Grade 12 Zoology Note



Nutrition is a process by which an organism obtains substances required for its proper growth, maintenance and to provide energy for all the activates.  Nutrition includes food intake, absorption, assimilation, biosynthesis, energy metabolism, catabolism and excretion. They are of two types;

1.Autotropic nutrition:

A type of nutrition in which organisms synthesize the organic materials they require from inorganic sources. Chief sources of carbon and nitrogen are carbon dioxide and nitrates, respectively. All green plants are autotrophic and use light as a source of energy for the synthesis, i.e. they are photoautotrophic some bacteria are also photoautotrophic; others are chemoautotrophic, using energy derived from chemical processes.

2.Heterotropic nutration:

The word heterotrophy has been derived from two Greek words-hetero means different and troph refers to nutrition of food. The organisms which derive their food from others are known as heterotrophic organisms. They depend for their food on other organisms, hence they are called consumers. All animals, human beings and non-green plans like fungi come under this category. They consume complex organic food prepared by autotrophs or producers and break it into simple from to derive nourishment. Thus the difference between heterotrophy and autotrophs is basically in the mode of production of food. Due to lack of chlorophyll, heterotrophs cannot synthesize their food while autotrophs can perform photosynthesis. Heterotrophs may be parasitic, saprophytic and holozoic.

1.Parasitic nutration:
Parasitic organisms are those which live on or inside other living organisms to derive their food. Such a mode of nutrition is known as parasitic nutrition. A parasite derives its food (nutrition) from the host in different ways the mode of feeding depends upon its habit, habitat, and modifications


2.Saprophytic nutration:

 Saprophytic organisms derive their food from decomposing dead organisms. The complex organic compounds become simpler in dead organisms when the decomposition sets in. They feed on substances which were once part of living organisms such as stored food, wood, leather and rotten plant products. The common examples of saprophtyes are fungi (moulds, mushrooms, yeasts) and many bacteria.
3.Holozoic nutration:
The word holozoic has been derived from Greek words: holo smeans whole and zoon means animal. Holozoic nutrition involves ingestion of complex organic substances. The food of most animals contains large organic substances. In this mode, small or large particles of food are consumed through an opening called mouth (Ingestion). Then these are hydrolyzed into simpler and soluble forms (digestion). Simplified products are absorbed into the body and the undigested product is removed from the body. Depending upon the diet, they are herbivorous, carnivorous, omnivorous, frugivorous, sanguivorous, cannibalism, coprophagous.


Food or nutrient:

Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as fats, proteins, vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism's cells to provide energy, maintain life, or stimulate growth.

Functions of food:

Food provides our bodies with what they need to;

1.stay alive, be active, move and work; new cells and tissues for growth;

3.stay healthy and heal themselves;


4.prevent and fight infections.

Food of human consists of;


Carbohydrates are one of the main types of nutrients. They are the most important source of energy for your body. Your digestive system changes carbohydrates into glucose (blood sugar). Your body uses this sugar for energy for your cells, tissues and organs.

Daily requirement of carbohydrates;

Normal    -      2400kcl/day

Pregnant -       2400+300kcl/day

Lactating -        2400+500kcl/day

Infants     -         90+110kcl/day

Categories of carbohydrates;

 i) Monosaccharides:

 It is the simplest form of the carbohydrate. The general formula is CnH2nOn. For e.g. glucose, fructose etc. they are soluble in water and usually sweet in taste. They are divided in to different categories on the basis functional group namely, aldoses, ketoses, etc

ii) Disaccharides:

They are formed by two molecules of the monosaccharides. For e.g. maltose, sucrose, lactose. They also soluble in water and sweet in taste.


iii) Polysaccharides:

They are formed by the large number of monosaccharides and having several million molecular weights. They are insoluble in water and not sweet in taste. The common polysaccharides are starch, glycogen and cellulose. Starch is the reserved food material in plant.

Function of carbohydrates;

Carbohydrates have five major functions within the body:

1.Energy supply, carbohydrates are the principle source of energy.

2.Avoiding the breakdown of amino acid  for energy.

3.Avoiding  ketosis from the breakdown of fatty acids.

4.Cellular and protein recognition.

5.Carbohydrates as building blocks.

6.Carbohydrates as reserve food as they stored in form of starch and glycogen.



Proteins are large molecules consisting of amino acids which our bodies and the cells in our bodies need to function properly. Our body structures, functions, the regulation of the body's cells, tissues and organs cannot exist without proteins. The human body's muscles, skin, bones and many other parts contain significant amounts of protein. In fact, protein accounts for 20% of total body weight. Protein is broken down in to amino acids.

Amino acids:

Amino acids are biologically important organic compounds composed of amine (-NH2) and carboxylic acid (-COOH) functional groups, along with a side-chain specific to each amino acid. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, though other elements are found in the side-chains of certain amino acids. About 500 amino acids are known and can be classified in many ways

Characteristics of amino acid;

1.These are the basic unit of protein.

2.These are colorless, crystalline solids.

3.These are soluble in water and insoluble in organic  solvents such as alcohol, acetone, etc.

4.There are 20 types of amino acid in nature.

5.The simplest amino acid is glycine.

Categories of amino acids;

They are divided in to two classes.

1.Essential amino acids:

Essential amino acids cannot be made by the body. As a result, they must come from food.The nine essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

2.Nonessential amino acids:

"Nonessential" means that our bodies produce an amino acid, even if we don't get it from the food we eat.They include: alanine, asparagine, aspartic acid, and glutamic acid.

Sources of protein:

The principle sources of proteins are both from plants and animals. In general the animal proteins are superior to plants proteins. There are two groups;

a.First class protein: The protein containing   all the types of amino acids. They are animal protein like egg, meat.

b.Second class proteins: The protein do not containing   all the types of amino acids. They are plant protein.

Types of protein:

On the basic of chemical nature and solubility they are of three types.

1. Simple protein: These are the proteins formed of peptide chain. Example are albumins, globulin, histones, prolamines, etc.

2.Conjugated proteins: These are the proteins formed in combination with non- protein molecule. Examples are casein, blood antigens, hemoglobin, etc.

3.Derived proteins: These are the proteins formed by partial hydrolysis of simple proteins and congulated proteins. Examples are peptone, proteoses, peptides, etc.

Functions of protein:

1.Many protein act as structural proteins and take part in building and reairing of the body tissue.

2.Protein provide the energy fuel.

3.Enzymes are made up of proteins.

4.Some hormones are protein such as insulin used to balance glucose.

5.Some protein help in blood clotting.

6. Some proteins are anti bodies or immunoglobins.

3. Lipids or fats:

Lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides, diglycerides, triglycerides, phospholipids, and others. The main biological functions of lipids include storing energy, signaling, and acting as structural components of cell membranes. Lipids have applications in the cosmetic and food industries as well as in nanotechnology.

Sources of fat:

Cooking oil,  butter, ghee, oil seeds, milk, meat, cheese, eggs, etc.

Classification of lipids:

1. Simple Lipids:
On hydrolysis gives fatty acids and alcohol (trihydric or monohydric).

Oils: Unsaturated fatty acid + glycerol.
Fats: Saturated fatty acids + glycerol,
Waxes: Fatty acids + mono or dihydric alcohol.
Simple glyceride: Contains same fatty acids. .
Mixed glyceride: Contains different fatty acids.

2. Compound lipids: (Complex lipids):
On hydrolysis gives phosphoric acid, various sugars, sphingosine, ethanolamine and serine in addition to fatty acids and glycerol.

a.Phospholipid:  Fatty acids + glycerol + phosphoric acid + nitrogenous base.
e.g. Lecithin :Fatty acids + glycerol + phosphoric acid + choline
Cephalin: Fatty acids + glycerol + phosphoric acid + ethanolamine.

b. Glycolipids: Glycerol + fatty acid + Carbohydrates (on hydrolysis).

They are sub classified as galactosyl diglyceride, cerebrosides and sulpholipids.

c) Sphingophosphoiplds: Fatty acids + sphingosine + phosphoric acid + choline.

3) Derived Lipids: Hydrolytic products of simple and compound lipids

i) Alcohols: Glycerol and other sterol
ii) Fatty acids
iii) Terpenoids

Functions of lipids:

1.Lipid provide energy fuel.

2.lipid act as thermal insulator.

3.Tryglycerides stored in adipose tissue as principle food reserve.

4.Lipids serve as solvents for fat soluble vitamins like A,D, E , and K.

5.They absorb mechanical impact around organs like eyeball preventing external shock.

6.Lipoprotein can prevent bacterial disease.


 A vitamin is an organic compound and a vital nutrient that an organism requires in limited amounts. An organic chemical compound is called a vitamin.

Fat soluble vitamins:

The fat-soluble vitamins, A, D, E, and K, are stored in the body for long periods of time and generally pose a greater risk for toxicity when consumed in excess than water-soluble vitamins. Eating a normal, well-balanced diet will not lead to toxicity in otherwise healthy individuals. However, taking vitamin supplements that contain megadoses of vitamins A, D, E and K may lead to toxicity. The body only needs small amounts of any vitamin.

Vitamin A (Retinol):

Vitamin A, also called retinol, has many functions in the body. In addition to helping the eyes adjust to light changes, vitamin A plays an important role in bone growth, tooth development, reproduction, cell division, gene expression, and regulation of the immune system.

Sources: Fish, liver oil, egg yolk, butter, cheese, milk, yellow and dark green leafy vegetable, papaya, tomatoes , carrots, guava, mango, etc.

Deficiency: Night blindness,  Xerophthalmia,  Reaterded growth, loss of glandular secretion, etc.

Vitamin D: Vitamin D plays a critical role in the body’s use of calcium and phosphorous. It works by increasing the amount of calcium absorbed from the small intestine, helping to form and maintain bones. Vitamin D benefits the body by playing a role in immunity and controlling cell growth. Children especially need adequate amounts of vitamin D to develop strong bones and healthy teeth.

Sources: Vitamin D is  found in oily fish (e.g., herring, salmon and sardines) as well as in cod liver oil. In addition to the vitamin D provided by food, we obtain vitamin D through our skin which produces vitamin D in response to sunlight.

Difeciency: Rickets or rachitis, Osteomalacea, teeth tetany.

Vitamin E:

 It is also known as beauty vitamin because it maintains germinal epithelium of gonads for proper reproductive function. Vitamin E benefits the body by acting as an antioxidant, red blood cells, and essential fatty acids from destruction.

Sources: About 60 percent of vitamin E in the diet comes from vegetable oil (soybean, corn, cottonseed, and safflower). Vitamin E sources also include fruits and vegetables, grains, nuts (almonds and hazelnuts), seeds (sunflower) and fortified cereals.

Deficiency: Reversible sterility in females, Sperm sterility in males, Macrocytic anaemina, muscular dystrophy.

Vitamin K:

Vitamin K is naturally produced by the bacteria in the intestines, and plays an essential role in normal blood clotting, promoting bone health, and helping to produce proteins for blood, bones, and kidneys.

Sources: Good food sources of vitamin K are green, leafy-vegetables such as turnip greens, spinach, cauliflower, cabbage and broccoli, and certain vegetables oils including soybean oil, cottonseed oil, canola oil and olive oil. Animal foods, in general, contain limited amounts of vitamin K.

Deficiency: Causes blood clotting, Hypoprothrombinaemia, Haemorrhage,

Water-Soluble Vitamins:

These types of vitamins require regular supply in the form of dietary sources or supplements. These are nontoxic and easily absorbed into the body through the gastrointestinal tract and then disseminated in the tissues. Water-soluble vitamins are easily dissolved in water, it would be advisable not to overcook them and use the left over cooking water as healthy options in soups and sauces.

Vitamin B 1 (thiamine): Part of an enzyme needed for energy metabolism, important to nerve function.

Sources: Found in all nutritious foods in moderate amounts: pork, whole-grain or enriched breads and cereals, legumes, nuts and seeds

Deficiency: Bery-bery, weight loss, weakness, nausea, constipation, etc.

Vitamin B2 (Riboflavin): Part of an enzyme needed for energy metabolism; important for normal vision and skin health.

Sources: Milk and milk products; leafy green vegetables; whole-grain, enriched breads and cereals.

Deficiency: Cheilosis, Glossitis, Keratitis, Saborrhic dermatitis.

Vitamin B3: Part of an enzyme needed for energy metabolism; important for nervous system, digestive system, and skin health.

Sources: Meat, poultry, fish, whole-grain or enriched breads and cereals, vegetables (especially mushrooms, asparagus, and leafy green vegetables), peanut butter.

Deficiency: Pellagra

Vitamin B5 : It act as cheek anti-dermatitis factor.

Sources: Widely distributed in foods.

Deficiency: Rare

Vitamin B6 : Part of an enzyme needed for protein metabolism, helps make red blood cells.

Sources: Meat, fish, poultry, vegetables, fruits.

Deficiency:  Dermatitis, paralysis

Vitamin B7 : It directly participated in the carboxylic rexn.

Sources: Liver, kidney, egg, yolk, milk, grains, etc.

Deficiency: Acne vugaris, anemia, nausea, etc.

Vitamin B: It act s as the coenzymes for synthesis protein. Part of an enzyme needed for making DNA and new.

Sources: Green leafy vegetable, cereals, liver, kidney, eggs, etc.

Deficiency: marcocytic  anaemia.

Vitamin B12 : Part of an enzyme needed for making new cells; important to nerve function.

Sources: Meat, poultry, fish, seafood, eggs, milk and milk products; not found in plant foods.

Deficiency: pernicious anaemia.


Vitamin C:

Vitamin C is a water-soluble vitamin that is necessary for normal growth and development. Water-soluble vitamins dissolve in water. Leftover amounts of the vitamin leave the body through the urine. That means you need a continuous supply of such vitamins in your diet.


Cantaloupe, Citrus fruits and juices, such as orange and grapefruit, Kiwi fruit, Mango, Papaya, Pineapple, Strawberries, raspberries, blueberries, cranberries, Watermelon, etc.

Deficiency:  Anemia, Bleeding gums, Decreased ability to fight infection, Decreased wound-healing rate, Dry and splitting hair, Easy bruising, Nosebleeds, Rough, dry, scaly skin, Swollen and painful joints, Weakened tooth enamel.


Minerals are important for your body to stay healthy. Your body uses minerals for many different jobs, including building bones, making hormones and regulating your heartbeat.


Major minerals





Needed for proper fluid balance, nerve transmission, and muscle contraction

Table salt, soy sauce; large amounts in processed foods; small amounts in milk, breads, vegetables, and unprocessed meats


Needed for proper fluid balance, stomach acid

Table salt, soy sauce; large amounts in processed foods; small amounts in milk, meats, breads, and vegetables


Needed for proper fluid balance, nerve transmission, and muscle contraction

Meats, milk, fresh fruits and vegetables, whole grains, legumes


Important for healthy bones and teeth; helps muscles relax and contract; important in nerve functioning, blood clotting, blood pressure regulation, immune system health

Milk and milk products; canned fish with bones (salmon, sardines); fortified tofu and fortified soy milk; greens (broccoli, mustard greens); legumes


Important for healthy bones and teeth; found in every cell; part of the system that maintains acid-base balance

Meat, fish, poultry, eggs, milk, processed foods (including soda pop)


Found in bones; needed for making protein, muscle contraction, nerve transmission, immune system health

Nuts and seeds; legumes; leafy, green vegetables; seafood; chocolate; artichokes; "hard" drinking water


Found in protein molecules

Occurs in foods as part of protein: meats, poultry, fish, eggs, milk, legumes, nuts


Trace minerals (microminerals)

The body needs trace minerals in very small amounts. Note that iron is considered to be a trace mineral, although the amount needed is somewhat more than for other microminerals.

Trace minerals





Part of a molecule (hemoglobin) found in red blood cells that carries oxygen in the body; needed for energy metabolism

Organ meats; red meats; fish; poultry; shellfish (especially clams); egg yolks; legumes; dried fruits; dark, leafy greens; iron-enriched breads and cereals; and fortified cereals


Part of many enzymes; needed for making protein and genetic material; has a function in taste perception, wound healing, normal fetal development, production of sperm, normal growth and sexual maturation, immune system health

Meats, fish, poultry, leavened whole grains, vegetables


Found in thyroid hormone, which helps regulate growth, development, and metabolism

Seafood, foods grown in iodine-rich soil, iodized salt, bread, dairy products



Meats, seafood, grains


Part of many enzymes; needed for iron metabolism

Legumes, nuts and seeds, whole grains, organ meats, drinking water


Part of many enzymes

Widespread in foods, especially plant foods


Involved in formation of bones and teeth; helps prevent tooth decay

Drinking water (either fluoridated or naturally containing fluoride), fish, and most teas


Works closely with insulin to regulate blood sugar (glucose) levels

Unrefined foods, especially liver, brewer's yeast, whole grains, nuts, cheeses


Part of some enzymes

Legumes; breads and grains; leafy greens; leafy, green vegetables; milk; liver


Balanced diet:

 A diet that consists of right amount of essential nutrients such as carbohydrates, proteins, fats, vitamins, minerals, roughage and water required by the body is called balanced diet.

 A balanced diet is important because your body’s organs and tissues need proper nutrition to work effectively. Without good nutrition, your body is more prone to disease, infection, fatigue, and poor performance. Children with a poor diet run the risk of growth and developmental problems. Bad eating habits can continue for the rest of their lives a person’s daily calorie intake should be based on age, gender, and physical activity level. Men generally need more calories than women, and active people need more calories than sedentary (inactive) people.


A term used to refer to any condition in which the body does not receive enough nutrients for proper function. Malnutrition may range from mild to severe and life-threatening. It can be a result of starvation, in which a person has an inadequate intake of calories, or it may be related to a deficiency of one particular nutrient (for example, vitamin C deficiency). Malnutrition can also occur because a person cannot properly digest or absorb nutrients from the food they consume, as may occur with certain medical conditions. Malnutrition remains a significant global problem, especially in developing countries.


A rapid deterioration in nutritional status in a short time can lead to marasmus, one form of acute malnutrition. Marasmus is the most common form of acute malnutrition in nutritional emergencies and, in its severe form, can very quickly lead to death if untreated. It is characterized by severe wasting of fat and muscle which the body breaks down to make energy. Wasting can affect both children and adults.


Some children with acute protein-energy malnutrition develop oedema. Oedema is an accumulation of fluid in the tissue, especially the feet and legs. Such children may not lose weight when developing acute protein-energy malnutrition because the weight of this excess oedema fluid counterbalances the weight of lost fat and muscle tissue. These children may look fat or swollen. Such children have kwashiorkor.

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