advance level biology 2014 paper 2 answer guide

ADVANCED LEVEL BIOLOGY PAPER 2 MARKING GUIDE (2014)

1(a)

tracheal system consists of tubes which are lined with chitin to give support; this ensures that they remain open during gaseous exchange;
trachea branch internally into numerous intercellular tracheoles which are thin and permeable; this increases the rate of diffusion of gasses between the tracheoles and the body cells.
The ends of the tracheoles are filled with fluid through which O₂ and CO² diffuse into and out of adjacent cells.
Many insects have air sacs in their tracheal system; these air sacs function as bellows during vigorous body movements speeding up the movement of gasses to and from the tissues
The large muscles located in the thorax and abdomen undergoes alternate contraction and relaxation leading to inspiration and expiration (1 x 6 = 6 marks)

(b)

Breathing is controlled involuntarily by the respiratory center located in the medulla oblongata of the brain
It has an inspiratory center which increases the rate and depth on inspiration and an expiratory centre which inhibits inspiration and stimulates expiration.
The respiration center is linked to the intercostal muscle, diaphragm, bronchi and bronchioles by the intercostals nerves, phrenic nerves and vague nerves respectively.
The main stimulus that controls breathing is the CO₂ concentration in blood
When the CO₂level in blood rises, chemoreceptors in the medulla, carotid and aorta are sensitized and they send impulses to the inspiratory center.
The expiratory centre temporarily inhibits inspiration by causing the external intercostals muscles to relax and expiration takes place
After expiration, the stretch receptors are no longer stimulated, and the expiratory center becomes inactive, inspiration can again begin (1 x 8 = 8)

(C)

A natural unpolluted pond has oxygen in solution but the concentration of O₂ in the water is very low (only 1% by volume)
The temperature of the pond may rise because of solar radiations that heat the water body; this reduces the solubility of O₂ in the water.
The counter current flow system is used by this fish to maximize the absorption of oxygen from water.
The water in which the fish lives is a denser and more viscous respiratory medium compared to air; this slows down the diffusion rate of gases.
The possession of numerous gills (4 in each chamber) with numerous thin permeable gill filaments help to increase the surface are for gaseous exchange.
The water that runs over the gills usually contains solid particles (food, mud etc.) which may reduce the permeability of the gill filaments
Gill rakers are used to filter out the solid particles and prevent them from blocking the pores on the gill filaments (1 x 6 = 6 marks) (Total = 20 marks)

2(a) (i) D Q, = 1, 0

(ii) Adaptation of femur to its function:

Hard compact bone provides mechanical support and prevents breakage
Cylindrical in shape, resist bending
Spongy epiphysial areas reduce weight for easy movements
Round head for movement in all directions
Cartilage reduces friction during movement
Rough periosteum provides surface for muscle attachment
The red marrow is responsible for RBC production, increases capacity of oxygen supply.
Blood vessels supply nutrients and takes away wasted (1 x 5 = 5 marks)

(b)(i) Joints

Points where two or more bones meet
Types: unmovable e.g., sutures of the skull; slightly movable e.g. symphyses between vertebrate and freely movable/ synovial joint;
Permit rotation of the head from side to side
Enables bones to glid over each to a limited extent providing movement.
Provides strength and support for the body; protects delicate structures which cannot withstand any kind of deformation
Permit movement in all during flexion and extension e.g., hinge joint (1 x 6 = 6marks)

(ii) Tendons

Attach muscles to bones
Prevents muscle rapture when subjected to a heavy load.
Ensures spatial/ fixed location of specific muscles to specify bones/ areas
Concentrate the pull of muscle over a small area (1 x 2 = 2 marks)

(iii) Ligaments

Connect bone to bone
Strengthen joints
Confine the movement of structures at each joint to a specific direction (1 x 2 = 2 marks)

(Total = 20 marks)

(3)(a)

Is part of the PNS which controls involuntary activities in the body
There are 2 division of the ANS namely; the sympathetic and parasympathetic nervous system.
The sympathetic nervous system forms ganglia close to the spinal cord while the parasympathetic nervous system forms ganglia close to the effectors
The effects of the two divisions are opposing (antagonistic) as shown below

Sympathetic nervous system	Parasympathetic nervous system
It releases noradrenaline at the effector	It releases acetylcholine at the effector
It is active during stress and danger	It is active during rest, that is, it controls routine
It increases rate of heart beat	Decreases rate of heart beat

(b) Steroid hormones

They are deriving from cholesterol and are produces by endocrine glands of mesodermal origin
They generally control long term responses of the body
Examples; oestrogen, progesterone, testosterone, aldosterone, etc.

Mode of action of steroid hormones

The hormone binds to a specific receptor in the cell membrane of the target cell forming a steroid- hormone receptor complex which diffuses into the nucleus and releases the hormone.
The steroid hormone then activates a specific gene to produce mRNA by transcription.
The mRNA passes out into the cytoplasm, and initiates the synthesis of the enzyme which brings out the desire effect.

It is the precision or sharpness of the image we see.
Visual acuity is greatest when the image falls on the fovea which contains only cones
This is because in the fovea, one cone synapses with only one bipolar neuron and the bipolar neuron synapses with only one ganglion cell; this 1:1 relationship increases visual acuity.

Visual activity also increases as the number of cones in a particular area increases (1 x 4 = 4 marks)

(e) Trichromatic theory of colour vision

Color vision is perceived by the three types of cones (light sensitive cells) in the retina (i.e., red, green and blue cones)
Each type of cone processes a different type of iodopsin that absorbs light of different wave lengths.
The trichromatic theory states that different colors are produced by the different degrees of stimulation of the three types of cones in the eye.
Equal stimulation of the three cone types produces the color sensation of white, when only red and green cones are sensitized, we see orange etc.
The back of any of these will lead to varying degrees of color blindness (1 x 5 = 5 marks)

(Total = 20 marks)

(4)(a)

In the buccal cavity, saliva is secreted from the salivary glands into the mouth cavity.
Saliva contains salts such as NaOH, NaHCO3, Ca2+ and K+ which provides the right pH for the action of enzyme,
Mucus in saliva Contains lysozyme, a lytic enzyme which kills bacteria that might have come in with food
Salivary amylase in saliva begins the hydrolysis of starch to maltose
In the stomach, the parietal or oxyntic cells secrete dilute HCl while the chief zymogen cells secrete the inactive enzyme pepsinogen and prorenin from the stomach wall into the stomach.
HCl renders the pH of the stomach contents acidic which is the pH ideal for optimum activity of stomach enzymes.
It helps to kill any bacteria present in the food we might have come in from the mouth.
It losses the fibrous and cellular components of food facilitating digestion.
It activates pepsinogen to pepsin and prorenin to rennin.
Pepsin breaks down proteins to smaller polypeptides
Rennin coagulates the soluble milk protein caseinogen into insoluble casein which is then digested by pepsin.
In the duodenum, bile is released from the gall bladder through eh bile duct and pancreatic juice is secreted into the duodenum from the pancreases.
Bile is produced in the liver and temporarily stored in the gall bladder. It contains bile salts such as NaHCO3 which neutralizes acidic chyme from the stomach creating an optimum pH for pancreatic enzymes.
Bile salt emulsify fats reducing their surface tension by breaking them into small droplets, increasing surface area for the action of lipase.
Pancreatic juice contains pancreatic amylase which breaks down starch to maltose
Pancreatic lipase which breaks down lipids to fatty acids and glycerol
Trypsinogen activated to trypsin by the hormone enterokinase with hydrolyses proteins to smaller polypeptides
Peptides which break down peptides to amino acids
Nucleases which break down nucleic acids into nucleotides.
In the ileum, Brunner glands in the intestinal wall secret fluids into numerous microscopic pits called crypts of Lieberkühn which then secret intestinal juice into the intestinal lumen which contains enzymes that complete the process of digestion.
Maltase breaks down maltose to two glucose molecules
Lactase breaks down lactose to juice and galactose
Sucrase breaks down sucrose to glucose and fructose
Nucleosidases break down nucleotides into pentose sugar, an organic and a phosphate group
Peptidase breaks down peptides into amino acids
Lipase breaks down lipids to fatty acids and glycerol

N/B: mouth = 3 marks, stomach 4 marks; duodenum = 4 marks; ileum = 4 marks (1 x 15 = 15)

(b)

The flow of saliva is initiated by the sight, taste or thought of food, that is, by reflex action.
The secretion of gastric juice is triggered by reflex action in which nerve impulses are released from the brain glands to secrete the hormone gastrin which stimulates the secretion of gastric juices.
Partially digested food in the duodenum stimulates the release of enterogastrone from the duodenal lining which inhibits the secretion of gastric juice
Acid chyme entering the duodenum stimulates the release of cholecystokinin from the intestinal wall which stimulates the release of bile from the gall bladder into the duodenum and secretion of pancreatic juice.
Secreting is also secreted from the duodenal lining which stimulates the secretion of gastric juice rich in NaHCO3 (1 x 5 = 5 marks) (Total = 20 marks)

(5)(a)(i) Genetic Engineering is the manipulation of gene (DNA) to produce useful products

It involves isolation, removal and cloning of useful genes (1 x 2 = 2 marks)

(ii) Biotechnology is the application of scientific and engineering principles to the production if materials by biological agents- Examples: fermentation of beer and wine (1 x 2 = 2 marks)

(b)(i) Production of insulin

Messenger RNA is extracted from human pancreatic tissue

The mRNA is treated with reverse transcriptase to manufacture copy DNA (cDNA).

The human regulator DNA is replaced by bacterial regulator DNA (marker gene) to ensure greater production endonuclease

A plasmid removed from bacterial cell is opened up at a specification point using the appropriate restriction nuclease

The cDNA is now attached to the plasmid using DNA ligase. The resultant plasmid carrying the human DNA for insulin is now called the plasmid vector.

The plasmid vector is reinserted into the plasmid free bacterial cell by using chemicals which make the wall permeable to the plasmid

The plasmid(s) replicate during fermentation of genetically engineering host bacteria.

This is followed by separation and purification of human insulin (1 x 8 = 8 marks)

(ii) production of cheese

Milk is first pasteurized by destroying unwanted micro-organisms.
Selected bacteria such as leuconostoc lactis which produces C0₂ and streptococcus lactis which produces lactic acid from milk sugar lactose are used
Lactic acid coagulates the milk protein (casein) to form solid curd in a liquid component, the whey.
Rennet is also added to clot the milk
After removal of whey, salt is added to the curds to serve as osmotic preservative
Preservation of the curd takes place for weeks and months in which in which enzyme driven changes take place that leads to the ripening and maturity of cheese. (1 x 8 = 8 marks)

(iii) manufacture of monoclonal antibodies

An organism e.g., mouse is injected with antigen, e.g., red blood cells of a sheep.
The antigens stimulate B-lymphocytes to produce anti-bodies.
The B-lymphocytes produces plasma cell which are removed from the spleen of the mouse
Tumor cells from the marrow of another mouse are collected-together with the plasma cells a hybridoma is gotten (tumor cells + plasma cells)
The resulting cells are incubated in a special medium
The hybridoma cells are then cloned on media in the laboratory
This is followed by assaying for the best line of the hybridoma cells
Large scale production is in an air-lift fermenter to prevent damage of the cells (1 x 8 = 8 marks)

(iv) commercial production of yoghurt

Fresh milk is heat treated and later cooled to incubation temperature
The fermenter is inoculated with a starter culture like Lactobacillus bulgaricus and Streptococcus thermophilus
It is then incubated at 40 degrees Celsius for about 6 hours.
bulgaricus breaks down milk protein into peptides
The peptide is used by L. thermophilus to produce formic acid
The formic acid is now used and lactose is broken down to lactic acid by L. bulgaricus
There is coagulation of the milk by lactic acid
Ethanol (acetaldehyde) is produced by each bacterial species giving the buttery taste.

(1 x 8 = 8 marks) (total = 20 marks)

(6)(a)(i) Xylem

Made up of vessels and tracheid
Consist of dead cells
Allows unobstructed passage of water and mineral salts
Has pits which permits horizontal transport
Narrow lumen to improve capillarity
Tapering ends overlap, giving additional mechanical strength
Long and tubular vessels, good conducting structures
Mark points annotated diagram

(ii) Parenchyma

Made up of living cells involved in food storage
Has a large sap vacuole, gives turgidity for support
Irregular in shape as packing tissue
Has thin cellular cell wall, pathway for water and mineral ions
Elongated and flattened cell offer protection from desiccation and infection
Plasmodesmata between adjacent cells, allow lateral transport between cells (1 x 5 = 5 marks)

(iii) Collenchyma

Made up of living cells; covering outer region of cortex, midrib of leaves
Elongated and polygonal cells
Tapering end; give mechanical support
Cell wall of cellulose; additional mechanical support (1 x 3 = 3 marks)

(iv) striated muscle

Numerous muscle fibres; thin myofibers; long, cylindrical with alternate light and dark bands/actin and myosin contract and relax; voluntary movement.
Oval nuclei at surface of each fibre; control cell activity
Numerous mitochondria interposed between muscle filament; presence of glycogen; provide energy for muscular action
Presence of vesicles triad involved in the uptake and release of Ca²⁴ ions
Fibres enclosed in sarcolemma; each has several motor neurons attached to its sheath; conduction of impulse; causes contraction of fibre
Bundles of fibres enclosed by collagen fibres and connective tissues; from tendons at the ends of muscles attach muscles to skeletal elements (1 x 6 = 6 marks) (total = 20 marks)

(7)(a)(i)

Mitosis	Meiosis
One mother cell gives two daughter cells	One mother cell gives four daughter cells
Each daughter cell diploid/ (2n)	Each daughter cell haploid/ (n)
Involves in asexual reproduction	Involved in sexual reproduction
No crossing over	Crossing over
Completed in one stage	Completed in 2 stages meiosis 1 and 2
Occurs during the formation of somatic cells and some spores	Occur during formation of gametes or spores

(ii)

Halfling of genetic material in gamete
Reconstitution in zygote during fertilization
Maintenance of species characteristics

(a)(i) Placenta

Link between mother and foetus
Supply food to foetus
Supply oxygen to foetus through umbilical vein
Elimination of waste through umblical artery
Defense of foetus, antibodies secretion
Passive immunity
Secretion of oestrogen and progesterone

(ii) Uterus

Implantation, development
Formation of corpus luteum
Secretion of progesterone and oestrogen
Contraction during birth

(iii) Pituitary gland

Secretion of FSH, – Luteinizing hormone – Oxytocin
Luteinizing hormone stimulates testosterone secretion
Oestrogen, progesterone, ovulation
Maintenance of corpus luteum
Prolactin – milk production and secretion

(8)(a)

Bipedal; opposable thumbs; larger brain; gestation usually long (40 weeks); longer period of parental care; highly developed communication system; almost hairless; exert control on the environment; found throughout the world

(b)(i) Homologous and characters

Homologous character’s structure which are fundamentally similar in form; having a common original; but serving different function at adult stage; e.g. force limbs of man and dog; while analogous characters are those with different origin; and structures but serve similar functions at adult stage; e.g, wings of birds and butter flies. (1 x 4 = 4 marks)

(ii) Convergent and divergent evolution

Convergent evolution: evolution in which complete organs or parts of organisms come to resembles each other; as a result of their sharing similar environments: and performing the same functions; e.g. the shark and a porpoise look alike, but a shark is a cartilaginous fish while a porpoise is a bony fish; while divergent evolution is evolution from a common ancestral line where numerous line of evolution arise; resulting in the basic pattern being modified to serve different functions; making descendants to fill a wide variety of niches; e.g. the forelimbs of a selection of vertebrates all come from a common pentadactyl pattern but are modified for various uses as in humans, cat, bat, birds, lizards, frog, whales (1 x 4 = 4 marks)

(c)

The creation of new species is known as speciation and may result from natural selection, mutation or from Lamark’s theory of “Use and disuse”

In natural selection

Organisms produce far more offspring that they can survive given the limited natural resources
Individuals within a population vary
These variation result from inherited characteristics
Some of these variations may render the organism either more adapted or less adapter to its environment.
Individuals with characteristics that make them more adapted to the environment survive the struggle for existence, grow and attain reproductive maturity and thus pass on their genes to their progeny
Individuals that possess disadvantageous characteristics die before sexual maturity and therefore fail to pass on their genes to their progeny (1 x 6 marks)

Mutation

Mutations result in random changes in the amount or chemical nature of DNA (genetic Material) in an organism
Individual that carries advantageous mutations will be selected for whereas those with disadvantageous mutation will be selected again (1 x 2 = 2 marks)

According to Landmark

Internal forces within organisms tend to be the determine factor of the extend to which the organs and the organisms grow
Each organ is formed at least partly as a matter of feed or want
Continual use of an organ leads to continuous development until development while lack of use leads to diminution until it completely disappears
This theory was criticized based on the fact that changes which occurred in the organism in the course of life were not transmitted to the offspring (1 x 4 = 4 marks) (total = 20 marks)

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