Final Review Sheet of Important Topics
Chapter 12
Nucleotides Are the Building Blocks of DNA
- DNA is a long molecule made of subunits called nucleotides that are linked together
- Each nucleotide has three parts:
1. a phosphate group
2. a five-carbon sugar molecule
3. a nitrogen base
- The five-carbon sugar is called deoxyribose
- the sugar molecule and the phosphate group are the same for each nucleotide in a molecule of' DNA
- the nitrogen base may be one of four different kinds
1. adenine
2. guanine
3. thymine
4. cytosine
- Adenine and guanine belong to a class of organic molecules called purines
- Thymine and cytosine are pyrimidines with a single ring of carbon and nitrogen atoms.
The DNA molecule is a Double Helix
- Maurice Wilkins and Rosalind Franklin, took some X-ray diffraction photographs of the DNA molecule that
suggested DNA resembled a tightly coiled helix
- James Watson and Francis Crick, used X-ray diffraction photographs, to build a model of DNA with the
configuration of a double helix,
- the DNA double helix consist of alternating sugar and phosphate units with a purine and pyrimidine held
together by a hydrogen bonds
- a purine is always paired with a pyrimidine because adenine (A) can form hydrogen bonds only with
thymine (T), and cytosine (C) can form hydrogen bonds only with guanine (G)
How DNA Is Copied
- The process of synthesizing a new strand of DN called replication
- enzymes called helicases open up the double helix by breaking the hydrogen bonds linking the
complementary bases.
- The point at which the double helix separates is called replication fork because of its y shape
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At the replication fork enzymes known as DNA polymerases move along each DNA strand adding
nucleotides to the exposed bases following the base-pairing rules
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in eukaryotic organisms usually have many replication forks that begin in the middle and move in both
directions, creating replicating "bubbles"
Genes in Eukaryotes Are Often Interrupted
- genes are frequently interrupted by long segments of nucleotides that have no coding information called
intervening sequences, or introns
- The nucleotide segments that code for amino acids are called exons because they are expressed
The Path of Genetic Information
- an organism's traits are determined by proteins that are built according to the plans specified in its DNA.
- Proteins are not built directly from genes
- The working instructions of genes are made of molecules of ribonucleic acid, or RNA
- RNA differs from DNA in three ways
1) RNA consists of a single strand of nucleotides instead of two strands
2) RNA contains the five- carbon sugar ribose rather than deoxyribose
3) RNA has a nitrogen-containing base called uracil (U) instead of thymine that is complementary
to adenine
- RNA is present in cells in three different forms with different functions:
1) messenger RNA (mRNA)
2) ribosomal RNA (rRNA)
3) transfer RNA (tRNA)
- All three types of RNA process the information from DNA into proteins, a process called gene expression
- Gene expression occurs in two stages:
1) Transcription - the information in DNA is transferred to mRNA
2) Translation - the information in mRNA is used to make a protein
- mRNA is appropriately named because it carries hereditary information from DNA and delivers it to the site
of translation
- During translation, mRNA serves as a template for the assembly of amino acids
- tRNA acts as an interpreter molecule, translating mRNA sequences into amino acid sequences
rRNA plays a structural role in ribosomes, the organelles that function as the sites of translation
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Transcription Making RNA
- transcription, the process that "rewrites" the information in a gene in DNA into a molecule of mRNA.
- In eukaryotic organisms, transcription occurs inside the nucleus
- In prokaryotic organisms, it takes place in the cytoplasm
- Transcription begins when an enzyme called RNA polymerase binding to a gene on a region of DNA called
a promoter.
- A promoter is a specific sequence of DNA that acts as a "start" signal for transcription
- RNA polymerase binds to a promoter and starts to unwind and separate the double helix's two strands
- anscription follows the same base-pairing rules as DNA replication except that uracil, rather than thymine,
pairs with adenine
- Transcription proceeds until the RNA polymerase reaches a stop signal on the DNA called a terminator
- Messenger RNA is an RNA copy of a gene used as a blueprint for a protein
- mRNA leaves the nucleus and enters the cytoplasm.
The Genetic Code
- After transcription, the genetic material is translated to the language of proteins
- the instructions for building a protein are written as a series of three-nucleotide sequences called codons
- Each codon along the mRNA strand either corresponds to an amino acid or signifies a stop signal
Assembling the Protein
- Translation begins when mRNA binds to the smaller ribosomal subunit in the cytoplasm
- the "start" codon of mRNA signals the beginning of a protein chain
- A tRNA molecule with the complementary anticodon arrives and binds to the codon, carrying its specific
amino acid with it
- a peptide bond between the adjacent amino acids, forming the first link of the protein chain
- When a stop codon is encountered the newly made protein is released into the cell
Mutations Are Changes DNA
- A change in the DNA of a gene is called a mutation which rarely happen
- Mutations in gametes can be passed on to offspring
- Mutations are an important basis of evolution
- Some mutations alter the structure of the chromosome
- Other mutations called point mutations change one nucleotide or just a few nucleotides in a gene.
- There are two general types of point mutations
1) Substitutions - one nucleotide in a gene is replaced with a different nucleotide. For example:
UGU becomes UGC which has little or no effect because UGU and UGC code for amino acidcysteine. But, if UGU changed into UGA, the codon would become a stop codon the protein
would be shortened and incomplete.
2) insertions and deletions - one or more nucleotides are added to or deleted from a gene. insertions
and deletions change the codon and causes a gene to be read in the wrong three-nucleotide
sequence called a frame shift mutation because the reading pattern is displaced one or two
positions.
What Causes Mutations?
- Some mutations are chemical mishaps that arise spontaneously
- Other mutations are induced by exposure to environmental agents called mutagens
- Mutagens include X rays and gamma rays, ultraviolet light, and certain chemicals or carcinogens
- Carcinogens are cancer-causing agents
Chapter 15
The theory of evolution consists of the following four major points:
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1. Variation exists within the genes of every species (the result of random mutation).
2. ln a particular environment, some individuals of a species are better suited for survival and so leave more
offspring (natural selection).
- 3. Over time, change within species leads to the replacement of old species by new species as less successful
species become extinct.
- 4. Evidence from fossils and other sources indicate species now on Earth have evolved (descended) from
ancestral forms that are extinct (evolution).
Charles Darwin
- Charles Darwin was the unpaid naturalist on a naval voyage of the HMS Beagle
- On the Galapagos Islands Darwin noticed the plants and animals resemble those of the nearby coast of
South America
- Darwin referred to such change as "descent with modification" or evolution.
- Darwin called the process by which populations change in response to their environment natural selection
- The changing of a species that results in its being better suited to its environment is called adaptation
- a population is a group of individuals that belong to the same species, live in a defined area, and breed with
others in the group
- Alfred Russel Wallace also described the idea of evolution by natural selection and
- Darwin and Wallace’s jointly presented their papers at a public scientific meeting.
- Darwin in 1859 had finally finished his book On the Origin of Species by Means of Natural Selection
Natural Selection Causes Change Within Populations
- Mutations and the recombination of genes are constant sources of new variations for natural selection to act
upon.
- microevolution to refer to change that occurs within a species over time
Isolation Leads to Species Formation
- populations of the same species living in different locations tend to evolve in different directions
- The condition in which two populations of the same species are separated from one another is called
isolation.
- As isolated populations of the same species become increasingly different the populations may no longer be
able to interbreed (breed with one another)
- When two populations cannot interbreed the populations are considered to be different species.
- Extinction Leads to Species Replacement
- events such as climatic changes and natural disasters result in some species becoming extinct, which means
that they disappear permanently.
- Species. that are better suited to the new conditions may replace those that become extinct
- biologists use the term macroevolution to refer to change among species over time
- The replacement of the dinosaurs by mammals is an example of macroevolution.
Fossils Provide Record of Macroevolution
- A fossil is the preserved or mineralized remains (bone, tooth, or shell) or traces (footprint, burrow, or
imprint) of an organism that lived long ago.
- Most fossils form when organisms are rapidly buried in fine sediments deposited by water, wind, or
volcanic eruptions
- Thus, the environments that are most conducive to fossil formation are wet lowlands, slow-moving streams,
lakes, shallow seas, and areas near volcanoes that spew out volcanic ash.
Anatomy and Development Reflect Macroevolution
- similarities in body structures, even though functions may be different, are said to be homologous
- Homologous structures share a common ancestry.
Does Evolution Occur Spurts
- The model of evolution in which gradual change over a long period of time leads to species formation is
called gradualism.
- This model of evolution, in which periods of rapid change in species are separated by periods of little or no
change, is called punctuated equilibrium.
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Chapter 17
The History of Life
relative dating - the age of a fossil is determined by comparing its placement with that of fossils in other layers
of rock. The rock layers form in order by age—the oldest layers on the bottom, with more recent layers on top.
index fossils - a species must have had a wide geographic range. It will be found in only a few layers of rock,
but these specific layers will be found in different geographic locations.
Radioactive Dating - Scientists use radioactive decay to assign absolute ages to rocks. Radioactive elements
decay, or break down, into nonradioactive elements at a steady rate, which is measured in a unit called a halflife.
A half-life is the length of time required for half of the radioactive atoms in a sample to decay.
In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive
isotopes it contains.
Carbon-14, has a half-life of about 5730 years.
Carbon-14 is taken up by living things while they are alive.
After an organism dies, the carbon-14 in its body begins to decay to form nitrogen-14
Carbon-12, the most common isotope of carbon, is not radioactive and does not decay
. The more carbon-12 there is in a sample compared to carbon-14, the older the sample is.
Formation of Earth
- Earth is about 4.5 billion years old
- pieces of cosmic debris were probably attracted to one another over the course of about 100 million years
Ideas About the origin of Life
- some scientists question whether life originated on Earth
- They suggest life on Earth had an extraterrestrial origin
- They hypothesize that life was carried here by an asteroid or by a meteorite
- Organic molecules make up about 2% by weight of some meteorites
A. Divine Creation
- Because the idea that life originated through divine creation cannot be tested by scientific methods, it falls
outside the realm of science.
B. Spontaneous Origin
- They hypothesize that molecules of non-living matter reacted chemically during the first 1 billion years of
Earth's history, forming a variety of simple organic molecules
- Changes that increased the stability of certain molecules would have allowed (selected) those molecules to
persist for a longer time
The Primordial Soup Model
- In the 1920s, the Russian scientist A. I. Oparin proposed a hypothesis that Earth's oceans were once a vast
primordial soup containing large amounts of organic molecules
- Oparin envisioned these molecules forming spontaneously in chemical reactions activated by energy from
solar radiation, volcanic eruptions, and lightning
- It was proposed that Earth's early atmosphere lacked oxygen
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the early atmosphere was instead rich in nitrogen (N2) and hydrogen-containing gases such as hydrogen
(H2), water vapor (H2O), methane (CH4), and ammonia (NH3)
Electrons in these gases would have been frequently pushed to higher energy levels by photons crashing into
them from the sun or by electrical energy in lightning
In 1953, Oparin's hypothesis was tested by Stanley Miller
Miller placed the proposed gases into an apparatus and then to simulate lighting, he zapped the mixture with
electrical sparks
After a few days, Miller found a complex mixture that included some of life's basic building blocks: amino
acids, fatty acids, and hydrocarbons
These results demonstrated that some basic chemicals of life could have formed spontaneously on the early
Earth under conditions like those in the experiment
The Bubble Model
- In 1986, the geophysicist Louis Lerman suggested that bubbles produced by wind, wave action, the impact
of raindrops, and the eruption of volcanoes cover about 5 percent of the ocean's surface at any given time
- because water molecules are polar, water bubbles tend to attract other polar molecules
- chemical reactions would proceed much faster in bubbles (where reactants would be concentrated) than in
Oparin's stagnant primordial soup
- Thus, life could have originated in a much shorter period of time than it could have according to Oparin's
model
- Also, inside the water bubbles the methane and ammonia required to produce amino acids would have been
protected from destruction by ultraviolet light.
The Puzzle of Life's Origin
- organic molecules is a long way from a living cell, and the leap from nonlife to life is the greatest gap in
scientific hypotheses of Earth's early history.
- Geological evidence suggests that about 200 to 300 million years after Earth cooled enough to carry liquid
water, cells similar to modern bacteria were common. How might these cells have originated?
Formation of Microspheres
- Under certain conditions, large organic molecules can form tiny bubbles called proteinoid microspheres.
- Microspheres are not cells, but they have some characteristics of living systems.
- the basic molecules of plasma membranes-proteins and lipids-tend to aggregate (gather together) in water
- Phospholipids, which form the bilayer of a plasma membrane and short chains of amino acids produced
aggregate into tiny vesicles called microspheres
- Scientists think that microspheres might have been the first step toward cellular organization
- Once the basic molecules were present the early oceans would have contained untold numbers of
microspheres-billions in each spoonful of sea water
- Over millions of years, those micro spheres that could survive longer by more efficiently incorporating
molecules and energy would have become more common
- Like cells, they have selectively permeable membranes through which water molecules can pass.
- Microspheres also have a simple means of storing and releasing energy. Several hypotheses suggest that
structures similar to proteinoid microspheres might have acquired more and more characteristics of living
cells.
- Still, microspheres could not be considered alive unless they had acquired the capacity to transfer their
abilities to offspring
Evolution of RNA and DNA
- How did amino acids link together to form proteins and how did nucleotides join to form long chains of
DNA
- short chains of RNA, can (with difficulty) be made to form spontaneously in water
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Some scientist speculate that early life could have developed on a solid surface rather than in water
In the 1980s, Thomas Cech found that certain RNA molecules can act like enzymes
RNA's three-dimensional structure provides surfaces with specific shapes for catalyzing reactions, much as
protein shapes do
Like DNA, RNA acts as an information-storing molecule.
Cech's work and experiments demonstrating that perhaps RNA was the first self-replicating informationstorage molecule.
After it had formed, such a molecule could also have catalyzed the assembly of the first proteins
But more important, such a molecule would have been capable of evolving through natural selection.
From this relatively simple RNA-based form of life, several steps could have led to the system of DNAdirected protein synthesis that exists now
Origin of Heredity Remains a Mystery
- Most researchers suspect that RNA was the first information- storing molecule to form and that RNA
"enzymes" catalyzed the assembly of the earliest proteins
- Scientists think that double-stranded DNA probably evolved later
- But because researchers do not yet understand how DNA, RNA, and hereditary mechanisms first developed,
science is currently unable to resolve disputes concerning the origin of life
- How life might have originated naturally and spontaneously remains a subject of intense interest, research,
and discussion among scientists
Free Oxygen
- Microscopic fossils, or microfossils, of single-celled prokaryotic organisms that resemble modern bacteria
have been found in rocks more than 3.5 billion years old
- Those first life forms must have evolved in the absence of oxygen, because Earth's first atmosphere
contained very little of that highly reactive gas.
- Over time, as indicated by fossil evidence, photosynthetic bacteria became common in the shallow seas of
the Precambrian.
- By 2.2 billion years ago at the latest, these organisms were steadily churning out oxygen, an end product of
photosynthesis.
- Next, oxygen gas started accumulating in the atmosphere.
- As atmospheric oxygen concentrations rose, concentrations of methane and hydrogen sulfide began to
decrease, the ozone layer began to form, and the skies turned their present shade of blue.
- Over the course of several hundred million years, oxygen concentrations rose until they reached today's
levels.
- The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved
new, more efficient metabolic pathways that used oxygen for respiration.
- Organisms that had evolved in an oxygen-free atmosphere were forced into a few airless habitats, where
their anaerobic descendants remain today.
Origin of Eukaryotic Cells
- About 2 billion years ago, prokaryotic cells—cells without nuclei—began evolving internal cell membranes.
The result was the ancestor of all eukaryotic cells.
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The Endosymbiotic Theory
smaller prokaryotes began living inside larger cells
Over time, a symbiotic, or interdependent, relationship evolved.
According to the endosymbiotic theory, eukaryotic cells formed from a symbiosis among several different
prokaryotic organisms. One group of prokaryotes had the ability to use oxygen to generate energy-rich
molecules of ATP.
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These evolved into the mitochondria that are now in the cells of all multicellular organisms.
Other prokaryotes that carried out photosynthesis evolved into the chloroplasts of plants and algae.
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by
prokaryotic organisms.
The Evidence
1. mitochondria and chloroplasts contain DNA similar to bacterial DNA.
2. mitochondria and chloroplasts have ribosomes whose size and structure closely resemble those of
bacteria.
3. like bacteria, mitochondria and chloroplasts reproduce by binary fission when the cells containing
them divide by mitosis.
Thus, mitochondria and chloroplasts have many of the features of free-living bacteria. These similarities
provide strong evidence of a common ancestry between free-living bacteria and the organelles of living
eukaryotic cells.
Chapter 19
Prokaryotes The Oldest Organisms
- Prokaryotes bacteria are the planet's most abundant inhabitants
- metabolically different groups of bacteria evolved
1. archaebacteria
2. eubacteria
- Most archaebacteria today are methanogens, ( use H2 to reduce CO2 to methane (CH4)
- Methanogens are obligate anaerobes, organisms that are poisoned by oxygen.
- Found in swamps and marshes and in the digestive tracts of cows and other herbivores
Eubacteria - larger of the two kingdoms of prokaryotes is the eubacteria.
- Eubacteria live almost everywhere. (fresh water, salt water, on land, and on and within the human
body)
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The cell walls of eubacteria contain peptidoglycan
Archaebacteria - look very similar to eubacteria.
- They are equally small, lack nuclei, have cell walls
- Archaebacteria lack the peptidoglycan and have different membrane lipids
- the DNA sequences of key archaebacterial genes suggest archaebacteria may be the ancestors of
eukaryotes.
- Many archaebacteria live in extremely harsh environments.
o methanogens produce methane gas and live in oxygen-free environments (thick mud and the
digestive tracts of animals.
o Hlaophiles - live in extremely salty environments, 10X saltier than sea water; (Great Salt
Lake & Dead Sea)
o Thermoacidophiles – thrive in hot and acidic environments such as Yellowstone sulfur hot
springs
Identifying Prokaryotes
- Prokaryotes can be identified by their:
1. shape
2. chemical nature of their cell walls
3. the way they move
4. the way they obtain energy.
Shapes
- Rod-shaped prokaryotes are called bacilli
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- Spherical prokaryotes are called cocci
- Spiral and corkscrew-shaped prokaryotes are called spirilla
Cell Walls
- Gram-positive bacteria have thick peptidoglycan walls and retain the dark color of the violet stain
- Gram-negative bacteria have much thinner walls inside an outer lipid layer. Alcohol dissolves the
lipid and removes the dye from the walls of these bacteria making these bacteria pink or light red.
Movement
- Some prokaryotes do not move at all
- Some are propelled by flagella, whiplike structures
- Other prokaryotes lash, snake, or spiral forward.
- Others glide slowly along a layer of slimelike material they secrete.
- Metabolic Diversity
- 1. heterotrophs, meaning that they get their energy by consuming organic molecules made by other
organisms.
A. chemoheterotrophs must take in organic molecules for both energy and a supply of carbon.
Most animals, including humans, are chemoheterotrophs
B. photoheterotrophs These organisms are photosynthetic, using sunlight for energy, but they
also need to take in organic compounds as a carbon source.
- 2. autotrophs make their own food from inorganic molecules
A. photoautotrophs -use light energy to convert carbon dioxide and water to carbon
compounds and oxygen in a process similar to that used by green plants.
B. chemoautotrophs - make organic carbon molecules from carbon dioxide
they use energy directly from chemical reactions involving ammonia, hydrogen sulfide,
nitrites, sulfur, or iron. Some chemoautotrophs live deep in the darkness of the ocean
obtaining energy from hydrogen sulfide gas that flows from hydrothermal vents
Releasing Energy
- obligate aerobes - Organisms that require a constant supply of oxygen in order to live
- obligate anaerobes - must live in the absence of oxygen
- facultative anaerobes - can survive with or without oxygen
Growth and Reproduction
- Binary Fission - replicates its DNA and divides in half, producing two identical “daughter” cells
- Conjugation – exchange of genetic information, a hollow bridge forms between two bacterial
cells, and genes move from one cell to the other.
- Spore Formation When growth conditions become unfavorable, many bacteria form structures
called spores or endospore
Importance of Bacteria
Decomposers - bacteria help the ecosystem recycle nutrients, therefore maintaining equilibrium in
the environment..
Nitrogen Fixers - Nitrogen gas (N2) makes up approximately 80 percent of Earth's atmosphere
However, plants cannot use nitrogen gas directly. Nitrogen must first be changed chemically to
ammonia (NH3) or other nitrogen compounds.
Human Uses of Bacteria bacteria are used in the production of a wide variety of foods
One type of bacteria can digest petroleum, making it very helpful in cleaning up small oil spills
Some bacteria remove waste products and poisons from water
Others can even help to mine minerals from the ground.
Still others are used to synthesize drugs and chemicals through the techniques of genetic engineering.
Viruses
In 1935, the American biochemist Wendell Stanley obtained crystals of tobacco mosaic virus.
Living organisms do not crystallize, so Stanley inferred that viruses were not alive.
Viruses are particles of nucleic acid, protein, and in some cases, lipids.
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Viruses can reproduce only by infecting living cells.
They enter living cells and, once inside, use the machinery of the infected cell to produce more viruses.
Most viruses are so small they can be seen only with electron microscope.
A typical virus is composed of a core of DNA or RNA surrounded by a protein coat.
A simple viruses has only a few genes, more complex ones may have more than a hundred genes.
virus's protein coat is called its capsid.
The capsid includes proteins that enable a virus to enter a host cell.
The capsid proteins of a typical virus bind to receptors on the surface of a cell and “trick” the cell into
allowing it inside.
Once inside, the cell transcribes and translates the viral genetic information into viral capsid proteins..
Because viruses must bind precisely to proteins on the cell surface most viruses are highly specific to the cells
they infect.
Plant viruses infect plant cells; most animal viruses infect only certain related species of animals; and bacterial
viruses infect only certain types of bacteria.
Viruses that infect bacteria are called bacteriophages.
Viral Infection
Some viruses replicate themselves immediately, killing the host cell.
Other viruses replicate themselves in a way that doesn't kill the host cell immediately.
Lytic Infection
In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst.
Bacteriophage T4 has a DNA core inside an intricate protein capsid that is activated by contact with a
host cell.
It injects its DNA directly into the cell.
The host cell cannot tell the difference between its own DNA and the DNA of the virus.
the cell begins to make messenger RNA from the genes of the virus.
The virus makes thousands of copies of its own DNA molecule.
The viral DNA gets assembled into new virus particles.
Before long, the infected cell lyses, or bursts, and releases hundreds of virus particles that may go on to
infect other cells..
Lysogenic Infection
In a lysogenic infection, a virus integrates its DNA into the DNA of the host cell, and the viral
genetic information replicates along with the host cell's DNA.
Unlike lytic viruses, lysogenic viruses do not lyse the host cell right away. Instead, a lysogenic virus
remains inactive for a period of time.
The viral DNA that is embedded in the host's DNA is called a prophage.
The prophage may remain part of the DNA of the host cell for many generations before becoming
active.
Retroviruses
Some viruses contain RNA as their genetic information and are called retroviruses.
When retroviruses infect a cell, they produce a DNA copy of their RNA.
This DNA, much like a prophage, is inserted into the DNA of the host cell.
There the retroviruses may remain dormant for varying lengths of time before becoming active,
directing the production of new viruses, and causing the death of the host cell.
Retroviruses get their name from the fact that their genetic information is copied from RNA to DNA
Retroviruses are responsible for some types of cancer in animals, including humans.
The virus that causes acquired immune deficiency syndrome (AIDS) is a retrovirus.
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Viruses and Living Cells
Viruses must infect a living cell in order to grow and reproduce.
Therefore, viruses can be considered to be parasites.
A parasite depends entirely upon another living organism for its existence, harming that organism in
the process.
Are viruses alive?
If we require that living things be made up of cells and be able to live independently, then viruses are
not alive.
Yet, viruses have many of the characteristics of living things.
After infecting living cells, viruses can reproduce, regulate gene expression, and even evolve.
Viruses are at the borderline of living and nonliving things.
Examples of Endosymbiosis
- many eukaryotic cells contain other organelles thought to be descended from bacteria
- Based on the theory of endosymbiosis, chloroplasts in the cells of plants and algae are descendants of
photosynthetic prokaryotes that were incorporated into a larger host cell
- As in mitochondria that are thought to have been the result of endosymbiosis
-
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Chapter 22
Obstacles to Living on Land
- lack of a protective ozone layer prohibited invasion of terrestrial plants
- ancestors of land plants were the aquatic algae
- Before the earliest plants could thrive in terrestrial habitats, they had to overcome three things:
1. Absorbing Minerals : a symbiotic relation between fungi and the roots of plants played a key role
- plants provide the fungi with carbohydrates and the fungi absorbed phosphorus and other minerals needed
by plants.
2. Conserving Water: the development of a watertight waxy outer covering called a cuticle made
- specialized pores called stomata enabled carbon dioxide to enter a plant and permit water vapor and oxygen
gas to exit
- water enters most plants primarily through their roots and exits primarily through stomata
3. Reproducing on Land: The eggs of the first plants were surrounded by jackets of cells, and a film of water
was required for a sperm to swim to an egg and fertilize it
- In advanced plants the sperm are enclosed in multicellular structures (pollen grains) that keep them from
drying out.
Vascular System Enabled Plants to Thrive on Land
- plants evolved and developed specialized tissues: roots, stems, leaves
- xylem - hard walled cells that transport water and dissolved minerals up from the roots
- phloem - soft- walled cells that conduct carbohydrates away from the leaves and stems,
Vascular Plants Are Characterized by Severeal Features
- plant growth is produced adding new cells to the tips of their body called meristems
- Ferns are the most abundant and most familiar group of seedless vascular plants today
- the life cycles of non-vascular plants are dominated by a gametophyte generation
- The word gymnosperm refers to the fact that gymnosperm seeds do not develop within a fruit (a mature
ovary)
- gymnosperms were the first seed plants
- The flowering plants, or angiosperms evolved from gymnosperms
- Seed plants produce two kinds of gametophytes:
1. a very tiny male gametophyte, or microgametophyte, that produces sperm
2. a relatively large female gametophyte, or megagametophyte, that produces eggs
- the spores that produce the microgametophytes are called microspores
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those that produce the megagametophytes are called megaspores
A pollen grain, which consists of only a few haploid cells surrounded by a thick protective wall,
If the egg inside of an ovule is fertilized, the ovule and its contents become a seed
Wind, insects, or other animals transport pollen grains
transportation of pollen grains to a female reproductive structure of a plant of the same species is called
pollination.
- When a pollen grain reaches a female reproductive structure a pollen tube grows from the pollen grain to an
ovule and enables a sperm to pass directly to an egg
Most Living Gymnosperms are conifers
- gymnosperms are trees that produce seeds m cones and are called conifers
- The tallest living vascular plants are the giant redwoods of coastal California and Oregon,.
- the bristlecone pine are the oldest more than 5,000 years old.
What Is a Seed
- a seed is a sporophyte plant embryo surrounded by a protective coat
- The hard cover of a seed is called the seed coat, which protects the embryo and other tissues in the seed
from drying out
- seeds have enabled plants to become better adapted to living on land in at least three other respects:
1. Dispersal : Seeds enable the offspring of plants to be dispersed to new locations
- Many seeds have appendages, such as wings, that help wind, water, or animals carry them
- dispersal prevents the parent and offspring from competing with each other
2. Nourishment : Most seeds have abundant food stored in them this food supply is a source of energy for a
plant embryo as it starts its growth
3. Dormancy : a seed may lie dormant for many years When conditions are favorable, particularly when
moisture is present, the seed will begin to grow into a young plant
Angiospenns Achieved Evolutionary Success on Land
- The most successful of all plants are angiosperms, seed plants that produce flowers
- Ninety percent of all living plants are angiosperms
What Is a Flower?
- Flowers are the reproductive organs of angiosperms
- The basic structure of a flower consists of the four concentric whorls: Calyx, Corolla, Androecium,
Gynoecium
1. Calyx - the outermost whorl of a flower, The calyx consists sepals which are modified leaves and protects a
flower from physical damage while it is a bud.
2. Corolla - the second whorl of a flower The corolla consists petals, which are also modified leaves
-the corolla produces vividly colored pigments and or/ fragrances to attract pollinators
3. Androecium – is the third whorl which produces the microgametophytes, or pollen grains -The androecium
is made up of stamens which consist of thread- like filaments that are each topped by a pollen-containing
sac called an anther.
4. Gynoecium - the fourth whorl houses the ovules, in which the megagametophytes develop
-The gynoecium consists of one or more pistils that are found in the center of a flower
-Ovules develop in a pistil's swollen lower portion, which is called the ovary
- The style has a swollen, sticky tip called the stigma, on which pollen lands and adheres
- When a flower is pollinated a pollen tube emerges from each pollen grain and grows through the style and
into the ovary.
Flowering Plants Coevolved With Animals
- certain insects are attracted by particular flowers Of all insect pollinators, the most numerous are bees
- Bees locate sources of nectar by odor at first, then by homing in on a flower's color and shape
- Red flowers are typically visited by hummingbirds which have keen vision and a poor sense of smell
- Certain angiosperms pollinated by bats have large, heavily scented, and pale-colored flowers that open at
night
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