Ch.6 Food and Humans

Question 1

What are autotrophs?

Answer 1

Autotrophs are organisms that can synthesize its own food and obtain nutrients (autotrophic nutrition).
e.g. plants - photosynthesis

Question 2

What are heterotrophs?

Answer 2

Organisms that cannot make their own food, they feed on organic matter to obtain nutrients (heterotrophic nutrition)

Question 3

What is the importance of food?

Answer 3

• provides energy to keep our body warm and support daily activities
• raw materials for growth and repair of body tissues
• substances that keep us healthy

Question 4

What substances does food contain?

Answer 4

Primary food substances (essential to life)
- carbohydrates
- lipids
- proteins
- water

Protective food substances (keep us healthy and help prevent diseases)
- vitamins
- minerals
- dietary fibre

Question 5

What are carbohydrates?

Answer 5

Carbohydrates are organic substances made up of carbon, hydrogen nad oxygen.
3 major types of carbohydrates
- monosaccharides
- disaccharides
- polysaccharides

Question 6

Why and how are monosaccharides an immediate source for body activities?

Answer 6

Monosaccharides are smal molecules and are soluble in water. They are readily absorbed in the intestines and are transported in the blood to every part of the body. Inside cells, glucose is broken down during respiration to release energy. It is an immediate energy source for body activities.

Question 7

How are disaccharides and polyssacharides absorbed in the intestines?

Answer 7

They must be broken down into monosaccharides before absorption can occur.

In the presence of a suitable enzyme, one dissacharide molecule can be broken down into two monosaccharide molecules with the addition of one water molecule (hydrolysis)

Polysaccharides is hydrolysed to form glucose with the action of different types of enzymes. The glucose can then be absorbed into the blood.

Question 8

What are the functions of carbohydrates in the human body?

Answer 8

• main source of energy, provide 17.1 kJ / g
• excess carbohydrates are converted to glycogen or lipids, glycogen is stored in the liver and in skeletal muscles
• monosaccharides as building blocks e.g. nucleic acids
• cellulose -> type of dietry fibre, the human body cannot digest cellulose

Question 9

What are lipids?

Answer 9

Lipids are organic substances made up of carbon, hydrogen and oxygen. Insoluble in water but soluble in organic solvents.

One main group of lipids: triglycerides
- saturated fats, solid at room temperautre and come from animal sources
- unsaturated fats, oily (liquid) at room temperature, come from plants and fish

Question 10

How are lipids absorbed in the digestive tract?

Answer 10

A triglyceride molecule is formed from one glycerol molecule and three fatty acid molecules by condensation. It must be broekn down into smaller molecules by hydrolysis, in the presence of water and a suitable enzyme

Question 11

What are the functions of lipids in the human body?

Answer 11

• source of energy, 38.9 kJ /g
• excess lipids are stored in adipose tissues
  -> found under the skin as subcutaneous fat
  -> insulating layer to reduce heat loss
  / found around internal organs to serve as shock-absorbers
• phospholipids -> major component of cell membrane
• involved in the transport and storage of fat-soluble vitamins
• cholesterol -> raw material for producing lipid hormones

Question 12

What are proteins?

Answer 12

Proteins are organic substances. Large complex molecules made up of carbon, hydrogen, oxygen and nitrogen. Some contain sulphur.

All proteins consist of subunits called amino acids.
20 types of amino acid to synthesize proteins
-> non-essential amino acids (can be made using other compounds in the body)
-> essential amino acids (cannot be made in the human body & must be included in our diet)

animal proteins usually include all
plant lack some -> vegetarians eat a wide variety of plants

Question 13

How are proteins absorbed?

Answer 13

In the digestive system, proteins in food are broken down into amino acids by hydrolysis in the prescence of water and suitable digestive enzymes. The amino acids are then absorbed into the bloodstream and carried to body cells.

Inside cells, amino acids are joined together by condensation to form polyypeptides. Proteins consist of one or more polypeptides.

Question 14

What will happen if more amino acids are absorbed than needed?

Answer 14

If more amino acids are absorbed than are needed, those in excess cannot be stored in the body. They are broken down in the liver by deamination.

During deamination, the nitrogenous part of the amino acids forms ammonia, which is converted to urea. The urea is then excreted in urine. The remaining part of the amino acid forms carbohydrates.

Question 15

What are the functions of proteins in the human body?

Answer 15

• Proteins are used mainly for growth and repair of body tissues. They are compoenents of various cellular structures e.g. cytoplasm, they are need for making new cells and body structures
• Important molecules e.g. enzymes, antibodies, some hormones are protieins
• Proteins can be a source of energy when the body is short of carbohydrates and lipids. 18.2kJ / g

Question 16

What are vitamins?

Answer 16

Vitamins are organic food substances. They have no energy value but are essential for maintaining good health. They help regulate metabolic reactions in our body. Although vitamins are only required in small amounts in our diet, a lack of vitamins will cause deficiency diseases.

Some vitamins are water-soluble, such as vitamins B and C. Some are fat-soluble, such as vitamins A and D. Excess water-soluble vitamins are excreted in urine, while excess fat-soluble vitamins are stored in body fat.

Question 17

What are the functions of Vitamin A in the body?

Answer 17

• For the formation of a visual pigment called visual purple in the retina, which is responsible for vision especially in dim light
• Maintains the healthy state of the cornea of the eyes, the skin, and mucous membranes that line the digestive, respiratory, and reproductive tracts.

Question 18

What are the symptoms of deficiency of Vitamin A?

Answer 18

• Night blindness, in which the person has poor vision in dim light
• Thickening of the cornea (blindness may result in severe cases)
• Dry skin and increased risk of infections of the respiratory tract

Question 19

What are the major food sources of Vitamin A?

Answer 19

• Liver, fish-liver oil, tuna fish, milk, cheese and eggs
• Carrots, tomatoes, pumpkins and green leafy vegetables contain carotene, a red-orange pigment which can be converted into vitamin A in the liver

Question 20

What are the functions of vitamin C in the body?

Answer 20

• Needed for the formation of healthy connective tissues
• Helps wound healing and keeps the gums and skin healthy

Question 21

What are the symptoms of deficiency of vitamin C?

Answer 21

Causes scurvy, which has the following symptoms:
- bleeding gums
- poor healing of wounds
- bleeding under the skin due to weakened capillary walls

Question 22

What are the major food sources of vitamin C?

Answer 22

• Fruits such as oranges, lemons, grapefruits, guavas, strawberries and kiwi fruit
• Green vegetables especially broccoli and bell peppers

Question 23

What are the functions of vitamin D in the body?

Answer 23

It helps the absorption of calcium and phosphate from food in the intestines. As calcium and phosphate are major components of bones and teeth, vitamin D is essential for the formation of strong bones and teeth, especially in children.

Question 24

What are the symptoms of deficiency of vitamin D?

Answer 24

• Rickets in young children -> the bones become to weak and soft to supportthe body weight, causing bowing of the legs and bending of the spine
• Osteoporosis in older adults, especially in women, the bones become less mineralized with calcium and phophat, and become brittle, leading to a higher risk of bone fracture

Question 25

What are the major sources of vitamin D?

Answer 25

• Liver, fish-liver oil, milk cheese and egg yolk are good sources of vitamin D.
• Vitamin D can also be formed in the human skin when it is exposed to sunlight.

Question 26

What are minerals?

Answer 26

Minerals are inorganic substances. They have no energy value and are needed in small amounts. The human body needs minerals for a wide range of functions, such as regulating metabolism and building some types of body tissues.

Question 27

What are the functions of calcium in the body?

Answer 27

• Calcium is a major component of bones and teeth. Children need a relatively large amount of calcium for the development of bones and teeth as they grow.
• Calcium also plays an important part in blood clotting and muscle contraction.

Question 28

What are the symptoms of deficiency of calcium?

Answer 28

• Rickets in children
• Osteoporosis in adults

Question 29

What are the major food sources of calcium?

Answer 29

Milk, cheese, yogurt, sardines, almonds and some green vegetables (e.g. broccoli)

Question 30

What are the functions of iron in the body?

Answer 30

Iron is important for making haemoglobin in red blood cells. Haemoglobin is a red pigment for carrying oxygen in blood.

Question 31

What are the symptoms of deficiency of iron?

Answer 31

Anaemia, people with anaemia feel tired and weak, because they do not have enough haemoglobin to carry oxygen in their body.

Question 32

What are the major food sources of iron?

Answer 32

Liver, beef, clams, beans, eggs and green leafy vagetables.

Question 33

What is dietary fibre?

Answer 33

Dietary fibre, or roughage, is the indisgestible parts of plant foods. It consists mainly of ceellulose from plant cell walls. Vegetables, fruit and wholemeal cereals are rich in dietary fibre.

Dietary fibre has no energy value to us because we do not have suitable enzymes to digest it, but it is important for maintaining a healthy digestive system. Dietary fibre stimulates peristalisis (i.e. the muscular movement of the digestive tract), helping the passage of food along the digestive tract. Insufficient intake of dietary fibre leads to constipation.

Question 34

What are the functions of water?

Answer 34

Makes up about 65% of the human body weight, has no energy value but essential to life due to its functions.
- It acts as a solvent and provides a medium for chemical reactions to take place.
- It is a reactant that takes part in some metabolic reactions (e.g. hydrolysis).
- The water in blood acts as a transport medium to carry substances around the body.
- Sweat is mostly water. The evaporation of sweat helps regulate the body temperature.

Humans lose water continuously through urination, sweating, breathing and egestion. Every person needs six to eight glasses of water, from drinks or from food, every day to replace the water loss.

Question 35

What is a balanced diet?

Answer 35

A balanced diet contains all the food substances in the right amounts and proportions. It provides us with enough energy and nutrients for body functions and daily activities.
(rev the book food pyramid)

Question 36

What are the factors affecting our dietary requirements?

Answer 36

Energy is needed for maintaining metabolism (including growth), muscle contractions when performing physical activities, and generating heat to keep the body temperature constant.

The exact amounts of energy and nutrients required, i.e. dietary requirement, vary from person to person. It depends on a number of factors:

1. Age
2. Gender and body size
3. Level of physical activity
4. Body status

Question 37

How does age affect the dietary requirements?

Answer 37

Children are in a stage of rapid growth and have a high metabolic rate. Moreover, children have a larger surface area to volume ratio than adults, so they lose heat faster than adults. All of these factors lead to a higher energy requirement per unit body mass in children.

Their diet should include relatively large amounts of energy-rich foods such as carbohydrates; more proteins to form new body cells; more calcium and vitamin D to form strong bones and teeth; and more iron to form red blood cells.

Question 38

How does gender and body size affect the dietary requirements?

Answer 38

Malles generally have a larger body size, more muscle mass and a higher metabolic rate than females, so they need more energy and proteins than females.

Females usually have a higher percentage of body fat compared to males. They aremore insulated and therefore require less energy to maintain their body temperature. However, females need more iron to compenssate for the iron lost each month in menstrual blood.

Question 39

How does level of physical activity affect the dietary requirements?

Answer 39

People who perform heavy physical activities need more energy** from their diet. For example, a construction worker or a professional athlete needs a deit rich in carbohydrates to provide enough energy for muscle contractions, and proteins for building muscles. On the contrary, an office worker of the same age and gender needs less energy.

Question 40

How does body status affect the dietary requirements?

Answer 40

Pregnant women need more carbohydrates, proteins, and a range of vitamins and minerals to support the growth and development of the foetus. Breast-feeding mothers also need more nutrients for milk production. They should also drink enough water but less tea or coffee and no alcoholic beverages.

Question 41

What health problems will be caused by an imporper diet?

Answer 41

A balanced diet supplies enough nutrients to maintain good health and enough energy to support daily activities. When energy intake is equal to energy output, the body weight will remain more or less the same.

An imporper diet can lead to malnutrition which causes many health problems. Malnutrition refers to both undernutrition and overnutrition.

Question 42

How does undernutrition happen and what health problems does undernutrition cause?

Answer 42

If our energy intake from food is less than energy output, the body will break down energy reserves to release energy to support normal body actvities. Glycogen stored in the liver and skeletal muscles will be used up first. Then, the fat under the skin and around internal organs is metabolized, causing weight loss.

If starvation continues, the body will start to use proteins (particularly those in muscles) as a source or energy. This causes serious health problems.

A severe deficiency of preotein in the diet causes kwashiorkor. Chilren with kwashiorkor suffer from stunted growt, anaemia, hair loss, and have a swollen belly because tissue fluid accumulates in the abdomen.

Question 43

How does overnutrition happen and what health problems does overnutrition cause?

Answer 43

If we eat too much or lack sufficient physical activity, our energy intake from food will be greater than our energy output. THe excess energy will be stored as fat in our body, causing weight gain. A person becomes overweight when his body wieght exceeds a normal range. A person is considered to be obese when he is seriously overweight.

Obesity can lead to many health problems such as high blood pressure, heart disease, diabetes, gallstones and serious damage to joints.