LECTURE 4: NUTRITION IN HUMAN BEINGS (CLASS X)

CLASS X   |    SCIENCE    |    LIFE PROCESSES

      Notes prepared by Subhankar Karmakar

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• HUMAN DIGESTIVE SYSTEM

The various organs of the human digestive system in sequence are:

Mouth, Oesophagus, Stomach, Small Intestine and Large Intestine. The glands which are associated with the human digestive system and form a part of the human digestive system are : Salivary glands, Liver and Pancreas. 

• Alimentary Canal:

Human alimentary canal which runs from mouth to anus is about 9 metres long tube. The ducts of various glands open into the alimentary canal. 

• 1. INGESTION

The organ for human ingestion is called mouth.

• 2. DIGESTION 

In human beings, digestion of food begins in the mouth itself. 

• A. Buccal Cavity:

The mouth cavity is also known as buccal cavity. It contains teeth, tongue and  salivary glands. The teeth cut the food, chew and grind it. Tongue mixed the small pieces of food mixed with saliva. Saliva contains an enzyme called Salivary Amylase, which converts Starch into sugar. Hence, Salivary glands helps chemical digestion by secreting enzymes. But due to short period of time the digestion remains incompleted. 

• B. Oesophagus

The food pipe is known as oesophagus. It carries food to the stomach. 

• Peristaltic movement
• The walls of the food pipe/oesophagus have muscles which can contract and expand alternatively. When slightly digested food enters the food pipe, the walls of the food pipe start contraction and expansion movements. This contraction and expansion movements of the food pipe walls are known as  peristaltic movement. 
• Peristaltic movement moves the food in all digestive organs throughout the alimentary canal. 

• C. Stomach
• Stomach is a J shaped organ present in the left side of the abdomen. Here food is broken down into a semi-solid paste. 

• Gastric Juice

Stomach wall contains three tubular glands which secrete gastric juice. The gastric juice contains hydrochloric acid, the pepsin enzyme and mucus. The gastric juice is acidic in nature. 

• Function of Pepsin enzyme

In the acidic medium pepsin breaks down the proteins into smaller molecules, often into amino acids. Therefore, the digestion of proteins start at stomach. 

• Function of Hydrochloric acid

Pepsin is only activated in an acidic medium. The function of the Hydrochloric acid in stomach is to make the gastric juice acidic, so that pepsin can start digesting proteins molecules. Another function of the hydrochloric acid is to kill any bacteria that may enter into the stomach through the food. 

• Function of mucus

The mucus helps to protect the stomach walls from its own secretion of hydrochloric acids. If mucus is not secreted, hydrochloric acid will cause the erosion of the inner lining of stomach leading to the formation of ulcers in the stomach. 

• Sphincter Muscle

The partially digested food from stomach passes to the small intestine. The exit of food from stomach is regulated by a gate called sphincter muscle which releases it in small amounts into the small intestine. 

• D. Small Intestine

The small intestine is the largest part of the alimentary canal of about 6.5 m long in an adult man. It is very narrow hence, it is called small intestine. It is arranged in a coil form. The small intestine in human beings is the site of complete digestion of food like carbohydrates, proteins and fats. 

Difference in small intestine in Herbivores and Carnivores

Herbivores eat cellulose which is difficult to digest. Hence, herbivores have longer small intestine, whereas carnivores eat meat which is easier to digest so they have relatively shorter small intestine. 

Secretions from two glands in small intestine: Liver and Pancreas

• Liver : Liver is a gland that secretes bile. Bile is a greenish yellow liquid made in the liver and stored in the gall bladder. Bile is alkaline in nature and conatains salts which helps to break the fats/ lipids present in the food. 

Functions of Bile

Bile performs two functions. 

• (i) it makes the acidic food coming from the stomach alkaline so that pancreatic enzymes can act on it.
• (ii) Bile salts break the fats present in the food into small globules so that enzymes can act and digest it. 

• Pancreas

Pancreas is a large gland which lies parallel to and beneath the stomach. Pancreas secretes pancreatic juice which contains digestive enzymes like pancreatic amylase, trypsin and lipase. 

Pancreatic amylase breaks down the starch.

Trypsin digests the proteins and lipase breaks down the emulsified fats. 

Functions of intestinal juice

• The intestinal juice contains many enzymes which converts complex carbohydrates into glucose, proteins into simple amino acids and fats into fatty acids and glycerol all of which are water soluble small molecules. 
• The chemical digestion of food is brought about by biological catalysts called enzymes. 

• 3. ABSORPTION

• The small intestine is the main region for the absorption of digested food. After digestion, the molecules become so small that they can pass through the walls of the small intestine which contain blood capillaries and go to our blood. 
• The inner surface of small intestine has millions of tiny finger like projections called villi.  The presence of villi gives the inner walls of small intestine a very large surface area which helps in the rapid absorption of digested food. 

• 4. ASSIMILATION

• The blood carries the digested food to all the parts of the body where it becomes assimilated as part of the cells and it is used by the body cells for obtaining energy as well as for growth and repair of the body. 
• The unused part of the food is stored in the liver in the form of a carbohydrate known as glycogen. The stored glycogen can be used when it is needed. 

• 5. EGESTION

• A part our food which can not be digested passes from small intestine to a wider tube which is called large intestine. It is called large as it is wider. 
• The walls of the large intestine also have villi which absorb most of the water from the undigested part of the food and hence, it becomes solid. 
• The last part of the large intestine is called rectum which stores the undigested food for some time and then be expelled from our body as stool. This process is known as Egestion or defecation and it is controlled by anal sphincter. 

Dental Caries

1. The hard, outer covering of a tooth is called Enamel. It is harder than bones. 

2. The part of tooth below enamel is called Dentine. Dentine is similar to bone. 

3. Inside the dentine, there is pulp cavity, which contains nerves and blood vessels. 

4. Formation of small cavities in the teeth due to the action of acid forming bacteria and improper dental care is called dental caries. 

5. If the teeth are not cleaned regularly, they become covered with a sticky, yellowish layer of foid particles and bacteria cells called dental plaque. 

Extra Notes:

The long, tube-like organ that is connected to the small intestine at one end and the anus at the other is called large intestine. The large intestine has four parts: cecum, colon, rectum, and anal canal. Partly digested food moves through the cecum into the colon, where water and some nutrients and electrolytes are removed. The remaining material, solid waste called stool, moves through the colon, is stored in the rectum, and leaves the body through the anal canal and anus. 

POLYATOMIC IONS

POLY-ATOMIC IONS

Ions that contained atoms of more than one element is known as poly-atomic ions.

Polyatomic ions are ions that are composed of two or more atoms that are covalently bonded together, and they carry an overall electric charge. These ions can be either positively or negatively charged, and they play an important role in chemistry and biochemistry.

Some examples of commonly encountered polyatomic ions include sulfate (SO₄^-2), nitrate (NO₃^-), carbonate (CO₃^-2), ammonium (NH₄⁺), and phosphate (PO₄^-3).

Polyatomic ions are often involved in chemical reactions, where they act as reactants, products, or catalysts. For example, sulfate is often used as a reactant in the production of fertilizers, while phosphate is a key component of DNA and ATP (adenosine triphosphate), which is the primary energy source for most biological processes.

Polyatomic ions are also important in the context of acid-base chemistry, as they can act as either acids or bases depending on the situation. For example, nitrate can act as a base in the presence of a strong acid, while ammonium can act as an acid in the presence of a strong base.

Overall, polyatomic ions play an important role in many areas of chemistry and biology, and a good understanding of their properties and behaviors is essential for anyone studying these subjects.

NAME	SYMBOLS	VALENCY
HYDROXIDE	OH	-1
ACETATE	CH₃COO	-1
CYANIDE	CN	-1
CHLORATE	ClO3	-1
CHLORITE	ClO2	-1
NITRATE	NO3	-1
NITRITE	NO2	-1
SULPHATE	SO4	-2
SULPHITE	SO3	-2
PHOSPHATE	PO4	-3
PHOSPHITE	PO3	-3
PERMANGANATE	MnO4	-1
HYDROGEN CARBONATE	HCO3	-1
CARBONATE	CO3	-2
SILICATE	SiO3	-2
CHROMATE	CrO4	-2
DICHROMATE	Cr2O7	-2
AMMONIUM	NH4	+1

Examples of Compounds having hydroxide (OH) ions

 

Compound Name	Formula	Uses
Sodium Hydroxide	NaOH	It is also called Caustic Soda. Used in manufacturing of paper, textiles, soaps etc.
Potassium Hydroxide	KOH	Used in the manufacturing of soaps and detergents.
Calcium Hydroxide	Ca(OH)2	It is also called Slaked Lime. Used as a construction materials.
Aluminium Hydroxide	Al(OH)3	Used in Antacid to neutralize acidity in stomach and treat ulcers.
Magnesium Hydroxide	Mg(OH)2	Used in Antacid to neutralize acidity and indigestion, heartburn.
Ammonium Hydroxide	NH4OH	Used in as Cleaning agent.
Barium Hydroxide	Ba(OH)2	Used in the production of Lubricants.

 

Examples of Compounds having Acetate (CH₃COO) ions

 

Compound Name	Formula	Uses
Sodium Acetate	CH3COONa
Acetic Acid	CH3COOH

 

Examples of Compounds having Cyanide (CN) ions

 

Compound Name	Formula	Uses
Potassium Cyanide	KCN
Hydrogen Cyanide	HCN

 

Examples of Compounds having Chlorate (ClO₃) ions

 

Compound Name	Formula	Uses
Potassium Chlorate	KClO3
Barium  Chlorate	Ba(ClO3)2
Calcium Chlorate	Ca(ClO3)2
Iron(III) Chlorate	Fe(ClO3)3
Zinc Chlorate	Zn(ClO3)

EXAMPLE: SOME COMMON COMPOUNDS CONTAINING HYDROXIDE IONS

Sodium Hydroxide NaOH

Potassium Hydroxide KOH

Calcium Hydroxide Ca(OH)₂

Aluminium Hydroxide Al(OH)₃

Acetate      (CH₃COO) (-1)

Sodium Acetate CH₃COONa

Cyanide.  (CN) (-1)

Potassium Cyanide KCN

Hydrogen Cyanide HCN

Chlorate (ClO₃) (-1)

Potassium Chlorate KClO₃

Chlorite (ClO₂) (-1)

Nitrate.    (NO₃) (-1)

Nitric Acid HNO₃

Potassium Nitrate KNO₃

Sodium Nitrate NaNO₃

Nitrite.     (NO₂) (-1)

Nitrous Acid HNO₂

Sulphate (SO₄) (-2)

Sodium Sulphate Na₂SO₄

Barium Sulphate BaSO₄

Zinc Sulphate ZnSO₄

Copper Sulphate CuSO₄

Sulphite.  (SO₃) (-2)

Phosphate (PO₄) (-3)

Phosphite. (PO₃) (-3)

Permanganate (MnO₄) (-1)

Hydrogen Carbonate (HCO₃) (-1)

Carbonate (CO₃) (-2)

Silicate (SiO₃) (-2)

Chromate (CrO₄) (-2)

Dichromate (Cr₂O₇) (-2)

Aluminate (AlO₃) (-3)

Ammonium (NH₄) (+1)

LECTURE 2: CHEMICAL EQUATIONS (CLASS X)

CHEMICAL EQUATIONS

The method of representing a chemical reaction with the help of symbols and formula of the substances involved in it, is known as a chemical equation. 

REACTANTS

The substances which take part in a chemical reaction are called reactants. 

The reactants are always written on the left hand side in an equation with a plus sign (+) between them. 

PRODUCTS

The new substances produced as a result of chemical reaction are called products. 

The products are always written on the right hand side in an equation with a plus sign (+) between them.

The arrow sign (→) is put in between the reactants and the products and always directed from left to right. 

A chemical equation is a short-hand method to represent a chemical reaction. 

TWO WAYS TO WRITE A CHEMICAL EQUATION

1. UNBALANCED CHEMICAL EQUATIONS. 

2. BALANCED CHEMICAL EQUATIONS. 

UNBALANCED CHEMICAL EQUATIONS

An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products. 

Example:  H₂ + O₂ → H₂O

H atoms in Reactants = 2, in Products = 2

O atoms in Reactants = 2, in Products = 1

BALANCED CHEMICAL EQUATIONS

A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. 

Example: Zn + H₂SO₄ → ZnSO₄ + H₂

Zn atoms in Reactants = 1, in Products = 1

H atoms in Reactants = 2, in Products = 2

S atoms in Reactants = 1, in Products = 1

O atoms in Reactants = 4, in Products = 4

BALANCING OF CHEMICAL EQUATIONS

The process of making the number of different types of atoms equal on both the sides of an equation is called balancing of chemical equation. 

(Steps are to be discussed in the class)

How to make a chemical equation more informative?

The chemical equation can be made more informative in three ways.

1. By indicating the physical states of the reactants and products.

2. By indicating the heat changes taking place in the reaction.

3. By indicating the conditions under which the reaction takes place. 

1. To indicate the Physical States of the Reactants and Products in an Equation.

We write 

For solids (s) , 

for liquids (l), 

for gas (g), 

for water solution or dilute (aq), 

for evolving gas ↑, 

for precipitates (insoluble solid product) ↓, 

Like 

Zn (s) + H₂SO₄(aq) → ZnSO₄ (aq) + H₂ (g) ↑

2. To indicate the heat changes in an equation

EXOTHERMIC REACTION

Those reactions in which heat is evolved are known as Exothermic Reactions.

Q. When calcium hydroxide reacts with carbon dioxide, white calcium carbonate precipitates and hydrogen gas evolved. Write the chemical reaction.

Ans. Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s)↓ + H₂O (l)

Q. What happens when we burn Methane ? Write its chemical reaction. 

Ans. When Methane (natural gas) burns in the presence of Oxygen from air, Carbon Dioxide and Water is formed along with a large quantity of heat. 

CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (l) + Heat energy

Burning of natural gas is an exothermic reaction. Infact, all combustion (burning) is exothermic reaction. 

Q. What happens when respiration takes place?

Ans. When glucose undergoes a slow combustion by combining with oxygen in our cells to produce energy in a process called respiration, carbon dioxide along with water and Energy is produced. 

C₆H₁₂O₆ (aq) + 6O₂ (g) → 6CO₂ (g) + 6H₂O (l) + Enegy

Hence, Respiration is aalso an Exothermic process as energy is produced during the reaction. 

Q. Write the chemical equation of burning of Magnesium wire in air. Is it an exothermic process?

Ans. When Magnesium wire burns in wire, Magnesium Oxide is produced along with heat and light energy. Hence, it is an exothermic reaction. 

2Mg (s) + O₂(g) → 2MgO (s) + Heat Energy + Light Energy

Q. Fill in the blanks

Decomposition of vegetables into  compost is an example of ___________ reaction.

Ans. Exothermic

ENDOTHERMIC REACTION

Those reactions in which heat is absorbed are known as Endothermic reactions. 

Q. What happens when Nitrogen and Oxygen are heated to a very high temperature? What type of reaction it is?

Ans. When Nitrogen and Oxygen are heated to a very high temperature it forms Nitrogen monoxide which is an endothermic reaction. 

N₂ (g) + O₂ (g) → 2NO (g)

"All the decomposition reactions are endothermic as they need energy to start the reaction"

(i). Like the decomposition of Calcium Carbonate is an endothermic reaction. 

(ii). Photosynthesis is also an endothermic reaction. 

(iii). Electrolysis of water to form hydrogen and oxygen is also a decomposition reaction. 

3. To indicate the conditions under which the reaction takes place. 

{If heat is required for a reaction to take place, then the heat sign delta (Δ) is put over the arrow of the equation. If the reaction takes place in the presence of a catalyst than the symbol or formula of the catalyst is also written above or below the arrow sign in the equation.}

1. When potassium chlorate (KClO₃) is heated in the presence of manganese dioxide (MnO₂) catalyst, it decomposes to form potassium chloride (KCl) and oxygen (O₂) gas.

2. Methanol (CH₃OH) is manufactured from carbon monoxide (CO) and hydrogen (H₂) under extreme pressure (300 atm) and temperature (300°C) and in the presence of ZnO + CrO₃

3. In photosynthesis, glucose is formed from Carbon Dioxide and Water under Sunlight and Chlorophyll as catalyst. 

Q. Convey the following information in the form of a balanced chemical equation:

On adding an aqueous solution of sodium hydroxide to an aqueous solution of copper sulphate copper hydroxide is precipitated and sodium sulphate remains in solution. 

Ans: NaOH (aq) + CuSO₄ (aq) ⟹ Cu(OH)₂ (s)↓ + Na₂SO₄ (aq)

It is an unbalanced equation. When balanced it becomes

2NaOH (aq) + CuSO₄ (aq) ⟹ Cu(OH)₂ (s)↓ + Na₂SO₄ (aq)

IRON OXIDES

There are two types of iron oxides. 

Iron (II) oxide FeO, and Iron (III) oxide Fe₂O₃

Iron (II) oxide FeO is known as Ferrous oxide.

Iron (III) oxide Fe₂O₃ is known as Ferric Oxide. 

Mixture of both the oxide is called Magnetic Iron Oxide (Fe₃O₄). 

Q. Write a balanced equation for the chemical reaction when heated iron metal reacts with steam to form iron (II, III) oxide and hydrogen. 

Ans. Fe (s) + H₂O (g) → Fe₃O₄ (s) + H₂ (g)

But it is an unbalanced equation, when balanced it becomes, 

3Fe (s) + 4H₂O (g) → Fe₃O₄ (s) + 4H₂ (g)

Q1. Translate the following statement into chemical equation and then balance the equation:

Hydrogen gas combines with nitrogen to form ammonia. 

Q2. Write the balanced chemical equation for the following reaction:

Sodium metal reacts with water to form sodium hydroxide and hydrogen. 

Q3. Write the balanced chemical equation for the following reaction:

(i) Aluminium reacts with copper chloride to form aluminium chloride and copper.

(ii) Aluminium hydroxide reacts with sulphuric acid to form Aluminium sulphate and water.

(iii) Manganese oxide reacts with hydrochloric acid to form manganese chloride, chlorine gas and water.

Q4. When the solution of substance X is added to a solution of potassium iodide, then a yellow solid separates out from the solution. 

a. What do you think substance X is likely to be?

b. Name the substance which the yellow solid consists of. 

c. Which characteristic of chemical reactions is illustrated by this example?

d. Write a balanced chemical equation for the reaction which takes place. Mention the physical states of all the reactants and products involved in the chemical equation.