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Secondary 4 Pure Biology Practice Paper 1
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Secondary 4 Pure Biology Quiz - Cells Biomolecules (Answer Key)
Total Marks: 40
Section A: Cell Structure and Organisation
1.
(a) Rough Endoplasmic Reticulum (Rough ER) [1]
(b) Protein synthesis [1]
(c) Muscle cells require more energy for contraction [1]. Mitochondria are the site of aerobic respiration which releases energy [1].
2.
(a) Plant cell [1]
(b) Provides structural support / Maintains cell shape / Prevents bursting under turgor pressure [1]
(c) Cell Y is an animal cell [1]. Animal cells do not perform photosynthesis, so they do not need chloroplasts [1].
3.
(a) Oxygen [1]
(b) Biconcave shape increases surface area for faster diffusion of oxygen [1] OR No nucleus allows more space for haemoglobin to carry oxygen [1]. (Accept either)
4.
(a) DNA (Deoxyribonucleic acid) [1]
(b) The nucleus contains genes/DNA which code for proteins [1]. These proteins (enzymes) control chemical reactions and cell activities [1].
5.
(a) Absent [1]
(b) Present [1]
(c) Small, temporary / Many small vacuoles [1]
Section B: Movement of Substances
6.
The net movement of particles [1] from a region of higher concentration to a region of lower concentration [1] (down a concentration gradient).
7.
(a) The net movement of water molecules [1] from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) [1] through a partially permeable membrane.
(b) The sugar solution has a lower water potential than the distilled water [1]. Water molecules move by osmosis [1] from the beaker into the visking tubing [1], causing the volume/level to rise.
8.
(a) Osmosis [1]
(b) The cytoplasm shrinks / pulls away from the cell wall [1]. The cell becomes plasmolysed [1].
(c) Animal cells lack a cell wall [1]. Water enters by osmosis, causing the cell to swell and burst (lyse) [1]. Plant cells have a strong cell wall that prevents bursting [1]. (Note: Question asks why plant cells do not burst, so 1 mark for cell wall presence is sufficient if linked to prevention of bursting).
9.
(a) Active Transport [1]
(b) 1. Energy (ATP) from respiration [1]
2. Carrier proteins [1]
10.
(a) Diffusion [1]
(b) Active Transport [1]
11.
A large surface area allows for a faster rate of absorption/diffusion [1]. It provides more space for carrier proteins/channels or contact with the soil/water [1].
12.
(a) The 1cm³ cube [1]
(b) It has a larger surface area to volume ratio [1]. This allows the acid to diffuse into the centre of the cube faster [1].
Section C: Biological Molecules and Enzymes
13.
(a) Glucose [1]
(b) Biuret Solution [1]
(c) Fatty acids and Glycerol [1] (Both must be correct)
14.
Add Benedict’s solution to the food sample [1]. Heat the mixture in a water bath (boil) [1]. A positive result is a colour change from blue to green/yellow/orange/brick-red precipitate [1].
15.
(a) A substance that speeds up the rate of a chemical reaction [1] without being used up/changed in the process.
(b) The enzyme has an active site with a specific shape [1]. The substrate has a complementary shape [1]. The substrate fits into the active site to form an enzyme-substrate complex [1].
16.
(a) As temperature increases, kinetic energy of enzyme and substrate molecules increases [1]. This leads to more frequent collisions between enzyme and substrate [1].
(b) High temperature breaks the bonds holding the enzyme structure together [1]. The enzyme denatures [1]. The shape of the active site changes, so the substrate no longer fits [1].
17.
(a) pH 2 (or acidic pH / pH 1-3) [1]
(b) The enzyme will denature [1] because the pH is too high/alkaline for pepsin, changing the shape of the active site [1].
18.
(a) The rate of reaction increases [1].
(b) All active sites of the enzyme molecules are occupied/saturated [1]. Adding more substrate cannot increase the rate further as there are no free active sites [1].
19.
Enzymes have a specific active site shape [1]. Only substrates with a complementary shape can fit into the active site [1].
20.
Metabolic reactions in the body would be too slow to sustain life without enzymes [1]. Enzymes lower the activation energy required for reactions to occur at body temperature [1].