Secondary 3 Biology Practice Paper 1

Answer Key: TuitionGoWhere Practice Paper - Biology Secondary 3 (Version 1)

Section A: Cellular and Molecular Basis of Life

Question 1 (a) (i) Site of aerobic respiration / produces energy in the form of ATP. [1] (ii) Site of protein synthesis. [1] (iii) Modifies, packages, and sorts proteins for secretion. [1] (b) Rough Endoplasmic Reticulum (RER) $\rightarrow$ Golgi body $\rightarrow$ Secretory vesicles. [3] (1 mark for each correct step in sequence).

Question 2 (a) Cell wall, Chloroplasts, Large central vacuole (Any two). [2] (b) Biconcave shape to increase surface area for oxygen diffusion [1]; No nucleus to provide more space for haemoglobin [1]; Small size to fit through narrow capillaries [1].

Question 3 (a) The net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. [2] (b) (i) Potato becomes flaccid/soft/shrunken. [2] (ii) The salt solution has a lower water potential than the cell sap [1]. Water moves out of the cell by osmosis [1] from a region of higher water potential to lower water potential across the partially permeable membrane [1].

Question 4 (a) (i) Carbon, Hydrogen, Oxygen [1] (ii) Carbon, Hydrogen, Oxygen, Nitrogen [1] (b) Add Benedict's solution to the sample [1]. Heat the mixture in a boiling water bath [1]. A change from blue to green/yellow/orange/brick-red precipitate indicates reducing sugars [1].

Question 5 (a) The enzyme has a specific 3D shape called the active site [1]. The substrate has a complementary shape that fits exactly into the active site [1], forming an enzyme-substrate complex [1]. (b) The rate of reaction decreases [1]. High temperature disrupts the bonds holding the tertiary structure [1], causing the active site to change shape (denature), so the substrate can no longer fit [1].

Section B: Human Body Systems

Question 6 (a) Teeth chew and grind food to increase surface area [1]; Stomach walls churn food to mix it with gastric juices [1]. (b) Numerous villi and microvilli increase surface area [1]; One-cell thick epithelium shortens diffusion distance [1]; Rich network of blood capillaries maintains a steep concentration gradient [1]; Lacteals absorb fats [1].

Question 7 (a) Arteries have thicker, more muscular and elastic walls [1] to withstand high pressure [1]. Veins have thinner walls and larger lumens [1]. (b) Veins carry blood at low pressure [1]. Valves prevent the backflow of blood to ensure one-way flow toward the heart [1].

Question 8 (a) Glucose + Oxygen $\rightarrow$ Carbon dioxide + Water + Energy [2] (b) Anaerobic respiration occurs during sprinting, leading to lactic acid buildup [1]. Panting provides extra oxygen [1] to oxidize lactic acid into $\text{CO}_2$ and water, repaying the oxygen debt [1].

Question 9 (a) High blood pressure in the glomerulus [1] forces small molecules (water, glucose, urea, salts) [1] through the basement membrane into the Bowman's capsule [1]. (b) When water potential of blood is low, the pituitary gland releases ADH [1]. ADH makes the collecting duct more permeable to water [1], increasing water reabsorption into the blood [1].

Question 10 (a) Infectious diseases are caused by pathogens and can be spread from one person to another [1]. Non-infectious diseases are not caused by pathogens and cannot be transmitted [1]. (b) Antibiotics target bacterial structures (e.g., cell wall synthesis) [1]. Viruses lack these structures and reproduce inside host cells [1], meaning antibiotics have no target to act upon [1].

Section C: Plants and Ecosystems

Question 11 (a) $6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{light/chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$ [2] (b) To destarch the leaf [1], ensuring that any starch found after the experiment was produced during the test period [1]. (c) Cells are columnar and tightly packed [1]; Located just below the upper epidermis to capture maximum sunlight [1]; Contain a high density of chloroplasts [1].

Question 12 (a) The loss of water vapor from the plant, mainly through the stomata of the leaves. [2] (b) Water evaporates from leaf cells (transpiration) [1]. This creates a water potential gradient [1]. Water is pulled up the xylem vessels via transpiration pull [1].

Question 13 (a) Energy enters the ecosystem via producers (sunlight) [1] and is lost as heat at each trophic level; it cannot be recycled [1]. (b) Only about 10% of energy is transferred to the next level [1]. Energy is lost through respiration, excretion, and uneaten parts [1]. Thus, there is insufficient energy to support a large biomass at the top [1]. (c) Burning of fossil fuels / Deforestation [1]. This increases atmospheric $\text{CO}_2$ [1], which traps more heat (greenhouse effect), leading to global warming/climate change [1].