IMPORTANT UPCOMING EXAMS QUESTIONS 

QUESTION1. Which one of the following is not an enzyme?

Ampere  (symbol:  A) 

The  ampere  is defined as ‘the constant current that, if maintained in two straight parallel conductors of infinite length and negligible cross-sectional area and placed one meter apart in a vacuum, would produce between them a force equal to 2 × 10–7  newtons per unit length’.

Coulomb  (symbol:  C)
The  coulomb  is defined as ‘the charge transported through any cross-section of a conductor in one second by a constant current of one ampere’.

 Volt  (symbol:  V) 
The  volt  is defined  as  ‘the potential difference between two points such that the energy used in conveying a charge of one coulomb from one point to the other is one joule’.

 Joule  (symbol:  J)
The  joule  is defined  as  ‘the work done when the point of application of a force of one newton is displaced one meter in the direction of that force’.

Ohm (symbol:  Ω) 
The  ohm  is defined  as  ‘the electrical resistance between two points of a conductor, such that when a constant potential difference of one volt is applied between those points, a current of one ampere results’.

Newton  (symbol:  N)
The  newton is defined  as  ‘the force which, when applied to a mass of one kilogram, will give it an acceleration of one meter per second per second’.

 Watt (symbol:  W)
 The  watt  is defined  as  ‘the power resulting when one joule of energy is dissipated in one second’.

 Farad  (symbol:  F)
The  farad  is defined as ‘the capacitance of a capacitor, between the plates of which there appears a difference in potential of one volt, when it is charged to 1 coulomb.

Weber* (symbol:  Wb) 
The weber is defined  as  ‘the magnetic  fl ux that, linking a circuit of one turn, produces a potential difference of one volt when it is reduced to zero at a uniform rate in one second’. (*pronounced ‘vay-ber’)

Tesla (symbol:  T) 
The  tesla  is defined  as  ‘one weber of magnetic  fl ux per square metre of circuit area’.

Henry  (symbol:  H) 
The  Henry  is defined  as  ‘the self- or mutual-inductance of a closed loop if a current of one ampere gives rise to a magnetic  flux of one weber’.

By ‘direction of current’  in metallic conductors, we mean the direction in which current  passes through the load. In other words, it is its direction through the external circuit,  never  within the source of potential difference. During the eighteenth century, the great  American scientist and statesman  Benjamin Franklin  (17061790), along with others, believed that an electric current was some sort of mysterious ‘fluid’  that  flowed inside a conductor from a high-pressure area to low pressure area. He naturally labelled high pressure as being ‘positive’  pressure, and low pressure as being ‘negative’  pressure and so he believed that an electric current  fl owed  from  ‘positive to negative’  – i.e. in a direction  opposite  to that of the drift of free electrons! Franklin’s mistaken theory on current direction was, unfortunately, reinforced during the following century, as result of experiments in electrolysis conducted by the English scientist  Michael Faraday  (1791–1867). Electrolysis is a method of depositing (‘plating’) metal on an electrode immersed in an electrolyte. Faraday noticed during his experiments that metal was removed from the positive electrode and deposited on the negative electrode, from which he, too, concluded that current moved from positive to negative, although he rejected Franklin’s idea that it was a ‘fluid’, in favour of it being a ‘field’. Over the following years, various rules (e.g. to determine the direction of magnetic  fields)  were devised, based on the mistaken belief that current in metallic conductors  fl owed from positive to negative. So, as strange as it might seem and despite today’s knowledge about current in metal conductors being a  fl ow of free electrons, Franklin’s current direction is still widely used as a convention in a great many textbooks, and is known as  ‘Franklinian’  or, more commonly,  conventional  flow.

Immune System

The immune system helps to monitor and fight infection and prevent  cancer.  It  includes  specialized  white  blood  cells—T cells,  B  cells, and  neutrophils—that  are  always  on  call  to  help. Your  body’s  immune  system  is  like  an  army  with  millions  of soldiers,  ready  to  fight  foreign  substances  such  as  germs  and viruses in the body. As we age, certain  parts  of  the  system  diminish  in  vitality, and we  have  to  be  more  alert  to  help  boost  the  system  to  work  at full  capacity.  In  autoimmune  diseases,  such  as  lupus,  the  immune system is out of control and attacks healthy tissues.

Dry Skin

Xerosis  (dry  skin)  is  a  common dermatological  skin  condition. Dry skin, or  xeroticeczema, can  be  labeled  as  xerosis, eczema craquele  (like  a  pattern  of  cracked  porcelain),  or  asteatotic eczema  (Plate2).  The  incidence  increases  with  age  and  is common in older individuals. The reduced  production  of  sebum  also  may  play  a  role  in  dry skin. Sebum contains  wax esters, triglycerides, and  squalene, all of  which protect  the  skin  from  the  environment. Certain  individuals  receiving  cholesterol-reducing  drugs  exhibit  dry  skin. Natural  moisturizing  factor,  a  substance  that  retains  water inside  keratinocytes  and  renders  them  plump,  also  plays  an important role in the pathophysiology of dry skin. Defects  in  the  stratumcorneum or barrier can result  in  transepidermal  water  loss,  which  dehydrates  the  skin  and  imparts a  dry  appearance.  An  impaired  barrier  may  also  make  skin more  susceptible  to  damage  from  exogenous  sources  such  as plants,  chemicals,  and even water.

Atoms look like miniature solar systems

 No one has ever seen an atom and no one ever will.  Atoms are so complex that they cannot be described in terms that laymen can understand. Scientists are constantly learning new things about the way atoms behave and are discovering more and more new particles within the atom. Our concept of an atom resembling a tiny solar system is nothing more than a ‘model’  – in other words, we are trying to describe something we can’t  fully understand in terms of something we can  understand.

Electrons are tiny particles that orbit the atom’s nucleus

Again, this is only a model to help us visualise what ‘might’ be going on inside the atom. In reality, this is unlikely to be the case. Electrons behave both as charged particles  and  as waves. Sometimes, scientists  fi nd it convenient to think of them as charged particles; at other times, they  fi nd it convenient to think of them as waves. In reality, they could be neither but something else completely!

An electric current is always a flow of free electrons

This is only true in the case of metallic conductors, such as copper and aluminium.  This is not necessarily the case in semiconductors, liquids and gases!  A  far better defi nition  of current is that it is a ‘fl ow of charges’.

Current flows at the speed of light

While the  effect  of current within a conductor may be detected more or less instantaneously, individual electrons drift along  very  slowly. Research suggests that an individual electron will not travel the length of a  fl ashlight’s  fi lament within the lifetime of that  fl ashlight’s  battery!

Conductors have lots of free electrons, therefore they must be negatively charged

Although conductors do have large numbers of free electrons, for every free electron, there is a corresponding proton within the atoms or positive ions. So conductors don’t have an overall charge; they are neutral.

Insulators ‘block’ current flow

Insulators don’t ‘block’ current  fl ow; they simply don’t have suffi cient charge carriers to  support current  fl ow.

Insulators contain few free electrons

Insulators actually contain billions of free electrons per cubic millimetre but, compared to conductors, this  fi gure is relatively small and certainly insuffi cient to support current  fl ow.

‘Conventional flow’ is a fl ow of positive charges in the opposite direction to electrons.

No. ‘Conventional  fl ow’ isn’t a  fl ow of anything. It’s simply a ‘direction’, mistakenly chosen, for current, from positive to negative.

The typical symptoms of diabetes occur as a result of the high levels of glucose in the bloodstream and its passage into the urine and other tissues. These are frequent urination and thirst. Thirst arises as a result of the dehydration caused by the frequent urination. Dehydration and loss of nutrient calories in the urine lead to weight loss and hunger. Passage of glucose into the tissues of the eye can cause fluctuating degrees of blurred vision. When these symptoms are prolonged and severe, as is typical with type 1 diabetes, serious changes occur in our blood chemistry due to the deficiency of insulin. Those changes, coupled with dehydration, result in dizziness, weakness, drowsiness, and ultimately coma, which if untreated can lead to death. Both type 1 and type 2 diabetes, when severe and inadequately treated, can be associated with coma and death. Although coma is less common in type 2 diabetes, it is more common for it to result in death, as people with type 2 diabetes tend to be older and to have more medical problems. Two other important points are worth noting. The first is that diabetes may not cause any symptoms. In fact, one of every four people believed to have diabetes is unaware of it and is undiagnosed. However, as diabetes of even moderate severity can lead to complications and shorten lifespan, it is important to make the diagnosis, even in people without symptoms. The second point is that the majority of people with diabetes may not have any symptoms from the elevated blood sugar, but it can still present with symptoms from its complications. Thus, people may be diagnosed with diabetes after presenting with symptoms of nerve damage or a heart attack or stroke. In fact, one of every three people admitted with a sudden heart event is found to have diabetes or  prediabetes of which he or she or the doctor was unaware. Neuropathy is present in two of every five patients with type 2 diabetes at the time of diagnosis, while eye damage is present in one of every five and kidney damage is present in one in ten, indicating that the diabetes was ongoing for many months or even years before diagnosis.

The son of a physician to  the royal family of Macedon, Aristotle was born in Stagira, Chalcidice, in the northeast of modern Greece. He was sent to Athens at 17 to study with Plato at the Academy, and remained there until Plato’s death 20 years later. Surprisingly, Aristotle was not appointed Plato’s successor to lead the Academy. He moved to Ionia, where he made a study of wildlife, until he was invited by Philip of Macedon to be tutor to the young Alexander the Great. Aristotle returned to Athens in 335 BCE to establish a rival school to the Academy, at the Lyceum. While teaching there, he formalized his ideas on the sciences, philosophy, and politics, compiling a large volume of writings, of which few have survived. After the death of Alexander in 323 BCE, anti-Macedonian feeling in Athens prompted him to leave the city for Euboea, where he died the following year.