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CHEMICAL TESTS: Benedict's solution is used to test for reducing sugar.It changes from blue to orange precipitate.To be more specific,it changes from blue to green to yellow to orange precipitate. Iodine solution is used to test for starch.It changes from yellow or brown to blue black. Biuret solution is used to test for protein.It changes from blue to purple. Ethanol is used to test for fats.It is called an alcohol emulsion test.It makes the water turns cloudy if fats is present. What is enzyme? -An enzyme is a specialised protein that is synthesized by cells. -Enzymes are biological catalysts that speed up the rate of chemical reactions. -Enzymes remain chemically unchanged at the end of reaction. Lock and key hypothesis of enzyme: -The active site of an enzyme has a specific shape that is complimentary to the substrate molecule. -An enzyme-substrate complex is formed when a substrate molecule(which is the key) wiith the correct shape enters and binds to the active site of the enzyme(which is the lock). -New products are formed when bonds are broken(called the anabolic reaction) -The products are then released ,resulting in the enzyme ready to be used again. -Some enzyme can also catalyse the reaction in reverse reaction(called the catabolic reaction) Effect of temperature: -Increased temperature causes the enzyme and substrate molecule to gain more kinetic energy.This increases the collisions between enzyme and substrates. -Enzyme activity increases with temperature until the reaction reaches the highest rate at the optimum temperature. -Beyond the optimum temperature,the shape of the active site starts to change to the protein structure. -Enzyme activity stops because the substrate can no longer fit into the active site. Effect of pH: -Individual enzymes have specific optimum pH for greatest enzyme activity. -Enzyme activity slows down at extreme pH as the active site changes its shape. -Enzymes are inactive or denatured at conditions far from the optimum range. -The substrate can no longer fit into the active site to form an enzyme-substrate complex. -The enzyme become irreversibly denatured at extreme pH values,hence can no longer catalyse any chemical reaction. PHOTOSYNTHESIS: -is a process by which green plants,with the help of sunlight and chlorophyll,use water and carbon dioxide as the raw materials to make carbohydrates(glucose). -During this process,oxygen gas is given off. -During the day,the rate of photsynthesis is so great that glucose are formed faster than they can be removed.A large amount of glucose is made in the leaf and is converted to starch for temporary storage in the leaf. -At night,photosynthesis stops and starch is reconverted to glucose. ADAPTATION OF ROOT HAIR CELLS: Function:to absorb water and mineral ions(or salts) from the soil. Adaptation: -It is projected as a finger like structure into the soil particles.This greatly provides a large surface area for the absorption of water and mineral salts. -Its large vacuole,which contained a more of concentrated cell sap,facilitates the absorption of water. -Its minute,thin and narrow structure is able to pass through the intercellular spaces of soil particles for efficient absoprtion of soil water and also dissolved mineral salts. ADAPTATION OF XYLEM VESSELS: Function:To transport water and dissolved mineral salts from the roots to the leaves. To provide mechanical support for the plant. Adaptation: -They are long,narrow,elongated,perforated tubes,stretching from the roots through the stem,to the leaves.They are stacked end to end like drain pipes for efficient conduction of water and mineral salts within the plant. -The cell wall is made of a hard substance called lignin(lignified wall).This features gives mechanical support to the plant. Lignin strengthens the walls and prevents the collapse of the vessel. ADAPTATION Of RED BLOOD CELL: Function:To transport oxygen to all parts of the body. Adaptation: -The cytoplasm in red blood cell contains the red pigment called haemoglobin.Haemoglobin combines with oxygen in the lungs and forms oxyhaemoglobin.This then is transported to all parts of the body.When the blood reaches the tissues,the oxygen is released immediately. -Its elastic,biconcave cells which is being curved inwards provide more surface area for absorbing and carrying oxygen. -The cells are minute,elastic and disc-like and they are able to squeeze through the thinnest blood capillaries.