GRADE 9 BIOLOGY NOTES Animal Nutrition WEEK 7 & 8 2ND TERM

The food an animal eat every day is called diet.

A balanced diet is a diet that contains all the main nutrients in the correct amounts and
proportions to maintain good health.

A balanced diet has these 7 components:

carbohydrates, proteins, fats, vitamins, minerals, water and fibre
Each of these carries out one or more of three basic functions.
• To provide energy – this is mainly the role of carbohydrates and fats. Proteins are
used for energy only if they are in excess of requirements for growth, development,
repair and replacement.
• To allow growth and repair of body cells and tissues. Proteins in
the diet provide a source of amino acids for cells to make their own proteins
• To regulate the body’s metabolism – vitamins and minerals are needed in very
small quantities in the diet to help regulate our metabolism.
The energy required for most of the body functions is the basal metabolic rate (BMR).
The BMR varies from person to person, but an adult requires about 7000kJ per day. So
even if you lie down and do very little you still need this energy.
Diet depends on age, sex and activity
 Children have a greater energy requirement than adults because they have a higher
basal metabolic rate (BMR).
 A young child may weigh less than an adult but may have a higher BMR per
kilogram per day because they are still growing.
 Young children also need more protein per unit of body mass because they are
constantly developing and need to make new cells.
 Elderly people generally have lower energy and protein needs and have a lower
BMR. However, they need to eat a balanced diet if they are to stay healthy.
 Women have a relatively higher fat content in their bodies than men. Fat is stored in
fat tissue, for example under the skin. Fat tissue has a lower metabolic rate than
muscle, so women generally have a lower energy requirement than men.
 The energy needs of occupations that involve physical activity are greater than less
active jobs that involve sitting at a desk.
 People who take part in vigorous physical sports also require high energy and high
protein diets. The extra protein is required for muscle development.
 Women need extra nutrients during pregnancy and when they are breast-feeding.
For example, a woman in the last three months of pregnancy may require about
0.8MJ more energy than the 9MJ recommended for a non-pregnant woman.
Sources Of Nutrients
Eating healthily
Diets vary from country to country. However, we should all eat from each of the food
groups shown in the food guide pyramid.
1. Carbohydrates
 Carbohydrates include sugars and starches, which provide us with energy that is
easily respired.
 Simple sugars are absorbed almost immediately by the stomach into the blood to
give an immediate source of energy.
 This energy is released as a result of respiration.
Sources of carbohydrates rice, potatoes, bread, yams, sugar and honey.

2. Proteins
 Protein are needed to repair and make new cells. You digest protein into amino
acids and then use these to make your own proteins.
 There are 20 different types of amino acid and your body must have all of these to
make its own protein.
 Cell membranes and cytoplasm contain a great deal of protein. Enough proteins are
needed to replace damaged cells in the body.
Sources of proteins meat, fish, milk and nuts.
3. Fats
 Fats are important as a long-term energy store. The fat is stored under the skin and
around the heart and kidneys.
 One gram of fat releases more than twice as much energy than can be released
from one gram of carbohydrate or protein.
 When we are short of energy our body uses the fat.
 They are good thermal insulators, since they cut down heat loss.
 Fats also give buoyancy to marine animals, for example whales have a thick layer of
blubber.
Sources of Fats
butter, cheese, fat in meats and fish, nuts.
Water
 Water makes up two-thirds of your body mass. You take in water when you drink or
eat.
 You could go without food for a number of weeks, but you would die in a few days
without water.
 Water is needed for chemical reactions to take place in solution. The blood
transports substances dissolved in water.
 Waste chemicals are passed out of our bodies in solution in the urine, and water in
our sweat cools us down.
 It is important that your intake of water each day equals your loss of water in urine,
faeces, sweat and breath.

Vitamins and Minerals

 Vitamins and minerals are needed in small quanties by the body in order to stay are
to stay healthy.
 Lack of them in the diet can develop symptoms of deficiency diseases:

Fibre
 Dietary fibre or roughage comes from plants. It is made up mainly of cellulose
from plant cell walls.
 Although it cannot be digested, it is an important part of the diet.
Sources of fibre/roughage
 bran cereals, cabbage, sweetcorn and celery.
 Fibre adds bulk to our food. Since it is not digested, it passes down the entire gut
from mouth to anus and does not provide any energy.
 The muscles of the gut wall need something to push against. Fibre helps the
movement of food in the alimentary canal by peristalsis so preventing
constipation
  Fibre absorbs poisonous wastes from bacteria in our gut. Many doctors believe
that a high- fibre diet lowers the concentration of cholesterol in the blood.
 Fibre reduces the risk of heart disease and bowel cancer.
Balancing energy levels
Getting the balance right
 The food eaten in a day should provide you with enough energy to get through
that day.
What happens if we eat too much?
 Eating more food than you need, your body stores the extra as fat.
 Energy intake is the energy you get in your food in a day in proteins,
carbohydrates and fats.
 Energy output is the energy your body uses in a day. If energy intake is greater
than energy output, then fat is stored in the body and body mass increases.
 We run the risk of becoming overweight or even obese.
 People with a low basal metabolic rate (BMR) are more likely to become
overweight or obese than those with higher BMRs.
 It is likely that their diet contains fattening foods, such as high fat foods and
refined foods with a lot of added sugar

 B. Malnutrition is the result of not eating a balanced diet.

 There may be:  wrong amount of food: too little or too much
 incorrect proportion of main nutrients
 lacking in one or more key nutrients

Effects of malnutrition
Effects of malnutrition
1. Obesity - Too much food (carbohydrate, fat or protein)
Major causes of obesity include:
 high intake of fatty foods and refined foods containing a lot of added sugar too little
exercise
 social and emotional stress, leading to ‘comfort eating’.
How to lose weight?
They could:
• eat less high-energy foods (lower their energy intake)
• take more exercise (increase their energy output).
A sensible approach to slimming should combine:
• a balanced diet with a lower intake of energy
• a gradual increase in exercise
• having an ideal, but achievable, target for weight reduction
Constipation
 Roughage or fibre is indigestible but adds bulk to our food.
 This is important for keeping food moving down the alimentary canal. The muscles
of the gut wall contract to squeeze the food along.
 Soft foods do not stimulate the muscles to contract as effectively as the harder,
indigestible foods that form roughage.
 If the movement of food is slow it will result in constipation making it difficult to
defecate.
 A diet containing fruit and vegetables contains lots of roughage; these are the best
foods to relieve constipation.
2. Coronary heart disease
 Too much saturated/animal fat in the diet results in high cholesterol levels.
 Cholesterol can stick to the walls of arteries, gradually blocking them.
 If coronary arteries become blocked, the results can be angina and coronary heart
disease.
3. Starvation
 Too little food can result in starvation.
 Extreme slimming diets, such as those that avoid carbohydrate foods, can result in
the disease anorexia nervosa.
 Worldwide, the most common form of undernutrition is protein energy malnutrition
(PEM).
 As the term suggests, this is caused by a lack of dietary energy and protein. In its
worst form it can lead to kwashiorkor or marasmus, which are terms to describe the
appearance of children with PEM.
 These are two different ways in which the body responds to lack of food. In both
conditions, children are underweight, though more so in marasmus.
 Children with marasmus have adapted better to lack of food and respond better
when given food.
Symptoms of kwashiorkor:
 oedema (swelling of the abdomen and legs); sparse, dry hair; flaky skin; fat
accumulation
Symptoms of marasmus:
 very low body mass; thin arms and legs; little muscle or fat; wizened, old- looking
face.
Vitamin D
 is needed for the small intestine to absorb calcium.
 It is also needed to regulate the deposition of calcium in bone cells.
 Deficiency symptoms include the lack of calcium in bones causing rickets in children.
 Bones fail to grow properly and become soft, so when children start walking the
bones bend with the weight of the body.
 Rickets can be prevented by eating foods rich in vitamin D like fish-liver oil, butter,
eggs and milk.
 In adults, deficiency gives rise to the condition known as osteomalacia, which leads
to a softening of the bones and an increased chance of fractures.
 Iron
 is needed to make the blood protein haemoglobin which is found in red blood cells.
 Haemoglobin is a protein combined with iron. It is needed to carry oxygen around
the body.
 Foods rich in iron include liver, meat, cocoa.
 If there is a lack of iron in the diet, a disease called anaemia can occur. An adult
needs about 16mg of iron each day.
 At puberty, girls need to make sure they have enough iron in their diet as they start
to menstruate (have periods).
 Lack of iron leads to a reduction in the number of red blood cells.
 The main symptoms of anaemia are tiredness and lack of energy, shortness of
breath, heart palpitations and a pale complexion.