general biology 122 portfolio.doc 3

8/9/2019 General Biology 122 Portfolio.doc 3

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General Biology 122 PortfolioSemester 2

Steffie Pierre


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The Evolution of populations

Evolutionary changes confined to only a single gene pool is referred to asmicroevolution. Macroevolution on the other hand refers to evolutionary changes

above the specie level, e.g. the appearance of feathers during the evolution of birdsfrom one group of dinosaurs.

Population is defined as a localized group of individuals that are cable ofinterbreeding and producing fertile offspring. Isolation of certain population maybe

experienced, where one is cut off from the other either via a natural

processes/disaster or through human activity. When this occurs the members ofthe population generally mate with one another inside the population rather than

with other members of another population and as a result, the gene poolisnarrowed. Gene pool is defined as the aggregation of genes within a population at

any one time. A gene is defined as a section of DNA that codes for a particular

function.

Mutation and sexual recombinations produces the variation that

makes evolution possible.

y Mutation brings about the formation of new genes and alleles, through theaddition, subtraction, elimination or substitution of amino acid bases within

the DNA molecule. Only a simple change in the base of a gene can cause greatchanges in the phenotype of an individual, these changes can causes diseases

such as sickle-cell anemia, or even change the color coat of a fury animal.

y In a sexually reproducing population, sexual recombination is far moreimportant than mutation. Sexual recombination rearranged alleles that havealready been in a gene pool through out generation to give a new

combination of alleles within every generation. Mutation and sexualrecombination go hand in hand because, in order for there to be a new

arrangement of alleles there needs to be some for of change within the gene

of that specie.

y


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The Origin of Species

Speciation is at the focal point of evolution and includes the isolation of populationswithin and environment. The appearance of new species is the source of biological

diversity. As it has been noted in the reviewed chapter above that the biological speciesconcept defines specie as an individual in a population that has the ability to interbreed

with another individual and produce a fertile offspring, but are unable to produce viable,fertile offspring with other members of other populations.

There are many biological factors that keep species from reproducing, these factorsare known as barriers: there are

1. Prezygotic Barriers this is before the zygote of formed, this impedes mating

between the species or hinders the fertilization of ova if members of differentspecies attempt to mate.

2. If a sperm from a species does overcome the prezygotic barriers andfertilization does occur via mating of two different species there arePostzygotic Barriers that come into practice. Postzygotic refers to after the

zygote is formed. This most times prevents the hybrid zygote from

developing into a viable fertile offspring.

To list of few identify what the Prezygotic barriers would be:

I.H

abitat isolation T

wo species different habitats within the same area andmay encounter each other rarely.

II. Temporal isolation Species that breed during different time of the day,

different seasons and different years cannot mix their gametes.

III.Behavioral isolation Courtship rituals that attract mates and otherbehaviors unique to specie are effective reproduction barriers even betweenclosely related species.

IV.Mechanical isolation Morphological differences can prevent specie mating,

e.g. even closely related plants will have flowers with different appearances

that attract different pollinators.

V. Gametic isolation Sperm of certain specie may not be able to fertilize theegg of another specie. There are also many other mechanisms that result inthis type of isolation. Sperms may not be able to survive in the reproduction

track of females of other specie or biochemical mechanisms may prevent thesperm form penetrating the membrane surrounding the other species egg.


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Postzygotic Barriers:

I. The genes of different parent specie may interact and impair the hybrids

development. Some creatures may occasionally produce an

offspring/hybridize. But that organisms will not complete developmentand those that do are very frail.

II. Some hybrids may be vigorous but they can still be sterile. Take in

account a mule, it a cross between a donkey and a horse both mating

partners are fertile and fully developed and are closely related that theyare able to suppress prezygotic and produce and offspring, but that

individual is sterile, therefore the mule becomes in one way or another

isolated from the population.

III.Some most time in plants specie the 1stgeneration hybrids are viable andfertile but when they mate with one another or with the parent offspring

the 2nd generation is feeble or sterile.

Speciation can take place with or without geographic separation

There are two types: Allopatric and Sympatric speciation.

Allopatric (other country) speciation; the gene flow within a population isinterrupted when there is a geographically isolation, that causes that population to

be divided into subpopulations. Take into account a lake, which water has subsided

due to natural reasons, this will result in smaller lakes that then becomes home toseparated populations. Geographic barriers are only able to keep populations apart

when the members of that population are unable to cross such barriers. Animalssuch as birds mountain lions are able to cross rivers, valleys and cannons, plants

are also known to override barriers because their pollen is transported by the wind.

Sympatric (same country) speciation; this takes place in geographically

overlapping populations. The only way in which speciation can occur when the

organisms are always in contact with each other, will include chromosomal changesand nonrandom mating that reduces the gene flow.


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Prokaryote

Domains Bacteria &Archaea

Simple cells with no nucleus or membrane-bound organelles. First organisms onEarth at least 3 billion years ago

Distributed globally including many extremophiles

Nutrition autotrophs & heterotrophs

All organisms require a source of energy & carbon

y Autotrophs can obtain all their C from CO2

y Heterotrophs require at least one organic nutrient, e.g., glucose

y Phototrophs obtain their energy from the sun

y Chemotrophs obtain their energy from chemical compounds

Bacteria

STRUCTURE: Systematic / phylogenetic relationships among bacteria are based ongenetic data, but structural properties are indispensable for identifying them

Cell wall unique, peptidoglycan

Peptidoglycan structural polysaccharides (sugars) cross-linked by peptides

(chains of amino acids). Two biochemical groups of bacteria:

y Gram positive bacteria (outer peptidoglycan layer will stain)

y Gram negative bacteria (inner peptidoglycan layer will not stain)

Pili (singular: pilus) & flagella

Pili = protein filaments that attach bacteria to other cells & substrates

Some prokaryotes have flagella (singular: flagellum)

Used for locomotion. The base of a bacterial flagellum is the only known wheel innature.


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What is taxis?

Motility allows some bacteria to move towards or away from stimuli

y Phototaxis.

y Chemotaxis

y Magnetotaxis

Asexual, through binary fission

Binary fission Daughter cells are identical copies

Neither mitosis nor meiosis occurs in prokaryotes

No true sexual reproduction, since neither mitosis nor meiosis exist inprokaryotes

Horizontal transfer of genetic material

Transformation Uptake of genetic material from the environment

Transduction Transfer of genetic material between prokaryotes by viruses

Conjugation Direct transfer of genetic material from one prokaryote to another;

sex pilus connects cells and draws them together; conjugation tube forms

Surviving harsh conditions

Endospore forms inside a bacterium and then persists through inhospitable

conditions

Bacteria Impacts on other organisms, including human society

Decomposition Note Louis Pasteurs experiments

Photosynthesis Especially common in cyanobacteria

N-fixation E.g., root nodules of beans

Symbiosis

Mu

tu

alism, commensalism, parasitismBioremediation Breaking down toxic waste


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Plant Diversity 1

The ferns are a more complex group of plants than the moss.They have made a

major evolutionary advancement over the moss since the ferns have an effectivetransport system of vascular tissue. The term fern, as with the term moss, is a

common name that actually includes four formal taxons or divisions. In all cases, the

plants in this group have vascular tissue, but no seeds or flowers. We will only dealwith the most familiar division, the Pterophyta. This is the division that includes all

of the more recognisable true ferns (most commonly seen within a region).Theother three divisions have few extant genera, do not resemble the ferns and are

briefly outlined in your text.

Fern Morphology and Anatomy:

i. General morphology and growth pattern.

Almost all ferns are larger and more complex plants than mosses. Their growth pattern

is distinctly different, growing more independently and not in the typical clump growth

form of the mosses.

The dominant plant is a diploid, sporophyte plant in the ferns. As we shall see later, the

gametophyte or haploid stage is reduced to a small transitional part of the life cycle.

Ferns range in size from a few tiny forms of about 1 cm to extremely large tropical tree

ferns reaching heights of almost 30 m. Most of the ferns tend to average about 0.5 to 1

m in height, but this can be misleading because of the growth habit of the ferns. In most

ferns, the majority of the plant grows underground, with only the leaves appearingabove the surface.

If an entire plant is removed for examination, the morphology appears somewhat

distinct. The underground stem or rhizome produces small adventitious roots along its

length. Periodically, clusters of several leaves or fronds grow up from the rhizome. As

they emerge, the young fronds (fiddleheads) are tightly coiled, but as they mature, the

fiddleheads uncoil into the typical, large mature frond. During dry periods or winter, the

fronds die back but the perennial plant survives, existing on stored food in the rhizomes.

ii. Anatomy:

The anatomy of the fern is almost as complex as for any of the seed plants. The ferns

possess almost all of the cell and tissue types found in seed plants. They do not use

secondary growth to increase their thickness, but they still possess the cell types

responsible for most secondary growth in higher' plants.


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a) The frond. The frond consists of a stalk or stipe that continues up through the

expanded blade as the rachis. The stipe functions by elevating the blade to enhance

photosynthesis. The blade of the frond serves as the photosynthetic structure for the

entire plant. As we shall see later, it also frequently has a role in reproduction.

Superficially, the blade may have a flat even appearance, but more frequently, it

appears to be finely notched or dissected into a number of smaller leaflets or pinnae.Internally, the blades are very similar, regardless of the outward appearance.

In cross section, the blade is seen to be separated into three distinct regions, the

epidermis, the cortex or mesophyll and the veins or vascular bundles. Each of these

regions is composed of one or more tissue and cell types.

The epidermis is a single cell layer made ofepidermal tissue and epidermal cells. These

cells, particularly on the lower surface of the blade, may be modified into specialized

guard cells. The unmodified epidermal cells secrete a waxy cuticle on the outer surface.

This is to prevent or minimize transpiration. The upper frond surface usually has a

thicker cuticle than the lower surface since there is less transpirational pressure on the

lower surface, due to shading. The guard cells function to reduce the water loss from

the interior of the frond and yet permit the required CO2 entry for photosynthesis. If

there is sufficient moisture in the frond and in the atmosphere to allow the guard cells

to remain turgid, the space between them will remain open and gas exchange will freely


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occur between the inner frond atmosphere and the outside atmosphere. If however,

there is too much transpiration, the guard cells will loss their turgidity quickly and thus

close the space between the cells. This greatly reduces the gas exchange (water vapour,

O2 and CO2). The entire complex of the paired guard cells, the space between the cells,

and a small space just inside the frond at the site of the guard cells is termed a stoma

(pl. stomata).

The mesophyll consists of a single tissue type, fundamental, and a single cell type,

parenchyma (parenchyma cells with chloroplasts are sometimes termed chlorenchyma).

These cells are the sites of the photosynthesis. They are usually loosely arranged with

ample air space between each cell, but there may be at compact layer of cells at the

upper surface, and several loose layers between this and the lower epidermis. If there is

a distinction between the two layers, the upper layer is termed the palisade mesophyll

and the lower layers the spongy mesophyll.

The vascular bundle is the most complex region of the fronds. The tissues and cells

found in this region are, at least from a vegetative perspective, the most important

evolutionary advancement of the ferns over the mosses. This is the region responsible

for the transport of minerals and water from the underground portions of the plants to

the photosynthetic tissue. The vascular tissue also transports the major product of

photosynthesis, glucose, from the fronds to the rest of the plant. This region has

permitted the plants to grow much larger and to exploit a far greater portion of their

environment.

The vascular bundles are made ofvascular tissue but unlike the other two regions, this

tissue is further separated into two sub-tissue types, xylem and phloem. The cells of

these sub-tissues are localized into groups where the phloem usually forms a ringaround the xylem.


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Fern Reproduction:

Ferns are capable of both sexual and asexual reproduction, but sexual reproduction is

far more prevalent and effective than asexual reproduction.

Asexual reproduction in the ferns is sometimes referred to simply as premonition. As

the rhizomes grow and branch underground, they periodically send up clusters of

fronds. If the rhizomes should subsequently break or somehow be separated between

two such clusters, the effect would be to have produced two individuals. This type of

reproduction is more prevalent with ferns growing in drier conditions.

As with the mosses, the sexual reproduction is intimately associated with the life cycle

of the plants. The first major difference between the mosses and the ferns is that the

dominant generation in the life cycle of the ferns is the sporophyte generation. To

complete a life cycle, the mature diploid fern sporophyte plants must produce haploid

spores. In most instances, the spores are produced on the underside of the fronds. The


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haploid spores (meiospores) are produced in sporangia which in turn are grouped into

clusters termed sori (sing.-sorus). The position of the sori varies, but in all instances they

are on the underside of the fronds. A few ferns produce fronds which have no function

other than to produce spores. These fertile fronds are produced later in the growing

season and arise from the centre of the cluster of vegetative fronds.

The sori produced on the vegetative fronds may have a protective flap of tissue covering

them while the spores are maturing. This flap or indusium is to prevent excess water

loss. It folds out of the way once the spores are mature and covered with a water proof

coat. The sporangia consist of a short stalk, a jacket of cells and an inner core of

sporogenous tissue. The jacket, besides being covered with thin-walled transparent

cells, has a band of thick-walled cells, the annulus, extending almost completely around

the periphery. At the end of the annulus are several thin walled lip cells. The

sporogenous tissue contains sporocytes (spore mother cells) which divide by meiosis to

produce morphologically identical meiospores. Since all spores are the same size and

shape, the ferns are termed homosporous.

Sori

The mature spores are ejected from the sporangium when the annulus expands

suddenly, tearing the jacket at the lip cells. The spores are flung out from under the

fronds to be picked up by wind currents and dispersed. Although tremendous numbers

of spores are produced by each fern, the requirements for damp shaded environments

greatly limit the number of spores that actually survive and produce gametophyte

plants.

Upon germination, the spores produce a delicate, tiny, haploid gametophyte

generation. The plant of this generation, termed a prothallus, is independent of the

sporophyte plant. The prothallus is usually heart-shaped and except in the centre, is

only 1 to 2 cells thick. It produces thread-like rhizoids that penetrate into the substrate.


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The majority of the cells are photosynthetic and there is no vascular tissue, no

epidermis, no cuticle and no stomata. The delicate nature of the prothallus makes it

extremely susceptible to desiccation and one of the weakest links in the life cycle of the

ferns. Most fern gametophytes are monoecious and produce male gametangia

(antheridia) and female gametangia (archegonia) on the same plant about 40 days after

germination. The archegonia are produced near the notch of the prothallus. The venteris imbedded in the gametophyte tissue while the 4 rows ofneck cells extended below

the prothallus. A single egg cell is produced in each archegonium, The antheridia are

scattered over the underside of the prothallus. Three jacket cells surround the sperm

producing cells. The actual sperm cells are multiflagellate. Hormonal control of the

timing of gamete maturation prevents both egg and sperm cells on the same prothallus

from maturing at the same time, thus favouring cross-fertilization.


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SEEDED PLANTS

Morphology and Anatomy ofFlowering Plants:

To deal with all the vegetative diversity of the angiosperms would be far more than this

course warrants. All of the unique features that allow different plants to exist in some of

the more diverse or difficult environments will be omitted. Instead, we will examine

some of the more universal features, which provide the base of the angiosperm

structure.

Each plant is made up of four separate organs, three of which are found in all vascular

plants, the roots, stems and leaves. The fourth organ, the flower, is unique to this group

and will be discussed with the section on reproduction.

Before beginning this section, one further separation of the angiosperms must be made.

The flowering plants or Division Magnoliophyta is further divided into class

Magnoliopsida (Dicotyledonae) commonly referred to as "Dicots", and class Liliopsida

(Monocotyledonae) commonly referred to as "Monocots". The dicots are represented

by: the majority of the woody angiosperms such as the oak, apple, elm and cherry trees;

the shrubs such as the lilac, spirea and dogwood; and the herbaceous plants such as

potato, dandelion, and daisy. The monocots are made up of such plants as the lilies,

orchids, bamboo, corn, grasses and reeds. While there are few absolute characteristics

to separate these two classes, the majority fit into the following table.

Comparison of Dicot and Monocot Characteristics

Dicotyledons Monocotyledons

2 seed leaves (cotyledons) 1 seed leaf

flower parts in 4's or 5's flower parts in 3's

vascular bundle in stem in a ring vascular bundle scattered

secondary growth present secondary growth absent

taproot system fibrous root system

net leaf venation parallel leaf venationleaf usually with petiole leaf with sheath


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Anatomy:

The vegetative anatomy of the flowering plants, allowing for some variation, is

remarkably consistent form one plant to another. The cell and tissue types are almost

identical to the ferns. These are outside protoderm, bulk ground meristem and the

area that will develop into vascular tissue, the procambium. These embryonic tissues orprimary meristems will in turn differentiate into three basic tissue systems. These tissue

systems are, outer or dermal system, the vascular tissue system and the remainder of

the plant or the ground (fundamental) tissue system. Each of the plant organs has

these tissue systems arranged in a particular fashion and comprised of a particular

group of cells. The cells and the arrangement depend on the different functions of the

organs to the plant as a whole.

a) The leaf:

The epidermis is similar to that of the ferns. The tissue that makes it up is epidermal and

the cell type is also termed epidermal. The same modifications of cuticle and guard cells

exist for the same reasons.

The mesophyll, made offundamental tissue and chlorenchyma cells, is usually more

frequently organized into distinct palisade and spongy layers than is found in the ferns.

The vascular bundles are similar to those of the ferns, but three new cell types appear in

the vascular tissue of the flowering plants. In the ferns, the xylem was made of

conducting elements called tracheids, while in the flowering plants there is also another


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type of conducting unit termed the vessel. Vessels begin their development in a similar

fashion to the tracheids, but at maturity, they lose their end walls. This forms a

continuous tube so the water and minerals do not have to travel in a zig-zag fashion but

rather can travel straight through the leaf. These tubes of vessels are continuous with

the vessels in the stems and roots and provide a more rapid and efficient route of

transport.

The phloem of the flowering plants is organized in a similar fashion to the vessels of the

xylem. Instead of sieve cells, the phloem contains sieve tube elements or cells. The

difference between these and the sieve cells is again because of the perforation of the

end walls and not a solid end plate with sieve units on the lateral walls. The sieve tubes

are anucleate at maturity but they still contain a living functional cytoplasm. The control

of the activity of this cytoplasm is brought about by a group of connected adjacent cells

termed companion cells. These tiny, elongate cells direct the sieve tube activity through

plasmodesmatal connections. The flowering plants do not have the sieve cells. Vascular

bundles of the leaves are usually surrounded by a special, single cell layer termed a

bundle sheath. The parenchyma cells of this sheath are responsible for transferring

large amounts of glucose that has been produced in the leaf mesophyll, to the phloem.

b) The stem:

The dicotyledons present one anatomical pattern while the other is found in the

monocotyledons. The monocotyledons stems have only three regions, an epidermis,

cortex and vascular bundles scattered throughout the cortex. The dicots have four

regions. The epidermis, cortex, a ring of vascular bundles and a central pith.

The epidermis is different from that of the ferns since it now must protect the stemfrom the hazards of an above ground environment. Also, the stems of these plant are

frequently photosynthetic so guard cells are also required.

The cortex varies according to the plants and the environment. Plants in drier regions

often have many sclerenchyma cells in their cortex, while those of more moderate areas

have parenchyme (chlorenchyma) and collenchyma. Collenchyma cells are living,

strengthening cells which have increased cellulose fibres in the walls. These cells are

usually found at the outer surface of the stems, frequently in the corners.

The pattern of organization of the vascular bundles of the dicots is a ring. The vascular

tissue is again subdivided into xylem and phloem and these two subtissues have the

same cell types as in the leaves of the flowering plants. The xylem of the vascular

bundles always is located on the inside of the phloem, but the phloem never rings the

xylem as in the fern rhizome vascular bundles. The scattered bundles of the vascular

tissue of the monocots has proportionately more vessels than that of the dicots.


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Dicot Stem


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Monocot stem

The pith, found only in the dicots, comprises the central region of the stem and ismade up ofparenchyma cells. These cells, rich in leucoplasts, are adapted to

store the products of photosynthesis and water.

c) The roots. Roots have the least cell and tissue differentiation of all the organs.They function in absorption, storage, transport and anchoring. The absorptionproperties are found only in the extreme tips of the roots and root branches. Afterapproximately 10 - 20mm from the tip, the root tissues mature and water andminerals can no longer be absorbed. The root epidermis develops a cuticle toprevent loss of the water already absorbed and to reduce the affect of harmfulsoil organisms.

At the extreme tip of the roots is a layer or cap of constantly replaced dead cells.

This root cap protects the root as it grows through the soils in search of sufficientwater and minerals. Behind the root cap is a zone where water is absorbed. Tofacilitate this process, many of the epidermal cells in this region developprojections out from their outer walls termed root hairs. The root hairs are lostafter the area of absorbtion in replaced by more mature tissues. The outer regionof the roots is again the epidermis

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