and kill insects as a source of minerals. With all these different strategies and environments, you can probably imagine that some pretty amazing plants are out there, from delicate mosses (see Chapter 14) to sturdy pine trees (see Chapter 15) and plants that produce colorful flowers (see Chapter 16). And in the soil around all these different plants the fungi grow (see Chapter 17), many of which form partnerships with plants called mycorrhizae.
Mycorrhizal fungi form intimate connections with plant roots that enable sharing between plants and fungi. The plants provide food for the fungi, whereas the fungus helps the plant absorb more water and minerals from the soil. Without their mycorrhizal partners, most plants couldn’t even survive.
Making Connections Between Plants and People
The lives of people are completely interwoven with the lives of plants:
People use plants to make clothing.
Cotton and flax plants are used to make cotton and linen clothing. Some of the dyes people use to give their clothing color also come from plants (see
Chapter 18
).
People get medicines from plants.
Digitalin for heart disease, aspirin to reduce fever, and artemisinin for malaria are just a few examples of the powerful drugs people have extracted from plants (see
Chapter 18
).
People use plants for building materials.
People use wood for houses, furniture, and tools, and they use straw as material for roofs or bricks.
People reduce their stress and improve their fitness by taking a walk and admiring the plants.
Seriously, reducing stress is important. Stress has major impacts on people’s health. And for many people, nature has a soothing effect.
People grow plants for food.
The origins of human agriculture stretch back at least 10,000 years. And the switch from hunting and gathering to farming changed the entire structure of human societies (see
Chapter 19
).
People can modify plants to make them more nutritious or to make them produce medicines.
Genetically modified foods are very controversial, but they have benefits as well as risks (see
Chapter 19
).
Plants support the ecosystems of which people are a part.
Without plants to supply food to the web of life, what would you eat? (For more on this topic, see
Chapter 20
.)
Plants help keep water clean.
You probably hear people talking about wetlands, how they’re important, and how they’re disappearing at a rapid rate, thanks to development. Wetlands are communities with certain types of plants and soils. As the rain falls across areas where humans live, it picks up lawn fertilizers, motor oil from cars, poop from pets, and more. If this runoff flows through a wetland before it enters our streams and lakes, the plants and bacteria in the wetlands will remove lots of the dangerous substances on the way. Having wetlands to slow the flow of water also helps prevent flooding.
Chapter 2
Peering at Plant Cells and Tissues
IN THIS CHAPTER
Exploring plant cells
Making more cells with meristems
Comparing simple and complex tissues
Plant structure and function depend on the cells and tissues that make up their organs. Plants grow from the tips of their branches and roots as cells divide to produce new cells. Cells differentiate, becoming specialized to perform specific functions and combining with other cells to form unique types of tissues in plants. This chapter presents the different types of cells, tissues, and tissue systems found in plants.
Building Cells from Four Types of Molecules
The molecules that form the structures in plant cells have many important functions for plants and people. Molecules are the building blocks that make up cells. You can think of molecules like little chemical Legos that are arranged and rearranged to build the structure of each living and growing cell. In multicellular organisms like plants, cells join together to form the tissues that make up the structure of the organism.
The cells of all living things, including plant cells, are primarily made of four types of big molecules, called macromolecules:
Carbohydrates
Proteins
Nucleic acids
Lipids
Carbohydrates
Carbohydrates are commonly referred to as sugars, and the foods you can think of that are naturally sweet — like fruit, for example — are probably high in carbohydrates. Plant cells use carbohydrates for storing energy and also to provide structure to the cell.
Several types of carbohydrates are important to plant cells:
Many sweet tasting carbohydrates are smaller, simple sugars, called
monosaccharides
by scientists.
Glucose is an example of a monosaccharide. Glucose is extremely valuable to cells because it can be used as a fast source of energy. Glucose can exist in the linear form shown in
Figure 2-1a
, but in the water-filled environment of a cell, the molecule loops around and binds to itself, forming a ring-shaped structure (shown in
Figure 2-1b
).
Monosaccharides may form bonds with each other to form larger structures.
When glucose bonds with fructose, the sugar found in fruit, they form the
disaccharide
sucrose, otherwise known as common table sugar (see
Figure 2-1b
). Plants make sucrose in their green structures and then ship it all around the plant body to provide matter and energy to all their cells.
Short chains of monosaccharides are called
oligosaccharides
(see
Figure 2-1c
). Oligosaccharides send signals to plant cells, triggering growth responses and defense mechanisms.
Long chains of monosaccharides form
polysaccharides
(see
Figure 2-1d
). You may have heard polysaccharides referred to as complex carbohydrates. Like monosaccharides, polysaccharides are important molecules for storing energy and building materials and then making them available to cells. For example, the starch found in rice, pasta, breads, and potatoes is a polysaccharide that’s an important source of energy for both plants and people. Plants reinforce the structure of their cells with the polysaccharide cellulose, which is one of the major components of the cell wall that surrounds and supports plant cells.
FIGURE 2-1: Carbohydrates.
GET YOUR FIBER HERE!
Fruits and vegetables, as well as other plant foods like nuts and whole grains, are an excellent source of fiber. But what is fiber? And why do plants have it? Fiber is the common name for certain plant polysaccharides like the cellulose that surrounds and supports plant cells. Cellulose is a long chain of glucose molecules strung together, but because of the way the glucose molecules join together in cellulose, our digestive systems can’t break them apart. When cellulose, or fiber, hits your digestive system, it just passes on through. Your body can’t access the glucose molecules at all. So, all that undigested fiber passes into your large intestine and helps give mass to your, er, waste, which keeps your large intestine healthy and functioning normally. Fiber can help lower blood cholesterol, control blood sugar, and help people lose weight. So, be sure to include plenty of plants in your daily diet!
Proteins
Plant cells couldn’t function without proteins. That’s because proteins perform essential jobs in cells, moving materials around, creating scaffolding for the cell, helping chemical reactions, controlling information flow, and sending signals.
Each protein has a unique shape that helps it do its job. To make a protein, cells link amino acids with strong bonds called peptide bonds (shown in Figure 2-2), forming long chains of amino acids called polypeptide chains. The polypeptide chains fold up, either singly or in groups, to form the final shape of the functional protein.
FIGURE 2-2: Amino acids link together to form proteins.
Proteins have so many functions in plant cells that a list could go on for two pages. Rather than overwhelm you with all those functions at once, I hit a few of the most important functions here and then introduce specific proteins as they’re needed throughout the book:
Enzymes
are proteins that speed up chemical reactions.
As they live and grow, plants are constantly building new molecules and breaking other molecules down. The speed of these chemical reactions by themselves wouldn’t be fast enough to keep up with the pace of life. So plant cells, just like all cells, use enzymes to make those reactions happen exactly when plants need them.
Structural proteins
support the cell.
Protein cables inside plant cells, called
cytoskeletal proteins,
provide supportive scaffolding from the inside. (For more details on cytoskeletal proteins, see the upcoming section “
Scaffolding and railroad tracks: The cytoskeleton
,” later in this chapter.) Outside the cell, proteins are woven into the plant
cell wall,
a protective layer that encases plant cells. (You can find out more about plant cell walls in the section “
Rebar and concrete: Cell walls and extracellular matrices
,” later in this chapter.)
Transport proteins
move materials into and within plant cells.
Plants need to move molecules in and out of their cells. Transport proteins located at the boundary of the cell help create passageways for these materials. Inside the cell, molecules and structures may use cytoskeletal proteins as tracks that allow them to move around the cell.
Receptor
proteins help plant cells communicate.
In order to receive signals, such as hormones, plant cells need receptors that specifically recognize each signal. Receptors, which are usually proteins, can be located on the surfaces or insides of cells.
Nucleic acids
Even if you haven’t heard the term nucleic acids before, I’m sure you’ve heard of DNA, which is short for deoxyribonucleic acid. Nucleic acids like DNA are molecular specialists in information: The molecules are a chemical code that stores information and can transfer it from one generation to the next.
Two types of nucleic acids are found in cells:
DNA stores the information that determines the structure and function of all cells on earth.
The structure and function of the cells lead to the traits of the organism, which is why people say that DNA determines your traits. People don’t talk about plants much, but if they did, they’d say that DNA determines the traits of plants, too. You can think of DNA like the hard drive on a computer — it’s the main place where information is stored. So, whether a plant becomes a mighty redwood or a tiny wildflower is ultimately encoded in the DNA of its cells. And just like the information in a computer, the information in DNA can be copied and transferred. When cells reproduce, they copy their DNA molecules and pass them on to the new cells.
RNA, or
ribonucleic acid,
is similar to DNA in structure, but more flexible in its functions.
Different types of RNA molecules perform different functions in cells: Some of them carry information around the cell, some of them help build proteins, and some of them control when proteins are made. In terms of information, RNAs are more like e-mails — they contain information, but they can travel around and cause things to happen.
Nucleic acids are made from nucleotides, which are complex molecules that consist of three parts (see Figure 2-3):
A 5-carbon sugar:
In RNA nucleotides, like the one shown in
Figure 2-3
, the sugar is
ribose
. In DNA nucleotides, the sugar is called
deoxyribose
. Deoxyribose looks just like ribose, except that it’s missing one oxygen atom.
A phosphate group:
Phosphate groups contain a phosphorous atom surrounded by oxygen atoms. Some oxygen atoms have extra electrons, making them ionized and giving them a negative electrical charge. DNA and RNA molecules are negatively charged because of these phosphate groups.
A nitrogenous base:
Nitrogenous bases are ringed molecules that contain the element nitrogen. Five different nitrogenous bases are found in nucleotides: adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U). DNA nucleotides contain A, C, G, and T, whereas RNA nucleotides contain A, C, G, and U.
FIGURE 2-3: Structure of a nucleotide (adenosine monophosphate, an RNA nucleotide).
Cells make DNA and RNA molecules by forming covalent bonds between nucleotides (see Figure 2-4). The chains formed by this process are called polynucleotides.
DNA molecules contain two polynucleotides attached to each other by hydrogen bonds, whereas RNA molecules contain just one polynucleotide chain. The two polynucleotide strands of DNA attach to each other by hydrogen bonds between the bases A and T, and between the bases C and G, forming base pairs that look like the rungs of a ladder. The two strands twist around each other, forming the double helix of DNA.
FIGURE 2-4: Polynucleotide chains.
The information code in DNA and RNA molecules depends upon the order of nitrogenous bases in the polynucleotide. Just like the 26 letters of the alphabet can write words, the pattern of chemical molecules A, C, G, and T spell out the information in DNA molecules, like the one shown in Figure 2-4. This information contains the instructions for building proteins and RNA molecules that determine the structure and function of cells. Similarly, the information in RNA molecules is spelled out in the order of the molecules A, C, G, and U.
The genetic information of all cells is stored in molecules of DNA that are folded around proteins to form structures called chromosomes. The order, or sequence, of the four kinds of nucleotides within each chromosome spell out the instructions that determine the traits of the organism.
Lipids
Lipids are molecules that don’t mix with water, like fats, oils, and waxes. Cells, including those of plants, use lipids to create boundaries around and within cells. Lipids are also an excellent way to store energy and building materials for growth, and many plants, including olives, nuts, and even corn use oils as storage molecules.
Molecules like lipids that don’t mix with water are called hydrophobic, which literally means water-fearing. In contrast, molecules that do mix with water are called hydrophilic, which means water-loving.
HUNGRY FOR HYDROCARBONS
The carbon-hydrogen bonds that make up lipid molecules store a great deal of usable energy. For example, you may have heard that fats have 9 calories per gram, whereas carbohydrates have 4 calories per gram. Gram for gram, fats store more than twice the amount of energy as carbs! But the human craving for hydrocarbons goes way beyond nutrition. When humans discovered the potential of these molecules, we completely redesigned our way of life around them. The use of oil and gas to light our world extended our usable time into the hours of darkness. We hunted several species of whale almost to extinction for the oil we could extract from their bodies. We drill for the crude oil formed by the decomposition of ancient life and dig for the coal produced from the remains of plants from the Carboniferous Period (coal is a carbon, but not a hydrocarbon). Our use of hydrocarbons expanded when we learned to harness their power to run machines. The Industrial Revolution transformed our landscapes as we built factories and railroads and expanded our cities. We could travel farther and build more than ever before.
Unfortunately, the side effects of this hydrocarbon habit are destruction of natural environments and pollution. One pollutant that’s making itself felt today is the carbon dioxide (CO2) released into the atmosphere when hydrocarbons are burned. Atmospheric CO2 has increased steadily since the Industrial Revolution, and so have global temperatures. It turns out that CO2 is a greenhouse gas that acts like a blanket and traps heat on the earth’s surface. People today must simultaneously solve the problems brought on by our hydrocarbon-fueled growth and figure out how we’re going to replace our favorite energy source when it’s gone! No one knows what the full extent of the consequences will be for the environmental changes we’ve caused and whether we can reverse the dangerous trends we’ve set in motion. On the energy front, we’re already searching for solutions — making our machines more fuel efficient at the same time that we try to develop alternative fuel strategies (like wind and solar). Only time will tell if our harnessing of hydrocarbons was too much of a good thing.
Four types of lipids are especially important in plant cells:
Triglycerides (fats and oils):Triglycerides store energy and building materials for growth. The structure of fats and oils is basically the same (see Figure 2-5): a 3-carbon molecule called glycerol forms the backbone to which three fatty acids attach. Most plants store oils, not fats.
The difference between whether a triglyceride is a fat or an oil depends on how many unsaturated bonds it has between its carbon and hydrogen atoms. Unsaturated bonds result from two carbon atoms sharing two pairs of electrons from each other, forming a double bond like the one shown in the bottom fatty acid in Figure 2-5. Carbon atoms that are doing a double handshake with each other can’t bond to as many hydrogen atoms, so the bonds are considered “not full” or unsaturated with hydrogen. Saturated fats contain lots of carbon atoms joined with single bonds, like the straight chains of fatty acids in Figure 2-5. Saturated fat molecules, like those in butter, can pack tightly together and are solid at room temperature. Unsaturated fats, like those in plant oils, have bent fatty acid chains, so they don’t pack as tightly and are liquid at room temperature.
Phospholipids:
Cells build boundaries called
membranes
out of
phospholipids.
(To sneak a peek at phospholipids in membranes, go to “Customs: Plasma membranes,” later in this chapter.) Phospholipids are similar in structure to triglycerides, but one fatty acid chain is swapped for a hydrophilic head group. So, phospholipids have a dual nature — they’re hydrophilic at one end, and hydrophobic at the other.
Steroids:
Several plant hormones are
steroids,
lipid molecules made of four connected carbon rings. These hormones, called
brassinosteroids,
control many aspects of plant growth and development and trigger responses that protect plants from stress.
Waxes:
Many plants use
waxes
as a protective coating on the surfaces of leaves and other structures. Waxes help prevent water loss and can protect plants from insects and fungal pathogens. Carnivorous plants use waxes to make themselves slippery so that flies and other insects will slide to their doom! Waxes are diverse structurally, but the backbone of a wax is a long chain of carbon and hydrogen that is similar to a fatty acid. Next time you notice the gloss on a leaf, chances are you’re looking at a plant wax.
FIGURE 2-5: Saturated and unsaturated bonds in a typical triglyceride.
Entering the World of Cells
All living things, from tiny bacteria to giant redwood trees, are made of cells. Cells are the smallest things that have all the properties of life, including the ability to reproduce, respond to signals, grow, and transfer matter and energy with their environment. Figure 2-6 shows many of these functions and the structures that perform them in a plant cell.
Based on a comparison of fundamental cell chemistry and hereditary material, all cells on earth can be divided into three groups, called domains. You can think of these three domains as three main branches on the family tree of life on earth:
Eukarya:
Plants, animals, fungi, and protists
Bacteria:
Familiar, single-celled microorganisms, like the bacteria in your yogurt or the bacteria that cause human diseases
Archaea:
Single-celled microorganisms that are found in all types of environments, but were first discovered in extreme environments like hot springs
FIGURE 2-6: Plant cells perform all the functions of life.
In terms of cell structure, the cells of Bacteria and Archaea are very similar because they’re both prokaryotic, while the cells of Eukarya are more complex because they’re eukaryotic. (See the section “The Library: Storing Information in DNA,” later in the chapter.)
The cells of organisms from all three domains have certain features in common. They all have a boundary that distinguishes the cell from the environment, they contain DNA, and they have the ability to make proteins. The next few sections present these common cell features in more detail.
Customs: Plasma membrane
The barrier that separates the inside of the cell from its environment is called the plasma membrane (see Figure 2-7). The plasma membrane is made of two layers of phospholipids, forming a phospholipid bilayer with the hydrophilic heads of the phospholipids pointing outward and the hydrophobic tails of the phospholipids sandwiched in the middle. (For more details on phospholipids, check out the section “Lipids,” earlier in this chapter.)
The job of the plasma membrane is to separate the chemical reactions occurring inside the cell from the chemicals outside the cell. Scientists say the plasma membrane is selectively permeable, which means it’s choosy about what enters and exits the cell.
FIGURE 2-7: The fluid mosaic model of plasma membranes.
Proteins are also an important part of plasma membranes and help the plasma membrane do its job:
Proteins called
receptors
detect signals from the environment of the cell and relay the signal to the inside of the cell.
Scientists call the process of transferring a signal across a membrane
signal transduction
.
Transport proteins
help control which molecules enter and exit the cell.
Transport proteins called
channel proteins
form little tunnels in the membrane that can allow small molecules to pass quickly through the membrane.
Another type of transport protein, called
carrier proteins,
pick molecules up on one side of the membrane and then change their shape to deposit the molecules on the other side.
Scientists refer to the structure of the plasma membrane as the fluid mosaic model of the plasma membrane. The membrane is a mosaic because it’s made of different components, including phospholipids and proteins. It’s fluid because it’s flexible and molecules can move within it.
You can think of the plasma membrane like an international border that controls what enters and leaves the country. The proteins that regulate movement across the membrane are the customs officials.
Just inside the plasma membrane is the cytoplasm of the cell, the fluid material that contains all the molecules and structures of the cell. The cytoplasm is a busy place, filled with chemical reactions and moving materials.
Botanists call everything inside a plant cell, besides the nucleus and the cell wall, the protoplast.
Think of the cytoplasm of a cell like downtown in a busy city. The buildings downtown are like the structures in the cell that specialize for different functions. (Scientists call these structures organelles.) The cars speeding through downtown are like the materials that constantly move around in cells.
The library: Storing information in DNA
Just like people store information in libraries, all cells store information in deoxyribonucleic acid. (For the scoop on DNA, see the earlier section “Nucleic acids.”) One major difference between prokaryotic and eukaryotic cells, however, is that they package their DNA differently:
Eukaryotic cells
separate their DNA from the cytoplasm in the nucleus of the cell by surrounding the DNA with a sphere of membrane called the
nuclear membrane
. Like the plasma membrane, the nuclear membrane is mostly made of phospholipids and proteins. However, the nuclear membrane is actually a double membrane made up of two phospholipid bilayers. Materials and structures can travel in and out of the nucleus through little protein tunnels in the nuclear membrane called
nuclear pores.
Prokaryotic cells
locate their DNA directly within the cytoplasm in a region of the cell called the
nucleoid
.
Factories: Ribosomes
Ribosomes are small structures in cells that help build proteins. Because proteins are very important workers in cells, all cells need ribosomes.
The ribosomes in all types of cells have a very similar structure:
Ribosomes are made of two types of molecules: a special type of RNA, called
ribosomal RNA
(rRNA)
,
and proteins.
The rRNA and proteins of ribosomes are twisted together to form two separate pieces: the
large subunit
and the
small subunit
. These subunits are built separately from each other and come together to form a completed ribosome when a cell begins to make a protein.
Think of ribosomes as little factories where proteins are built.
To make a protein, cells complete two processes:
Transcription:
In the nucleus, cells copy the instructions for the protein from the DNA into a new molecule, called
messenger RNA
(mRNA). The mRNA leaves the nucleus and carries the instructions to the ribosomes out in the cytoplasm of the cell.
Translation:
Ribosomes organize the mRNA and other molecules that are needed to build proteins and help to put proteins together.
Exploring Plant Cells
Plants, like other eukaryotes, have cells that are highly organized, with lots of compartments for different functions. In addition to the nuclear membrane that walls off the DNA, other membranes form structures called organelles that perform specialized tasks for the cell. Plants and animals are both eukaryotes, so their cells have lots in common. In fact, most people would be very surprised to learn how much they have in common with plants!
Almost all eukaryotic cells, including those of plants and animals, contain the following structures (see Figure 2-8):
Plasma membrane
Ribosomes
Nucleus
Endoplasmic reticulum
Golgi apparatus (sometimes called
dictyosomes
in plant cells)
Mitochondria
Cytoskeleton
Vesicles, vacuoles, and lysosomes
FIGURE 2-8: Structures in a typical plant cell.
In addition, plants have four structures, some of which are found in other eukaryotes, but which are not found in animal cells):
Cell wall
Plastids, including chloroplasts
Large central vacuole
Plasmodesmata
