Contents
-Nutrients
-Nutrition in Humans
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Nutrients
-Enzymes
-Nutrients
· Carbohydrates
· Fats
· Proteins
· Water
Why do we need food?
-To give us energy for our bodily functions and everyday activities
-To grow
-To keep us healthy and fight diseases
-To repair and replace damaged and worn out tissues
Food
-Made up of three components: Nutrients, water and fibre.
-Nutrients are made up of: Carbohydrates, Fats, Proteins, Vitamins and Minerals.
-Different types of food have different roles in maintaining good health.
-Food is broken down by enzymes to be used by the body.
-Carbohydrates and Fats can be broken down into simpler elements like carbon, hydrogen and oxygen.
-Protein can be broken down into carbon, hydrogen, oxygen and nitrogen.
Carbohydrates
-Iodine test for starch
This starch test is performed by adding a few drops of iodine solution to the sample.
Starch present: Iodine turns from brown to blue-black.
Starch not present: Iodine remains brown.
-Test for reducing sugars
Reducing sugars :
- -Glucose, Galactose, Fructose (Monosaccharides)
- -Maltose, Lactose (Disaccharides) [NO SUCROSE]
This sugar test is performed by adding a equal amount of Benedict’s solution to the sample and bringing the mixture to a boil in a hot water bath for 5 mins.
Benedict’s solution:
Light Blue – No precipitate is formed, sugar is absent.
The presence of sugar is indicated by the formation of precipitate from green, through to yellow and orange, to brick red.
Fats
-Emulsion test for fats
The presence of fats can be identified with the emulsion test.
The test is done by dissolving the sample liquid in ethanol.
Water is added to the mixture. (Fat is insoluble in water.)
If a white cloudy emulsion is formed, fat is present.
Proteins
-Biuret test for proteins
The presence of proteins can be identified with the Biuret test.
The test is done by dissolving the sample liquid in ethanol.
Water is then added to the mixture.
If a violet solution is formed, Protein is present.
Carbohydrates
-All carbohydrates are compounds of carbon, hydrogen and oxygen.
The ratio of H:O is 2:1
-Is the principal source of energy
-Structural Compounds
- Cellulose (Cell wall of all plant cells)
- Lignin and DNA (part of the nucleus)
-All carbohydrates consist of the following molecules:
- Monosaccharide (simple sugars)
Can be absorbed into bloodstream through intestine directly.
- Glucose and Fructose
- Fruits, honey, corn syrup
- Glucose is used directly in respiration to release energy.
- Galactose
Does not occur in free form in foods.
- Disaccharide (complex sugars)
Too big to pass through intestines. (Only mono saccharides can pass)
ß(Hydrolysis Reaction)-
- Glucose + Glucose - (Condensation Reaction) à Maltose + Water
ß (Hydrolysis Reaction)—
- Glucose + Galactose –(Condensation Reaction) à Lactose + Water
ß (Hydrolysis Reaction)--
- Glucose + Fructose – (Condensation Reaction)à Sucrose + Water
Sucrose
- Found in sugar cane, sugar beets and are used for sweetening foods, soft drinks, etc.
Lactose
- Found in milk from lactating mammals
Maltose
- Found in malted cereals and germinating grains.
- Poly saccharide
- Long chain/ Polymers of monosaccharides.
- A polysaccharide is made up of many monosaccharides joined together in a reaction known as polymerization.
- Starch, Glycogen, Cellulose, Beta glucan and pectin.
- Starch, cellulose and glycogen are polysaccharides formed from condensation of many glucose molecules, to store glucose for future use and provide structural support.
Starch
-Two types of molecules
- Amylose, Long continuous chains ( curled chain somewhat like a coil of rope)
- Amylopectin, Long chains with considerable side-branching of the molecule
-Polymer of glucose
- Glucose + Glucose à Maltose à Starch
-Storage form of carbohydrates in plants for later use (glucose) as energy
- Stored as starch granules in plastids in plant cells or tissue.
Glycogen
-Storage form of carbohydrates in animals in the liver and skeletal muscle tissues.
-Polymer of glucose
- Highly branched chains of glucose units
Starch and Glycogen are suitable to be storage molecules
- Insoluble in water
- Large molecules; unable to diffuse across cell membranes (would not be lost from the cell easily)
- Easily hydrolyzed when needed
- Compact ; occupy less space
Cellulose
-Structural polysaccharides:
- Long cable-like bundles of fibrils in the cell walls of all plant cells
- Consists of glucose units linked together to form straight chains
- Differs from starch and glycogen because the glucose units are linked differently, giving each molecule added stability
-Used to construct rigid cell walls
-Cellulose is insoluble and takes long time to digest. Cellulose isdigested by cellulase.
-Nutritionally called fiber or roughage.
- Most enzymes do not have the enzymes to break the molecular linkages
- Aids peristalsis
- Herbivores digest cellulose with micro-organisms present in their gut.
Fats
-Consist of carbon, hydrogen and oxygen
-Contains less oxygen atoms in proportion to hydrogen than in carbohydrates.
-A molecule of fat consists of glycerol with chains of fatty acids attached to it.
-Most fats are triglycerides
-Fats provide twice as much energy as carbohydrates.
-Insoluble in water.
-Excess food stored as fats under skin and around organs, serving as an insulating layer and protecting organs from physical injuries.
-Stored fat is used as a reserved supply of energy.
-Fats act as a medium for the absorption and transport of fat-soluble vitamins A,D,E and K.
-Solvent for hormones
-Restrict water loss from the skin surface.
Types of fats
-Unsaturated fats
· Contains less than the maximum amount of hydrogen possible.
· Carbon atoms can be made to accept additional hydrogen atoms.
· Crooked molecules
· Fatty acids are bent to prevent molecules from being squeezed together.
· Exist as liquids at room temperature, e.g. oils.
· Provide some protection against cardiovascular disease.
· Lowers bad LDL cholesterol.
· Maintains beneficial HDL cholesterol
· Lowers triglycerides ( amount of fats) circulating in the blood.
· Found in vegetable oils
-Saturated Fats
- Those where all the possible places on the carbon atoms where hydrogen could be attached are filled.
- “Straight” molecules
- Exist as solids at room temperature, e.g. waxes.
- Increase level of cholesterol in blood.
- Diet rich in cholesterol and saturated fats increases the risk of heart disease.
- Found in animal fats
Proteins
-Contains Carbon, Hydrogen, Oxygen and Nitrogen
-Made up of many basic units called amino acids joined together in long chains which maybe folded or twisted in various ways
-There are about 20 different amino acids, 9 of them essential for keeping the body healthy.
-Amino acids link up to form polypeptides / peptones.
-A polypeptide is made of 5 different amino acids joined by peptide bonds, formed in a condensation reaction.
-Polypeptides are in turn, linked up to form a long chain of amino acids.
-Interactions between amino acids cause polypeptides to fold, coil, bend, or twist, resulting in a shape that is most stable for that particular sequence of amino acids.
Protein formation
-A protein molecule is made up of one or more long chains of amino acids folded together. The chains are coiled or folded to give the protein a three dimensional shape.
-Thus protein have a distinctive shape to perform specific function, and allow protein to recognize and bind to specific molecules.
Protein denaturation
-Weak bonds are easily broken by heat and chemicals such as acids and alkalis. When these bonds are broken, the protein loses its three-dimensional shape, thus denaturing the protein as the protein loses its specific shape and loses its function.
Why are Proteins broken down in the body?
- An animal cannot directly absorb the proteins it takes in because protein molecules are too large to pass through living cell surface membranes.
- These protein molecules must be broken down by enzymes during digestion.
- Digestion is a series of hydrolytic reactions. The proteins are first hydrolysed into short polypeptides (or peptones), and then hydrolysed into amino acids.
- Amino acids are simpler and much smaller molecules than proteins, soluble in water. They are small enough to diffuse through living membranes, thus can be easily absorbed into an animal’s body.
- When amino acids enter the body cells, they are linked up again to form the protein needed by the animal.
Sources of Protein:
-Animal proteins: lean meat, fish, egg, and milk.
-Plant proteins: Peas, beans, nut and bean curd.
Functions of Proteins:
-Make new cells for body to grow
-Repair and replace damaged and worn-out tissues.
-Make enzyme, hormones, antibodies and haemoglobin.
-Give energy
-Stabilise the pH of the blood.
-Maintain the concentration of cytoplasm by controlling osmosis.
Water
-60-70% of the body weight is water.
-Water is lost by perspiration , urination and breathing.
-Water is a major component of
- Protoplasm in our cells.
- Blood plasma
- Lubricant of joints
- Tissue fluids
- Digestive fluids
-Special properties of water
- Water has a high heat capacity to absorb heat without a corresponding rise in temperature.
- Ice is less dense than water
- Hydrogen bonds are formed between water moleculesà Cohesive forces à high surface tension à water movement up the plant
- Adhesive forces between water and other surfaces. E.g. Water molecule’s attraction to walls of xylem.
- Water is a very good solvent
- Incompressible
Water is required:
- Act as solvent to dissolve food substances, hormones and waste materials.
- Helping to transport digested food, hormones and waste materials in and around the body
- Required in all chemical reactions of the body; water acts as a medium for enzymes to act
- Digestion of foodà hydrolysis
- Removal of excretory waste
- Regulation of body temperature ( High heat capacity of water, sweating cools body)
- Diffusion of oxygen and carbon dioxide in and out of lungs
Why plants need water
- Water keeps plants turgid and plant upright
- Transports mineral salts from roots to leaves through the xylem
- One of the raw materials needed for photosynthesis
- Transports food substances from the leaves to other parts of the plant through the phloem
Nutrition In Humans
Ingestion – Process of taking in food through the mouth
Digestion – Process where large, complex food molecules are broken down into simpler, smaller and soluble molecules.
Absorption – The process of the passage or movement of digested food into blood.
Assimilation – Cells use the absorbed food to form new cells or parts of cells, or to provide energy.
Egestion – Removal of undigested food from body as faeces.
Mechanical Digestion
-Process of chewing, mashing and breaking up of food into smaller particles.
-Increases surface area for enzyme action later on.
Chemical Digestion
-Breakdown of macromolecules to simple units.
In animals, digestion usually happen outside the body cells -à Extracellular
Mouth
-Mechanical digestion
-Teeth grind and break down food (mastication), exposing large surface area for enzyme action
-Chemical Digestion
Starch – Salivary Amylase à Maltose
-3 pairs of salivary glands, secretes slightly alkaline (pH 7.5) saliva, which contains salivary amylase (ptyalin) and mucus that moistens the food and helps food to pass from mouth to oesophagus.
Tongue
-Mixes food with saliva
-Rolls food into a small, slippery ball (bolus) and are carried down the oesophagus.
-During swallowing, the epiglottis, a flap of tissue that bends down and closes the trachea to prevent food from entering the trachea.
-The bolus enters the oesophagus.
Oesophagus
-No digestion occurs here
-A narrow, muscular tube continuing from mouth to stomach.
Movement in alimentary canal
-Rhythmic, wave-like contraction and relaxation of the gut
-Peristalsis
Muscle layer
-Inner layer: Circular muscle
-Outer layer: Longitudinal
-Antagonistic action: When one set of muscles contracts, the other relaxes
- Contraction of circular muscles: lumen constricts
- Relaxation of longitudinal muscles: lumen shortens
- Relaxation of circular muscles: lumen dilates
- Contraction of longitudinal muscles: lumen lengthens
Stomach
-Distensible muscular bag, with thick muscular walls.
-Churns and breaks up food (mechanical digestion)
-Gastric glands secretes Gastric juice, which contains hydrochloric acid:
- Lowers pH
- Stop action of salivary amylase à no more starch digestion
- Kills bacteria
- Allow pepsin to work
- Protein – Pepsin à Peptones (polypeptides)
- Rennin curdles milk proteins:
Caseinogen (soluble) -- Rennin à Casein (Insoluble)
-Two rings of muscles, one at enterance, another at exit (of stomach).
- Controls food entering and leaving stomach.
- Proteins and fats remains in stomach for 2 to 3 hours
- Carbohydrates remain for only 1 hour
- Food becomes semi-fluid, partially digested and acidic when it leaves t he stomach.
Small intestine
-6 metre long
- U-shaped upper part à duodenum
- Long coiled lower part à ileum
Associated Organs
-Aid in digestion, but not part of alimentary canal
-Liver
Liver
-Largest organ, dark red, located at upper abdomen, below diaphragm
-Produces bile (greenish yellow liquid)
Gall bladder
-Small bag that lies under the surface of the liver
-Stores bile, which is secreted into duodenum via bile duct
-Bile contains bile salts
- Emulsify fats
- Larger surface area for enzymes to digest fats
- Neutralise acid from stomach
- Provide pancreatic and intestinal enzymes to work
Pancreas
-Connected to duodenum by pancreatic duct
-Secretes into duodenum, pancreatic juice that contains 3 different enzymes to digest carbohydrates, fats and proteins
-Sodium carbonate, which helps to neutralize stomach acid.
Duodenum
-Pancreatic juice (pancreas) contains
- Pancreatic Amylase
Starch – Pancreatic Amylase à Maltose
- Trypsin
Protein – Trypsin à Peptones
- Lipase
Fats – Lipase à Fatty acids + Glycerol
Duodenum and Ileum
-Completion of starch digestion
-Secretes alkaline intestinal juice (intestinal glands) which contains
- Maltase
Maltose – Maltase à Glucose
- Sucrase (invertase)
Sucrose – Sucrase à Glucose + Fructose
- Lactase
Lactose – Lactase à Glucose + Galactose
- Erepsin
Peptone – Erepsin à Amino Acids
Ileum
-Glucose and amino acids pass through the wall of ileum into the bloodstream
-By process of diffusion and active transport
-Glycerol and fatty acids diffuse into the epithelium and combine to form fat globules before they enter into the lacteal.
-Water, vitamins and mineral salts are also absorbed here
Adaptations of ileum to absorb food efficiently
-Shape of long tube, gives more time for digested food to be absorbed
-Folded inner surface, increases surface area for absorption, allows more food to be absorbed in a given time (faster rate of absorption)
-Has many small, finger-like projections à Villi
- Assists in absorption of all digested food end products into the bloodstream through wall of ileum.
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-Villus is only one cell thick, increases rate of absorption à shorter distance for nutrients to travel into blood
-Numerous tiny blood vessels, capillaries present in each villus to join to form a blood vessel, which carries blood towards the liver. Lacteal (lymphatic capillary) in each villus to transport fats away from ileum. à Capillaries transport digested food away from ileum to liver to be taken to rest of the body. Diffusion gradient maintained between blood and inside ileum.
The large intestine
-About 1.5 metre
-Broader than small intestine
-Consists of
· appendix
· caecum
· colon which is shaped like an inverted “U” and is the main portion of the large intestine which absorbs mineral salts and water from indigestible food.
· Rectum, a short muscular tube which store faeces until they are ready to be expelled.
Function of large intestine
-Most of the water and mineral salts are reabsorbed into the body at the large intestine.
-Whatever undigested or not absorbed food becomes a semi-solid waste called faeces.
-Faeces are stored in the rectum until they are ready to be expelled out of the anus à Egestion
Anus
-Exit of alimentary canal
-Opening through which faeces passes out of.
-Sphincter muscles controls opening and closing of anus.
The liver, and its role in assimilation and digestion.
Hepatic Portal Vein
-Helps in transportation of digested food to the liver.
Assimilation
-Blood carries absorbed food from the small intestine to the liver.
-In the liver, some of the food may be stored or further broken down. The rest of the food is circulated to all the body cells for other purposes.
Use of absorbed food by cells of the body
-Glucose
- Energy source for cells
- Glucose combines with oxygen during respiration to produce a lot of energy that is needed for life activities
-Amino Acids
- Make new cells for growth
- Replace worn out cells
- Repair damaged cells
- Synthesis of enzymes and hormones
-Fats
- Form parts of a cell such as cell membrane and nuclear membrane
- Source of energy when there is insufficient glucose in the body
Role of liver in metabolism
Fat Metabolism
-Convert fats to substance that can be stored or used
-Excess fats are stored in adipose tissues that are found in the abdomen, beneath the skin, around the heart and kidneys
-Reddish brown organ located beneath the diaphragm, partly overlaps the stomach.
-Plays an important role in the metabolism of the body
- Metabolism refers to the chemical reactions that take place in all living cells
- Can be breaking down into simpler substances or building up a complex molecule
Glucose metabolism
-Excess sugars are converted to glycogen and temporarily stored in liver.
Amino Acids metabolism
-Excess amino acids cannot be stored and have to be converted to other substances through deanimation
- Deanimation is the breakdown of amino acids by the liver which leads to production of glucose and urea
Functions of liver
Related to digestion and assimilation:
· Regulation of blood glucose (Glucose metabolism)
-Keeps amount of glucose in blood constant
-Excess glucose is converted to glycogen and stored.
-Glycogen converted to glucose when blood glucose level drops
· Deanimation of amino acids (Amino Acid Metabolism)
· Fat metabolism à Conversion of fats into substances that can be stored or used
· Bile production
Unrelated to digestion and assimilation
- Iron Storage
-Breaks down haemoglobin and releases iron
- Heat production
- Detoxification
-Breaks down harmful substances like benzoic acid and alcohol to less harmful substances
-E.g. Alcohol can be broken down to compounds that can be used in respiration to provide energy for cell activities
Alcohol à Acetaldehyde à Carbon Dioxide + Water + Energy
Metabolism of alcohol
-Liver removes 95% of alcohol from blood so that it becomes harmless to body.
-Prolonged alcohol consumption can damage the liver à Liver Cirrhosis
