1. The following word equation represents a biological process that occurs in green plants.
Carbon (IV) oxide + water → Glucose + Product E
(a) Name the cell organelle where the illustrated process takes place in green plants.
Chloroplast; Acc chloroplasts; (1 mark)
(b) (i) Give the likely identity of product E.
Oxygen; Acc \(O_2\); (1 mark)
Here's the text from the image:
(b) (ii) Suggest ways in which the rate of production of E can be increased. (3 marks)
Optimum Temp./Temp.; Acc. Increase in Temp./Temp.
Optimum Light Intensity/Light; Acc. Increase in Light Intensity;
Increasing Concentration of \(CO_2\);
Increasing Water availability/amount of Water;
(c) Suggest one possible source of carbon (IV) oxide if the above process was artificially conducted in a school laboratory. (1 mark)
Sodium hydrogen Carbonate/sodium bicarbonate/NaHCO3;
Dry ice
(d) Explain how the illustrated process is significant in nature. (2 marks)
(d) Explain how the illustrated process is significant in nature. (2 marks)
Air purification/removes/reduces the Carbon(IV)Oxide/CO₂ in the atmosphere & regulates amount of CO₂ in the atmosphere;
Increases the concentration of oxygen in the atmosphere (used for respiration) / production of oxygen for other organisms;
Production of glucose/sugar/food;
2. In an experiment, the number of red blood cells present in three samples of blood labelled F, G and H was estimated. Different concentrations of salt solution were then separately added to the samples. After an hour, the number of red blood cells present in each sample was counted and recorded as shown in the table below.
Blood sample | Salt solution % concentration added | Number of red blood cells |
---|---|---|
F | 1 | Number remained the same |
G | 0.6 | Fewer cells observed |
H | 0.4 | No cells observed |
(a) Name the physiological process being investigated in the experiment.
OSMOSIS
(b) Account for the results made in blood sample F.
The Conc. of cell sap cytoplasm was equal to that of 1.0% salt soln. The salt soln. was Isotonic to the cell cytoplasm. Hence, no net out of water molecules is out of cell (no cell remained same) /no cell was hemolysed or the conc. of cell cytoplasm was lower than that of 1.0% salt soln. The salt soln. was hypertonic to the cell cytoplasm; hence net out of water molecules out of cell.
3. A genetic investigation on a certain population established that, in human beings, premature baldness is controlled by a dominant gene, N, located on the Y chromosome.
(a) Work out the phenotypic ratio of the offspring of a couple comprising of a normal mother and a father with premature baldness.
In humans, sex is determined by the presence of sex chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome 1 (XY)
Since the gene for premature baldness is located on the Y chromosome, it can only be passed from father to son. Daughters will not inherit the Y chromosome and therefore cannot exhibit the trait.
(b) What is the probability that this couple would have a daughter with premature baldness?
0%
(c) Name two sex-linked traits in human beings associated with the X-chromosomes.
Hemophilia/Haemophilia
Color/color blindness
Muscle dystrophy/Duschenne muscle dystrophy
During an ecological study in a lake ecosystem, a group of students made the following observations on the feeding relationships among some organisms.
Lobsters feed on algae
Small fish feed on lobsters, worms and caterpillars
Caterpillars feed on algae
Worms feed on caterpillar
Large fish feed on small fish
Penguins feed on small fish, lobsters and worms.
(a) From the students' observations, construct a food web for the ecosystem. (5 marks)
(b) From the food web constructed in 4(a), extract a food chain with the penguin as a secondary consumer.
Algae -> Lobsters -> Penguins
(c) Explain how spillage of oil from water vessels is likely to affect this lake ecosystem.
- Prevent exit of CO2; causing suffocation/death of living organisms
- Prevent entry/diffusion of air/ \(CO_2\); limiting/preventing/reducing photosynthesis/no photosynthesis
- Prevents entry of air/ \(O_2\); causing suffocation/death of organisms
- Prevents/reduces penetration of light; limiting/preventing/no photosynthesis/reducing photosynthesis
- Clogs respiratory surfaces; limiting G.E/causes suffocation/death
5 The following diagram represents part of a cell structure as seen under an electron microscope.
(a) (i) Identify the structure represented. (1 mark)
cell Membrane; / plasmalemma; / plasma Membrane
(ii) State two functions of the structure. (2 marks) Enclosing cell contents/protection of inner cell inclusions/organelles Selective transport/controls entry and exit of materials/regulates the materials in/out of the cell
(iii) Suggest two ways in which the functioning of the structure can be impaired. (2 marks)
In the extremes of pH/acids/strong bases; / Deny for increasing pH
Extremes in Temp/too low/too high Temp.
(b) Name two structures found in plant cells but not in animal cells. (2 marks)
chloroplasts/plastids /sap vacuole /Cell Wall / Tonoplasts
(c) What is the purpose of staining cells before observing them under a light microscope? (1 mark)
For Clarity during Observation/making Structures More distinct/More Clear/More Visible
SECTION B (40 marks)
Answer question 6 (compulsory) and either question 7 or 8 in the spaces provided after question 8.
6 An investigation was carried out to monitor trends of growth in a group of boys and girls for a period of 20 years. Their average weights were recorded at two years' intervals as shown in the table.
Age (Years) | Average Weights (kg) - Boys | Average Weights (kg) - Girls |
---|---|---|
0 | 2.4 | 2.4 |
2 | 11.0 | 11.4 |
4 | 14.5 | 15.5 |
6 | 18.2 | 19.6 |
8 | 21.7 | 26.8 |
10 | 25.2 | 27.4 |
12 | 27.7 | 31.5 |
14 | 37.2 | 35.4 |
16 | 44.5 | 44.5 |
18 | 46.8 | 52.6 |
20 | 48.6 | 55.6 |
(a) On the same axes, draw line graphs of average weights of girls and boys against their ages.
b) (i) From the graph, determine the
weight of boys at the age of 13 years.
\(32 \pm 1 kg \)
(ii) growth rate in girls between the 13th and 14th year.
38.5 - 34.5 = 4 kg
40.1 - 39 = 1.1 kg
c) Account for the trend in the growth of girls between the 13th and 14th year.
Exponential/fast/rapid growth; it is the puberty/adolescence/development of secondary sexual characteristics
increase in growth rate.
(d) Apart from sex and age, state three other factors that affect the rate of growth in humans. (3 marks)
Basal metabolic rate
Health
Hormones
Diet
Genes
(e) Other than weight, state a parameter that can be used to establish growth in humans. (1 mark) Height
(f) Why do girls above 12 years require more iron in their diet than boys of the same age? (2 marks) Girls menstruate thus require iron to replace the blood lost.
Girls Menstruate; hence require iron to compensate for the blood loss
7 a) Explain the effects of hypothyroidism in adults. (4 marks)
(b) Describe the hearing process in humans. (16 marks)
7(a) Myxoedema/Myxedema/Swollen Thyroid gland/goiter; due to underproduction of the thyroid hormone/thyroxine; reduced production of Thyroxine hormone leads to the overworking of the Thyroid gland in an attempt to produce more Thyroxine hormone (Causing the Swelling); this further leads to low metabolic rate/ reduced body temperature/reduced breathing rate/heart rate; Causes mental/physical sluggishness, obesity/increased body weight and retention of body fluid/Oedema/swollen feet/putty face;
(b) The (funnel-shaped) Pinna; Collects / Concentrates/directs sound waves into the (external) auditory meatus/Canal; Sound waves strike the eardrum/tymphanum/tympanic membrane; Causing it to vibrate; and transforms sound waves into vibrations; The vibrations are transmitted to the ear ossicles/Malleus, incus and stapes; (The ossicles are suspended by muscles tensor tympani and stapedius; the muscles prevent excessive vibrations which could damage the inner/delicate membranous labyrinth) the ossicles (further form a system of levers that) amplifies; and transmits vibrations; to the oval window/fenestra ovalis; the oval window vibrates; and transmits the vibrations to the fluids/perilymph and endolymph; in the inner cochlea.
The vibrations (in the cochlea) stimulate the sensory cell hairs (hair cells), to generate nerve impulses, which are transmitted to the brain, through the auditory nerve; for interpretation. The intensity of the stimulus transmitted to the brain enables the brain to interpret the impulses as sound of specific pitch/loudness. Vibrations/are dissipated/exit/released through the round window. (Total 22. Max 16)
8 (a) Describe how urea is formed in humans. (5 marks)
(b) Describe the path followed by urea from the site of formation until it is eliminated from the body. (15 marks)
Urea is formed in the Liver, where excess amino acids are deaminated/amino grp is removed; the amino grp reacts with hydrogen (im) atom/hydrogen, to form ammonia; which is toxic; ammonia combines with co2, to form urea (which is less toxic).
B. (Urea formed in the liver) is carried in blood, thru the hepatic vein, into the vena cava; blood containing the urea then enters the heart/right auricle & R.V; leaves the heart thru pulmonary artery, into the lungs; (sout of it thruoy) P.V; to the heart/L.A/L.V; leaves thru the aorta, into the kidneys, via the renal artery; to afferent arteriole; where ultrafiltration occurs; (resulting to form the (glomerular) filtrate), which enters the Bowman's capsule; into PCT; loop of henle/descending & ascending; to d.C.T; urea enters the Collecting tubule/duct; in urine; into the pelvis; then ureter; then into urinary bladder (for temporary storage); from where it exits the body through the urethra.
8.(a) How Urea is formed
Urea is formed in the liver where excess amino acids are deaminated/ amino group is removed; the amino group reacts with hydrogen atom/ hydrogen ion; to form ammonia, which is toxic; ammonia combines with Carbon (IV) oxide (in the Ornithine cycle); to form Urea (which is less toxic);
(b) (Urea that is formed in the liver) is Carried in blood, through the hepatic vein, into the vena Cava; blood Containing the urea then enters the heart/right auricle/right auricle and Ventricle; leaves the heart through the Pulmonary artery; into the lungs; (and out of the lungs through) the Pulmonary veins; to the heart/left auricle/ left auricle and left Ventricle; (leaves through) the aorta; into the Kidney; Via the renal artery; to afferent arteriole; glomerulus; where ultrafiltration occurs; resulting in the formation of the (glomerular) filtrate; which enters the Bowman's Capsule; into the Proximal Convoluted tubule; loop of Henle/ descending and ascending loop of Henle; Distal Convoluted Tubule; Urea enters the Collecting tubule/ Collecting duct in urine; into Pelvis; into the ureter; then into Urinary bladder (for temporary Storage); from where it exits the body through the Urethra.