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Name: ___________________________________
Biochemical Processes
VCE Biology- Unit 3
1. Define the term enzyme.
An enzyme is an organic catalyst. They are proteins that alter the rate of reactions – usually to speed them
up to a biologically useful rate. Many reactions occur naturally but at extremely slow rates. Enzymes only
alter the rate (amount produced in a given time) of a reaction. They do not alter the final amount of product
2. What is the ‘Lock and Key’ model?
Specific enzymes catalyse (alter the rate) of specific reactions. Enzymes bind with the substrates (reactants
or ingredients) to form a temporary enzyme substrate complex. The enzymes have areas called active sites.
The shape of a specific substrate molecule will match the active sites on a specific enzyme. Only the correct
enzyme with the correct molecular shape will bind to the substrate molecule, in the same way that a
particular key will open a lock.
3. Use the terms substrate, enzyme and product to explain the role of enzymes in living organisms.
Substrates are materials that are to be processed. The processing could be a breakdown reaction (e.g.
digestion) or a synthesis reaction (e.g. making proteins). The material present at the end of the reaction are
the products. Enzymes allow the formation of product from substrate in a time that allows the efficient
operation of an organism. Many of the reactions catalysed by the enzyme would otherwise occur too slowly.
4. Do enzymes increase the amount of product produced in a reaction?
No. They alter the time it takes to produce the product.
5. With respect to reactions involving enzymes, what is meant by the rate of reaction?
The rate of reaction refers to the amount of product produced in a given time. For example, the rate of
reaction could be measured in micrograms of product produced per minute.
6. What factors affect activity of enzymes?
Temperature, pH, the amount of enzyme present, and the initial substrate concentration.
7. Do all enzymes work efficiently under the same conditions?
Different enzymes work best in particular environments. Digestive enzymes produced in the stomach work
most efficiently in a low pH environment (acidic). Enzymes present in the ice fish of Antarctic waters work
best at about 4° C.
8. What is the enzymes’ active site and how is it formed?
Enzymes are proteins. The folding of the protein into its tertiary structure provides a site that matches with
specific substrates. This site is called the active site.
9. Enzymes can be denatured. How and what are the consequences?
Enzymes are proteins so they can be denatured by
- high temperatures (break the H bonds and van der Waals forces destroying the quaternary and tertiary
- extremes of pH (break the ionic bonds destroying the quaternary and tertiary structure)
Denaturation by extremes of pH is usually reversible but denaturation by high temperatures, i.e. about 60° C
is not. This means the active sites are permanently altered and the enzyme can no longer function. In terms
of the lock and key hypothesis the shape of the key is altered.
Name: ___________________________________
VCE Biology- Unit 3
10. Is energy used by living organisms?
Energy is never used. In doing work, energy is converted from one form to another and at the end of the
process may be unusable. Most organisms store energy in chemicals such as fat or starch. The energy is
made available to do cellular work during cellular respiration.
11. Why do cells need energy?
Cells need energy to do cellular work. Processes that require energy are: cell division, synthesis of new parts
and materials, muscular contraction, active transport and nervous conduction.
12. What is the difference between anabolic and catabolic reactions?
Anabolic reactions are those involving the building or synthesis of molecules whereas catabolic reactions
are breakdown reactions.
13. What is the difference between exergonic and endergonic reactions? Give an example of each type.
Exergonic reactions (breaking things) release energy: e.g. cellular respiration.
Endergonic reactions (making or doing things) require an input of energy for them to proceed: e.g. any
synthesis reaction such as protein synthesis.
14. What is ATP (Adenosine Tri Phosphate) and explain its role in cells.
ATP is a molecule containing adenosine attached to ribose which is bound to a chain of 3 phosphate groups.
Energy is released for cellular reactions when the terminal phosphate group is removed to form ADP. ATP
is the immediate source of energy for cells. When energy is released by cellular reactions, it is stored in
15. What is the major difference between heterotrophic and autotrophic organisms?
Autotrophic organisms make their own organic materials through processes such as photosynthesis or
chemosynthesis. Heterotrophs rely on an external source of ready-made organic material. For example, you
are a heterotroph and use organic materials found in animal or plant material that you eat.
16. List the different sorts of organic compounds that heterotrophs require. What form is each type of
compound in to allow movement into or out of cells?
Nucleic acids
Form absorbed
amino acids
fatty acid and glycerol
Name: ___________________________________
VCE Biology- Unit 3
17. Write down the word and chemical equations for photosynthesis.
carbon dioxide + water + light energy -------------------------------> glucose + oxygen + water
(this process occurs in plant cells that contain chlorophyll)
6CO2 + 12H2O -------------------------------> C6H12O6 + 6O2 + 6H2O
18. Where does photosynthesis occur?
Photosynthesis occurs in chloroplast-containing cells if they are exposed to light and are supplied with
carbon dioxide and water.
19. Draw a diagram of a leaf section. Use labels to show how various materials involved in photosynthesis
move to and from the site of production.
CO2, H2O
O2, H2O
CO2, H2O
20. What is the role of pigments in photosynthetic organisms and why is there a range of different pigments?
Pigments trap the light energy required for the photosynthetic process. Different pigments trap different
wavelengths (colours) of light. Green pigments are effective at absorbing red and blue light. A range of
pigments means that a plant can trap a wider range of light. Seaweeds that live in deeper water tend to have
more red pigments. These are best for absorbing blue light, which penetrates water to a greater depth. The
pigments a photosynthetic organism has will enable it to photosynthesise efficiently in its particular
21. Explain what happens in the light-dependent and light-independent stages of photosynthesis.
In the light-dependent stage, light is absorbed by chlorophyll, causing electrons to be emitted. Some of the
energy is used to make ATP. Water is split and oxygen given off. In the light-independent stage, through the
Calvin cycle, hydrogen from the light stage is added to carbon dioxide to form carbohydrate. ATP in the
light stage provides the energy for this.
22. What is the role of NADP in photosynthesis?
NADP is used to carry H ions from the grana to the stroma where the Calvin cycle takes place.
Name: ___________________________________
VCE Biology- Unit 3
Cellular Respiration
23. Write down the word equation for aerobic cellular respiration.
glucose + oxygen -------------------------------> carbon dioxide + water + energy released
24. Convert the above equation to a balanced chemical equation.
C6H12O6 + 6O2 +36Pi + 36ADP -------------------------------> 6CO2 + 6H2O + 36ATP
25. Write down the word equation for anaerobic respiration in:
a. animals
glucose -------------------------------> lactic acid + 2ATP
b. plants.
glucose -------------------------------> carbon dioxide + alcohol + 2ATP
26. Explain what happens in the 3 main stages of aerobic respiration.
1. Glycolysis. This occurs in the cytoplasm. Glucose is converted to pyruvate and 2ATP are produced.
2. Krebs cycle. This occurs in the matrix of the mitochondria. Hydrogen ions are removed, carbon dioxide is
formed and 2 ATP are produced. The hydrogen ions and electrons are picked up by the coenzymes NAD
and FAD.
3. Electron transport chain. This occurs in the inner membranes of the mitochondria and requires oxygen.
Reduced NAD and FAD provide electrons, which are passed down the electron transport chain producing 32
ATP. The oxygen is used to make water.
27. Aerobic respiration is said to be more efficient than anaerobic respiration. Explain.
Aerobic respiration is more efficient as the glucose molecule is broken down to simple inorganic materials,
carbon dioxide and water, and the maximum amount of energy is extracted – enough to make 36 molecules
of ATP.
Anaerobic respiration represents the partial breakdown of a glucose molecule to alcohol and lactic acid (still
large molecules) and release only enough energy to make 2 molecules of ATP.
28. Photosynthesis is similar to respiration. Do you agree?
Respiration can be thought of as photosynthesis in reverse. The reactants of one reaction are the products of
the other! They are different in terms of energy. Respiration is an exergonic reaction. Photosynthesis is an
endergonic reaction.
29. What compounds do animals use as an immediate energy source, a short-term energy store, and for longterm energy storage?
ATP is the source of energy for immediate use within cells. Animals convert glucose to glycogen for shortterm storage. In the longer term, the favoured storage material is fat. This is because a gram of fat stores
about double the energy that carbohydrates or proteins can store.