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Friday, 2 November 2012

Biology Chapter 6 Form 4


topic6.1

Nutrients and Nutrition
Nutrients are the chemical substances in food that are required for the nourishment of an organism. They are required by every living cell in the body for metabolic reactions that are vital to life as well as for the synthesis of other compounds needed by the body, reproduction and the growth and repair of damaged tissues. Examples of nutrients are carbohydrates, proteins, lipids, minerals and vitamins.
Nutrition, on the other hand, is the entire process by which organisms obtain nutrients and energy from food. This includes the process of digesting food and utilising the absorbed nutrients for growth, maintenance and the repair of damaged tissues. Based on the strategies they deploy to obtain nutrients, living organisms can be divided into two groups. They are autotrophs and heterotrophs.

Autotrophs
Autotrophs are organisms which carry out autotrophic nutrition. Autotrophs get their name from the words auto which means self and trophos which means feed. This means that they can synthesise their own food by processing simple inorganic substances such as carbon dioxide, water and minerals to produce nutrients such as carbohydrates, lipids and proteins needed by the organism itself. This process is achieved with the help of light or chemical energy.
Autotrophs can be divided into two groups. They are:
i. Photoautotrophs
ii. Chemoautotrophs
Photoautotrophs
These are organisms that synthesise organic molecules (food) from carbon dioxide and water using sunlight as a source of energy and the process known as photosynthesis. Photo means light. So, photosynthesis means the synthesis using sunlight as a source of energy. Examples of photosynthetic autotrophs are green plants and algae.
Chemoautotrophs
Chemoautotrophs are organisms that synthesise organic molecules (food) using energy obtained by the oxidation of inorganic substances such as nitrates and sulphides. The synthesis is called chemosynthesis which comes from the word chemo which means chemical. So, chemosynthesis means the synthesis using chemicals as a source of energy. Most chemoautotrophs are bacteria, such as sulphur bacteria, which oxidise hydrogen sulphide to sulphur.
Heterotrophs
Heterotrophs are organisms which carry out heterotrophic nutrition. Heterotrophs get their name from the words hetero which means other and trophos which means feed. These organisms are not able to synthesise their own nutrients but depend on ready-made food such as plants and animals. Heterotrophic nutrition is then nutrition in which energy and organic compounds (foods) are obtained by breaking down other organisms (plant or animal tissues) which are digested and absorbed.
Heterotrophs can be divided into three groups. These are:
i. holozoics
ii. saprophytes
iii. parasites
Holozoics
Holozoics are organisms which feed by ingesting solid organic substances and digesting, absorbing and assimilating them into their bodies; finally, these substances are egested out of their bodies. The three groups that carry out holozoic nutrition are:
a. Herbivores (herb = green crop). These organisms only eat plants.
b. Carnivores (carn = flesh). These are organisms which only eat animals.
c. Omnivores (omni = all). These organisms eat both plants and animals.
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Nepenthes sp. (pitcher plants) is an example of a carnivorous plant which carries out holozoic nutrition
Saprophytes
Saprophytism is carried out by any organism that feeds on dead and decaying organic matter. The organism is called a saprophyte. Saprophytes are also known as decomposers as they decompose dead organic matter into simpler molecules. Examples are bacteria and fungi which digest the organic matter externally using digestive enzymes before absorbing them as nutrients. Examples of saprophytes are rhizopus (bread mould) and yeast.
Parasites
Parasitism is defined as a close association wherein an organism feeds on other living organisms to obtain nutrients. The organisms which gain from this association are known as parasites while the losers are called the hosts. The parasites absorb nutrients from their hosts Examples of parasites are fleas, various bacteria, fungi and gastrointestinal worms.
Parasites can live inside or outside the bodies of their hosts. Endoparasites are the parasites that live inside the bodies of their hosts (endo = inside). Examples are tape worms (Taenia sp.) and round worms (Ascaris sp.).
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The tapeworm is an example of a endoparasite
Ectoparasites are the parasites that live outside their hosts (ecto = outside). Examples are mosquitoes and mites (they suck blood from other organisms).
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Lice: an example of ectoparasites
The classification of organisms according to the types of nutrition they undertake is shown below.
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Classification of organisms according to nutrition process

A Balanced Diet
A balanced diet is a diet that contains the major nutrients which include carbohydrates, proteins, vitamins, minerals, water, roughage or dietary fibre and lipids in the correct proportions. A balanced diet is essential for the healthy growth and development of the body. The table below shows the nutrients and their functions.
Nutrients and their functions
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The food pyramid
A guide to a balanced diet can be obtained from the food pyramid. See the figure below. A healthy diet consists of more vegetables, fruits and grain products which are at the bottom of the pyramid. Items higher on the pyramid must be consumed less and include fats, oils and sugar.
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The food pyramid
Daily Energy Requirements
Our body needs energy to carry out vital body functions such as maintaining blood pressure and body temperature, sustaining regular heartbeats and breathing. Energy is also required for the body to carry out the biochemical reactions that take place at the cellular level. These include cell division, cell growth, active transport, protein synthesis, etc. The sum of all these biochemical reactions is called metabolism. The energy requirements for the metabolic activities are derived from the nutrients absorbed by the body.
The energy demand of the body over a specified period of time to carry out metabolic activities is called the metabolic rate. It is measured in kilojoule (kJ) units. The higher the metabolic rate, the more will be the energy required for the metabolic activities. Our metabolic rate is higher when we are running and lower when we are sleeping.
The energy required to carry out the biochemical reactions that keep the vital body functions going is called the basal metabolic rate (BMR). The BMR depends on various factors such as a person’s weight, state of health, sex, age as well as the climate. For example, the BMR of a man when sleeping is different to the BMR of a woman when sleeping. Similarly, the BMR of a child when sleeping is different to that of an adult when sleeping.
Generally, women have a lower BMR than men and children have a higher BMR than adults. A person living in a cold climate has a higher BMR than a person living in a hotter climate. There are two main factors influencing the energy requirements of the body. These are:
i. The basal metabolic rate (BMR)
ii. Physical activities
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The variables influencing the body’s energy needs
For example:
A 50kg football player training for 1.5 hours daily would require over 23,027.4 kJ daily, whereas a 50kg female tennis player training for the same duration would require approximately 9,838.98 kJ daily. (Source: http://www.bestsyndication.com/?q=20080318_online_calorie_counter.htm)
The knowledge about the body energy needs can help an individual to stay healthy. A person who takes a diet containing the calories equal to the energy needed by the body will remain slim and healthy. If the diet contains excess energy, the energy turns into fats and the person gains weight. On the other hand, if the diet contains inadequate energy, the person will lose weight.


Energy Contents of Food
Our body needs energy to carry out vital body functions such as maintaining blood pressure and body temperature, sustaining regular heartbeats and breathing. Energy is also required for the body to carry out the biochemical reactions that take place at the cellular level. These include cell division, cell growth, active transport, protein synthesis, etc. The sum of all these biochemical reactions is called metabolism. The energy requirements for the metabolic activities are derived from the nutrients absorbed by the body.
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A food calorimeter to determine the energy value of food
The amount of energy that is produced from the oxidation of one gramme of food is known as the energy value of the food. It is measured in joules per gramme (Jg-1). The amount of energy in food can also be expressed as calories.
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Different types of food have different energy values. The table below shows the energy values of different types of food.
Energy values of different types of food
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Vitamins
Vitamins are complex organic compounds needed in tiny amounts by humans and animals to maintain normal good health. Vitamins are not synthesised by the human or animal body (except vitamin D), so they are obtained from the diet. Vitamins can be easily destroyed by heat.
General functions of vitamins
The function of vitamins is to act as coenzymes which control various metabolic reactions. Vitamins do not provide energy but are essential for efficient metabolism, growth, protection and energy regulation in cellular respiration.
Classification of vitamins
Altogether, 13 different types of vitamins have been identified. They can be divided into two groups as follows:
i. water-soluble vitamins
ii. fat-soluble vitamins
Water-soluble vitamins
Water-soluble vitamins dissolve only in water. They are circulated freely around the body and are absorbed directly into the blood circulatory system. Excess consumption of these vitamins will be excreted and there is no toxicity when taken in large amounts. Examples of water-soluble vitamins are vitamins B1, B2, B3, B6, B12, folic acid, vitamin H and vitamin C.
Fat-soluble vitamins
These vitamins are only dissolved in oil, fat and organic solvents. They are absorbed together with fat and bile. They are difficult to excrete and any excess amount is stored in the body. As such, excess consumption is dangerous. Examples of fat-soluble vitamins are vitamins A, D, E and K. .
Deficiency in vitamins
If a person is deficient in one or more vitamins, he/she may develop vitamin deficiency diseases. Different types of vitamins may cause different deficiency diseases as shown in the table below.
Sources, functions and effects of deficiency of vitamins B1, B2, B3, B5, B6, B12
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B2
  • What are vitamins?
  • What are water-soluble vitamins?
  • What are fat-soluble vitamins?
Minerals
Minerals are inorganic nutrients found in food or drinks. They cannot be synthesised by the body and must be obtained from the diet. They do not provide energy to our body but are essential for various body functions such as biochemical reactions and developing the molecules. The minerals are classified into two groups:
i. Macrominerals
These minerals are required by the body in relatively large quantities (major minerals) of more than 100 mg per day Examples of these minerals are calcium, magnesium, phosphorus, sodium, potassium and chlorine.
ii. Microminerals
These minerals are required by the body in small amounts of less than 20 mg per day. These minerals have their own specific functions. Examples are iron, iodine, zinc and molybdenum.


Dietary Fibre
Dietary fibre or roughage is indigestible plant matter. Basically, it is the fibrous materials in the diet that consist mainly of the cellulose of the cell walls of plants.
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Food high in fibre content
Dietary fibre is not a nutrient and the stomach cannot digest it. However, it is still important for the digestive process as it helps the food to move through the digestive system and hold water so that the faeces remains soft, thus easing defecation.
In addition, the dietary fibre also lowers the cholesterol level in the blood, reduces the risk of heart diseases and colon cancer. Dieticians recommend that about 25-50 g of fibre should be incorporated into the diet each day to ensure good health. Examples of foods high in fibre contents are fruits, grains, cereals, pasta, legumens, nuts, seeds and vegetables.
Deficiency of dietary fibre can increase the risk of constipation, bowel irregularities, haemorrhoids, diverticulosis and colorectal cancer. Constipation occurs when the flow of the digested food in the large intestine is not smooth and is very slow. In this case, the faeces is dry and hard because much water has been absorbed into the body. As the result, the defaecation is difficult and painful.
Water
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A human body mass is made of 70% of water. Without water, humans only can survive for three or four days. Water is important to the human body due to the following reasons:
i. All metabolic reactions take place in solution, so water plays a role as a medium for such reactions.
ii. In homeostasis, water plays the main role in thermoregulation. Thermoregulation is the ability of the body to maintain its body temperature at a particular level regardless of any internal or external temperature changes in the environment. For example, on a hot day, sweat glands under the skin secrete sweat onto the surface of the skin. When the sweat evaporates, it cools the skin, thus maintaining the internal body temperature.
iii. As blood plasma consists of 92% of water, water plays a role as a medium for the transportation of digested food, oxygen, excretory substances, minerals and hormones to the entire body.
iv. Water also helps in the excretory process. Excretory wastes such as urea, uric acid and excess minerals are removed from the body through perspiration and urination.
v. Water is also important as a lubricant in our body. It helps to reduce friction between the bones in the joints.
Choosing Appropriate Diets for Different Target Groups
Different groups of people need different diets in order to cater to the proper nutritional needs of their bodies. Different diets are needed depending on the age, lifestyle, health condition and specific nutritional needs of people, especially those with specific diseases. The table below show groups of people and guidelines for the diet of specific groups.


Malnutrition


Malnutrition
Malnutrition is the health condition faced by people eating an improper or unbalanced diet. It can due to eating less food (under-nutrition), eating too much food (over-nutrition) or bad eating habits (imbalanced nutrition). There are many health effects resulting from malnutrition and we shall look at them in detail.
Protein Deficiency
Protein deficiency gives rise to two common health problems. They are:
i. Kwashiorkor
ii. Marasmus
Kwashiorkor
Kwashiorkor is a health problem related to poverty and is prevalent in developing countries such as in Africa and South Asia because of protein deficiency in the diet. It usually affects children aged one to four years. Children suffering from kwashiorkor have severely bloated abdomens (pot bellies), flaky skins, thin muscles and are underweight. Their growth is also stunted.
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Children with kwashiorkor
Marasmus
Marasmus is widespread in developing countries and occurs among children between nine to 12 years of age. it is mainly due to poverty and lack of protein and energy providing nutrients. The symptoms are "an old man's face", being excessively underweight, thin muscles and stunted growth.
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Children with marasmus
Effects of Calcium, Phosphorus and Vitamin D Deficiencies
Calcium, phosphorus and vitamin D deficiencies in the diet may cause many health problems such as osteoporosis and osteomalacia.
Osteoporosis
Osteoporosis is a disease of the bones and is due to an insufficient dietary intake of calcium; it is very common among the aged. The lack of calcium causes the bones to become brittle, porous and fracture easily especially at the hips and backbone. In severe situations, the backbone shortens and bends forward.
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The bent over backbones structure of osteoporosis
Osteomalacia
Osteomalacia is the softening of the bones due to the deficiencies of calcium, phosphorus, and vitamin D in the dietary intake. It always occurs in pregnant women while in children, it is known as rickets.
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Bones in the legs of a rickets victim
Effects of an Excessive Intake of Nutrients
Not all health problems are due to the lack of nutrients in the dietary intake. Health problems are also caused by over-nourishment (excessive intake of food). The effects of an excessive intake of various nutrients are shown below.
Excessive intake of carbohydrates
The excessive intake of carbohydrates is one of the bad habits occurring when consuming food. This excessive intake can lead to various diseases such as obesity and diabetes mellitus.
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People with excessive intake of carbohydrates
Obesity is a condition of a person who is overweight. If a person is obese, the risks of developing various diseases, such as cardiovascular diseases, strokes, brain haemorrhages, high blood pressure, atherosclerosis, and diabetes mellitus, are increased.
Diabetes mellitus is a disease due to the presence of excess glucose in the blood. This happens when too much sugar is in the dietary intake (including carbohydrates) and the pancreas is not producing enough hormone insulin to convert the glucose to glycogen. Diabetes can lead to various diseases such as kidney diseases, cataracts, blindness and heart problems. In addition, wounds become very difficult to heal.
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Patient with diabetes mellitus
Excessive intake of lipids
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Coronary artery in human filled by plague
Excessive lipids (saturated fats) in the dietary intake may cause many diseases such as hypertension, high blood pressure and atherosclerosis.
Atherosclerosis is a situation when there is deposit of plaque in the internal lining of the blood vessels. This deposit blocks the blood flow and in severe cases, it even stops the blood flow altogether, leading to heart attacks (myocardial infarction).
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Cardiovascular diseases caused by an excessive intake of lipids
Excessive intake of minerals
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Kidney stones most made of calcium and oxalate
Excessive intake of minerals, such as salty food, in the dietary intake can lead to various diseases such as high blood pressure, heart problems, strokes and the formation of kidney stones.
Kidney stones are formed because of an excessive intake of salt and the lack of water in the diet. Kidney stones develop from the crystallisation of urine which accumulates in the kidneys. The stones are made of calcium and oxalate. Their presence complicates the kidney function and make urination painful. The stones can be expelled together with the urine.




  • Human Digestive System
    The human digestive system also called the gastrointestinal system. This system starts at the mouth and ends at the anus. The parts along the mouth and the anus are called the alimentary canal. The parts of the human digestive system are shown in figure below.
    Duodenum is located at the first part of small intestine while the rest of small intestine is known as ileum. The large intestine consists of caecum, colon, and rectum. Small intestine and large intestine are the longest parts in this system. From the ducts to the gut, there are some accessory organs connected to this part; the liver, the gall bladder and the pancreas.
    Physical digestion and chemical digestion
    The digestion involves two processes which is physical and chemical digestion. The breaking down of food particles is the physical digestion. Chewing food particles is an example of the process in which the food particles will be broke into smaller particles. This process is important to increase the surface in the chemical process. Peristalsis is the other physical digestion involves in the digestion of food. This process helps to move the food particles down the elementary canal.
    The physical digestion is too different from the chemical digestion. If the physical digestion is the process involve of the body part such as teeth, ileum, colon and others. Chemical digestions are the processes that involve the chemicals contained in our body. This type of digestion involves the process of breaking down the food particles into the small and simple molecules and also into soluble. These processes involving hydrolysis; the enzyme reactions in the presence of water and each enzyme are specific for a type of food.
    Some of the chemical contained in our body and known as digestive juices. The digestive juices are; saliva, gastric juice, pancreatic juice and intestinal juice. All these juice contain enzymes that involve in the hydrolysis process. Each enzyme has their own factors to maximize their performance. For example, an enzyme needs an acidic medium to perform well. In the stomach, hydrochloric acids will prepare an acidic medium for the bile secreted to facilitate digestion of fats. Digestive juices are secreted by the digestive glands.
  • Food Digestion
    Food digestion is a process where large and complex organic compounds of food components, consisting of carbohydrates, proteins, and lipids, are broken down into simpler molecules by the digestive enzymes through the process of hydrolysis. The digestive break-down of food components and the digestive products produced are:
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    The final products of the digestive processes are glucose molecules, amino acids, glycerol and fatty acids which can be absorbed by the cells so that they can carry out the metabolic processes.
    The Human Digestive System
    The human digestive system starts at the mouth and ends at the anus. It is sometimes called the gastrointestinal system and has a length of about 7-9 m long. The human digestive system is shown in the figure below.
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    The human digestive system
    The duodenum is located at the first part of the small intestine while the rest ofthe small intestine is known as the ileum. The large intestine consists of the caecum, colon and rectum. The small and large intestines are the longest parts of the digestive system. There are some accessory organs connected to the system such as the liver, the gall bladder and the pancreas. They also have roles to play in the digestive process.
    The food enters the mouth into the oesophagus, then to the stomach, small intestine and large intestine before it is excreted at the anus. Various digestive processes consisting of physical digestion and chemical digestion occur as at various stages of the digestive system as the food moves from the mouth to the anus.
    Physical Digestion and Chemical Digestion
    The digestion involves two processes. They are:
    i. physical digestion
    ii. chemical digestion
    Physical Digestion
    Physical digestion is the breaking down of large pieces of food into smaller ones by mechanical means. The physical digestion occurs at various parts of the digestive system. The table below shows the physical digestion at the parts of the digestive system involved.
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    Chemical digestion
    A chemical reaction breaks down complex food into simpler molecules using specific digestive enzymes. The process is called hydrolysis. The digestive juices, such as saliva, gastric juice, pancreatic juice and intestinal juice, contain enzymes which help in the hydrolysis process. In the stomach, hydrochloric acid provides an acidic environment for the enzymes to function while bile secreted by the liver emulsifies the fats and helps in the digestion of fats.
    Digestion of Carbohydrates, Protiens and Lipids in the Human Body
    We shall look at the digestion of carbohydrates, proteins and lipids through the digestive system.
    The mouth
    The first digestion process of the food occurs in the mouth. It involves the physical digestion of chewing food by the teeth. This process breaks the food into smaller sizes, thus increasing the surface area of the food for the action by the enzymes. Here, the first chemical digestion also takes place where food is mixed with saliva secreted by salivary glands. The saliva juice contains water, an enzyme called salivary amylase and mucus. The salivary amylase breaks down the starch into maltose (simple sugar) according to the following equation:
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    The mucus moistens the food particles, rolling and shaping them into a food lump called the bolus.
    The oesaphagus
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    The moist food bolus is swallowed and moved through the muscular tube line called the oesophagus. The movement of the bolus along the oesophagus is achieved by a process called peristalsis. Peristalsis is a series of rhythmic wave-like movements caused by the musclar contraction and relaxation of the longitudinal and circular muscles along the oesophageal wall. The peristalsis continues until the food reaches the stomach. The figure below shows the peristalsis along the oesophagus.
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    Peristalsis along the oesophagus
    The stomach
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    The stomach is the main organ of digestion and is located below the diaphragm. The lining of the stomach contains the gastric gland that secretes gastric juice. The food is chewed through the muscular relaxation and contraction of the stomach muscles. In the process, it is mixed with the gastric juice to become a semi-fluid and partly digested food called chyme. The figure below shows the secretion of gastric juice in the stomach.
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    Secretion of gastric juice
    The environment in the stomach is highly acidic due to the hydrochloric acid contained in the gastric juice. This environment (pH 1.5-2.0) is necessary for the optimal action of the enzymes. Besides this, it stops the activity of the salivary amylase and at the same time kills bacteria and parasites in the food.
    Protein Digestion
    Besides the gastric juice containing the hydrochloric acid, there are also digestive enzymes in the stomach called the pepsin and rennin. These enzymes are responsible for the digestion of the proteins. Pepsin hydrolyses protein into polypeptide.
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    On the other hand, the enzyme rennin curdles milk. The enzyme catalyses the soluble milk protein (caseinogens) to become insoluble milk protein (casein).
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    The contraction and relaxation of the stomach moves the chyme, the semi-solid and partly digested food, from the stomach into the duodenum of the small intestine.
    The small intestine
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    Small intestine
    The small intestine is divided into three structural parts:
    i. The deodenum
    ii. The jejunum
    iii. The ileum
    The deodenum
    The duodenum is the first part of the small intestine and it receives the chyme directly from the stomach. Here, the chyme is broken down using the enzymes. The duodenum does not have any glands that secrete digestion juices but it only receives secretions from the gall balder of the liver and the pancreas.
    The Liver
    The liver secretes bile and stores it in the gall bladder. Bile is not an enzyme but it aids in the emulsifying of lipids by breaking them down into tiny droplets, increasing the surface area for the action of the enzymes. Bile also functions to create the alkaline environment (pH 7.6-8.6) in the duodenum necessary for the optimum action of the digestive enzymes (produced by the pancreas) and at the same time, it helps to reduce and neutralises the acidity of the chyme. Bile flows into the duodenum via the bile duct.
    The Pancreas
    Pancreas secrete pancreatic juice containing three digestive enzymes, namel, the pancreatic amylase, trypsin and lipase which flow into the duodenum via the pancreatic duct. These enzymes help in the digestion of starch, proteins and lipids in the chyme and function optimally in an environment with the pH 7.1-8.2.
    The digestion of starch, proteins and lipids
    The digestion of starch, proteins and lipids occurs in the duodenum using enzymes obtained from the pancreas.
    i. Starch
    Strach is converted to maltose using pancreatic amylase,
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    ii. Proteins
    The polypeptides are broken down by the enzyme trypsin into peptides,
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    iii. Lipids
    Lipids are broken down by the enzyme lipase into fatty acids and glycerol. They are small enough to be absorbed directly by the epithelial lining of the small intestine,
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    The ileum
    The ileum is located at the bottom part of the small intestine. The functions of the ileum are to absorb bile and the secretion of enzymes for the digestion of peptides and disaccharides. The products of the digestion of the peptides are amino acids while the products of the digestion of disaccharides are the monosaccharides which are absorbed directly along with fatty acids and glycerol. The vitamins and minerals are very small molecules which can be absorbed directly by the body without undergoing digestive processes.
    The digestion of proteins
    Protein digestion involves the breaking down of peptides into amino acids using the enzyme erepsin,
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    The end products of the protein digestion are fatty acids and glycerol which are small enough to be absorbed directly by the epithelial lining of the ileum.
    The digestion of carbohydrates
    The digestive process breaks carbohydrates into disaccharides and finally into monosaccharides. Monosaccharides are the end products and exist either in the form of glucose, fructose or galactose; they are absorbed by the epithelial lining of the ileum.
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    The Digestive System of Ruminants
    Ruminants (cows, goats and sheep) feed on plant materials which contain a large amount of cellulose. Cellulose is a polysaccharide and is extremely insoluble. It can be broken down into glucose with the help of the enzyme called cellulase. So, the ruminants are adapted in order to digest cellulose with the help of this enzyme.
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    The digestive system of a ruminant
    In ruminants, the digestive system consists of a stomach with the following four chambers :
    i. The rumen
    ii. The reticulum
    iii. The omasum
    iv. The abomasum
    Inside the first two chambers are large populations of bacteria and protozoa. The microorganisms secrete enzymes called cellulase which help in the digestion of cellulose. This also allows the ruminants to carry out rumination, the process of rechewing partially digested food.
    The relationship between the microorganisms and the ruminants is symbiotic where both parties benefit from the relationship. The ruminants obtain food from the digestion of the cellulose while the microorganisms obtain food, shelter and space.
    The digestive process of the ruminants consists of four stages, one at each of the stomach chambers:.
    Step 1. The rumen
    When a ruminant first chews and swallows grass, it enters the rumen. The rumen is a large fermentation chamber with a very high population of bacteria and protozoa. The bacteria secrete the enzyme called cellulase necessary for the break-down of the cellulose. Parts of the digestive products (glucose and fatty acids) are absorbed by the ruminant while the others are absorbed by the bacteria and protozoa.
    Step 2. The reticulum
    The reticulum is the second chamber in a ruminant's digestive system. In this chamber, a further hydrolysis of cellulose is undertaken. At some point, the partially digested food in the form of balls called "cud" is returned to the mouth (regurgitated) to be chewed again. This helps to further break down the cellulose. This movement of the partly digested food to the mouth is helped by the antiperistalsis of the eosophagus.
    Step 3. The omasum
    After the second chewing, the food flows directly to the omasum. This is the third chamber of the ruminant’s stomach. Here, the product of cellulose digestion, glucose, is absorbed by the body. Water is drained from the cud and absorbed into the body.
    Step 4. The obamasum
    The obamasum is known as the true stomach. Here, the gastric juice (containing the hydrochloric acid) is secreted to complete the digestion of proteins and other food substances. The food (chyme) is passed to the small intestine where it is further digested in the normal way and absorbed by the body.
    The Digestive System of Rodents
    Rodents (mice, squirrels) have a different digestive system from ruminants. They have a long caecum located between the small and large intestines. In the caecum, there is a high concentration of symbiotic bacteria and protozoa which secrete the cellulase to digest cellulose.
    In order to obtain the maximum nutrients, rodents eat some of their faeces and allow the food to pass through the digestive tract twice. The first faecal pallets produced at night are normally soft and watery containing partially digested food. These faecal pallets are eaten again and pass through the digestive tract for a second round of digestion. In this way, more nutrients are absorbed. The second dry and hard faecal pallets are produced during the day.
    Problems Associated with Food Digestion
    There are a few problems associated with the digestion of food, namely:
    i. The incomplete digestion of food
    ii. Gallstones in the gall bladder
    The incomplete digestion of food
    Incomplete digestion is caused by the types of food that we consume and the way they are consumed. Excessive intake of food at any one time, oily food, hot food (such as strong curries), and not chewing properly are some of the most common factors causing the incomplete digestion of food. They may lead to nausea, vomiting and abdominal pains.
    To ensure the complete digestion of food, the food must be chewed slowly and oily and hot food should be avoided. In this way, the digestive enzymes can function optimally and food will be completely digested.
    Gallstones in the gall bladder
    When bile contains an excessive amount of cholesterol, there is a tendency for the cholesterol to crystallise and form gall stones in the bile duct. The gallstones vary in size, from the size of sand to the size of a ping pong ball depending on the severity of the gallstone formation.
    A problem occurs when the gallstones become big enough to obstruct the movement of bile from the gall bladder to the stomach. When this happens, the digestion of lipids cannot take place. This leads to the following symptoms:
    i. prolonged and continuous pains
    ii. nausea and vomiting
    iii. fever or chills
    iv. yellowish colour of the skin or whites of the eyes
    v. clay-coloured stools
    The gallstones may also be formed in the pancreatic duct. In this case, the gallstones may block the flow of the pancreatic juice leading to severe pains and incomplete digestion of food.




absorption and assimilation of digested food



Adaptations of the Digestive System
The digestive system is suitably adapted to increase the rate of absorption and this is achieved via the following:
i. Increasing the surface area of the lining of the small intestine by having a long intestine (about 5-6 metres long) and a folded surface which is is covered by a finger-like projection called the villi.
ii. The thin epithelial wall of about one cell thick. This allows the easy flow of the movement of the digestive system across the wall.
iii. A moist surface.
iv. Plenty of blood vessels for efficient transportation of digestive products.
The figure below shows the location of the villi in the small intestine and its structure. :
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The adaption of the digestive system (1) small intestine (2) A section of a small intestine to show the villi (3) Enlarged illustration of a villus (4) Epithelium with microvilli and goblet cell
Absorption of Digested Food
Depending on the type of digestive products, various mechanisms are utilised that allow these products to be absorbed from the lumen of the intestine.
Monosaccharides (glucose, galactose, fructose)
Their absorption across the epithelial cells into the blood capillaries is achieved through secondary active transport and facilitated diffusion mechanisms. They are absorbed directly into the blood capillary network contained in each of the villi.
Fatty acids and glycerol
Fatty acids and glycerol utilis the simple diffusion mechanism to move across the epithelial cells. The movement is achieved by first transforming the fatty acids and glycerol into tiny droplets of lipids which then move into the lacteals located at the centre of each the villus. The lacteals combined to form a larger vessel of the lymphatic system and a network throughout the body.
Fat-soluble vitamins
Fat-soluble vitamins diffuse directly across the epithelial cells and directly into the lacteal located at the centre of each villus.
Water-soluble vitamins
Water-soluble vitamins diffuse directly into the blood capillary network contained in the villi.
Water
Water is absorbed via osmosis.
Transportation of Nutrients to Body Cells
At the villus, the water-soluble nutrients (monosaccharides, amino acids and minerals) enter the blood capillaries whereas the lipid-soluble nutrients enter the lacteal and then into the lymphatic vessels. The blood capillaries bring the nutrients into the liver via the hepatic portal vein first for assimilation (regulating, processing and filtering) before sending them to the heart to be circulated throughout the body. On the other hand, the lymphatic vessel connected to the heart is where lipid-soluble nutrients are circulated throughout the body.
Functions of the Liver
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The functions of the liver are:
i. Regulation of the glucose level in the blood
ii. Deamination
iii. Storage
iv. Detoxification
v. Production of bile
vi. Synthesis of plasma proteins
Regulation of the glucose level in the blood
The liver functions to regulate the amount of glucose released into the body system. In a situation where the sugar level in the blood is high, the liver stores the glucose as glycogen.
Deamination
Deamination is the process where amino acids are broken down into glucose and urea. In this way, the liver can regulate the amount of amino acids in the blood so that it remains constant in the blood. When an excess amount of amino acids is present in the blood, deamination occurs and the glucose and urea are released from the body via urination.
Storage
The liver can act as a storage for nutrients. Examples of nutrients stored in the liver are the fat-soluble vitamins A and D and water soluble B12. At the same time, it can also store minerals ions such as iron, potassium, cobalt, zinc and copper.
Detoxification
The liver also functions as a detoxifier of poisonous substances. There are many toxic substances entering the body such as alcohol, drugs, and other harmful chemicals. The liver metabolises these toxic substances and the products are excreted from the body through urination.
Secretion of bile
The liver secretes bile which is stored in the gall bladder. Bile contains greenish bile pigments and bile salts which are transported to the duodenum for the digestion and absorption of fats and fat-soluble vitamins. The process of digestion involves the emulsification of fats into tiny droplets which increase the surface area for optimal action by the lipase.
Synthesis of blood plasma proteins
The liver is a site for the synthesis of blood plasma protein proteins such as prothrombin and fibrinogen. These plasma proteins are necessary for blood clotting processes.
Assimilation of Digested Food by the Liver and Cells
Assimilation is a process where absorbed food in the liver or cell is utilised for the purposes of growth, reproduction and repair. The assimilation process of the liver and cells is shown in the table below.
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Formation Of Faeces And Defecation



What is Defecation?
After the digestion process in the small intestine, the left-over products, consisting mostly of undigested food substances and dietary fibre, enter the colon (large intestine). The undigested food moves along the colon aided by the rhythmic contraction and relaxation of the colon muscle walls (peristalsis) where further absorption of water (90% of it) and other minerals (with the help of symbiotic bacteria) takes place. The final compressed food residue is called faeces.
The faeces consists of mainly undigested food residue, dead epithelial cells, bile pigments and bacteria which are stored temporarily in the rectum. When the rectum is full, the faeces is expelled out of the anus via the contraction and relaxation of the sphincter muscles. The process of the expulsion of the faecal materials out of the body through the anus is called defecation.
Structure of the large intestine
The large intestine is about 1.5 metre long and consists of three main components:
i. the caecum and appendix
ii. the colon
iii. the rectum
See the figure below.
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The structure of the large intestine
The main functions of the large intestine are the following:
i. Absorption of 90% of the water, compressing the undigested food into faecal materials.
ii. Absorption of minerals with the help of symbiotic bacteria.
iii. Storage of the faecal materials before defecation.
The Formation of Faecal Materials
There are various processes occurring in the large intestine before the faecal materials are formed. These are:
i. Absorption of water and compression of faecal materials
About 90% of the water content of the undigested food materials are absorbed here. This makes the food residue hard and it becomes more of a semi-solid. It is also compressed and compacted to become faeces.
ii. Absorption of minerals with the help of symbiotic bacteria
The symbiotic bacteria, Escherichia E. coli, which are present in the colon, undergo metabolic processes and produce vitamins B and K which are absorbed through the colon wall.
iii. Lubrication of the faecal materials
The faecal materials are lubricated by the mucus secreted by the wall of the colon and move along the colon via the action of peristalsis.
iv. Storage
The faecal materials are stored for about 12-24 hours before defecation. The defecation is achieved via the relaxation and contraction of the anal sphincter muscles which expell the faeces out through the anus.
Problems related to Defecation
There are a number of problems related to defecation. They are:
i. Constipation
ii. Haemorrhoids (piles)
ii. Colon cancer
Constipation
Constipation is the condition in which the faecal materials are dry, hard and difficult to expel out of the anus. Constipation is caused because a large amount of water has been removed, making the faeces dry and hard; its movement along the colon is also slow.
Constipation can be overcome by following diet that is rich in fibre. Food that is rich in fibre can facilitate the movement of undigested food materials along the colon. Consuming more liquids also helps in overcoming the problem of constipation.
Haemorrhoids (piles)
Haemorrhoids is the condition of abnormally swollen and inflamed veins in the rectum and anus. It is caused by prolonged constipation where too much pressure is being applied to the rectum, causing the blood veins to swell and bulge. In extreme cases, the veins can rupture causing bleeding during defaecation.
Colon cancer
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Colon cancer
Colon cancer is a growth developing in the tissues of the colon. There are many reasons for the cancer to develop; the main one would be a diet deficient of fibre as well as infrequent elimination of faeces. The prolonged contact between the colon and undigested food, containing toxic substances such as carcinogens, can lead to the formation of cancer.
Eating Habits



Good Eating Habits
Good eating habits means consuming food in the right proportions and of the right quality at the right time intervals. These include:
i. Eating at the right time and not taking too many snacks
ii. Practising a balanced diet
iii. Consuming the right amount of water
iv. Consuming food rich in fibre
v. Use the food pyramid as a guide to food intake
vi. Eating food in the right amounts without over- or under-eating
vii. Avoiding food rich in sugar, fats and salt
Health Problems Related to Bad Eating Habits
There are many health problems related to bad eating habits. They are:
i. Obesity
ii. Anorexia nervosa
iii. Bulimia
iv. Gastritis
Obesity
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Obesity can be defined as a body weight and size of about 20% above normal. It is caused by the excessive storage of energy in the form of fats resulting from the excessive intake of energy-rich food such as carbohydrates and fats. Lack of exercise also contributes to obesity. People with obesity are susceptible to various diseases such as cardiovascular diseases, hypertension and diabetes mellitus. Obesity can be reduced by the practice of having a balanced diet and regular exercise.
Anorexia nervosa
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Anorexia (an –"without", orexis – "appetite") is a psychological eating disorder mostly affecting adolescent girls and women and is characterised by a constant fear of weight gain and a change in the body shape. As a result, the person has no appetite for food, suffers excessive weight loss and has a distorted image of a healthy body. Sufferers continue to think that they look overweight although in actual fact, they are bone-thin.
This condition can lead to various diseases such as disruption in the functions of the heart, endocrine and reproductive systems. It can be overcome by proper counselling to correct the fear of gaining weight and other emotional stresses.
Bulimia
Bulimia (boulima – "ravenous hunger") is a psychological eating disorder where there are occasions when the person has the urge to consume a large amount of food (binge eating) in a short period of time and is unable to stop eating during the binge. This is quickly followed by a sense of guilt of having taken too much food and purging the food out of the body via self-induced vomiting. In some cases, laxatives are used to get rid of the food.
The person with bulimia may have the normal body mass, but the repeated purging of the food out of the body may result in injury to the digestive tract at the same time causing an imbalance of salts and minerals in the body. This increases the risks of other diseases such as failure of the kidneys, liver or heart. This disease can be overcome by counselling to eliminate the psychological urge of consuming too much food in a short period of time and feeling guilty about it.
Gastritis
Gastritis is the condition in which the epithelial lining of the stomach is inflamed and eroded. In a normal body, the epithelial lining of the stomach wall is covered with mucus which protects the lining from hydrochloric acid. The prolonged and continuous absence of food in the stomach causes the acid to act on the lining and damage it. In severe cases, the damage can develop into a hole causing a gastric ulcer. There is a possibility that stomach cancer may also develop
Gastritis is due to bad eating habits such as the over-consumption of alcohols, drugs, ( e.g., aspirin), irregular food intake and stress. The symptoms of gastritis include pains in the upper abdomen, loss of appetite, heartburns, nausea and loss of weight.
Evaluating Eating Habits
Good eating habits are important for the maintainance of good health. Apart from good eating habits, emphasis must also be given to the amount of nutrients in the food, its freshness and the amount of food additives such as colouring agents and preservatives being added to the food.
Good eating habits are also reflected in the body weight and size. The body weight and size can be measured using the body mass index (BMI). The following table shows the BMI as an indicator of the body size and weight which reflect the eating habits.
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the importance of a healthy digestive system


Effects of a Defective Digestive System
A defective system is a system that does not function normally. There are many parts in the digestive system and the defect of any part of this system will have an overall effect on the process of digestion. We shall look at each of the parts, the defects that might occur and the effects that follow.
The Mouth
Any defect in the mouth may be related to the process of chewing. This can lead to solid food not being properly broken down; the food is then not properly digested.
The Salivary Glands
A defect in the salivary glands normally means the defective secretion of saliva. This leads to the improper digestion of food in the mouth. The food might also taste different from its normal taste.
The Oesophagus
Defects in the oesophagus include its weak relaxation and contraction. The food bolus moving down the oesophagus is impaired.
The Stomach
Problems in the stomach include a lack of the secretion of mucus, acids and enzymes. This will cause poor food digestion and the formation of stomach ulcers.
The Duodenum
Defects in the duodenum include a damaged epithelial lining. This reduces the efficiency of nutrient absorption.
The Large Intestine
Defects in the large intestine include poor contraction and relaxation of the stomach muscles. They will result in the slow movement of food down the colon, leading to constipation.
Taking Care of the Digestive System
We need to care of our digestive system. This is to ensure that the system is functioning properly and the nutrients are absorbed efficiently and assimilated by the cells. There are several practices one can follow to ensure that the digestive system is healthy. These include:
i. Having a balanced dietary intake
ii. Drinking a lot of water
iii. Taking food at regular time intervals
iv. Avoiding junk food and food with high sugar and fat contents


macronutrients and micronutrients in plants

Elements Required by Plants
Elements are required by plants to synthesise organic molecules (carbohydrates, nutrients, minerals) necessary for their optimal growth and development. An element such as carbon dioxide is obtained directly from the atmosphere whereas elements such as hydrogen and oxygen are obtained from water from the soils. Other elements in the form of minerals are obtained from the soils.
The elements required by plants can be classified as follows:
i. Macronutrients
ii. Micronutrients
Macronutrients
Macronutrients are elements that are required by plants in large quantities. These elements include carbon, hydrogen, oxygen, nitrogen, potassium, calcium and magnesium.
Micronutrients
Micronutrients are elements that are required by plants in small quantities. These elements include boron, molybdenum, iron, copper and zinc.
Knop’s Solution
Knop’s solution is a complete cultured solution containing all the necessary elements needed for optimal growth and development. The contents of Knop’s solution are:
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Plants can be grown using a cultured solution such as Knop’s solution. The function of a particular element to the growth and development of the plant can also be determined by eliminating a particular element from Knop’s solution. The physical characteristics of the plants, such as the colour of the leaves, height of the plant and thickness and hardness of the stems, are then observed and compared with the control culture containing all the elements as in Knop’s solution.
Functions and Effects of Nutrients Deficiencies in Plants
The functions of macronutrients and micronutrients and the effects of their deficiencies in plants are shown the table below.
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Topic 6.10


The Discovery of Photosynthesis
Many experiments were conducted by scientists leading to the discovery of photosynthesis. We shall look at the prominent scientists who contributed immensely to the discovery of photosynthesis. They are:
i. Jean Baptista van Helmont
ii. Joseph Priestley
iii. Jan Ingenhousz
Jean Baptista van Helmont
Jean Baptista van Helmont conducted the experiment in 1640 and he was able to show that the growth of plants is due to the water absorbed by the plants and not because of the soil. The figure below shows the experiment conducted by Van Helmont.
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Experiment showing that the growth of plants is due to the absorption of water
Van Helmont used a young willow tree weighing 2.3 kg and soil weighing 91 kg. He watered the plant regularly and covered the pot it was planted in with a metal plate drilled with tiny holes to allow the flow of gas and water. The metal plate prevented dust from mixing with the soil.
After five years, the plant grew achieving the weight of 76.6 kg, an increase of 76.6 kg - 2.3 kg = 74.3 kg. However, the soil weight was 90.65 kg, a decrease of 91kg - 90.65 kg = 0.35 kg, indicating almost no change. He concluded that the increase in the weight of the plant was due to water and not the soil.
Joseph Priestley
Joseph Priestley conducted his experiment in 1772. In the experiment, he was able to show that plants emit gases that can support combustion and respiration. The figure below shows the experiment conducted by Priestley.
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Experiment showing that plants emit gas that supports combustion and respiration
In the first experiment, lighted candles and a mouse were placed in an airtight container. Very soon, the flame was extinguished and the mouse died. This was due to the lack of oxygen to support the combustion and respiration.
In the second experiment, a lighted candle and mouse were placed in an airtight container together with a plant. Priestley found that the flame did not go off and the mouse remained alive. This indicated that the plant was able to replenish the oxygen consumed by combustion and respiration. At that time, Priestley did not know that the gas emitted by the plant was oxygen.
Jan Ingenhousz
Ingenhousz carried out his experiment in 1779 and found that leaves emit oxygen in the presence of sunlight. In addition, he showed that the green portion of the plant (chlorophyll) is responsible for the emission of oxygen. His findings revealed that sunlight and chlorophyll are the important components for photosynthesis.
The Structure of Leaves
The main organ for photosynthesis is the leaf. It is highly adapted to receive the maximum amount of sunlight and for the diffusion of carbon dioxide into the leaf and oxygen out of the leaf. It is also very well adapted for the absorption of minerals and water from the roots.
The figure below shows the cross-section of a leaf. The cross -sectional structure shows the following parts of the leaf:
i. The cuticle
ii. The upper epidermis
iii. The palisade mesophyll
iv. The spongy mesophyll
v. The lower epidermis
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The cross section of a leaf
The structure, features and the functions/adaptations of the leaf for photosynthesis are shown in the table below
The structure, features and the functions/adaptations of the leaf for photosynthesis
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Adaptation of Plants of Different Habitats to Carry Out Photosynthesis
Plants from various habitats (plants in tropical areas, floating plants, plants in the deserts and submerged plants) have unique characteristics to ensure that photosynthesis can be carried optimally.


Topic 6.11


The Structure of Chloroplast
The structure of chloroplast is shown in the figure below:
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The structure of chloroplast
There are three main components in chloroplast:
i. The stroma
ii. The grana (singular: granum)
iii. The starch grains
The Stroma
The stroma is a gel like (semi-fluid) matrix which fills the chloroplast. In the stroma, there are the grana and starch grains. The stroma also contains enzymes responsible for the dark reaction (reaction without light) of photosynthesis.
The Grana
Grana are made of stacks of thylakoids. A thylakoid is the membrane-like structure of the plant where the chlorophyll (the green pigment) is embedded. The light reaction of photosynthesis (reaction with light) takes place in the thylakoids.
Starch grains
Starch grains are embedded in the stroma. They act as temporary places for the storage of photosynthetic reactions.
The Mechanism of Photosynthesis
There are two types of photosynthesis. These are:
i. Light photosynthesis
ii. Dark photosynthesis
Each of these types of photosynthesis involves a different mechanism. We shall at each of them in detail.
Light Photosynthesis
Light reactions take place in the presence of light and occur in the thylakoids of the grana. Light energy captured by the chlorophyll releases electrons and energy from the chlorophyll molecules. At the same time, the light energy splits the water molecules into hydrogen ions (H+) and hydroxyls ions (OH-). This process is called photolysis.
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The electrons released by the chlorophyll combine with hydrogen ions (H+) to form hydrogen atoms.
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The hydroxyl ions lose their electrons and form hydroxyl groups which are broken down to form water and oxygen.
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The energy released from the chlorophyll molecules is used in the production of the adenosine triphosphate (ATP) which results in energy rich molecules. The final products of light reactions are hydrogen, water, oxygen and ATP. The ATP and hydrogen are used in dark reactions.
Dark Photosynthesis
Dark photosynthesis occurs in the absence of light and takes place in the stroma of the chloroplast. This reaction is assisted by photosynthetic enzymes and in the presence of ATP produced in light reactions. In these reactions, the atmospheric carbon dioxide which diffuses into the leaves is combined with hydrogen (produced in the light reactions) and is reduced to glucose (simple sugar).
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The glucose produced by the dark reactions is converted to starch and is stored as starch grains in the chloroplast. It is then transformed into sucrose and circulated around the plant. Starch is also used to produce the cellulose of the cell walls. Glucose may also be converted to proteins and fats required by the plant.
Similarities and Differences between Light and Dark Reactions
The similarities between light and dark reactions are as follows:
i. Both reactions occur in the chloroplast
ii. Both are photosynthetic reactions
The differences between light and dark reactions are as follows:
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Topic 6.12

Factors Affecting the Rate of Photosynthesis
Photosynthesis only takes place in the presence of light, as well as when there are carbon dioxide, water and chlorophyll available. The rate of photosynthesis therefore depends on the following factors:
i. Light intensity
ii. Carbon dioxide concentration
iii. The temperature
iii. The amount of water available
Light intensity
If the amount of carbon dioxide and the temperature are kept constant, the rate of photosynthesis is directly proportional to the light intensity. This means that as the light intensity increases, the rate of photosynthesis increases. This relationship is true to a certain point where the light intensity is concerned. Beyond this point, the rate of photosynthesis remains constant. Any further increase in the light intensity has no effect on the rate of photosynthesis. This point is called the saturated point and beyond this point, we say that the rate of photosynthesis has saturated.
The figure below shows the effect of light intensity on the rate of photosynthesis.
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The relationship between light intensity and the rate of photosynthesis
Beyond the saturation point, the rate of photosynthesis remains constant even if the light intensity is being increased further. This is because the temperature and the concentration of the carbon dioxide become the limiting factors governing the rate of photosynthesis.
If the light intensity is increased further, there will come a point where the chlorophyll will be damaged and the rate of photosynthesis will slow down.
Carbon dioxide concentration
The relationship between the concentration of carbon dioxide with the rate of photosynthesis is similar to the relationship of light intensity with the rate of photosynthesis discussed above. This is to say that, if the light intensity and the temperature are kept constant, the concentration of carbon dioxide is directly proportional to the rate of photosynthesis. The higher the concentration of carbon dioxide, the higher is the rate of photosynthesis.
This relationship holds true until a saturation point. Beyond this point, any increase in the concentration has no effect on the rate of photosynthesis. The rate remains constant. The figure below shows the relationship between the concentration of carbon dioxide with the rate of photosynthesis.
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The relationship between the concentration of carbon dioxide with the rate of photosynthesis
The temperature
When the light intensity and concentration of the carbon dioxide are kept constant, an increase in the temperature increases the rate of enzyme activities and hence, increases the rate of photosynthesis. The rate increases until the maximum rate at the temperature of about 25-30 degrees Centigrade is reached. If the temperature is increased further, the enzymes are denatured and the rate of photosynthesis drops drastically. At a sufficiently high temperature, all the enzymes are denatured and no photosynthesis can take place.
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The relationship of the temperature with the rate of reactions
The amount of water available
The amount of water available is not a limiting factor for photosynthesis. This is because the amount of water needed for photosynthesis is very small. However, the amount of water available affects the rate of photosynthesis indirectly. When the amount of water available is insufficient, the plant wilts and the stomata in the leaves close. In this situation, the diffusion of carbon dioxide is unable to take place and photosynthesis cannot be carried out.
Differences in the rate of photosynthesis throughout the day
The rate of photosynthesis is not constant throughout the day but fluctuates depending on the intensity of light and the temperature. In the early morning, the rate of photosynthesis is low because the light intensity and the temperature are low; it slowly increases and reaches its maximum at noon when the light intensity and the temperature are at the maximum.
The rate of photosynthesis saturates at midday because the concentration of carbon dioxide becomes the limiting factor. In the evening, the rate of photosynthesis decreases and reaches its minimum point at sunset. When there is no sunlight, the dark reaction of photosynthesis takes place. The figure below shows the variations in the rate of photosynthesis throughout the day.
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Variations in the rate of photosynthesis throughout the day
The productivity of crops and the rate of photosynthesis
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The green house
Plants grow very well in the tropics where the temperature, sunlight and rainfall are at an optimum. However, this is not the case in countries located in the northern and southern hemispheres where four seasons – winter, spring, autumn and summer – exist. In such places, the rate of photosynthesis and hence, the productivity of crops, vary throughout the year.
The productivity of crops is highest in summer when there is sufficient light intensity and a suitable temperature. In winter, there is no crop productivity since there is minimal sunlight and the temperature is the lowest. In order to ensure a continuous supply of crops, such as fruits and vegetables, some plants are grown in green houses.
In the green houses, farmers can control and regulate the amount of light intensity, temperature, carbon dioxide as well the amount of water so as to create the optimum conditions for photosynthesis and hence, maximise the crop yields. These conditions allow crop productions throughout the year regardless of changes in the weather outside the green houses.
Topic 6.13

Why Are Plants Important?
Green plants are sources of energy for many living organisms including humans and other heterotrophs. Life on earth cannot be sustained without the presence of green plants. Other examples of the importance of plants are:
i. The ecosystem
Green plants emit oxygen and release carbon dioxide. The plants help in the balance of nature in the ecosystem by replenishing the oxygen in the atmosphere which is used by other living organisms.
ii. Climate control
Plant helps to control the climate. The destruction of forests on a massive scale leads to global warming. Excessive clearing of these forests at slopes leads to soil erosion. Plants also help in water catchment areas to ensure continuous water supplies for human consumption. Plants in the city, such as in parks, help to cool the city and make it more conducive for living.
iii. Medicine
Plants are the sources of many types of medicine which can cure diseases. Most of the plants in the forests have not been fully explored for their potential in the development of new drugs and vaccines. The indiscriminate clearing of the forests means that these potential sources are lost forever.
A Caring Attitude Towards Plants
A caring attitude towards plants would result in the following:
i. No indiscriminate clearing of forests. Selected logging should be encouraged.
ii. Replanting of plants soon after logging or forest clearing.
iii. Systematic and sustainable forest management.
iv. The clearing of forests is mainly for wood. Alternative products to replace wood for the construction industry should be encouraged.


Topic 6.14

Need to Improve the Quality and Increase the Quantity of Food
The need to improve the quality of food and increase food production is due to the increasing human population and hence, an increase in the demand for food. The population of Malaysia is expected to reach 70 million in 10 years' time and appropriate action based on the national food production policy must be taken so that adequate food is available for everyone.
Diversification in food production in one of the alternatives to ensure that sufficient amounts of food are made available to everyone. The most efficient way of improving the quality of food and increase food production is by the use of technology.
Methods of Improving the Quality of Food and Increasing Food Production
There are various ways in which technology can be used to improve the quality of food and increase production. Examples where technology can be used are:
i. Direct seeding
ii. Hydroponics
iii. Breeding
iv. Tissue culture
v. Genetic engineering
vi. Soil management
vii. Biological control
Direct Seeding
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Seeding machine
Technology can be used in seeding such as in the planting of paddy. A special drilling machine is used to sow the seeds directly into the soil. In this way, the seeding can be done faster and efficiently and production costs are lowered. In addition, higher production is achieved.
Hydroponics
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Hydroponics
Hydroponics is the planting and growing of plants in a cultured solution instead of in the soil. The cultured solution contains all the necessary macronutrients and micronutrients. Normally, the hydroponics is carried out in green houses where the light intensity, concentration of carbon dioxide and the temperature can be controlled to provide optimum conditions for the growth of the plants.
Selective Breeding
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Several cows of the same types
Selective breeding is a process whereby parents of plants or animals of desirable characteristics and traits are chosen to produce offspring. In the case of plants, better yields of high nutritional values, greater resistance to diseases and a short maturity time are chosen. This means that only high quality and quantity products are being produced.
Tissue Culture
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Tissue culture
Tissue culture is the growing of tissues of a living organism in a cultured solution of suitable nutrients and hormones. This is carried out outside the body of the plants. Many plants, such as oil palm, papayas, bananas, etc., have been produced or cloned in large quantities via tissue cultures. The clones have the same traits and characteristics as the parents, including better yields of high nutritional values, great resistance to diseases, a short maturity time, etc. In this way, high quality products are produced.
Genetic Engineering
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Genetically produced food (maize)
Genetic engineering is the manipulation of the DNA involving the deletion or insertion of the gene (segment of DNA) to produce a new organism with desirable traits. The organism produced via genetic engineering is called a genetically modified organism (GMO). The GMO has been used extensively in agriculture to improve crop productions in terms of the yields, nutritional contents as well as resistance to pathogens and pests.
Soil Management
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Tractor working the soil
The soil is the medium for the growth of plants. The management of the soil in terms of its chemical, physical and biological properties is important to ensure that the soil texture, the contents of the organic matter, water contents and microorganisms are always available for every cycle of the crop production. This ensures that the soil quality is sustainable for each crop cycle.
Some practices of good soil management are crop rotations, use of a controlled amount of fertilisers, contour planting to prevent erosion and the use of plant legumes as a ground cover to increase soil fertility and prevent soil erosion.
Biological Control
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Lady birds
Biological control is the natural control of pests using natural predators. Such a method is environmentally friendly as no poisonous or toxic chemical pesticides are involved. Examples of natural biological control methods are the use of ladybirds which prey on mealybugs which suck the juices from leaves, flowers and fruits. The rats which destroy paddy plants can be controlled by introducing snakes and owls which are natural predators of rats.


Topic 6.15

The Need for Food Processing
Food processing is a method of transforming raw food materials into food suitable for human consumption. The main purpose of food processing is to eliminate food spoilage. Food spoilage is caused by:
i. The action of microorganisms
ii. The oxidation of food
The action of microorganisms
The action of microorganisms, such saprophytic bacteria and fungi, on carbohydrates and protein in the food produces products with unpleasant smells; they are toxic when consumed.
The oxidation of food
The oxidation of food is the reaction between oxygen and food; this results in changes in the taste, colour and nature of the food. The oxidation of bananas and apples causes their change of colour when they are cut.
There are various reasons for food processing. These are:
i. Extending the life span of the food
ii. Avoiding wastage of food
iii. Diversify the use of food
iv. For sufficient food supplies
Methods of Food Processing
Food processing and preservation have been practised from early days. The techniques involved are adding of sugar, salt or vinegar to the food, drying in the sun, smoking, fermentation and cooking. The modern methods of food processing are:
i. Pasteurisation
ii. Sterilisation
iii. Refrigeration
iv. Canning
v. Irradiation
The basic principle of food processing is to kill the microorganisms, thus preventing (inhibiting) their activities or growth. When the microorganisms are killed or when they are inactive, the food lasts longer. The methods of food processing and their effects on the microorganisms are shown in the table below.
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Effects of Processed Food on Health
Processed food is normally devoid of nutritional contents. This is because the vitamins and nutrients have been destroyed during the heating process. In addition, processed food contains many chemicals in the form of food preservatives, flavouring, colouring, stabilisers, etc. Some of these chemicals are harmful to health.
It is advisable to consume more fresh organic fruits and vegetables than processed food. When choosing processed food, it is a good practice to read the food labels to determine the type of chemicals present in the food. In this way, we are aware of the type and the quality of the processed food before consuming it.






















































































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