BIOLOGY MAY/JUNE 2006 PAPER 1

1

Correct

B The electron microscope has a 0.5 nm resolution while the light microscope has one of 0.2 µm i.e. 200 nm.

Incorrect

A ______

C ______

D ______

2

Correct

C Golgi bodies, lysosomes and cytoplasm all have single cell membranes while mitochondria and nuclei have double membranes.

Incorrect

A ______

B ______

D ______

3

Correct

B Golgi bodies are abundantly found in secretory cells like goblet cells. The other cells in the list are not secretory.

Incorrect

A ______

C ______

D ______

4

Correct

C Increased surface area to volume ratio increases the area for molecules to move into cells. Increased molecular movement increases active transport rate.

Incorrect

A Cell walls are completely permeable and do not affect active transport efficiency.

B Same as option B.

D Active transport does not require a partially permeable membrane.

5

Correct

D All prokaryotes contain ribosomes for protein synthesis.

Incorrect

A All prokaryotes have cell membranes.

B Prokaryotes divide by binary fission.

C Prokaryotes do not have mitochondria.

6

Correct

C Magnification = image length/object length. The image has a 1.75 cm i.e. 17500000 nm thick membrane. The actual membrane thickness is 7 nm. M = 17500000/7 = 2.5 × 10^6.

Incorrect

A ______

B ______

D ______

7

B Hydrolysis is the breakdown of larger molecules into smaller ones

Correct with the addition of water i.e. converting starch to glucose.

Incorrect

A Condensation is the formation of complex molecules from simple ones i.e. starch from glucose.

C Polymerization is the formation of polymers from monomers.

D Synthesis is any formation process.

8

Correct

A Starch digestion is tested with Benedict’s solution which turns brick red in the presence of reducing sugars.

Incorrect

B Biuret’s test is for proteins.

C Ethanol emulsion test is for fats.

D Iodine test is for the presence of starch.

9

A Amylose has α 1, 4 linkages with no branches.

Correct

Incorrect

B Cellulose has β 1, 6 linkages.

C Amylopectin has both α 1, 4 and 1, 6 linkages.

D Cellulose has β 1, 6 linkages and amylopectin has both α 1, 4 and 1, 6 linkages.

10

Correct

C Hydrophobic interactions are found in both tertiary and quaternary structures.

Incorrect

A ______

B ______

D ______

11

Correct

C Peptide bond has C=O and N-H bonds.

Incorrect

A The bond doesn’t have C=O.

B The bond doesn’t have C=O or N-H.

D The bond doesn’t have N-H.

12

Correct

D Water movement in the xylem depends in molecular cohesion-adhesion forces.

Incorrect

A Density does not affect water transport.

B Solvent properties do not affect water movement

C Heat capacity does not affect water transport.

13

Correct

A At 37 °C the product concentration increases until it becomes constant since the enzyme is saturated. From 37 °C to 80 °C, increased temperature increases enzyme activity, so the graph slope for this experiment is steeper than X. However, the enzyme denatures at high temperatures so less product is formed.

Incorrect

B Product concentration is decreasing and not becoming constant in graph 2.

C Product concentration in graph 2 is the same as that in graph 1.

D Same as option B.

14

Correct

D Non-competitive inhibition occurs at sites other than the active site. This changes the enzyme 3-D structure which cannot be reversed by introducing more substrate.

Incorrect

A ______

B ______

C ______

15

Correct

B Active transport is molecular movement from an area of lower concentration to an area of higher concentration i.e. against a concentration gradient, and requires energy.

Incorrect

A Active transport involves moving against a concentration gradient.

C Diffusion is molecular movement from an area of higher concentration to an area of lower concentration i.e. down a concentration gradient

D Osmosis is water molecule movement down a water potential gradient.

16

Correct

C Molecular size and diffusion distance are inversely proportional to the diffusion rate.

Incorrect

A Conc. gradient is directly proportional to diffusion rate.

B Surface area is directly proportional to diffusion rate.

D Conc. gradient and surface area are directly proportional to diffusion rate.

17

Correct

A Water molecules move into the potato tissue via osmosis causing an increased pressure potential.

Incorrect

B Solute potential increases as solute concentration decreases by water movement into the tissue.

C The water potential becomes less negative as the tissue water potential increases when water moves into it via osmosis.

D The water potential becomes more negative as the solution water potential decreases when water moves out of it via osmosis.

18

Correct

D DNA replication in the S phase occurs before mitosis or prophase happens.

Incorrect

A Nucleus breakdown happens during prophase in mitosis.

B mRNA is not needed for mitosis.

C Centrioles migrate in prophase.

19

Correct

B DNA replicates before prophase, giving 46 chromosomes and 92 chromatids. Spindle formation and nuclear envelop breakdown occur in prophase and not before that.

Incorrect

A ______

C ______

D ______

20

Correct

A DNA replication takes place in interphase just before mitosis. Nucleotides are utilized in the replication.

Incorrect

B ______

C ______

D ______

21

Correct

A A nucleotide contains a pentose sugar, a nitrogenous base and a phosphate group.

Incorrect

B This is only a nitrogenous base.

C These are two nucleotides joined by hydrogen bonds.

D These are two phosphodiester bonds and a free phosphate.

22

Correct

C The generation produced by one division will have hybrid DNA because of semi-conservative replication.

Incorrect

A The generation will have only N14 DNA after multiple divisions.

B The DNA will not contain only N15 after bacteria are introduced to N14.

D This solution is obtained after more than one division.

23

Correct

B Out of 6000 nucleotides, 3000 will be used for transcription from the sense strand. 3 nucleotides represent 1 amino acid translated, so 3000 nucleotides will give 1000 amino acids.

Incorrect

A ______

C ______

D ______

24

Correct

B If 20% bases are cytosine, guanine will also be 30%. The remaining pyrimidines makeup 40%, in which there is 20% adenine. This, when transcribed, gives 20% uracil.

Incorrect

A ______

C ______

D ______

25

Correct

B As humidity increases, water vapour concentration outside the leaves increases. Water vapour in the leaves stops diffusing out of the leaves because of the concentration gradient, so vapour loss decreases with humidity increase.

Incorrect

A Temperature increase causes increased vapour loss through diffusion.

C Light intensity increase causes increased vapour diffusion and water loss.

D Increased wind velocity removes water vapour from the leaf surrounding, increasing the water vapour concentration which therefore increases loss of vapour via diffusion.

26

Correct

D The structure is a lignified xylem vessel.

Incorrect

A ______

B ______

C ______

27

Correct

C Water moves up the xylem due to molecular cohesion-adhesion forces as well as an increasing water potential gradient caused by a decreased potential in the leaves which causes it to move up via osmosis.

Incorrect

A Water is not actively moved in the xylem.

B Water potential is decreased in the leaves, and osmosis in roots helps water move into the roots and not the xylem.

D Translocation occurs in phloem.

28

Correct

C Tissue fluid contains phagocytes, but no platelets or proteins which are too big to pass into the fluid from the capillaries or cells.

Incorrect

A ______

B ______

D ______

29

Correct

D The curve shifts to the right when oxygen affinity decreases and cells require more oxygen i.e. in case of high CO2 concentration and low pH.

Incorrect

A ______

B ______

C ______

30

Correct

C The duration when both valves are closed is between 1 and 2, and 3 and 4 i.e. 0.07 seconds.

Incorrect

A ______

B ______

D ______

31

Correct

D Cartilage and goblet cells are present in the trachea and bronchi, while smooth muscle is present in the bronchi and bronchioles, and cilia in the trachea and bronchioles.

Incorrect

A ______

B ______

C ______

32

Correct

C Phagocytes invade the alveolar walls in response to inflammation and release the enzyme elastase to digest elastin the walls.

Incorrect

A ______

B ______

D ______

33

Correct

B Nicotine causes accumulation of cholesterol in the vessels which are deposited and form plaques that obstruct the vessels.

Incorrect

A Tumours do not form in vessels by smoking.

C Tar sticks to the cilia in the trachea and bronchioles and not to artery walls.

D Carbon monoxide causes CO poisoning which does not block arteries.

34

Correct

D All three organisms contain DNA and so have genes.

Incorrect

A ______

B ______

C ______

35

Correct

D The greater the people with drug resistant strains, the more incurable cases of TB, which makes the drug more ineffective.

Incorrect

A Streptomycin is an antibiotic and is not antiviral.

B Overcrowding increases disease incidences but does not decrease drug effectiveness.

C The newly activated bacterium would also be effectively treated with the same antibiotic as long as it is not drug-resistant.

36

Correct

B Antigens on cell surfaces stimulate T helper cells which in turn cause B lymphocytes to divide and produce plasma cells that release antibodies in response to the antigen.

Incorrect

A ______

C ______

D ______

37

Correct

A The babies receive already activated antibodies from mother’s milk but do not receive any active lymphocytes which can give secondary responses and produce memory cells. So the antibodies provide temporary immunity.

Incorrect

B The number of antibodies is insignificant since they eventually break down and immunity will still be lost.

C The antibodies function in the babies as well but only temporarily.

D The baby does no inherit immunity but receives antibodies from mother’s milk.

38

Correct

D A niche is an organism’s influence in a single community. The tree acts as a habitat and food source, and also maintains external conditions in its community.

Incorrect

A A community is different species living or interacting in the same area.

B Ecosystem involves all the biological organisms and communities and their interactions together.

C A habitat is an area occupied by a single species.

39

Correct

B The food web contains all the organisms between which energy transfer is occurring.

Incorrect

A Inorganic minerals and sunlight are not organisms.

C Decomposers are also organisms involved in energy transfer.

D Primary, secondary and tertiary consumers, as well as decomposers, all make up the food web, and a single individual species does not.

40

Correct

B Denitrification releases fixed nitrogen in the soil as ammonia into the atmosphere.

Incorrect

A Ammonification releases ammonium ions into the soil for plants.

C Nitrogen fixation fixes nitrates in the soil for plants.

D Same as option C.