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Form 4 Biology Note

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The 7 Basic Food Substances
All the food we eat is made up of the following 7 basic substances:

1. Carbohydrates
2. Fats
3. Proteins
4. Vitamins
5. Minerals
6. Fibre
7. Water
Carbohydrates, fats, proteins and vitamins are organic substances because they contain carbon in their molecular structure. Water and minerals are inorganic substances since they don’t contain carbon.

Carbohydrates, fats and proteins are needed in bulk in our diet, while vitamins and minerals are needed in smaller amounts. A person whose diet lacks any of these nutrients suffers from malnutrition, and this may give rise to a deficiency disease. Food gives us energy. The amount of energy needed by our body isn’t the same for everyone. The amount of energy needed to live depends on the person’s sex, job, attitude, age and other factors like if the person is a pregnant woman. 1. Carbohydrates

Carbohydrates are organic substances made up of carbon, hydrogen and oxygen. They are very important because they provide energy for the body. There are 3 types of carbohydrates: sugars, starch, and cellulose.

A. Sugars

Glucose (C6H12O6)

Fructose (sugars in fruit)

Sucrose (table sugar)

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Lactose (found in milk)

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Maltose (found in barley grains)

B. Strach

Found in bread, potatoes, rice, cereals etc. Plants store food as starch.

C. Cellulose

Found in all unrefined plant food. An important source of fibre.

Carbohydrates are all made up of molecules of glucose bonded (joined) together. The simplest form of carbohydrate is glucose. Two molecules of
glucose joined together with a bond, form maltose, lactose and sucrose sugars. Starch, cellulose and glycogen are formed when 3 or more glucose molecules are joined together with bonds.

Glucose’s molecule is represented by a hexagon:
A single sugar molecule is called a monosaccharide. Examples of monosaccharides are glucose and fructose.


Sucrose, maltose and lactose are all disaccharides because they have 2 sugar molecules bonded together.

Starch, cellulose and glycogen are all polysaccharides because they are made up of 3 or more sugar molecules bonded together.

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Carbohydrates are found in cereals, pasta, bread, fruit, potatoes sugary food such as ice cream etc.
Glucose’s chemical formula is the following: C6H12O6.
Plants store food as starch, while animals store food as glycogen. Both glycogen and starch are polysaccharides. Polysaccharides are NOT sweet but ARE insoluble. 2. Fats

Fats are organic substances. Lipids are fats in a liquid state. Fats are useful for our body, because they:

provide energy,

can be stored for later use,

build up cell membranes,

layers serve as an insulating layers under mammal’s skins and

and oils on the surface of the skin makes the skin waterproof.

Fat is found in vegetable oil, milk, fried foods, eggs, beef etc. The simplest fat molecule is made up of 1 molecule of glycerol and 3 fatty acids bonded together.
Fatty Acids


Fatty Acids
Fatty Acids

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3. Proteins
Proteins are organic substances made up of hydrogen, carbon and oxygen, nitrogen and sometimes they contain sulphur. Proteins are needed by the body to grow and repair tissues (a cellular structure), they are components of cell membranes, are used to produce enzymes (biological catalysts) and hormones. The simplest possible protein is an amino acid, thus proteins are made up of amino acids, which can be represented as any form of shape (circle, rectangle, square).

Amino acids are joined together by peptide bonds. When 2 amino acids connected together with a peptide bond, a dipeptide forms. When 3 or more amino acids are joined together, a polypeptide is formed.

Amino Acid



When proteins are heated, they are denatured; they change shape, its properties and functions are destroyed. Food rich in proteins are milk, meat, eggs, nuts, fish etc. 4.Water is vital for animals and almost all living organisms. It makes up to one third of the human body mass. Water is an inorganic substance with the chemical formula H2O.
Water is important for animals because it gives support to aquatic animals, gametes (sex cells like sperms and eggs) travel in a watery medium, sweating has a cooling effect on the body, and urine and tears are mostly made up from water. There is water even in the joints, so that reduces friction when bones move. Even blood is partially made up of water.

Water is also needed by plants, to make leaves turgid, guard cells move by osmosis and water takes part in the chemical reaction in which plants make there food (by photosynthesis). Some seeds germinate with the help of water. Page 4

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5. Minerals
Many minerals are important for our body. There are other trace elements not listed in the table which are useful for other bodily functions.
Fibre is mainly cellulose from plant cell walls. Humans cannot digest fibre, but it is important because it helps food to pass from the gut, and prevents constipation. Food rich in fibre are whole meal bread, bran, cereals, fresh
fruit and vegetables.

Food Tests
Test for Starch: with Iodine solution. If result is positive, a blue-black precipitate forms.
Test for Glucose: with Benedict’s Solution and the mixture is heated. If the result is positive, an orange brown solution forms.
Test for Proteins: with Copper Sulphate and Sodium hydroxide. A purple colour forms if the tested food contains proteins.
Test for Fats: with Ethanol (alcohol) A miillky whiite solution forms in presence of fat.
Test for Vitamin C: with DCPIP. A blue to a collourlless liquid forms in co our ess
presence of vitamin C.

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Enzymes are biological catalysts. A catalyst enhances the speed of a chemical reaction. Thus, enzymes are catalysts, which enhance the speed of the chemical reactions taking place in the body.
Properties of Enzymes
Enzymes are proteins, therefore, they become denatured by heat, which means that when heated above 40oC, they change shape and do not work anymore. When the temperature is lower than normal, enzymes become inactive. Enzymes are specific, which means that every enzyme catalysis only one type of food substance, for example, the enzyme amylase catalysis only starch, and does not take part in any other chemical reaction involving another food substance.

Enzymes do not take part in the proper chemical reactions (they do not react), they just enhance the speed, and this property makes them used over and over again. An enzyme catalysis a reaction involving a substrate; the particular nutrient the enzyme acts on. When the reaction is complete, a product is produced. An example is amylase acting on starch. Amylase, which is an enzyme, acts on its substrate (starch), to produce a product (maltose), which is a simpler type of carbohydrate. The rate of productivity by enzymes is very affected by temperature and by pH. The graph shows the rate of the activity by the enzymes in relation to temperature. The rate increases slowly when the temperature rises between 10oC to 40oC, but when the temperature rises further, activity decrease drastically, because enzymes are being denatured.

The graph here below shows the sensitivity of enzymes to pH. It is a bell-shaped graph, showing that the enzymes work best that at their optimum pH, which in this case is pH 2.
Effect of pH on Enzymes
Effect of Temp. onEnzymes

The Lock and Key Theory
The lock and key theory is how scientists believe
enzymes catalyze their substrate. It is shown in this  Biology Form 4 Notes (2003-2004)2005

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Economic Important of Enzymes
Enzymes can be artificially made and used in Biological washing powders. These washing powders contain enzymes that work at a suitable temperature (e.g. 40oC) and dissolve food stains from fabrics. They are specific to particular stains. Protease is used for tenderising meat and removing hair from hides. Amylase is used to covert starch to sugars to make syrups and juices. Enzyme Inhibitors

There are some poisons, such as cyanide and arsenic that block the enzymes’ active site, therefore the substrate cannot enter the active site and the reaction doesn’t take place. Certain pesticides block the active site of pests’ enzymes so that its respiratory system stops working and the pest dies.

The teeth are made of hardest substance found in the body. Humans have 4 types of teeth:
Incisors: Adapted for cutting food.
Canines: for holing and tearing.
Premolars: For chewing and grinding food.
Molars: For chewing and grinding food.
Humans aged 6 months begin to grow 20 milk teeth (baby) teeth. Once he or she is an adult, 32 permanent teeth will be developed.
The tooth is made up of 2 sections, an exposed Crown and the Root which is embedded in the gum. The enamel (calcium phosphate: CaPO3) is the upper part of the crown. It is very hard. Then beneath it there is the dentin. The tooth is primary made of dentin, which is a substance, similar to bone but harder. The central region of the tooth is the pulp cavity. It contains the pulp, which is composed of connective tissue with blood vessels, nerves etc. the pulp is connected to the blood capillaries, which give nutrients and oxygen to the dental cells.

Tooth decay (dental caries) is caused by bacteria in the mouth which produce acids to digest food stuck in and between the teeth.
To prevent tooth decay, varies activities must be regularly done:

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Brushing teeth with a fluoride toothpaste
Regular visits to the dentist
X-rays of the jaw to ensure that no cavity is being developed where the dentist cannot see
Use tooth floss
Wash mouth with a suitable mouth wash

Herbivores have different a dental system since they eat only vegetable matter. In herbivores, there is a gap called diastema between the incisors and the molars. Instead of the upper incisors, herbivores have a hard pad to pull leaves and grass out of the branches or soil. They have no canines and
molars have a flat surface. Their teeth have an open root, which means that they grow continuously. Carnivores’ molars have cusps, to ensure that food is better chewed. They have canines, and upper incisors, while teeth have a closed root unlike herbivores. The following article shows more clearly the difference between carnivores and herbivore dentition.

Feeding can be divided into 4 types:
1. Saprophytic: Saprophytic organisms such as fungi and some bacteria (called decomposers) that feed on dead decaying matter. Saprophytes are useful to the environment because they recycle nutrients.

2. Parasitic: When parasitic organisms feed on or in another organism harming it.
3. Holozoic (heterotrophic): Animals feed heterotrophically, because they must search for their food. Herbivores eat vegetable matter and have special bodily structures to help them digest cellulose. Carnivores eat meat and are usually predators. Omnivores, such as humans eat both meat and vegetable matter.

4. Holophytic (autotrophic): Plants feed with this type of feeding. They are able to make their own food by photosynthesis.
Holozoic Nutrition
The digestive system can be divided into various stages, but it is basically divided into 5 main stages:
1. Ingestion: food is ate, chewed and mixed with saliva.
2. Digestion: Begins from the mouth by salivary amylase (starch-breaking enzyme) and continues till the duodenum (first part of the small intestine), were enzymes break down food into simpler soluble products (Glucose, amino acids, fatty acids and glycerol), stage by stage, and prepares nutrients for absorption.

3. Absorption: the blood absorbs soluble products in the ileum (second part of the small intestine).
4. Assimilation: the nutrients are then assimilated (taken to) various organs around the body.
5. Defecation (Egestion): Undigested matter such as fibre is egested (moved
out) of the body. [Do not mix excretion with egesting or defecation! Excretion is the removal of waste products made by chemicals reaction within the cells; e.g. excreting urine].

Now the 5 stages will be examined more in detail.
The first stage, ingestion, is the actual eating of food, i.e. using teeth. Digestion
The second stage, digestion begins from the mouth. It is divided into 2 other parts: 1. Physical digestion: teeth crush food to increase surface area for enzyme action to break down food.
2. Chemical digestion: food is mixed with enzymes and digestive juices to breaks down food into the 3 soluble products of digestion. The chemical digestion continues till the duodenum. Chemical digestion also begins in the mouth. When food is mixed with saliva, the enzyme salivary amylase starts breaking down starch into maltose

Chemical Digestion in more detail
Saliva contains salivary amylase, mucus, water and lysozyme (which is also an enzyme) that kills bacteria. The food, after that it is chewed, forms into a bolus, (a ball) of mixed food with saliva that goes down the oesophagus (or gullet). Between the mouth and the oesophagus there is the epiglottis. The epiglottis is a flap that closes so as to prevent food entering the windpipe (trachea). The oesophagus is made up of two layers of muscle cells. On layer is circular while the other runs lengthwise. When they contract and relax, they push down food downwards in a movement called peristalsis. Therefore food does not go down by gravity (astronauts would NOT survive in space if it would!). The food is pushed down to the stomach.

The stomach is made up of layers of muscles that make it twist and squeeze so that food is mixed with gastric juices. There are about 35 million gastric glands that produce gastric juice. Gastric juice contains:

Pepsinogen: an inactive form of pepsin that is then activated by the hydrochloric acid.
Pepsin: digestive enzyme, which breaks down proteins into smaller polypeptides.
Mucus: Protects the stomach wall from being digested by the enzymes (prevention of self-digestion).
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Hydrochloric acid (chemical formula HCl) kills bacteria and provides and acidic, optimum pH for pepsin to work.
After 3 to 4 hours of digestion, food becomes chyme. At intervals it is passed into the small intestine. The first part of the small intestine is called the duodenum. The duodenum receives digestive juices for 3 different places: intestinal wall, pancreas and the liver.

From the intestinal wall, mainly 5 enzymes are produced:
1. Trypsin: breaks down polypeptides into dipeptides.
2. Maltase: breaks down maltose into glucose.
3. Lipase: breaks down fats (lipids are liquid fats) into fatty acids and glycerol. 4. Peptidases: breaks down dipeptides into amino acids
5. Sucrase: breaks down sucrose into glucose
These enzymes are summarised below in the following table:
Enzymes from the


Fatty acids and glycerol

From the liver, the duodenum receives no enzymes, but gets bile. Bile is a green chemical, which helps to break down large fat molecules for lipase to act on it: this process is called emulsification. It has a detergent effect, and it is stored in the gall bladder and it is secreted from the gall bladder to the duodenum through the bile duct. Digestion ends here.

Food has been all broken down into their soluble products, glucose, amino acids, fatty acids and glycerol. They can be now absorbed into the blood stream from the ileum.
The liver
The liver is the largest internal organ in vertebrates. It does the following functions: synthesis of proteins, immune and clotting factors, and oxygen and fat-carrying substances. Its chief digestive function is the secretion of bile, a solution critical to fat emulsion (emulsification) and absorption. The liver also removes excess glucose from circulation and stores it until it is needed. It converts excess amino acids into useful forms and filters drugs and poisons (alcohol, pills etc) from the bloodstream, neutralizing them and excreting them in bile. The liver has two main lobes located just under the diaphragm on the right side of the body.

The Ileum
The ileum is a very long part of the gut so that absorption takes places efficiently. Here, soluble products: glucose, amino acids, fatty acids and enter glycerol enter the blood stream through millions of small finger-like structures called villi. The villi are tiny, to increase surface area for absorption. Each villus is covered with tiny ‘hairs’ called microvilli, that are actual villi but smaller, like root hairs on a root in plants. Villi have a thin lining and a good blood supply to allow blood to absorb the soluble nutrients. Food passes through the intestine with the help of muscular contraction (peristalsis) of the intestinal wall, which is also moist to allow food to pass well and to enhance the speed of absorption.

The villus’s structure is shown here;
Glucose and amino acids are absorbed by the blood capillaries, which are very thin blood vessels. Fatty acids and glycerol, being large molecules are absorbed by the lacteal first before draining into the blood stream.

The Large Intestine
The large intestine is divided into the colon and rectum. The colon is the part where water is absorbed. In the rectum, faeces (undigested food such as fiber) are stored until it is egested out of the body through the anus, within 24-48 hours after eating. The rectum wall is covered with a layer of mucus to ease the passage of faeces. This process is called defeacation.

The Caecum and the Appendix
The caecum and the appendix are vestigial organs, i.e. they do not have any known function in humans. In herbivores called ruminants, (such as rabbits) the caecum and appendix contain cellulose-digesting bacteria that produce the enzyme cellulase to digest cellulose in plant cells.

Digestion in Herbivores
Herbivores such as cows, sheep and horses are called ruminants because they contain a special digestive system. They have a special type of dentition, different from carnivorous dentition, to allow them to extract grass from soil easily. Their small intestine is about 40 meters long, to allow them to digest cellulose completely, before it reaches the end of the gut.

Their gut contains cellulose-digesting bacteria. These bacteria produce the enzyme cellulase that catalysis the reaction that breaks down cellulose into soluble sugar (glucose). The bacteria gain shelter and protection as well as food from the ruminants so their relation is a mutualistic one (both benefiting from one another). These bacterial are housed in the caecum and appendix, so in the ruminants, they are not vestigial organs as in humans.

Ruminants have a special type of stomach called rumen. The rumen is a large stomach that contains 3 other chambers. While the ruminant is grazing, grass is swallowed and enters the rumen. When the animals stops eating, it regurgitates the grass (brings the already swallowed food back to its mouth), little by little to allow it to be chew and swallowed properly and then the food enters into the other 3 chambers to further digest the food before it goes into the small intestine. The following article helps you understand how the ruminant’s digestive system works.

More information about the Liver

Hepatic Vein
Hepatic portal vein
Hepatic Artery
The liver receives blood mixed with the soluble products of digestion from the hepatic portal vein. The liver receives blood rich in oxygen from the heart through the hepatic artery. Then the blood leaves the liver through the hepatic vein which also carries a lot of heat since inside the liver, a lot of chemical reactions occur.

What is Respiration and Why do we need it?
Respiration is a chemical reaction catalysed by enzymes. It takes place in each and every mitochondria of the cells. Respiration is done to obtain
energy needed by the body. For vital functions to take place, the body needs energy. It also needs energy to keep a constant body temperature and to transport chemical messages. Plants need energy for active transport to take place.

Gas exchange
Differences between respiration and breathing:
Respiration is carried out in all cells to obtain energy.
Breathing is the exchange of gases, in case of humans and other organisms, the removal of carbon dioxide and obtaining oxygen.
In large organisms such as mammals, respiratory surfaces are required for gas exchange (breathing, not respiration) to take place efficiently. In humans, like all mammals, lungs are used for this purpose.

There are two types of respiration: Aerobic (oxygen involved) and anaerobic (no oxygen involved).
Anaerobic Respiration
Anaerobic means without oxygen, and thus this type of chemical reaction involves only sugars (obtained from digestion of food). Energy is released by the chemical breaking of bonds in organic molecules (containing carbon) present in sugars and other carbohydrates, obtained from digestion. There is more than one type of anaerobic respiration; it depends on the organism.

One very common type of anaerobic respiration is alcohol fermentation represented in this equation below:

C6 H 12 O6 → 2CO2 + 2C 2 H 5OH + energy ( 210 kJ )

This type of reaction (alcohol fermentation) is done by yeast. As it produces alcohol, it is important for world economy for the production of beer, wine and other alcoholic drinks. Yeast’s most important function is surely in the production of bread. Anaerobic respiration is also important for the economy as certain

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anaerobic bacteria produce lactic acid, which is used to make butter, yoghurt cheese and other dairy products. Some other types of bacteria produce methane gas (CH4), a flammable gas used for cooking and fuelling machinery, lighting, and used in the production of hydrogen, hydrogen cyanide, ammonia, ethyne, and formaldehyde.

Anaerobic respiration takes place in humans as well. During strenuous exercise, blood vessels cannot provide enough oxygen for muscle cells to do proper aerobic respiration; in this case, anaerobic respiration takes place in the muscles. In these reactions, lactic acid (slightly poisonous) is produced and can cause cramps. After the exercise, the lactic acid is converted into carbon dioxide and water by oxygen. This whole process is known as oxygen debt.

Making Bread
This is a simple method to make bread.

Some yeast and sugar and mixed with a little warm water.

After some time, the mixture froths and this indicates that yeast cells are becoming active.

The yeast liquid is mixed with flour, salt and warm water to make the dough.

The dough is then kneaded for a few minutes to ensure that all the yeast and the rest of the ingredients and evenly distributed.

The dough is left in a warm place for fermentation is take place. Yeast produces alcohol and carbon dioxide and this gas causes the dough to rise. After an hour, the dough should have doubled its size.

The dough is baked in a hot oven and yeast cells die. Alcohol, with a low boiling point evaporates almost immediately and the carbon dioxide leaves the bread with small holes inside it.

Aerobic respiration
Aerobic respiration is the respiration, which involves oxygen. An example of aerobic respiration is shown here in this equation:

The enzymes catalyze the oxidation of glucose to form carbon dioxide and water. 2830kJ of energy are released by oxidizing 180 grams of glucose. Energy is stored in the body as ATP (adenosine triphosphate), because glucose alone does not provide energy.

As enzymes catalyse this reaction, it is controlled also by temperature, so when the body temperature rises above 40oC, respiration slows down because heat denatures enzymes.
The lungs
The lungs are the respiratory surface of mammals, birds, reptiles and some amphibians.
Voice box

Pulmonary Artery
Pulmonary Veins
The Air Passage
The air passes through a number of passages before it goes to the bloodstream to be used up. First the air passes through the nose and through the trachea, which is surrounded by rings of cartilage to stay stiff. The nose and trachea have special cells on their walls. There are some cells with cilia; hair-like structures that are continuously beating up and down. These trap germs as well as dust from the air. Another type of special cells in the epithelium of the nose and trachea are the mucus-secreting cells. These have a hole in them from where mucus is secreted. After the trachea, the air passes through the bronchi, bronchioles, terminal

Oxygen and carbon dioxide are exchange in the alveoli by diffusion. Numerous alveoli create a large surface area for gas exchange. Oxygen is carried in the red blood cells (rbc) while carbon dioxide is carried in the plasma as Hydrogen Carbonate (HCO3-) ions.

The alveoli are adapted for gas exchange by a number of factors: 1. They have a thin film of water to ensure good and fast gas exchange by diffusion surrounds the alveoli. In fact, some of this water evaporates and there is always some water vapour in our exhaled breath.

2. Alveoli are surrounded by a lot of blood capillaries
3. Blood capillaries are very thin to allow diffusion.
4. There are many air sacks for a large surface area.

While breathing in, the rib cage moves upwards and outwards, the diaphragm flattens and the volume in the chest increases. Since the volume increases the pressure decreases and the air is drawn into the lungs.

While you exhale, the rib cage moves inwards and downwards, the diaphragm relaxes (dome shaped) and the volume in the chest decreases. Since the volume decreases pressure increases and the air is expelled out of the lungs. Smoking and its Negative Effects

Cigarettes contain 3 harmful chemicals: 1) Tar, 2) nicotine and while it is burning it produces 3) carbon monoxide. Apart from these, the cigarettes contain many other chemicals. Some of these are irritants. Irritants and chemicals that annoy the lungs. Other chemicals are carcinogens; may cause cancer. The smoke produced by the cigarettes is very harmful, it affects the epithelium in two ways: it irritates the goblet cells, making them produce more mucus. Secondly, it slows down, or even stops the beating of the cilia, so that they can no longer sweep out the mucus. Coughing can only clear the build up of mucus in the lungs. This is known as smoker’s cough.

Some diseases caused by cigarettes are bronchitis, emphysema and lung cancer. Bronchitis: This disease results as much of the epithelium is damaged and destroyed by the cigarettes’ smoke and irritants. Germs and irritants penetrate deeper into the lung tissue and so the body’s defence cell move into attack. Their remains, along with the mucus make up phlegm, which must be coughed and spat everyday. Bronchitis causes more than a 1000 deaths every year and it is a disease, which mostly causes loss of workdays.

Emphysema: Emphysema causes the walls between alveoli become torn and broken, while the others left become thicker. This causes the lungs to have a smaller surface area for gas exchange. The sufferer coughs and wheezes and struggles for breath. This illness can cause permanent disability and eventually death.

Lung Cancer: Carcinogenic chemicals (chemicals which can cause cancer) cause lung tissue to divide in an uncontrolled manner. This growth is called a tumour or cancer. The tumour spreads through the lung destroying other healthy tissue. Cancerous cells may go into the bloodstream and secondary tumour may arise. This disease, although it can be treated if detected in the early stages, it is Page 24

usually found too late and the victim dies.
Other Lungs diseases
Pneumonia: Certain bacteria and viruses cause this illness. These cause the alveoli to get filled with fluid and cell debris. Oxygen starvation results since a much of the alveoli block gas exchange.

Tuberculosis (TB): It is cause by a bacillus (pathogenic bacteria). This disease can be treated and cured nowadays. The germs doesn’t do much harm but sometimes, the bacillus may spread out through the lungs causing sever
damage. Dust Diseases: These diseases are caused when large amounts of dust are breath during work. Stonecutters, miners and asbestos workers may catch illnesses such as silicosis, pneumoconiosis and asbestosis respectfully. Special precautions must be taken because once caught, these diseases are incurable. Air Pollution

The air is polluted by mainly 5 different gases: carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen dioxide and ozone. 4 of them are poisonous for the human body, namely carbon monoxide CO, sulphur dioxide SO2, nitrogen dioxide NO2 and ozone O3.

Carbon dioxide CO2 is not a toxic gas in moderate concentrations, but it contributes to global warming, thus it is a greenhouse gas (traps the sun’s heat, causing global temperature to rise, changing climate and endangering animal and plant species). CFC’s (chlorofluorocarbons) although not considered pollutants, convert ozone in the protective ozone (O3) layer back into oxygen (O2), thus it makes a hole in this layer, letting harmful ultraviolet rays from the sun penetrate the atmosphere, causing skin cancer.

Sulphur Dioxide and Nitrogen Dioxide rise from industrial effluent and car exhaust. They are both toxic gases and in order to block nitrogen dioxide from escaping into the air, cars should be equipped with catalytic converters. These devices convert nitrogen oxides and carbon monoxide into carbon dioxide, harmless nitrogen and water, with the help of rare catalysts.

Carbon monoxide is also produced by cars and other burning sources that are not properly ventilated such as gas heaters and fire places in enclosed rooms. It is a harmful gas because it combines with the blood, preventing it from absorbing oxygen. Even in small concentrations it may be fatal.

Certain electrical machinery and photocopiers produce ozone (O3) gas. Although ozone is useful in the ozone layer, which is 20-50 km above sea level, it is highly poisonous and can contribute to acid rain.

Glossary For Half Yearly Terms To Study
Nutrition: the study of food.
Basic Nutrients: The 7 basic food substances that are: Carbohydrates, Fats, Proteins, Vitamins, Minerals, Fibre and Water.
Carbohydrates: 1 of the bulk material of which food is made of. An organic substance from which the body gets energy.
Fats: Made up of fatty acids and glycerol; another bulk material found in food. Proteins:

Substances made up of carbon, hydrogen, oxygen, nitrogen and

sometimes sulphur. Used for growth and repair or tissue.
Vitamins: Organic substances needed in small amounts by the body. Some are coenzymes and other help to prevent illnesses. Minerals: Important substances needed in small quantities to prevent illnesses. Fibre: An insoluble, non-digested substance used to sweep out undigested food out of the body; roughage

Water: Very important chemical; the most abundant compound in the Universe and in the body.
Sugars: Carbohydrates used to get energy.
Glucose: C6H12O6 Final product of digestion of carbohydrates. Fructose: A sugar found in fruit.
Sucrose: Table sugar.
Lactose: Found in milk.
Maltose: Found in barley grains.
Starch: Found in bread, potatoes, rice and cereals. A chemical used by plants to store food; an insoluble polysaccharide.
Monosaccharides: Sugar with one glucose molecule. Fructose is also a monosaccharides.
Disaccharides: Sugars with more than one glucose molecule attached together by bonds.
Polysaccharide: three or more sugar molecules are bonded together; insoluble. Glycogen: The chemical used by animals to store food.
Glycerol: Part of the fat molecule.
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Fatty acid: There are 3 fatty acids in a fat molecule.
Amino Acid: The final product of digestion of proteins.
Peptide bonds: the bond by which amino acids are attached.
Dipeptide: 2 amino acids attached together by peptide bonds. Polypeptides: 3 or more amino acids attached together by peptide bonds. Peptide Bonds: Bonds attaching amino acids together to form dipeptides and polypeptides.

Foods rich in Protein: Meat, eggs, nuts.
Urine: The body’s excretorial waste.
Calcium: Found in Milk, cheese, mineral water; used for growth and repair of bone and cartilage tissue. Prevents rickets; malformed bones. Iron: Found in tomatoes, liver and kidneys. Part of haemoglobin in rbc. Prevents anaemia (tiredness, headaches).

Phosphorous: Found in many foods; important for bones and teeth. Sodium: Found in salt. Prevents cramps.
Iodine: Found in sea food, and drinking water. Helps to prevent goitre. Vitamin A: Found in liver and carrots. Prevents night blindness (exophthalmia). Vitamin D: Found in fish liver oil. Prevents richets.

Vitamin E: Found in milk, egg yolk, lettuce. Prevents sterility. Vitamin K: Found in cabbage, spinach, fish liver. Important for blood coagulation.
Fat soluble Vitamins: Vitamins A, D, E, K.
Water Soluble Vitamins: Vitamins B1, B2, B6, C.
Vitamin B1: Found in Pork, eggs, leafy green vegetables. Prevents beriberi (weakness, irregular heartbeat, partial paralysis)
Vitamin B2: Found in liver, milk, dark green vegetables. Prevents Skin lesions. Niacin (B6): Found in liver, poultry, canned tuna. Prevents pellagra (metal confusion, diarrhoea)
Vitamin C: Found in citrus fruit. Prevents Scurvy. (bleeding gums) Enzymes: Biological catalysts.
Denatured: Proteins like enzymes get denatured by heat (loses its properties). Substrate: The food on which an enzyme acts.
Active site: Where the substrate enters.
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Biological Washing Powders: Washing powders that contain enzymes. Protease: An enzymes used for tenderising meat.
Amylase: Found in saliva and duodenum. Used in industry to convert starch to sugars to make syrups and juices.
Cyanide: Enzyme inhibitor.
Arsenic: Enzyme inhibitor.
Incisors: Teeth adapted for cutting food.
Canines: for holing and tearing.
Premolars: For chewing and grinding food.
Molars: For chewing and grinding food.
Crown: The upper part of the tooth.
Root: The lower part of the tooth.
Dental Caries: Tooth decay.
Cusps: ‘hills’ on the teeth of carnivores and omnivores. Saprophytic: When saprophytic organisms such as fungi and some bacteria that feed on dead decaying matter. Saprophytes are useful to the environment because they recycle nutrients.

Parasitic: When parasitic organisms feed on or in another organism harming it. Holozoic (heterotrophic): Animals feed heterotrophically, because they must search for their food. Herbivores eat vegetable matter and have special bodily structures to help them digest cellulose. Carnivores eat meat and are usually predators. Omnivores, such as humans eat both meat and vegetable matter. Holophytic (autotrophic): Plants feed with this type of feeding. They are able to make their own food by photosynthesis.

Ingestion: food is ate, chewed and mixed with saliva.
Digestion: Begins from the mouth by salivary amylase (starch-breaking enzyme) and continues till the duodenum, were enzymes chemically break down food into simpler soluble products, stage by stage, and prepare nutrients for absorption. Absorption: the blood absorbs soluble products.

Assimilation: the nutrients are then assimilated (taken to) various organs around the body.
Defecation (Egestion): Undigested matter such as fiber is egested (moved out) of the body. [Do not mix excretion with egesting or defecation! Excretion is the removal of waste products made by chemicals reaction within the cells;

excreting urine.
Physical digestion: teeth to increase surface area for enzyme action to break down food.
Chemical digestion: food is mixed with saliva and salivary amylase breaks down some starch from the food (if there is) into maltose. The chemical digestion continues till the duodenum.
Lysozyme: Chemical found in the saliva used to kill bacteria. Oesophagus: Gullet.
Pepsinogen: an inactive form of pepsin that is then activated by the hydrochloric acid.
Pepsin: digestive enzyme, which breaks down proteins into smaller polypeptides. Mucus: Protects the stomach from being digested by the enzymes. Hydrochloric acid (HCl acid): kills bacteria and provides and acidic pH for pepsin to work.

From the intestinal wall:, Mainly five enzymes are produced: Trypsin: breaks down polypeptides into dipeptides.
Maltase: breaks down maltose into glucose.
Lipase: breaks down fates (lipids) into fatty acids and glycerol. Peptidases: breaks down dipeptides into amino acids
Sucrase: breaks down sucrose into glucose
From the pancreas mainly 4 chemicals are produced:
Sodium hydrogen carbonate (NaHCO3): neutralizes acids from the stomach and provides alkaline pH in the duodenum.
Trypsin: breaks down starch into maltose.
Pancreatic amylase: breaks down starch into maltose.
Lipase: Breaks down fats into fatty acids and glycerol.
Liver: The largest and very important internal organ found in the body. Among its functions, it produces bile, breaks down drugs and alcohol, and converts the final products of digestion into glycerol for storage. The liver cells help the blood to assimilate food substances and to excrete waste materials and toxins, as well as products such as steroids, oestrogen, and other hormones. The liver also stores Page 29

iron, vitamin A, many of the B-complex vitamins, and vitamin D. Detoxification: One of the functions of the liver, where the liver breaks down drugs.
Deamination: The destruction of red blood cells so that the body forms new ones. This function is carried out by the liver, in fact, the liver is a source of iron. Duodenum: The first part of the small intestine. It continues digestion of food and it receives enzymes from the intestinal wall
and from the pancreas. It receives bile that the liver produced from the gall bladder.

Gall Bladder: An organ used to store bile.
Bile: A green chemical used for emulsification.
Emulsification: The process by which bile does detergent action on lipids. Fat molecules are too large to be absorbed by the blood so it is broken down into smaller molecules by the bile.
Hepatic Artery: The artery that gives blood from the heart to the liver. Hepatic Portal Vein: The vein that transports blood rich in soluble products of digestion from the ileum to the liver.
Hepatic Vein: The vein that transports blood from the liver to the heart. Ileum: A long part of the gut where digestion stops and absorption starts. Absorption is done by the villi surrounding its walls. It ends in the large intestine. Villi: Small structures found on the walls of the ileum where absorption stakes place. There are millions of them to ensure that all nutrients have been absorbed. Microvilli: Even smaller villi on the large villi in the ileum. Mucus-Secreting Cell: Cells present in the trachea, nose, stomach wall, the intestinal wall and on the epithelium of the villi, also called goblet cells. Epithelium: The first thin layer of cells of the villi and other small structures in the body.

Lacteal: The structure found in the villi that absorbs fat droplets. Venule: The vein that carries amino acids and monosaccharides. They are found in the villi.
Arteriole: The vein that transports blood in the villi.
Appendix: A vestigial organ located the between the ileum and colon. Caesium: Another vestigial organ located near the appendix.
Vestigial Organ: An organ that has no known functions. Vestigial organs found in the body are the caesium and the appendix. Ancient human beings who ate Page 30

mainly vegetable matter probably used these organs. Then, by evolution, these organs ceased from being used. They were home to cellulose-digesting bacteria. Large Intestine: Part of the alimentary canal. It is dividing into the colon and rectum.

Colon: The first part of the large intestine where water and fluid are absorbed. It ends in the rectum.
Herbivores: Vegetable eating animals.
Ruminants: Herbivores with a special type of stomach called a rumen. Cellulose: A cellulose-digesting enzyme produced by certain bacteria found in herbivores.
Mutualistic Relationship: A type of relationship between organisms where both animals are benefiting from each other. An example of such relationships is the relationship between the cellulose-digesting bacteria in the caesium and appendix of ruminants.

Rumen: A large stomach with 3 compartments found in ruminants. Regurgitation: Ruminants bring the food they have already eaten and swallowed back to their mouth to continue chewing it.
Respiration: A chemical reaction catalysed by enzymes where (in case of aerobic respiration) oxygen combines with glucose to form carbon dioxide, water and energy.
Aerobic: A type of respiration where oxygen is involved.
Anaerobic: A type of respiration that does not involve oxygen and doesn’t produce as much energy as aerobic respiration.
Mitochondria/Mitochondrion: An organelle found in all cells that do respiration. Gas exchange: The process where oxygen is absorbed by the blood and carbon dioxide is exhaled out of the body. Don’t mix gas exchange with respiration. Respiration is a chemical reaction while gas exchange is just the exchange of gases.

Organic Molecules: Molecule containing carbon.
Alcoholic Fermentation: A type of anaerobic respiration where alcohol is a product of the chemical reaction.
Lactic Acid: An acid produced in muscle tissues during strenuous exercise when there is lack of oxygen.
Oxygen Dept: When lactic acid is produce, a state called oxygen debt occurs, Page 31

when after exercise the body continues breathing heavily so re gain all the oxygen needed by the muscle cells to break down lactic acid in carbon dioxide and water. Aerobic respiration: A type of respiration where oxygen is involved. An example of this type of respiration is alcoholic fermentation.

Lungs: Major organs in some animals needed for gas exchange. Trachea: Otherwise called windpipe. The second pipe from where air passes and is filtered by cilia and mucus secreting cells. Rings of cartilage to make it stiff surround this structure and so that it doesn’t get bent.

Bronchus: One of the pipes from which air passes before going inside the lungs. There are two bronchi and they are attached to the trachea. Rings of cartilage to make it stiff surround these structures.

Alveoli: Also called air sacks. The place where the actual gas-exchange takes place. Tiny structures surrounded by many blood vessels to ensure that gas exchange takes place rapidly and efficiently.

Pleural Membrane: A thin membrane that covers the inside of the ribs and the outside of the lungs. A film of moisture between the two layers lets them slide easily over each other as the lungs move.

Intercostals: Muscles between they ribs that contract and relax during inhalation and exhalation.
Inhalation: Breathing in.
Exhalation: Breathing out.
Breathing: A series of movements made by intercostals, the rib cage and pectorals to enable the air to get into the lungs. These movements are shown here in this diagram.
Ribs: Bones surrounding the lungs.
Bronchioles: Small pipes from which air passes. These are found inside the lungs. Pulmonary Vein/Artery: Blood vessels from which blood passes from and into the heart. They are connected to the lungs and the heart.

Diaphragm: A muscle present only in mammals to ease inhalation and exhalation. This muscle is found under the lungs.
Plasma: Part of the fluid in blood.
Hydrogen carbonate ions: Carbon dioxide is transported in the blood by this ion. HCO3-.
Blood capillaries: Very, very small blood vessels that surround alveoli. They are Page 32

very thin and tender and are found in many other places in the body. Tar: A chemical found in cigarettes.
Carbon monoxide: A poisonous gas released by lightened cigarettes. Nicotine: Colourless, oily, liquid alkaloid, C10H14N2 that constitutes the principal active chemical constituent of tobacco.
Epithelium: A layer of cells that serves as a protective covering over a surface, such as the outside of an organ or the lining of a cavity wall in the body. Goblet Cells: Mucus secreting cells.
Diseases caused by smoking: Bronchitis, Emphysema and Lung Cancer Other lung Diseases: Pneumonia, TB (Tuberculosis) and Dust Diseases. Poisonous gases in the air: Carbon monoxide, sulphur dioxide, nitrogen dioxide, ozone.

There are mainly 4 organs that help the body to keep a constant body environment: the lungs, the liver, the skin and the kidneys. Lungs
The lungs are responsible to exchange of gases in the body. They exchange carbon dioxide with oxygen from the air. Also, the lungs must provide the oxygen with a temperature of around 37 degress Celsius so that chemical reactions involving oxygen can take place.

The Liver
The liver is a major organ in the human body that makes a large amount of chemical reactions that produce heat (chemical reactions that produce heat are called exothermic).
Therefore, the liver produces all the necessary heat for the body to keep its internal temperature around 37oC.
The skin is responsible for transferring excess heat from inside the body to the outside environment. For that reason it is one of the organs that does homeostasis. It also protects the body from germs.

The kidneys are responsible for osmoregulation, i.e. to control the amount of water in the body, by filtering blood from salts, water and waste products (urea). Blood is involved and so the kidneys are also part of homeostasis, because blood transports heat and helps to keep the body at a constant temperature.

The Excretory System
The excretory system is the system responsible for the disposal of waste material produced by the body –Urine. The major organs in the excretory system are the kidneys. The body can survive with just one kidney, but with none, the person must use the kidney machine (explained in the following pages) or else he or she dies. The function of the kidneys is to filter blood from urea (waste produced by chemical reactions in the body) excess water, and excess salts. This process is called ultra-filtration and it is done by nephrons (explained further in the following pages)

The Kindey
The diagram below shows the kidneys, the bladder and blood vessels connected to it.

Renal Vein: The vein that transports blood OUT OF the kidneys. Blood in the renal vein is deoxidized or reduced (without oxygen) and filtered by kidneys, thus it is clean.
Renal Artery: The artery that transports blood INTO the kidneys. Blood in the
renal artery is full of oxygen but also full of waste (urea and salts) thus it has to be filtered.

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Ureters: Carry urine (urea, excess water, excess salts) into the bladder. Bladder: The structure, which stores urine before it is excreted out of the body. Ring of Muscle: A ring of muscle that is kept closed before one goes to the toilet to excrete the urine. They control the passage of urine out of the body. Urethra: The last structure from which urine passes before going out of the body. Renal Vein

Renal Artery

Right Kidney

The nephron is the structure, half inside a pyramid and the other half inside the cortex, where blood is filtered (ultra-filtered) from urea, excess water and salts. The structure of the nephron is shown above.

Blood in the renal artery is oxygenated and with urea.
Glomerulus: A network of blood capillaries.
Selective re-absorption: Not everything is re-absorbed at once, but every tubule re-absorbs a particular nutrient.
The renal artery is wider than the blood vessel through which it moves out. This increases pressure in the glomerulus. The pressure causes some constituents of blood to leak out of the capillary tube.

The filtrate contains glucose, urea, water and salts. Proteins and Erythrocytes (red blood cells) are too large and they don’t pass through the capillary walls. This filtration takes place on a microscopic scale. It is known as ULTRAFILTRATION. This takes place in the Bowman’s capsule. The First Coiled Tubule: Here, all the glucose that passed from the capillary walls to the nephron is re-absorbed. In a diabetic person, not all glucose is reabsorbed and it is found in Urine. Since each part of the nephron re-absorbs the useful nutrients one at a time, it is called a selective re-absorption. Loop of Henle: Here some water is re-absorbed. The amount of water re-absorbed depends on the concentration of blood. If it is concentrated (has little water), a lot of water will be re-absorbed. If it is not that concentrated it will re-absorb less Page 37

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water. The amount of water re-absorbed also depends on a chemical called ADH (Anti-diuretic hormone). ADH is produce by the pituitary gland in the brain and causes thirst; hence, more water will be re-absorbed by the loop of henle. When there is a lot of ADH, urine is full of waste and with relatively few water. When ADH is not found in the blood, urine is in large amounts, very dilute (full of water) and with few waste.

Second Coiled Tubule: Here some salts (Na+, Cl-) are re-absorbed. Collecting Duct: Here, urea, water and salts pass down the ureter into the bladder which stores urine. Urine is a mixture of urea, water and salts. Constituents of Blood and Urine

The Skin

The skin is the organ responsible for: Protection, Sensitivity, and Temperature Control (Homeostasis).
As a Protective Organ
The skin acts as a barrier against foreign bodies (germs). In some animals, it has the same colour as its surroundings (camouflage), other animals are covered in spines or produce an oil to make it water proof.

As a Sense Organ
The skin contains many receptors or sense organs (heat receptors, cold receptors, pressure receptors, pain receptors, touch receptors) and these make the skin sensitive.
As the Organ which Controls Temperature
Warm blooded animals are called Endothermic or homoeothermic (warmblooded). This means that they have a constant body temperature. Some animals have blubber (thick fat layer) under their skin to keep warm in very cold weather; e.g. Penguins, polar bears)

Ectothermic or poikilothermic (cold-blooded) animals have their internal temperature controlled by their surroundings. In fact, some reptiles (cold-blooded animals) stay long hours in the sun to heat up their bodies. The Human Skin

The diagram below shows a cross section of the skin. The human skin has 3 layers: the epidermis (made up of dead cells) the dermis (where there are the major living cells and nerves) and the fat layer (full of fat for insulation).

Sweating (oil glands produce sweat that Shivering takes Place (uncontrolled passes through the sweat duct and constriction of muscles)
evaporates through the sweat pore)
Hair erector muscle relaxes and hair is Hair erector muscle contracts and hair loosened and touches with skin so that no erects so that air and heat is trapped heat and air is trapped.

Aorta: The largest artery found in the body. It receives oxygenated blood from the heart and then divides into many arteries all around the body. Vena Cava: The largest vein found in the body. It transports de-oxygenated blood to the heart from the rest of the body. De-oxygenated blood is then transported to the lungs to be oxygenated.

Atrium: One of the upper chambers of the heart.
Tricuspid valve: A valve that lets blood to pass from the right atrium to the right ventricle.

Ventricle: one of the lower chambers of the heart.
Bicuspid valve: the valve that lets blood to pass from the left atrium to the left ventricle.
Pulmonary Vein: The vein that carries oxygenated blood to the left atrium. Semi-lunar valves: the 2 valves which let blood pass from the lower ventricle to the aorta and the pulmonary artery.
Pulmonary Artery: The artery that carries deoxygenated blood from the heart to the lungs.
Tendon: Special fibres in the heart muscle.
A Double circulation
This diagram shows the double circulation of the blood. The arteries are on the right hand side of the diagram while the veins are on the left hand side.

The following table shows the various blood vessels of the body, their route and function.

blood from the body tobthe right atrium of theb heart.
The Difference between Arteries and Veins
The main difference between arties and veins is that arteries carry blood from the heat to all the other tissues in the body while veins carry blood from the body to the heart. Usually, veins carry deoxygenated blood and arteries carry oxygenated blood. One exception is that the pulmonary artery carries deoxygenated blood from the body to the heart and the pulmonary vein carry oxygenated blood from the heart to the lungs. Veins have valves so that blood goes in the right direction; arteries don’t have valves because blood flows with a lot of pressure inside the arteries and backflow of blood is impossible. Arteries have a thin lumen (inner structure of the blood vessel, where blood passes) because blood flows with a high pressure and the walls have to be wide, while veins have a wide lumen.

Blood is the main fluid found in the body. The functions of blood are the following: •

The fluid that carries all the nutrients and oxygen around the body to all cells

Controls the amount of water and chemicals in the body tissues

The body has about 6 litres of blood (9% body mass). There are 4 blood groups in humans, namely A, B, O and AB (rarest) Blood is made up of Erythrocytes (Red Blood Cells), Leucocytes (white blood cells), and Plasma.

Erythrocytes (red-blood cells)
Erythrocytes are numerous, have no nucleus and have a bi-concave shape (for a larger surface area) to carry oxygen (O2) more efficiently.
Red-blood cells are made in the bone marrow and their life span is about 4 months. Deamination (taking away iron from the red-blood cells, hence, destroying them to be replaced by new ones) takes place in the liver.

Erythrocytes contain haemoglobin that when it is oxygenated, haemoglobin becomes oxyhaemoglobin. Carbon dioxide travels in the plasma as (hydrogen carbonate ions) HCO3- ions. This also helps erythrocytes to carry O2.

Carbon monoxide (CO) combines with the haemoglobin 300 times faster than O2, thus it is very harmful. This gas is produced by cigarettes and burning of fuels such as in cars.
People living in high altitudes have a greater number of Erythrocytes since less oxygen is present in the air. Their body has adapted to the environment. This is known as acclimatization.

These two diagrams above show erythrocytes, viewed from the front and a cross section.
Leucocytes are lager than Erythrocytes. They‘re colourless, and are made in the red bone marrow and the lymph glands. There are various types of leucocytes: Phagocytes and Lymphocytes are two of these types.

Phagocytes engulf the germs, which leaves remains of dead germs and leucocytes called pus. The process by which phagocytes engulf germs is similar to the way amoebas feed and is known as phagocytosis.

Lymphocytes produce antibodies, detect the germ’s antigen and it can either make the germ burst, or clump together, or make them harmless.
Platelets are Fragments of cells also found in the blood.

Plasma is a sticky fluid, containing water, salts, food substances, urea, hormones, platelets, prothrombin, blood proteins, fibrinogen (for blood clotting), globulin (helps to destroy germs), albumin (makes blood thick and viscous).

Blood Clotting
When a blood vessel is damaged, platelets enter the wound. Platelets activate prothrombin into thrombin. Then thrombin activates fibrinogen into fibrin, which is insoluble and forms solid threads that forms the cloth.

Hemophilia is a genetic disease where blood fails to clot.
Tissue Fluid
Tissue fluid is a liquid found around cells. This watery liquid keeps the cells in the right condition, providing them with oxygen and all the necessary nutrients. Tissue fluid is drained from blood capillaries. It is a yellowish in colour because it contains urea when it is full of waste.

Useful substances pass from the tissue fluid to the cells and urea, excess
water and waste substances pass from the cells to the tissue fluid.
Tissue fluid drains in the lymph vessels. Lymph vessels transport the fluid called lymph. Lymph vessels also have valves like veins do.
Along these lymph vessels, there are lymph nodes. Lymph nodes are structures that produce cells similar to white blood cells that fight germs. When there is an infection, these lymph nodes become swollen and painful. Inside them, bacteria and germs are being trapped and killed by these cells.

What is Photosynthesis?
Photosynthesis is a chemical reaction in which carbon dioxide and water is changed to glucose by the action of chlorophyll and with sunlight energy.

Water goes upwards from

Photosynthesis is performed by plants, green algae, and plant-like protists such as the Euglena. To photosynthesize, a plant, or other heterotrophic organism, needs Carbon dioxide, water, light and chlorophyll.

Plants store food as starch. Thus, after producing glucose, the plant transforms glucose into starch, which is an insoluble polysaccharide, to be stored. Glucose goes down the stem towards the roots in the Phloem vessels in the vascular bundles, while water goes upwards the stem from the roots through the xylem vessels in the vascular bundles.

To find out if the plant has performed photosynthesis, you must do a starch test on a leaf. If the leaf has starch, then it must have photosynthesized but if the leaf has no

starch, that means the plant has not photosynthesized and it used up all the starch it had in the leaf to stay alive.
Testing a Leaf for Starch
1. Cut a leaf from a plant and boil it in a beaker with water to soften it. 2. Dip it in alcohol (ethanol) to decolorize it. The leaf must be put in a boiling tube dipped in warm water. Don’t heat up the boiling tube with alcohol because it is flammable.

3. Put the decolorized leaf again in the warm water to soften it again. 4. Put the leaf on a white tile and add two drops of iodine on the leaf. Results for Iodine test
If the iodine turns blue-black, then the leaf has starch, hence it has photosynthesized. De-starching
De-starching occurs when the plant doesn’t make any photosynthesis (e.g. because it is in the dark) and so the plant uses its stored starch stored for energy. It turns starch into glucose and uses it up.

The Importance of Photosynthesis
Photosynthesis is the process in which plants get the energy from. Without it, plants wouldn’t exist. Thus photosynthesis is indirectly useful for other animals, which eat plants.
Photosynthesis releases oxygen as a by-product of its reaction. Oxygen is used by almost all living organisms for the breakdown of glucose and release of energy.

Inside a Leaf
Photosynthesis happens in plants, exactly in the chloroplasts that are found
in leaves. The green part of the plant is usually the leaf, and this is because chloroplasts have a special green chemical called chlorophyll that converts sunlight into chemical energy.

The following picture shows a cross section of a typical leaf.

The waxy cuticle is the uppermost part of the leaf. It makes the leaf waterproof and protects the leaf from losing water. It is transparent.
The upper epidermis is the second layer of the leaf, but the first layer that is made up of living cells. The cells in this layer don’t have chloroplasts, so that light passes directly into next layer;

The palisade layer is a thick layer of elongated cells packed with chloroplasts. It is here that most photosynthesis takes place.
The spongy layer is characterized by air spaces between the cells, so diffusion of gases takes place efficiently, as photosynthesis uses carbon dioxide and produces oxygen. The cells in the spongy layer also have chloroplasts. The palisade and the spongy layer are made up of cells called
mesophyll cells. The lower epidermis is similar to the upper epidermis, with the cells making it up that don’t have chloroplasts, but this layer has stomata; tiny holes from which exchange of gases takes place. Stomata are surrounded by two guard cells, which are the only cells in the lower epidermis that have chloroplasts. These cells have thin cell walls on the outer side but wide cell walls on the inner side.

In the leave there are also vascular bundles (plant veins) that are made up of xylem and phloem vessels. Water and soluble minerals pass from the xylem vessels while sugars pass from the phloem vessels.

How are leaves adapted for photosynthesis
Leaves have numerous adaptations to ease photosynthesis.
They have a large surface area, for absorbing light and carbon dioxide. Leaves are arranged so that they don’t over-shadow each other, and all of them receive light.
They have a lot of stomata in the lower epidermis for gas exchange, carbon dioxide gets in and oxygen does out while photosynthesis takes place. Leaves are thin to allow fast diffusion of carbon dioxide.

The waxy cuticle and epidermis are transparent to allow light passage
throughout the leaf.
The place were most photosynthesis takes place; the palisade layer, is found near the upper side of the leaf, were most of the light comes. The palisade layer is made up of palisade mesophyll cells, which are packed with chloroplast, and these organelles move around the cell so as to find the best position to find light.

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There are air spaces around the spongy mesophyll cells to allow gas circulation.
Glucose and sugars
In the chemical reaction of photosynthesis, glucose and other sugars are produced. With these, the plant can do a number of things:
1. Respiration: like any other living thing, plants need energy. Plants and animals do this my oxidizing glucose in the process called respiration, releasing water and carbon dioxide.
2. Translocation: this means that the excess sugars produced by the leaves are transported into other parts of the plant, through the phloem vessels, that cannot make photosynthesis, such as roots, to supply their needs. 3. Production of cell material: from sugars, the plant can make other important chemical and material such as proteins, fats and oils. In order to make some of these materials, the plants must also have other minerals absorbed from the soil such as nitrogen, sulphur and potassium. For instance, the plant must have a supply of nitrogen in order to produce proteins.

4. Conversion to starch: Enzymes in the plant convert glucose into starch. This is done so that glucose can be stored. Since glucose is soluble, it cannot be stored; it can only be used straight away or transported. Thus the plant converts it into starch, which is insoluble and stores it. Starch is stored in special storage organs, which are formed by part of the plant
swelling up. These storage organs can be formed in roots, leaves or stems. When energy is needed and no glucose is formed by photosynthesis, such as when it is dark, the chain of glucose molecules, which makes starch, uncoils back into single glucose molecules in a process called hydrolysis. When a plant performs hydrolysis, starch is mobilised, which means it can now be moved or transported in a solution since glucose is water-soluble.

5. Storage in germination structures: the plant stores some food for the next generation by storing starch or fat in their seeds and fruits. When a seed germinates, food passes from the seed to the new growing plant until it can make its own food by photosynthesis. Some plants store food in tubers or bulbs that can also germinate.

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Important Minerals for Plants
As mentioned above, apart from carbon dioxide and water, the plant needs other substances important for the formation of other material. Some minerals needed by plants are listed here.

If the soil is deficient in some of these important nutrients, one must add fertilizers in order to replenish the soil with vital minerals. Fertilisers can be either artificial, such

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as NPK (Nitrgen, Phosphorous, Potassium), super phosphates or natural, such as humus and manure. These increase crop yield, however, they are expensive and can decrease soil fertility in the long run.

Important terms in Botany
Water cultures: A full water culture is a solution, which has all the necessary minerals so that a plant to grow healthy.
Hydroponics: It is the method to grow plants without soil; in fact, it is sometimes called soil-less culture. Plants are grown with water cultures. Some advantages that this method has are that the crop yield is increased and the soil doesn’t have to be fertilized each year.

Limiting Factors
Limiting factors stop the rate of photosynthesis from increasing further. The rate of photosynthesis is affected by water, temperature, level of carbon dioxide, and light. The relationship between each and every one of these factors and photosynthesis are described below:

If light increases, photosynthesis increases.
If water is plenty, photosynthesis increases.
If carbon dioxide is plenty, photosynthesis increases.
When temperature increases photosynthesis increases, up to a certain point, or else, above 35oC, photosynthesis halts completely in most plants. Despite this, when one factor is increasing, the other factors cause the rate of photosynthesis to stay constant anyway. This is shown in the graphs below:

The first organism in a food chain is always a producer. Producers make their own food from the sun by photosynthesis. Plants are an example of a producer. The other organisms in the chain are called consumers because they consume (eat) the organism before them. The first consumer is called the primary consumer, then there is the secondary consumer and so on. The last
organism in a food chain is always called the top carnivore.

The primary consumer is always a herbivore because it eats plants or another producer. The secondary consumer is a carnivore because it eats other animals. If an organism eats both plants and animals, then it is called an omnivore. The arrows in the food chain represents the flow of energy or the phrase is eaten by. The ultimate source of energy is always the sun, but it is usually not included in a food chain.

More often than not, an organism doesn’t eat only one type of food, i.e. any animal eats more than one species of organism. In order to represent this situation, a food web is produced. A food web is a collection of food chains mixed together to get a clearer picture of what animals eat what. An example of a food web is given here below.

A food web gives us more information about the feeding of animals than food chains. Despite this though, it doesn’t give us the number of organisms involved. To show the number of organisms involved in a food chain, a Pyramid of Numbers. The first (bottom) layer in the pyramid is always the producer. Then following it are the primary consumer, then the secondary and so on. Two examples of a pyramids of numbers are shown here below.

In order to show the dry mass of the organisms in a food chain, a Pyramid of biomass is produced.

hen energy flows from one organism to the other, some energy is always lost; That is the pyramid of biomass is always the shape of normal upright pyramid instead as shown in the above diagram.

Short note on Xylem and Phloem Vessels
Plant veins are called vascular bundles. These are present in the leaves, in the stem and in the roots; it is the important for the transport of materials throughout the plant. The vascular bundles are made up of two vessels namely the Xylem and the Phloem vessels. The xylem vessels carry water and minerals up from the roots to the leaves while the phloem vessels carry sugars solutions from the leaves to the rest of the plants.

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