Introduction to Plants and

Botany
• Botany is the scientific study of plants.

• This definition requires an understanding of the concepts “plants” and

“scientific study”

• It may surprise you to learn that it is difficult to define precisely what a

plant is.
• Your present concept of plants is probably quite accurate:

Most plants have green leaves, stems, roots, and flowers

• but you can think of exceptions immediately.
• Plant:

• Algae are problematical.

• One group, the green algae similar to plants in biochemistry and cell
structure, but it also has many significant differences.

• Some botanists conclude that it is more useful to include green algae

with plants;

• Others exclude them, pointing out that some green algae have more
in common with the seaweeds known as red algae and brown algae
• Arbitrarily declaring that green algae are or are not plants solves
nothing;

• The important thing is to understand the concepts involved and why

disagreement exists
• Plant Definition:

• Cellulose Wall
• Producing starch as storing material
• Chloroplast that contain Chlorophyll b
• Thylakoid which stacked to form Grana in their chloroplasts
 Scientific Method

• Until the 15th century, several methods for analyzing and explaining
the universe and its phenomena were used,

• Religion and speculative philosophy were especially important.

• Starting before the 1400s, a new method, called the scientific

method, slowly began to develop.
 Fundamental Principals of Scientific Method

1. Source of information:

• All accepted information can be derived only from carefully

documented and controlled observations or experiments.

• Claims emanating from priests or prophets—or scientists—cannot be

accepted automatically; they must be subjected to verification and
proof.
 2. Phenomena that can be studied:

• Only tangible phenomena and objects are studied, such as heat,

plants, minerals, and weather.

• Anything that cannot be observed cannot be studied.

 3. Constancy and universality:

• Physical forces that control the world are constant through time and
are the same everywhere.

• Water has always been and always will be composed of hydrogen and
oxygen; gravity is the same now as it has been in the past.
 4. Basis:

• The fundamental basis of the scientific method is skepticism, the

principle of never being certain of a conclusion, of always being
willing to consider new evidence.

• No matter how much evidence there is for or against a theory, it does

no harm to keep a bit of doubt in our minds and to be willing to
consider more evidence.
 Scientific Method

• Scientific studies basically begin with a series of observations,

followed by a period of experimentation mixed with further
observation and analysis.

• At some point, a hypothesis, or model, is constructed to account for

the observations: A hypothesis
• A hypothesis (unlike a speculation) must make predictions
that can be tested.
• A hypothesis must be tested in various ways.

• It must be consistent with further observations and experiments,

• It must be able to predict the results of future experiments: One of

the greatest values of a hypothesis or theory is its power as a
predictive model.
• If its predictions are accurate, they support the hypothesis;

• if its predictions are inaccurate, they prove that the hypothesis is

incorrect.
• If a hypothesis continues to match observations, we have greater
confidence that it is correct, and it may come to be called a theory.
 Note the four principles of the scientific method here.
• First, the hypothesis is based on observations and can be tested with
experiments; we do not accept it simply because some famous
scientist declared it to be true.
• Second, tangible phenomena that we can either see directly or
measure with instruments.
• Third, if we repeat the experiment anytime or anywhere, we expect
to get the same results.
• Fourth, we interpret the evidence as supporting the hypothesis, but
we keep an open mind and are willing to consider new data or a new
hypothesis.
• In former times, if a theory had sufficient support, it was referred to
as a “law”, such as the laws of thermodynamics or the law that for
every action there is an equal and opposite reaction.

• Physicists occasionally still do this but biologists never use the term
“law.”
• Even though we have tens of thousands of observations that plants
are composed of cells, there is no “law that all plants are composed
of cells” instead we just treat this as a well supported theory.

• No biologist expects that there will be a discovery that shows that

plants are not actually made up of cells, but we simply do not ever
use the term “law.”
• Many people attempt to discredit the theory of evolution by natural
selection by saying that it is merely a theory of evolution, not a law of
Evolution.

• These people do not realize that their argument is nonsensical.

 Using Concepts to Understand Plants

• The growth, reproduction, and death of plants—indeed, all aspects of

their lives—are governed by a small number of basic principles.
1. Plant metabolism is based on the principles of chemistry and
physics.

• All the principles you learn in your chemistry or physics classes are
completely valid for plants.
2. Plants must have a means of storing and using information.

• As you may already know, genes are the primary means of storing this
information.
• 3. Plants reproduce, passing their genes and information on to their
descendants.
4. Genes and the information they contain, change.

• As plants make copies of their genes during reproduction, accidental

changes (mutations) occasionally occur, and this causes the affected
gene and its information to change.
5. Plants must survive in their own environment.

• They must be adapted to the conditions in the area where they live. If
they are not adapted to that area’s conditions, they grow and
reproduce poorly or die prematurely.
6. Plants are highly integrated organisms.

• The structure and metabolism of one part have some impact on the
rest of the plant.
7. An individual plant is the temporary result of the interaction of genes
and environment.

• Be careful to consider differences between an individual plant and

that plant’s species (the group made up of all similar plants).
• 8. Plants do not have purpose or decision-making capacity.

• It is easy to speak and write as if plants were capable of thinking and

planning.

• We might say, “Plants produce roots in order to absorb water”;

however, this suggests that the plants are capable of analyzing what
they need and deciding what they are going to do.
• Assuming that plants have human characters such as thought and
decision-making capacity is called anthropomorphism, and it should
be avoided.

• Similarly, assuming that processes or structures have a purpose is

called teleology, and it too is inaccurate.
 Origin and Evolution of Plants

• Life on Earth began about 3.5 billion years ago.

• At first, living organisms were simple, like present-day bacteria, in

both their metabolism and structure;

• however, over thousands of millions of years cells gradually increased

in complexity through evolution by natural selection.
• As early organisms became more complex, major advances occurred.

• One was the evolution of the type of photosynthesis that produces

oxygen and carbohydrates.

• This photosynthesis is present in all green plants, but it first arose

about 2.8 billion years ago in a bacterium-like organism called a
cyanobacterium.

• Later, cell structure became more efficient as subcellular components

(organelles) evolved.
• A particularly significant evolutionary step occurred when DNA
became located in its own organelle—the cell nucleus.

• Because this step was so important and occurred with so many other
fundamental changes in cell metabolism, we classify all cells as
prokaryotes if they do not have nuclei (bacteria, cyanobacteria, and
archaeans) or as eukaryotes if they do have nuclei (all plants, animals,
fungi, and algae).
• By the time nuclei became established, evolution had produced
thousands of species of prokaryotes.

• The newly evolved eukaryotes also diversified.

• Those with chloroplasts evolved into algae and plants; those without
evolved into protozoans, fungi, and animals.
• All organisms are classified into three large groups called domains:

• domain Bacteria, domain Archaea, and domain Eukarya; within

Eukarya are kingdom Plantae, kingdom Animalia, kingdom Myceteae
(fungi), and protists (eukaryotes that do not fit easily into the other
three eukaryotic kingdoms).
• Some protists are closely related to Plantae because some green
algae became adapted to living on land and gradually evolved into
true plants.

• As a consequence, early plants resembled those green algae, but as

more mutations occurred and natural selection eliminated less
adaptive ones, plants lost algal characteristics and gained more
features suited to surviving on land.
• Algae are so well suited to life in oceans, lakes, and streams that they
still thrive even though most features present in modern, living algae
must be more or less identical to those present in the ancestral algae
that lived more than 1 billion years ago.

• Like the algae, ferns are well-adapted to certain habitats and have not
changed much in 250 million years; they too have many relictual
features.

• Modern conifers are similar to early ones that arose about 320 million
years ago.
• The most recently evolved group consists of the flowering plants,
which originated about 100 to 120 million years ago with the
evolution of several features: flowers; broad, flat, simple leaves; and
wood that conducts water with little friction.
• The members of the aster family (sunflowers and daisies) have many
features that evolved recently from features present in ancestral
flowering plants.

• These are derived features (technically known as apomorphic

features; formerly called advanced features) (i.e., they have been
derived evolutionarily from ancestral features).

• The terms “primitive” and “advanced” are avoided in that they imply
inferior and superior.
 Diversity of Plant Adaptations

• More than 297,000 species of plants exist today.

• An unknown number of species, perhaps also several hundred

thousand, existed at one time but have become extinct.

• Virtually all of this diversity came about through evolution by natural

selection—survival of the fittest;

• The existence of 297,000 types of living plants means that there must
be at least 297,000 ways of being fit on today’s Earth.
 Algae and Global Warming

• Photosynthesis removes carbon dioxide from the atmosphere and

helps keep Earth cool enough for us to live.

• Various organisms other than plants are photosynthetic and help

reduce the amount of carbon dioxide in our air.
• Two types of bacteria, called “purple bacteria” and “green bacteria,”
have an unusual type of photosynthesis that differs from that of
plants but allows those bacteria to absorb carbon dioxide from the
environment and keep it out of the air.

• Purple bacteria and green bacteria are both rather rare, so they do
not remove very much carbon dioxide.
• Other bacteria, called “cyanobacteria,” are extremely common and
carry out a type of photosynthesis that is very similar to that of
plants.

• The total amount of cyanobacteria in the world is great enough that

they remove significant amounts of carbon dioxide from the air.

• Unfortunately, all bacteria are tiny and their bodies are rather
delicate, so they break down quickly after they die and the carbon
atoms in their bodies are converted back into carbon dioxide.
• Algae, the close relatives of plants, are a group of organisms that are
important allies in our attempts to combat global warming.

• There are many types of algae (most are named by the color of their
pigments, such as red algae, green algae, brown algae, and so on),
and all carry out photosynthesis that is almost identical to that of
plants.

• Furthermore, algae are abundant in oceans, lakes, and rivers as well

as in moist soils, rocks, and even tree bark.
• Just like plants, algae absorb carbon dioxide as they photosynthesize
and lock it into the molecules of their bodies.

• Like bacteria, many algae are so delicate they decompose quickly

after they die, so they do not keep carbon dioxide out of the air for
long.
• Microscopic algae, called coccolithophorids (or just coccoliths), make
a shell of calcium carbonate.

• This Shell is so dense that as soon as the coccoliths die, their bodies
sink to the bottom of the oceans.

• The cold temperatures there slow decay to such a degree that the
shells do not break down for thousands, even millions of years.
• Consequently, as these microscopic algae grow and then die, carbon
dioxide is removed from the atmosphere for very long times.

• One of the possibilities for combating global warming is to make

these algae grow faster and more abundantly by fertilizing the oceans
in areas where coccoliths already live.