Chapter 3 Biological Substances Flashcards
Define the term enzyme [3] (2014/B10 E)
The enzyme is a biological catalyst that is a protein in nature [1]. It speeds up the rate of a chemical reaction without being chemically changed at the end of the reaction, by lowering the activation energy for a reaction to occur [1]. Enzymes are highly specific in their
actions. [1]
Fig. up 4.1 shows a section of photographic film
The top layer is made up of silver particles and embedded in a layer of gelatin, which is a type of protein.
In an investigation, a 20 mm length of photographic film was placed into each of three boiling tubes, with protease added
Explain the results in boiling tubes 1 [2], 2&3 [2] (2013/A4)
Test tube 1: pH 2 solution, silver particles in suspension and gelatin layer dissolved
Test tube 2: pH 7, no change
Test tube 3: pH 10, no change
- Boiling tube 1: The gelatin layer has been digested by protease as the temperature and pH are optimal [1] for the action of protease. As a result, the silver particles are no longer held in place by the gelatin and are released from the gelatin [1] into the liquid.
- Boiling tubes 2 and 3: In these 2 tubes, the high pH caused the protease to denature. [1] As a result of the loss of the active site of the enzyme, [1] digestion of gelatin is not able to take place.
Describe the role of a named enzyme in digestion [4] (2011/B4)
- Any named digestive enzyme is acceptable: e.g.salivary amylase
- Source: secreted from the salivary glands [1]
- Site of action: into the mouth [1]
- Substrate: where it acts on starch molecules and breaks them down in the presence of water [1]
- Product: into 2 maltose molecules. [1]
Describe the properties of enzymes [6] (2013/B10 OR)
- Enzymes are proteins in nature. [1]
- Enzymes are biological catalysts which speed up chemical reactions by lowering the activation energy needed to start the reaction. [1]
- Enzymes remain chemically unchanged at the end of the chemical reaction and hence enzymes can be reused and are needed in small amounts. [1]
- Enzymes are specific in action due to their three-dimensional shape. They act on a specific substrate as they bind to the active site of the enzymes, forming enzyme-substrate complexes. [1]
- Enzymes catalyse reversible reactions. [1]
- Enzymes are affected by temperature and pH and work best at optimum temperature and pH. [1]
Biological washing powders contain one or more enzymes. Suggest the advantages of using biological powders compared to those without enzymes [4] (2014/B10 OR)
- Lower temperature needed hence lesser electricity used and lower energy cost as most enzymes have an optimal temperature of 30-35.[1]
- Biological washing powder may contain specific enzymes which can remove specific stains more easily such as lipase which can catalyse/digest fat stains into fatty acids and glycerol and remove the stains more easily. [1] (include eg of enzyme; biological stain; digested products and more easily removed)
- As the enzymes remain chemically unchanged at the end of the reaction, a small amount of biological powder is needed for each wash. [1]
- Biological washing powders speed up stain removal as compared to those without enzymes. [1]
List the functions of water. [4] (Self)
- A solvent for chemical reactions
- As a key component in tissues
- Controlling body temperature
- Transporting dissolved substances
Glucose + fructose = ?
Sucrose
Glucose + Galactose = ?
Lactose
Single sugars are also known as?
Monosaccharides
Define a condensation reaction (self)
A condensation reaction is a chemical reaction in which two simple molecules are joined together to form a larger molecule with the removal of one molecule of water.
Define hydrolysis. (Self)
Hydrolysis is a reaction in which a water molecule is needed to break up a complex molecule into smaller molecules.
Describe the process of the test for reducing sugars. (Self)
Benedicts’s test
- Place 1ml of food sample into the test tube
- Place and equal amount of Benedict’s solution into the sample
- Shake mixture and place in boiling water bath for 2-3 minutes.
State the possible outcomes of the Benedict’s test and what it means.
Solution remained blue > No reducing sugar
Blue to green precipitate > Traces of reducing sugar
Blue to yellow or orange precipitate > moderate amount of reducing sugar
Blue to brick red precipitate > Large amount of reducing sugar
State the structure, role and occurrence of starch (self)
Structure
Many glucose molecules joined together in a chain
Role
Storage form of carbohydrate in plants. It’s can be converted to glucose when needed to provide energy for cellular activities.
Occurrence
Storage organs e.g. potato tubers
State the structure, role and occurrence of cellulose (self)
Structure
Many glucose molecules joined together in an alternating fashion, forming a chain
Role
The cellulose cell wall protects plant cells from bursting or damage. Being undigestible in the human digestive system, it serves as dietary fibres that prevent constipation.
Occurrence
Cell walls of plants
