chapter 4: nutrients

Question 1

why do we need food? and what are some examples?

Answer 1

1. provides energy for vital activities
   -during photosynthesis, green plants use light energy from sun to convert raw materials from their surroundings into food such as carbs
   - food contains stored energy called chemical energy
2. food helps organisms to stay healthy
   - eg. vitamin c found in limes prevent gums from bleeding and teeth from falling out
   - eg. calcium, found in milk, needed to keep bones and teeth strong
3. provides raw materials to make new protoplasm
   -body of living organism undergoes wear and tear
   > and is able to grow, reproduce and repair worn out parts
   >to do this, organisms must make new protoplasm from certain substances in food

Question 2

what are the functions of water?

Answer 2

1. a solvent for chemical reactions
   - chemical reaction taking place in living things
   - plants need water for photosynthesis
2. a key component of tissues
   - key component for cells tissue fluid, digestive juices and blood
3. controlling body temperature
   - a component of sweat
   -when sweat evaporates from skin surface, latent heat is removed
   > body cooled down
4. transporting dissolved substances

Question 3

how is water needed for transporting dissolved substances in animal cells and how is water used for plant cells?

Answer 3

in animal cells,
- transport digested products from the small intestines to all the other parts of the body
- transports waste products from cells for removal from the body

in plants, water is needed:
- for photosynthesis
- to keep the cells turgid or firm
- needed to transport mineral salts up the plant through the xylem
- to transport food substances made in the leaves to all the other parts of the plant

Question 4

how is water lost and how much water does a normal, healthy adult need?

Answer 4

• water is lost from the body in exhaled air, sweating, in the urine and in faeces
• a normal healthy adult requires 3 litres of water

Question 5

what are carbohydrates?

Answer 5

carbohydrates are organic molecules made of the elements: carbon, hydrogen and oxygen
- hydrogen and oxygen are present in the ratio of 2:1

Question 6

what are monosaccharides and what are some examples of it?

Answer 6

• they cannot be digested into smaller molecules
• can pass through cell membrane and be absorbed by the cells
• glucose, fructose, galactose
• all have the same chemical formula: C6 H12 O6
  > atoms arranged differently within the molecules
  > different arrangements give the sugars different chemical and biological properties

Question 7

where are the three monosaccharides found?

Answer 7

• glucose: found in plants and animals
• fructose: common in plants, rare in animals
• galactose: present in milk sugar in mammals

Question 8

what are some examples of disaccharides?

Answer 8

maltose, sucrose and lactose

Question 9

what is condensation and what are some examples?

Answer 9

• the formation of disaccharides from monosaccharides
  eg: glucose x2 > maltose
  glucose + fructose > sucrose
  glucose + galactose > lactose

Question 10

what is hydrolysis?

Answer 10

A chemical reaction in which water is used to break down a compound

Question 11

what are some examples of polysaccharides and why is it stored the way it is?

Answer 11

• starch, glycogen and cellulose
• glycogen and starch are stored of glucose
  are stored like this because:
  > insoluble in water and will not affect water [potential of the cell
  > large molecules which cannot diffuse through the cell membranes so they will not be lost from the cell
  > can be easily hydrolysed to glucose when needed
  eg. tissue respiration
  > have compact shapes so occupies less space than individual glucose molecules

Question 12

what are the reducing sugars?

Answer 12

• all monosaccharides and disaccharides except for sucrose
• glucose, fructose, galactose, maltose, lactose

Question 13

what is the test for reducing sugars? describe the test and possible results

Answer 13

benedicts test:
1. place 2cm3 of food sample in the test tube
2. add 2cm3 of benedicts solution to the food sample
3. shake the mixture and place it in a boiling water bath for 2-3 minutes
results:
- solution remained blue: no reducing sugar
- blue to green precipitate: traces of reducing sugar
- blue to yellow or orange precipitate: moderate amount of reducing sugars
- blue to brick red: large amount of reducing sugar

Question 14

what are complex carbohydrates?

Answer 14

• polysaccharide consists of many monosaccharide molecules joined together.
• produced by the condensation of many similar molecules to form a long molecule
• starch, cellulose and glycogen are complex carbohydrates made of numerous glucose molecules
• glucose molecules link in different ways
  > giving rise to different structures

Question 15

what is the structure, role and occurrence of starch?

Answer 15

structure: starch molecule made of several thousands of glucose molecules joined together

role: storage form of carbohydrates in plants
- when needed, it can be digested to form glucose to provide energy for cell activities

occurrence: in storage organs of plants
eg: potato tubers and tapioca

Question 16

what is the structure, role and occurrence of cellulose?

Answer 16

structure: a starch molecule is made of several thousand glucose molecules joined together
- bonds between the glucose units are different from that in starch

role: - cellulose cell wall protects plant cells from bursting or damage
- cannot be digested in our intestines
- serve as dietary fibres that prevent constipation

occurrence: present in the cell walls of plants

Question 17

what is the structure, role and occurrence of glycogen?

Answer 17

structure: it is a branched molecule
- made up of many glucose molecule joined together

role: it is a storage form of carbohydrates in mammals
- when needed, it is digested to glucose to provide energy for cell activities

occurrence: stored in the liver and muscles of mammals

Question 18

describe the hydrolysis of starch.

Answer 18

-starch in the food we eat may be hydrolysed or digested in our alimentary canal
- when starch hydrolysed > bonds within the polysaccharide are broken and the glucose molecules are released
- enzyme amylase digests starch to form maltose
- maltose hydrolysed by the enzyme maltase to form glucose

Question 19

what are the functions of carbohydrates?

Answer 19

1. needed as a substrate for respiration
   > to provide energy for cell activities
2. to form supporting structures
   > eg, cell walls in plants
   3.to be converted into other organic compounds such as amino acids and fats
3. for the formation of nuclei acids
   > like DNA
4. To synthesis lubricants
   >eg. Mucus which consists of a carbohydrate and protein
5. Synthesis the nectar in some flowers
   > nectar: a sweet liquid that plants produce to attract insects

Question 20

What are fats?

Answer 20

• fats are like carbohydrates
  > are organic molecules made up of the elements carbon, hydrogen and oxygen
  > BUT unlike cards, fats contain much less oxygen in proportion o hydrogen

Eg. Tristearin ( beef fat)
C57 H110 O6
- the proportions of th elements that make up fats are not fixed
> no general formula for fats

Question 21

How and what is fats broken down into?

Answer 21

-broken down into similar compounds by hydrolysis
- hydrolysis to fatty acids and glycerol

Fat molecule + 3H2O >glycerol + 3 fatty acid molecules

Question 22

What are the sources of fats?

Answer 22

• foods that are rich in fat
  > butter, cheese, fatty meat, olives, many nuts, peas, beans, seeds of caster oil and palm oil
• the meat of most fishes and ‘ white meat’ have relatively less fats
  > some fishes such as herring and salmon have a lot of fats

Question 23

What is the test for fats? Describe the test and possible results

Answer 23

• ethanol ( alcohol) emulsion test
  ON LIQUID FOOD:
  1. Add 2cm3 of ethanol to a drop of coconut oil in a dry test tube and shake the mixture throughly
  2. Add 2cm3 of water to the mixture and shake the mixture

ON SOLID FOOD:
1. Crush the peanut into small pieces and place the pieces in a dry test tube. Add 2cm3 of ethanol and shake throughly
2. Allow solid particles o settle.
Carefully decant the ethanol into another dry test tube containing 2cm3 of water

Results:
- if a cloudy white emulsion is formed, fat is present
- if the solution remains clear, no fat is present

Question 24

What are the functions of fats?

Answer 24

1. A source and store of energy
2. An insulating material that prevents excessive heat loss
   > eg. Animals like seals have a thick layer of fat ( blubber) beneath the skin which helps reduce the loss of body heat
3. A solvent for fat-soluble vitamins and many other vital substances such as hormones
4. Essential part of protoplasm > esp in cell membrane
5. Way to reduce water loss from skin surface

Question 25

How does fats reduce water loss from the skin surface?

Answer 25

• glands in the skin secrete an oily substance
  > forms a thin layer over the skin surface reducing the rate of evaporation of water
• oily substance also reduces the rate of heat loss from the skin

Question 26

What are proteins?

Answer 26

Proteins are organic molecules made up if elements carbon, hydrogen, oxygen and nitrogen
- sulfur may also als be present
Proteins are present in protoplasm

Question 27

What are the building blocks of proteins?

Answer 27

• built from simpler compounds known as amino acids.
• amino acid is made up of an amino group
  (-NH2) ,
• acidic group (-COOH)
• side chain ( denoted by R)
  General formula: on page 63:)
• R may sometimes contain sulfur, acidic groups, amino groups, and/or hydroxyl groups (-OH) in place of one or more hydrogen atoms
  -20 different naturally occurring amino acids
  > eg. Methionine & valine
• they differ because of their different R groups
  > amino acids are combined in various ways to form millions of different protein molecules

Question 28

how are amino acids folded to give proteins a three dimensional shape?

Answer 28

• many amino acids molecules are joined in a linear manner to form polypeptide
• polypeptides may join together to form an even longer chain of amino acids
• protein molecule made of one or more such chains folded together
  > polypeptide chains folded together to form a more complex, three dimensional chain

Question 29

why must proteins be broken down in the body ? how is it broken down?

Answer 29

• why: an animal cannot directly absorb the proteins it takes in
  > protein molecules are too large to pass through living cell surface membranes
  > protein molecules must be broken down by an enzyme during digestion
• digestion: a series of hydrolytic reactions
• proteins are first hydrolysed into short polypeptides
• and are then hydrolysed into amino acids

Question 30

what is the test for proteins? describe the test and the possible results.

Answer 30

• the biuret test
  > biuret solution is a blue solution made of sodium hydroxide and copper (II) sulfate

test:
1. add 2cm3 of sodium hydroxide solution to 2cm3 of egg white solution in a test tube and shake it throughly
2. add 1% copper (II) sulfate solution, drop by drop, shaking after every drop OR
add an equal volume of biuret solution to the egg white solution
3. shake well and allow the mixture to stand for 5 minutes

• if the colour of the biuret solution remains blue, mo protein is present
• if the colour of the biuret solution turns violet, protein is present

Question 31

where are proteins found?

Answer 31

• can be found in both animal and plant foods
  > milk, eggs, seafood and meat such as chicken and lean beef
  > these are some animal foods rich in proteins
• plant foods rich in protein
  > soya beans, nuts, grains and vegetables
  -*** remember that all enzymes are proteins

Question 32

what are the functions of proteins?

Answer 32

• proteins used in the:
• synthesise of new protoplasm, for growth and repair of worn-out body cells
• synthesise of enzymes and some hormones
• formation of antibodies to combat diseases

Question 33

what are the effects of protein deficiency?

Answer 33

• the average adult human being needs 50-100g of protein a day
• children who do not get enough protein may end up with a protein deficiency disease
  > kwashiorkor
• such children usually have swollen stomachs
  > their skin cracks and becomes scaly