Classes of Food… • Nutrition is the process by which living organisms obtain food

they need to grow and repair body tissues.

• Food can be divided into 7 main classes:

(a) Carbohydrates (b) Proteins

(c) Fats (d) Fibre

(e) Water (f) Vitamins

(g) Minerals

Classes of Food… • Functions of Each Class of Food

Classes of

food

Carbohydrates Proteins Fats

Sources - Starch (nrad, rice, potato

etc.)

- Cellulose (vegetables &

fruits)

-Glycogen (stored in liver &

muscle cells)

Meat, fish, egs, beans,

lentils and vegetables

which are rich in plant

proteins

Butter, cheese, vegetable

oils, nuts

Functions Sources of energy for

physical activities and

keeping the body warm

- For the growth of new

cells

- Repair of damages

tissues

- Required for the

formation of enzymes,

hormones, haemoglobin

and antibodies

-Sources of energy during

extreme starvation

- Fats underneath the skin

act as an insulator and

help to keep the body

warm

- Fats stored around the

internal organs protect

them against physical

injury

-As a medium of transport

for fat-soluble vitamins (A,

D, E, & K)

Vitamins… • Vitamins

(a) are organic compounds that are essential for maintaining

good health

(b) are required in small amounts

(c) do not provide any energy

• A deficiency in vitamins may cause deficiency diseases.

• There are 2 kinds of vitamins:

(a) Fat-soluble vitamins: vitamin A, D, E & K

(b) Water-soluble vitamins: vitamins B & C

• The main sources, functions and effects of vitamin deficiency

Vitamin Main Source Functions Deficiency diseases

A -Carrots, egg yolks,

liver, fish

-Maintains healthy skin

-For good night vision

-Dry, scaly skin

-Night blindness

B Cereals, lover, eggs,

milk, yeasts,

vegetables

-Maintains a healthy nervous

system

-Helps in the breakdown of

carbohydrates to release energy

-Helps in the formation of red

blood cells

-Beri-beri (disease of the

nervous system

-Pellagra (skin disease)

-Anaemia

C Fruits & Vegetables -Maintains healthy skin, teeth, and

gums

-Heals wounds

-Increases the body’s resistance to

diseases

-Scurvy

D Liver, eggs, dairy

products, formed in

the skin under

sunlight

-Helps in the absorption of calcium

and phosphorus

-Formation of strong teeth and

bones

-Rickets (weak bones and

dental decay)

E Seeds, nuts. Whole

germ, vegetable oils,

whole grains

-Maintains fertility

-Prevents cell damage

-Sterility

-Poor nerve and muscle

functions

K Liver, egg yolk,

green vegetables

-Promotes blood clotting -Prolonged bleeding

Minerals… • Minerals

(a) are inorganic substances vital for maintaining

good health

(b) are needed in small amounts by the body

(c) do not provide any energy

• A deficiency in minerals may cause deficiency

diseases.

• Excess minerals are excreted through sweat and

urine

• The main sources, functions and effects of mineral deficiency

Mineral Main Source Functions Deficiency diseases

Calcium -Milk, eggs,

anchovies,

yoghurt, green

vegetables

-Build strong teeth & bones

-Helps blood clotting

-Form normal functioning of nerve

and muscle activities

-Rickets in children

-Osteoporosis in adults

-Prolonged bleeding

Sodium Table salt, cheese,

processed food

-Maintains balance of body fluid

-For normal functioning of nerves

-Muscle crapms

Potassium Fish, bananas,

meat, nuts

-For normal functioning of nerve

and muscle activities

-Maintains balance of body fluid

-Weak muscles

-Paralysis

Iron Liver, meat,

seafood, green

vegetables

-Needed for formation of

haemoglobin in red blood cells

-Anaemia

Iodine Seafood, iodised

sale

-Needed to make the hormones of

the thyroid gland

-Goiter (swollen neck)

Phosphorus Cheese, milk,

eggs, fish

-To make healthy bones and teeth

-Helps in muscle contraction

-Rickets

-Tooth decay

-Weak muscle

Dietary Fibre… • Dietary fibre

(a) is made up of cellulose from plant call walls

(b) cannot be digested by our digestive system

(c) is obtained from cereals, fruits, and, leafy vegetables

• Importance of dietary fibre

(a) Provide bulk to the contents in the large intestine

(b) Stimulates peristalsis, the rhythmic muscular contractions along the alimentary canal

(c) Prevents Constipation

• Water

(a) water is very important to the body

(b) About 70% of the body is made up of water

(c) Water does not provide any energy

(d) Importance of water:

- Transport of digested food, respiratory gases and excretory products

- As a solvent for chemicals to dissolve in

- As a medium for biochemical reactions

- Needed for the production of mucus

- Helps to regulate body temperature

(e) Water is lost through urine, sweat and exhaled air

The Importance of a Balanced Diet… • A Balanced Diet

• Diet refers to the daily food we eat.

• A balanced diet consists of all the seven classes of food taken in the right amounts to meet the daily requirements of the body.

• A balanced diet

(a) provides energy for daily activities

(b) prevents diseases

(c) Provides nutrients needed for growth

Factors that Determine a Balanced Diet… 1. Age

• A child needs more carbohydrates and proteins than an older person for continuous growth.

• A teenager needs plenty of carbohydrates to remain active. They also need plenty of proteins to make new cells and plenty of calcium to make strong bones and teeth.

2. Sex

• Men require a higher energy intake than a woman from the same age group.

• Heat loss is faster in men than in women because men have a lower body fat content.

Factors that Determine a Balanced Diet… 3. Physical activity and occupation

• A more active person requires more energy.

• A person who does heavy work like a farmer requires more energy than a person who does lighter work like a clerk.

4. Body size

• A bigger-sized person needs more energy than a smaller-sized person because smaller-sized person have a bigger surface area per unit volume.

3. State of health

• A person recovering from illness needs more of certain nutrients.

• A pregnant woman requires more energy than a woman who is not pregnant.

4. Climate

• People living in cold countries need more energy to keep their body warm

• People living in warmer climates do not need as much energy.

Calorific Value of Food… • Calorific value or energy value of food refers to the amount of energy

released from one gram of food.

• The calorific value of food is measured in calories (cal) or joules (J).

• 1 calorie (cal) = 4.2 joules (J)

Energy value of main food classes:

• Carbohydrates: 17kJ g-1

• Protein: 18kJ g-1

• Fat: 39kJ g-1

Planning a Balanced Diet…

Bread, cereals, and potatoes are the main sources of complex carbohydrate

Fruits supply most of

our dietary vitamin C Vegetables are

important to every

diet

Milk and dairy products

contain calcium, proteins and

vitamins

Meat, poultry and fish are

good sources of iron, zinc and

vitamin B

Eaten in moderation, sugary

and fatty foods can form part

of healthy, balanced diet.

Human Digestive System… • Digestion is the process of breaking down large complex food molecules

into smaller and simpler molecules.

• Digestion takes place in the alimentary canal.

• There are two types of digestion:

(a) Physical digestion is the breaking down of large pieces of food into smaller pieces using teeth and the churning actions of the alimentary canal.

(b) Chemical digestion involves the breaking down of complex food molecules into small soluble molecules by digestive enzymes. These molecules are then transported by the blood circulatory system to every cell in the body.

• Enzymes are protein that speed up biochemical reactions in the cells.

• Complex food molecules are broken down into their smaller molecules so that these molecules can dissolve and diffuse through the wall of the small intestine.

• End products of digestion: (a) carbohydrates glucose

(b) proteins amino acids

(c) fats fatty acids and glycerol

Human Digestive System…

Muscles relax

Muscles contract

Bolus moves along oesophagus by peristalsis

Mouth

Oesophagus

Stomach

Small Intestine

Large Intestine

Rectum

Anus

Sequence of the parts of

the alimentary canal

involved in food

digestion and absorption:

Human Digestive System…

Teeth- cut tear

and grind food.

Oesophagus- Tube

connecting mouth to

stomach.

Tongue – Helps

swallow food.

Liver- Excess amino

acids converted to urea.

Produces bile.

Pancreas – Secretes

pancreatic juice which

contains enzymes to break

down carbohydrates,

proteins and fats.

Gallbladder – Stores

bile. Bile neutralizes

stomach acid.

Salivary glands –

Secretes amylase to

break down starch.

Stomach – Secretes

gastric juice to break

down proteins.

Hydrochloric acid

kills bacteria.

Small intestine –

Food substances

absorbed into

blood.

Anus – Faeces

removed.

Rectum – Stores faeces Large intestine –

Excess water

reabsorbed into

blood.

Duodenum – Receives

pancreatic juice and

bile.

• Process of Digestion along the Alimentary Canal

Gland/ organ Secretion Contents of secretion Digestive action/ function

Salivary

glands

(mouth)

Saliva -Salivary amylase -Salivary amylase breaks down starch

into maltose.

Gastric

glands

(stomach)

Gastric

juices

-Hydrochloric acid -Stop the action of the salivary enzymes.

-Kills bacteria in the food.

-Provides an acidic medium for the action

of enzymes in the stomach.

-Proteases -Break down proteins into polypeptides

or peptones.

-Casein -Coagulates liquid milk protein.

Liver Bile (stored

in the gall

bladder)

-Neutralizes the acid produced by the

stomach.

-Provides an alkaline medium for the

action of the enzymes in the pancreatic

juice.

-Emulsifies fats and oil into small

globules. This increases the surface area

for the action of enzymes in the

pancreatic juice.

Pancreas Pancreatic

juice

-Pancreatic amylase -Break down starch into maltose.

-Proteases -Break down proteins into polypeptides.

• Process of Digestion along the Alimentary Canal

Gland/ organ Secretion Contents of secretion Digestive action/ function

Pancreas Pancreatic

juice

-Lipase -Breaks down fats into fatty acids and

glycerol.

Intestinal

gland

Intestinal

juice

-Maltase -Break down maltose into glucose.

-Protease -Breaks down polypeptides into amino

acids.

Absorption of Digested Food… • Absorption is the diffusion of end products of digestion through the walls

of the small intestine into the blood capillaries.

• The characteristics of the walls of the small intestine adapted for absorption:

(a) The small intestine is long (about 6 metres). This ensures that digested food is absorbed before it reaches the large intestine.

(b) The inner surface of the ileum is covered with millions of finger-like projections called villi (singular: villus. The villi increase the surface area for the rapid absorption of digested end products.

(c) The walls of the small intestine have many blood capillaries to transport digested food.

(d) The intestinal wall is very thin so that digested food can diffuse easily into the blood capillaries.

• The digested food absorbed into the blood capillaries is then transported to the liver.

• From the liver, the nutrients are transported to the heart to be pumped to all parts of the body.

The inner surface of the small intestine (villi)…

Reabsorption of Water and Defacation…

3. The undigested food

undergoes decay and

becomes faeces. Faeces

are stored temporarily in

the rectum before being

pushed through the anus.

4. The process off

removing faeces from the

body is called defecation. Anus

Large Intestine

1. The bulk of

the undigested

food that is not

absorbed move

along the large

intestine.

2. In the large

intestine, water is

absorbed into the

bloodstream.

Healthy Eating Habits… • Roughage or dietary fibre helps undigested food to move along the large

intestine.

• If there is lack of dietary fibre in the diet, undigested food moves very slowly through the large intestine and too much water will be reabsorbed into the blood.

• As a result, the faeces become hard and dry and this result in constipation.

• Practise healthy eating habits by:

(a) eating a balanced diet

(b) drinking at least 7 glasses of water a day

(c) consuming less fats, sugars, and salt

(d) eating plenty of vegetables and fruits

(e) eating in moderation

• Unhealthy eating habits may lead to many diet-related diseases:

(a) Consistently eating more than the daily requirement may lead to obesity.

(b) Eating too much of oily food may lead to heart diseases.

(c) A high intake of salt may lead to high blood pressure.

(d) A high intake of sugar may lead to diabetes.