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
Holozoic nutrition
Saprophytic nutrition
Parasitic nutrition
Meaning
Take in organic matter by feeding on other organisms.
Feed on dead organisms or non-living organic matter.
Live on or inside the body of other organisms and obtain organic food from them.
Example
Animals like humans and cows
Many bacteria and fungi
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
The simplest form
Examples
Glucose, fructose, galactose (Fruits) Monosaccharides
(Simple sugars)
(Taste sweet and soluble in water.)
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 different enzyme are present.
(hydrolysis)
Glucose+ Glucose=maltose
(Germinating barley)
Glucose+ galactose=lactose
(Milk)
Glucose+ fructose=sucrose
(Table sugar)
Polysaccharides
(Multiple sugars)
(Do not taste sweet and are insoluble in water.)
They are long chains of monosaccharides joined together by condensation.
1.
Starch— the storage form of carbohydrates in plants (rice, potato, bread)
2.
Glycogen— the storage form of carbohydrates in animals (liver, meat)
3.
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
Found in
Fats
Animals
Oils
Plants
State at room temperature
Common examples
— Cholesterol
Solid
Fatty meat, lard, butter
Liquid
Corn oil and peanut oil
1.
A lipid made in liver and found in many foods.
2.
A component in cell membranes and sex hormones
3.
Two kinds: HDL and LDL, which HDL is good (take away the fats) and LDL is bad
4.
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
Fat- soluble
Vitamin
C
Water- soluble
Importance
It is needed to form a visual pigment in the retina of our eyes. The pigment is necessary for vision in dim light.
It also keeps the cornea of the eyes, the skin, the lining of the alimentary canal and the breathing system healthy.
It is needed for the growth and repair of connective tissues. It therefore helps heal wounds and is important to healthy gums and skin.
It is easily destroyed by oxygen in air or high temperatures.
A deficiency of it leads to
1.
poor vision in dim light or even night blindness
2.
drying up of cornea and skin
3.
easy infection of lining of the lungs and trachea
Scurvy
1.
2.
3.
weak and bleeding gums, resulting in loose teeth the body bleeds easily, causing bruises under the skin slow recovery of wounds
Found in
1.
Fish-liver oil, milk and green vegetables are rich in vitamin A.
2.
Carrots contain an orange pigment called carotene, which can be converted to vitamin A in the liver.
Fresh vegetables and fruits (especially broccoli, guavas and kiwifruits) are rich in vitamin C.

Vitamin
D
Fat- soluble
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 weight of their body.
Easy bone fractures in adults
1.
2.
Fish-liver oil and dairy products are rich in vitamin D.
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.
Importance Found in Type
(Ca, Fe, I, K, P)
Calcium It is essential for the formation of bones and teeth, blood clotting and muscle contraction.
Children need a lot of calcium to harden their bones and develop teeth as they grow up.
A deficiency of it leads to
1.
Rickets
2.
Bleeding/haemor rhage
Some green vegetables (broccoli), milk, cheese and other dairy products are rich in calcium.
Iron It is a component of haemoglobin, a pigment in red blood cells that carries oxygen around the body.
Anaemia
People have anaemia 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
Glucose
Starch
Lipid/oil
Food test
Using Clinistix paper
Iodine test
(Grease) spot test
Use
Clinistix paper
Reducing sugar Benedict’s test Benedict’s solution
Iodine solution
Filter paper
Positive result
From pink to purple.
From blue to form brick-red precipitate (ppt.)
From brown to dark-blue/blue-black.
A translucent spot is left.
(It disappears after immersing it in an organic solvent.)
Negative result
Remain pink.
Remain blue.
Remain brown.
A wet mark is left.
Emulsion
Test(ethanol→s
Water and ethanol
Clear solution to milky solution. Two separate layers are formed with oil
Protein ample→water)
Using Albustix Albustix Form yellow to green. layer on the top.
Remain yellow. paper paper
— 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
Cooked rice
Food substances found
Starch, some sugar
Sugar, proteins, oils
Proteins, some oils
Proteins, some oils
Sugar
—
Balanced diet
Milk
Minced pork
Minced fish
Orange juice
Crushed vegetables (spinach)
Food substance
Carbohydrates
Lipids
Energy value/ Energy given out (kJ/g)
17.1
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
— Children need more energy since they grow actively.
2.
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.
3.
Level of activity
— People doing activities that are more muscular require more energy.
4.
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
1.
eat less fat
2.
add bulk to food
3.
eat less food
4.
get many minerals and vitamins
Disadvantage
There are some amino acids only found in animal cells 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.