MODULE BIOSL 2: ANALYSE ENERGY
FLOW IN ECOSYSTEMS
Learning Outcome: BIOSL 2.2 – Apply knowledge of nutrition in human health.
Performance Criteria: PC - 2.2.1 to 2.2.8
ANIMAL NUTRITION (PC 2.2.1 – 2.2.8)
BALANCE DIET
• A diet containing all food types in
correct proportions as needed by the
body.
CLASSES OF FOOD
CARBOHYDRATES
C, H, O elements
Energy
Stored as starch in plants and glycogen
(fats) in animals
Can be divided into:
Monosaccharides /simple sugars (e.g. glucose, fructose, galactose)
Disaccharides (e.g. maltose, sucrose, lactose)
Polysaccharides –insoluble in water (e.g. starch, cellulose, lignin, pectin)
LIPIDS
C, H, O elements
Membranes
Energy
Thermal insulation – skins
Electrical insulation – nerves
Mechanical protection
Plants – unsaturated
Animals – saturated
PROTEINS
C, H, O, N, S elements
Membranes
Enzymes
Hormones
Antibodies
Building and repairing cells/tissues
Cell organelles
MINERALS & VITAMINS
• VITAMINS
There are many types of vitamins, e.g. A, B, C, D, and K.
They are essential for proper growth and good health.
They also play important role in chemical reactions of the body.
Vitamin C is needed for good health, healthy skin and wound healing.
Vit C also helps in formation of collagen for the skin and blood vessels.
Vitamin D helps body absorb calcium from food and is needed for strong
bones and teeth.
Vitamin B12 helps prevent malfunctioning of nervous system.
Sources; milk, liver, fruits and vegetables.
vitamin source Function Deficiency
A (Retinol) Fish, egg yolk, liver, kidneys, Maintains healthy skin and good Night blindness, healthy nose
butter, cheese, carrots vision membranes
B2 Yeast, egg yolk, liver, rice, Required for normal growth in Poor growth and beriberi,
kidneys, wheat. children. pellagra
C (Ascorbic Citrus fruits, green vegetables Help making the connective Scurvy associated with
acid) tissues which binds cells together. bleeding gums.
Helps in the building of strong
teeth, bones, and gums.
D (Calciferol) Animal fats, butter, fish liver, Needed for proper bone and Rickets in children, bone
sun basking, yolk. teeth formation. fractures (osteomalacia) in
adults.
Helps in the absorption of
calcium and phosphorus
K Found in leafy vegetables; Helps in blood clotting Poor recovery of wounds
spinach cabbage.
MINERALS
They are essential for general good
health.
There are different minerals needed by
the body, like calcium, iron, fluoride,
iodine and phosphorus.
Phosphorus and calcium are needed for strong bones and teeth.
Iodine is for making hormone thyroxin.
Iron is needed for making haemoglobin in the red cells.
Fluoride is for making strong enamel to resist decay.
Sources; meat, egg, milk, fruits and green vegetables
Mineral source Function Deficiency
Iron Green vegetables, liver, egg Responsible for haemoglobin Anaemia (lack of red blood
yolk, kidneys, milk formation cells)
Iodine Sea food, iodised table salts, Forms thyroglobulin in thyroid Goitre (enlarged thyroid
cheese glands glands)
Phosphorus Nuts, cheese, eggs, fish, Responsible for the formation of Rickets in children, bone
meat Bones and teeth. fractures (osteomalacia) in
adults
Calcium Milk, cheese, green Teeth and bones formation. Also Scurvy and sometimes
vegetables. helps in blood clotting, transmission rickets
of impulses between
nerves/neurones
Sodium and Vegetables and table salt Nerve and muscle function, Cramps after excessive
potassium responsible for change in difference I exercise
membranes
ROUGHAGES (FIBRES)
Fibres are cellulose.
They form part of the cell wall, and they
cannot be digested by digestive enzymes and
can only be digested by bacteria found in most
herbivores.
It absorbs water in the digestive parts and
softens the faeces and preventing constipation
(difficulty in defecation).
It is found in citrus fruits, cereals, whole grain products such as (brown bread, all
brown flakes, and brown rice).
It keeps the colon healthy.
WATER
It is essential for many reactions in the body.
Our body requires about 2L of water daily.
Importance of water in the body:
Reaction medium, metabolic reactions
take place in water.
Transport substances around the body
Form liquid part of the blood
Helps cool the body through sweating.
The body gets water through drinking and in food.
Water needs to be replaced since it is lost in various ways:
(i) Through skin during sweating
(ii) As urine
(iii) In faeces
(iv) Through exhaling Poor diet may results in malnutrition and deficiency diseases.
FOOD TESTS
Food Nutrient Methodology Positive Result Expected
STARCH - Place a food sample on a white tile Blue-black colour
(Use Iodine Solution) - Add 3 drops of iodine solution on the piece of food
GLUCOSE - Put a food solution in a test tube Brick red colour
Also called Testing for reducing sugars - Add a 5 drops of Benedict’ s soln, shake & place the mixture in (Also, green, orange and yellow
a warm water bath for 2 minutes indicate presence of glucose in
(Use Benedict’s Solution or Fehling’s small amounts)
solution)
PROTEIN - Put the food solution in a test tube Purple colour
Also called the biuret test. - Add 5 drops of copper (II) sulphate and shake
(Use Copper sulphate solution & Sodium - Add a 5 drops of Sodium hydroxide and shake
hydroxide solution)
FATS/LIPIDS -Place a food sample in test tube & add a ethanol and shake Milky white colour
(a) Emulsion test - Allow the mixture to settle and then decant the top layer into
another tube with water
(b) Using Filter paper Greasy opaque mark appears
- Place a food solution on a filter paper and leave it to dry on paper.
TESTING FOR VITAMIN C
Add 1cm3 of DCPIP solution to a test tube.
Add a small amount of food sample (as a solution)
A positive test will show the blue colour of the dye disappearing.
ENZYMES
Properties of Enzymes:
• Proteins
• Biological catalysts
• Speed up chemical reactions in living cells.
• Not used up in reactions
• Anabolic and catabolic
• pH sensitive
• Temperature sensitive
• Substrate specific
Enzymes & pH
Different enzymes are affected differently by different pH conditions.
A rise or fall in pH condition affects the activity of enzymes.
Some enzymes work best under acidic conditions whereas others prefer neutral or
alkaline conditions.
The pH at which an enzyme would catalyse a reaction most effectively is called its
OPTIMUM pH.
Example: Amylase works best at pH 7 – 8 & Pepsin works best at pH 2
Enzymes & Temperature
Very low temperatures inactivate enzymes which results in very low rates of chemical
reactions.
An increase in temperature speeds up the activity of an enzyme, therefore increasing
the rate of reaction.
Enzymes work best at temperatures called the optimum temperature.
Temperatures above 50 degrees denature enzymes, i.e. leads to a change in the protein
structure of the enzyme, this result in reactions proceeding very slowly to maintain
life.
Most organisms are killed by very high temperatures due to extremely low chemical
reactions which cannot maintain life processes.
Enzymes and Substrate Specificity
Substances which are acted upon by enzymes
are called SUBSTRATES and they have
SPECIFIC SHAPES.
Enzymes catalyse reactions by binding at their
active site.
The shape of the active site corresponds to the
shape the molecules of the substrate.
The substrate molecule will only fit perfectly to a specific enzyme if their shape
corresponds like a LOCK and KEY
The reaction is then catalysed when the Enzyme-substrate complex is formed.
The product is then released, and the enzyme is free to catalyse the next reaction.
The LOCK and KEY model (hypothesis) explain enzyme action because:
Only the correct enzyme-substrate combination can work.
Higher temperatures make the enzyme and substrate molecules to move more quickly,
this also means the substrate molecules enter the active site of the enzyme and the
product molecules leave the active site quickly.
DIGESTION
It is the breaking down of large insoluble food substances into smaller soluble particles that
can be absorbed.
This process takes place in the alimentary canal (gut), which is a tube that extends from the
mouth to the anus. When straightened, a mature gut measures between 7.5m and 9.0m long
Types of digestion
1) Physical digestion (mechanical digestion)
The breaking down of food substances through the action of teeth and muscular contractions.
It involves the processes of chewing and peristalsis. During chewing the teeth tear, cut crush /
grind food into smaller particles with a large surface area for enzyme action.
2) Chemical digestion
The conversion of large food substances through the action of enzymes.
Stages involved in the human digestion.
1. Ingestion; the taking in of food through the mouth
2. Digestion; the breaking down of large insoluble food molecules into smaller soluble
particles.
3. Absorption; the passage of digested food through the intestinal walls (in the ileum) to the
body fluids. i.e. the circulatory system
4. Assimilation; the building up of body’s own materials from the absorbed food substances.
i.e. usage of the absorbed food substances.
5. Egestion; The discharge of the undigested, unabsorbed material form the alimentary canal.
It is done through the anus.
HUMAN DIGESTIVE SYSTEM
THE MOUTH
Ingestion and mastication (chewing) takes
place in the mouth (buccal cavity).
Teeth serve to grind food into smaller particles
for easy swallowing and increasing the surface
area for enzyme activity.
The saliva moistens / lubricates the food.
The tongue helps to work the food into a ball
called food bolus to be swallowed easily.
The enzyme salivary amylase produced by
salivary glands under the tongue begins the
chemical digestion of starch into maltose.
OESOPHAGUS
When food is swallowed, the soft palate closes
the opening of the nasal cavity and epiglottis
closes opening the trachea to avoid choking.
The food bolus is then pushed down through
the oesophagus the process of peristalsis.
Approximately 10” long
It secretes mucus.
If acid from the stomach gets in here that’s
heartburn.
STOMACH
• J-shaped muscular bag
• stores the food
• Mixes food with digestive juices
• Protein digesting enzymes e.g. Pepsin, Renin
• Acid provides optimum pH for Pepsin, kills
bacteria & stops amylase
• Mucus protects walls
• Food found in the stomach is called chyme.
• Gastric gland: the gastric glands have three types of cells that secrete different
components of the gastric juice: mucus cells, chief cells, and parietal cells.
• Parietal cells: secrete hydrochloric acid (HCl). HCl converts pepsinogen to pepsin.
• Mucus cells: secrete mucus, which lubricates and protects the cells lining the stomach.
• Chief cells: secrete pepsinogen, an inactive form of the digestive enzyme pepsin.
SMALL INTESTINE
• The upper part is wider and called Duodenum, it is about 20cm long.
• The rest of the small intestine is called the ileum and it’s the longest part of the gut,
about 6m to 7m.
• The final stages of digestion take place in the duodenum.
Duodenum
• Bile: a greenish fluid made in the liver and stored in
gall bladder, is secreted into the duodenum to
emulsify fats, i.e. making them digestible.
• Pancreatic juice: an alkaline made by the pancreas
and contains several enzymes:
Trypsin – This converts some proteins peptides.
Pancreatic amylase – Acts on starch converting it to maltose.
Lipase - This breaks down fats into glycerol and fatty acids.
Other digestive enzymes contained in the pancreatic juice and the intestinal juices are:
maltase, lactase, sucrase, peptidase.
Note also, that the pancreatic juice contains sodium hydrogen carbonate which is alkaline
in order to provide the suitable pH needed by the request of the enzymes.
Though the cells of the gut are partly made of proteins, they are not attacked by
proteases for the following reasons:
The protein enzymes are secreted in an inactive form and only become active when
inside hydrochloric acid.
There is mucus secretion which also serves to protect the gut cells from self-digestion.
Ileum
The digestive process of the duodenum continues here shortly, and the walls of the
ileum also secrete intestinal juice which completes digestion.
The ileum is the site for absorption of the digested food material. The ileum is
adapted to carry out its function because of the following features:
It is long thus increasing the surface area for absorption.
The epithelium cells are very thin for easy and rapid diffusion of food
substances.
It has many folds (finger-like projections called villi) on the inner lining thus
increasing the surface are for absorption.
It is surrounded by a large network of blood capillaries to allow for easy
diffusion and rapid transport of food substances to other parts of the body.
The end products of
digestion (glucose, amino
acids, glycerol, and fatty
acids) are absorbed into
the blood stream through
diffusion and active
transport, and they reach
the liver through the
hepatic portal vein.
SUMMARY OF DIGESTIVE ENZYMES
LOCATION GLANDS ENZYME SUBSTRATE PRODUCT
Mouth Salivary Amylase Starch Maltose
Stomach Gastric Pepsin Protein Peptides
Rennin Milk protein Coagulated milk
Duodenum Pancreas Amylase Starch Maltose
Lipase Fats Fatty acids & Glycerol
Trypsin Protein & Peptides Amino acids
Ileum Ileum Lactase Lactose Glucose + Galactose
Lipase Fats Fatty acids + Glycerol
Maltase Maltose Glucose + Glucose
Sucrase Sucrose Glucose + Fructose
Peptidase Peptides Amino acids
ASSIMILATION
This is whereby the end products of digestion are used within the body.
1. Glucose
Used by all cells during respiration.
Excess glucose is converted to glycogen and stored in the liver.
2. Amino acids
They are used to make protoplasm (living material), hormones and enzymes.
Used to repair and replace worn out tissues.
Excess amino acids are deaminated by the liver to form urea which is excreted in
urine.
3. Fatty acids & glycerol
These recombine in the lacteal to form fat globules.
They are stored under the skin and around organs for heat insulation and as an energy
store.
Used by cells for respiration when glucose and glycogen are used up.
LARGE INTESTINE
The large intestine is divided into the caecum, colon, and rectum.
The caecum is a swollen sac located in the
lower right-hand portion of the abdominal
cavity.
The colon plays a very important role in
the re-absorption of water from the
undigested waste food.
The rectum, about 15 cm, is the terminal
portion of the large intestine. At the exit
of the rectum, called the anus, is a round
muscle, the anal sphincter that closes the
anus. The rectum stores faeces and release
them through the anus at interval. The
release of faeces is called egestion /
elimination / defecation.
Faeces are a mixture of substances such as;
Undigested food mainly the cellulose
Dead and living bacteria from the alimentary canal
Mucus and dead cells from the gut walls. The cells lining the gut have a limited life
span.
Surplus bile and other secretions which colour the faeces.
The large intestine has a smooth mucosal lining (only the rectum has folds) that secretes
mucus to lubricate the waste materials.
ACCESSORY ORGANS
Not part of the path of food but play
a critical role. Include: Liver, gall
bladder, and pancreas
Gall bladder:
Stores bile from the liver,
releases it into the
duodenum.
Fatty diets can cause
gallstones.
Pancreas:
• Produces digestive enzymes (trypsin, amylase, lipase).
• Secretes insulin: when blood glucose level is HIGH, the pancreas secretes hormone
insulin into the blood, it stimulates liver cells to convert excess glucose into glycogen
and then store it, hence reducing blood sugar level.
• Secretes Glucagon: when blood glucose is LOW, the pancreas secretes hormone
glucagon into the blood, it stimulates liver cells to convert stored glycogen back to
glucose, hence increasing blood sugar levels.
The Liver
1. Deamination
A process whereby excess
amino acids are broken down
by the liver into glycogen and
urea (nitrogenous waste).
The human body cannot store excess amino acids; therefore, they are taken to the liver
for deamination where the amino group is removed, and the residues converted to
glycogen for storage.
2. Fat metabolism
Breaking down of fats into CO2 and H2O to release energy.
3. Detoxification
The conversion of harmful substances into less harmful ones, e.g.
Chemical substances in drugs and alcohol are broken down into harmless
substances.
Used hormones are broken down into inactive forms.
Ammonia produced during Deamination is converted into less poisonous
substance called urea – to be excreted through the kidneys.
Dead red blood cells are broken down and the iron stored. The other waste
forms bile.
4. Formation of bile
The liver produces bile salts which are important in the emulsification and
subsequently absorption of fats.
5. Storage organ
A number of substances used by the body (such as bile, glycogen, iron, vitamin A, B,
D) are stored in the liver.
6. Regulation of blood sugar
The liver is able to convert glucose, amino acids and other substances to an insoluble
carbohydrate called glycogen.
Some of the glucose may be from the hepatic portal vein carrying blood rich in
digested food from the ileum to the liver.
When the glucose level is higher than normal range (80mg /100cm3 to 160mg/100cm3
of blood) the pancreas secretes insulin hormone into the blood which activates the
liver cells to convert glucose to glycogen.
If the concentration of blood sugar falls below 80mg/100cm3 of blood, the pancreas
secretes another hormone – glucagon which activates the liver cells to convert
glycogen to glucose.
A DIAGRAM TO REMEMBER
NON-COMMUNICABLE DISEASES
DIABETES (relate diet to prevention & management)
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HYPERTENSION (relate diet to prevention & management)
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CANCERS OF COLON, RECTUM, STOMACH & THROAT (relate diet to prevention &
management)
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