(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)    (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)    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) 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.

(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)      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)    (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

-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.

-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.

-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.