What makes some entrepreneurs tick while others fail. Why do people in some cultures and regions display a better entrepreneurial spirit compared to people in other cultures or areas? Read on for an overview of the major factors that influence entrepreneurship.

 How Cultural Factors Influence Entrepreneurship
  • Culture refers to the customary practices and beliefs that have a significant impact on the basic values, perceptions, preferences, and behaviors of people.

    Culture and entrepreneurship intervene in many ways.

    • People traditionally engaged in businesses have a pro business attitude and disdain working as employees.
    • Many people fall outside the establishment and remain unsuited for the traditional job market due to a strong culture of independence or other reasons.
    • Business school students come under the missionary zeal of teachers who exhort them to become entrepreneurs even if the opportunity cost is very high.
    • The culture of consumerism where people desire material goods encourages entrepreneurship within the area as returns from a business become more than returns from a job.

    • People engaged in jobs and other services pressure their children to find secure jobs and crush their entrepreneurship spirit at a very early age.
    • A culture of thrift where people spend less and save for a rainy day discourages entrepreneurship within the local community as the returns from a business become less attractive compared to returns from a job.
    • Cultures where people are risk averse and do not attach much importance to hard work and persistence are not conducive to entrepreneurship.
  • How Political Environments Support or Suppress Entrepreneurship

    The following are some of the ways in which the political environment influences entrepreneurship:

    1. What makes some entrepreneurs tick while others fail. Why do people in some cultures and regions display a better entrepreneurial spirit compared to people in other cultures or areas? Read on for an overview of the major factors that influence entrepreneurship.

      • How Cultural Factors Influence Entrepreneurship

        Culture refers to the customary practices and beliefs that have a significant impact on the basic values, perceptions, preferences, and behaviors of people.

        Culture and entrepreneurship intervene in many ways.

        • People traditionally engaged in businesses have a pro business attitude and disdain working as employees.
        • Many people fall outside the establishment and remain unsuited for the traditional job market due to a strong culture of independence or other reasons.
        • Business school students come under the missionary zeal of teachers who exhort them to become entrepreneurs even if the opportunity cost is very high.
        • The culture of consumerism where people desire material goods encourages entrepreneurship within the area as returns from a business become more than returns from a job.

        • People engaged in jobs and other services pressure their children to find secure jobs and crush their entrepreneurship spirit at a very early age.
        • A culture of thrift where people spend less and save for a rainy day discourages entrepreneurship within the local community as the returns from a business become less attractive compared to returns from a job.
        • Cultures where people are risk averse and do not attach much importance to hard work and persistence are not conducive to entrepreneurship.
      • How Political Environments Support or Suppress Entrepreneurship

        The following are some of the ways in which the political environment influences entrepreneurship:

        • Government support to economic development through infrastructure development, facilitation, industrial parks, and the like all encourage entrepreneurship.
        • High taxes that cut into the returns usually discourage entrepreneurs. On the other hand, tax holidays to encourage business attract start-ups.
        • The availability of infrastructure and utilities such as good roads, power, communication facilities, and lack of corruption and bureaucratic delays in obtaining such utilities encourage entrepreneurship.
        • Economic freedom in the form of favorable legislation and few hurdles to start and operate businesses encourage entrepreneurship.
        • While most businesses accept laws related to the safeguard of labor rights and the environment, some countries have retrograde laws that make compliance very difficult and time consuming. Such legal hurdles create a barrier to entrepreneurship.

        Unstable political conditions where government policies change frequently discourage business, as investors fear for the safety of their investments.

      • How Economic Factors Influence Entrepreneurship

        The nature of the economy is a major factor that influences entrepreneurship.

        • The general purchasing power of the people, manifested by income levels and economic prosperity of the region, plays a major role in the success of entrepreneurial ventures.
        • During times of economic slowdown or recession, the purchasing power declines and people remain reluctant to invest, affecting entrepreneurship adversely.
        • In a subsistence economy, most of the people are engaged in agriculture, consuming most of their output and bartering the rest for simple goods and services. Entrepreneurial opportunities are few in such scenarios.
      • Availability of Resources as a Major Factor that Affects Entrepreneurship

        Critical factors that influence entrepreneurship include the availability of resources such as capital, human assets, raw materials, infrastructure, and utilities.

        • Capital remains indispensable to start an enterprise. The availability of capital allows the entrepreneur to bring together other factors and use them to produce goods or services.
        • The importance of human assets or employees can never be underestimated. No enterprise succeeds without a skilled and committed workforce.
        • The very existence of the business depends on the availability of raw materials to process.
        • Physical infrastructure and utilities such as good roads, parking, communication facilities, and power all play a crucial factor in the seamless functioning of a business.
      • How Entrepreneurial Skill Sets and Psychological Orientation Affects Entrepreneurship

        All other factors notwithstanding, the success of an entrepreneurial venture depends on the entrepreneur. The entrepreneur is the leader and driver of the venture, and requires the following skill-set and orientation for success:

        • Hard work and persistence
        • Ability to manage and minimize risk
        • Ability to draw up a comprehensive business plan, and having a contingency plan ready
        • A strong need-orientation that provides the inclination to achieve things

        With the collapsing trade barriers bringing in greater opportunities, and job security passé, the conditions for entrepreneurship are better than ever before.




Evolution is the process by which modern organisms have descended from ancient ancestors. Evolution is responsible for both the remarkable similarities we see across all life and the amazing diversity of that life — but exactly how does it work?

Fundamental to the process is genetic variation upon which selective forces can act in order for evolution to occur. This section examines the mechanisms of evolution focusing on:

  • Descent and the genetic differences that are heritable and passed on to the next generation;
  • Mutation, migration (gene flow), genetic drift, and natural selection as mechanisms of change;
  • The importance of genetic variation;
  • The random nature of genetic drift and the effects of a reduction in genetic variation;
  • How variation, differential reproduction, and heredity result in evolution by natural selection; and
  • How different species can affect each other’s evolution through coevolution.

The components of natural selection: variation, differential reproduction, and heredity

Descent with modification

We’ve defined evolution as descent with modification from a common ancestor, but exactly what has been modified? Evolution only occurs when there is a change in gene frequency within a population over time. These genetic differences are heritable and can be passed on to the next generation — which is what really matters in evolution: long term change.

Compare these two examples of change in beetle populations. Which one is an example of evolution?

1. Beetles on a diet
Imagine a year or two of drought in which there are few plants that these beetles can eat.
First generation of starving beetles
All the beetles have the same chances of survival and reproduction, but because of food restrictions, the beetles in the population are a little smaller than the preceding generation of beetles. Second generation of starving beetles
2. Beetles of a different color
Most of the beetles in the population (say 90%) have the genes for bright green coloration and a few of them (10%) have a gene that makes them more brown.
First Generation
Some number of generations later, things have changed: brown beetles are more common than they used to be and make up 70% of the population. Second Generation

Which example illustrates descent with modification — a change in gene frequ

ency over time?

The difference in weight in example 1 came about because of environmental influences — the low food supply — not because of a change in the frequency of genes. Therefore, example 1 is not evolution. Because the small body size in this population was not genetically determined, this generation of small-bodied beetles will produce beetles that will grow to normal size if they have a normal food supply.

The changing color in example 2 is definitely evolution: these two generations of the same population are genetically different. But how did it happen?

Mechanisms of change

Each of these four processes is a basic mechanism of evolutionary change.

A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make genes for brown coloration more frequent in the population than they were before the mutation.
Some individuals from a population of brown beetles might have joined a population of green beetles. That would make genes for brown coloration more frequent in the green beetle population than they were before the brown beetles migrated into it.
Genetic drift
Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation — but just by chance. These chance changes from generation to generation are known as genetic drift.
Genetic drift
Natural selection
Imagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation.
Natural Selection

Download this series of graphics from the Image library.

All of these mechanisms can cause changes in the frequencies of genes in populations, and so all of them are mechanisms of evolutionary change. However, natural selection and genetic drift cannot operate unless there is genetic variation — that is, unless some individuals are genetically different from others. If the population of beetles were 100% green, selection and drift would not have any effect because their genetic make-up could not change.

So, what are the sources of genetic variation?


Genetic variation

Without genetic variation, some of the basic mechanisms of evolutionary change cannot operate.

There are three primary sources of genetic variation, which we will learn more about:

  1. Mutations are changes in the DNA. A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations.
  2. Gene flow is any movement of genes from one population to another and is an important source of genetic variation.
  3. Sex can introduce new gene combinations into a population. This genetic shuffling is another important source of genetic variation.
Genetic shuffling
Genetic shuffling is a source of variation.



Mutation is a change in DNA, the hereditary material of life. An organism’s DNA affects how it looks, how it behaves, and its physiology — all aspects of its life. So a change in an organism’s DNA can cause changes in all aspects of its life.

Mutations are random
Mutations can be beneficial, neutral, or harmful for the organism, but mutations do not “try” to supply what the organism “needs.” In this respect, mutations are random — whether a particular mutation happens or not is unrelated to how useful that mutation would be.

Not all mutations matter to evolution
Since all cells in our body contain DNA, there are lots of places for mutations to occur; however, not all mutations matter for evolution. Somatic mutations occur in non-reproductive cells and won’t be passed onto offspring.

For example, the golden color on half of this Red Delicious apple was caused by a somatic mutation. The seeds of this apple do not carry the mutation.

The only mutations that matter to large-scale evolution are those that can be passed on to offspring. These occur in reproductive cells like eggs and sperm and are called germ line mutations.

A single germ line mutation can have a range of effects:

  1. No change occurs in phenotype
    Some mutations don’t have any noticeable effect on the phenotype of an organism. This can happen in many situations: perhaps the mutation occurs in a stretch of DNA with no function, or perhaps the mutation occurs in a protein-coding region, but ends up not affecting the amino acid sequence of the protein.
  2. Small change occurs in phenotype
    Cat with curled-ear mutation

    A single mutation caused this cat’s ears to curl backwards slightly.

  3. Big change occurs in phenotype
    Some really important phenotypic changes, like DDT resistance in insects are sometimes caused by single mutations. A single mutation can also have strong negative effects for the organism. Mutations that cause the death of an organism are called lethals — and it doesn’t get more negative than that.

There are some sorts of changes that a single mutation, or even a lot of mutations, could not cause. Neither mutations nor wishful thinking will make pigs have wings; only pop culture could have created Teenage Mutant Ninja Turtles — mutations could not have done it.

The causes of mutations

Mutations happen for several reasons.

  1. DNA fails to copy accurately
    Most of the mutations that we think matter to evolution are “naturally-occurring.” For example, when a cell divides, it makes a copy of its DNA — and sometimes the copy is not quite perfect. That small difference from the original DNA sequence is a mutation.

    Following cell division, the copied DNA is imperfect

    To download this image, right-click (Windows) or control-click (Mac) on the image and select “Save image.”
  2. External influences can create mutations
    Radioactive signMutations can also be caused by exposure to specific chemicals or radiation. These agents cause the DNA to break down. This is not necessarily unnatural — even in the most isolated and pristine environments, DNA breaks down. Nevertheless, when the cell repairs the DNA, it might not do a perfect job of the repair. So the cell would end up with DNA slightly different than the original DNA and hence, a mutation.

    Gene flow

    Gene flow — also called migration — is any movement of individuals, and/or the genetic material they carry, from one population to another. Gene flow includes lots of different kinds of events, such as pollen being blown to a new destination or people moving to new cities or countries. If gene versions are carried to a population where those gene versions previously did not exist, gene flow can be a very important source of genetic variation. In the graphic below, the gene version for brown coloration moves from one population to another.

    Gene flow in beetle populations

    Sex and genetic shuffling

    Shuffling of
	  gene combinations

    Sex can introduce new gene combinations into a population and is an important source of genetic variation.You probably know from experience that siblings are not genetically identical to their parents or to each other (except, of course, for identical twins). That’s because when organisms reproduce sexually, some genetic “shuffling” occurs, bringing together new combinations of genes. For example, you might have bushy eyebrows and a big nose since your mom had genes associated with bushy eyebrows and your dad had genes associated with a big nose. These combinations can be good, bad, or neutral. If your spouse is wild about the bushy eyebrows/big nose combination, you were lucky and hit on a winning combination!

    This shuffling is important for evolution because it can introduce new combinations of genes every generation. However, it can also break up “good” combinations of genes.


    Development is the process through which an embryo becomes an adult organism and eventually dies. Through development, an organism’s genotype is expressed as a phenotype, exposing genes to the action of natural selection.

    Studies of development are important to evolutionary biology for several reasons:

    Explaining major evolutionary change
    Changes in the genes controlling development can have major effects on the morphology of the adult organism. Because these effects are so significant, scientists suspect that changes in developmental genes have helped bring about large-scale evolutionary transformations. Developmental changes may help explain, for example, how some hoofed mammals evolved into ocean-dwellers, how water plants invaded the land, and how small, armored invertebrates evolved wings.

    Mutated fly with two pairs of wings Mutated fly with legs instead of antennae
    Mutations in the genes that control fruit fly development can cause major morphology changes, such as two pairs of wings instead of one. Another developmental gene mutation can cause fruit flies to have legs where the antennae normally are, as shown in the fly on the right.

    Learning about evolutionary history
    An organism’s development may contain clues about its history that biologists can use to build evolutionary trees.

    Developmental stages of embryos
    Characters displayed by embryos such as these may help untangle patterns of relationship among the lineages.

    Limiting evolutionary change
    Developmental processes may constrain evolution, preventing certain characters from evolving in certain lineages. For example, development may help explain why there are no truly six-fingered tetrapods.

    Artificial selection

    Long before Darwin and Wallace, farmers and breeders were using the idea of selection to cause major changes in the features of their plants and animals over the course of decades. Farmers and breeders allowed only the plants and animals with desirable characteristics to reproduce, causing the evolution of farm stock. This process is called artificial selection because people (instead of nature) select which organisms get to reproduce.

    As shown below, farmers have cultivated numerous popular crops from the wild mustard, by artificially selecting for certain attributes.

    Artificial selection in the mustard family

    These common vegetables were cultivated from forms of wild mustard. This is evolution through artificial selection.

    Misconceptions about natural selection

    Because natural selection can produce amazing adaptations, it’s tempting to think of it as an all-powerful force, urging organisms on, constantly pushing them in the direction of progress — but this is not what natural selection is like at all.

    First, natural selection is not all-powerful; it does not produce perfection. If your genes are “good enough,” you’ll get some offspring into the next generation — you don’t have to be perfect. This should be pretty clear just by looking at the populations around us: people may have genes for genetic diseases, plants may not have the genes to survive a drought, a predator may not be quite fast enough to catch her prey every time she is hungry. No population or organism is perfectly adapted.

    Second, it’s more accurate to think of natural selection as a process rather than as a guiding hand. Natural selection is the simple result of variation, differential reproduction, and heredity — it is mindless and mechanistic. It has no goals; it’s not striving to produce “progress” or a balanced ecosystem.

    Formula for natural selection

    Evolution does not work this way
    Evolution does not work this way.

    This is why “need,” “try,” and “want” are not very accurate words when it comes to explaining evolution. The population or individual does not “want” or “try” to evolve, and natural selection cannot try to supply what an organism “needs.” Natural selection just selects among whatever variations exist in the population. The result is evolution.

    At the opposite end of the scale, natural selection is sometimes interpreted as a random process. This is also a misconception. The genetic variation that occurs in a population because of mutation is random — but selection acts on that variation in a very non-random way: genetic variants that aid survival and reproduction are much more likely to become common than variants that don’t. Natural selection is NOT random!



A computer is a machine that can be programmed to manipulate symbols. Its principal characteristics are:

  • It responds to a specific set of instructions in a well-defined manner.
  • It can execute a prerecorded list of instructions (a program).
  • It can quickly store and retrieve large amounts of data.

Therefore computers can perform complex and repetitive procedures quickly, precisely and reliably. Modern computers are electronic and digital. The actual machinery (wires, transistors, and circuits) is called hardware; the instructions and data are called software. All general-purpose computers require the following hardware components:

  • Central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions organized in programs (“software”) which tell the computer what to do.
  • Memory (fast, expensive, short-term memory): Enables a computer to store, at least temporarily, data, programs, and intermediate results.
  • Mass storage device (slower, cheaper, long-term memory): Allows a computer to permanently retain large amounts of data and programs between jobs. Common mass storage devices include disk drives and tape drives.
  • Input device: Usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer.
  • Output device: A display screen, printer, or other device that lets you see what the computer has accomplished.

In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.

II, Computer sizes and power

Computers can be generally classified by size and power as follows, though there is considerable overlap:COMP

  • Personal computer: A small, single-user computer based on a microprocessor.
  • Workstation: A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and, in general, a higher-quality monitor.
  • Minicomputer: A multi-user computer capable of supporting up to hundreds of users simultaneously.
  • Mainframe: A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.
  • Supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second.

Supercomputer and Mainframe

Supercomputer is a broad term for one of the fastest computers currently available. Supercomputers are very expensive and are employed for specialized applications that require immense amounts of mathematical calculations (number crunching). For example, weather forecasting requires a supercomputer. Other uses of supercomputers scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data (e.g. in petrochemical prospecting). Perhaps the best known supercomputer manufacturer is Cray Research.

Mainframe was a term originally referring to the cabinet containing the central processor unit or “main frame” of a room-filling Stone Age batch machine. After the emergence of smaller “minicomputer” designs in the early 1970s, the traditional big iron machines were described as “mainframe computers” and eventually just as mainframes. Nowadays a Mainframe is a very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. The chief difference between a supercomputer and a mainframe is that a supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs concurrently. In some ways, mainframes are more powerful than supercomputers because they support more simultaneous programs. But supercomputers can execute a single program faster than a mainframe. The distinction between small mainframes and minicomputers is vague, depending really on how the manufacturer wants to market its machines.


It is a midsize computer. In the past decade, the distinction between large minicomputers and small mainframes has blurred, however, as has the distinction between small minicomputers and workstations. But in general, a minicomputer is a multiprocessing system capable of supporting from up to 200 users simultaneously.


It is a type of computer used for engineering applications (CAD/CAM), desktop publishing, software development, and other types of applications that require a moderate amount of computing power and relatively high quality graphics capabilities. Workstations generally come with a large, high-resolution graphics screen, at large amount of RAM, built-in network support, and a graphical user interface. Most workstations also have a mass storage device such as a disk drive, but a special type of workstation, called a diskless workstation, comes without a disk drive. The most common operating systems for workstations are UNIX and Windows NT. Like personal computers, most workstations are single-user computers. However, workstations are typically linked together to form a local-area network, although they can also be used as stand-alone systems.

N.B.: In networking, workstation refers to any computer connected to a local-area network. It could be a workstation or a personal computer.

Personal computer:

It can be defined as a small, relatively inexpensive computer designed for an individual user. In price, personal computers range anywhere from a few hundred pounds to over five thousand pounds. All are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet and database management applications. At home, the most popular use for personal computers is for playing games and recently for surfing the Internet.

Personal computers first appeared in the late 1970s. One of the first and most popular personal computers was the Apple II, introduced in 1977 by Apple Computer. During the late 1970s and early 1980s, new models and competing operating systems seemed to appear daily. Then, in 1981, IBM entered the fray with its first personal computer, known as the IBM PC. The IBM PC quickly became the personal computer of choice, and most other personal computer manufacturers fell by the wayside. P.C. is short for personal computer or IBM PC. One of the few companies to survive IBM’s onslaught was Apple Computer, which remains a major player in the personal computer marketplace. Other companies adjusted to IBM’s dominance by building IBM clones, computers that were internally almost the same as the IBM PC, but that cost less. Because IBM clones used the same microprocessors as IBM PCs, they were capable of running the same software. Over the years, IBM has lost much of its influence in directing the evolution of PCs. Therefore after the release of the first PC by IBM the term PC increasingly came to mean IBM or IBM-compatible personal computers, to the exclusion of other types of personal computers, such as Macintoshes. In recent years, the term PC has become more and more difficult to pin down. In general, though, it applies to any personal computer based on an Intel microprocessor, or on an Intel-compatible microprocessor. For nearly every other component, including the operating system, there are several options, all of which fall under the rubric of PC

Today, the world of personal computers is basically divided between Apple Macintoshes and PCs. The principal characteristics of personal computers are that they are single-user systems and are based on microprocessors. However, although personal computers are designed as single-user systems, it is common to link them together to form a network. In terms of power, there is great variety. At the high end, the distinction between personal computers and workstations has faded. High-end models of the Macintosh and PC offer the same computing power and graphics capability as low-end workstations by Sun Microsystems, Hewlett-Packard, and DEC.

III, Personal Computer Types

Actual personal computers can be generally classified by size and chassis / case. The chassis or case is the metal frame that serves as the structural support for electronic components. Every computer system requires at least one chassis to house the circuit boards and wiring. The chassis also contains slots for expansion boards. If you want to insert more boards than there are slots, you will need an expansion chassis, which provides additional slots. There are two basic flavors of chassis designs–desktop models and tower models–but there are many variations on these two basic types. Then come the portable computers that are computers small enough to carry. Portable computers include notebook and subnotebook computers, hand-held computers, palmtops, and PDAs.

Tower model

The term refers to a computer in which the power supply, motherboard, and mass storage devices are stacked on top of each other in a cabinet. This is in contrast to desktop models, in which these components are housed in a more compact box. The main advantage of tower models is that there are fewer space constraints, which makes installation of additional storage devices easier.

Desktop model

A computer designed to fit comfortably on top of a desk, typically with the monitor sitting on top of the computer. Desktop model computers are broad and low, whereas tower model computers are narrow and tall. Because of their shape, desktop model computers are generally limited to three internal mass storage devices. Desktop models designed to be very small are sometimes referred to as slimline models.

Notebook computer

An extremely lightweight personal computer. Notebook computers typically weigh less than 6 pounds and are small enough to fit easily in a briefcase. Aside from size, the principal difference between a notebook computer and a personal computer is the display screen. Notebook computers use a variety of techniques, known as flat-panel technologies, to produce a lightweight and non-bulky display screen. The quality of notebook display screens varies considerably. In terms of computing power, modern notebook computers are nearly equivalent to personal computers. They have the same CPUs, memory capacity, and disk drives. However, all this power in a small package is expensive. Notebook computers cost about twice as much as equivalent regular-sized computers. Notebook computers come with battery packs that enable you to run them without plugging them in. However, the batteries need to be recharged every few hours.

Laptop computer

A small, portable computer — small enough that it can sit on your lap. Nowadays, laptop computers are more frequently called notebook computers.

Subnotebook computer

A portable computer that is slightly lighter and smaller than a full-sized notebook computer. Typically, subnotebook computers have a smaller keyboard and screen, but are otherwise equivalent to notebook computers.

Hand-held computer

A portable computer that is small enough to be held in one’s hand. Although extremely convenient to carry, handheld computers have not replaced notebook computers because of their small keyboards and screens. The most popular hand-held computers are those that are specifically designed to provide PIM (personal information manager) functions, such as a calendar and address book. Some manufacturers are trying to solve the small keyboard problem by replacing the keyboard with an electronic pen. However, these pen-based devices rely on handwriting recognition technologies, which are still in their infancy. Hand-held computers are also called PDAs, palmtops and pocket computers.


A small computer that literally fits in your palm. Compared to full-size computers, palmtops are severely limited, but they are practical for certain functions such as phone books and calendars. Palmtops that use a pen rather than a keyboard for input are often called hand-held computers or PDAs. Because of their small size, most palmtop computers do not include disk drives. However, many contain PCMCIA slots in which you can insert disk drives, modems, memory, and other devices. Palmtops are also called PDAs, hand-held computers and pocket computers.


Short for personal digital assistant, a handheld device that combines computing, telephone/fax, and networking features. A typical PDA can function as a cellular phone, fax sender, and personal organizer. Unlike portable computers, most PDAs are pen-based, using a stylus rather than a keyboard for input. This means that they also incorporate handwriting recognition features. Some PDAs can also react to voice input by using voice recognition technologies. The field of PDA was pioneered by Apple Computer, which introduced the Newton MessagePad in 1993. Shortly thereafter, several other manufacturers offered similar products. To date, PDAs have had only modest success in the marketplace, due to their high price tags and limited applications. However, many experts believe that PDAs will eventually become common gadgets.

PDAs are also called palmtops, hand-held computers and pocket computers.

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Motility in Alimentary Canal Food is moved through digestive tracts by cilia or by specialized musculature, and often by both. Movement is usually by cilia in acoelomate and pseudocoelomate metazoa that lack the mesodermally derived gut musculature of true coelomates. Cilia move intestinal fl uids and materials also in some eucoelomates, such as most molluscs, in which the coelom is weakly developed. In animals with well-developed coeloms, the gut is usually lined with two opposing layers of smooth muscle: a longitudinal layer, in which smooth muscle fibers run parallel with the length of the gut, and a circular layer, in which muscle fi bers embrace the circumference of the gut . A characteristic gut movement is   segmentation,   the alternate constriction of rings of smooth muscle of the intestine that constantly divide and squeeze contents back and forth …

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During meiosis II, the chromosomes condense and become attached to a new spindle apparatus  (prophase II).  They then move to positions in the  equatorial plane of the cell  (metaphase II),  and their centromeres split to allow the constituent sister chromatids to move to opposite poles  (anaphase II),  a phenomenon called  chromatid disjunction. 
During  telophase II,  the separated chromatids—now called chromosomes—gather at the poles and daughter nuclei form around them. Each daughter nucleus contains  a  haploid set of chromosomes. Mechanistically, meiosis II is therefore much like mitosis. However, its products are haploid, and unlike the products of mitosis, the cells that emerge from meiosis II are not genetically identical. Pair of homologous chromosomes Homologue 1 Centromeres One chromatid Chiasma Two chiasmata Homologue 2 Synapsis and crossing over Tetrad Recombinant chromatids
 One reason these cells differ is that homologous chromosomes pair and disjoin from each other during meiosis I. Within each pair of chromosomes, one homologue was inherited from the organism’s mother, and the other was inherited from its father. During meiosis I, the maternally and paternally inherited homologues come together and synapse. They are positioned on the meiotic spindle and become oriented randomly with respect to the spindle’s poles. Then they disjoin. For each pair of chromosomes, half the daughter cells produced by the first meiotic division receive the maternally inherited homologue, and the other half receive the paternally inherited homologue. Thus, from the end of the first meiotic division, the products of meiosis are destined to be different. These differences are compounded by the number of chromosome pairs that disjoin during meiosis I. Each of the pairs disjoins independently. Thus, if there are 23 pairs of chromosomes, as there are in humans, meiosis I can produce 223  chromosomally different daughter cells—that is, more than 8 million possibilities. To test your understanding of this concept go to Solve It: How Many Chromosome Combinations in Sperm?

Introduction to HTML

Remember what HTML stands for? It stands for HyperText Markup Language.

Let’s look in more detail what this means.

‘Markup’ in computing means adding extra data to text in order to tell computers more information about that text. For example, in HTML we tell the computer which parts of the HTML document are to be displayed, which parts make up the navigation, even which parts are titles and which are content.

What is a HTML document?

A HTML document is just what it sounds like – a document that contains HTML! It’s nothing more special than that. All we have to do is type our HTML into a document in a writing program – for example Notepad, or even Microsoft Word – and we have a HTML document.

Starting from the next lesson of this course we’re going to make our own simple HTML pages on our own computers, and learn all about HTML as we go.

First let’s understand what makes HTML special.

What are HTML tags?

HTML is just normal text, with additional information. This additional information is delivered through tagsTags are the fundamental building blocks of HTML.

A tag looks like this:


Anything inside the “<” and “>” symbols defines the tag.

Can anything be a HTML tag?

Yes and no. Technically you could put anything inside a “<” and “>” symbol. However, browsers only understand certain tags, so unless you use the tags that are officially defined as part of HTML then your tags will not work correctly.

We will learn all about the important HTML tags as we proceed through this course.

More about tags

Tags can be both opened and closed. For example, let’s look at a <span> tag (don’t worry about what a <span> tag is for now – we’ll get to it later):

<span>This is inside my span! I can put anything I like here.</span>

You can see that a tag is opened by having an initial tag such as <span>. It is then closedwith a second tag that has an additional “/” symbol. Anything can go between the opening and closing tags – this is known as the tag contents.

This whole example from the opening tag to the tag contents to the closing tag is known as a HTML element. In this case we have created a span element, because we are using a span tag to define the element.

Elements are made up of tags.

Self-closing Tags

Some tags don’t require opening and closing tags, they can effectively open and close themselves in just one tag. These are often known as self-closing tags.

Technically in HTML 5, which is currently the most advanced version of HTML, self-closing tags don’t actually close themselves, but it’s a helpful way to picture what is happening. (If you’re interested in why: it’s because HTML is similar to a markup language called XML. In XML tags are required to either be closed in a pair, or to self-close. HTML is not as strict as XML, so you don’t have to self-close your tags. However, it doesn’t hurt, and keeps your HTML neat so it is not a bad habit to have.)

A self-closing tag looks like this: <tag />

Tags that can exist on their own, i.e. be self-closed include: <img />, <link /> and <meta />, amongst others.

Again, we will understand more about each of these tags as we encounter them when we start building our own website!

Tag attributes

The last important concept to understand about tags is that tags can have attributes as well as contents. Let’s add an attribute to our <span> tag from before:

<span class=”exampleTag”>This is inside my span! I can put anything I like here.</span>

Now our tag has a class attribute. Attributes can have values. In this case our attribute has the value exampleTag.

As with tag names, attributes can technically be anything. For example, we could have said:

<span lemon=”fruityAttribute”>This is inside my span! I can put anything I like here.</span>

This gives our <span> tag an attribute named“lemon” and with a value of “fruityAttribute”.

However, just like with tags there are certain attributes that are important and have meaning. We will learn about these as we learn about each tag.

Putting it all together

Here we can see all of the parts that make up an element.

Make sure you understand which part of the element is a tag, which part is an attribute, which part is an attribute value and which part is the element contents.


Let’s consider the general features of RNA. Although both RNA and DNA are nucleic acids, RNA differs from DNA in several important ways: 

1. RNA is usually a single-stranded nucleotide chain, not a double helix like DNA. A consequence is that RNA is more flexible and can form a much greater variety of complex three-dimensional molecular shapes than can double-stranded DNA. An RNA strand can bend in such a way that some of its own bases pair with each other. Such intranwkcular base pairing is an important determinate of RNA shape. 

2. RNA has ribose sugar in its nucleotides, rather than the deoxyribose found in DNA. As the names suggest, the two sugars differ in the presence or absence of just one oxygen atom. The RNA sugar contains a hydroxyl group (OH) bound to the 2′-carbon atom, whereas the DNA sugar has only a hydrogen atom bound to the 2′-carbon atom. As you will see later in this chapter, the presence of the hydroxyl group at the 2′-carbon atom facilitates the action of RNA in many important cellular processes. Like an individual DNA strand, a strand of RNA is formed of a sugar-phosphate backbone, with a base covalently linked at the 1′ position on each ribose. The sugar-phosphate linkages are made at the 5′ and 3′ positions of the sugar, just as in DNA; so an RNA chain will have a 5′ end and a 3′ end. 

3. RNA nucleotides (called ribonucleotide,) contain the bases adenine, guanine, and cytosine, but the pyrimidine base uracil (abbreviated U) is present instead of thymine. Uracil forms hydrogen bonds with adenine just as thymine does. In addition, uracil is capable of base pairing with G. The bases U and G form base pairs only during RNA folding and not during transcription. The two hydrogen bonds that can form between U and G are weaker than the two that form between U and A. The ability of U to pair with both A and G is a major reason why RNA can form extensive and complicated structures, many of which are important in biological processes.

4. RNA—like protein, but unlike DNA—can catalyze biological reactions. The name ribozyme was coined for the RNA molecules that function like protein enzymes.