Part 1: Multiple choice
The most abundant chemical substance in living organisms is
Water forms approximately what percentage of the body mass of a mammal?
Of the body mass of a mammal, the percentage of water found inside the cells is about
Blood plasma is an example of water found
The structural and functional unit of all living organisms is the
A prokaryotic cell is one whose genetic material
Which of the following is a prokaryote?
The bacterial cell wall contains
Cell walls of fungi are made of
Which kingdom has no cell walls, is multicellular and heterotrophic?
A multicellular autotrophic organism with a cellulose cell wall is a
Which of the following is an invertebrate?
Which of the following is a vertebrate?
The semi-permeable structure surrounding all cells is the
The gel-like substance of the cell, mostly water, is the
The organelle that controls the cell's activities and contains genetic material is the
The organelle that carries out photosynthesis is the
Vacuoles in plant cells are
The energy-production centres of the cell are the
Dysfunction of mitochondria leads directly to
The network of membranes used to transport materials inside the cell is the
Which structure is found in plant cells but not in animal cells?
Which is NOT a general role of water in organisms?
Water helps living organisms maintain a stable internal temperature mainly because of its
Metabolism includes
In catabolic reactions complex molecules are
An example of an anabolic process is
The synthesis of proteins from amino acids is
In cellular respiration the products from glucose are
Activation energy is
Enzymes speed up reactions by
Enzymes are made of
In the "lock and key" model the "key" is the
At the end of an enzyme-catalysed reaction the enzyme
Which of the following directly slows an enzyme's activity?
The effect of water on metabolic reactions is best described as
If the nuclear membrane were removed from a eukaryotic cell it would resemble
Cell walls of plants are permeable to
Which kingdom includes yeast?
A protist that is autotrophic is
Part 2: Written questions and problems
1. [Give reasons] Explain: water helps living organisms to maintain a stable internal temperature despite external fluctuations.
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Water forms most of the body and has a high specific heat (hydrogen bonds), so large amounts of heat produce small temperature changes; its high latent heat of vaporization also allows cooling by sweating or transpiration.
2. [Give reasons] Give a reason: water is called the universal solvent in biological systems.
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Its polar molecules dissolve salts, sugars, gases and other polar substances, allowing reactions and transport.
3. [Give reasons] Give a reason: dry seeds can remain alive for a long time without germinating.
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They contain very little water, so metabolism is almost stopped until water arrives.
4. [Give reasons] Give a reason: the cell wall of a plant cell is permeable to water and salts.
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Cellulose forms a loose network with pores, so substances pass freely to the plasma membrane which does the selecting.
5. [Give reasons] Give a reason: the plasma membrane is described as semi-permeable.
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It allows water and some substances to pass but regulates or blocks others.
6. [Give reasons] Give a reason: vacuoles are important to plant cells.
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The large vacuole stores water, food and excess salts and gives the cell turgidity and support.
7. [Give reasons] Give a reason: mitochondria are called the power houses of the cell.
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They carry out the final stages of aerobic respiration that produce most of the cell's ATP.
8. [Give reasons] Give a reason: bacteria are classified as prokaryotes.
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Their genetic material is not enclosed in a nuclear membrane and they have no membrane-bound organelles.
9. [Give reasons] Give a reason: enzymes are needed for metabolic reactions inside cells.
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The reactions have high activation energy and the cell cannot be heated to supply it; enzymes lower the activation energy so the reactions occur at body temperature.
10. [Give reasons] Give a reason: an enzyme that works on one substrate cannot work on a different one.
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The active site has a specific shape that fits only its own substrate (lock and key).
11. [Give reasons] Give a reason: boiling destroys the activity of an enzyme.
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Heat breaks the bonds that hold the three-dimensional shape of the protein, so the active site is deformed (denaturation).
12. [Give reasons] Give a reason: respiration is a catabolic process.
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Glucose, a complex molecule, is broken down to CO₂ and water with release of energy.
13. [Give reasons] Give a reason: photosynthesis is an anabolic process.
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It builds glucose from simple molecules and consumes light energy.
14. [Give reasons] Explain why the cytoplasm of a cell has an important role in keeping its shape.
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Being mostly water, it creates an internal pressure that resists the pressure around the cell.
15. [Give reasons] Explain how water takes part in the transport of gases in the body.
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O₂ and CO₂ dissolve in blood plasma and cell fluids and are carried by the circulating fluid.
Part C — Define / compare
16. [Define] Define the cell.
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The structural and functional unit of all living organisms.
17. [Define] Define metabolism.
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All the biochemical reactions in a living cell, divided into catabolic and anabolic processes.
18. [Define] Define activation energy.
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The minimum amount of energy needed to start a chemical reaction.
19. [Define] Define an enzyme.
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A protein catalyst in living cells that speeds up a chemical reaction by lowering activation energy and remains unchanged afterwards.
20. [Define] Define the substrate and the active site.
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The substrate is the substance acted on by the enzyme; the active site is the part of the enzyme to which it binds specifically.
21. [Compare] Compare prokaryotic and eukaryotic cells.
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- Prokaryote: no nuclear membrane, no membrane organelles, small (bacteria).
- Eukaryote: nuclear membrane and organelles such as mitochondria and plastids (protists, fungi, plants, animals).
22. [Compare] Compare catabolism and anabolism.
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Catabolism breaks complex molecules down and releases energy (respiration); anabolism builds complex molecules and consumes energy (photosynthesis, protein synthesis).
23. [Compare] Compare plants and animals (cell wall, nutrition, movement).
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Plants: cellulose wall, autotrophic, usually fixed. Animals: no wall, heterotrophic, usually able to move.
24. [Compare] Compare vacuoles in plant and animal cells.
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Plant: few and large, central. Animal: numerous and small.
25. [Compare] Compare invertebrates and vertebrates with two examples each.
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Invertebrates have no backbone (jellyfish, insects); vertebrates have a backbone (fish, mammals).
Part D — Problems
26. [Problem] A person has a mass of 80 kg. Find the mass of water in the body, inside the cells and outside the cells.
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56 kg; 37.6 kg; 18.4 kg.
0.70 × 80 = 56; 0.47 × 80 = 37.6; 0.23 × 80 = 18.4.
27. [Problem] What fraction of the body's water is outside the cells?
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≈ 33 % (one third).
23/70 = 0.329.
28. [Problem] Calculate the masses of O₂ used and CO₂ and H₂O formed when 36 g of glucose is oxidised in respiration.
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O₂ 38.4 g; CO₂ 52.8 g; H₂O 21.6 g.
n = 0.2 mol; ×6 = 1.2 mol each: 1.2 × 32, 1.2 × 44, 1.2 × 18.
29. [Problem] How many grams of CO₂ must a plant absorb to make 60 g of glucose, and how much oxygen is released?
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88 g CO₂; 64 g O₂.
60/180 = 1/3 mol glucose; ×6 = 2 mol CO₂ and 2 mol O₂.
30. [Problem] For 18 g of glucose formed in photosynthesis, find the mass of CO₂ used, water used and O₂ released.
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CO₂ 26.4 g; H₂O 10.8 g; O₂ 19.2 g.
n = 0.1 mol; 0.6 mol each: 0.6 × 44, 0.6 × 18, 0.6 × 32.
31. [Problem] An enzyme reaction has activation energy 75 kJ/mol without the enzyme and 25 kJ/mol with it. By what percentage is the barrier lowered?
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66.7 %.
(75 − 25)/75 = 0.667.
32. [Problem] An enzyme forms 18 mg of product in 6 minutes. Find the rate of reaction.
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3 mg/min.
Rate = 18/6.
33. [Problem] The rate of an enzyme reaction is 4 mg/min at 20 °C and doubles for each 10 °C rise up to the optimum 40 °C. Find the rate at 40 °C.
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16 mg/min.
20→30: 8; 30→40: 16.
34. [Problem] Three glycine molecules (M = 75) join to form a tripeptide. How many water molecules are released and what is the molar mass of the tripeptide?
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2 molecules of water; 189 g/mol.
3 × 75 − 2 × 18 = 225 − 36 = 189.
35. [Problem] 50 g of fresh seeds lose 10 g when dried completely. Find the percentage of water in the fresh seeds.
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20 %.
10/50 × 100.
36. [Problem] A fresh leaf has mass 5.0 g and after drying 1.2 g. Find the percentage of water.
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76 %.
(5.0 − 1.2)/5.0 = 0.76.
37. [Problem] A person's daily water intake is 2.4 L. Output: urine 1.5 L, skin 0.5 L, breath 0.4 L, faeces 0.1 L. Find the net water balance.
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−0.1 L (a loss of 100 mL).
Output = 2.5 L; 2.4 − 2.5 = −0.1.
38. [Problem] Catalase decomposes hydrogen peroxide: 2H₂O₂ → 2H₂O + O₂. What mass of O₂ is produced from 34 g of H₂O₂ and what volume at STP?
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16 g O₂; 11.2 L.
34/34 = 1 mol H₂O₂ → 0.5 mol O₂ = 16 g; 0.5 × 22.4 = 11.2 L.
39. [Problem] The respiration of 1 mol of glucose releases about 2800 kJ. How much energy is released by 90 g of glucose?
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1400 kJ.
90/180 = 0.5 mol; 0.5 × 2800.
40. [Problem] A cell has a mass of 2.0 ng and is 70 % water. What is the mass of water and the dry mass?
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1.4 ng water; 0.6 ng dry mass.
0.7 × 2.0 = 1.4; 2.0 − 1.4 = 0.6.