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O-level Biology: Animal Nutrition

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O-level Biology: Animal Nutrition
« on: September 08, 2014, 09:44:30 AM »
Animal Nutrition  Animals eat to grow, repair etc. They  simply eat to live. In this unit we will study how animals make use of what  they eat. The journey of the food from the mouth to the anus through the  alimentary canal includes 5 steps:
  • Ingestion: Taking in pieces of food into  the mouth
  • Digestion: The break down of large,  insoluble food molecules into smaller more soluble ones by chemical and  mechanical means.
  • Absorption: Taking the digested food  molecules into the cells
  • Assimilation: Making use of the digested  food molecules for example to release energy or grow etc.
  • Egestion: The elimination of undigested  food materials through the anus
*Don’t confuse egestion with excretion,  excretion is to get rid of waste products of metabolism.
The alimentary canal (gut or digestive  tract) is made up of several organs working together to perform all the  processes mentioned above. Starting with the mouth and ending with the anus.
The Mouth: The mouth performs several functions:
Mechanical Digestion: The action of the teeth biting a small piece of food from a large one is considered mechanical digestion, the teeth also tears  and grinds the food into a bolus to give it larger surface area for faster  chemical digestion.
Chemical Digestion: beneath the tongue lies  a salivary gland which secrets saliva into the mouth, this saliva contains  water and mucus to lubricate the food bolus and amylase enzyme that breaks down  starch in the food into maltose.
After this the tongue pushes the food bolus  into the oesophagus.
The Oesophagus: This is a tube  that transports the food from the mouth deep into the body to the stomach.
 The food is pushed downwards by the muscles in the walls of the oesophagus, this process is called Peristalsis. Muscles contract and relax creating a wavy motion to push the  food down.
The Stomach: Here the food stays for a while. The  stomach is a flexible bag that performs both mechanical and chemical digestion.
Mechanical Digestion: The walls of the stomach contain muscles that contract and relax together mixing the food with  the content of the stomach and turning it into liquid chyme, this process is  called churning.
Chemical Digestion: The walls of the stomach also secretes a liquid called “Gastric Juice” which contains Hydrochloric  acid, Mucus, and pepsin enzyme. The pepsin enzyme digests proteins into simpler  polypeptides, while the hydrochloric acid is to provide optimum pH for the  enzyme and the mucus is to lubricate the food and protect the walls of the  stomach from the acid.
After a few hours, the sphincter which is a  muscular valve opens allowing the food into the small intestine.
 The Small Intestine: The small intestine is where most digestion  and absorption takes place. It is divided into two sections, duodenum and  ileum. The walls of the small intestine contain several types of liquids that  help in providing suitable conditions and digest the food. These liquids are:
Bile Juice: it comes from the liver, stored  in the gall bladder. It is squirted along the bile duct in the duodenum. The  bile works on fats only, fats are very difficult to digest because they are  very insoluble, the bile contains bile salts that breaks fats into tiny  droplets that float in the content of the small intestine, making it easier for  the lipase to digest fats into fatty acids and glycerol, this process is called  emulsification.
Pancreatic Juice: it comes from the pancreas and secreted along the pancreatic duct. It contains enzymes and sodium  hydrogen carbonate, which neutralises the hydrochloric acid that was added to  the food in the stomach, creating better conditions for the enzymes to work.  The pancreatic juice contains the following enzymes:
  • Amylase to digest starch into Maltose
  • Trypsin to digest proteins to polypeptides
  • Lipase to digest fats into fatty acids and  glycerol
Small intestine liquid: The small intestine  itself also secrets a liquid that consists of lots of enzymes to make sure  carbohydrates, fats and proteins are digested to their simplest form, these  enzymes are:
For carbohydrates:
  • Maltase to digest maltose into glucose +  glucose
  • Sucrase to digest sucrose into glucose +  fructose
  • Lactase to digest lactose into glucose +  galactose
For Fats:
  • Lipase to digest fats into fatty acids and  glycerol
For proteins:
  • Protease for further digestion of  polypeptides to amino acids.
Absorption in small intestine: Absorption in the  small intestine takes place in the second section, the ileum. The walls of the  ileum are fully adapted for absorption. The interior walls of the ileum is  covered with a layer of villi, each villus is covered with another layer of  micro villi.
Each villi has a branch of blood capillaries in it as well as a lacteal which is a lymph vessel, the lacteal absorbs fats and lipids with vitamins dissolved in them into The lymphatic system.
Villi and microvilli are adapted to absorption by:
  • They give a very large surface area for  faster diffusion of food molecules
  • Each villus contains a large network of  blood capillaries transporting more blood, thus faster diffusion
  • Each villis is one cell thick, reducing the  diffusion distance and making it faster
  • Each villi contains a lacteal which absorbs  fats
The Large Intestine: By the time the food reaches the large  intestine, there is not much left of it, only some water, minerals, and fibers.  The water and the minerals are absorbed into the blood, while the fibers and  dead cells of the alimentary canal are stored in the rectum then excreted  through the anus (egestion).
 Assimilation Of The Absorbed Food  Molecules: After the food  molecules are absorbed from the alimentary canal, it is transported to the liver by a special blood vessel called The Hepatic Portal Vein. The liver is an organ that is considered a  gland too. It carries out several jobs to “sort out” the food molecules it  receives. Each type of nutrient has its own fate in the liver.
Glucose: when the absorbed glucose reaches  the liver, the liver allows as much as needed by the body to pass to the  circulatory system to by used for respiration or other processes. The excess  glucose is converted to glycogen and stored in the liver cells, when the blood  is short in glucose, glycogen will be converted back into glucose and secreted  to the blood. Some glucose will also be converted to fats as an energy reserve.  These functions are controlled by the Insulin and Glucagon hormones which are  made in the pancreas.
Amino Acids: some amino acids will be used  by the liver cells to make proteins, the rest will be allowed into the blood  stream to be absorbed by the body cells which also convert it to proteins. If  the body contains enough amino acids, the excess will undergo a process called Deamination, this involves the break down of amino acids into carbohydrates and amino group,  which is then converted to ammonia then converted into urea, which is part of  the waste product of the body, urine.
A part from sorting out food molecules, the  liver performs the following jobs too:
  • Dealing with old red blood cells:
     The liver changes dead red blood cells to  iron and bile. Iron is stored in the liver, large amounts of iron give it the  red colour and used to build up new red blood cells. The bile is stored in the  gall bladder to be used in digesting food again.
  • Detoxification:
     The liver breaks down toxic materials such  as alcohol which damages cells to fats. Alcoholics are known to have liver  diseases.
  • Helps in generating heat:
     The liver contains a very large number of  cells, which means a lot of metabolic reactions take place in it producing lots  of energy to warm the blood.
  • Making fibrinogen:
     This is a plasma protein which helps in  blood clotting when the skin is cut.
Teeth: Teeth are small, calcified, whitish structures found in the jaws (or mouths) of many vertebrates that are used to break down food.
Types of  mammalian teeth:
 Incisors: They are 4 in front of each jaw.
 They act like a blade to cut food(eg.  To cut a bite of a sandwich) they have a (chisel-like surface).
 Canines: They are  two in each jaw.
 They are very pointed, in humans they are used for the same purpose as incisors.
 However in carnivores they are longer and sharper and used to kill the prey.
 Premolars: 4 on the sides of each jaw
 They are used to cut and grind food.
 Molars: They are  6 at the back of
 Each jaw, 2 of them are wisdom teeth. They have the same use as Premolars.
Note: remember that we have two jaws, so 4  incisors in each jaw means that we have a total of 8 incisors in our mouth. We  have 16 teeth in each jaw, 32 in the whole mouth.
The tooth is divided into two parts, the  crown and the root.
Parts of the tooth:
Enamel: Made of calcium salts, it is very strong.
Dentine: It is covered by the enamel and surrounds the pulp cavity.
The pulp cavity: It contains the nerves and  blood vessels.
The part of the tooth above the gum is  called the crown, the part buried in the jawbone is called the root. The enamel  covers the crown, the root is covered by cement. And the tooth is held in place  by fibres.
Tooth Decay: when we eat, some food  particles stay in our mouth. Bacteria that lives in our mouth feed on these food  particles, they respire anaerobically producing lactic acid. Like any acid,  lactic acid reacts with the enamel and dissolves it away reaching the dentine,  here we feel the toothache.

 Methods Of preventing Tooth Decay:
  • Reduce sugar intake to prevent bacteria  respiring
  • Brush teeth to remove the plaque layer of  bacteria and saliva on our teeth and nuetralise mouth
  • Use toothpaste or water containing fluoride  because it is absorbed by the teeth and helps stopping the attack by acid
  • Pay regular visits to the dentist.
Adding Fluoride To Water[/t][/t]
  • Advantages
    • Suitable amounts prevent tooth decay
    • It is a cheaper method of teeth caring
  • Too much causes teeth molting, illness and abdominal pain
  • It is expensive


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