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UACE Biology paper  2011

Answer all questions

  1. In Bryophytes, gametes are produced by
  2. gametophytes through mitosis.
  3. sporophytes through meiosis.
  4. sporophytes through mitosis.
  5. gametophytes through meiosis.
  6. Squamous epithelium is made up of thin and delicate sheets of cells as an adaptation to
  7. rapid cell division.
  8. facilitation of liquid movement.
  9. shortening diffusion distance.
  10. protecting the body from abrasion,
  11. In a non-dividing cell, the percentage of guanine is 40%. The percentage of adenine in the cell is

30

20

40

10

BIOLOGY UACE

  1. Which one of the following is a likely character in a human population, illustrated in figure 1.

Height.

Ear size.

Blood groups.

Finger length.

  1. Which one of the following properties of wa­ter facilitates its efficient transportation of glucose?
  2. Forms hydrogen bonds with other mole­cules.
  3. Has high surface tension.
  4. Has a low freezing point.
  5. Has a high boiling point.

Figure 2 shows the banding pattern of a myofibril when relaxed.

BIOLOGY UACE

Which one of the following occurs in refer­ence to the A band when the myofibril is contracted?’

  1. Becomes lighter.
  2. Becomes narrower.
  3. Disappears.
  4. Becomes wider.
  5. A companion cell has a large nucleus because
  6. it supports the sieve tube element which lacks a nucleus.
  7. it controls a large volume of cytoplasm.
  8. movement of materials in the sieve tubes is an active process.
  9. of its high metabolic rates.
  10. Which one of the following is correct about the refractory period in an axon of a nerve
    fibre?
  11. Inhibitory postsynaptic potentials are gen­erated.
  12. Voltage activated sodium channels open.
  13. The axon cannot transmit impulses.
  14. The axon can transmit impulses at higher voltage.
  15. What would be the water potential of a cell if its pressure potential is 500 kPa and its solute potential is Q 4900kPa?

-4400 kPa

4400 kPa

5400 kPa

-5400 kPa

  1. Which one of the following results when a gamete with non-disjunction is fertilized?

Duplication

Translocation

Monosomy

Polyploidy

  1. In an individual whose energy intake is 50, 000kJ per day, loses 1dm3 of sweat in a day dur­ing manual work. Given that the latent heat of vaporization of sweat is 2.45kJcm3, the percentage of energy lost by the individual during the work is

4.22.

5.0.

4.90.

7.65.

  1. The volume and surface area of four A, B, C and D are shown in the following table:

Animals

Volume

Surface area

 

/cm3

/cm2

A

1

6

B

8

24

C

64

96

D

64

28

Which one of the organisms would need a specialized respiratory system

  1. Figure 3 shows pyramids of energy A, B, C and D in different areas of an ecosystem.

Pyramid biology

In which pyramid does the primary consumer make most efficient use of the producer?

  1. Which one of the following factors has the greatest limiting influence on the population
    growth of an alga at the bottom of a pond?
  2. Light.
  3. Carbon dioxide,
  4. Minerals.
  5. Oxygen.
  6. A non-mutualistic role of bacteria in ruminant animals is that they
  7. secrete enzymes for hydrolysis of carhydrates.
  8. break down food into small fragments to ease enzyme action.
  9. produce bacterial protein which is used by the ruminant.
  10. are preyed on by the ruminants.
  11. Photosynthetic bacteria differ from green plants in that
  12. they lack chlorophyll.
  13. their source of energy is through oxida­tion of hydrogen sulphide.
  14. their source of energy is through oxida­tion of iron salts.
  15. their source of hydrogen is hydrogen sul­phide.
  16. Gametes are haploid because

A   two replications of DNA occur during meiosis.

  1. homologous chromosomes separate dur­ing meiosis.
  2. crossing over occurs during prophase.

D   chromatids do not separate during meiosis.    

  1. Which one of the following would be the immediate problem to a fish when taken out of water?
  2. Insufficient oxygen supply.
  3. Lack of support.
  4. Drying up of gills.
  5. Lack of food.
  6. Which one of the following is least likely to occur when organisms of similar species compete for same limited resources?
  7. Range restriction.
  8. Aggression towards each other.
  9. Extinction
  10. Co-existence.
  11. Parthenogenesis differs from asexual reproduction, parthenogenesis involves
  12. two organisms of different sexes.
  13. fertilization.
  14. formation of gametes.
  15. mixing of genetic material.
  16. Which one of the following factors does not affect the distribution and abundance of an
    organism?
  17. Mimicry.
  18. Predation.
  19. Human species.
  20. Speciation.
  21. Which one of the following processes decreas­es the glucose level in the blood?
  22. Break down of fats.
  23. Synthesis of glycogen.
    C. Breakdown of proteins.
  24. Breakdown of glycogen.
  25. Which one of the following is true about ac­tive transport?
  26. Requires a semi-permeable membrane.
  27. Occurs in both living and non-living cells.
  28. Uses up oxygen.
  29. Involves movement of molecules along a concentration gradient.
  30. Which one of the following is not involved in a physiological homeostatic process?
  31. Positive feedback.
  32. Receptors.
  33. Effectors.
  34. Control mechanism
  35. Lack of iodine in the diet causes cretinism because iodine
  36. controls metabolism.
  37. is essential in the formation of metabolic enzymes.
  38. influences growth of bones.
  39. is required for synthesis of thyroxine.

 

  1. Plant species where 2n = 12, the chromosome number in its endosperm cells after
    fertilization is
  2. 6.
  3. 12.
  4. 18.
  5. 24. g
  6. Individuals lacking desired qualities are pre­vented from mating during artificial selection
    using the following methods except
  7. extermination.
  8. segregation.
  9. sterilisation.
  10. cross-breeding.
  11. Fats yield more energy per unit mass molecule than carbohydrates because fats posses
  12. more carbon atoms.
  13. more hydrogen atoms.
  14. fewer carbon atoms.
  15. fewer oxygen atoms.
  16. Which one of the following human activities can lead to acid rain?
  17. Mining coal.
  18. Use of fossil fuels.
  19. Sewage disposal in water bodies.
  20. Commercial farming.
  21. According to Mendel, all the following are correct except
  22. each characteristic of an organism is con­trolled by a pair of alleles.
  23. each allele is transmitted from genera­tion to generation in a discrete unit.
  24. there are several varieties of alleles from each parent.
  25. each organism inherits one allele of each pair, from each parent.
  26. Which one of the following illustrates a tropic response
  27. Capitulum of flowers closes in low light intensity.
  28. Closed petals of tulip flowers open high temperatures.
  29. Pollen tubes grow towards the micropyle of the ovule in a flower.
  30. Leaves of mimosa fold down when touched.
  31. Which one of the following is an adaptation of the kidney in a fresh water fish?
  32. Large glomeruli.
  33. Long loop of Henle.
  34. Well-developed collecting duct.
  35. Few glomeruli.
  36. Figure 4 shows the oxygen dissociation curves for mudfish, human foetus, adult human and an active flying bird.

Which curve is most likely to be that of an active flying bird?

  1. R.
  2. S.
  3. T.
  4. P.

 

  1. A layer of wax is deposited over chitin in exoskeletons because
  2. wax reduces the weight of the exoskeletons.
  3. Chitin is permeable to water.
  4. wax allows flexibility of the body.
  5. Chitin alone is not hard enough for protection.
  6. Which one of the following conditions may limit the chances of variation in the offspring plants?
  7. Dioecism.
  8. Self-incompatibility.

C Protandry.

  1. Hermaphrodism.
  2. Which one of the following would be an effect of increased competition on a stable population?
  3. Increasing the environmental resistance thereby increasing the population.
  4. Lowering the environmental resistance thereby increasing the population.
  5. Lowering the environmental resistance thereby decreasing the population.
  6. Increasing the environmental resistance thereby decreasing the population.
  7. Which one of the following occurs to the axon membrane during an action potential? It is
  8. polarized with inside negative while out­side is positive.
  9. depolarized with inside negative while outside is positive.
  10. depolarized with inside positive while out­side is negative.
  11. polarized with inside positive while out­ side is negative.
  12. Structures of common origin modified in various to adapt animals to different modes is an illustration of
  13. Homologous structures.
  14. convergent evolution.
  15. analogous structures.
  16. comparative anatomy.
  17. Which one of the following is an advantage of social behaviour among animals?
  18. No incidence of cannibalism.
  19. Decreased susceptibility to disease.
  20. Increased reproductive efficiency.
  21. Decreased competition.
  22. Which one of the following classes does a cen­tipede belong to?
  23. Arachnida.
  24. Diplopoda.
  25. Chilopoda.
  26. Crustacea.

Solution

  1. A 11.C 21.D                31.C               

2.C                   12.D               22.B                32.A

  1. D 13.B 23.C                33.D

4.C                  14.A                24.A                34.B

5.A                  15.D                25.D                35.D

6.B                  16.D                26.C                36.B

7.D                  17.B                27.D                37.C

  1. C or D 18.A 28.B                38.A

9.A                  19.D                29.B                39.C

10.D                20.C or D        30.C                40. NONE

 

Explanation for the answers for section A

  1. The answer is A

Baryophytes undergo alternation of generation in which a haploid gametophyte generation alternates with a diploid spo rophyte generation. Production of gametes by the gametophyte is by mitosis so that the gametes are also haploid. The gametes then fuse to form a diploid zygote which grows into a diploid sporophyte. The sporophye produces spores by meisosis and  so the spore are also haploid. Spores then germinate and grow into the gametophyte.

  1. The answer is C

Diffusion of materials across an epithelium occurs across the thickness of the cells constituting the epithelium. Being thin and delicate, the cells of the squamous epithelium shorten the diffusion distance, i.e. the distance across which materials have to move during diffusion.

  1. The answer is D.

According to the rules of base pairing, guanine (G) pair with cytosine (C) and adenine  (A)  pairs with thymine (T).

As such the ratio of G:C is 1:1 and that of A : T is also 1:1 thus, if G is 40%even C is 40%.

As such A and T constitute 20% which they share in a ratio 1:1 thus, A constitutes 10% and T also 10%

  1. The answer is C

The graph indicates discrete values of the character with no intermediate, i.e. separate bars. This is a representation of discontinuous variation. Such variation is only possible for qualitative characteristics such as Blood groups; tongue rolling; skin colour; eye colour etc.

 Note: continuous variation occurs for quantitative characters such as height. Ear size, finger length etc. such characters can take on any value and may have intermediate values. Continuous variation is represented by a histogram. i.e.

  1. The answer is A

Glucose is a polar molecule which is capable of forming hydrogen bonds water is also polar and forms hydrogen bonds with itself and other polar molecules. This property facility the dissolution of glucose in water which it is transported.

 

  1. The answer is B

During skeletal muscle contraction the actin and myosin filaments slide parallel to one another.

This shortens the sarcomere. The 1-band (the A- band in the question) becomes narrower.

7.The answer is D

The nucleus of a cell controls all the metabolic activities of the cell and such, the size of the nucleus of a cell is directly proportional to the metabolic activity  of the cells.

The companion cell is a site of intense metabolic activity and thus has a large nucleus.

Note:

Although the sieve element is metabolically inert., it is just mere speculation that the companion cell provides for its metabolic needs.

  1. The answer is C and D

Refractory period is the period of inexcitability that accompanies the recovery phase of the axon. It is divided into two: an a absolute refractory period during which the axon completely cannot transmit an impulse and relative refractory period during which it is possible to generate an impulse provided that the stimulus is stronger than usual, i.e. of higher voltage.

Note:

During this period, the sodium ion channels are closed.

Inhibitory post synaptic potential is concerned with synaptic transmission only.

  1. The answer is A

Water potential (Ѱ), solute potential (Ѱs) and pressure (Ѱp) are related by the following equation.

Ѱ         =          Ѱs +  Ѱp          (the cell  equation)

Ѱs is negative while Ѱp  is positive.

  • Ѱs =          -4900kpa;        Ѱp       = + 500pa
  • Ѱ =          -4900k pa        +          500k pa
  • Ѱ =          -4400kpa

Hence the water potential of the cell is -4400kpa

  1. The answers is D

Non-disjunction is the failure of sister chromatids to separate during meiosis.

As a result, some gametes are produced with a diploid genetic constitution while others are empty. When such gametes fertilized, a higher degree of chromosome complement is formed. For example, triploid and higher chromosome complements are formed. This is called polyploidy.

  1. The answer is C.

Volume of sweat, Vs               =          1dm/ day.

Lu of sweat                              =          2. 45kJcm-3

=>heat lost in sweat, Q out           =        Vs x L v

                                                                =             (1000 x 2.45)

Q out                 =          2450kJ/day

Energy intake, Q in                 =          50,000 KJ/day

  • % energy loss =         

 

  • =          2540 X  100   

                                                            50000

          energy loss                  =          4: 90%

Hence percentage energy loss during work is 4;90 %

 

 

  1. The answer is D

An organism that most needs a specialized respiratory system is one that the least surface area to volume ratio. In such an animal, diffusion alone cannot suffice its respiratory needs.

The surface area to volume ratio of these different animals are as shown;

Animals

S.A  /  V ratio

A

B

C

D

6/1 =6

24/8=4

96/ 64 = 1.5

28/64 = 0.4374

 

Hence animal that has the least surface area to volume ratio and therefore needs specialized respiratory system.

13 The answer is B

I energy pyramid, bars are proportional to the total energy utilized to each trophic level. Those shown indicate three trophic levels: producers, primary consumer and secondary consumers. In this case, the larger the size bar that corresponds to primary consumers, the more the energy they obtain from the producer and therefore the more efficient they utilize their producers.

This is show by pyramid B.

  1. The answer is A

Algae are photosynthetic organism. As such factors limiting their population so by limiting their photosynthetic activity.

The pond surface is usually covered with a layer of lower plants which limit the amount of light reaching the bottom of the pond. Therefore, the greatest limiting factor of population growth of a algae at the bottom of the pond is light.

  1. The answer is D

In a mutualistic relationship both organism involved benefit and no harm is done to either organism.

If any of the organism does harm to the other, then relationship becomes non-mutualistic. Therefore, that the bacteria in the gut of ruminant animals are preyed on them is a non-mutualistic role.

16 The answer is D

Photosynthetic bacteria also obtain energy from sunlight like the green plants. However, they differ from green plants in that source of their hydrogen is hydrogen sulphide instead of water which is used by green plants.

  1. The answer is B.

Gametes are haploid because homologous chromosomes separate during anaphase I of meiosis

In the second division, which occurs without further duplication of DNA, each chromosome is divided into two chromatids that move to two different daughter cell.

Hence each (daughter cell) gametes has half the genetic material of that of the parent cell, i.e. is haploid.

  1. The answer is A

When a fish is taken out of water, the gills clamp up together. This reduces their effective surface area for gaseous exchange. Therefore, the immediate problem to a fish when taken out of water is insufficient oxygen supply.

  1. The answer is D

According the competitive exclusion principle, no two organism of the same species can occupy the same ecological niche. That is similar species of organisms that compete with each other for the same resources cannot co-exist.

However, they may impose restriction on their range of living or develop aggression towards each other. Otherwise, they may evolve into new separate species needing different resources, hence to extinction of the competing strains.

  1. The answer is C or D

Parthenogenesis is the development of a new individual from an unfertilized egg. There are two kinds of parthenogenesis: diploid and haploid parthenogenesis. In diploid parthenogenesis, the eggs (gametes) are diploid because they are formed by mitosis while in haploid parthenogenesis the eggs (gametes) are haploid because they are formed by mitosis.

No fertilization is necessary and only one sex is necessary. Also some degree of genetic mixing occurs due to crossing over at prophase 1 of meiosis.

In a sexual reproduction, no gametes are formed and there is no genetic mixing.

  1. The answer is D

Mimicry, predation and human activities are some of the factors that affect the distributions o organism.

Note:

Speciation is the process by which one or more species arise from previously existing species. It only affects the number of species present in an area but does not affect distribution and abundance of a given species of organisms.

  1. The answer is B

 The liver is the major organ that regulates the blood glucose level. One way in which it reduces the blood glucose level when it is higher than normal is by synthesizing glycogen from glucose.

Note:

When the blood   glucose   level is lower than normal, the liver can increase the glucose level by; breakdown of glycogen to glucose, and break drown of proteins and fats to produce residues that can be used to synthesize glucose by the process of gluconeogenesis

 

  1. The answer C

Active transport is the process by which materials are transported across a living cells membrane against a concentration gradient, using metabolic energy in form of ATP.

As such, active transport:

  • Uses up oxygen
  • Is inhibited by metabolic poisons
  • Does not occur in non-living cells.

Note:

Although active transport it takes place across a semi permeable membrane, this is not major requirement. The most important requirement is metabolic energy in form of ATP. This is why it cannot take place in non-living cells even though their membranes may still be semi-permeable.

  1. The answer is A

A physiological homeostatic process involves:

  • Receptors
  • Control mechanism
  • Effectors.
  • Norm or set point.

Note:

Positive feedback is a destabilizing mechanism which creates more instability of a system and therefore cannot be used as a homeostatic mechanism. The normal mechanism employed in physiological homeostatic process is negative feedback. Here, a change in the value of the controlled factor initiate a series of processes that bring back the factor to normal.

  1. The answer is D

Iodine is the most important regent in the formation of thyroxine. Thyroxine is an important metabolic hormone that is also important in influencing the growth of bones.

Cretinism is a condition in which the amount of thyroxine is very low in blood as a result of iodine deficiency in the diet. it is characterized by:

  • Poor bone development leading to stunted growth
  • Mental retardation.

This condition is diagnosed in infancy. If it goes unnoticed, it results in myxedema later in life. This is characterized by slow mental activity, decreased metabolic rate and swelling of face, tongue and loss of scalp hair.

  1. The answer is C

Given 2n         =          12

  • n =          6
  • however, the endosperm cell are triploid, i.e. 3n
  • number of chromosomes in endosperm cells

=          3x 6

=          18

  1. The answer is D.

Artificial selection is the process by which human encourage the breeding of animals with desired qualities while preventing those with undesired qualities from breeding. This is done by:

  • Segregation: animals with desired characters are bred together in a segregated area so that they do not mate with others whose characteristics are not desired.
  •  Sterilization: animals with undesired characters are sterilized so that they are unable to mate and therefore they cannot pass their characters onto the next generation.
  • Extermination: animals with undesired characters are killed before they reach reproductive age.

Note:

Cross-breeding is part of artificial selection but is not a means of preventing individual with undesired qualities from mating.

  1. The answer is B

Fats have a higher caloric valve, i.e. yield more energy per unit mass on oxidation than carbohydrates. This is because fats possess a higher proportion of hydrogen and an almost insignificant proportion of oxygen compared with carbohydrates. The    hydrogen is used in the respiratory chain in the mitochondria to form ATP

  1. The answer is B.

Fossil fuels yield carbon dioxide when burnt. Carbon dioxide is an acid gas. It dissolves is rain water to form acid rain. The other gas produced from the use of fossil fuels is sulphur dioxide which is also acidic and causes acid rain.

Note:

Coal mining does not yield any gas but use of coal as a\ fuel yield carbon dioxide which is an acidic gas

Sewage disposal in water bodies only causes eutrophication but does not cause acid rain.

Commercial farming reduces the incidence of acid rain production because the plant the absorb the excess carbon dioxide from the atmosphere.

  1. The answer is C

According to medal, characteristics of diploid organism are controlled by alleles occurring in pair and of a pair of such alleles. Only one be carried in a single gamete, i.e. each parent has only a one variety of an allele of each pair.

Also. Each offspring inherits one allele of each pair, one from each parent.

Each allele s transmitted from generation to generation in a discrete unit.

  1. The answer is C

Tropism is a growth movement of part of a plant in response to a directional stimulus.

In tropic responses, the direction of the response is related to that of the stimulus and ,in almost all cases, the plant part moves towards or away from the stimulus. each response is named according to the nature stimulus.

Thus:

Stimulus

Names of response

Example

Air

Light

Gravity

Water

Chemical

 

touch

aerotropism

phototropism

geotropism

hydrotropism

chemotropism

 

thigmotropism

Pollen tubes away from air

Plant shoots towards light

Plant roots grow downwards

Plant roots towards moisture

Fungal haphae grow towards nutrients

Tendrils od peas twin a round their support.

 

Note:

The other objectives indicate nastic responses; movement od a plant to non-directional or diffuse stimulus

Both tropic responses and nastic responses occur in plants

 

  1. The answer is A

Fresh water fishes are liable to osmotic influx of water across the gills part  and lining of the mouth and pharynx..

The overcome this problem in three ways:

  • possessing numerous large glomeruli
  • extensive reabsorption of salt from the glomerular filtrate
  • active uptake of salt by chloride secretary cells in the gills.
  1. The answer is D

A active flying bird demands much energy and therefore has high metabolic rate. To supply oxygen to the tissue rapidly, their haemoglobin must release it readily. This is the reason why it has its dissociation curve to the far right of all the organisms represented.

Note:

Mudfish, live in muddy water logged burrow where oxygen tension is very low. Its haemoglobin has very high affinity for oxygen and is represented by curve R, i.e.  lies to the far left.

Foetal haemoglobin has higher affinity for oxygen than for an adult human because it has to pick oxygen from maternal blood; its curve is to the left of that o an adult human. Thus curve S represents foetal haemoglobin while T is for adult human.

  1. The answer is D
  • Chitin is highly permeable to water. Therefore, if the exoskeleton of an insect were made up of chitin alone. It would lose a lot of  water from its body by evaporation.
  • Wax water repellent and impervious. Therefore, layer of wax on the chitin of the exoskeleton prevents water loss from the body of the insect and prevents desiccation.
  1. The answer is D

Variation in flowering plants occurs as a result of cross-fertilization. Therefore, any feature of flowering plant that prevent cross-pollination limits variation. Hermaphrodism is one such character that encourages self-pollination and therefore limits chances of variation

Note:

Dioecism, protandry and self-incompatibility encourage  cross-fertilization and therefore promote variation.

  1. The answer is B

 Competition is one of the factors that constitute environment resistance. others include, predation, diseases, etc. Therefore, reduction in competition reduces environmental resistance and thus encourages population growth.

  1. The answer is C

In resting state, the axon members are polarized with the outside positive and the inside negative.

During an action potential, the cell membrane becomes more permeable to sodium ions so that there is an influx of sodium ions in the cell. This depolarizes the membrane; the inside becomes positive while the outside negative.

`38. The answer is A

Establishment evolutionary   relationship on basis of structure similarities and difference among organism is called comparative anatomy. Under this:

Homologous structures are structures common origin modified in various ways to adapt animals to different modes of life. For example, the pentadactyl limb system.

This is case of divergent evolution

Analogous structures have different origin but are adapted to perform similar functions.

For example, wing of   birds and insects. This is a case of convergent evolution.

  1. The answer is C

Social behaviors animals have the following advantages

  • Increased reproductive efficiency resources.
  • Improved protection of available resource
  • Improved degree of protection against predators and /or intruders.

Its disadvantages include;

High incidence of cannibalism

Increased susceptibility to diseases.

Increased competition for resources

  1. There answer is C.

A centipede belongs to phylum Arthropoda, subphylum myriapoda and class chilopoda

Note:

Diplopoda is the class to which millipedes belong

Class Arachnida include the tick and spider

Class Crustacea include a wide range of aquatic arthropods, e.g. crayfish, water flea and the wood louse.

SECTION B

  1. Fungi were originally classified under the plant kingdom.

(a) outline the feature of the fungi made it necessary to place them in their own kingdom

(b) explain why the fungi are wide spread and in vast numbers.

(c ) what is the economic importance of fungi?

Solution :

  • – They lack chlorophyll and therefore unable to photosynthesize.

They are heterotrophic feeders.

  • The body is usually a mycelium; a network of fine tubular filaments called hyphae.
  • They store glycogen instead of starch

Others

  • They reproduce by means of spores.
  • Their cell walls are made of chitin not cellulose.
  •  
  • They reproduce asexually. This increases their chance of multiplication as only one organism is required
  • They reproduce by means of spores which are usually produced in large numbers and dispersed over a wide area.
  • Spores can withstand severe conditions and therefore allow fungi to colonize a diverse range of habitats
  • They are saprophytic feeders and therefore can grow on any kind of decaying organic matter.

Others

They can feed parasitically on other living organism, both plants and animals.

  • Yeast is used in fermentation to produce alcohol

Yeast is also used in baking of bread.

Most mould decompose organic matter may lead to rotting of fruit and food

Others

Some fungi are agents of diseases in both plants and animals

Penicillins produced penicillium natatum, a fungus, is an antibiotic.

The fungus in mycorrhiza relationships provides plants with mineral salts and water.

  1. (a) Explain the meaning of the Hardy-Weinberg equilibrium principle

(b) State four conditions that must be fulfilled in order for the principle to hold true

(c ) Brown eyes in a human population is caused by  a dominant. If in a population, 84% of the people have brown eye, using Hardy-Weinberg formula, determine the percentage of the population who are.

  • Heterozygous for eye colour. show your working.
  • Homozygous dominant for eye colour.show your working

Solution

  • Provided there are no disruptive influence such as mutations or selection, the frequency of alleles in a population remains constant, generation after generation.

There is continued movement of gene (gene flow) within the population due to breeding but the overall gene frequencies remain constant. This stability is referred to as genetic equilibrium.

  • No mutation occurs

Mating must be random

The population must be large.

No emigration or immigration from or into the population should occur

Others

Generations should not overlap

All genotypes should be equally fertile, so that no selection occurs.

  • Let the allele for brown eyes be B

The allele for other eye colour be b

Frequency of allele B be p

Frequency  of allele b be q

Given BB+ Bb constitute 84%

The hardy-Weinberg equation states

P2 +2pq + q2                =          1

given p2 + 2pq             =          0.84

            q2                     =          1 – 0.84

            q2                     =          0.16

            =>q                  =          0.4

Also p + q                   =          1

            P                      =          1-0.4

            P                      =          0.6

=> (0.6)2 + 2pq                       =          0.84

            2pq                  =          0.84-0.36

            2pq                  =          0.48

Hence 0.48% of the population are heterozygous.

(ii) from above

 

P          =          0.6

=>        BB       =          p2        =          (0.6)2

.;          BB       =          0.36

% 0f    BB       =          36%                                                                                                    

hence, the percentage of individual homozygous dominant for eye colour is 36%                                                                                                                                                              

 

  1. (a) Describe the adaption of each of the following tissue for their functions, giving one example of a site where each of them is found.

(i)  Stratified tissue

(ii) Collagen tissue

  • Explain how the structure of preteins enable them to form body tissue and structure

 

Solution

  • – Stratified epithelium consists of a number of layers of cells. It’s therefore thick,

             forming a tough impervious barrier.

  • Cells are continually replaced form the mitotic divisions of the germinal layer. This allows the epithelium to withstand the continued force of wear and tear.
  • In some areas, the cells on the surface are transformed into a dead horny layer of keratin. This protects the inner cells from abrasion.

External skin surface

Others

Lining of the buccal cavity

Lining of the vagina

Lining the upper third of the esophagus

(ii)   Collagen  consist of three polypeptide chains coiled round each other to form triple helix.The chains are interlinked by hydrogen bonds which makes the entire structure tough and inextensible. This provide great tensile strength

It is found in tendons

  • Structural proteins such as keratin have a secondary structure in form of an extended spiral helices with cross linking disulphide bridge between neighbouring chains. This provides hardness allowing keratin to be found in wool, hair and nails.

Other structure proteins with parallel polypepetide chains-linked at many points are collagen and elastic. They are both found in muscles.

 

 

  1. (a) Explain what is meant by alternation of generation.

(b) State two difference and two similarities between pollen grains of a flowering plant and the spore of moss.

  • Differences
  • Similarities

(c ) How are ferns better adapted to live on land than mosses?

  • Suggest why Bryophytes are
  • Restricted to growing in damp environment
  • Able to grow successfully on land

 

  • Alternation of generation is the alternation between a diploid spore producing sporophyte generation and a haploid gametes gametophyte generation in a single life cycle of a plant in the same cycle. The alternates between a diploid (2n) sporophyte generation and haploid (n) generation.

 

  • Differences

Spore

Pollen grains

Can germinate into an independent plant structure

Not gametes

Others:

Remain viable over a long period of time

Cannot form an independent plant structure.

Male gametes

 

Are viable for only a limited time

 

  • Similarities

They are both formed by meiosis

They are both haploid

Others

They are both light and dispersed by wind.

  •  
  • Ferns are vascular plants containing vascular tissue made up of xylem ad pheom
  • They sporophyte generation has true roots, stems and leaves
  • Their bodies are supported by xylem because it contains lignified cells of great strength and rigidity.

Others:

  • The true leave trap more light for photosynthesis
  • They lack a well-developed root system and rely on diffusion across the whole plant body and the root like rhizoids to obtain water

They are delicate and small.

They lack a cuticleThey can easily be subjected to desiccation in drier environment

 

They depend on water for the movement of male gamest towards female gametes during fertilization.

Have chlorophyll and are therefore capable of photosynthesizing 

They grow in clusters and therefore strengthen their positions on the soil.

They reproduce both sexually and a sexually. This increases their chances of survival on land

  1. Figure 5 show light saturation curve of photosynthesis for plants of same species growing under different light intensities.

  • Compare the effect of intensity on the carbon dioxide uptake in the types of plants.
  • Describe the state of the light plants at point P
  • Explain what happens biomass in region Y
  • State an environment factor that affects the shape of the graph other than carbon dioxide

Solution:

  • Similarities

Carbon dioxide uptake increase initially at low light intensities and the decreases gradually at higher intensities, to reach constant valves.

Differences

Light plants

Shade plants

–          Initial rate of carbon dioxide uptake is high at low light intensities

–          Carbon dioxide uptake   starts below zero.

–          reach a constant at a higher light intensity.

–          higher   saturation value

–          Initial rate of uptake carbon dioxide is high at low light intensities

–          Carbon dioxide uptake starts at zero

–          reach a constant at a lower light intensity.

–          lower  saturation value

 

  • The plant is in a state of compensation point at point P. Here is no net uptake of carbon dioxide because the rate of photosynthesis equals the rate of respiration.
  • In region Y the plant biomass decrease

Explanation

The rate of respiration of the plants is higher than photosynthesis. There is more food breakdown than synthesis.

  • Temperature
  1. Figure 6 illustrates two different mechanisms of gaseous exchange in fish A and B

Biology uace

  • State two differences between the two systems of oxygen concentration (2marks)

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

 

  • Explain the physiological advantage of fish A over B(2marks)

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

 

  • Describe how a gill is structurally adapted as a respiratory surface (4marks)

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

 

Solution

  •  

Differences

Fish A

Fish B

-oxygen concentration of blood is above 50% at the end of the gill plate.

– water always has a higher oxygen concentration than blood

 

Other

Oxygen concentration of the blood increase linearly along the gill plate.

 

-oxygen concentration of the blood  is  about 50% at the end of the gill plate.

Initially water has a higher oxygen concentration, but at the end of the gill plate, the oxygen concentration blood and water are the same.

Oxygen concentration of the blood increase first rapidly then decreases gradually and reaches a constant valve at 50%

 

  • Fish A maximizes gaseous exchange than fish B

Fish A maintains a steep concentration gradient between the water and blood that the fish picks up enough oxygen from the water and deposits sufficient quantities of excess carbon dioxide in it.

 

  • Highly folded into filaments to increases surface area gaseous exchange
  • It is covered with a thin highly permeable membrane to reduce the diffusion distance.
  • It has a rich blood to increases the efficiency to gaseous exchange.
  • It’s wet in order to increase chance of picking up gases readily dissolve in the moisture.
  • Numerous filaments increase the surface area

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