Grade 10 Life Sciences - Chemistry of Life & Ecosystems
Introduction:
Living things and their surroundings are composed of diverse chemical substances, which interact to sustain life processes.
Atoms, the fundamental particles of matter, form elements. Each element has unique properties and cannot be broken down into simpler substances by chemical means.
Elements are represented by one- or two-letter abbreviations (symbols) on the periodic table (e.g., Hydrogen is H, Oxygen is O).
Key elements in living organisms: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Sodium (Na), Potassium (K), Calcium (Ca), Sulfur (S), Iodine (I), Iron (Fe), Magnesium (Mg). These elements are crucial for building biomolecules and maintaining physiological functions.
Molecules are formed by combining two or more atoms through chemical bonds (e.g., O + O = O_2).
Compounds contain atoms of two or more different elements bonded together in a fixed ratio (e.g., 2H + O = H_2O).
Molecules and compounds constitute cells, the basic structural and functional units of life. They participate in various biochemical reactions necessary for life.
Essential compounds in cells include carbohydrates, lipids, proteins, nucleic acids, and water. These compounds perform specific roles essential for cell survival and function.
Specific Aim 1:
What is an element? An element is a substance that cannot be broken down into simpler substances by chemical means and is composed of atoms with the same number of protons.
What is a molecule? A molecule is a group of two or more atoms held together by chemical bonds.
Explain the difference between a molecule and a compound. A molecule is formed when two or more atoms combine, whereas a compound is formed when atoms of two or more different elements combine chemically in a fixed ratio.
Name two compounds found in living organisms. Water (H2O) and glucose (C6H{12}O6).
Careers Focus: Dietician and Nutritionist:
Job Description: Planning food and nutrition programs for individuals and groups, overseeing meal preparation to ensure nutritional standards are met, disease prevention through promoting healthy eating habits, and conducting research on nutritional requirements and the impact of diet on health.
Education: Grade 12 pass at Bachelor level with Mathematics and at least one Science subject (preferably Life Sciences). A four-year Bachelors degree in Dietetics or Nutrition is required and includes practical training in hospitals, clinics, or community health centers.
Skills: Enjoy working with people, strong communication and counseling skills, ability to translate scientific information into practical advice, and possess strong computer skills for data analysis and research.
Molecules for Life:
Molecules and compounds are classified as organic or inorganic based on their elemental composition and structure. This classification helps in understanding their roles in biological systems.
Organic Compounds:
Always contain carbon (C) and hydrogen (H). Carbon atoms form the backbone of organic molecules, allowing for complex structures.
Often contain oxygen (O) and may include nitrogen (N) and phosphorus (P). These additional elements contribute to the diversity and functionality of organic compounds.
Examples: carbohydrates, proteins, lipids, nucleic acids, and enzymes. Each of these plays a crucial role in cell structure and function.
Inorganic Compounds:
Contain other elements but do not usually contain hydrogen and carbon together (except carbonates). Inorganic compounds are essential for various biological processes.
May contain carbon (e.g., carbon dioxide). Carbon dioxide is a key reactant and product in metabolic pathways.
May contain hydrogen (e.g. water). Water is essential as a solvent and reactant in cells.
Example : Sodium bicarbonate (NaHCO3), water (H2O).
Key Question:
What is the difference between organic and inorganic compounds? Organic compounds contain carbon and hydrogen, forming complex structures. Inorganic compounds lack carbon-hydrogen bonds and are generally simpler in structure.
Activity 2: Making Models of Molecules and Compounds:
Build models of hydrogen, oxygen, carbon dioxide, water, methane, and ammonia using color-coded polystyrene balls and toothpicks to visualize their structures.
H2: Hydrogen (H + H)
O2: Oxygen (O + O)
CO2: Carbon Dioxide (C + O + O)
H2O: Water (H + H + O)
CH4: Methane (C + H + H + H + H)
NH3: Ammonia (N + H + H + H)
Identify which models are compounds (CO2, H2O, CH4, NH3), organic (CH4), and inorganic (CO2, H2O).
Organic Compounds:
Made up of carbon, hydrogen, and oxygen atoms, typically arranged in complex structures that determine their function.
Carbohydrates:
Function: primary energy source for cells and structural components of plants and some animals.
Classes: small, simple molecules (e.g., glucose) and large, complex molecules (e.g., starch, cellulose) that are polymers of simple sugars.
Monosaccharides: simple sugars (e.g., glucose, fructose, galactose) that serve as the basic building blocks of carbohydrates.
Disaccharides: double sugars (e.g., sucrose – glucose + fructose, lactose – glucose + galactose) formed by joining two monosaccharides.
Polysaccharides: large carbohydrate molecules (e.g., starches and cellulose) made up of many monosaccharide units linked together.
Starches: store energy in organisms and break down into glucose to provide energy (found in maize, rice, wheat, and potatoes; glycogen is the form of starch in animal cells stored in liver and muscles).
Cellulose: main component of plant cell walls, indigestible in humans (forms fibre or roughage) and provides structural support to plants.
Testing for Carbohydrates:
Glucose: Benedict’s solution or Fehling’s A and B solutions, heated (turns red-brown if glucose is present). This tests for reducing sugars.
Starch: iodine solution (turns blue-black if starch is present) due to the formation of a complex between iodine and starch.
Cellulose: Schultz’s solution (turns purple).
Key Questions:
What are the main groups of organic compounds found in living organisms? Carbohydrates, lipids, proteins, and nucleic acids.
What functions do organic compounds have in living organisms? Energy storage, structural support, catalysis, and genetic information.
What are enzymes and why are they so important? Enzymes are biological catalysts that speed up chemical reactions in cells, essential for metabolism and other life processes.
Skills Focus: Testing for Glucose:
Mix 2 ml Fehling’s A solution and 2 ml Fehling’s B solution, or 4 ml Benedict’s solution in a test tube; 2 ml glucose solution, then heat until mixture boils. The heat facilitates the reaction between glucose and the reagent.
Observe the color change. Orange or reddish-brown indicates glucose, showing the presence of reducing sugars.
Skills Focus: Testing for Starch:
Put about 5 ml of cornflour or flour in a test tube or on a saucer, add one or two drops of iodine solution. Iodine interacts with starch to form a complex.
The cornflour will change to a blue-black colour indicating starch, confirming its presence.
Activity 3: Testing Substances for Glucose or Starch:
Test raw potato, carrot, apple, paper, and sweets for glucose and starch and record results in a table to analyze their carbohydrate content.
Lipids:
Contain carbon, hydrogen, and oxygen; phospholipids also contain phosphorus, making them essential components of cell membranes.
Importance of Lipids:
Energy storage (fats and oils store more energy per gram than carbohydrates) and cell membrane structure (phospholipids form the lipid bilayer).
Lipid molecules consist of three fatty acids joined to a glycerol molecule through ester bonds. These bonds determine the properties of the lipid.
Unsaturated fatty acids (found in plants) are liquid at room temperature (e.g., sunflower and olive oil) due to the presence of double bonds that create kinks in the fatty acid chains.
Saturated fatty acids (found in fats from animals) are solid at room temperature (e.g., butter and lard) because they lack double bonds and pack tightly together.
Generally, unsaturated fats are healthier than saturated fats; saturated fats are linked to high blood cholesterol and heart disease due to their impact on cholesterol metabolism.
Skills Focus: Testing for Fats:
Put two drops of cooking oil into a test tube, add 5 ml of solvent such as carbon tetrachloride or ether, shake until all the oil disappears. The solvent dissolves the oil, making it easier to observe.
Put a drop of pure solvent on blotting paper or filter paper and another mixture of oil solvent next to the control drop, then wait until the solvent evaporates. Compare the translucent spot left by the oil solvent mixture with the control drop. Results are placed in a table.
Write the results you obtained in a table..
Proteins:
Contain carbon, hydrogen, oxygen, and nitrogen; some contain sulfur, phosphorus, and iron, contributing to their diverse functions.
Importance of Proteins:
Cell structure (e.g., cytoskeleton), cell functions (enzymes, hormones), form body tissues (muscle), and carry oxygen (hemoglobin).
Proteins are sensitive to extreme temperatures and pH levels, which can disrupt their structure and function.
Made of long chains of amino acids in a uniquely folded pattern. There are 20 amino acids that combine in distinct arrangements, which gives the protein the correct shape and functionality.
Skills Focus: Testing for Proteins:
Millon’s Reagent Test: Dilute egg white solution, add 1 ml of Millon’s reagent (mercuric nitrate in nitric acid), heat gently until the mixture boils resulting in a brick-red color to indicate the presence of protein due to the reaction with tyrosine and other aromatic amino acids.
Biuret Test: Add 10 ml of 20% caustic soda (NaOH), a few drops of copper sulfate (CuSO_4) solution mix with egg white. A violet color indicates the presence of protein, resulting from the complex formation between copper ions and peptide bonds.
Enzymes:
Proteins that act as catalysts to speed up chemical reactions without being changed themselves, facilitating biological processes efficiently.
Sensitive to extreme temperatures and pH changes, which can denature them and affect their activity.
Role of Enzymes: regulate and make possible every single chemical reaction in living cells. The reaction rate would be too slow w.o enzymes for life to be sustained.
Work by the lock-and-key model, where the substrate fits into the enzyme’s active site to form a product. The active site is specific to the substrate, ensuring precise reactions.
Important Note:
Enzymes are sensitive to temperature and pH levels. Optimal conditions are required for enzyme activity.
Enzymes can be denatured when its shape changes permanently due to heat or other factors, losing its function. Once denatured, it cannot function.
Activity 6: Explain how enzymes work:
The diagrams will show how an enzyme works and explains each of the diagrams, illustrating the substrate binding, transition state, and product release.
Activity 7: Investigate the effect of temperature on enzyme action:
Amylase in saliva breaks down cooked starch into maltose. Record time for black color to fade for each temperature, indicating the rate of starch breakdown.
Specific Aim 2: 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7 WORK in a group.
Enzymes are sensitive to pH:
Every enzyme has an optimum or best pH at which it functions best, and becomes denatured and can no longer function if its too acidic or alkaline, impacting the enzyme's structure and active site.
Activity 8: Investigate the effect of pH on enzyme catalyse:
Catalyse, enzymes in plant and animal tissues that break down hydrogen peroxide into water and oxygen. Write a hypothesis; identify dependent and independent variables in the investigation to understand the effect of pH on enzyme activity.
Work carefully with acid and peroxide.
Enzymes in everyday life:
Used in biological washing powders containing proteases to break down protein stains, lipases for fats, and amylases for starch.
Other uses: In baby foods (to predigest food), brewing, rubber, dairy, and baking industries to make the product easy to digest and improve texture.
Activity 9: Investigate the action of a ‘biological’ detergent
*Two soft boiled eggs in two beakers w. biological and one w ordinary washing powder dissolve equal amounts of non-biological and ‘biological’ detergents in two glasses/ beakers w cold water. Observe the breakdown of the egg stains.
1 What Enzymes were present in the washing powder? Explain how you know this. Analyze which stains were removed to infer the enzymes present.
*Nucleic Acids*:
Are compounds for life found in all cells. Nucleic acids play an important role in controlling the structure and functions of the cell by directing protein synthesis and inheritance.
Structure of nucleic acids
*Contain the elements carbon, hydrogen, oxygen, nitrogen, and phosphorus. There are two types: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
RNA:
*Found in the cell cytoplasm and on ribosomes, involved in protein synthesis.
Plays a role in building protein from Amino acids by translating genetic code.
DNA:
*Found in nucleus, stores genetic information.
Stores the information from which Amino acids must be produced in each type of cell, dictating cell function and development.
Vitamins:
*Vitamins are complex organic compounds found in small amounts in natural foods, essential for health.
Needed to keep bodies Healthy and for normal metabolic processes in humans; animals obtain them from the food they eat. They act as coenzymes in various biochemical reactions.
Deficiency related diseases: rickets (vitamin D), scurvy (vitamin C), and night blindness (vitamin A).
RDA for selected Nutrient required by Teenagers:
To check nutrient values found in different food with RDA for those table 1.3 to show food to ensure adequate intake.
Inorganic Compound
3.1 - Water
*It is the most important inorganic molecule for living organisms, essential for all life processes.
Makes up 60-70% of cell and is required for metabolic processes. It acts as a solvent, reactant, and temperature regulator.
3.2 Minerals
Are inorganic compounds that living things require in order to remain healthy. Plants acquire this from the soil.
Plants take in minerals from the soil, which are essential for their growth and development.
Fertilizers aid this process by providing essential nutrients to the soil.
Indigenous Knowledge Systems
Marago Grown in South Africa to use leaves like spinach, valuable for protein, magnesium, and calcium, offering nutritional benefits.
Animal Macro and Micro-Elements
Related to deficiency diseases, highlighting the importance of balanced mineral intake.
Minerals needed by animals, ex/ Dairy products: Calcium (development of strong teeth and bones).
Salt meat: Sodium helps maintain the body’s water balance.
Question: Take care when working with the solvent and do not inhale or drink. Solvents can be toxic.
Mineral: Animal and plant sources provide essential nutrients.
Plant macro and micro elements
Macroelement
Calcium and root development poor growth if deficient.
Magnesium (for the formation of chlorophyll) causes yellowing of leaves, impairing photosynthesis.
Activity 11 Analyze nutritional content on food packaging: To understand the composition and nutritional value of different foods.
The use of fertilizers can harm the environment by causing mineral salts from the soil to leach into water sources.