Friday, 10 June 2011



Food undergoes six major processes:

1. Ingestion : process of eating

2. Propulsion : passing of food down the GI tract swallowing : voluntary peristalsis : reflex, involuntary, involves alternating contractions of muscles in body walls of GI organs

3. Mechanical digestion

prepares food for chemical digestion includes chewing, mixing with saliva by tongue action, churning in stomach...

4. Chemical digestion

catabolic steps in which food is broken down to basic building blocks accomplished by enzymes in digestive juices

5. Absorption : passage of food particles into the blood-lymph

6. Defecation : elimination of indigestible food substances

Concept of Balance Diet

A balance diet is one which contains the correct proportions of all the different food requirement of the body.

A balanced diet should supply enough energy for each day activities

A balance diet consist of the following food requirement

Carbohydrates and lipids to provide energy for all the activities in the body

Protein to build new tissues for growth and repair damaged tissues

Vitamins to prevent diseases and for normal healthy development

Mineral salts which are essential for normal healthy growth and development

Fibres as roughage to stimulate peristalsis and prevent constipation

Water which is needed as medium for all chemical reactions in the cells. It helps to transport substances that are needed by the cells and remove metabolic wastes. It also help to distribute and regulated body heat

Factors affecting the daily energy requirement of the body

 Individual requires energy that is sufficient to carry out all living processes such as heart beating, breathing, growing, excreting and regulating body temperature of 37 C

Energy is obtained from the oxidation of glucose during cell respiration

The unit for energy is joule (J)

The energy value or calorific value is the quantify of heat produced when one gram of food is completely oxidised. Example of energy value in certain food are as follow

Carbohydrates 22.2 kJ per gram

Protein 17.2 kJ per gram

Lipids – 38.5 kJ per gram

One calorie or 4.2 J is the quantity of heat required to raise temperature of 1 gram of water by 1C. The energy value in a certain food can be determined by using the following formula

Energy value = (Mass of water gram x Increase in temp C x 4.2) mass of food (g)

The daily energy requirement of the body varies from individual to individual and depends on the following factors



Body size and weight


Heterotrophic Nutrition

Heterotrophic Nutrition

Heterotrophic nutrition is the nutrition of organisms which need ready made complex organic molecules, they obtain these wither directly from plants, or from organisms which have fed on plants. Thus heterotrophic organisms are the consumers in an ecosystem.

Organism that carry out heterotrophic nutrition are called heterotrophs
Holozoic Nutrition

Involves feeding by ingesting complex organic matter which are then digested and absorbed

Example of organisms with holozoic nutrition are animals and insectivorous plants


Feed on the dead remains of other organisms(dead organic material).

Secrete enzymes onto the food, then soluble products are absorbed

Involves feeding by absorbing their required nutrients from dead organic matter.

Extracellular digestion.

Responsible for decay.

The decomposers in an ecosystem.

Fungi such as Rhizopus are saprobionts. Bacteria and fungi like musrooms, yeast and Mucor (bread mould)


Obtain food from another living organism, the host

There is a close association between the host and the parasite

The host suffers some degree of harm.

Taenia, the pork tapeworm, is a parasite, the adult is an endoparasite of human beings, thus we are the primary host, it is found attached to the wall of the small intestine of an infected individual, where it absorbs the soluble products of digestion.


Large surface area for absorption

No alimentary canal

Thick outer covering (tergument)

Suckers and hooks for attachment to gut wall, to resist peristalsis

Large numbers of offspring produced

Reduced nervous system


Chemosynthesis is a process certain organisms use to produce energy, akin to photosynthesis, but without the utilization of sunlight.

The energy comes from the oxidization (burning) of chemicals which seep up from the Earth's crust.

The organisms that use chemosynthesis,

all bacteria, manufacture carbohydrates and other organic molecules from the oxidization of sulfates or ammonia. The hydrogen they use comes from hydrogen sulfite, whereas the nitrogen comes from ammonia or nitrates.

The organisms that use chemosynthesis are found around hydrothermal vents on the ocean floor.

They are adapted to circumstances which would have been commonplace billion of years ago, leading some to call them descendants of the earliest life on Earth.

Autotrophic Nutrition

Autotrophic nutrition involves the use of an external energy source to make the complex organic molecules that we call food from inorganic substances

The organism that carry out autotrophic nutrition are called autotrophs.

Plants use light energy from the sun as their external energy source, this type of autotrophic nutrition is photosynthesis.

During photosynthesis carbon dioxide and water are used to manufacture carbohydrates.

Light energy is trapped by chlorophyll and used to fix carbon dioxide, firstly to reduce it to carbohydrates.

Plant manufacture all the other organic molecules that they need from these carbohydrates and very small quantities of mineral ions obtained from the soil.

Type of Nutrition

There are two types nutrition

Autotrophic nutrition
  • Synthesise the organic food from inorganic substances
  • Types
    • Chemosynthesis
    • Photsynthesis

Heterotrophic nutrition
  • Organism depend on autotrophs or other organisms as a source of energy as they cannot synthesise their own food
  • Holozoic
  • Saprophytism
  • Parasitism