Enzymes

• General tips for writing a test or examination in Life Sciences:

  • Answer ALL the questions
  • Number the answers correctly according to the numbering system used in the question paper
  • Present answers according to the instructions of each question
  • Do ALL drawings in pencil and label them in blue or black ink
  • Draw diagrams, tables, or flow charts only when asked
  • Diagrams in question papers are NOT necessarily drawn to scale
  • Do NOT use graph paper for drawing graphs
  • Use a non-programmable calculator, protractor, and compass where necessary
  • Write neatly and legibly
• • Ensure you have all necessary stationery for the exam
• How to approach your Life Sciences test or examination:

  • Test papers consist of TWO sections: SECTION A and SECTION B
  • For multiple-choice questions in Section A, evaluate each option and eliminate incorrect ones
  • Some questions require only a LETTER response, while others need both a LETTER and a NAME
  • Use correct spelling for biological terminology
  • Use scientific names and avoid common names
  • Instruction verbs and mark allocation per question indicate the information required in your answer
• Scientific skills:

  1. Calculations:

  • Simple calculations involving addition, subtraction, multiplication, and division
  • Show working step by step
  • Include units in the final answer

  2. Presentation of data:

  • Data can be presented in tables or graphs

  3. Tables:

  • Used to record investigation results
  • Must have appropriate headings, rows, and columns
  • Independent variable on the left, dependent on the right
  • Example table provided for children born with sickle cell disease in different regions
• Drawing graphs:

  • Understand line graphs, bar graphs, histograms, and pie charts
  • Provide a heading with independent and dependent variables
  • Label X and Y-axis with units
  • Determine appropriate scale for axes
  • Bars in bar graphs should be of equal width with equal spaces
  • Use a compass and protractor for pie charts
• Scientific investigations:

  • Terms and meanings associated with investigations provided
  • Includes Observation, Hypothesis, Aim, Variables, Controlled variables, Control, Accuracy, Validity, Results, Conclusion
  • Tips for improving reliability of results listed
• Formulating a hypothesis:

  • Hypothesis must have two variables, state relationship, be testable, and list independent variable first
  • Example hypothesis question provided with possible formulated hypotheses
• The Chemistry of Life:

  • Organic molecules contain C, H, O, and sometimes N, P
  • Cells made up of proteins, carbohydrates, lipids, nucleic acids, and vitamins
  • Inorganic compounds do not contain carbon, e.g., water, gases, minerals
  • Water is essential for life, consists of 1 O bonded to 2 H (H2O)
  • Minerals divided into macro and micro elements with functions and deficiency diseases listed
• Potassium (K):

  • Required for functioning of nerves and muscles
  • Needed to activate plant enzymes
  • Poor heart and muscle function in animals
  • Chlorosis (leaves become yellow due to a shortage of chlorophyll) in plants
• Calcium (Ca):

  • Required for formation of bones and teeth in animals
  • Functions in blood clotting
  • Plays a role in the permeability of cell membranes
  • Rickets in humans
  • Poor root growth in plants
• Phosphorus (P):

  • Required for formation of bones and teeth in animals
  • Rickets in humans
  • Stunted growth in plants
  • Component of cell membranes and nucleic acids
• Iron (Fe):

  • Required in synthesis of haemoglobin
  • Helps to form chlorophyll in plants
  • Anaemia in humans
  • Chlorosis in plants
• Iodine (I):

  • Component of the hormone thyroxin secreted by the thyroid gland in humans
  • Goitre (swelling of neck or larynx) in humans
• Carbohydrates:

  • Made up of carbon (C), hydrogen (H), and oxygen (O)
  • Ratio of H atoms to O atoms is 2:1
  • Divided into monosaccharides, disaccharides, and polysaccharides
  • Test for glucose: Benedict solution
  • Test for starch: Iodine solution
• Lipids (fats and oils):

  • Contain carbon (C), hydrogen (H), and oxygen (O)
  • Ratio of H to O is greater than 2:1
  • Saturated fats and unsaturated fats
  • Cholesterol is a lipid found in the human body
• Proteins:

  • Made up of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N)
  • Proteins are large molecules made up of amino acids
  • Proteins are sensitive to temperature and pH
  • Test for proteins: Biuret test
• Enzymes:

  • Enzymes are proteins that speed up chemical reactions
  • Involved in anabolic and catabolic reactions
  • Lock-and-key model of enzyme action
  • Effect of temperature and pH on enzyme activity
• Nucleic acids:

  • Made up of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and phosphorous (P)
  • DNA and RNA
  • DNA carries hereditary characteristics
  • RNA plays a role in protein synthesis
• Vitamins:

  • Organic compounds required in small quantities by animals
  • Essential for normal metabolism, growth, and development
• Cell wall:

  • Rigid, non-living layer found outside the cell membrane in plant cells
  • Made of cellulose
  • Support structure that protects and gives rigidity to plant cells
• Cell membrane:

  • Forms the outer living boundary of the cytoplasm
  • Selectively permeable and controls movement of substances
  • Diffusion, osmosis, and active transport
• Nucleus:

  • Controls the activities of the cell
  • Chromosomes carry hereditary characteristics
• Cytoplasm:

  • Stores substances and allows circulation
  • Contains dissolved nutrients and waste products
• Mitochondria:

  • Found in plant and animal cells
  • Cylindrically shaped with a double membrane
  • Contains folds called cristae for chemical reactions
• The inner membrane of the mitochondrion contains folds known as cristae
• Cristae increase the inner surface area of the mitochondrion where chemical reactions take place
• The mitochondrion is filled with a semi-fluid substance called the matrix
• The mitochondrion releases energy during cellular respiration
• Ribosomes are small round structures that occur in plant and animal cells
• Ribosomes are the sites of protein synthesis
• The Endoplasmic Reticulum (ER) is a membranous network found in plant and animal cells
• There are two types of ER: Rough ER (has ribosomes on its surface) and Smooth ER (has no ribosomes on its surface)
• The ER transports substances from one part of the cytoplasm to another
• The Golgi body consists of a stack of flat membrane-bound sacs called cisternae
• The Golgi body plays a role in producing and processing secretions like mucus and saliva
• Plastids only occur in plant cells
• There are 3 types of plastids: chloroplasts, chromoplasts, and leucoplasts
• Chloroplasts are mainly found in the photosynthesizing parts of a plant like the leaves
• Chloroplasts are surrounded by a double membrane and filled with a fluid matrix called stroma
• Chloroplasts contain disc-shaped membranes called lamellae or thylakoids