Type of Nutrition

Type of Nutrition

• Nutrition – process by which organisms obtain energy and nutrients from food, for growth, maintenance and repair of damaged tissues.
• Nutrients – the important substances which are required for nourishment of an organisms.
• Living organisms are divided into two groups (based on the nutritional habits): autotrophs and heterotrophs.

 (i) Autotroph

• Autotrophs – organisms that are able to synthesise complex organic compounds from raw, simple inorganic substances (water and air) by using light or chemical energy. These organisms manufacture their own food by photosynthesis or chemosynthesis.
• Photoautotrophs – chlorophyll containing organisms that utilise solar energy for building organic substance.
• Photoautotropic nutrition = holophytic nutrition.
• Chemoautotrophs – organisms synthesise organic substances by utilising chemical energy.

Autotrophs	Example
Photoautotroph	Trees
Chemoautotroph	Bacteria

(ii) Heterotroph

• Heterotrophs – organisms that are not able to synthesise their own nutrients but they obtain the nutrients from other organisms.
• Holozoic nutrition – organisms feed by ingesting solid organic matter that digested and absorbed into the bodies.
• Saprophytism – organisms feed on dead and decaying organic matter.
• Parasitism – organisms obtains nutrients (absorbs readily digested food) by living on / in the body of another living organisms (the host)

Heterotrophs	Example
Saprophyte	Fungi
Holozoic nutrition	Carnivores
Carnivorous plants (Holozoic nutrition)	Venus traps and pitcher plants
Parasites	Lice and fleas

Seven Important Classes of Food

1. Carbohydrates (provide energy)
2. Proteins (Build new tissues / important in growth and repairing damaged tissues)
3. Fats (provide energy / storage of extra foods)
4. Water (act as medium for biochemical reaction / transportation of substances)
5. Vitamins (prevent diseases / efficient metabolism / important for normal growth)
6. Minerals (important for normal growth and development of teeth, bones and muscles)
7. Roughage / Dietary fiber (prevent constipation / stimulate peristalsis)

 Factors Affecting Daily Energy Requirement
Balance diet is essential for healthy growth and development of the body.

1. Age – children and teenagers need more energy due to their high metabolic rate.
2. Sex – male adult needs more energy due to in males have high metabolic rate.
3. Pregnancy and lactation – pregnant women need more energy due to support the growing foetuses and produce milk for their babies.
4. Occupation – an active person requires high energy due to the person does a lot of heavy work.
5. Size or body weight – a person smaller in size has a larger surface area per unit volume. Thus, the rate of heat loss is high.
6. Climate – people living in cold countries need more energy to maintain body temperature.
7. Genetics – genetics disposition in certain person may decide different metabolic rate.
8. Health – In sufficient secretion of thyroxine hormone may cause lower in metabolic rate.
9. Lifestyle – An active person requires higher energy than a passive person

Energy Content of Food

• Bomb calorimeter – used to calculate the energy value of various types of food samples.
• One calorie (cal) = 4.2 joules (J)
• Energy value of food (kJ g^-1) = (4.2 x mass of water x increase in temperature) / (mass of food sample x 1000), specific heat capacity of water, C = 4.2 J g^-1 ˚C^-1; mass of water in g; temperature in ˚C and mass of food sample in g.