1 (a) FIGURE 1.1 shows a type of variation, illustrated in polygenic inheritance in human height. FIGURE 1.1 (i) Differentiate characteristics between continuous and discontinuous variation. [3 marks] Continuous variation Discontinuous variation Has intermediate group/phenotypes Has no intermediate group/phenotypes Quantitative inheritance/ characteristics can be measured Qualitative inheritance/ characteristics cannot be measured Caused by environmental and genetic factors// phenotypic expression is influenced by environmental factor Caused by genetic factors only// phenotypic expression is not influenced by environmental factor Characteristic is controlled by two or more genes/ polygenes Characteristic is controlled by one gene/ different allele at a single locus Shows a normal distribution curve Shows a discrete distribution curve Individual cannot be grouped into distinct and discrete phenotype Individual can be grouped into distinct and discrete phenotype (ii) State another example of the type of variation in 1 (a) (i). [1 mark] Human height// skin colour in human//IQ//human weight/mass.
(b) FIGURE 1.2 shows three types of natural selection. FIGURE 1.2 (i) Identify the type of natural selection B and state one suitable example. [2 marks] B: Disruptive selection Any suitable answer: Beak size and shape of Galapagos finches/Beak size and shape of Cameroon finches (ii) Compare types of natural selection A and C. [3 marks] Similarities: Mechanism of evolution/both result in adaptation of an organism to its environment/ reduce genetic variability Directional Selection Stabilizing selection Operate in response to environmental change over time Operate in stable environment Acts against one of extreme Phenotype Acts against both of extreme Phenotype Another extreme phenotype is favored Intermediate phenotypes are favored Any 2 answers A B C
2 FIGURE 2 shows the mechanism of enzyme action. FIGURE 2 (a) Name the part of the enzyme labelled U. [1 mark] Active site (b) ‘Enzyme is a macromolecule made up of protein that acts as a biological catalyst to speed up the rate of chemical reaction.’ State the possible level and shape of protein that made up enzyme structure. [2 marks] Level of protein: Tertiary / Quaternary Shape of protein: Globular (c) Give one (1) property of enzymes related to structure labelled U. [1 mark] Enzyme possess active sites where the substrate molecules bind to for reaction to take place Active site is highly specific for a particular substrate in a reaction (d) Explain the mechanism of enzyme action in FIGURE 2. [5 marks] Substrate collides with enzyme // substrate binds to active site of enzyme The binding induces a slight change in the conformation of the active site of enzyme The active site becomes fully complementary with the substrate To form enzyme-substrate complex
Once the reaction has occurred, enzyme-substrate complex broken down Product is formed and released from active site Active site of enzyme change back to its original conformation 3 (a) FIGURE 3.1 shows a process to produce ATP from breakdown of glucose FIGURE 3.1 (i) Name substrate A and enzyme R. [1 mark] Substrate A : Fructose 6-phosphate Enzyme R : Phosphofructokinase ATP Glucose Glucose 6-phosphate A Enzyme R ADP Fructose 1,6-bisphosphate Glyceraldehyde 3-phosphate Dihydroxyacetone phosphate Pyruvate Acetyl-CoA Krebs cycle CoA X NAD+ NAD+ FAD NAD+
(ii) State type of ATP production in glycolysis. [1 mark] Substrate level phosphorylation (iii) Describe any step in which ATP is produced by 3(a)(ii). [2 mark] -1,3- bisphosphoglycerate donate one phosphate group to ADP -forming 1 molecule of ATP// -phosphoenolpyruvate donate one phosphate to ADP -forming one molecule of ATP (b) (i) Describe briefly process X in presence of oxygen before entering the Krebs cycle. [3 marks] Pyruvate undergoes decarboxylation by removing CO2 2C fragment is oxidised forming acetate Coenzyme A/ CoA attached with acetate forming Acetyl-CoA (ii) Describe the production of FADH2 in Krebs cycle. [2 marks] FAD receives 2 hydrogen// FAD reduces by 2 hydrogens. from succinate Succinate oxidise into fumarate (c) FIGURE 3.2 shows the protein involved in oxidative phosphorylation process. FIGURE 3.2 Intermembrane space
(i) Label intermembrane space in FIGURE 3.2. [1 mark] (ii) Predict what will happen to the process in FIGURE 3.2. if there is inhibitor for ATP synthase. Justify your answer. [2 marks] Less ATP is produced H+ cannot flow back from intermembrane space to matrix of mitochondria through ATP synthase// ATP synthase cannot phosphorylate ADP into ATP// Less chemiosmosis 4 (a) FIGURE 4 shows a route for electron flow in light dependent reaction. FIGURE 4.1 (i) What is the importance for the route of electron flow shown in FIGURE 4.1? [1 mark] To produce ATP (to be used in light independent reaction) (ii) Explain the photoactivation of electrons during this process. [4 marks] Process occurs at Photosystem I/PSI /PS700. Photosynthetic pigments/ antennae molecules/light harvesting complexes absorb photon/ light energy Light energy/ photon transfer to reaction center / chlorophyll a (2) electrons become excited/ photoactivated/ to high energy level (2) electrons accepted/captured by primary electron acceptor
(iii) Give two (2) differences between the route in FIGURE 4.1 with noncyclic photophosphorylation. [2 marks] Cyclic photophosphorylation Non-cyclic photophosphorylation Cyclic electron flow Non-cyclic/ linear electron flow Produce ATP only Produce oxygen, NADPH, ATP Involve PSI only Involve PSI and PSII Not involve photolysis of water Involve photolysis of water Source of electron is PSI Source of electron is water Final electron acceptor PSI Final electron acceptor NADP+ (b) FIGURE 4.2 shows a phase in light independent reaction occurring in stroma. FIGURE 4.2 (i) Identify the phase in FIGURE 4.2. [1 mark] Reduction (ii) What is the role of R in stage shown in FIGURE 4.2? [1 mark] Add/ donate/ supply phosphate group to 3-phosphoglycerate/X to form 1,3-bisphosphoglycerate (iii) Identify Y and describe reaction Q that produces Y. [3 marks] Y is glyceraldehyde 3-phosphate //G3P 1,3-bisphosphoglycerate accepts electron/ reduced by NADPH and loses a phosphate group to form glyceraldehyde 3- phosphate/G3P
5 FIGURE 5 shows the transportation of CO2 from respiring tissues to lungs. FIGURE 5 FIGURE 5 (a) Identify enzyme X. [1 mark] Carbonic anhydrase (b) What is the significance of haemoglobin in resisting pH changes in red blood cells? [1 mark] Haemoglobin acts as a buffer (c) 60% of CO2 is transported in the form of bicarbonate ions. How are bicarbonate ions formed in this pathway? [4 marks] -CO2 from tissue cells diffuse/enter the red blood cell/erythrocyte. -CO2 combines with water to form carbonic acid. -This reaction is catalysed by carbonic anhydrase. -The carbonic acid dissociates into bicarbonate ions / HCO3 - and hydrogen ions / H+ -Bicarbonate ions / HCO3 - diffuses out of RBC and transported in blood plasma to lungs. Enzyme X
6 Organic compounds synthesized in the leaves of a plant can be transported to the plant’s root. This transport is called translocation and occurs in the phloem tissue of the plant. (a) State the hypothesis used to describe the translocation process. [1 mark] Pressure flow hypothesis (b) Based on the hypothesis in (i), describe how high hydrostatic pressure is generated in the phloem’s sieve tube. [4 marks] -Sucrose is transported by active transport -from source to companion cells and sieve tube -Accumulation of sucrose in sieve tube -lowers the water potential in sieve tube -Water from xylem enter sieve tube by osmosis (creating high hydrostatic pressure) (c) A mutation occurs on the companion cells of the plant, reducing its ability to transport solute. Suggest how this condition affects the translocation process. [1 mark] Translocation slows down 7 FIGURE 7 shows a functional unit of the human kidney. FIGURE 7
(a) Identify structure M and O. [2 marks] Structure M : Distal (convoluted) tubule Structure O : (Descending limb) Loop of Henle (b) Name the process in urine formation involved in P. [1 mark] Ultrafiltration (c) Give two (2) adaptations of structure N that increase the efficiency of reabsorption. [2 marks] Long and winding/ highly coiled Increase surface area for reabsorption Have microvilli Increased surface area Numerous/ many mitochondria Provide energy/ ATP for active transport Only one cell thick of epithelial cell Increase diffusion Surrounded to a blood capillary/ peritubular capillary Efficient diffusion of absorbed substances (d) Give an example of ions that secreted into M. [1 mark] K+ //H+ 8 (a) FIGURE 8.1 shows the action potential in a neuron FIGURE 9.1
(i) According to FIGURE 9.1, identify the resting potential. [1 mark] A and F (ii) What happens to the membrane potential of the neuron when the intensity of a stimulus is less than the threshold level? [1 mark] Remain in resting potential/state // No action potential / Action potential will not be generated // No impulse transmission (iii) Briefly explain phase E. [3 marks] -Voltage-gated potassium (K+ ) ion channel close slowly/ some remain open -Causing excess potassium ions diffuse out of the cell/ axon/ membrane. -The axon/cell/membrane become more negative than -70mV / resting potential / -75mV -Cell / axon/ undergoes hyperpolarization. -Voltage-gated sodium ion (Na+ ) channels are closed. (b) FIGURE 9.2 a part of the junction between two neurons. FIGURE 9.2 (i) Identify the structures labelled X and Y. [2 marks] X : Synaptic vesicle Y : Pre-synaptic membrane/cell/neuron // synaptic knob / synaptic (end) terminal Y Z X
(ii) What is the role played by calcium ions (Ca2+) during synaptic transmission? [1 mark] (High concentration / accumulation of Ca2+ ions) Stimulate / induce / cause / trigger synaptic vesicle to fuse with pre-synaptic membrane // synaptic vesicle to release neurotransmitter into synaptic cleft (via exocytosis) (iii) Describe what happens when neurotransmitters bind to structure Z. [2 marks] -Structure Z/ Ligand gated ion channel open -Sodium ions/ Na+ diffuse / influx into /the cell/ axon -Depolarize the post-synaptic membrane. -Post-synaptic membrane undergoes EPSP -Action potential generated 10 (a) FIGURE 10.1 shows the structure of an antibody. FIGURE 10.1 (i) Define antibody. [1 mark] A protein secreted by plasma cells in response to the presence of specific antigen. (ii) State the type of antibody as shown in FIGURE 10.1 [1 mark] IgG / IgD / IgE (iii) Label antigen binding site in the FIGURE 10.1 [1 mark] Antigen binding site
(b) FIGURE 10.2 shows the mechanism of immune response. FIGURE 10.2 (i) Name cell Y. [1 mark] Helper T cell (ii) Identify cell Z and briefly describe the function of cell Z in this immune response. [3 marks] -Cell Z is B cell -Clonal selection/ proliferates and differentiates into plasma cells and memory B cells -Plasma cells will secrete antibodies -Antibodies bind with antigen forming antigen-antibody interactions (c) Differentiate between primary and secondary immune responses. [3 marks] Primary immune response Secondary immune responses Slow response / lag phase is longer Fast response / lag phase is very short Amount / concentration / magnitude of antibody produced is low Amount / concentration / magnitude of antibody produced is high Short-lived antibody Long lived / long lasting antibody First antibody produced is IgM First antibody produced is IgG Antibody has lower affinity towards antigen Antibody has greater affinity towards antigen