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CHAPTER 6 NUTRITION
Learning objectives:
- State the types of nutrition
- Explain autotrophic and heterotrophic nutrition
- Classify organisms according to the types of nutrition
6.1 Types of Nutrition
1. Nutrition is the process in which organisms obtain energy and
nutrients from food for
growth, maintenance and repair of damaged tissues.
2. Nutrients are used for energy and growth that includes
proteins, carbohydrates, fats,
vitamins, minerals and water.
3. Nutrition includes the following processes:
a. Ingestion
i. Taking food into the body by mouth
b. Digestion
i. Breaking up ingested food mechanically and chemically into
smaller
molecules to be absorbed
c. Absorption
i. Process which nutrients are absorbed via lining of intestinal
tract into blood
capillaries and blood stream
d. Assimilation
i. Nutrients are absorbed into the cells for the use of
metabolism
4. Nutrition is divided into two:
a. Heterotrophic nutrition: obtain nutrients by feeding on
organic matter which
unable to produce own food
b. Autotrophic nutrition: synthesising nutrients from simple
inorganic compounds.
Able to produce own food as such plants produce food from
photosynthesis.
6.1.1 Autotrophic Nutrition
1. Autotroph are organisms that capable of synthesising their
own organic substances from
inorganic compounds.
2. Types of autotroph:
a. Photoautotroph: organisms that carry out photosynthesis to
produce organic
substances
b. Chemoautotroph: organisms carry out chemosynthesis which they
use energy from
oxidation of inorganic substances
i. Sulphur bacteria use energy released from oxidation of
hydrogen suphide to
form carbohydrates
ii. Nitrifying bacteria (Nitrosomonas sp, Nitrococcus sp.)
obtain energy by
oxidising ammonia to nitrate
iii. Nitrobacter oxide nitrates into nitrites
6.1.2 Heterotrophic Nutrition
1. Holozoic nutrition
a. Animals feed by ingesting solid organic matter
b. Specialised digestive system
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c. Herbivores, omnivores, carnivores, detritivores
2. Saprophytic nutrition
a. Saprophytes carry out saprophytism nutrition that feed on
dead and decaying
matter
b. Extracellular digestion secrete enzymes onto food and digest
externally before
absorbing the nutrients
c. Saprophytic fungi and saprophytic bacteria
d. Also called decomposers
3. Parasitism nutrition
a. Feed on other organisms hosts
b. Digest hosts cells before absorbing them
c. Harm hosts: tapeworms, ticks, lice, fleas
Saprophytes vs Parasites
Saprophytes Parasites
Simple methods of nutrition: use variety of food sources
Highly adapted to obtain nutrients from hosts
Feed and obtain energy on dead, decaying matter
Lives on or in the body of hosts and obtain energy from them
Bacteria and fungi Viruses, protozoans, fungi, bacteria,
Aerobic and anaerobic Aerobic
6.2 Concept of Balanced Diet
Learning objectives
- Explain necessity for balanced diet
- Explain factors affecting daily energy requirement of human
body
- Determine energy value in food samples
- Determine nutrient content in different food samples
- Explain functions and sources of vitamins, roughage/dietary
fibre and minerals in a diet to
maintain health
- Explain function of water in body
- Justify selection of appropriate balanced diet for specific
target group
6.2.1 Classes of food
Carbohydrates Supply energy
Protein Provide materials for growth and repair
Lipids/fats Provide energy and stores excess food Dissolve fat
soluble vitamins
Vitamins Organic compound required in small amount
Minerals Inorganic substances required for teeth, bones,
muscles
Dietary fibre/roughage Stimulates peristalsis and prevent
constipation
Water Medium for all chemical reactions in cell, transportation,
excretion and body temperature control
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6.2.2 Factors affecting daily energy requirement
1. Carbohydrates and fats provide energy required for the
body.
2. Energy required by the body is generated by the oxidation of
molecules obtained from food
during cellular respiration.
3. Energy in food is measured in kilojoules (J).
4. Energy required are for body heat, maintain Basal Metabolic
Rate (BMR) and energy for
physical activities.
5. BMR Basal: minimum background energy that needed to maintain
vital life processes such
as heartbeat, nerve impulses, breathing, opt temperature,
chemical changes, physical
posture.
6. Metabolism is the sum of all chemical reactions in the
body.
7. Factors affecting daily energy requirements:
Climate People live in cold countries need more energy to
maintain body temperature
Age Children and young adults need more energy than old
people
Size Bigger build person need more energy than smaller build
Health condition Pregnant woman need more energy Lactation
energy requirement for breast-feeding mother increases
Gender Men have higher metabolism than women
Occupation People with heavy and active work need more
energy
Lifestyle Active person need more energy
8. Dietary requirements
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6.2.3 Energy content in food
1. Energy value amount of energy contained in unit weight of
substance when it is
completely oxidised.
2. Energy value of food is measured in units of joule per gram
(J/g) or kilojoules per gram
(kJ/g).
3. Cellular respiration releases energy.
4. Energy value of the main classes of food:
a. Carbohydrates: 16 kJ/g
b. Protein: 17 kJ/g
c. Fat: 38 kJ/g
5. Energy value of food is measured with bomb calorimeter.
a. A known mass of food is completely burnt in a bomb
calorimeter
b. Heat released is transferred to a known volume of water
c. Temperature increase of water is measured by using
thermometer
d. Amount of energy is calculated: Q = mct; where m is mass of
water, c = 4.2 J/gC and
t is temperature
A cup of tea with milk 150kJ
A piece of bread with butter 600kJ
One fried egg 650kJ
One serving of salad 20kJ
One serving of curry chicken 300kJ
6.2.4 Vitamins
1. Play important role as organic compound in various enzymatic
reactions and building and
maintaining body tissues.
2. Divided into two:
a. Fat-soluble vitamins (ADEK)
b. Water-soluble vitamins (BC)
3. The skin can synthesise vitamin D using sunlight.
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6.2.5 Minerals
1. Minerals are essential inorganic elements needed in small
quantities for chemical
reactions and building molecules in the body.
2. Minerals are grouped into:
a. Macro-minerals needed in bigger quantity which are calcium,
magnesium,
potassium, phosphorus, sodium
b. Micro-minerals needed in small quantity are iodine, iron,
copper, fluorine, zinc
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6.2.6 Roughage
1. Dietary fibre reduce cholesterol level, reduce heart diseases
and colon cancer.
2. Roughage is indigested plant matter that consist of
cellulose.
3. Human alimentary canal has no cellulase enzyme to digest
cellulose fibre.
4. Functions of roughage include:
a. Adds bulk to food and enables alimentary canal muscles to
grip it and keep it moving
(peristalsis), especially in large intestine
b. Help retain water and absorb poisonous substances from
gut
c. Softens faeces
5. Absence of roughage can cause constipation and increase risk
of colon cancer.
6.2.7 Water
Functions of water:
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6.3 Malnutrition
Learning Objectives
- Definition of malnutrition
- Effects of malnutrition by using examples
- Describe ways to reduce chance of contracting health problems
due to ones diet
- Describe ways to reduce effects of certain health problems
1. A person suffers from malnutrition experience symptoms
like:
a. Daily diet lacks such vitamins, mineral salts
b. Protein n diet is of poor quality
c. Body does not assimilate sufficient of digested food products
due to intestinal
infection or worm infestations
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Health problems Preventive steps
Cardiovascular disease - Atherosclerosis
Reduce intake of saturated fats and salt
Overweight, obesity Reduce intake of carbohydrates and
calories
Diabetes mellitus Reduce intake of refined sugar
QUICK CHECKPOINT!
1. Name the diseases due to lack of vitamin D and iron. [2
marks]
2. Explain how an unbalanced diet may cause health problem to a
person. [10 marks]