Food Substance PDF

## Ch5 Notes ### 5.4 A Food and Humans **(26) Name:** Halley Ting ### 5.1 The Food Requirements of Humans 1. **Food provides us with:** * energy for supporting daily activities and keeping us warm * raw materials for growth and repair of body tissues * substances that are important for maintaining health. 2. **Food contains seven types of food substances (食物物質) that are essential to health:** * **Food substance that provides energy** * Carbohydrates (碳水化合物) * Lipids (脂質) * Proteins (蛋白質) * **Food substance that does not provide energy** * Minerals (礦物質) * Vitamins (維生素) * Dietary fibre (食用纖維) * Water 3. **Functions and food sources of carbohydrates, lipids and proteins:** | Food substance | Function | Food sources | | :----------------------- | :------------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Carbohydrates | Sugars and starch (澱粉) act as the main energy source for body activities. Glycogen (糖原) acts as energy reserves. Cellulose (纖維素) is a source of dietary fibre. | Sugars: fruits, honey, milk and table sugar Starch: abundant in rice, wheat, potatoes and taros | | (monosaccharides (單糖), disaccharides (雙糖) and polysaccharides (多糖)) | | | | Lipids | They act as energy reserves. Fat in adipose tissues (脂肪組織) around the internal organs acts as a shock absorber. Subcutaneous fat (皮下脂肪) acts as a heat insulator. They are involved in the absorption, transport and storage of lipid-soluble vitamins (A, D). They are used to produce some hormones (激素). Phospholipids are the major component of cell membranes. | Fatty meat, seeds, nuts, milk and dairy products Omega-3 fatty acids: olive oil, almond, egg, salmon, avocado | | Proteins | They are used for growth and repair of body tissues. They are used to produce enzymes, antibodies (抗體), haemoglobin (血紅蛋白) and some hormones. They are broken down to release energy if carbohydrates and fat stored are used up. | Meat, fish, eggs, beans, milk and dairy products | **Inside cells, amino acids are joined together by condensation to form long chains called polypeptides. Proteins consist of one or more polypeptides.** **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 a process called deamination.** **During deamination, the nitrogenous part of the amino acids (the amino group) forms ammonia, which is converted to urea. The urea is then excreted in urine. The remaining part of the amino acid forms carbohydrates (or sometimes lipids).** **Diagram:** * Image depicting a protein molecule being broken down into amino acids by hydrolysis. * Image depicting the formation of a polypeptide by condensation of amino acids. * Image depicting deamination in a liver cell. 4. **Functions, sources and deficiency diseases (營養缺乏病) of minerals, vitamins and dietary fibre:** | Food substance | Function | Deficiency | Food sources | | :------------- | :-------------------------------------------------------------------- | :---------------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | Calcium (鈣) | A component of bones and teeth. Involved in blood clotting (血液凝固), muscle contraction and sending messages in the nervous system (神經系統). | Rickets (軟骨病) in children Osteoporosis in adults | Canned sardines, milk, dairy products, tofu and some green vegetables | | Vitamin C, D | | | | | Iron (鐵) | Iron is important for making haemoglobin in red blood cells. Haemoglobin is a red pigment for carrying oxygen in blood. | Anaemia (貧血) | Beef, liver, beans, cabbage, spinach and raisins x milk | **Anaemia, people with anaemia feel tired and weak, because they do not have enough haemoglobin to carry oxygen in their body for respiration to release energy.** | Food substance | Function | Deficiency | Food sources | | :------------- | :----------------------------------------------------------------------- | :---------- | :---------------------------------------------------------------------------------------------------- | | Dietary fibre | Helps faeces pass out of the body by adding bulk to food to stimulate peristalsis (蠕動) along the gut and holding water to make faeces softer | Constipation | Vegetables, fruits and wholemeal (全麥) products | | Calcium loss and osteoporosis | | | | **As people get older, calcium loss from bones gradually increases and bone mass decreases. This causes bones to soften gradually, leading to joint pain and bending of bones a severe loss of calcium leads to osteoporosis. The bones become porous and brittle, increasing the risk of bone fractures.** **Normal bone tissue (x22) Bone disease of a person with osteoporosis (x26) To prevent osteoporosis, we should maintain an adequate intake of calcium, especially when we are young so that a high maximum bone mass can be reached. The risk of osteoporosis can also be lowered by weight bearing exercise such as walking, jogging, basketball and badminton.** **Diagram:** * Image depicting how calcium moves from the bones to the bloodstream. * Image depicting different levels of bone density between healthy bone and a bone with osteoporosis. 5. **Functions, sources and deficiency diseases (營養缺乏病) of Vitamins:** **Vitamin A** | Function | Symptoms of deficiency | Major food sources | | :------------------------------------------------------------------------------------------------------------------------------------------ | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | For the formation of a visual pigment called visual purple in the retina, which is responsible for vision especially in dim light | 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 | Liver, fish-liver oil, tuna fish, milk, cheese and eggs are rich in vitamin A. Carrots, tomatoes, pumpkins and green leafy vegetables contain carotene, a red-orange pigment which can be converted into vitamin A in the liver. | | Maintains the healthy state of the cornea of the eyes, the skin, and mucous membranes that line the digestive, respiratory, and reproductive tracts | | | **Diagram:** * Image depicting the structure of a human eye with a section labelled as "retina," highlighting the visual pigment. * Image showing the structure of a molecule of vitamin A. **Vitamin C** | Function | Symptoms of deficiency | Major food sources | | :------------------------------------------------------------------------------------------------------ | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Needed for the formation of healthy connective tissues | Causes scurvy, which has the following symptoms: bleeding gums poor healing of wounds bleeding under the skin due to weakened capillary walls | Fruits such as oranges, lemons, grapefruits, guavas, strawberries and kiwi fruit Green vegetables especially broccoli and bell peppers Remember that the content of vitamin C in fresh fruits and vegetables decreases after storing for a long time. Cooking at high temperatures also destroys vitamin C in foods. | | Helps wound healing and keeps the gums and skin healthy | | | **Diagram:** * Image depicting the structures for a healthy connective tissue and a connective tissue affected by a deficiency of Vitamin C. **Vitamin D** | Function | Symptoms of deficiency | Major sources: | | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | 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. | Rickets in young children-the bones become too weak and soft to support the 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 phosphate, and become brittle, leading to a higher risk of bone fracture. | 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. | **Diagram:** * An image with a labelled diagram of a child exhibiting symptoms of rickets. **5. Functions of water in the body:** * As a reactant * As a medium of transport * As a medium for chemical reactions * As a cooling agent to help regulate body temperature * As a major component of lubricating fluids (潤滑液) **Test for glucose using glucose test strips:** * Dip the test end of the strip into a sample. **Diagram:** * A diagram showing the steps for the glucose test strip method. **Benedict's test for reducing sugars:** * Add 2 cm³ of Benedict's solution to an equal volume of sample. Heat in a water bath for five minutes. **Diagram:** * A diagram showing the colour changes in Benedict's solution when exposed to reducing sugars. **Grease spot test for lipids:** * Add a drop of the sample to a piece of filter paper. Treat it with an organic solvent and observe it against light. **Diagram:** * Image showing the steps for the grease spot test. **lodine test for starch:** * Add a few drops of iodine solution to the sample. **Diagram:** * Diagram showing the colour change when iodine solution is added to starch. **Test for proteins using protein test strips:** * Dip the test end of the strip into a sample. **Diagram:** * A diagram showing the steps for the protein test strip method. **Test for vitamin C using DCPIP solution:** * Add the sample drop by drop to blue DCPIP solution and observe the colour changes. **Diagram:** * A diagram showing the reaction between DCPIP solution and Vitamin C, highlighting the colour changes. ### 5.2 Balanced Diet 1. A balanced diet (膳食) consists of all the food substances in the right amounts and proportions. 2. We should maintain a balance between the energy input and energy output to stay healthy. 3. The food pyramid (食物金字塔) can be used as a guideline to plan a balanced diet. 4. Factors affecting our dietary requirements: | Factor | Description | Reason | | :----- | :----------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | Age | Children require the greatest amount of energy per unit body mass. | Children are in a stage of rapid growth and have a high metabolic rate. | | | Children and teenagers need large amounts of proteins, calcium and iron. | Children have a larger surface area to volume ratio than adults, so they lose heat faster than adults. They are growing actively. These nutrients are needed for building body tissues. | | | | | | Sex | Males need more energy than females. | Males have a higher metabolic rate, higher rate of heat loss, larger body size, and are more muscular. | | | Males need more proteins than females. | Proteins are needed to build and repair muscles. | | | Females need more iron than males. | Iron is needed to replace the loss of iron during menstruation (月經). | | | Females usually have a higher percentage of body fat compared to males. They are more insulated and therefore require less energy to maintain their body temperature. However, females need more iron to compensate for the iron lost each month in menstrual blood. | | | Level of activity | People who are more physically active need more energy. | Energy is needed for muscular activities. | | | A construction worker or a professional athlete needs a diet rich in carbohydrates to provide enough energy for muscle contractions, and proteins for building muscles. | | | Dy status | Pregnant women need more energy, proteins and iron. | Energy and protein are needed for growth of the foetus (胎兒). Iron is needed for the formation of foetal red blood cells. These nutrients are needed for milk production. | | | Breast-feeding mothers need an extra supply of various types of nutrients. | | **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.** 5. Eating too little implies energy input is less than energy output. The body will break down energy reserves to release energy to support normal body activities. 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 of energy. This causes serious health problems. 6. Eating too much implies energy input is greater than energy output. The excess energy will be stored as fat in our body, causing weight gain. A person becomes overweight when his body weight exceeds a normal range. A person is considered to be obese when he is seriously overweight. Obesity (肥胖症) is the condition of being seriously overweight. 7. People who are overweight or obese have a higher risk of a number of diseases like diabetes mellitus (糖尿病), high blood pressure, heart disease, stroke (中風) and arthritis (關節炎). 8. Nutrition labels provide information about the energy and nutrient contents of food. **Diagram:** * Image depicts a food pyramid with section labelled by food groups.

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