Chap 5 class 9 the fundamental unit of life

 Introduction:-

Cell is the building block of all living organisms

Discovery of cell:- 

• Robert Hooke (1665) discovered cell.
• He discovered cell by self designed microscope.
• On viewing thin cutting of cork , he discovered empty spaces containing walls.
• Cells resembled honey comb like structure.

Evolution of cell Theory:- 

• Robert Hooke discovered cell.
• Robert Brown discovered nucleus in a cell 
• Schleiden and Schwann proposed cell theory.

Cell Theory:- 

• Cells are structural and functional unit of life.
• All Organisms are made up of cells .
• All cells arises from pre existing cells only.
• Nucleic acid is the genetic material in all cells.
• Cells interact with each other which results in organisms function.
• Basic chemical composition is more or less similar in all cells.

Cell type:-

Based on internal complexity in cell structure ; two types

Prokaryotic cell :-

• Membrane bound cell organelles are absent.
• Seen in Bacteria.
• No distinct nucleus.
• No definite nuclear membrane.
• Compartmentalization is not seen
• Chromosome single.
• Size :- generally small (1-10micro meter) 1 micro meter  = 10^-6m

Eukaryotic cell:- 

• Membrane bound organelles are present .
• Seen in plants , animals and fungi .
• Distinct nucleus present
• Well defined nucleus ( true nucleus)
• Compartmentalization is seen in eukaryotic cells.
• More than one chromosome
• Size : generally large (5- 100 micro meter)

Size of cells:- 

Cells exist in a variety of shapes and size.

Shapes of cells:- 

Shape of cell vary with functions they perform.

Based on number of cells present in body:- 

Unicellular Organism:-

• One cell constitute the organism 
• Single cell perform the basic functions that are characteristic of Organisms.
• Example:- Amoeba , Chlamydomonas, Paramecium , bacteria etc.

Multicellular organisms:-

• Many cells constitute the organism.
• There is a division of labour in multicellular organisms.

Eukaryotic cells:- characteristics :-

• Membrane bound organelles are present .
• Seen in plants , animals and fungi .
• Compartmentalization is seen in eukaryotic cells.
• Membrane bound nucleus is present.
•  Genetic material is well organised.

Cell organelles:- 

• A cell is made up of components called cell organelles.
• A cell is able to live and perform all its function because of these organelles.
• A cell have more or less same organelles , irrespective of their functions and Organism they found in.

Organelles:- 

Nucleus , Cell membrane,Ribosome , vacuole, SER ,RER , Mitochondria , Golgi bodies , lysosomes etc.

Are all eukaryotic cells identical?

No .

Difference between plant cell and animal cell:-

Plant cell:- 

• Cell wall is present 
• Vacuoles are big and lesser in number.
• Plastids are present
• Single Golgi apparatus called dictyosome present.
• Centriole absent

Animal cells:- 

• Cell wall is absent 
• Vacuoles are small and greater in number.
• Plastids are absent (except Euglena)
• Single complex prominent Golgi body present (dictyosome)
• Centriole present.

Plasma membrane :- 

• Also called cell membrane or selectively permeable membrane.
• It is thin , delicate , outermost , Living covering of the cell.
• It ensure protection.

Active transport :- 

• Movement of molecules across the membrane require energy.
• Movement occur against the concentration gradient.
• ATP provide the energy input from cell.

Passive transport:-

•  Movement of molecule across plasma membrane require no energy from cell .
• Movement occur along concentration gradient by diffusion or osmosis

Osmosis:- Movement of water from region of higher concentration to a region of lower concentration .

Example:- unicellular freshwater organism and most plant cells tend to gain water through osmosis. 

Absorption of water by plant roots is an example of osmosis.

Diffusion:- movement of gases from region of higher concentration to a region of lower concentration.

Behaviour with different Solution:- 

Hypotonic Solution:- Solution in which water concentration is higher than that inside the cell

Cell swell .

Animal cell may also burst

Hypertonic Solution:- Solution in which water concentration is less than that inside the cell

Cell shrink.

Plant cell undergoes plasmolysis.

Isotonic Solution :-  Solution in which water concentration in solution is same as that inside the cell

Structure of Plasma membrane:- 

• It is made up of lipids and proteins .
• Structure seen only through electron microscope.
• Lipid bilayers structure

Function of plasma membrane:- 

• It provides protection to cell.
• It allow movement of substances in and out of cell.
• Flexibility enable cells to engulf food and other materials from surrounding . Example:- Endocytosis in Amoeba.

Cell wall :-  

• It rigid , non living , Fully permeable outermost covering of plant cells and some.fungi.
• It is composed of cellulose.
• Plasmodesmata:- tiny holes through cell wall and middle lamella.

Functions of cell wall:- 

• Provide structural strength to plants 
• Prevent bursting of cells in hypotonic solution.
• Helps to connect neighbouring cells.provide protection against injury and infections

Plasmolysis :- when a living plant cell loses water through osmosis, there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is called plasmolysis

Nucleus:-

•  It is a spherical / oval structure near centre of a cell.
• It is present in both plants and animal cells 

Structure of nucleus:- 

Nuclear membrane :-

•  Double layered covering of nucleus.
• Space between two membranes is called perinuclear space .
• Seperates materials inside nucleus from cytoplasm

Nuclear pore:- 

• Pores on nuclear membrane which allow transfer of material from nucleus  to outside
• Formed by fusion of two membranes

Nucleoplasm/ nuclear matrix/ karyolymph- 

• Fluid enclosed by nuclear membrane.
• Support chromosomes and nucleolus 
• Acts as a site for RNA and DNA synthesis.

Nucleolus:-

•  Structure embedded in nucleoplasm
• Composed of proteins and RNA
• ribosomes formation takes place.

Chromatin :-

•  Thin , thread like structure embedded in nucleoplasm .
• contains RNA, DNA and proteins.

Chromosomes:- 

• Rod shaped structure 
• Formed when chromatin condensed together when the cell is about to divide.
• It contain information for inheritance of characters from parents to next generation in the form of DNA (Deoxyribonucleic acid)
• Functional segment of DNA is called gene

Function of nucleus :-  

• Control centre of the cell
• Help in movement of ribosome proteins and RNA through nuclear pores between nucleolus and cytoplasm.
• Help in cellular respiration.
• Genes present inside chromosomes decide the heredity characters.
• Chromosomes contained in nucleus play a crucial role during cell division.

Cytosol:- Fluid present inside the cell.

Cytoplasm:-

•  The fluid content inside the plasma membrane.
• Fluid + cell Organelles
•  It contains dissolved nutrients and waste products 
• It controls the shape of cell to an extent.
• Organelles present inside the cytoplasm perform specific functions without which cell cannot function as a whole.
• Helps in cellular respiration

Protoplasm:- Cytoplasm+ nucleus

Cell Organelles:- 

•  Every cell has a membrane around it to keep its own contents separate from the external environment.
• Large and complex cells, including cells from multicellular organisms need a lot of chemical activities to support their complicated structures and function
• To keep these activities ofdifferent kinds seperate from each other, these cells use membrane bound little structures within themselves.
• We will discuss about  Endoplasmic reticulum, Golgi bodies, Lysosomes, mitochondria, Plastids and vacuoles

Endoplasmic reticulum:- 

• It is a large network of membrane bound tubes and sheets.
• It looks like long tubules or round or oblong bags (vesicles).

Types:- Two types

• Smooth endoplasmic reticulum [SER]
• Rough endoplasmic reticulum [RER]

Rough endoplasmic reticulum:- 

• Ribosome attached to its surface so it is rough.
• Proteins manufactured in ribosomes transported other parts through ER.

Smooth Endoplasmic reticulum:- 

• Fat molecules and lipids are manufactured here.
• Help in detoxification of chemicals.

Functions of ER:-

• It helps in membrane biogenesis because protein is formed by RER and lipid is formed by SER.
•  ER acts as chemical to transport material to different parts of cell.
• Detoxifying poisons and drugs.
• ER works as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell.

Golgi apparatus:- 

• Named after Camille Golgi who first described it 
• It is a network of membrane bound vesicles arranged parallel to each other in stack called cisterns.
• These membranes often have connections with the membranes of ER and therefore constitute another portion of a complex cellular membrane system.
• Located near nucleus in animal.
• Freely distributed in plant cells and is called Dictyosomes

Functions of Golgi apparatus:

• Material manufactured in ER is dispatched to various parts inside or outside the cell through Golgi bodies.
• It stores cell secretion. 
• It stores , modify and pack products in vesicles 
• It forms lysosomes.
• It formd pectin.

Lysosomes:-

• It is a membrane bound vesicles containing variety of digestive enzymes.
• It is formed by golgi bodies.
• Enzymes are formed by RER.

Functions:-

• Digest waste materials/worn out organelles.
• Defense against bacterial and viral infection.
• Waste disposal system of cell.
• During cell damage, lysosomes burst and the enzymes digest their own wall.
• Termed as"Suicidal bags of cell."

Mitochondria:-

• Also called plastosome , plastochondria and power house of the cell.
• Energy is released in the form of ATP molecules.
• It can synthesis their own protein as they have their own DNA and ribosomes. That's why it is called semi-autonomous bodies/ strange organelle.

 Structure of mitochondria:-

Outer membrane:- 

• Smooth and porous
• Continuous limiting boundary of mitochondria

Inner membrane:- 

• Deeply folded 
• Folds provide greater surface area to generate ATP

Cristae:- 

• Inner membrane is compartmentalized into various cristae.

Matrix :-

•  Ground substance/space enclosed by inner membrane.

Plastids:-

• Organelle present in plant cells only
• It bear specific colour imparting pigments.
• Two types:- two types

1.  Chromoplasts(coloured plastids) and
2.  Leucoplast( white or colourless plastids)

Chromoplasts which contains chlorophyll pigments is called chloroplast . It provides green colour to cells. 

Chloroplast also contains yellow or orange pigments.

Leucoplast stores starch , oils and proteins.

Plastids are also double layered organelle.

Ground substance is called stroma.

It contains own DNA and ribosome so called semi-autonomous / strange organelle.

Vacuoles:-

• Vacuoles are storage sacs for solid or liquid contents.
• It is small sized in animal cells 
• plant cells have very large vacuoles.
• In plant it occupy 50-90% of the cell volume.
• Membrane of vacuole is called tonoplast.
• It provides turgidity and rigidity to the cell.
• It store amino acids, sugars, various organic acids and some proteins.
• In unicellular organism like Amoeba , specialised vacuoles also play important roles in expelling excess water and some wastes from the cell.

Cell division:- 

The process by which new cells are made is called cell division.

Types:- two types.

1. Meiosis and
2. Mitosis

Meiosis/ Reductional division:-

• It occurs in Germinal cells to form gametes i.e. sperm in male and ovum in female.
• It is called Reductional division because number of chromosome in daughter cells get reduced to half on division.

Mitosis/Equational division:-

• It occurs in somatic cells.
• It is called Equational division because on division number of chromosome remain same in daughter cells.

Page number 59

Question 1. Who discovered cells, and how?

Answer: Robert Hooke discovered cells in 1665 while examining a thin slice of cork through a self-designed microscope. He saw that the cork resembled the structure of a honey comb consisting of many little compartments. These small boxes are called cells.

Question 2. Why the cell is called the structural and Junctional unit of life?

Answer: A cell is capable of independently carrying out all necessary activities of life. So, they are called basic or functional unit of life.

Page number 61

Question 1. How do substances like C02 and water move in and out of the cell? Discuss.

Answer: CO2 moves by diffusion and H2O move by osmosis through cell membrane.

Question 2. Why is the plasma membrane called a selectively permeable membrane?

Answer: It is called selectively permeable membrane because it allows the entry and exit of some substances, not all.

Page number 63:-

Question 1. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

Answer:

Page number 65

Question 1. Can you name the two organelles we have studied that contain their own genetic material?

Answer: The two organelles which have their own genetic material are:

1. Mitochondria 2. Plastids

Question 2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Answer: The cell will not be able to revive and lysosomes will digest it.

 

Question 3. Why are lysosomes known as suicide hags?

Answer: When the cell gets damaged, lysosomes may burst, and the enzymes digest their own cell. Therefore lysosomes are known as suicide bags.

Question 4. Where are proteins synthesised inside the cell?

Answer: The proteins are synthesised in the ribosomes that are also known as protein factories.

Page number 67

Question 1. Make a comparison and write down ways in which plant cells are also different from animal cells.

Answer:

Question 2. How is prokaryotic cell different from a eukaryotic cell?

Answer: Prokaryotic cell is generally smaller in size (1-10 pm), nuclear region is poorly defined, the cell organelles are not membrane-bound and has a single chromosome.

Eukaryotic cell is generally larger in size (5-100 pm), nuclear region is well defined with nuclear membrane. Membrane-bound cell organelles are present and has more than one chromosome.

 

Question 3. What would happen if the plasma membrane ruptures or breaks down?

Answer: If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out.

Question 4. What would happen to the life of a cell if there was no Golgi apparatus?

Answer: Golgi apparatus has the function of storage, modification and packaging of the products in vesicles. If there were no Golgi bodies, packaging and dispatching of materials synthesised by the cell will be stocked.

Question 5. Which organelle is known as the powerhouse of the cell? Why?

Answer: Mitochondria is known as powerhouse of the cell because it releases the energy required for different activities of life.

Question 6. Where do the lipids and proteins constituting the cell membrane get synthesised?

Answer: Lipids and proteins are synthesised in ER [Endoplasmic Reticulum].

 

Question 7. How does Amoeba obtain it’s food?

Answer: Amoeba take it’s food by the cell membrane which forms the food vacuole.

Question 8. What is osmosis?

Answer: Osmosis is the process of movement of water molecule from a region of higher water concentration through a semi-permeable membrane to a region of lower water concentration.

Question 9. Carry out the following osmosis experiment:

Take four peeled potato halves and scoop each one out to make potato cups, one of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water.

Now,

(a) Keep cup A empty

(b) Put one teaspoon sugar in cup B

(c) Put one teaspoon salt in cup C ‘

(d) Put one teaspoon sugar in the boiled potato cup D

Keep these for two hours. Then observe the four potato cups and answer the following:

(i) Explain why water gathers in the hollowed portion of B and C.

(ii) Why is potato A necessary for this experiment?

(iii) Explain why water does not gather in the hollowed out portions of A and D.

Answer:

(i) Water gathers in B and C because in both the situations there is difference in the concentration of water in the trough and water in the cup of Potato. Hence, osmosis takes place as the potato cells act as a semi-permeable membrane.

(ii) Potato A is necessary for this experiment for comparison, it acts as a control.

(iii) Water does not gather in the hollowed out portions of A and D. As cup of A does not have change in the concentration for water to flow. For osmosis to occur one of the concentration should be higher than the other.

In cup D, the cells are dead and hence the semi-permeable membrane does not exists for the flow of water and no osmosis takes place.

Thank you :-)

Life processes chap 6 class 10

 

What are life processes?

The processes which together perform their maintainence job are called life processes.

Important life processes are:-

• Nutritional processes
• Respiration
• Transpotation
• Excretions
• 
  

Need of nutrition:- To get energy for growth, development, synthesising protein and other substances in the body.

Source:- Food rich in carbohydrates , fat, vitamins etc. (Balanced diet)

Mode of nutrition:- On the Basis of type of raw material:-two types

•  Autotrophic nutrition
• Heterotrophic nutrition 

Autotrophs:- Organisms make their own food itself from inorganic substances .(CO2 and H2O)

Example:- Green plants , cyanobacteria.

Autotrophic nutrition:- 

Mode of nutrition which is adopted by autotrophs.

Autotrophs makes their food by the process of photosynthesis.

Photosynthesis:- process by which autotrophs takes up substances (carbon dioxide and water) from outside and convert them into stored form of energy (starch).

Process takes place in the presence of sunlight and chlorophyll.

Stored carbohydrate are utilized slowly by plants whenever needed.

Reaction involved in photosynthesis:-

CO2 + H2O ( sunlight , chorophyll)-- > C6H12O6 + O2 + energy

Event occurs during the process of photosynthesis:- 

1. Absorption of light energy by chlorophyll

2. Conversion of light energy into chemical energy and splitting of water into H2 and O2

3. Reduction of CO2 to carbohydrate.

Note:- 

• In cross section ,green Dots are cell organelles called chloroplast.
• Chloroplasts contain CHLOROPHYLL.
  
  
  

Do all these events need to take place one after other? Justify with example.

No.

In desert plants , CO2 is taken up by plants at night and prepare an intermediate.

During day , energy absorbed by chlorophyll is acted upon intermediate to produce carbohydrate

How do plants exchange gases?

• By stomata (at leaf)
• By lenticels(at stem)
• By roots surface

Stomata:- 

Location:- Tiny pores on the surface of leaf

Function:- 

• gaseous exchange
• Transpiration (loss of water from the aerial part of plant)
• Photosynthesis .

Stomatal apparatus:-

• pore
• Guard cells ( contains chlorophyll)
• Subsidiary cells 

Function of guard cells:- 

• Opening and closing of pores 
• Guard cell swell when water flow into them 
• Due to this , stomatal pore open 
• When guard cell shrink , pore closes.
  
  
  

How plants take up material for meet their energy requirements?

• From air :- it takes CO2 ,
• Sunlight is trapped by chlorophyll.
• From soil it takes water and. Other nutrients like nitrates, nitrites, iron, magnesium, phosphorus etc. for healthy growth.

2. Heterotrophs:- 

• Organisms which depend upon plants directly or indirectly for their nutrition are called heterotrophs.
• It take complex substances and broken down into simpler ones with the help of  biocatalysis called enzymes.

Holozoic nutrition :- 

• Organism takes up solid food and break it inside the body 
• Example:- Amoeba, Cow, lion and man

On the basis of material intakes , it is of 3 types :- 

• Herbivores ;- eat herbs . Example :- cow, deer 
• Carnivores :- eat flesh. Example :- lion , tiger.
• Omnivores :- eat herbs and meat . Example :- man

Saprophytic nutrition:- 

• Organism which take food from dead and decay material.
• These break down the food material outside the body and then absorb it .
• Example :- fungi like yeast , mushroom and bread moulds

Parasitic nutrition :- 

• Organism which live either in or on the host body and harm it .
• Types :- Two types 
• Ectoparasite:-  Live on the body of host. 
• Example :- lice and ticks 
• Endoparasite :- live inside the body of host .
• Example :- leeches and tapeworm.

How do organisms obtain their nutrition ?

• Different organisms obtain 
• their nutrition in different ways:-
• Example:- In Amoeba (unicellular Organism) , food is taken in by the entire surface .

Process involved :-

Pseudopodia--> capture food --> take in (food vacuole) --> digestion of food in food vacuole--> undigested food moves to the surface of cell and thrown out.

In Paramecium (unicellular Organism) :-

Food is taken in with the help of cilia present all over the body.

Ingestion occur at specific spot called gullet.

Nutrition in Multicellular organisms:- 

Steps involved :-

• Ingestion (intake of food).
• Digestion (break down of food)
• Absorption ( movement of digested food into blood)
• Assimilation (utilisation of material
• Egestion (removal of waste)

Digestive system in human:-

Consist of digestive gland and alimentary canal

Parts involved in alimentary canal 

• Mouth 
• Oral cavity/ buccal cavity
• Oesophagus / food pipe
• Stomach (J shaped)

• Small intestine
• Large intestine
• Rectum 
• Anus

Digestive glands:-

• Salivary gland
• Gastric gland 
• Liver  and pancreas
• Intestinal gland

Function of oesophagus:- pushes the food into stomach by peristaltic movement.

Stomach:- contains gastric glands that secrete HCl , mucus and pepsin

HCl:- provide acidic medium for action of pepsin . Pepsin is a proteolytic enzyme.

Kill harmful bacteria that enters the food.

Mucus:- protect inner lining of stomach for corrosive action of HCl

Pepsin:- digest protein

Further details are mentioned in table 

Absorption at small intestine:- 

• Inner lining of small intestine has small finger like projections called villi .
• Villi provide greater surface area for absorption.
• It is richly supplied with blood vessels.
• Blood vessels take away the absorbed food to each and every cell of the body.
• In each cell this energy is utilised for obtaining energy, building up new tissues and repair the old tissues.

Absorption of water at large intestine:-

• Unabsorbed food is sent to large intestine.
• More villi absorb water material.
• Rest removed from body via anus.
• Exit of waste material is regulated by anil sphincter.

Breathing Vs Respiration

Enzyme :- these are biocatalyst which increases the rate of reaction (metabolic reaction) but itself remain same.

Breakdown of glucose by various pathways:-

First step :- breakdown of glucose into pyruvate.

Takes place in cytoplasm

 Anaerobic respiration :- 

• Occur in absence of oxygen
• Pyruvate gets converted into ethanol , carbon dioxide and energy
• Example :- yeast
• Takes place in cytoplasm.

Aerobic respiration :-

• Presence of oxygen.
• Pyruvate gets converted into CO2 ,H2O and energy
• Example :- Homosapiens (the man)
• Takes place in mitochondria.

Lack of O2 :- 

• Pyruvate gets converted into lactic acid and energy.
• Lactic acid produces cramps.
• Occur in muscle cells during vigorous exercise.
• Takes place in cytoplasm.

The energy released during cellular respiration is immediately used to synthesise a molecule of ATP.

ATP used as fuel in all the life activities.

Energy released by 1 mole of ATP is 30.5 KJ

Aerobic respiration in Plants :-

• Plant exchange gases through stomata and the large intercellular spaces ensures that all cells are in contact with air.
• Carbon dioxide and oxygen are exchanged by diffusion  

Direction of diffusion depends on :-

• Environmental conditions and 
• Requirements  of the plant.

At night :- 

• No photosynthesis occur.
• So carbon dioxide elimination is the major exchange.

During day:- 

• CO2 used for photosynthesis 
• So no Carbon dioxide release.
• Oxygen release is the major events.

Aerobic respiration in aquatic organisms :- 

• Use dissolved oxygen in water
• Amount of dissolved oxygen is low as compared to amount of oxygen in air. So breathing rate in aquatic organisms is high.
• Fishes take in water through their mouths and passes it to gills where the dissolved oxygen is taken up by blood.

Aerobic respiration in terrestrial Organisms :-

• Use oxygen in atmosphere 
• Oxygen is absorbed by different organs in different animals.
• All these organs have a structure that increases the surface area which is in contact with oxygen rich atmosphere.
• Since exchange of Carbon dioxide and oxygen has to take place across the surface and the surface is very fine and delicate so it has to be protected.
• In order to protect these surface, these organs are placed within body.
• Also there have to be passages that will take air to this area.

Human respiratory system:- 

Nostril :- Air is taken into the body through the nostril.

Nasal chamber :- 

• Consist of fine hair and mucus 
• Hair filter the air passing through nostril.
• Mucus stick unwanted substances coming along with air.

Trachea:-

•  contain rings of cartilage
• Ensures air passage does not collapse

Bronchi:-

•  Trachea divide into two and enter into lungs 
• Now trachea , after entering into lungs is called bronchi

Bronchioles :- bronchi further divided into bronchioles 

Alveoli :- 

• bronchioles finally terminate in balloon like structure which are called alveoli 
• Alveoli provide a surface where exchange of gases can take place.
• Wall of alveoli contain an extensive network of blood vessels which carry oxygen to different body cells and carbon dioxide to outside by alveoli surface.
• 
  
  
  
  

Exchange of gases between alveoli blood and tissue :- 

• Since in humans body size is large , the diffusion pressure alone cannot take care of O2 delivery to all parts of body .
• So respiratory pigment (haemoglobin) is present in RBCs  whic combine with oxygen and take up it to tissues which are deficient in oxygen.
• CO2 is more Soluble in water and hence is mostly transported in the dissolved form in our blood.
• Residual volume:-  quantity of air that remains in the lungs after deepest forceful expiration.

Transportation in Human Beings:- 

• Human beings like other multicellular organisms need regular supply of food and oxygen etc. 
• This function is performed by circulatory system or transport system.

Circulatory system in human beings consists of:-

• A pumping organ - Heart
• Blood vessels - Arteries , veins and capillaries
• A circulatory medium - blood and lymph

Our pump - the heart

• Muscular organ which is as big as our fist.
• Four chambered to prevent oxygen rich blood from mixing with blood containing CO2 .
• Atrium are thick walled 
• Left side of heart carry oxygenated blood bring by pulmonary vein from lungs.
• This oxygenated blood is then pumped to rest of body by dorsal aorta
• Right side of heart carry deoxygenated blood bring by Vena Cava from different body parts.

Process step by step :- 

Step 1:- Oxygen rich blood from lungs comes to thin walled left atrium. 

This atrium relaxed when it is collecting this blood.

Step 2:- Left Atrium contract so that blood is transferred to left ventricle.

Left ventricle relax this time.

Step 3:- Left ventricle contract and blood is pumped out to the body

Step 4:- De oxygenated blood comes from body to right atrium, as it expands.

Step 5:- The right atrium contracts and the right ventricle dilates.

This transfer blood to right ventricle.

After this blood pumps to lungs for oxygenation.

Valves ensures that blood does not flow backward when atria or ventricles contract.

Double circulation:- Blood travels twice through the heart in one complete cycle of the body.

Pulmonary circulation :- Blood moves from heart to lungs and back to the heart.

Systemic circulation :- Blood moves from heart to rest of the body and back to the heart.

Fishes have two chambered heart.

Amphibians and reptiles have three chambered heart.

The tubes - blood vessels 

Arteries , veins and capallaries

Capillaries:- On reaching an organ or tissue, Arteries divides into smaller and smaller vessels to bring the blood in contact with all the individual cells.

The smallest vessels have one celled thick wall and called capillaries

Exchange of material between blood and surrounding cells takes place across this thin wall.

The capallaries then join together to form veins.

A circulating medium :- 

• Blood and lymph

Blood:- 

• A fluid connective tissue 
• Two components :-
• Solid components - blood  corpuscles and
• Liquid component - plasma

Plasma :-  A yellow colour fluid contain 90% water and 10% organic substances like proteins (Albumin, Globulin , inorganic mineral ions)

Functions of Plasma:- Transport food , carbon dioxide and nitrogenous wastes in dissolved form .

Functions of platelets :- 

Platelets plugs the leaks (if occur) in the blood vessels by helping to clot the blood at these points of injury.

Lymph / Tissue fluid :- Through the pores present in the walls of capallaries some amount of plasma , proteins and blood escape into intercellular spaces in the tissue to form lymph

Properties of lymph:-

Similar to plasma of blood but colourless and contains less protein

How lymph circulate:-

• Lymph drain into lymphatic capallaries.
• Lymphatic capallaries join to form large vessels
• Lymph vessels open into larger veins.

Functions of lymph:- 

• Lymph carries digested and absorbed fat from intestine
• It drains excess fluid from extra cellular space back into blood.

Blood pressure:- 

•  Force that blood exerts against wall of a vessel is called blood pressure.
• BP is greater in arteries 
• BP is less in veins

Systolic pressure:- Pressure f blood inside the artery during ventricular systole (contraction) is called systolic pressure.

Normal systolic pressure is about 120 mm of Hg

Diastolic pressure :- pressure of blood inside the artery during ventricular diastole (relaxation) is called diastolic pressure.

Normal diastolic pressure is 80 mm of Hg.

Sphygmo-mamo-meter :- Instrument that measured BP.

Hypertension / high BP:-  caused by constriction of arterioles.

Results in increased resistance to blood flow 

Can lead to rupture of artery

Transportation in plants:- 

• If the distance between the soil contacting organs and chlorophyll containing organs are small, then energy and raw material can easily diffuse to all parts of plant body.
• But if these distances become large , diffusion process will not be sufficient to provide raw material in leaves and energy in roots 
• So a proper system of transportation is essential

Transport of water by xylem and phloem :- 

• Vessels and tracheids of roots , stem and leaves are interconnected.
• This forms a continuous system of water conducting channels reaching all parts of plants.
• At roots , cells in contact with soil actively take up ions.
• This create concentration difference between root and soil.
• So to eliminate  this difference water moves into root from the soil.
• In this way  there is steady movement of water into root xylem , creating a column of water that is steadily pushed upward.
• Along with this evaporation of water molecules from stomata also create a suction which pulls water from xylem cells of root.
• This evaporation is called transpiration.

Transpiration :-  loss of water in the form of vapour from aerial parts of plants.

Role of Transpiration:- Help in absoption and upward movement of water and minerals.

Help in temperature regulation.

Transport of food and other substances by phloem :- 

• The transport of soluble product of photosynthesis is called translocation.
• Phloem transport this Soluble product .
• Phloem also transport amino acids and other substances ( derived by root , stem etc)
•  Translocation of food and other substances takes place by sieve tubes and companion cells .
• It occur in both upward and downward direction.
• Occur by active transport so energy use.

Mechanism :- 

• Material like sucrose is transferred into phloem tissue by using energy from ATP 
• This increases osmotic pressure of tissue causing water to move into it.
• This pressure move material in the phloem to tissues which have less pressure.
• This allow phloem to move material according to plants need.

Excretion:- 

• The biological process of removal of harmful metabolic nitrogenous wastes from the body .
• Unicellular Organism remove waste by simple diffusion.
• Multicellular organisms have specialized organs to do this job .

Excretion in human beings:- 

• Consists of :-
• One pair of kidney
• One pair of ureter
• A urinary bladder
• A urethra

How is urine produced?

Purpose:-

• To filter out waste products from blood .
• Waste products are nitrogenous wastes like urea (human beings) or uric acid (birds) or Ammonia( aquatic life)
• Basic filtration unit is nephron
• Nephron is structural and functional unit of kidney.

Mechanism :- 

Step 1 :- Glomerular filtration :-

•  The first step in urine formation is filteration of blood, which is carried out by glomerulus and is called glomerular filtration.
• Glomerulus reside in Bowmans' capsules.

Step 2:- Tubular reabsorption :- 

• Useful substances from filterate like Na+ ,K+ , C6H12O6 etc are reabsorbed by capillaries surrounding nephron into blood.

Step 3:- secretion :- 

• Urea , extra water and salts are secreted into tubules which open into collecting duct and then into ureter.
• Ureter take the urine from kidney to urinary bladder and then it come out through urethra.
  
  
  

Hemodialysis / Artificial kidney:- 

• A device used to remove nitrogenous wastes products from blood through dialysis.
• Meant for kidney failure patient.

Excretion in plants :- 

• O2 released during photosynthesis 
• H2O by Transpiration 
• Waste may be stored in leaves, bark etc which fall off from tree.
• Waste products stored as gums , resin in old roots .
• Plants excrete some waste into soil around them.

Acids, bases and salts class 10

 Introduction :-

Properties of acids :-

• Produce hydrogen ions [H+] ions in water.
• Sour taste
• Turn blue litmus red
• Act as electrolytes in Solution.
• React with several metals releasing hydrogen gas.
• React with carbonates releasing CO2 (g)
• Destroy body tissues.
• Corrode metal surface quickly.

On the basis of origin, acids are classified as:- 

Organic acids :- 

• Acids derived from living organisms like plants and animals.
• For example :- 
• Citric acid is present in fruits e.g. Citrus reticulate (orange)  and Citrus lemon (lemon)
• Acetic acid present in vinegar.
• Oxalic acid present in tomato.
• Tartaric acid present in tamarind.
•  Lactic acid present in sour milk and curd.

Mineral acids :- 

• Also called inorganic acids .
• They are dangerous.
• For example :- Sulphuric acid [H2SO4] , Hydrochloric acid [HCl]

On the basis of their strength, acids are classified as:- 

Strong acids and weak acids.

Strong acids :- 

• Complete dissociation into its ions in aqueous solutions.
• Example:- Nitric acid [HNO3] ,
• Sulphuric acid [H2SO4],
• Hydrochloric acid [HCl] etc.

Weak acids:- 

• Acids which do not completely dissociate into its ions in aqueous.
• Example:- Sulphurous acid [H2SO4] , carbonic acid [H2CO3], Acetic acid [CH3COOH]

On the basis of their concentration, acids are classified as :- 

Dilute acids :- have a low concentrations of acids in aqueous solution.

Concentrated acids:- have a high concentration of acids in aqueous solutions.

On the basis of number of hydrogen ion, acids can be classified as:- 

Monoprotic acids :- 

Acids which produces one mile of H+ ions per mole of acid. Example:- HCl , HNO3

Diprotic acid:- 

Acids which produces two miles of H+ ions per mole of acid. Example:- H2SO4.

Triprotic acid:- 

Acids which produces three moles of H+ ions per mole of acid. Example:- H3PO4 (phosphoric acid)

Polyprotic acid:- Acids which produces more than three moles of H+ ions per mole of acid.

Chemical properties of acids:- 

(1) Acids react with active metal to give hydrogen gas.

• Acid + metal -- > salt + hydrogen gas.
• HCl (l) + Zn (s) --- > ZnCl2 (s) + H2(g)
• H2SO4 (l) + Zn (s) --- > ZnSO4 (s) + H2 (g)

(2) Acid react with metal carbonate and metal hydrogen carbonate to give carbon-di-oxide.

• Metal carbonate / Metal hydrogen carbonate + Acid -- > salt + water + carbon dioxide
• Na2CO3 (s) + 2HCl (aq) --- > 2NaCl(aq) + H2O (l) + CO2
• NaHCO3 (s) + 2HCl (aq) --- > 2NaCl(aq) + H2O (l) + CO2

(3) Acids react with bases to give salt and water . This reaction is called as neutralization reaction.

• NaOH + HCl --> NaCl + H2O
• Base + acid --> salt + water
• (4) Acids react with metal oxides to give salt and water.
• CuO + H2SO4 -- > CuSO4 + H2O

Properties of base :- 

• Produce hydroxide ions [OH-] in water.
• Water soluble base are called alkalies.
• Bitter taste 
• Corrosive in nature.
• Turn red litmus blue.
• Act as electrolyte in solution.
• Neutralize solutions containing H+ ions.
• Have a slippery, "soapy" feel.
• Dissolve fatty material.

On the basis of their strength, bases are classified as :- 

(a) Strong bases :-

•  bases which completely dissociate into its ions in aqueous solution.
• Example:- sodium hydroxide [NaOH]
• Potassium hydroxide [KOH] ,
• Lithium hydroxide [Li(OH)],
• Calcium hydroxide [Ca(OH)2]

(b) Weak bases :- 

• Bases which donor completely dissociate into its ions in aqueous solution. 
• Example:- Ammonium hydroxide [NH4OH] , Magnesium hydroxide Mg(OH)2

On the basis of their concentration, bases are classified as :-

(a) Dilute bases :- Have a low concentration of alkali in aqueous solution.

(b) Concentrated bases:- have a high concentration of alkali in aqueous solution.

Chemical properties of bases:- 

(a) Reaction with metals :- 

• Certain reactive metals such as zinc, aluminium and tin react with alkali solution on heating and hydrogen gas is evolved
• Example:- Zn + NaOH -- > Na2ZnO2 + H2

(b) Reaction with acids :-

• Base react with acids to form salt and water. 

• Example :- NaOH + HCl -- > NaCl + H2O
• KOH + HCl -- > KCl + H2O

(c) Reaction with non-metallic oxides:- 

• Non metallic oxides are generally acidic in nature .
• Non metal  oxide+ base -- > salt + water
• CO2 + NaOH -- > Na2CO3 + H2O

Strength of acid or base solutions :- 

• A. Scale for measuring hydrogen ion concentration in a solution , called pH scale has been developed.
• The p in PH stands for "potenz " in German, meaning power . So p = potential or power H = hydrogen.

pH = 7 i.e. neutral solution i.e H3O+ = OH-

pH > 7 i.e basic solution i.e H3O+<OH-

pH >7 i.e Acidic solution i.e H3O+ >OH-

pH of some common substances.

• Gastric juice = 1.2pH
• Lemon juice = 2.2 pH
• Wine = 4.0 pH
• Rain = 5.5pH
• Pure water, human blood = 7.5 pH
• Baking soda = 8.5 pH
• Detergent , Milk of magnesia = 10.0 pH
• Bleach = 12.5pH
• Sodium hydroxide solution= 14pH

Importance of pH in every day life:-

(1) pH sensitivity of plants and animals:- 

• Human body works in a narrow range of pH 7.0 to 7.8 
• When acid rain [pH<5.6] flows into rivers, it lower the pH of river water.
• Thus survival of aquatic life in such river becomes difficult.
• So acidity can be lethal for plants and animals.

pH in human digestive system:-

• Stomach secretes HCl to kill bacteria in food.
• Mucus prevent the inner lining of stomach from corrosive nature of HCl.
• During indigestion the stomach produces too much acid and cause pain and irritation.
• To get rid of this pain , people use antacids such as magnesium hydroxide (milk of magnesia) ; a base to neutralize excess acid.

pH and tooth decay:- 

• Tooth enamel is the hardest substance in body; made up of calcium phosphate.
• It does not dissolve in water but corroded when pH of mouth is lower than 5.5 
• This acidic medium is produced by degradation of sugar and food particles present in mouth.
• To prevent tooth decay we clean our mouth after eating.
• Also clean teeth by toothpaste ( basic) to neutralize excess acid.

(4) pH as self defence mechanism by plants and animals:-

• Certain animals like bee and plants like nettle secrete highly acidic substances for self defence. 
• Both secrete methanoic acid.

Addition of acids or bases to water:-

• The process of dissolving an acid , specially nitric acid [HNO3] or sulphuric acid [H2SO4] or a base in water is a highly exothermic.
• As a rule :- Always add acid to water not water to acid.
• Acid must be added to water with constant stirring.
• Water must not be added to acid because heat generated cause the mixture to splash out and cause burns.

Indicators:-

• Indicators are those chemical substances which behave differently in acidic and basic medium and help in determining the chemical nature of the substances.
• Acid Base indicators indicate the presence of an acid or a base by changes in acidic or basic medium.

Indicators can be natural or synthetic.

Olfactory indicators:- Those indicators whose odour changes in acidic or basic medium.

Onion:- smell of onion diminished in a base and remain as it is in an acid.

Vanilla :- odour of vanilla essence disappears when it is added to a base.

Odour of vanilla essence persists when it is added to an acid.

Turmeric:- In acids , yellow colour of turmeric remains yellow.

In bases, yellow colour of turmeric turns red.

Phenolphthalein:- Phenolphthalein remains colourless in acids but turn pink in bases 

Methyl orange:- methyl orange turns pink in acids . It becomes yellow in bases.

Litmus:- 

• Litmus is a natural indicator. It's solution is a purple dye which is extracted from lichen.
• Acids turn blue litmus red.
• Bases turn red litmus blue.
• Water is essential for acids and bases to change colour of litmus paper.

Note:- litmus paper will act as an indicator only if either the litmus paper is moist or the acid or base is in the form of aqueous solution

Reason:- Bases and acids release OH- and H+ ions respectively in aqueous solutions.

Summary of indicators:- 

Indicator->acidic med ->basic med
Litmus solution --> Red --> Blue
Methyl orange--> pink --> yellow
Phenolphthalein-> colourless-> pink
Turmeric-->yellow-->red

Properties of salts:-

• Salts forms by combination of acid and base through neutralization reaction.
• The acidic and basic nature of salts depends on the acid and base combined in neutralization reaction.
• The most common salt is sodium chloride NaCl or table salt which is forms by combination of sodium hydroxide and hydrochloric acid.
• NaOH + HCl -- > NaCl + H2O
• Other examples include Epsom salts [MgSO4] used in both salts , ammonium nitrate [NH4NO3] used as fertilizers and baking soda [NaHCO3] used in cooking.
• The pH of salts solution depends on strength of acid and base combined in neutralization reaction.

Common salt :- A raw material for chemicals such as 

• Sodium hydroxide
• Baking soda
• Washing soda
• Bleaching powder etc.

Sodium hydroxide:-

• When electricity is passed through an aqueous solution of sodium hydroxide (brine) ,it decompose to form sodium hydroxide.
• 2NaCl (aq) + 2H2O (l)---> 2NaOH (aq) + Cl2(g) + H2(g)
• The method is called chlor alkali process.
• Chlorine gas is given off at anode.
• Hydrogen gas at cathode.
• Sodium hydroxide solution is formed near cathode.

Uses:-

H2 GAS:- 

• used as fuel.
• Ammonia is used for fertilizer.

Cl2 GAS:- 

• used in water treatment,in swimming pool.
• Pesticides, CFCs , disinfectants etc. 
• H2 + Cl2 --> HCl.

Use of HCl :- 

• Used in cleaning steel
• In manufacturing of NH4Cl
• In medicine and cosmetics

Uses of NaOH:-

•  In de-graeasing metals, soaps and detergents.
• In paper making
• In artificial fibres.

Bleaching powder:- CaOCl2

• Produced by the action of Chlorine on dry slaked lime [Ca(OH)2]
• Ca(OH)2 + Cl2 -- > CaOCl2 + H2O

Uses:- 

(1) For bleaching

• Cotton and linen in textile industry.
• Wood pulp in paper factories.
• Washed clothes in laundry.

(2) as an oxidizing agent in many chemical industries.
(3) for disinfecting drinking water to make it free of germs.

Baking soda:- NaHCO3

• It is produced using NaCl , H2O , CO2 and NH3 as raw material.
• NaCl + H2O + CO2 + NH3 -- > NH4Cl + NaHCO3
• When heated
• 2NaHCO3 + heat --> Na2CO3 + H2O + CO2.
• It is a mild base.

Uses:- 

• Used in kitchen for making crispy pakoras and for faster cooking.
• For making baking powder (mixture of baking soda and mild edible acid such as tartaric acid)
• When baking powder is heated and mixed with water following reaction takes place:- 
• NaHCO3 + H+ (from any acid) --> CO2 + H2O  + sodium salt of acid
• CO2 produced during reaction causes bread or cake to rise making them soft and spongy.
• Used as antacid .
• Used is soda acid fire extinguishers.
• Used in industrial processes.

Washing soda:- Na2CO3. 10H2O

• Produced by heating Baking soda and then recrystallization of sodium carbonate.
• Na2CO3 + 10H2O -- > Na2CO3.10H2O

Uses:- 

• used in glass , soap and paper industries 
• Used in manufacture of sodium compounds such as borax.
• Used as a cleaning agent for domestic purpose.
• Used for removing permanent hardness of water.

Are the crystals of salts really dry?

• No because they contain water of crystallization.
• When heated the crystals, water is removed and colour changes .
• If moisten the crystals again with water, colour of crystals reappear.
• Example:- hydrated copper sulphate -- > CuSO4.5H2O
• Hydrated sodium carbonate --> Na2CO3.10H2O
• Gypsum CaSO4.2H2O

Plaster of Paris (CaSO4.1/2H2O)

• On heating gypsum at 100°C  ,it loses water molecules and become calcium sulphate hemihydrate (CaSO4.1/2H2O)
• This is called plaster of Paris.
• Uses :- used by doctors for supporting fractured bones.
• Used for making toys , materials for decoration for making surface smooth.

Characteristics:-

• white powder 
• On mixing with water, it changes to gypsum once again giving a hard solid mass.
• Ca SO4.1/2H2O + 3/2 H2O -- > CaSO4.2H2O

Class 10 Ques ans

Page number 6

Question 1
Why should a magnesium ribbon be cleaned before burning in air ?
Answer:
Magnesium gets covered with a layer of magnesium oxide when kept in air for a long time. This layer hinders the burning of magnesium. Hence, it is to be cleaned before burning.

Question 2
Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
Answer:
(i) H2 + Cl2 → 2HCl
(ii) 3 BaCl2 + Al2(SO4)3 → BaSO4 + 2 AlCl3
(iii) 2Na + 2H2O → 2NaOH + H2↑

Question 3
Write a balanced chemical equation with state symbols for the following reactions :
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water

Answer:
(i) BaCl2 (aq) + Na2SO4 (aq) → BaSO4(s) + 2NaCl (aq)
(ii) NaOH (aq) + HCl(aq) → NaCl(aq) + H2O(l)

Page Number: 10

Question 1
A solution of a substance ‘X’ is used for white washing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

Answer:
(i) The substance whose solution in water is used for white washing is calcium oxide (or quick lime). Its formula is CaO.

CaO (s) + H2O (l) -- > Ca(OH)2 (aq)

Question 2
Why is the amount of gas collected in one of the test tubes in text book Activity 1.7 (i.e., electrolysis of water) double of the amount collected in the other? Name this gas. [CBSE 2015 (Delhi)]
Answer:
In Activity 1.7, water is electrolysed to give H2 gas at one electrode and O2 gas at the other electrode.

2H2O(l) → 2H2(g) + O2(g)
Thus two molecules of water on electrolysis give two molecules of hydrogen gas and one molecule of oxygen gas or in other words the amount of hydrogen gas collected would be double than that of oxygen gas.

Page Number: 13

Question 1
Why does the colour of copper sulphate solution change when an iron nail is dipped in it ?
OR
An iron nail is dipped in the solution of copper sulphate for about 30 minutes. State the change in colour observed. Give reason for the change. [CBSE 2015 (Delhi)]

Answer:
When an iron nail is dipped in copper sulphate solution, the displacement reaction takes place. The colour of copper sulphate solution fades due to the formation of light green solution of iron sulphate.

Fe + CuSO4 --- > FeSO4 + Cu

Question 2
Give an example of a double displacement reaction other than the one given in Activity 1.10 (NCERT Text Book).
Answer:
Sodium hydroxide and hydrochloric acid react to form sodium chloride and water.

NaOH (aq) + HCl (aq) -- > NaCl (aq) + H2O (l)

Question 3
Identify the substances that are oxidised and the substances which are reduced in the following reactions.
(i) 4Na(s) + O2(g) → 2Na2O(s)
(ii) CuO (s) + H2(g) → Cu (s) + H2O(l)
Answer:(i) Substances oxidised is Na as it gains oxygen and oxygen is reduced.

(ii) Substances reduced is Cu as hydrogen is oxidised as it gains oxygen.

NCERT Solutions for Class 10 Science Chapter 1 Textbook Chapter End Questions

Question 1
Which of the statements about the reaction below are incorrect ?
2 PbO(s) + C(s) → 2Pb (s) + CO2(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced

(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) All
Answer:
(i) (a) and (b)

Question 2
Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a

a) combination reaction
(b) double displacement reaction
(c) decomposition reaction
(d) displacement reaction
Answer:
(d) Displacement reaction.

Question 3
What happens when dilute hydrochloric acid is added to iron filings ? Tick the correct answer :

a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Answer:
(a) Hydrogen gas and iron chloride are produced.

Question 4
What is a balanced chemical equation ? Why should chemical equations be balanced ?
Answer:
A balanced chemical equation has an equal number of atoms of different elements in the reactants and products.
The chemical equations should be balanced to satisfy the law of conservation of mass.

Question 5
Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Answer:
(a) 3H2 (g) + N2 (g) → 2NH3 (g)
(b) H2S (g) + 3O2 (g) → SO2 (g) + 2H2O(l)
(c) 3BaCl2 (aq) + Al2(SO4)3 (aq) → 2AlCl3 (aq) + 3BaSO4 ↓(s)
(d) 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)

Question 6
Balance the following chemical equations :
(a) HNO3 + Ca (OH)2 → Ca (NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
Answer:
(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O

(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl

Question 7
Write the balanced chemical equations for the following reactions :
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Answer:
(a) Ca (OH)2 + CO2 → CaCO3 + H2O
(b) Zn + 2AgNO3 → Zn(NO3)2 + 2 Ag
(c) 2Al + 3 CuCl2 → 2AlCl3 + 3 Cu
(d) BaCl2 + K2SO4 → BaSO4 + 2KCl

Question 8
Write the balanced chemical equation for the following and identify the type of reaction in each case :
(a) Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium
(b) Zinc carbonate(s) → Zinc oxide (s) + Carbon dioxide (g) bromide(s)
(c) Hydrogen (g) + Chloride (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)

Answer:
(a) 2KBr (aq) + Bal2(aq) → 2Kl(aq) + BaBr2(s)
Type : Double displacement reaction

(b) ZnCO3 (s) → ZnO (s) + CO2 (g)
Type : Decomposition reaction

(c) H2 (g) + Cl2 (g) → 2HCl(g)
Type : Combination reaction

(d) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
Type : Displacement reaction

Question 9
What does one mean by exothermic and endothermic reactions ? Give examples.
Answer:
Exothermic reactions : Those reactions in which heat is evolved are known as exothermic reactions. 

An exothermic reaction is indicated by writing “+ Heat”on the products side of an equation.

Example :
(i) C (s) + O2 (g) → CO2 (g) + Heat
(ii) N2 (g) + 3H2 (g) → 2NH3 (g) + Heat

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

An endothermic reaction is usually indicated by writing “Heat” on the product side of a chemical equation.
Examples :
(i) C (s) + 2S (s) → CS2 (l) – Heat
(ii) N2 (g) + O2 (g) → 2NO(g) – Heat

Question 10
Why is respiration considered an exothermic reaction ? Explain.
Answer:
Respiration is an exothermic process because during respiration glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with the production of energy.

C6H12O6 + 6O2 --- > 6CO2 + 6H2O + energy.

Question 11
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer:
In a decomposition reaction, a single compound breaks down to produce two or more simpler substances.
For example:

2H2O (l) --- > 2H2 + O2

While, in a combination reaction, two or more substances simply combine to form a new substance.
For example:

2H2 + O2 --- > 2H2O

Question 12
Write one equation each for the decomposition reactions where energy is supplied in the form of heat, light or electricity.
OR
Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity. [CBSE 2015 (Delhi)]
Answer

Question 13
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer:
In displacement reactions, a more reactive metal displaces a less reactive metal from its solution. For example,
Fe(s) + CuSO4(aq) → Cu(s) + FeSO4(aq)
This is a displacement reaction where iron displaces copper from its solution.
In double displacement reactions, two reactants in solution exchange their ions. For example,
AgNO3(aq) + NaCl (aq) → AgCl(s) + NaNO3 (aq)
This is a double displacement reaction where silver nitrate and sodium chloride exchange Cl– and NO3– ions between them.

Question 14
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Answer:

AgNO3 + Cu --- > Cu(NO3)2 + Ag

Question 15
What do you mean by a precipitation reaction ? Explain by giving examples.
Answer:
A reaction in which an insoluble solid called precipitate is formed that separates from the solution is called a precipitation reaction.
Example : When a solution of iron (III) chloride and ammonium hydroxide are mixed, a brown precipitate of iron (III) hydroxide is formed.

FeCl3 + NH4OH --- > Fe(OH)3 + NH4Cl

Question 16
Explain the following in terms of gain or loss of oxygen with two examples each:
(a) Oxidation and
(b) Reduction.
Answer:
(a) Oxidation : The addition of oxygen to a substance is called oxidation.
Example :
(i) S(s) + O2(g) → SO2(g) (Addition of oxygen to sulphur)
(ii) 2Mg(s) + O2 (g) → 2MgO(s) (Addition of oxygen to magnesium)

(b) Reduction : The removal of oxygen from a substance is called reduction.
Example: (i) CuO + H2 Heat−→−− Cu + H2O
Here, copper oxide is being reduced to copper because oxygen gets removed from copper oxide.

(ii) ZnO + C → Zn + CO
Here, zinc oxide is being reduced to zinc because oxygen gets removed from zinc oxide.

Question 17
A shiny brown colored element ‘X’ on heating in the air becomes black in color. Name the element ‘X’ and the black coloured compound formed.
Solution:
The shiny brown colored element X is copper metal (Cu). When copper metal is heated in air, it forms a black colored compound copper oxide. So, the black colored compound is the copper oxide or copper (II) oxide, CuO.

Question 18
Why do we apply paint on iron articles?
Solution:
Rust is a soft and porous substance, which gradually falls from the surface of an iron object, and then the iron below starts rusting. Thus, rusting of iron (or corrosion of iron) is a continuous process which, if not prevented in time, eats up the whole iron object. So, when we apply paint on iron articles it reduces the rusting of iron.

Question 19
Oil and fat containing food items are flushed with nitrogen. Why?
Solution:
Packaging fat and oil containing foods in nitrogen gas can prevent rancidity. When the fat and oil present in food materials gets oxidised (in air), their oxidation products have an unpleasant smell and taste. When it is surrounded by unreactive gas, nitrogen, there is no oxygen (of air) to cause its oxidation and make it rancid.

Question 19
Explain the following terms with one example each.
a. Corrosion
b. Rancidity
Solution:
a. Corrosion is the process in which metals are eaten up gradually by the action of air, moisture or a chemical on their surface. Corrosion is caused mainly by the oxidation of metals by the oxygen of air.
Example: Rusting of iron is the most common form of corrosion. When an iron object is left in damp air for a considerable period of time, it gets covered with a red-brown flaky substance called ‘rust’. This is called rusting of iron.
b. The condition produced by aerial oxidation of fat and oil in food which is marked by an unpleasant smell and taste is called rancidity.
Example: Rancidity can be retarded by keeping food in a refrigerator.
The refrigerator has a low temperature inside it. When the food is kept in a refrigerator, the oxidation of fat and oil in it is slowed down due to low temperature. So, the development of rancidity due to oxidation is retarded.