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Biology Chapter 5
Heterotrophs
— Humans are heterotrophs; the mode of nutrition of humans is heterotrophic nutrition. We are totally
dependent on other organisms.
— Different modes of heterotrophic nutrition:
Heterotrophic nutrition
Meaning
Example
Holozoic nutrition
Take in organic matter by feeding on other
organisms.
Animals like humans and
cows
Saprophytic nutrition
Feed on dead organisms or non-living organic
matter.
Many bacteria and fungi
Parasitic nutrition
Live on or inside the body of other organisms and
obtain organic food from them.
Parasites like tapeworms
Food substances
— Food is essential to us:
1. It produces us with energy for doing activities and keeping us warm.
2. It provides us with raw materials for growth and repair of body tissues.
3. It contains substances that are important for maintaining health.
— Food substances can be divided into two types and they are:
1. Primary food substances (essential to life)
2. Protective food substances (to stay healthy)
Carbohydrates
— It is made up of C, H, O ions, the chemical formula is Cx (H2O) y and H:O=2:1.
— It is a primary food substance, which is organic and has energy value.
Group
Formation
Examples
Monosaccharides
(Simple sugars)
(Taste sweet and
soluble in water.)
The simplest form
Glucose, fructose, galactose (Fruits)
Disaccharides
(Double sugars)
(Taste sweet and
soluble in water.)
— Formed when two monosaccharides
combine, in the presence of an
enzyme. (Condensation)
— Can be broken down into two
monosaccharides when water and a
Glucose+ Glucose=maltose
(Germinating barley)
Glucose+ galactose=lactose
(Milk)
Glucose+ fructose=sucrose
different enzyme are present.
(hydrolysis)
Polysaccharides
(Multiple sugars)
(Do not taste sweet
and are insoluble in
water.)
They are long chains of monosaccharides
joined together by condensation.
(Table sugar)
1.
2.
3.
Starch— the storage form of
carbohydrates in plants (rice,
potato, bread)
Glycogen— the storage form of
carbohydrates in animals (liver,
meat)
Cellulose— the main component
of plant cell walls (all cell wall)
— Functions
1. Main energy source of the body (give energy in food oxidation)
2. As storage: in form of starch in plant cells and glycogen in animal cells
3. Make plant cell walls by cellulose
4. Cellulose is an important source of dietary fibre that keeps us healthy
Lipids
— It is made up of C, H, O ions, the ratio of H and O is 2:1.
— It is a primary food substance, which is organic and has energy value.
— Insoluble in water but dissolve in organic solvents (ethanol)
— Triglycerides are the common type of lipids.
— Formed from the condensation of three fatty acid molecules and one glycerol molecule
Fats
Oils
Found in
Animals
Plants
State at room temperature
Solid
Liquid
Common examples
Fatty meat, lard, butter
Corn oil and peanut oil
— Cholesterol
1. A lipid made in liver and found in many foods.
2.
3.
4.
A component in cell membranes and sex hormones
Two kinds: HDL and LDL, which HDL is good (take away the fats) and LDL is bad
If too much cholesterol is present in blood, it may deposit on the wall of the blood vessels. This leads to
narrowing of the blood vessels. If the blood vessel is a coronary vessel supplying blood to the heart
muscles, it may reduce blood supply to the heart and cause coronary heart disease/ heart attack/ heart
disease.
5.
Excess lipids will be stored in adipose tissues in the body. These tissues are found under the skin as
subcutaneous fat or around internal organs.
— Functions
1. Make cell membranes
2. A source of energy: provide energy for body activities
3. Main energy store in form of fats in animals and oils in plant seeds
4. Involved in transporting and storing fat-soluble vitamins in the body
5. As heat insulation layer under skin in mammals to reduce heat loss
6. As a food reserve
7. As a shock-absorber to protect the internal organs
Proteins
—
—
—
—
It is made up of C, H, O, N (S) ions.
It is a primary food substance, which is organic and has energy value.
The basic building blocks of proteins are amino acids (at least 20 kinds).
Each amino acid molecule has a carbon atom in the center, which carries a carboxyl group, an amino group, a
side chain and a hydrogen atom. Each amino acid has its own specific side chain.
— When the amino group of an amino acid and the carboxyl group of another are joined by condensation, a
dipeptide is formed.
— Further combination of the dipeptide with other amino acids forms a polypeptide.
— A protein consists of one or more polypeptide chains. It can be hydrolyzed to amino acids in the presence of
water and a suitable enzyme.
— Different amino acids are joined together in thousands of different combinations to create different
polypeptides or proteins.
— There are non-essential amino acids (made by our body) and essential amino acids (obtained from diet). Both
two are important to our bodies.
— Functions
1. As building materials of body for growth and repair. (Muscles and brain tissues consist of proteins,
enzymes, antibodies and some hormones are proteins.)
2. Provide energy for the body activities (as the last energy resource)
3. They cannot be stored. The liver breaks them down. The amino group is removed from the amino acid
and changed to urea. (deamination) The urea is passed out in urine. The remaining parts of the amino
acids are converted into carbohydrates or lipids.
— A lack of protein in diets may lead to a deficiency disease called kwashiorkor. (In children in developing
countries where meat, eggs and milk are limited. They grow poorly and have a swollen belly because of the
accumulation of tissue fluid.)
— Source
1. Animal proteins: chicken, pork
2. Plant proteins: bean, peanut
Vitamins
— They are organic food substances needed in small amounts.
— They have no energy value but they help regulate many metabolic reactions.
— Our body can make some of them while the rest have to be obtained from the diet.
Type
Soluble
Vitamin
A
Fatsoluble
Importance
A deficiency of it leads to
It is needed to form a visual
1.
pigment in the retina of our
eyes. The pigment is
2.
necessary for vision in dim
light.
3.
It also keeps the cornea of
the eyes, the skin, the lining
of the alimentary canal and
the breathing system healthy.
Found in
poor vision in dim light 1.
or even night blindness
drying up of cornea
and skin
easy infection of lining 2.
of the lungs and
trachea
Fish-liver oil, milk
and green
vegetables are rich
in vitamin A.
Carrots contain an
orange pigment
called carotene,
which can be
converted to
vitamin A in the
liver.
Vitamin
C
Watersoluble
It is needed for the growth
Scurvy
and repair of connective
1. weak and bleeding
tissues. It therefore helps
gums, resulting in
heal wounds and is important
loose teeth
to healthy gums and skin.
2. the body bleeds easily,
causing bruises under
It is easily destroyed by
the skin
oxygen in air or high
3. slow recovery of
temperatures.
wounds
Fresh vegetables and
fruits (especially
broccoli, guavas and
kiwifruits) are rich in
vitamin C.
Vitamin
D
Fatsoluble
It promotes the uptake of
calcium and phosphate ions
from the gut. They are
essential for keeping bones
and teeth strong. Therefore,
vitamin D is particularly
important to actively growing
children.
1.
2.
Rickets in children
(Have weak legs, which
may bend under the
1.
Fish-liver oil and
dairy products are
rich in vitamin D.
weight of their body.
Easy bone fractures in
adults
2.
Can be produced
by the skin under
sunlight.
Minerals (Inorganic food substances needed in small amounts)
— They have no energy value but are important in regulating many metabolic reactions and building up body
tissues.
Type
(Ca, Fe, I, K, P)
Calcium
Importance
It is essential for the
formation of bones and
teeth, blood clotting and
muscle contraction.
A deficiency of it leads
to
1.
2.
Found in
Rickets
Some green vegetables (broccoli),
Bleeding/haemor milk, cheese and other dairy
rhage
products are rich in calcium.
Children need a lot of
calcium to harden their
bones and develop teeth as
they grow up.
Iron
It is a component of
haemoglobin, a pigment in
Anaemia
People have anaemia
red blood cells that carries
oxygen around the body.
may faint easily
because there is not
enough haemoglobin
to carry oxygen.
Beef, liver and green vegetables
are rich in iron.
Dietary fibre (roughage) (organic food substance consists mainly of cellulose from plant cell walls)
— It does not give us energy because we do not have the enzyme to digest it.
— It holds a lot of water to enable faeces to remain soft.
— It also adds bulk to food to stimulate its movement along the alimentary canal. (peristalsis)
In this way, faeces can be passed out of the body more easily.
— A deficiency of dietary may lead to constipation.
— Only plant foods (vegetables, fruits and cereals) contain dietary fibre.
Water (Made up of H and O ions) (Inorganic and does not have energy value)
1. acts as a solvent to dissolve many chemicals in the body
2. acts as a medium for chemical reactions to take place
3. acts as transport medium
4. acts as a cooling agency to help regulate body temperature
5. a reactant in some metabolic reactions
— It is taken into the body by drinking water/ eating food.
— It is taken out from the body in the form of sweat, urine and expired air.
Food Test
Food substance
Food test
Use
Positive result
Negative result
Glucose
Using Clinistix
Clinistix
From pink to purple.
Remain pink.
paper
paper
Reducing sugar
Benedict’s test
Benedict’s
solution
From blue to form brick-red
precipitate (ppt.)
Remain blue.
Starch
Iodine test
Iodine
solution
From brown to
dark-blue/blue-black.
Remain brown.
Lipid/oil
(Grease) spot
test
Filter
paper
A translucent spot is left.
(It disappears after immersing it
in an organic solvent.)
A wet mark is left.
Emulsion
Test(ethanol→s
Water and
ethanol
Clear solution to milky solution.
Two separate layers
are formed with oil
ample→water)
Protein
Using Albustix
paper
layer on the top.
Albustix
paper
Form yellow to green.
Remain yellow.
—
—
—
—
Wordings: Add a drop of solution / Dip the paper into the sample. (the well of a spot plate)
Test set (with testing factor)
Control set (without testing factor, used to compare to result)
We do not need to measure the volume of the solution very accurately because we only want to know the
presence or absence of certain food substances.
— If we are given solid food, we should cut the solid into very small pieces or squeeze the juice from the solid.
— Clinistix paper can be found from a drug store since it is used to detect glucose in urine. (diabetes)
Benedict’s test
1. Mix equal volumes of food sample and of Benedict’s solution in a test tube.
2. Boil the mixture in a water bath for 5 minutes.
3. Observe for any changes in the mixture. (Brick-red precipitates)
Energy content of food
— Apparatus and materials: foods, boiling tube, thermometer, burning, stand, electronic balance.
— Food has chemical energy, during the process of burning, the chemical energy is converted to heat energy
which can be measured by thermometer.
— To ensure it is a fair test, we need to have the same volume of water and initial temperature.
— This experiment is not accurate because some chemical energy is converted to light energy. There is heat lost
to the air. And the distance between the boiling tube and the burning spoon is not fixed.
— Result: Peanut (Oils and proteins) contains more energy than white bread (carbohydrates).
DCPIP solution
— Vitamin C is ascorbic acid. It is a powerful reducing agent. It can reduce DCPIP (dichlorophenolindophenol
sodium salt) and changes the colour of it from blue to colourless (decolourization).
— The more the amount of vitamin C present, the less the amount of fruit juice used to decolorize the DCPIP
solution.
— Procedure:
1. Add DCPIP solution to a test tube.
2. Fill up a syringe with vitamin C solution/fruit juice.
3.
Add in vitamin C drop by drop. Stop when the DCPIP solution becomes colourless/the original colour of
the fruit juice.
4. Record the amount of vitamin C solution/fruit juice used.
— Result: Fresh lemon＞Fresh orange＞Fresh green pepper＞Mr. Juicy orange＞Boiled orange
— We need to measure the volume of DCPIP solution and fruit juice accurately because we are using the
volume of fruit juice to compare the amount of Vitamin C.
— Vitamin C is destroyed by boiling. (The longer time of boiling, the little the amount of Vitamin C.) Therefore,
we better eat fresh fruits and vegetables to get more Vitamin C.
Food
Food substances found
Cooked rice
Starch, some sugar
Milk
Sugar, proteins, oils
Minced pork
Proteins, some oils
Minced fish
Proteins, some oils
Orange juice
Sugar
Crushed vegetables (spinach)
—
Balanced diet
—
—
—
—
Food substance
Energy value/ Energy given out (kJ/g)
Carbohydrates
17.1
Lipids
38.9
Proteins
18.2
Energy unit: kJ(kilojoules), C(kilocalories), c(calories)
We must have a balanced diet to maintain health and meet the energy needs of our body.
It consists of all the food substances in the right amounts and proportions.
Dieticians apply two concepts: the six basic food groups and the food pyramid.
1. Fat, oil, salt and sugar (Eat less)
Eating too many may lead to overweight and heart disease; too much salt will harm the kidneys.
2. Dairy products (Eat moderately)
3. Meat, eggs and beans (Eat moderately)
They are rich in protein, vitamins and minerals, which are needed for growth and repair of the body, and
maintaining health.
4. Vegetables (Eat more)
5. Fruits (Eat more)
They are rich in vitamins, minerals and dietary fibre that help us maintain health.
6. Cereals and grains
They provide us with energy readily. Some of them are rich in dietary fibre.
Factors affecting our dietary requirement
1. Age
2.
3.
4.
— Children need more energy since they grow actively.
Gender
— In general, males need more energy than females since they usually a larger body side and a more active
lifestyle than females.
— There is less subcutaneous fat in males and so they lose heat more rapidly than females.
Level of activity
— People doing activities that are more muscular require more energy.
Body status
— Pregnant women need more carbohydrates, protein, minerals and vitamins because their foetuses need
energy and raw materials for making new tissues.
— Breast-feeding mothers need an extra supply of nutrients in the diet for milk production.
Health problem
1. Obesity (the energy intake is greater than the energy needs)
— If we eat too much, the excess energy will be stored as fats in the body. When our body weight exceeds a
normal level, we are overweight. Obesity is the condition of seriously overweight.
— Overweight people have a higher risk of developing high blood pressure and heart disease.
— Their joints may easily become damaged because of their weight.
2. Anorexia nervosa (the energy intake is less than the energy needs)
— Malnutrition and various deficiency diseases will result if we eat too little and get not enough nutrients.
— People with this problem are thin because the nutrients stored in the body will soon be consumed.
— Anorexia nervosa is a kind of mental illness. The patients consider themselves fat even though they are very
slim. They fear of putting on weight and refuse to eat.
— Without proper treatment, they will become dangerously weak or even die.
High Protein diet
— People think that they will only get protein so their body can use stored fat to provide energy for body
activities. Therefore, they can keep fit.
— It is a wrong concept because meat contains lipids and proteins.
Vegetarian
Advantage
Disadvantage
1.
eat less fat
There are some amino acids only found in animal cells
2.
3.
4.
add bulk to food
eat less food
get many minerals and vitamins
but are essential to us. Vegetarians cannot get them.
They may eat eggs and drink milk, which provide
essential amino acids because they are animal
proteins.
Besides, they may eat a variety of plant food to get
different food substances.