Ch.22 Gas Exchange

HOW ARE GILLS RELATED TO GAS EXCHANGE IN AQUATIC ENVIRONMENTS?
Gills are adapted for gas exchange in aquatic environments. In a fish, gas exchange is enhanced by ventilation of the gills (moving water past the gills), and countercurrent flow of water and blood. Cold water holds more oxygen than warm water. Fresh water holds more oxygen than salt water. And turbulent water holds more oxygen than still water. Therefore, fish go to whichever that is the easiest for them to breath in the oxygen.

WHAT ARE TETRAPODS?
Tetrapods seem to have evolved in shallow water. This is because fossil fish with legs had lungs and gills. Legs may have helped them lift up to gulp air. The fossil fish illustrates these air-breathing adaptations. The first tetrapods on land diverged into three major lineages. Amphibians use small lungs and their body surfaces. Nonbird reptiles have lower metabolic rates and simpler lungs. Birds and mammals have higher metabolic rates and more complex lungs.

WHAT IS ALVEOLI?
Alveoli are well adapted for gas exchange. High surface area of capillaries and high surface are of alveoli. In alveoli, oxygen diffuses into the blood, and carbon dioxide diffuses out of the blood. Basically, It is the place in the body where carbon dioxide and oxygen change places in the lungs. It is the place in the body where carbon dioxide and oxygen changes in the lungs.

SUMMARY:
The process of gas exchange is the interchange of oxygen and carbon dioxide between an organism and its environment. Three phases of gas exchange are breathing, transporting of oxygen and carbon dioxide in blood, and body tissues take up oxygen and release carbon dioxide. Cellular respiration requires a continuous supply of oxygen and the disposal of carbon dioxide. Respiratory surfaces must be thing and moist for diffusion of O2 and CO2.  Compared to water, using air to breathe has two big advantages; air contains higher concentrations of O2. And air is lighter and easier to move. For humans to breathe, from the nasal cavity air next passes to the pharynx, past the vocal cords, into the trachea, into the paired bronchi, into bronchioles, and finally to the avaoli. Smoking is very bad for lungs and the respiratory system. It can cause lung cancer, heart disease, and emphysema. Breathing is the alternate inhalation and exhalation of air. Inhalation occurs when the rib cage expands, or when the diaphragm moves downward. Exhalation occurs when the rib cage contracts, or when the diaphragm moves upward. Not all air is expelled during exhalation. One-way flow of air in birds reduces dead air and increases their ability to obtain oxygen. Breathing is usually under automatic control. The heart pumps blood to two regions, the right side pumps oxygen poor blood to the lungs, and the left side pumps oxygen rich blood to the body. In the lungs, blood picks up O2 and drops off CO2. In the body tissues, blood drops off O2 and picks up CO2. Most CO2 in the blood is transported as bicarbonate ions in the plasma. In the placenta, capillaries of maternal blood and fetal blood run next to each other. Fetal hemoglobin attracts O2 more strongly than adult hemoglobin. Thus, fetal blood takes oxygen from maternal blood. At birth, CO2 in fetal blood increases. Breathing control centers initiate breathing.

KEY TERMS:
- Gills: specialized body parts that promote gas exchange in fish and amphibians
- Tracheal systems: specialized body parts that promote gas exchange in arthropods
- Lungs: in tetrapods that live on land such as amphibians, reptiles, birds, and mammals
- Trachea: held open by cartilage rings
- Alveoli: grapelike clusters of air sacs, where gas exchange occurs
- Mucus: protection of lungs, which can be damaged by smoking
- Breathing control centers: in the brain sense and respond to CO2 levels in the blood
- Hemoglobin: transports oxygen, buffers blood, and transports CO2
- Human fetus: instead of breathing with lungs, exchanges gases with maternal blood in the placenta
- Placenta: an organ attached to the lining of your womb during pregnancy

This diagram shows where the blood from comes from, and goes to. Right Heart receives blood from the body and pumps it through artery to the lungs where it picks up oxygen. •Left Heart receives oxygen-rich blood from the lungs and pumps it through the aorta to the body.

http://www.youtube.com/watch?v=bwXvqSqAgKc

This video talks briefly about the respiratory system.


5 Facts:
1) Animals exchange O2 and CO2 across moist body surfaces.
2) In the human respiratory system, branching tubes convey air to lungs located in the chest cavity.
3) Without healthy cilia, smokers must cough to clear dirty mucus from the trachea.
4) Negative pressure breathing ventilates our lungs.
5) A drop in blood pH increases the rate and depth of breathing.

Ch.21 Nutrition and Digestion

WHAT IS ACID PEPSINOGEN AND HCl?

Stomach stores food and breaks it down with acid and enzymes. In this case, Acid is pH 2, and parietal cells secrete hydrogen and chloride ions, which combine to make HCl. Acid kills bacteria in food and breaks apart cells in food. Pepsinogen and HCl produce pepsin. Pepsin production activates more pepsinogen production, which is a positive feedback for digestion. Pepsin begins the chemical digestion of proteins. Acidic gastric juices mix with food to produce acid chyme.

WHAT ARE THE FUNCTIONS OF THE LIVER?

The liver performs many functions. One of the main function of liver is processing nutrient laden blood from the intestines. Blood from the digestive tract drains to the liver. Also other functions are glucose in blood is converted to glycogen and stored in the liver. Liver synthesizes many proteins including blood clotting proteins and lipoproteins that transport fats and cholesterol. Liver also changes toxins to less toxic forms and it produces bile.

WHAT IS THE HUMAN HEALTH PROBLEM OF OBESITY?

Obesity may reflect our evolutionary past. Overnourishment is consuming more food energy than is needed. World health organization recognizes obesity as a major global health problem. Of all the people in the United States, 30% are obese, 35% are overweight, and 155 of children and adolescents are overweight. Obesity leads to diabetes, cancer, and cardiovascular disease.

SUMMARY:

Most animals are herbivores, carnivores, or omnivores. Animals obtain and ingest their food in different ways, suspension feeding, substance feeding, fluid feeding, or bulk feeding. And food is processed ingestion first, digestion second, absorption third, and elimination last. Sponges digest food in vacuoles, while most animals digest food in compartments. Cnidarians and flatworms have a gastrovascular cavity with a single opening, the mouth. Teeth break up food, saliva moistens it, and tongue tastes, shapes the bolus of food, and moves it toward the pharynx. The Heimlich maneuver can dislodge food from the pharynx or trachea during choking. Brain damage will occur within minutes if no airway is open. Nutrients pass across the epithelium and into blood. Blood flows to the liver where nutrients are processed and stored. Blood from the digestive tract drains to the liver. The length of the digestive tract often correlates with diet. For example herbivores and omnivores have relatively longer digestive tracts than carnivores. Many hervivores have specializations of the intestine that promote the growth of cellulose.

Nutrients are oxidized inside cells to make ATP. ATP is the main energy currency in a cell. Excess energy can be stored as glycogen or fat. The eight essential amino acids can obrained from animal protein, and the proper combination of plant foods. The essential proteins are the ones that animals cannot produce. Food labels indicate serving size, calories per serving, amounts of selected nutrients per serving and as a percentage of daily value, and recommendations for daily limits of selected nutrients.

KEY TERMS:

- Herbivores: plant eaters

- Carnivores: meat eaters

- Omnivores: eating both plants and other animals

- Pyloric sphincter: regulates the passage of food from the stomach to the small intestine

- Diarrhea: occurs when too little water is reclaimed

- Constipation: occurs when too much water is reclaimed

- Colon bacteria: production of biotin, vitamin K, B vitamins

- Appendix: located near the small intestine and colon and makes a minor contribution to immunity

- BMR: the energy a resting animal requires each day

- Metabolic rate: the BMR plus the energy needed for physical activity

Valine is needed for muscle metabolism, tissue repair, and for the maintenance of proper nitrogen balance in the body. Valine is found in high concentration in the muscle tissue. It can be used as an energy source by muscle tissue. It may be helpful in treating livere and gallbladder disorders, and it is good for correcting the type of severe amino acid deficiencies that can be caused by drug addiction. Dietary sources of valine include dairy products, grain, meat, mushrooms, peanuts, and soy proteins.

5 FACTS:

1) Mechanical digestion breaks food down into smaller pieces.

2) Chemical digestion breaks down large organic molecules into their components.

3) Most animals have an alimentary canal with mouth, anus, and specialized regions.

4) Enzymes from cells of the intestine continue digestion.

5) Small intestine is the major organ of chemical digestion and nutrient absorption.

Ch.20 Unifying Concepts of Animal Structure and Function

WHAT ARE THE ORGAN SYSTEMS AND FUNCTIONS OF THEM?

-Endocrine system controls body functions

-Skeletal and muscular systems support and move the body

-Circulatory system transports the food and oxygen

-Respiratory system absorbs oxygen and releases carbon dioxide

-Integumentary system covers and protects the body

-Excretory system disposes of certain wastes

-Lymphatic and immune systems protect the body from infection and cancer

-Reproductive system perpetuates the species

-Digestive system absorbs food

-Nervous system controls body functions

WHAT ARE THE FUNCTIONS OF SKIN?

The main function of the integumentary system is protection of the body. Epidermis, which is the outer layer that lines on the surface resists damage, decreases water loss, and prevents penetration by microbes. Dermis, which is the inner layer of the skin is sensory information, synthesis of vitamin D, and temperature regulation.

HOW DO HUMANS PROMOTE HOMEOSTASIS?

Homeostasis is an internal steady state. Humans promote homeostasis by adding clothing when we are cold, dehydrated, eating when our calories are running low, and urinating when our bladders are full. Negative feedback mechanisms permit only small fluctuations around set points.

SUMMARY:

Animals have four main categories of tissues, epithelial, connective, muscle, and nervous tissue. Epithelial cells come in three shapes, which are squamous like a fried egg, cuboidal, as tall as they are wide, and columnar, taller than they are wide. Stratified epithelial cells are stacked on top of each other. Connective tissue can be grouped into six major types. Skeletal musclecauses voluntary movements, cardiac muscle pumps blood, and smooth muscle moves walls of internal organs, such as the intestines. Supporting cells insulate axons and nourish neurons. Each tissue performs specific functions. The heart has epithelial, connective, and nervous tissues. An organ system usually consists of many organs.

New imagin technology reveals the inner body. New technologies show body organs without surgery. X-rays help to see bones and teeth. Magnetic resonance microscopy (MRM) provides three-dimensional images of very small structures. PET helps indentifying metabolic processes at specific body locations. The skin consists of two layers, epidermis on the surface and dermis inside. Animals must exchange materials with the environment. Respiratory system exchanges gases. Digestive system acquires food and eliminates wastes. Excretory system eliminates metabolic waste. adaptations that increase surface area promote exchanges with the environment.

KEY TERMS:

- Anatomy: structure

- Physiology: function

- Neurons: carry signals by conducting electrical impulses

- Endocrine system: control of body functions

- Skeletal/muscular system: support and move the body

- Circulatory system: transportation of the food and oxygen

- Respiratory system: absorption of oxygen and release carbon dioxide

- Integumentary system: cover and protection of the body

- Excretory system: dispose of certain wastes

- Lymphatic and immune system: protection of the body from infection and cancer

The skin has three layers—the epidermis, dermis, and fat layer (also called the subcutaneous layer). Each layer performs specific tasks.

https://www.youtube.com/watch?v=kyxKDYUF-RM&feature=player_embedded

5 FACTS:

1) Epithelial tissue covers the body and lines its organs and cavities.

2) Connective tissue binds and supports other tissues.

3) Bioengineers are learning to produce tissues and organs for transplants.

4) Organ systems work together to perform life’s functions.

5) Each organ system has one or more functions. 

 

Ch.19 The Evolution of Vertebrate Diversity

WHAT ARE CHONDRICHTHYANS?

Sharks and rays have a flexible skeleton made of cartilage

Most sharks are fast-swimming predators, with sharp vision and a keen sense of smell

Electrosensors on their heads and a lateral line system aid them in locating prey

Most rays are adapted for life on the bottom, with dorsoventrally flattened bodies and eyes on the top of their heads

WHAT ARE THE FEATURES OF BIRDS FROM REPTILES?

Birds are reptiles with feathered wings, endothermic metabolism, and a number of adaptations for flight

–Loss of teeth

–Tail supported by only a few small vertebrae

–Feathers with hollow shafts

–Strong but light honeycombed bones

Flight is very costly, and birds are endotherms with a high rate of metabolism

Birds have relatively large brains and display complex behaviors

WHAT FOUR GROUPS OF APES DO HOMINOIDS INCLUDE?

Orangutans are shy and solitary and live in rainforest trees and the forest floor. Gorillas are the largest of the apes and are fully terrestrial. Chimpanzees make and use tools. Humans and chimpanzees diverged from a common ancestor between 5 and 7 million years ago. They share 99% of their genes. The other group is human.

SUMMARY:

Jawed vertebrates with gills and paired fins include sharks, ray finned fishes, and lobe finned fishes. The three lineages of jawed fishes are class chondrichthyes includes sharks and rays, ray-finned fishes and lobe-finshave lungs or lung derivatives, and lobe-finned fishes have muscular fins supported by stout bones. Ray finned fishes have internal skeleton reinforced with a hard matrix of CaPO3, flattened scales covered with mucus, operculum to move water over the gills, and buoyant swim bladder. Lobe fins have muscular pelvic and pectoral fins, supported by rod shaped bones. New fossil discoveries are filling in the gaps of tetrapod evolution. Amphibians include frogs, salamanders and caecilians. Reptiles and mammals are amniotes. The major derived character of this clade is an amniotic egg with an amnion, a private pond in which the embryo develops. Living birds evolved from a lineage of birds that survived the Cretaceous extinctions. Mammalians generally have larger relative brain size than other vertebrates and a relatively long period of parental care. Humans have the biggest brain among all the living things. There are three main types of mammals; eutherians, marsupials, and monotremes. The human story begins with our primate heritage from monkeys. Apes have relatively large brain size and flexible behavior. Gorillas, chimpanzees, and humans have a high degree of social organization. The oldest possible hominid yet discovered, Sakelanthropus tchadensis, lived about 7 to 6 million years ago. The fossil record suggests that hominid diversity increased dramatically between 4 to 2 million years ago.

KEY TERMS:

- tetrapods; jawed vertebrates with limbs and feet

- Amphibians: the first tetrapods able to move on land

- Birds: evolved from a lineage of small, two-legged dinosaurs called theropods

- Mammals: endothermic amniotes with hair, which insulates their bodies and mammary glands, which produce milk

- Monotremes: egg-laying mammals

- Placenta: structure that allows nutrients from the mother’s blood to diffuse into the embryo’s blood

- Marsupials: their offspring complete development attached to the mother’s nipples, usually inside a pouch or marsupium

- Tarsiers: second group of primates

- Anthropoid; group that includes monkeys, apes, and humans

- Gibbons: the only fully arboreal apes

A Homo Sapiens is one of a group of subspecies of Modern Humans, including human beings. The name of Homo Sapiens is wise, or wise man. They are bipedal (walking on two legs) Their backs are straight, not bent (Standing like this may have made tool carrying and tool-use easier.) They have a highly developed brain, which allows for language use

 

 

5 FACTS:

1)    A phylogenetic tree for chordates is based on a sequence of derived chracters.

2)    Birds are feathered reptiles with adaptations for flight.

3)    Mammals are amniotes that have hair and produce milk.

4)    The hominid branch of the primate tree is only a few million years old.

5)    Larger brains mark the evolution of HOMO.

Ch. 16 The Origin and Evolution of Microbial Life: Prokaryotes and Protists

WHAT MAKES THE DIVERSITY OF PROKARYOTES?
Complex eukaryotic cell evolved when prokaryotes took up residence within larger prokaryotes. Protists are the most nutritionally diverse of all eukaryotes. Some of them are photoautotrophs, containing chloroplasts. Some are heterotrophs, absorbing organic molecules or ingesting larger food particles. Still others, called mixotrophs, combine photosynthesis and heterotrophic nutrition. Protists also can be divided by habitats.

WHAT ARE THE DIFFERENCES BETWEEN BACTERIA AND ARCHAEA?

Archaea: cell membrane contains ether linkages; cell wall lacks peptidoglycan; genes and enzymes behave more like Eukaryotes; have three RNA polymerases like eukaryotes; and extremophiles

Bacteria: cell membrane contains ester bonds; cell wall made of peptidoglycan; have only one RNA polymerase; react to antibiotics in a different way than archea do.

WHAT MAKES THE PROTISTS ANCESTOR OF EUKARYOTES?

Kingdom protista consists of the single-celled eukaryotes as well as a variety of not very morphologically complex multicellular eukaryotes. All protists are eukaryotes, but protists are so diverse that few other general characteristics can be cited without exception. In fact, protists vary in structure and function more than any other group of organisms at the cellular level, many protists are exceedingly complex the most elaborate of all cells. We should expect this of organisms that must carry out within the boundaries of a single cell all the basic functions performed by the collective of specialized cells that makes up the bodies of plants and animals.

SUMMARY:
Prokaryotes have lived way longer than eukaryotes. They live in cold, hot, salty, acidic, and alkaline habitats. Although some bacteria are pathogenic and cause disease,  most on our bodies are benign or beneficial. There are two prokaryotic domains, bacteria and archaea, diverged soon after life on Earth arose. Prokaryotic cell walls maintain cell shape, provide physical protection, and prevent the cell from bursting in a hypotonic environment. Some prokaryotes stick to the substrate or each other with pili.P Prokaryotic DNA forms a circular chromosome. Smaller rings of DNA called plasmids carry genes that may provide resistance to antibiotics or metabolize rare nutrients, among other metabolic activities Many prokaryotes can transfer genes, such as antibiotic resistance genes, within or between species.Pathogenic bacteria cause disease by producing poisonous exotoxins or endotoxins. Endotoxins produce septic shock, bacterial meningitis, and food poisoning.
Protists constitute several kingdoms within the domain eukarya. They obtain their nutrition in a variety of ways: algae are autotrophic protists. Protozoans are heterotrophic, eating bacteria and other protists. Fungus-like protists obtain organic molecules by absorption. Protists are eukaryotes, with membrane-bound chromosomes, multiple chromosomes, and flagella or cilia with 9+2 pattern of microtubules. Euglenozoans are diverse clade of protists. their common feature is a crystalline rod of unknown function inside their flagella. Amoebas move and feed by pseudopodia. Members of the clade amoebozoans include many free-living amoebas, soma parasitic amoebas, and slime molds. Foraminiferans and radiolarians move and feed by means of threadlike pseudopodia. Red algae are typically soft bodied, but some have cell walls encrusted with hard, chalky deposits. Green algae split into two groups, the chlorophytes and the charophytes.

KEY TERMS:
- Exotoxins: proteins secreted by bacterial cells
- Endotoxins: components of the outer membrane of gram-negative bacteria, released when the cell dies or is digested by a defensive cell
- Symbiosis: close association between organisms of two or more species
- Diplomonads: possibly the most ancient surviving lineage of eukaryotes
- Parabasalids: heterotrophic protists with modified mitochondria that generate some energy anaerobically
- Alvelates: have membrane-enclosed sacs or alveoli beneath the plasma membrane
- Dinoflagellates: important members of marine and fresh water phytoplankton
- Ciliates: use cilia to provide moments and feed
- Apicomplexans: animal parasites such as plasmodium, which causes malaria
- Foraminiferan: live in marine and freshwater. They have porous tests with small pores through which pseudopodia extend

 Ciliates (csillósok)

-covered with cilia, move by beating cilia

-have 2 kinds of nuclei:  macronucleus to control cell life functions and micronucleus (1 or more) for reproduction

eg.  Paramecium (papucsállatka)

http://www.youtube.com/watch?v=gblKiwlPp3c

5 FACTS:

1) Prokaryotes are diverse and widespread

2) Prokaryotes are origin of eukaryotes

3) Various structural features contribute to the success of prokaryotes

4) Diplomonads and parabasalids have modified mitochondria

5) Amoebozoans have lobe-shaped pseudopodia

Ch.15 Tracing Evolutionary History

WHAT ARE THE DIFFERENCES BETWEEN NATURAL SELECTION AND EVOLUTION?
Evolution is a gradual process in which something changes into a different and usually more complex or better form whereas natural selection is the process in nature by which, according to Darwin's theory of evolution, only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated.

HOW DOES EVOLUTION OCCUR?
Evolution is the change in frequency of the alleles in a gene pool over time. Evolution occurs with mutations and natural selections. WHat happens is that in a population of species, not all of them are the same. For example, there is a whole colony of fish. Some of the fish are faster than the others. They reproduce and pass on their genes which make their offspring fast as well. The other fish that aren't as fast, die out because they are not fast enough. The fast fish soon become more common, making the species as a whole faster. This occurs in several stages, where the slowest fish are removed each time, and the faster ones reproduce more often. The second aspect is that these fish will often have differences in their genetic codes, called mutations. While bad mutations will normally result in fatality and not get passed on, some are useful and result in increased survival. When these mutations build up, the species we previously had may then become completely different from what is here now. The two groups cannot cross breed, and have become different species.

WHAT TYPE OF EVOLUTIONARY EVENT HAS OCCURRED?
Natural selection and a genetic bottleneck. The DDT resistance is a classic example of natural selection, only the most resistant organisms surviving the treatment and establishing a new, resistant population. The near disappearance of the mosquito population for several years with the new population showing reduced fertility is characteristic of a genetic bottleneck. Only a very small number survived and the genetic diversity in the population is greatly reduced. The survivors are forced to undergo massive inbreeding and reduced fertility is quite common.


SUMMARY:
A recipe for life is raw materials, suitable environment, and energy sources. The conditions on early Earth made the origin of life possible. The chemical and physical conditions made abiotic synthesis of monomers (1st stage), formation of polymers (2nd stage), packaging of polymers into protobionts (3rd stage), and self-replication (4th stage.) In 1953, Stanley Miller tested the Oparin-Haldane hypothesis. He set up an airtight apparatus with gases circulating past an electrical discharge, to stimulate conditions on the early Earth. An alternative hypothesis states that submerged volcanoes and deep-sea hydrothermal vents may have provided the chemical resources for the first life. Cells and protobionts share four characteristics: structural organization, simple reproduction, simple metabolism, and simple homeostasis. The eukaryotic cell probably originated as a community of prokaryotes, when small prokaryotes capable of aerobic respiration or photosynthesis began living in larger cells. Oldest fossils of eukaryotes are about 2 billion years old. Sliding plates are earthquake zones. Also colliding plates form mountains. Those are geologic processes occur at plate boundaries. The supercontinent pangaea altered habitats and triggered the greatest mass extinction in Earth's history. Extinction is the fate of all species and most lineages. The history of life reflects a steady background extinction rate with episodes of mass extinction. Types of extinctions are classified by how shallow/deep water the species lived in. For example, permian extinction, cretaceous extinction.
Human development is paedomorphic, retaining juvenile traits into adulthood. In the evolution of an eye or any other complex structure, behavior, or biochemical pathway, each step must bring a selective advantage to the organism possessing it and must increase the organism's fitness. Other novel structures result from exaptation, the gradual adaptation of existing structures to new functions Natural selection doesn't anticipate the novel use: each intermediate stage must be adaptive and functional. Evolutionary trends do not mean that evolution is goal directed. Natural selection results from the interactions between organisms and their environment. If the environment changes, apparent evolutionary trends may cease or reverse. Systematics classifies organisms and determines their evolutionary relationship. Taxonomists assign each species a binomial consisting of a genus and species name. A phylogenetic tree is a hypothesis of evolutionary relationships within a group. Cladistics uses shared derived characters to group organisms into clades, including an ancestral species and all its descendents. Shared ancestral characters were present in ancestral groups. Molecular systematics compares nucleic acids or other molecules to infer related ness of taxa.


KEY TERMS:
- Macroevolution: major changes over evolutionary time
- Radiometric dating: measurement of the decay of radioactive isotopes
- Geologic record: defined by major transitions in life on Earth
- Continental drift: the slow, continuous movement of Earth's crustal plates on the hot mantle
- Adaptive radiation: a group of organisms forms new species, whose adaptations allow them to fill new habitats or roles in the communities
- Evo-devo: a field that combines evolutionary and developmental biology
- Homeotic genes: master control genes that determine basic features, such as where pairs of wings or legs develop on a fruit fly
- Species selection: the unequal speciation or unequal survival of species on a branching evolutionary tree
- Phylogeny: the evolutionary history of a species or group of species
- Convergent evolution: where analogous similarities result from in similar environments

This is a famous picture of evolution. It started out with the ape on the left, and ends with human being now on the right. It didn't happen just at once, but it took couple steps in between to become a human being from an ape. Also it took extremely long time. Like I said in the beginning, some apes who have different and better genes than others keep being alive, and other apes died out because of some reasons. And whoever that is still alive keep raising their children which are more likely to have "better" genes. This is how evolution occurs. This shows a microevlution.

http://www.youtube.com/watch?v=fVPadCMKJ_8


5 FACTS:
1) Homologous genes have been found in organisms separated by huge evolutionary distances
2) Molecular clocks help track evolutionary time. It can be calibrated in real time by graphing the number of nucleotide differences against the dates of evolutionary branch points known from the fossil record.
3) Life is divided into three domains: the prokaryotic domains Bacteria and Archaea and the eukaryote domain Eukarya.
4) There have been two major episodes of horizontal gene transfer, with transfer of genes between genomes by plasmid exchange, viral infection, and fusion of organisms: gene transfer between a mitochondrial ancestor and the ancestor of eukaryotes, and gene transfer between a chloroplast ancestor and the ancestor of green plants.
5) Shared characters are used to construct phylogenetic trees.

Ch.14 The Origin of Species

WHY CAN'T MULES MATE?
The basic reason why mules cannot reproduce is that a mule does not have a even number of chromosomes. They have 63 chromosomes because a horse and a donkey have different numbers of chromosomes. During mitotic cell division, each of the chromosomes copies itself and then distributes these two copies to the two daughter cells. In contrast, when the mule is producing sperm or egg cells during meiosis, each pair of chromosomes need to pair up with each other. Since the mule doesn't have an even number of homologous pairs, meiosis is disrupted and viable sperm and egg are not formed.

WHAT ARE PREZYGOTIC REPRODUCTIVE BARRIERS?
There are two general categories of reproductive isolating mechanisms: prezygotic, or those that take effect before fertilization, and postzygotic, hybrids between members of different populations through ecological, temporal, ethological, mechanical, and gametic isolation.

WHAT IS THE PHYLOGENETIC SPECIES CONCEPT?
The phylogenetic species concept defines a species as a set of organisms representing a specific evolutionary lineage. The concept of a species as an irreducible group whose members are descended from a common ancestor and who all possess a combination of certain traits. It is less restrictive than the biological species concept. Also it permits successive species to be defined even if they have evolved in an unbroken line of descent, with continuity of sexual fertility. However because slight differences can be found among virtually any group of organisms, the concept tends to encourage extreme division of species into ever-smaller groups.


SUMMARY:
Linnaeus used physical characteristics to distinguish species. His binomial system is the basis of taxonomy, the naming and classification of life's forms. The biological species concept defines a species as a group of populations whose members can interbreed and produce fertile offspring with each other but not with members of other species. Most organisms are classified based on observable phenotypic traits; the morphological species by its ecological niche. According to the phylogenetic species concept, a species is the smallest group that shares a common ancestor and forms one branch on the tree of life.
There are two types of reproductive barriers. Prezygotic barriers, which includes temporal isolation, habitat isolation, behavioral isolation, mechanical isolation, and gametic isolation. Also postzygotic barriers, which includes reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown.
Geographically separated from other populations, a small population may become genetically unique as its gene pool is changed by natural selection, mutation, or genetic drift in allopatric speciation. A laboratory study has documented the beginning of reproductive isolation as fruit fly populations adapted to a new food source. Researchers have identified the specific genes involved in some cases of speciation, which is the evolution of reproductive barriers. Hybrid zones are regions in which members of different species overlap and produce at least some hybrid offspring. Over time, reinforcement may strengthen prezygotic barriers to reproduction, or fusion may reverse the speciation process as reproductive barriers weaken and extensive gene flow occurs. In stable hybrid zones, a limited number of hybrid offspring continue to be produced. Adaptive radiation can occur when populations are provided with expanded opportunities following mass extinctions, the colonization of a diverse new environment, or the evolution of new structures. The punctuated equilibrium model draws on the fossil record, where many species change most as they arise from an ancestral species and then change relatively little for the rest of their existence. But some species have evolved by the gradual accumulation of changes. The time interval between speciation events varies considerable, from a few thousand years to tens of millions of years.

     +       =

A Mule is a hybrid of a horse and a donkey. However mules cannot mate. Therefore a mule is an animal that never reproduce. A mule is not considered as a specie, because species have to be able to inbreed. In order to make a mule, a horse and a donkey needs to mate.

http://www.youtube.com/watch?v=zl1a1n6XR9g

KEY TERMS:
- Species: as a group of organisms whose members can breed and produce fertile offspring, but who do not produce fertile offspring with members of other groups
- Taxonomy: the branch of biology that names and classifies species and groups them into broader categories
- biological species concept: species as a group of populations whose members have the potential to interbreed in nature and produce fertile offspring
- Morphological species concept: classification is based mainly on phenotype
- Ecological species concept: identification of species in terms of their ecological niches, focusing on unique adaptations to particular roles in a biological community
- Phylogenetic species concept: a species as the smallest group of individuals that shares a common ancestor and that forms one branch on the tree of life.
- Reproductive barrier: a biological feature of the organism itself
- Allopatric speciation: populations separated by a geographic barrier
- Polyploid: their cells have more than two complete sets of chromosomes
- Sympatric speciation: a new species arises within the same geographic area as a parent species

5 FACTS:
1) Reproductive barriers keep species separate
2) In allopatric speciation, geographic isolation leads to speciation
3) In sympatric speciation, speciation takes place without geographic isolation
4) Reproductive barriers may evolve as populations diverge
5) Hybrid zones provide opportunities to study reproductive isolation