Mendel’s theory of Genetics

Mendel was curious about how traits were transferred from one generation to the next, so he set out to understand the principles of heredity in the mid-1860s. Peas were a good model system, because he could easily control their fertilization by transferring pollen with a small paintbrush. This pollen could come from the same flower (self-fertilization), or it could come from another plant’s flowers (cross-fertilization). First, Mendel observed plant forms and their offspring for two years as they self-fertilized, or “selfed,” and ensured that their outward, measurable characteristics remained constant in each generation. During this time, Mendel observed seven different characteristics in the pea plants, and each of these characteristics had two forms (Figure 3). The characteristics included height (tall or short), pod shape (inflated or constricted), seed shape (smooth or winkled), pea color (green or yellow), and so on. In the years Mendel spent letting the plants self, he verified the purity of his plants by confirming, for example, that tall plants had only tall children and grandchildren and so forth. Because the seven pea plant characteristics tracked by Mendel were consistent in generation after generation of self-fertilization, these parental lines of peas could be considered pure-breeders (or, in modern terminology, homozygous for the traits of interest). Mendel and his assistants eventually developed 22 varieties of pea plants with combinations of these consistent characteristics.

Mendel not only crossed pure-breeding parents, but he also crossed hybrid generations and crossed the hybrid progeny back to both parental lines. These crosses (which, in modern terminology, are referred to as F1, F1 reciprocal, F2, B1, and B2) are the classic crosses to generate genetically hybrid generations

When conducting his experiments, Mendel designated the two pure-breeding parental generations involved in a particular cross as P1 and P2, and he then denoted the progeny resulting from the crossing as the filial, or F1, generation. Although the plants of the F1 generation looked like one parent of the P generation, they were actually hybrids of two different parent plants. Upon observing the uniformity of the F1 generation, Mendel wondered whether the F1 generation could still possess the non dominant traits of the other parent in some hidden way.

When looking at the figure, notice that for each F1 plant, the self-fertilization resulted in more round than wrinkled seeds among the F2 progeny. These results illustrate several important aspects of scientific data:

  1. Multiple trials are necessary to see patterns in experimental data.
  2. There is a lot of variation in the measurements of one experiment.
  3. A large sample size, or “N,” is required to make any quantitative comparisons or conclusions.

In Figure 4, the result of Experiment 1 shows that the single characteristic of seed shape was expressed in two different forms in the F2 generation: either round or wrinkled. Also, when Mendel averaged the relative proportion of round and wrinkled seeds across all F2 progeny sets, he found that round was consistently three times more frequent than wrinkled. This 3:1 proportion resulting from F1 x F1 crosses suggested there was a hidden recessive form of the trait. Mendel recognized that this recessive trait was carried down to the F2 generation from the earlier P generation.



Heat Transfer


Heat can be transferred from place to place in measurable quantities. Heat can be transferred in three ways, which are; by conduction, convection and radiation.

Heat transfer by Conduction.

Heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighbouring atoms and molecules, transferring some of their energy (heat) to these neighbouring particles. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another.

NOTE: The rate of heat flow is proportional to Difference in temperature. This means that no flow of heat if there is no difference in temperature.

It is known that the rate of heat flow, in Joules per second(J/s)through a substance is proportional to the difference in temperature between its ends. Thus,

ΔQ/Δt = kA (T2 – T1)/L

Therefore, K = QL/A(T2 – T1)

Where ΔQ/Δt is the rate of heat flow,

A is the cross-sectional area,

T2 is the higher Temperature, T1 is the lower temperature

L is the distance(m) between the two ends at temperatures T1 and T2,

K is the constant of proportionality, known as the thermal conductivity. The S.I unit of thermal conductivity is Joule per seconds, per meter, per degree Celsius(J/s./m/C) or Watt per meter, per Kelvin (Wm-1K-1)

Note: materials with high thermal conductivity(k) value are known as good conductors while materials with a small thermal conductivity value, are known as insulators.

Note: The temperature gradient is equal to (T2 – T1)/L

U values and R-Value

The R-Value combines the thickness l, and the thermal conductivity k, in one number. It is directly proportional to the material thickness. R is a property attributed to a slab of a specified thickness

R = L/k

The lower the thermal conductivity of the material of which a slab is made, the higher the R-value of the slab.

The U value of a building element is the inverse of the total thermal resistance of that element. The U-value is a measure of how much heat is lost through a given thickness of a particular material.

U = k/L

Inserting this equation into the equation above,

ΔQ/Δt = UA(T2 – T1)


Question 1: Calculate the thermal conductivity through a conductor when 30 kW of heat flows through it having a length of 4 m and area of 12 m2m2 if the temperature gradient is 40 K.

Given :
Heat flow Q = 30 kW, length L = 4 m, Area A = 12 m2, temperature difference ΔT = 40 K.

The thermal conductivity is given by,
k = QL/AΔT
= (30000×4)/(12×40)
= 250 W/m K.

2.A major source of heat loss from a house is through the windows. Calculate the rate of heat flow through a glass window 2.0m x 1.5m in area and 3.2mm thick, if the temperatures at the inner and outer sufaces are 15.00C and 14.00C, respectively. ( k = 0.84J/s./m/C)


Given Values;

A = 2.0 x 1.5 = 3.0m2, l = 3.2mm = 3.2 x 10-3m, T1 = 15.00C, T2 = 14.00C

Rate of heat flow ΔQ/Δt = kA (T1 – T2)/L

Therefore, ΔQ/Δt = 0.84 x 3.0 (15.0 – 14.0)/3.2 x 10-3

= 2.52 (1.0)/3.2 x 10-3

= 2.25/3.2 x 10-3

= 787.5J/s.

Crop Production (Energy Crop)

What are Energy Crop?

Energy crops are a type of biomass. Biomass is any organic matter which is available on a renewable basis through natural processes or as a by-product of human activity such as agricultural crops and crop residues, wood and wood waste, and portions of the municipal solid waste stream. Biomass is used to generate electricity, and to produce fuels and other consumer products.

KEY POINT: *Some Energy crops are grown specifically for use as fuel and offer high output per hectare with low inputs*

An energy crop is a plant grown as a low-cost and low-maintenance harvest used to make biofuels, such as bioethanol, or combusted for its energy content to generate electricity or heat. Energy crops are generally categorized as woody or herbaceous plants; many of the latter are grasses.

Some examples of energy crops are rapeseed, maize seed, soybean, castor seed, sesame, groundnut kernel, mustard seed, sun flower, palm fruit, and  grasses.Two leading non-food crops for the production of cellulosic bioethanol are switchgrass and giant miscanthus.


Energy crops can be used for a range of energy markets, for dedicated biomass power stations or co-firing at existing coal power stations.

On a smaller scale the crop can be burnt directly as chip (or bought pelletised) on farm to generate heat, qualifying under the Renewable Heat Initiative as it is now more widely densified into energy crop pellets for use in dedicated boilers at home or in business.

Energy crops can be used to generate electricity, and for the production of transportation fuels such as ethanol.

In electricity Generation, Energy crops could fuel a significant number of energy production facilities in the United States. According to a report by the Union of Concerned Scientists, energy crops and crop residues could potentially generate the same amount of electricity generated by coal in the Midwest.

Another way energy crops can be used to generate electricity is in a steam boiler, which is the same process used to convert coal to electricity. Energy crops can be used alone or cofired with coal.


What is matter:  matter is made of atoms. Atoms are the smallest particle of matter. They are so small that you cannot see them with your eyes or even with a standard microscope. A standard sheet of paper is about a million atoms thick. Matter is the air you are breathing. Matter is the computer you are reading from now. Matter is the stuff you touch and see. And it is more. Matter is defined as anything that has mass and takes up space.


Some states(phases) of matter are;

1. SOLIDS:  Solids hold their shape at room temperature. The pencil that you left in the desk at school will still be the same shape when you return tomorrow.


Even in solids there is a small space between the atoms. Depending on how tight the atoms are packed determines the density matter. This means that a one inch block of wood is not as dense as a one inch block of gold. There is more space between the atoms of the wood than the atoms of the gold.

2. LIQUIDS: Liquids do not hold their shape at room temperature. There is space between the atoms of a liquid and they move slightly all of the time. This allows you to stick your finger into water and pull it back out, letting the water fill back in where your finger once was. When a solid is heated above its melting point, it becomes liquid, given that the pressure is higher than the triple point of the substance.

3.GASES: A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container.In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small (or zero for an ideal gas), and the typical distance between neighboring molecules is much greater than the molecular size. A gas has no definite shape or volume, but occupies the entire container in which it is confined. A liquid may be converted to a gas by heating at constant pressure to the boiling point, or else by reducing the pressure at constant temperature.

4. PLASMA: Plasma does not have definite shape or volume. Unlike gases, plasmas are electrically conductive, produce magnetic fields and electric currents, and respond strongly to electromagnetic forces. Positively charged nuclei swim in a “sea” of freely-moving disassociated electrons, similar to the way such charges exist in conductive metal. In fact it is this electron “sea” that allows matter in the plasma state to conduct electricity. Lightning, electric sparks, fluorescent lights, neon lights, plasma televisions, some types of flame and the stars are all examples of illuminated matter in the plasma state.

5. Bose-Einstein condensates: In 1995, technology enabled scientists to create a new state of matter, theBose-Einstein condensate (BEC). Using a combination of lasers and magnets, Eric Cornell and Carl Weiman cooled a sample of rubidium to within a few degrees of absolute zero. At this extremely low temperature, molecular motion comes very close to stopping altogether. Since there is almost no kinetic energy being transferred from one atom to another, the atoms begin to clump together. There are no longer thousands of separate atoms, just one “super atom.” A BEC is used to study quantum mechanics on a macroscopic level. Light appears to slow down as it passes through a BEC, allowing study of the particle/wave paradox. A BEC also has many of the properties of a superfluid — flowing without friction. BECs are also used to simulate conditions that might apply in black holes.



The equilibrium price is where the supply of goods matches demand. When a major index experiences a period of consolidation or sideways momentum, it can be said that the forces of supply and demand are relatively equal and that the market is in a state of equilibrium.
A market is in equilibrium when no economic agent in the market has any reason to alter his or her behavior. This is the case at the equilibrium price. That is, there is no reason for Price to change unless either the supply or the demand changes.

An increase in demand causes the demand curve to shift out, which generates a higher price and induces suppliers to increase the quantity supplied. What can cause demand to shift? Demand shifts when income, the price of a substitute or complement, consumer expectations, population, or consumer tastes change.



The supply curve is always upward sloping left to right, with the demand curve downward sloping. The intersection of these curves indicate the equilibrium price point, or the price at which a supplier can offer goods and a consumer is willing to purchase them.

Introduction of a New Technology changes cause shifts along the supply and demand curves, which effectively moves the equilibrium price point up or down. For example, new technology developed in 1999 resulted in a reduction in the cost of manufacturing flat screen televisions that used liquid crystal displays. The  new technology cause an increase in the supply of flat screen televisions and a decrease in price of flat screen televisions.

An improvement in technology tends to reduce the costs of production; cheaper production costs generate an increase in supply, this leads to an increase in demand.

If a good becomes obsolete because technology has produced an effective substitute good that performs the same function at a lower price, demand will drastically shift inward from right to left. This lowers the equilibrium price point to levels where suppliers cannot profitably supply the good.

As the number of firms in a market decreases, the supply curve will shift to the left and the equilibrium price will rise.



Tastes are assumed to be relatively stable over time.A change in demand cannot be attributed to a change in tastes before other possible reasons for the change are carefully considered. The law of demand states that the relationship between price and quantity demanded is an inverse relationship, i.e., that fewer units are demanded at higher prices than at lower prices. Demand reflects consumers’ willingness and ability to buy the commodity.

A change in consumer tastes can cause a shift in demand, thereby causing a decrease in supply, resulting to a reduction in price. Again, make sure you understand the difference between a change in the quantity demanded and a change in demand. A change in quantity demanded is caused by a change in the price of the good itself; a change in demand is caused by a change in one of the other factors of demand.



Taxes reduce both demand and supply, and drive market equilibrium to a price that is higher than without the tax and a quantity that is lower than without the tax.

If buyers have many alternatives to a good with a new tax, they will tend to respond to a rise in price by buying other things and will, therefore, not accept a much higher price. If sellers easily can switch to producing other goods, or if they will respond to even a small reduction in payments by going out of business, then they will not accept a much lower price. The incidence of the tax will tend to fall on the side of the market that has the least attractive alternatives and, therefore, has a lower elasticity.

Without a tax, the equilibrium price will be at Pe and the equilibrium quantity will be at Qe.After a tax is imposed, the price consumers pay will shift to Pc and the price producers receive will shift to Pp. The consumers’ price will be equal to the producers’ price plus the cost of the tax. Since consumers will buy less at the higher consumer price (Pc) and producers will sell less at a lower producer price (Pp), the quantity sold will fall from Qe to Qt.

Diagram illustrating taxes effect


A subsidy shifts either the demand or supply curve to the right, depending upon whether the buyer or seller receives the subsidy. If it is the buyer receiving the subsidy, the demand curve shifts right, leading to an increase in the quantity demanded and the equilibrium price. If the seller receives the subsidy, the supply curve shifts right and the quantity demanded will increase, while the equilibrium price decreases.

Marginal subsidies on production will shift the supply curve to the right until the vertical distance between the two supply curves is equal to the per unit subsidy; when other things remain equal, this will decrease price paid by the consumers (which is equal to the new market price) and increase the price received by the producers. Similarly, a marginal subsidy on consumption will shift the demand curve to the right; when other things remain equal, this will decrease the price paid by consumers and increase the price received by producers by the same amount as if the subsidy had been granted to producers. However, in this case, the new market price will be the price received by producers. The end result is that the lower price that consumers pay and the higher price that producers receive will be the same, regardless of how the subsidy is administered.




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The word cargo refers in particular to goods or produce being conveyed – generally for commercial gain – by ship, boat, or aircraft, although the term is now often extended to cover all types of freight, including that carried by train,van, truck, or intermodal container.

Freight is usually organized into various shipment categories before it is transported. An item’s category is determined by:

  • the type of item being carried. For example, a kettle could fit into the category ‘household goods’.
  • how large the shipment is, in terms of both item size and quantity.
  • how long the item for delivery will be in transit.

Shipments are typically categorized as household goods, express, parcel, and freight shipments.



Freight is used especially when you transport goods by a train or by a truck. The goods become cargo when they are transported by a ship or by a plane.

Cargo and Freight are two terms related to transporting of goods. The term “freight” is used when the volume of goods are loaded on a semi-trailer on a truck or on a semi-trailer on a train. This is the main reason why there is a freight truck and a freight train. The “freight” is also the term used for the payment when the certain goods are transported. However, freight can also mean a cargo being transported via truck, train, plane, and ship. But mail can’t be considered as freight. Freight can refer to many things. It may mean the product, merchandise, amount payable, or money charged. Most cargo being transported can be referred to as freight.

“Cargo,” on the other hand, is usually used when the goods are transported via plane or ship. This is the main reason why there are cargo ships and cargo planes. Mail may also be called cargo. The term “cargo” is used specifically on goods only; it does not mean the payment or the money being charged for the transport. This means any product that is being transported is always called a cargo. Containers are usually used in transporting the goods called cargo.



The categories of cargoes include;

1. Gas Cargo

Gas is one of the more unusual cargoes to move across our oceans. In its raw state, it has none of the free-flowing, easy-to-load properties of liquid cargoes, such as crude oil and grain. So, to make it easier to transport it is converted into that same liquid state by extreme cooling or pressurisation.

The gas itself is normally propane or methane, known as LPG (link to gas in dictionary) and LNG (link to gas in dictionary) respectively and can be used in a variety of applications from environmentally-friendly fuels and refrigerant to propellant in packaged aerosols and in industrial chemical processes.

2. Liquid Bulk Cargo

All of us will have come across liquid bulk cargoes in everyday life in one from or another. From gasoline to fuel our cars, to fruit juices and cooking oil for consumption in the home, it’s difficult to live the lives we live today without them.

These free-flowing liquid cargoes, which also include crude oil, liquefied natural gas and chemicals, are not boxed, bagged or hand stowed. Instead, they are poured into and sucked out of large tank spaces, known as the holds, of a tanker.

3. Dry Bulk Cargo

 From grains to coal and from sugar to cocoa, dry bulk cargoes cover a range of produce and raw materials that have two features in common: they are unpacked and are homogeneous. These two properties make it easier for dry bulk cargoes to be dropped or poured into the hold of a bulk carrier.

As the name suggests, dry bulk cargoes need to be kept dry, any moisture that finds its way into the cargo could ruin the entire load, at considerable cost to the ship owner. It may also be surprising to learn that many dry bulk cargoes are classified as ‘Dangerous Goods’ requiring special attention during loading, transportation and discharge, as they could shift during shipment, causing ship instability.

4. Refrigerated Food Cargo

When we go to the supermarket to buy fresh produce, most of us do not stop to consider where that produce has travelled from. In fact, you may be surprised to learn that less than half the apples sold in major British supermarkets originate from Britain; more likely they have come from European Union states, or even as far a field as New Zealand.

Such fragile and time sensitive cargoes require special transportation that will keep goods at the right temperature to maintain freshness, run to strict schedules to ensure that the produce reaches its final destination in the optimum condition. To meet these demands, special refrigerated cargo ships house temperature-controlled containers suitable for the safe carriage of chilled or frozen cargoes, referred to reefer containers.

A wide range of commodities are shipped under refrigeration, including: fresh fruits and vegetables, fresh and frozen meats, poultry, and seafood, dairy products and eggs, fresh juices and frozen concentrates, and live plants and flowers.

 5. Special Purpose Cargo

There are many different types of cargoes shipped around the world, some more unusual than others. While containers, crude oil and dry bulk get the most attention, other cargoes that fall outside of these categories are just as important to daily life.

Over-sized goods, such as a non-motorised barges or road sections, are one such cargo, while heavy cargoes, such as industrial generators and reactors, also require special treatment. Another specialist cargo is livestock, which needs to be transported in comfortable surroundings so that the cattle or sheep reach their final destination undistressed and in optimum condition.

6. Passengers

It is not just commodities that move from A to B by ship: many of us have experienced life at sea as a cargo, simply by taking a cross-Channel ferry from Dover to Calais. With the many safety and quality considerations necessary for carrying passengers, a cargo of people is in fact not so different to the many others of cargoes carried.

Passenger ships need to cater for the demands of people, be that with the provisions of seating, refreshments, entertainment and/or sleeping facilities. For passenger ships on longer journeys, a huge amount of food and fresh water stores need to be on board and there must be proper facilities for the storage of waste water and the massive amount of rubbish generated.

7. Unitised Cargo

Manufactured products and perishable goods come in a variety of shapes and sizes, often with considerable storage constraints. Consequently, these cargoes need to be treated very differently to free-flowing dry bulk cargoes, like grain.

Unitised cargoes can be very diverse, covering forest products, metals and metal goods, machines, electronics, food chemicals, raw materials, and investment and consumer goods, among others.



Reference: Marine Soft tech.

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Electrolysis is a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is also important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell.

It also refers to the decomposition of a substance by an electric current. The electrolysis of sodium and potassium hydroxides, first carried out in 1808 by Sir Humphrey Davey, led to the discovery of these two metallic elements and showed that these two hydroxides which had previously been considered un-decomposable and thus elements, were in fact compounds

Electrolysis of molten alkali halides is the usual industrial method of preparing the alkali metals:

Na+ + e → Na(l) = –2.71 v
Cl → ½ Cl2(g) + e = –1.36 v
Na+ + Cl → Na(l) + ½ Cl2(g) = –4.1 v


Ions in aqueous solutions can undergo similar reactions. Thus if a solution of nickel chloride undergoes electrolysis at platinum electrodes, the reactions are

Ni2+ + 2 e → Ni(s) = –0.24 v
2 Cl → Cl2(g) + 2 e = –1.36 v
Ni2+ + 2 Cl → Ni(s) + Cl2(g) = –1.60 v




First law of electrolysis

In 1832, Michael Faraday reported that the quantity of elements separated by passing an electric current through a molten or dissolved salt is proportional to the quantity of electric charge passed through the circuit. This became the basis of the first law of electrolysis:

m = k \cdot q


m = eQ

where; e is known as electrochemical equivalent of the metal deposited or of the gas liberated at the electrode.

Second law of electrolysis

Faraday discovered that when the same amount of current is passed through different electrolytes/elements connected in series, the mass of substance liberated/deposited at the electrodes is directly proportional to their equivalent weight.



Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced. Negatively charged ions move to the positive electrode during electrolysis.




A metallic object to be plated with copper is placed in a solution of CuSO4.

a) To which electrode of a direct current power supply should the object be connected?
b) What mass of copper will be deposited if a current of 0.22 amp flows through the cell for 1.5 hours?


a) Since Cu2+ ions are being reduced, the object acts as a cathode and must be connected to the negative terminal (where the electrons come from!)

b) The amount of charge passing through the cell is

(0.22 amp) × (5400 sec) = 1200 c
(1200 c) ÷ (96500 c F–1) = 0.012 F

Since the reduction of one mole of Cu2+ ion requires the addition of two moles of electrons, the mass of Cu deposited will be

(63.54 g mol–1) (0.5 mol Cu/F) (.012 F) = 0.39 g of copper.


How long must a 20.0 amp current flow through a solution of ZnSO4 in order to produce 25.00 g of Zn metal.


  • Convert the mass of Zn produced into moles using the molar mass of Zn.

Mass of Zn = 25.00g, molarmass of Zn = 65gmol-1

Mole = mass/molarmass

Mole = 25/65 = 0.3846mol

  • Write the half-reaction for the production of Zn at the cathode.

Zn2+(aq) + 2e  Zn(s)

  • Calculate the moles of e required to produce the moles of Zn and convert the moles of electrons into coulombs of charge using Faraday’s constant.

1 mole of Zn liberate 2F (2 x 96500)C

0.386 mole will liberate: (2 x 96500 x 0.3846/1) = 74231C

  • Calculate the time using the current and the coulombs of charge.

Q = I x t

t = Q / I

t = 74231/20

t = 3712secs = 62 minutes = 1.03hr

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INVENTORY or stock refers to the goods and materials that a business holds for the ultimate purpose of resale. Inventory is often the largest item in the current assets category, and must be accurately counted and valued at the end of each accounting period to determine a company’s profit or loss.


Inventories are assets items for sale in the ordinary course of business or goods that will be used or consumed in the production of goods to be sold. The investment in inventories is frequently the largest current asset of merchandising and manufacturing businesses. Therefore description and measurement of inventory require careful attention.

Inventories encompass goods purchased and held for resale, for example,merchandise purchased by a retailer and held for resale, computer software held for resale, or land and other property held for resale. Inventories also encompass finished goods produced, or work in progress being produced, by the enterprise and include materials, maintenance supplies, consumables and loose tools awaiting use in the production process. Inventories do not include machinery spares which can be used only in connection with an item of fixed asset and whose use is expected to be irregular; such machinery spares are accounted for in accordance with Accounting Standard (AS) 10, Accounting for Fixed Assets.


Merchandising Companies:

Inventories are assets items for sale in the ordinary course of business or goods that will be used or consumed in the production of goods to be sold. The investment in inventories is frequently the largest current asset of merchandising and manufacturing businesses. Therefore description and measurement of inventory require careful attention.A merchandising company ordinarily purchases its merchandise in a form ready for sale. It reports the cost assigned to unsold units left on hand as merchandise inventory. Only one inventory account, merchandise inventory, appears in the financial statements. Example of such a merchandising company is Wal-Mart.

Manufacturing Companies:

Manufacturing companies produce goods which may be sold to merchandising companies as well as directly to customers. Manufacturing companies normally have three inventory accounts. These are:

  • Raw materials

  • Work in process

  • Finished goods

Raw Materials:

The cost assigned to goods and materials on hand but not yet placed into production is reported as raw materials inventory. Examples include the wood to make a base ball bat and the steel to make a car. These materials can be traced directly to the end product.

Work in Process:

Some units are not completely processed at any point in a continuous process. The cost of the raw material on which production has been started but not completed, plus the direct labor cost applied specifically to this material and a ratable share of manufacturing overhead costs, constitute the work in process inventory.

Finished Goods Inventory:

The costs identified with the completed but unsold units on hand at the end of the fiscal period are reported as finished goods inventory .


Perpetual Inventory System:

Under a perpetual inventory system, a continuous record of changes in inventory is maintained in the inventory accounting. That is, all purchases and sales (issues) of goods are recorded directly in the inventory account as they occur.

The accounting features of a perpetual inventory system are:

  1. Purchases of merchandise for resale or raw materials for production are debited to inventory rather than to purchases.

  2. Freight-in, purchases returns and allowances, and purchase discounts are recorded in inventory rather than in separate accounts.

  3. Cost of goods sold is recognized for each sale by debiting the account cost of goods sold, and crediting inventory.

  4. Inventory is a control account that is supported by a subsidiary ledger of individual inventory records. The subsidiary records show the quantity and cost of each type of inventory on hand.

The perpetual inventory system provides a continuous record of the balances in both the inventory account and the cost of goods sold account.

A method of accounting for inventory that records the sale or purchase of inventory in near real-time, through the use of computerized point-of-sale and enterprise asset management systems. Perpetual inventory provides a highly detailed view of changes in inventory and allows real-time reporting of the amount of inventory in stock, hence, accurately reflecting the level of goods on hand.

Under a computerized recordkeeping system, additions to and issuance from inventory can be recorded nearly instantaneously. The popularity and affordability of computerized accounting software have made the perpetual system cost-effective for many kinds of businesses. Recording sales with optical scanners at the cash register has been incorporated into perpetual inventory systems at many retail stores.

Periodic Inventory System:

Under a periodic inventory system, the quantity of inventory on hand is determined, as its name implies, on the periodically. all acquisitions of inventory during the accounting period are recorded by debits to a purchases account. The total in the purchases account at the end of the accounting period added to the cost of the inventory on hand at the beginning of the period to determine the total cost of the goods available for sale during the period. Ending inventory is subtracted from the cost of goods available for sale to compute the cost of goods sold. Note that under a periodic inventory system, the cost of goods sold is a residual amount that is dependent upon a physical count of the ending inventory.

The physical inventory count required by a periodic system is taken once a year at the end of the year. However, most companies need more current information regarding their inventory levels to protect against stock outs or over purchasing and to aid in the preparation of monthly or quarterly financial data. As a consequence, many companies choose a modified perpetual inventory system in which increases and decreases in quantities only – not dollar amounts – are kept in a detailed inventory record.  It is merely a memorandum device outside the double entry system which helps in determining the level of inventory at any point in time.

Whether a company maintains a perpetual inventory in quantities and dollars, quantities only, or has no perpetual inventory record at all, it probably takes a physical inventory once a year. No matter what type of inventory records are in use or how well organized procedures for recording purchases and requisitions, the danger of loss and error is always present. Waste, breakage, theft, improper entry, failure to prepare or record requisitions, and any number of similar possibilities may cause the inventory records to differ from the actual inventory on hand. This requires periodic verification of the inventory records by actual count, weight, or measurement. These counts are compared with the detailed inventory records. The records are corrected to agree with the quantities actually on hand.

Insofar as possible, the physical inventory should be taken near the end of a company’s fiscal year so that correct inventory quantities are available for use in preparing annual accounting reports and statements. Because this is not always possible, however, physical inventories taken within two or three months of the year’s end are satisfactory, if the detailed inventory records are maintained with a fair degree of accuracy.


A company had the following transactions during the current year.

Beginning inventory  100 units at $6 = $600
Purchases  900 units at $6 = $5,400
Sales  600 units at $12 = $7,200
Ending inventory  400 units at $6 = $2,400

The entries to record these transactions during the current year are shown below:

Perpetual Inventory System Periodic Inventory System
1. Beginning inventory, 100 units at $6:
The inventory account shows the inventory on hand at $600
2. Purchase 900 units at $6:


     Accounts Payable


3. Sale of 600 units at $12:
Accounts receivable




Cost of goods sold




4. End of Period Entries for Inventory Accounts:
No entry necessary
1. Beginning inventory, 100 units at $6:
The inventory account shows the inventory on hand at $600
2. Purchase 900 units at $6:
Purchases 5,400
     Accounts Payable 5,400
3. Sale of 600 units at $12:
Accounts receivable 7,200


No Entry

4. End of Period Entries for Inventory Accounts:
Inventory (Ending by count) 2,400
Cost of goods sold 3,600
     Purchases 5,400
     Inventory (beginning) 600

When a perpetual inventory system is used and a difference exists between the perpetual inventory balance and physical count, a separate entry is needed to adjust the perpetual inventory account. Assume that at the end of the reporting period, the perpetual inventory account reported an inventory balance of $4,000, but a physical count indicated $3,800 was actually on hand. The entry to record the necessary write-down is as follows:

Inventory over and short 200


Perpetual inventory overages and shortages generally represent a misstatement of cost of goods sold. The difference is a result of normal and expected shrinkage, breakage, shoplifting, incorrect record keeping, and the like. Inventory over and short would therefore be adjustment of cost of goods sold. In practice, the account inventory over and short is sometimes reported in the “Other revenues and Gains” or “Other Expenses and Losses” section of the income statement, depending on its balance.

In a periodic inventory system, the account inventory over and short does not arise because there are no accounting records available against which to compare the physical count. Thus, inventory overage and shortages are buried in cost of goods sold.


The marketing mix is a business tool used in marketing and bymarketers. The marketing mix is often crucial when determining a product or brand’s offer, and is often associated with the four P’s: price, product, promotion, and place.

In service marketing, however, the four Ps are expanded to the seven P’sor Seven P’s to address the different nature of services.

The term “marketing-mix” was first coined by Neil Borden, the president of the American Marketing Association in 1953. It is still used today to make important decisions that lead to the execution of a marketing plan. The various approaches that are used have evolved over time, especially with the increased use of technology.

Besides, with the advent of digital marketing, marketers are suggesting new P’s, or are saying that digital marketing has changed the way these P’s used to work.

The new P’s:

  • People
  • Participate
  • Personalize
  • Product
  • Process
  • Pay
  • Partner

But many, including Illinois University, suggest that the P’s have only changed and there is no need for new P’s. The way these P’s have changed is discussed here by using the first two P’s only. Product has new terms introduced. Now products are not developed by a company alone; the concept of co-creation and crowd sourcing have jumped in. Promotion is carried out with user created content.

It’s simple! You just need to create a product that a particular group of people want, put it on sale some place that those same people visit regularly, and price it at a level which matches the value they feel they get out of it; and do all that at a time they want to buy. Then you’ve got it made!

There’s a lot of truth in this idea. However, a lot of hard work needs to go into finding out what customers want, and identifying where they do their shopping. Then you need to figure out how to produce the item at a price that represents value to them, and get it all to come together at the critical time.

But if you get just one element wrong, it can spell disaster. You could be left promoting a car with amazing fuel-economy in a country where fuel is very cheap; or publishing a textbook after the start of the new school year, or selling an item at a price that’s too high – or too low – to attract the people you’re targeting.

The marketing mix is a good place to start when you are thinking through your plans for a product or service, and it helps you avoid these kinds of mistake

KEY NOTE: The 4Ps of marketing is just one of many lists that have been developed over the years. And, whilst the questions we have listed above are key, they are just a subset of the detailed probing that may be required to optimize your marketing mix.



  • What does the customer want from the product /service? What needs does it satisfy?
  • What features does it have to meet these needs?
    • Are there any features you’ve missed out?
    • Are you including costly features that the customer won’t actually use?
  • How and where will the customer use it?
  • What does it look like? How will customers experience it?
  • What size(s), color(s), and so on, should it be?
  • What is it to be called?
  • How is it branded?
  • How is it differentiated versus your competitors?
  • What is the most it can cost to provide, and still be sold sufficiently profitably?



  • What is the value of the product or service to the buyer?
  • Are there established price points  for products or services in this area?
  • Is the customer price sensitive? Will a small decrease in price gain you extra market share?
  • Or will a small increase be indiscernible, and so gain you extra profit margin?
  • What discounts should be offered to trade customers, or to other specific segments  of your market?
  • How will your price compare with your competitors?



  • Where do buyers look for your product or service?
  • If they look in a store, what kind? A specialist boutique or in a supermarket, or both? Or online? Or direct, via a catalogue?
  • How can you access the right distribution channels?
  • Do you need to use a sales force? Or attend trade fairs? Or make online submissions? Or send samples to catalogue companies?
  • What do your competitors  do, and how can you learn from that and/or differentiate?


  • Where and when can you get across your marketing messages to your target market?
  • Will you reach your audience by advertising online, in the press, or on TV, or radio, or on billboards? By using direct marketing mailshot? Through PR? On the Internet?
  • When is the best time to promote? Is there seasonality in the market? Are there any wider environmental issues that suggest or dictate the timing of your market launch, or the timing of subsequent promotions?
  • How do your competitors do their promotions? And how does that influence your choice of promotional activity?



Marketing activation is the execution of the marketing mix  as part of the marketing process. The activation phase typically comes after the planing phase during which managers plan their marketing activities and is followed by a feedback phase in which results are evaluated with marketing analytics.

Before executing its marketing activities, a firm will benefit from identifying which customer groups to target. “By focusing on some fewer influencers only, activation can become more efficient and higher returns can be expected.”

Customer data is a significant source of information for planning marketing activation. A common practice is to use customer relationship management tools and techniques to augment the impact of marketing activation because CRM “provides an integrative framework in which marketing activation and customer activities collaborate to increase patronage.

Brand activation, sometimes called brand engagement which focuses on building a longer term emotional connection between the brand and the customer; and activation based on direct-response marketing will focus on generating immediate sales transactions are two types of Marketing activation which are used as part of Marketing Strategy. 

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