biology chapter 4

Question 1

why do we need food

Answer 1

all living organisms need food. the food we eat contains chemical substances that are essential for us

Question 2

what does the food do

Answer 2

• food provides energy for all cell activities
• food substances are needed to make new cells for growth
• food helps us stay healthy

Question 3

what is a nutrient

Answer 3

a substance which is needed for growth, repair and metabolism. The three main nutrients are carbohydrates, proteins and lipids.

Question 4

what does the nutrient contain

Answer 4

nutrients include carbohydrates, fats, proteins and water. Carbohydrates, fats and proteins are three major types of biological molecules found in living organisms.

Question 5

why is water important

Answer 5

water is an essential component of all body tissues. About 70% of our body weight is made up of water. Hence, water is extremely important to life

Question 6

what does the water do

Answer 6

• water is an important solvent
• water helps in controlling body temperature
• water is needed for photosynthesis in plants
• water is involved in the transport of dissolved substances

Question 7

how much water do we need

Answer 7

water is lost from the body in exhaled air, urine and faeces, through sweating. To replace the amount of water lost daily, a normal, healthy adult in a temperate climate requires about three litres of water a day.

Question 8

what are the factors of the amount of water needed by a person

Answer 8

• how active a person is - people who play sports or carry out physical labour need more water
• how healthy a person is- some diseases, such as diabetes that is poorly managed, cause sufferers to pass much more urine, so they need more water than healthy people do
• environmental conditions- people living in hot or dry climates generally need more water than those living in temperature climates

Question 9

what are carbohydrates

Answer 9

organic molecules made up of the elements carbon, hydrogen and oxygen.

Question 10

what are the two main groups of carbohydrates

Answer 10

carbohydrates may be classified into two main groups - sugars and complex carbohydrates

Question 11

what are some of the single sugars

Answer 11

glucose and fructose

Question 12

what are some of the double sugars

Answer 12

maltose and sucrose

Question 13

what are some of the complex hydrates ( polysaccharides )

Answer 13

starch, cellulose and glycogen

Question 14

what are sugars

Answer 14

sugars are sweets and soluble in water. When dissolved in water, they lower the water potential. Sugars provide us with energy to do work.

Question 15

what are single sugars

Answer 15

single sugars are small molecules. They cannot be further digested into smaller molecules. They can pass through the cell membranes and be absorbed into the cells. Single sugars are also called monosaccharides.

Question 16

give some information about glucose and fructose

Answer 16

the common single sugars are glucose and fructose. Glucose is found in plants and animals. Fructose is common in plants but rare in animals. Glucose and fructose have the same chemical formula, C6H1206, but their atoms are arranged differently within the molecules. The different arrangements give the sugars their different chemical and biological properties.

Question 17

what are double sugars

Answer 17

double sugars are so termed because each molecule of a double sugar is made up of two molecules of single sugars bonded together. Double sugars are also called disaccharides. Common double sugars are maltose and sucrose, they have the same chemical formula, C12H22O11, however, their atoms have different arrangements within the molecules

Question 18

what is a maltose

Answer 18

maltose occurs in germinating grains. Maltose consists of two glucose molecules bonded together.

Question 19

can a double sugar be separated into single sugars

Answer 19

a double sugar can be split into two single sugar molecules by using a substance called an enzyme

Question 20

what is a sucrose

Answer 20

sucrose can be found in sugarcane stems, sweet fruits and certain storage roots such as carrots. Sucrose is not found in mammals. It is a molecule made up of one glucose molecule and one fructose molecule joined together.

Question 21

what is the word equation for sucrose and water

Answer 21

glucose + fructose —> sucrose + water

Question 22

how can we test for reducing sugars

Answer 22

glucose, fructose, galactose, maltose and lactose are also known as reducing sugars. Reducing sugars will produce a brick-red precipitate when boiled with benedict’s solution

Question 23

what are complex hydrates

Answer 23

a complex hydrate or polysaccharide consists of many monosaccharide molecules joined together to form a long molecule.

Question 24

what are some of the complex hydrates

Answer 24

starch, glycogen and cellulose are complex carbohydrates made up of numerous glucose molecules. The glucose molecules are linked in different ways, giving rise to different structures. Hence starch, glycogen and cellulose have different chemical and biological properties.

Question 25

how can we test for starch

Answer 25

starch can be detected by the iodine test. A few drops of iodine solution to any substance containing starch will produce a blue-black colour from a brown or orange colout

Question 26

write the steps down to test for starch

Answer 26

1. add the iodine solution directly to the substance to be tested in solid or liquid form, and look for a colour change

Question 27

write the steps down to test for reducing sugar

Answer 27

1. add the benedict’s to the solution, the suspension to be tested.
2. heat for 2 minutes in water both at boiling point and look for a colour change

Question 28

write the steps down to test for protein

Answer 28

1. add the biuret’s to the solution, the suspension to be tested and look for a colour change, when it turns deep purple it is present

Question 29

write the steps down to test for lipid

Answer 29

1. add the ethanol to the solution, the suspension to be tested and shake thoroughly.
2. then add the water and look for a colour change

Question 30

what are the functions of carbohydrates

Answer 30

• as a source of energy
• to form supporting structures, such as cellulose cell walls in plants
• for the formation of nucleic acids like DNA
• to make lubricants, such as mucus whihc covers the inner surface of the trachea and traps the dust particles preventing them form entering the lungs
• to make nectar in flowers, which attracts insects for pollination

Question 31

what are fats

Answer 31

fats, like carbohydrates, are organic molecules made up of the elements in carbon, hydrogen and oxygen. Unlike carbohydrates, fats contain much less oxygen in proportion to hydrogen

Question 32

what are sources of fats

Answer 32

fats can be animal fats or plant fats. foods that are rich in fats include butter, cheese, fatty meat, olives, many nuts, peas and palm oil

Question 33

how can we test for fats

Answer 33

the ethanol emulsion test is a test for the presence of fats. A cloudy white emulsion is formed when ethanol and water are added to fats. Am emulsion is a suspension of small drops of a liquid in another liquid

Question 34

what are the functions of fats

Answer 34

• a source and store of energy, especially for animals
• an insulating material that prevents excessive heat loss
• a solvent for fat-soluble vitamins and many other vital substances such as hormones
• an essential part of cells, especially in cell membranes
• a way to reduce water loss from the skin surface. glands in the skin secrete an oily substance. this oily substance also reduces the rate of heat loss form the skin.

Question 35

what are proteins

Answer 35

proteins are organic molecules made up of the elements carbon, hydrogen, oxygen and nitrogen. another element, sulfur may also be present. proteins are always present in all cells. their molecules are the largest and most complicated of all food substances

Question 36

what are amino acids

Answer 36

a protein molecule is built up from simpler compounds known as amino acids. amino acids have different sizes and shapes. they are joined together to form a long thread like structure called polypeptide. The polypeptide is then folded to form a three dimensional molecule called protein.

Question 37

why must proteins be broken in the body

Answer 37

an animal cannot directly absorb the proteins it takes in because protein molecules are too large to pass through cell membranes. these protein molecules must be broken down by enzymes during digestion

Question 38

what are the sources of proteins

Answer 38

proteins can be found in both animal and plant foods. Milk, eggs, seafood and meat such as chicken are some animal foods rich in proteins. Plant foods rich in proteins include soya beans, nut, grains and vegetables such as french beans.

Question 39

how can we test for proteins

Answer 39

proteins can be detected by the biuret test. The biuret reagent is a blue solution made up of sodium hydroxide and copper sulfate. It turns violet when proteins are present.

Question 40

what are the functions of proteins

Answer 40

• to make new cytoplasm, which is used for growth and repair of worn out tissues
• to make enzymes and some hormones
• for the formation of antibodies to combat diseases
• to make chromatin in chromosomes