A:

Opportunity Cost and Social Cost: Explanation and Impact on Government Decision to Develop a New Oil Field in Kribi

1. Opportunity Cost

Definition and Explanation:
Opportunity cost refers to the value of the next best alternative that is foregone when a decision is made. It is not just about monetary costs but also includes the benefits that could have been obtained from the alternative use of resources. For example, if the government allocates land and capital to develop an oil field in Kribi, the opportunity cost might be the benefits from investing that same land and capital into agriculture or tourism instead.

Example:
Suppose the government chooses to develop the oil field. The opportunity cost could be the potential income from tourism if the land were preserved as a national park, or the benefits from expanding agriculture in the region.

2. Social Cost

Definition and Explanation:
Social cost encompasses all the costs to society resulting from an economic activity, including both private costs (borne directly by the producer or consumer) and external costs (costs imposed on third parties or the environment). Externalities such as environmental pollution, health hazards, and loss of biodiversity are key components of social costs.

Example:
Developing the oil field might generate economic benefits such as revenue and employment, but it could also lead to environmental degradation, air and water pollution, and health problems among local communities. These negative effects are social costs because they impact society beyond the direct stakeholders involved in the oil extraction.

3. Impact on Government Decision-Making for Developing the Oil Field in Kribi

a. Considering Opportunity Cost:

• The government must evaluate whether developing the oil field maximizes national benefits. If resources (land, capital, labor) could generate higher returns elsewhere, such as in agriculture or renewable energy, then the opportunity cost of pursuing oil development is high.
• For example, if tourism in Kribi, with its beaches and natural scenery, could generate more sustainable revenue than oil extraction, the government might decide against developing the oil field to avoid foregone tourism benefits.

b. Considering Social Cost:

• The government should also account for externalities associated with oil development. If environmental degradation leads to long-term health costs, loss of biodiversity, or climate change impacts, these social costs could outweigh short-term economic gains.
• For instance, if oil spills or pollution threaten fisheries or local livelihoods, the social costs could be substantial, prompting the government to implement strict regulations or consider alternative development options.

c. Cost-Benefit Analysis:

• The decision involves weighing the economic benefits (such as increased revenue, employment, and energy security) against the opportunity costs and social costs.
• If the social costs are high and the opportunity costs indicate better alternative uses of resources, the government might opt to delay or forego oil development, or implement measures to mitigate environmental damage.

opportunity cost helps the government recognize what they forgo when choosing oil development over other possibilities like tourism or agriculture. Social cost ensures they consider wider societal impacts, especially environmental and health-related externalities. A thorough cost-benefit analysis incorporating these costs would lead to more sustainable and informed decisions regarding the development of the Kribi oil field.

A:

Economic theory is usually developed to help explain economic happenings around us and so we get to talk of the concept of a production possibility frontier (PPF). A PPF shows the maximum combinations of two goods or services that an economy or on economic entity can produce at a given time with its available resources and technology. It is possible to have a PPF with increasing costs, decreasing costs or constant costs. This essay focuses on the most realistic option of a PPF which is that with increasing costs.

In order to derive a PPC with increasing costs, the following assumptions are made:

That an economy can produce only two goods- capital goods and consumer goods ;

That there is a fixed quantity and quality of resources our given period of time;

That there are increasing costs of production or that there are diminishing returns to production or that resources are not perfectly adaptable between different uses.

That technology is fixed.

On the basis of these assumptions, it is possible to envisage the following production possibility schedule and the resultant production possibilities curve.

Production possibilities.

Production possibilities curve

20 40 60 Consumer goods

Points A, B, C and D are points on the PPC while points E is within the PPC. Point F is out of the PPC. Point E can produced when resource are not fully or efficiently used while profit F cannot be produced at present.

A PPG can enable us explain the basic economic concepts of scarcity, choice and opportunity cost.

Scarcity means limited in supply. At a given time and with the resources and technology available, it is not possible to produce output combination F because of scarcity of economic resources as we see this product combination is out of the PPG.

Given that an economy cannot provide all of what it wants, it is bound to make choices. Making a choice means making a decision to take one thing out of some given possibilities. The economy can for instance chose to produce 70 capital goods and zero consumer goods or 50 capital goods and 30 consumer goods etc.

In the process of making a choice, there are opportunity costs. An opportunity cost is the cost of something in terms of the next best forgone alternative. For instance, to move from product combination B to product combination C entails an opportunity cost. Twenty 20 units of capital goods would have to be given up in order to produce 10 additional units of consumer goods. Twenty capital goods are thus the opportunity cost of 40 capital goods.

It is this seen that a PPG can be used to explain the basic economic concepts of scarcity, choice and opportunity cost and may equally be used to explain other concepts like economic growth etc.

A:

A production possibilities frontier or curve (PPC) shows the possible combinations of goods that an economy or an economic entity like a firm or a plant can produce when all its resources are fully and efficiently utilized with its given level of technology. This concept is of prime importance in illustrating the basic economic

concepts of scarcity, choice, opportunity cost as well as the notion of economic growth .A careful explanation of the notion of a PPC with the relevant assumptions would enable us see why it is impossible for a country to increase the production of both capital goods and consumer goods once on its PPC as well as throwing lighten other related issues.

Consider a given country, say Lilyputia for which we proceed to develop its PPC. We further assume that:

The quantity and quality of economic resources available for use in Lilyputia during the year are fixed.

Two broad categories of goods are to be produced i.e capital goods and consumer goods.

Some resources are better adapted to the production of capital goods than to the production of consumer goods. (If we assume all resources are equally efficient or adapted in the production of both goods, then we would have a straight line PPC and not a concave shaped PCC as in this case).

Technology is fixed and does not advance during the year.

On the basis of the aforementioned assumptions, we can come up with the following production combinations for capital goods and consumer goods.

With the help of these production combinations, it is then possible to derive the following PPC by plotting the aforementioned product combinations as shown on

We now assume that this economy of Lilyputia is currently producing 40 units of capital goods and 300 units of consumer goods i.e point B. If the economy now

wants to increase the production of consumer goods to 500 units, it can only do so by reducing the production of capital goods to 20 units so as to produce 200 additional units of consumer goods. In other words, the opportunity cost in this case of producing 200 additional units of consumer goods is 20 units of capital goods. This is so for the simple reason that there is a limit to the amount of consumer goods and capital goods that can be produced at any given time period with available technology and resources etc. This means that more of a good can only be produced by reducing the potential output of the other good. In short, given the assumptions of a PPC as earlier outlined, it is impossible for Lilyputia or for any other country to increase the production of both capital goods and consumer goods at the same time when the country is already on its PPC.

We can further elucidate on the aforementioned point by assuming that Lilyputia is producing at point X which is NOT a point on its PPC but a point INSIDE its PPC. It then becomes possible to increase the production of both capital goods and consumer goods by moving to ANY point on its PPC and by either FULLY and EFFICIENTLY using its resources.

If again we consider another point like point Y which is NOT on Lilyputia’s PPC, it may be possible to produce more of capital goods and consumer goods if and only if there is an outward shift of the PCC. We then talk of economic growth which may have been brought about by say the discovery of additional resources, improved technology, etc.

By way of conclusion, we Can say that given the assumptions of a PPC, it is impossible to produce more of capital goods and consumer goods once on a PPC. If this were to be possible, then it would be a violation of the very concept of a PPC which concept illustrates:

(i)            Scarce resources i.e there is a limit to the amount of what we can produce at a given time with available resources and technology thus obliging us to make a choice;

(ii)            Opportunity costs i.e more of a given good can only be obtained by reducing the potential production of another goods.

A:

The meteorologist just like any other natural scientist can easily “hold other things constant” while studying the effects which changes on X may have on Y. It follows that the predictions of the meteorologist would likely be more accurate compared to those of the poor economist. Given that the economist cannot hold other things constant, the most he/she can do is to assume that other things remain constant and this explains why propositions in economics often begin with the phrase “if other things remain equal” (ceteris paribus).

Although the meteorologist is generally more accurate in predicting weather changes than the economist is at predicting what will happen to the economy, it does not follow that the predictions of the economist are that unreliable. The fact that all people are different is not so much of a handicap to the economist or to the social scientist as it may appear at first sight. While the behaviour of any one person may be unpredictable, this is not necessarily true of the whole group. It follows that the economist is capable of making generalizations about economic groups (workers, investors, producers, importers etc) which are quite dependable guides on their expected behaviour. Econometrics may in the near future render predictions in Economics a little bit more reliable although the accuracy gap between the two sciences is likely to remain

A:

The price mechanism in a market economy is what determines what, how and for whom to produce through the interaction of buyers and sellers. The price mechanism is essentially a process by which buyers express what they want to buy and sellers respond by indicating what they are willing to sell. Their combined activities result in the prevailing market price at which the good or service is exchanged.

Consumers determine what will be produced through their spending decisions, or money votes, i.e. consumer sovereignty. Producers will then produce those goods desired, but since they are profit motivated, they will produce only those goods and services that are profitable. They will use the cheapest and most effective combinations of factors of production for maximum profit, and as such determine how the goods are produced. Those consumers, who can pay the price, get to enjoy these goods. In effect, for whom the good is produced is also decided by the market. In this way the price system acts, as it were, like a sophisticated computer, registering people’s preferences for different goods, transmitting these preferences to those responsible for producing the goods, and moving the factors to produce them. Thus the essential feature of the price mechanism or price system is the price signal.

The price system seems to be the best mechanism for allocating resources in many ways.

One advantage is that the price mechanism can run on its own. The fact that its workings are automatic means that there is no need for costly and cumbersome artificial coordination of economic decisions by the government or ruling body, and so massive bureaucratic costs are eliminated.

The aforementioned feature also means that the economy can respond rapidly to changing demand and supply conditions.

The market system is equally very efficient. The whole structure and organization of the market is the most conducive for generating wealth. People are able to work in careers of their own, and can invest in whatever businesses they want. This freedom and the pursuit of self-interest generates economic efficiency.

There is an optimal allocation of resources in that there is economic efficiency. In a highly competitive market situation, there will be both allocative and productive efficiency. This means that the right amount of every commodity is produced and they are produced at the least cost.

The market system is also argued to be the best allocator of resources for society because it allows for private ownership of wealth. This prevents the ruling body from having too much power and in so doing, safeguards the existence of personal liberty and choice. If private ownership of property were limited or controlled, then the ruling body would accumulate wealth and power at the expense of society.

There are however many instances in which the price mechanism has failed to provide the best allocation of resources. When this happens, there is said to be market failure.

One major disadvantage of the price system is that it fails to provide for the poor and the needy because the allocation of resources is based on a consumer’s purchasing power, not need. This results in the production of luxury goods for the rich at the expense of basic necessities of the starving poor. As a result of the inequality of income and wealth, the claims of consumer sovereignty and choice become questionable.

The high level of competition that is necessary for efficient production of goods is also very often absent in the real world. Monopolies and Oligopolies often dominate in markets. They often charge high prices and earn abnormal profit at the expense of consumers.

Advertising and aggressive marketing strategies also disrupt the effective functioning of the price system. This is because demand is distorted by persuading consumers to and even tricking them into buying what these firms are selling.

Another weakness of the price system or market failure arises because of the failure of the price system to take into account both the explicit and the implicit costs of production. Only private costs and benefits are taken into consideration by the price system. It follows that there wouldn’t be a socially desirable level of production of goods without external costs and/or benefits taken into consideration. The practices of some firms may therefore be socially undesirable and bringing about pollution, under and over production etc.

A free market economy will also result in the so called trade cycle, where there are periodical booms and

slumps. This will result in alternating periods of unemployment and inflation. Such instability may discourage investment.

We may end up evoking an ethical objection to the market economy. It is held that a free-market economy, by rewarding self-interested behaviour, may encourage selfishness, greed, materialism and the acquisition of power.

By way of conclusion, it can still be said that the price system or the market economy is by far the most awesome wealth generating economic system mankind has ever known. This is true both in theory and through empirical evidence. The fall of the command economies of the world further strengthens the case for the market system. The price system however has its own weaknesses as earlier pointed out. The best way to allocate resources thus seems to be to have limited government intervention in what is basically a market economy using the price system.

A:

(a) Disadvantages of preparing and viewing cells under the electron microscope

-Preparation of material is time consuming

-Requires staining with heavy metals which may produce artefacts

-Fixation of material for viewing is done in a vacuum and cells cannot be observed alive.

-Produces black and white images seen in one plane

-Cannot be used without electricity

(b)

Animal cell under an electron microscope

(c)      Dfferences between animal cell and chlorenchyma

(d)      Why electron microscopes are not found in labouratories in Cameroon schools

-       They are very expensive to buy and are very bulky

-       Requires expert training to manipulate

They are complicated and difficult to repair

A:

-Lipids are involved in the passive transport of substances across membranes.

-Hydrophobic molecules such as oxygen and hydrocarbons can dissolve and pass through the lipids of the membrane easily.

-Lipids are impermeable to all ions.

Functions of proteins in the plasma membrane

-There are two types of membrane proteins; integral and peripheral proteins.

-Integral proteins span the membrane while peripheral proteins are attached to the surface of the membrane, and are involved in anchoring the membrane to the sub-membrane cytoplasmic structures. A single intergral protein may perform a combination of tasks such as; active transport of substances to regulate pH and ion concentration, enzyme functions, receptor sites for hormones and cell adhesion forming intercellular junctions.

A:

-Microfilaments made of the protein actin would increase in number since they are responsible for the contractile activity of muscles.

-Smooth ER that stores calcium involved in the contraction process would increase in she and grow.

-Mitochondria that provide energy for the contraction of muscles and other cellular activities would increase in number

(c)    (i) How cancer cells diffed from body cells

-Cancer cells escape from the control mechanisms that regulate division in normal cells

-They do not need to be anchored to a solid surface to grow.

-They seem to be unaffected by density­dependent inhibition and will pile up on one another in cell cultures.

-They either donot require growth factors or manufacture their own growth factors.

-Unlike normal cells, cancer cells can divide indefinitely. If they stop dividing they stop at random points in the cell cycle, not at the restriction points.

(ii)  How chemotherapy slows the growth of cancerous cells and side effects

-Cancer is uncontrolled cell division. Chemotherapy and other cancer therapies like radiation slow tumour growth by interfering with cell division.

-Cell division is most rapid in the skin and digestive tract lining, where it replaces lost cells, so the side effects of chemotherapy are greatest on the skin and intestinal lining.

-The side effects of chemotherapy are hair loss, nausea, and loss of appetite.

A:

-Epithelia are classified according to the shape of the cells (squamous, cuboidal, or columnar and ciliated) and the number of layers (simple, stratified, or pseudostratified).

-Depending on the epithelium type and its location it may serve protective, absorptive, or secretory functions.

-Epithelia cover all internal and external body surfaces.

-A special type of epithelium, endothelium, makes up the walls of blood and lymph vessels.

(b)     Connective/Supporting Tissue

-Connective tissues consist of cells and extracellular matrix. They may serve different functions: structural support (e.g. bones), connections (e.g. ligaments and tendons), protection (e.g. fat pads), transport of respiratory gases and defence (blood).

-Connective tissue is made of cells, (e.g. fibroblasts, chondrocytes and osteocytes); extracellular fibres (e.g. reticular, elastic and collagen); and ground substance.

-Cells: provide defence and produce the supportive structures, fibroblast (secrete the protein ingredients of the extracellular matrix e.g. collagen and elastin), macrophages (amoeboid cells that engulf bacteria and dead cell debris by phagocytosis), mast cells (contain small granules to prevent blood clotting, increase permeability of capillaries and venules)

-Materials: e.g. hyaluronic acid, chondroitin sulphate, heparin sulphate function as a medium through which nutrients can diffuse from blood vessels to nourish the cells *

-Structural glycoproteins: e.g. fibrin, collagen, elastic fibres are proteins that give connective tissue its strength

-long threads made of elastin protein join connective tissue to adjacent tissue

-Depending on the type (e.g. loose, dense), connective tissue may serve different functions; including structural support, connections, elasticity and protection.

-Dense connective tissue or fibrous connective tissue: contains a great proportion of fibres, fewer cells and less ground substance. E.g tendons (attach muscles to bones), ligaments (join bones together at joints) -Loose connective tissue has an abundance of cells and ground substance, but relatively few fibres. It is soft and pliable and

serves as a kind of packing material between other tissues and organs.

-It is found between muscles, allowing one to move freely over the other.

-It supports small blood vessels, lymphatic vessels and nerves.

-Adipose tissue is made of loose connective tissues with a high population of adipocytes

-Cartilage is a form of connective tissue that is much firmer than dense connective tissue.

It consists of a dense network of fibres embedded in a gel-like intercellular material which confers firmness but also permits flexibility. The cells are called chondrocytes (produce collagen and chondroitin sulphate)

-There are various types of cartilage: hyaline (found at the end of bones where they articulate with one another and found in the nose, larynx, trachea and bronchi of the respiratory system and the precursor of the vertebrate skeleton), elastic (very flexible and when deformed, it immediately returns to normal position, and is found in the external ear, epiglottis and auditory tube)’ and fibrocartilage (found in intervertebral disks and associated with dense fibrous tissue in tendons and ligaments

-Bone is a mineralized connective tissue made of hydroxyapatite and osteoblasts.

-Compact bone consists of repeating unit called osteon or Haversian system

-Bone is a rigid firm form of connective. The hardness of a bone is caused by the presence of calcium phosphate; the small degree of elasticity possessed by bone is caused by the presence of organic collagen fibres. The cells of bone are called osteocytes.

Bone are of two types; compact and spongy bone

(c)    Muscle tissue

-Muscle cells are contractile cells. Specialized proteins allow the cells to 'shorten. Their ability to contract provides a mechanism for movement of the internal organs and locomotion of the entire organism.

-Muscle tissue can be divided into 3 major types: Skeletal, Cardiac and Smooth.

-Skeletal muscle is attached to bones.

-Cardiac muscle is found in the heart.

-Smooth muscle is found in vessels,'ducts, skin, and internal organs.

-Muscle tissue may be controlled by nerves, hormones, local chemicals, or itself depending on the type and location.

-Skeletal muscles are under voluntary control. They are attached to bones or fascia and constitute the flesh of the limbs and body wall. They contain fibres (myofibrils), are long, multinucleated and arranged in parallel bundles, -unlike smooth and cardiac muscle, each skeletal myofibril is innervated by a neuron.

-By light microscopy, the cells of both cardiac and skeletal muscle show the presence of transverse striations.

-For this reason, both of these muscle types are referred to as "striated"

-The striated appearance results from the presence of a highly organized network of actin and myosin protein filaments which utilize cellular energy and function in muscle contraction.

-Smooth muscle is not under voluntary control and comprises the walls of most of the viscera and blood vessels of the body. There is one centrally placed nucleus per cell.

-Cardiac muscle is involuntary, striated in appearance and contracts rhythmically and automatically. It is found only in the myocardium (the muscle layer of the heart).

-Each cell has a single, centrally located nucleus and joins end to end with other cardiac muscle cells at specialized junction zones called intercalated discs. These junctions allow the spread of excitation to pass from one fibre to another and harness the contraction of individual cells so that overall muscle shortening can occur.

(d)    Nervous Tissue

-It is composed of two major types of cells: neurons and support cells (glia).

-Neurons have specialized dendrites for receiving signals, a cell body for cell maintenance and integration, an axon for sending signals rapidly over long distances, and many terminals to make synapses with other cells.

-The cell bodies of neurons in the peripheral nervous system (PNS) are located in groups called ganglia.

-Glial (glue) cells are supportive cel is, providing nourishment and other aids to neuron function.

-Nerves are bundles of axons surrou ided by glial (Schwann) cells and some connective tissue.

Individual axons may be either sensory or„ motor in function.

-astrocytes (astroglia) provide physical support to neurons clear up debris surround capillaries in the brain (blood brain barrier)

-Oligodendrocyte produces myelin sheaths around the axon in the central nervous system (CNS)

-Schwann cells produce myelin sheaths around axon in the peripheral nervous system

-The cell body contains the nucleus and metabolic machinery of the cell. Proteins and neurotransmitter substances that carry signals between cells are synthesized there.

-The neuroglia cell nuclei serve several important functions: Provide nutritional support for the neurons, surround blood vessels to regulate what types of substances are allowed to pass to the neurons. This function is referred to as the blood brain barrier, form myelin sheaths around axons to speed impulse transmission and engulf “foreign invaders such as bacteria.

A:

(a)    (i) Chemical constituents of plasma membrane

-The main constituents of the plasma membrane are phospholipids, proteins and carbohydrates.

-The phospholipids which are amphipathic molecules are regularly organized in the membrane according to their polarity: two layers of phospholipids form the lipid bilayer with the polar part of the phospholipids pointing to the exterior of the layer and the non-polar

phospholipid chains in the interior. -Proteins can be found embedded in the lipid bilayer and there are also some carbohydrates bound to proteins and to phospholipids in the outer face of the membrane.

-Molecules of cholesterol are present which prevents membrane solidification.

(ii) Differences between smooth and rough endoplasmic reticulum

-The endoplasmic reticulum is a delicate membranous structure contiguous to the nuclear membrane and present in the cytoplasm. It forms an extensive net of channels throughout the cell and is classified into rough or smooth types.

-The rough endoplasmic reticulum has a great number of ribosomes attached to the external side of its membrane while smooth endoplasmic reticulum does not have ribosomes attached to its membrane.

-The main functions of the rough endoplasmic reticulum are synthesis and storage of proteins made in the ribosomes while the smooth endoplasmic reticulum plays a role in the synthesis of lipids, and in muscle cells, it is important in the conduction of the contraction stimulus.

(b)    Morphological, chemical and functional comparism of lysosomes and peroxisomes Similarities:

Lysosomes and peroxisomes are small membranous vesicles that contain enzymes and enclose residual substances from internal or external origin degrading them.

-They are both enclosed by a single unit membrane

Differences:

-Lysosomes have digestive enzymes (hydrolases) that break substances to be digested into small molecules while peroxisomes contain enzymes that degrade mainly long-chained fatty acids and amino acids and that inactivate toxic agents including ethanol. They contain the enzyme catalase, responsible for the break down of toxic hydrogen peroxide (H2O2) to water and molecular oxygen.

(c)    Components and functions of the cytoskeleton

-The cytoskeleton is a network of very small tubules and filaments distributed throughout the cytoplasm of eukaryotic cells. It is made of microtubules, microfilaments and intermediate filaments.

-Microtubules are formed by molecules of a protein called tubulin. Microfilaments are made of actin and myosin, the proteins that participate in the contraction of muscle cells.

-The cytoskeleton is responsible for the support of the normal shape of the cell; it also acts as a facilitator for substance transport across the cell and for the movement of cellular organelles. For example, the sliding between actin-containing filaments and the protein myosin “creates pseudopods.

-In cells of the phagocytic defense system, like macrophages, cytoskeleton is responsible for the plasma membrane projections that engulf the external material to be interiorized and attacked by the cell

A:

(a)      Tissues are fixed to maintain them in life like forms. The tissues are killed and the proteins positioned before degenerative changes occur.

-They are sectioned to be of thin slices that would allow light to pass through them to enable viewing.

-Tissues are stained to render them visible by increasing the contrast between the various structures.

-Stains react chemically with the structures of the cell or adhere to them.

(b)     (i) Structure and functions of lysosomes

 -Lysosomes are simple sacs containing digestive enzymes such as proteases, nucleases and lipases.

-They are surrounded by a single unit membrane and found only in eukaryotic cells.

-These enzymes are synthesized on the rough endoplasmic reticulum arid carried to the Golgi apparatus.

-The Golgi vesicle containing the enzymes buds off forming primary lysosomes.

-Larger secondary lysosomes are formed by the fusion of primary lysosomes with small vacuoles -They also fuse with worn out organelles (autophagosomes) and eliminate them.

Functions

-Digests particles made in the cell or taken into the cell from the outside through endocytosis.

-They carry out autophagy; fuse with unwanted particles and digest their content, which are used as food.

-The contents are sent out through exocytosis if they were bacteria engulfed through phagocytosis.

-They help in the breakdown and elimination of ageing organelles in cells.

-They release enzymes out of cells that help in the replacement of cartilage with bone. Acrosomes release enzymes that digest the egg membrane for sperm penetration

-Are implicated in the reabsorption of the tadpole tail during metamorphosis and digestion of the increased uterus after birth.

(c)       Main stages of cell fractionation

-Cell fractionation involves the separation of cell organelles to study their structures

-Life tissue is chopped in cold isotonic-buffer solutions or ruptured by ultrasonic waves.

-Chopped tissue is ground in a homogeniser

-The homogenate is transferred to a centrifuge which spins the mixture at different speeds -Organelles sediment separately

(ultracentrifugation)

A:

(b) (ii) Neuroglia cells are the parking and supporting tissues of the nervous system. The cells and their functions are;

-Protoplasmic astrocyte: Stores energy as glycogen

-Fibrous astrocyte: Provide nutrients from blood to neurones

-Microglia: Contains lysosome and is phagocytic

-Oligodendrocyte: Produce insulating myelin surrounding the axon

-Schwann cell: Produce insulating myelin

-Ependymal cell: Lines the brain and spinal cord.

A:

(a) Rough Endoplasmic Reticulum

-They are made up of a network of sac like tubular cavities called cisternae, bounded by a unit membrane. The membranes are covered with ribosomes and are continuous with the nuclear membrane. They are prominent in enzyme secreting cells.

Diagram of the endoplasmic reticulum

Functions:

-Provide large surface area for synthesis

-Permit rapid transport of synthesised molecules (proteins) within cells and, from inside to outside cells.

(b)    Cilia

-They develop from basal bodies produced when the centrioles of some cells divide. They are made up of longitudinal fibrils, two in the centre surrounded by nine outer pairs; all enclosed in a unit membrane. Make a large diagram of the fibrils.

cell membrane

Structure of cilia

Functions:                                 

-Kicks off liquids and particles away from surfaces by rhythmic contraction and relaxation,

-Used in locomotion by some cells.

(c)    Golgi apparatus 

-They appear as closely packed parallel curved pockets in cross section. The pockets are bounded by unit membranes and are called cisternae.

-Tiny vesicles arise from the edges of the cisternae. Some of these vesicles become lysosomes while some fuse with and enlarge the plasma membrane. Others carry secretions to the plasma membrane for release to the exterior.

-Carbohdrates are added to proteins from the ER in the Golgi body to foxm glycoproteins (mucus)

Diagram of the Golgi apparatus

(d)    Ribosomes

They are small near circular structures made up of two sub units. In prokaryotic cells; the ribosome is 70s while those of eukaryotic cells are 80s.

Functions:

-Sites of protein synthesis. Moves along mRNA molecule, one or many (polysomes). When at a particular codon, tRNA with the corresponding anticodon brings coded amino acid for protein synthesis.

A:

(a)    Influence of Electron microscope on our idea of membrane structure.

-The electron microscope offers a higher resolution and magnification power.

-This has enabled the detailed structure of the

plasma membrane to be observed and studied.

-The various component molecules are distinctively seen to compose of proteins, phospholipid bilayer and molecules of cholesterol.

-It has also revealed that the phospholipids have phosphate heads facing outwards and hydrocarbon tails facing inwards.

-Some proteins go through the membrane while others do not.

(b)

 Ultrastructure of a plant cell

(i) -Drawn thickness = 6cm i.e. 6 x 10² = 0.06m

.'.Drawn thickness =(6 x IO^-2) m

 thickness » 7nm » (7 x 10^-9) m

Drawn thickness = actual thickness x magnification

Magnification =drwan thickness / actual thickness

Substitute:

Magnificaton = 0.06/7*10^-9 

Mag =  8.57 *10⁶

NB: Measure the thickness of the diagram drawn using your ruler if it is not given arid use the value obtained as the drawn thickness when necessary.

(ii)  Differences between magnification and resolution

-Magnification gives a larger image for clear viewing without distinguishing between components while the resolution shows distinct parts of the object viewed showing the various components as distinct entities.

A:

(a)    (i) Role of carbohydrates in the structure of plant and animal cells.

-The micro fibrils of plant cell wall contains cellulose molecules held by hydrogen bonds which makes it rigid and protect the internal structures from mechanical injury.

-Plant cells store reserved food as starch

-Glucose when in some cells alter the osmotic concentration which may lead to the influx of water enabling such cells attain turgidity.

-Carbohydrates combine with protein at cell membranes to form glycoproteins which are antigens.

-They help to distinguish between self and non­self.

(ii) Proteins

-Channel and carrier proteins at cell membranes help in the transport of substances across membranes.

-Some of the proteins go through the membrane and form pores where simple diffusion occurs while others float and transport substances by rapidly spinning.

-Some proteins in cell membranes are enzymes. They catalyse metabolic reactions at cell surfaces.

-The structure of some proteins at cell membranes gives a particular shape which acts as reception sites for some hormones.

-Plasma proteins like fibrinogen help to form a clot, thereby preventing excessive loss of blood when vessels are wounded.

-Some cells contain collagen and keratin which gives mechanical strength.

(ii) Lipids

-Cell membranes contain a phospholipid bilayer that controls the movement of polar molecules within cells.

-The layer is fluid with the phosphate heads facing outwards and hydrocarbon tails inward. This gives stability to the membrane.

-Some cells contain a waxy outer covering which prevents desiccation.

-Cholesterol present at cell membranes prevents close parking of phospholipids, thereby softening cell membranes, making them flexible.

-Cholesterol plugs also prevent the escape of polar molecules.

(b)    How antibiotics treat bacterial diseases

-Destroy pathogenic bacteria by digesting them (biostatic)

-Inhibit growth of the pathogenic bacteria

-Interfere in the metabolism of the pathogen and block protein synthesis, nucleic acid synthesis and disrupt the functioning of the cell membrane, capsing the pathogen to die.

A:

(a)    (i) Diffusion

It is the net movement of molecules or ions from a region of high concentration to that of low concentration.

It occurs in living and non-living systems where ever there is a concentration gradient and does not require energy e.g. movement of CO² and O² across respiratory surfaces such as gills of fish and alveoli in mammals.

(iii)  Active transport

-It is the movement of substances against a concentration gradient by the use of energy from ATP across cells.

-Cells that carry out active transports regularly have numerous mitochondria and high concentrations of ATP.

-Actively transported molecules can be carried by protons or protein molecules e.g. sodium/potassium pump which pumps Na⁺ out of the cell and K⁺ in, to generate impulses; active absorption of digested food in the gut and active absorption of mineral ions by root hairs.

(iv)     Pinocytosis

-Form of endocytosis by which a living cell engulfs minute droplets of liquid by the use of energy.

- Involves the infolding or invagination of the cell surface membrane forming vesicles e.g. uptake of nutrients from the follicles by human egg cells, pick up of thyroxin from the follicles of the gland.

(v)       Phagocytosis

-Process by which solid substance, are brought inside the cell by invagination of cell membranes using energy.

-The cell invaginates to form a depression containing the particles.

- The depression pinches off to form a vacuole, the inner surface derived from the outer surface of the cell membrane e.g. mode'of feeding of amoeba, action of phagocytes to destroy foreign particles.

(b)    (i) Features that affect the rate of diffusion

-Cell surface area, concentration gradient, type of molecule, length of diffusion path, temperature and Permeability of path

(ii)  Why active transport is affected by O² concentration while diffusion is not affected.

-Active transport uses energy derived from ATP.

-     ATP is produced during aerobic respiration.

-     A decrease in O² concentration will reduce the amount of ATP generated which will affect active transport.

-     Diffusion is a passive process which does not require energy in the form of ATP.

A:

A:

(a)    Definition of a unit membrane

-A unit membrane is the external boundary of cells and some organelles.

-All membranes have the same structure as revealed by electron micrograph.

-A unit membrane is trilamella with a phospholipid bilayer and protein molecules.

-The phospholipids are fluid with phosphate head that faces outwards and hydrocarbon tails facing inwards.

-Some proteins go through the membrane while others do not.

-The membrane is 7nm thick.

(b)     Functions of cell membranes

-Controls passage of materials in and out of cells by the use of channel and carrier proteins.

-Recognition of other cells by glycoproteins called antigens

-Reception site for hormones and neurotransmitters.

-Transmission of nerve impulses

-Insulation of nerves

-Forms barrier between cells and their surrounding membranes inside cells (intracellular membranes) act as reaction surfaces, act as intracellular transport system and provide separate compartments isolating different chemical reactions

(c)     The sequence of events between one cell division and the next

-     This sequence is called the cell cycle.

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(c)    Why cardiac muscles are myogenic

-The impulses that cause their contractions originate from the heart muscle itself. They contract rhythmically from the time of formation till the death of the organism.

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(b) Differences between plant and animal cells

(c) How substances move in and out of cells

-Simple diffusion: Movement of substances across cells through pores following a concentration gradient e.g. CO? and O2 through channel proteins. -Facilitated diffusion: Movement of glucose and amino acids by the help of carrier proteins. The proteins pick up the substances and rapidly spin, dropping them inside the cells.

-Active transport: Carrier proteins use energy to transport substances against their concentration gradients e.g. uptake of glucose at the intestine, sodium-potassium pump during the transmission of impulses, and active loading of sugar to the phloem. Active bulk uptake of liquids (pinocytosis) or solids (phagocytosis) and bulk transport of substances out of cells using energy (exocytosis).

-Osmosis: Movement of water from an area of high water potential to those of low water potential through a selectively permeable membrane e.g. water uptake by root hairs, gain of turgidity by cells.