Al Biology 1989 Paper 1 Marking

AL BIO 1989 Paper I 1.

Alex Lam

Section A

Dormancy describes the state of an organism (either as adults or sometimes during their life cycle) in which growth and development cases, 1 and the metabolic rate may fail to the point that it is only just sufficient to keep the cells alive. 1 Dormancy enables an organism to withstand unfavorable conditions (e.g. drought, food shortage and winter cold) because in this way, the organism can survive for a long period of time without exhausting its food reserve. 1 It also allows time for dispersal by natural agents, whilst at the same time allowing any internal changes to take place. 1 (4)

2.

Instinctive behaviors are complex, inborn, stereotyped behaviour patterns of immediate adaptive survival value to the organism and are produced in response to changes in the environment. (They are unique to each species and are handed down from generation to generation and have important survival significance.) 1 One suitable example e.g. pain withdrawal reflex.  Learned behaviours are those adaptive changes in an individual’s behavior as a result of previous experience or learning. 1 One suitable example e.g. "automatic" braking by an automobile driver confronted with an obstacle; finding one’s way through a maze.  (4)

3.

(a)

Water potential is a measure of the tendency of water to leave a solution. 1 Osmotic potential is a measure of the tendency of a solution to pull water into it, it always has a negative value. 1

(b)

Binary fission is an asexual way of reproduction in which one organism divides into two (e.g. binary fission in bacteria), 1 whereas in fragmentation, one organism may give rise to several new individuals (e.g. fragmentation in Spirogyra). 1

(c)

Phototaxis is the movement of an entire cell or organism towards a unilateral light source (e.g. Euglena swims towards light).

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AL BIO 1989

Alex Lam

1 Photoperiodism is a phenomenon related to the response of an organism to variations in daylength (e.g. flowering response in plants). 1 (6)

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AL BIO 1989 4.

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One mark for each curve : FSH

1 1

LH

1

oestrogen

1

progesterone

1

events occurring in the ovary

2

events occurring at the uterine lining

2 (8)

For example :

5.

(a)

Spermatophyta : for selective absorption of water and water －soluble solutes into the central stele , 

(b) Echinodermata : for locomotion / attachment ,  (c) Platyhelminthes : for excretion / osmoregulation ,  (d) Pteridophyta : for reproduction ,  N.B. Correct spellings for the taxonomic group names are required.

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A pyramid of biomass is based on the total amount of living material at each

)

trophic level at any one time

)

1 OR it shows the standing crop / biomass present at a given time

)

Thus producers might be few or small, but at the same time they could be being produced at a massive rate to feed the larger number of grazing consumers. 2 Example : The food chain in a fertile, productive field which is being constantly grazed by cows. 1 (4) 7.

If the toxic chemical e.g. DDT / heavy metals  cannot be metabolized and excreted, 1 it would accumulate in the body of the organism and passes from one trophic level to another.  As energy is lost from one trophic level to another by respiration, reproduction etc. 1 The consumers at the higher trophic level have to feed on a large number / biomass of smaller consumers which in turn feed on a larger number / biomass of producers, thus the concentration of the toxic chemical will be the highest at the top consumer level. 1 (4)

8.

(a)

A = tidal volume  B = inspiratory reserve volume  C = residual volume  D = vital capacity  N.B. correct spelling is required.

(b)

A =

the volume of gas being breathed in or out by a normal subject at rest

1 B =

the difference between inspiratory capacity and tidal volume

1 OR

=

The extra amount of air ( in addition to the tidal volume) that a normal subject

can take into the lung during a deep inspiration.

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AL BIO 1989 C =

Alex Lam

the amount of air that remains in the lungs even after a maximum expiration 1

D =

the maximum volume of gas that can be exhaled following a maximum inspiration 1 (6)

9.

(a)

A － lag phase, cells were adapting to the new environment and synthesizing the necessary macromolecules for multiplication. 1 B － log or exponential phase, conditions were favorable and cells multiplied at a rapid rate. 1 C － stationary or steady phase, nutrient started to decrease and toxic wastes increased, rate of growth equaled to the rate of death, therefore cell number remained stationary. 1 D － death or decline phase, nutrients depleted and toxic wastes accumulated to such an extent that death rate was high, resulting in a decrease of cell number. 1 (6)

(b)

The turbidity curve represents the total number of cells, live or dead, present in the culture medium. (2)

(c)

log 6 - log 4 1,000,000 - 10,000 = 10 hr - 4 hr 6 hr 990,000 = 6 = 165,000

(2)

= 1.65 × 10 5 cell/hour (or 2.75 × 10 3 cell/min.) (d)

(i)

Part B may be less steep and part C lower because unsterile medium contains microorganisms which would compete with the yeast for food

2)

OR Part B may level off and then drops because the presence of toxigenic organisms in the medium may stop growth

2)

any 1 OR Part B may be much steeper because of the possible boostering effect in the presence of certain microorganisms (synergism)

2) (2)

(ii)

Part B may be less steep and / or prolonged and part C lower because anaerobic metabolism is less efficient, therefore lover growth rate; accumulation of acids and / or alcohol may inhibit yeast growth also.

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(iii)

Part A may be shorter, B steeper, C may or may not be higher, D steeper The curve shift to the left. Increase in temperature accelerates both growth and death rate. (2)

(e)

By continuously or periodically adding nutrients, removing waste products and excess cells from the culture medium. (2)

(f)

Examples such as : (Any 2, 1 mark each) －

continuous culture used in industries to extract cells, acids, alcohols, amino acids, antibiotics and other microbial products.

－

sewage treatment tanks with continuous addition of raw sewage and removal of effluent and solids.

－

microflora in the intestine with addition of food and removal of faeces

－

any other ecological niche where input of nutrients and removal of cells and wastes are shown to maintain a steady microbial population. (2)

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AL BIO 1989 10. (a)

Alex Lam

grain － for food 1 straw － for bedding and fodder for farm animals, etc. 1 (2)

(b)

(i)

intermediate density

1 (ii)

high density

1 (iii)

intermediate density

1 (3) (c)

The extra nitrogen is mostly taken up by the stem and leaves of the plants. 1 This can be shown by the fact that at low density the increase in total dry weight is due to an increase in the weight of straw rather than grain. 1 (2)

(d)

NO2－

NH4 nitrifying bacteria

NO2

NO3－ which is then absorbed by the plants.

(3) (e)

(i)

Low concentration of fertilizer combined with high density.

1

(ii)

Low concentration of fertilizer combined with intermediate density

1 (2)

(f )

No, too high a plant density : may result in intraspecific competition for light / water, etc. 1 man increase the chance of spreading of infectious diseases

both of which would

lower the yield 1 Too high a fertilizer concentration may also affect the uptake of water and dissolved mineral salts as this would create a hypertonic environment. 1(bonus) (2) (g)

Advantages : －

contains the whole range of required mineral elements

－

increases the organic matter content of the soil with consequent benefits to cation exchange capacity, water holding capacity and soil structure

1) 1)

any 2

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minimize pollution

1)

Disadvantages : －

bulky and the cost of collection and handling

1)

－

may spread disease causing organisms

1)

any 2 －

have a foul smell

1) (4)

(h)

Knowledge of genetics applied to plant breeding to produce crop plant of desired qualities

2)

OR Knowledge of ecology applied to agricultural practises e.g. weeding to lessen interspecific competition

2)

any 1 OR Other suitable answer

2) (2)

11.

(a)

When air temperature rose to above 31°C, there were rapid increases of vaporization of sweat from body surface and the rate of blood flow in skin blood vessels increased. Increased vaporization from skin implies increased sweat production → increased evaporative heat loss. Increased blood flow in skin blood vessels implies dilation of skin blood vessels → more heat brought from body core to surface and dissipated to the surroundings by convection conduction and radiation (3)

(b)

(i)

Rate of heat delivered from the body core to the skin remained almost unchanged as indicated by the relatively constant blood flow to the skin The decrease in skin temperature is the result of increasing heat loss (mainly by convection) due to the steepening of the temperature gradient between the body and the surrounding air. (2)

(ii)

The change represents a balance between the increase in the rate of heat delivered from the body core to the skin due to the rise in skin blood flow and the marked increase of vaporization of sweat and hence evaporative heat loss from the body surface. (2)

(c)

Between 29°C and 31°C, least energy is required to maintain the body temperature No active means of trying to increase heat loss or to increase heat production. 1 Below 29°C, the increase in metabolic rate parallels the rise in heat loss, indicating that the processes for increasing heat production to balance the heat loss are responsible for the change in metabolic rate.

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2 Above 31°C, metabolic rate becomes higher because active means of increasing heat loss from the body (e.g. increase in sweat production, and vasodilation of skin blood vessels) are involved.

1)

OR this might be due to increased metabolism of the peripheral tissue as skin temperature approaches core temperature

1)

any 1 (4) (d)

Involuntary muscle contraction (shivering)

(e)

Diagram ‘indication involvement of the following

(1)

1

the thermoregulatory centers at the hypothalamus.

1

2

changes in air temperature detected by skin thermoreceptors.

1

3

changes in the temperature of blood detected by hypothalamic thermoreceptors.

1

4

the heat loss / conservation responses.

1

5

the feedback mechanism.

1 (5)

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For example : Air-temperature

Skin cold receptor

Skin warm receptor

Thermoregulatory centres in hypothalamus

Heat gain

Heat loss Thermoreceptor in hypothalamus (Spinal cord, viscera)

‧ Constriction of skin blood vessels ‧ Contraction of erector-pili muscle of hair ‧ Shivering ‧ Exercising

(f)

Temperature of blood

‧ Dilation of skin blood vessels ‧ Relaxation of erector-pili muscle of hair ‧ sweating

Putting on clothes.



The clothes can provide insulator, and hence reduce heat loss by convection forms the body surface to the surrounding air. 1 Curling up  Adopting a curled up body posture can reduce heat loss by decreasing the exposed surface area of the body. 1 (3) OR Other suitable answers with correct explanations



each)x2

1

each)x2 (3)

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AL BIO 1989 12. (a)

Alex Lam

Refer to graph : Title of graph

1

Properly drawn and fully labelled x and y axes

1

Plot the 2 sets of data correctly using different symbols and lines for the 2 graphs

2

Give a key to each graph

1 (5)

(b)

(i)

Sensitivity is greatest in the range 3000 － 4000 Hz. 1 Auditory threshold is sound frequency dependent : further elaboration e.g. high threshold for sound < 500 Hz and > 10000 Hz, low threshold for sound around 4000 Hz. 1 (2)

(ii)

The whole curve will shift upward in a uniform manner, i.e. higher sound intensity threshold will be required for the whole frequency spectrum. 1 Wax accumulation in the external ear canal interferes with the transmission of air －borne sound to the tympanic membrane. 1 Therefore, higher sound intensity is required to activate the sensory mechanism of the inner ear. 1 (3)

(iii)

Refer to graph

(2)

(c)

Hearing ability declines with age, particularly in high frequency range.

(2)

(d)

About 120 － 4700 Hz.

(2)

(e)

Flowchart indicating involvement of the following : 1.

tympanic membrane

2.

Ear ossicle



－

transmission



－

amplification



3.

vibration of endolymph inside cochlea



4.

basilar membrane



5.

sensory hair cells



6.

tectorial membrane



7.

auditory nerve



N.B. Deduct  mark from total if answer not in the form of a flowchart.

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For example : sound wave ↓ vibration of tympanic membrane ↓ vibration of ear ossicles ↓ vibrations amplified and set up pressure waves in fluid of the cochlea ↓ vibration of basilar membrane ↓ hairs of sensory hair cells touch the tectorial membrane (hair cell stimulated) ↓ nerve impulse generated and transmitted to brain via auditory nerve

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