WHAT IS REFLEX ARC

Reflex Arc 

Meaning

A reflex arc is the pathway followed by a nerve impulse during a reflex action (quick, automatic response without thinking).

 Reflex actions are controlled mainly by the spinal cord, not the brain (brain gets the information later).

•  Steps / Pathway of Reflex Arc

1. Receptor (Sense organ)
   Detects stimulus (like heat, pain)

2. Sensory neuron
   Carries message from receptor to spinal cord

3. Spinal cord (Relay neuron / Interneuron)
   Processes the message quickly

4. Motor neuron
   Carries message from spinal cord to muscles

5. Effector (Muscle/Gland)
   Gives response (movement)

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 Example: Touching a Hot Object

Stimulus: Heat from hot pan
Receptor: Skin receptors detect heat/pain
Sensory neuron: Sends impulse to spinal cord
Spinal cord: Immediately sends response signal
Motor neuron: Carries impulse to arm muscles
Effector: Arm muscles contract
Response: Hand is pulled back quickly

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Diagram Line (for exam writing)

Receptor → Sensory neuron → Spinal cord (relay neuron) → Motor neuron → Effector

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 2-line Board Exam Answer

A reflex arc is the route taken by nerve impulses during a reflex action.
Example: When we touch a hot object, the impulse goes from skin → spinal cord → muscles, and the hand is withdrawn immediately.

OUR ENVIRONMENT

 

OUR ENVIRONMENT

 Environment – The surrounding of any living organism is termed as its Environment.

 Enzymes – Enzymes are particular chemicals which convert the complex molecules into simpler ones. 

Biodegradable substances	Non-biodegradable substances
Substances that can be broken down into simpler molecules by the action of enzymes are biodegradable substances. Egs. Kitchen wastes, paper, leaves, etc. These substances do not prove harmful to the environment. Instead enriches the fertility of the soil after its decomposition.	Substances that cannot be broken down into simpler form are called Non-biodegradable substance. Egs. Glass, plastic, etc These substances persist in the environment for a long time and harm the members of ecosystem.

 Ecosystem – The interaction between the living and non-living components of the environment constitutes an Ecosystem.

 Components of ecosystem

Biotic Components	Abiotic Components
Living components of the ecosystem are called biotic components Egs. Plants, animals, microorganisms	Non living components of the ecosystem are called abiotic components Egs soil, sunlight, rainfall, temperature

 Natural ecosystems – Forests, ponds, lakes, etc

Artificial ecosystem – garden, crop fields, etc

 

Producers	Consumers	Decomposers
Organisms which produce their own food are called producers. Egs. Green plants, blue green algae	Organisms which depend on producers directly or indirectly for their food are called consumers. Egs. Herbivores and carnivores.	Organisms that decompose the dead and decaying matter are called as decomposers. Egs microorganisms

 

Food Chain: The transfer of food energy from one tropic level to another is called food chain.

Primary Consumers(Herbivores): The animals which obtain their food energy directly by feeding on Plants. Eg. Grasshopper, Deer, cattle.

Secondary Consumers: The animals which depend on herbivores for their food. Eg. Frog, Lion, Tiger.

Tertiary Consumer: The animals which obtain their food by feeding on secondary consumers. Eg. Snake

Ecological Pyramids: Graphical representations of the successive tropic levels and the relation among them are called as “Ecological pyramids”

 Food web: Complex network of interconnected food chain, forms a food web.

Ø  Energy flow is unidirectional.

Ø  Only 10% of the energy available at any tropic level is getting transferred to next level.

Bio magnification / Biological magnification: Increase in concentration of toxic substance from one tropic level to another.

 Environmental Problems

1)     Depletion of Ozone layer

2)     Garbage disposal

 Depletion of Ozone layer

Ozone (O3) – This formed by 3 atoms of oxygen.

This is deadly poisonous.

This filters the harmful UV radiations. (UV radiations causes skin cancer)

Depletion of Ozone – the reason for the depletion of ozone layer is the use of the synthetic chemicals like chlorofluorocarbon (CFC)

 Garbage disposal

This is one of the major problems we face now-a-days.

Improvement in our life style is resulting in generation of more waste material.

Use of disposable things and changes in the packaging system is resulting in generation of non-biodegradable wastes

 

 

METALS AND NON METALS [CLASS 10]

 

Metals And Non-Metals

 Physical properties of Metals and Non-Metals

METALS	NON-METALS
Metals are in solid state at room temperature. (mercury is in liquid state)	Non-metals are usually gases or solid at room temperature (bromine is in liquid state)
Metals are generally hard (Sodium and Potassium are soft) Melting and Boiling point is high (Gallium and Caesium melts on palm)	Non-metals are generally soft. Melting and Boiling point is low (Diamond is hardest substance)
Metals are Lustrous	Non-metals are non lustrous (Iodine is exception)
Metals are malleable (Can be beaten into sheets)	Non-metals are not malleable
Metals are ductile (Can be drawn into wires)	Non-metals are not ductile
Metals are good conductors of electricity	Non-metals are bad conductors of electricity (graphite is good conductor)
Metals are sonorous (makes sound when strike to hard surface)	Non-metals not sonorous
Oxides of metals are basic in nature	Oxides of non-metals are basic in nature

 ¨      Chemical Properties

 ·        With Oxygen (metals burn in air)

Metal + Oxygen à Metal Oxide

 Copper when heated in air, it combines with oxygen to form copper oxide (black oxide)

    2Cu + O₂ à2CuO 

 Aluminium forms Aluminium oxide

    4Al + 3O₂ à 2Al₂O₃

 In general, Metal oxide is basic in nature.

 Amphoteric Oxides – Some of the metal oxides are Acidic as well as basic in nature.

They react with both, acids as well as bases to produce salt and water.

Al₂O₃ + 6HCl à 2AlCl₃ + H₂O

Al₂O₃ + 2NaOH à2NaAlO₂ + H₂O

Metal oxides are usually insoluble in water

 Water soluble metal oxides are called as “Alkalis”

    Na₂O + H₂O à 2NaOH

    K₂O + H₂O à 2KOH

 Rate of reaction of metals with Oxygen

§  Potassium and Sodium react vigorously and catch fire if kept open.

(To prevent accidental fires these metals are stored under kerosene)

§  A thin oxide layer is formed on the surface of the metals like aluminium, magnesium, zinc, etc. when exposed to air at ordinary temperature.

(This oxide layer prevents the further oxidation of the metal)

§  Iron does not burn on heating but iron filings burns vigorously when sprinkled in the flame of the burner.

§  Copper does not burn. But it forms a black layer of copper oxide when heated.

§  Silver and Gold do not react with oxygen even at high temperature.

 Anodising – This is the process of forming a thick layer of Aluminium.

When exposed to air, aluminium forms a thin oxide layer. This prevents the further corrosion of the metal.

 ·        With water

Metal + Water à Metal Oxide + Oxygen

Metal Oxide + Water à Metal Hydroxide

 Sodium and potassium reacts violently with cold water

The reaction is highly exothermic and so the hydrogen released in the reaction catches fire.

2K + 2H₂O à 2KOH + H₂ + heat energy

2Na + 2H₂O à 2NaOH + H₂ + heat energy

 The reaction with Calcium too is exothermic. But the heat released is not sufficient for hydrogen to catch fire.

Ca + 2H₂O à Ca(OH)₂ + H₂

ü  Calcium floats on water because the bubbles of hydrogen gas stick to the calcium metal.

 ü  Magnesium reacts with hot water to form magnesium hydroxide and hydrogen.

Magnesium too floats on water as the bubbles of hydrogen gas.

 Aluminium, Iron and Zinc reacts with steam to form its oxide and hydrogen.

    2Al + H₂O à Al₂O₃ + 3H₂

    3Fe + 4H₂O à Fe₃O₄ + 4H₂

 Lead, Copper, silver and gold do not react with water at all.

 

·        With Acids

Metal + Dilute Acid à Salt + Hydrogen

 Mg + 2HCl à MgCl₂ + H₂

2Al + 6HCl à 2AlCl₃ + 3H₂

Zn + 2HCl à ZnCl₂ + H₂

2Fe + 6HCl à 2FeCl₃ + 3H₂

The reaction is different in case of Nitric Acid (HNO₃)

ü  Nitric acid is a strong oxidising agent. It oxidise the oxygen produced to water and itself gets reduced to nitrogen oxide.

Magnesium and Manganese react with very dilute nitric acid to evolve H₂

 Reactivity – Mg > Al > Zn > Fe

 ·        Metal with Solutions of other Metal Salts

Metal A + Salt solution of B à Salt solution of B + Metal B

Reactive metals displace less reactive metals from their compounds or molten state.

Fe + CuSO₄ à FeSO₄ + Cu

Zn + CuSO₄ à ZnSO₄ + Cu

·        Metals react with Non-Metals

Reactivity à tendency to attain stable electronic configuration

Noble gases à stable configuration

 Formation of sodium chloride

Sodium (Na) – Atomic number – 11

Electronic configuration – 2,8,1

Chlorine (Cl) – Atomic number – 17

Electronic configuration – 2,8,7

Sodium loses one electron and forms Na⁺

Chlorine gains one electron and forms Cl^-

Sodium and chlorine ions attract each other and are held by strong electrostatic force of attraction and forms sodium chloride (NaCl)

 Ionic Compounds – The compounds formed by transfer of electrons from metal to non-metal are known as ionic compounds

 Formation of Magnesium Chloride

Properties of Ionic Compounds

1) Physical nature – Ionic compounds are solids at room temperature. These are hard substance due to the strong force of attraction.

2) Melting and Boiling Point – MP and BP of ionic substances are too high as large amount of energy is required to break the strong inter-ionic attraction.

3) Solubility – Ionic compounds are soluble in water and insoluble in organic solvents like petrol, kerosene, etc.

4) Conduction of electricity – Ionic compounds conducts electricity in its solution or molten state. (Movement of ions is responsible for the conductivity). They do not conduct electricity in its solid state.

 Occurrence of Metals

Earth’s crust – major source of metals

Sea water – soluble salts like sodium chloride, magnesium chloride

§  Minerals – The elements or compounds which, occurs naturally in earth’s crust are known as minerals.

§  Ores – Minerals which contain a very high percentage of particular metal is called Ores.

 1) Less Reactive Metals – Found in Free State (gold, silver, platinum and copper)

2) Highly Reactive Metals – Never exists in Free State (K, Na, Ca, Mg, Al)

3) Moderately reactive – these are found in earth’s crust in their oxides, sulphides or carbonates form (Zn,Fe, Pb)

 Steps involved in extraction of metals

 

 Metallurgy – The process of extraction of metals from their respective ores is termed as Metallurgy.

Gangue – Impurities such as soil, sand, etc associated with the ores is called as gangue.

 Extraction of metals

 ¨      Metals low in activity series

Oxides of these metals are heated to reduce to metals.

2HgS + 3O₂ à 2HgO + 2SO₂

2HgO à 2Hg + O₂

 2CuS + 3O₂ à 2Cu₂O + 2SO₂

2Cu₂O + Cu₂S à 6Cu +SO₂

 

¨      Metals in middle activity series

These metals occur in the form of sulphide or carbonate ores.

Sulphides and carbonates are converted to metal oxides.

Metals oxides are then reduced to metal

 Roasting – Roasting is the process of strong heating sulphides ores in the presence of excess air.

    2ZnS + O₂ à 2ZnO + SO₂

 Calcination – Calcination is the process of strong heating of carbonate ores in limited supply of air.

    ZnCO₃ à ZnO + CO₂

     Metal oxides formed are reduced to metals b using suitable reducing agent (like carbon)

    ZnO + C à Zn + CO

 In some cases, displacement reactions are used to reduce the metal oxide.

Highly reactive metals displace and reduce the lesser reactive metal from it’s compound.

3MnO + 4Al à 3Mn + 2Al₂O₃ + heat

Fe₂O₃ + 2Al à 2Fe +  Al₂O₃ + heat

 

¨      Metals on the top of Activity Series

Electrolytic reduction method is used to obtain these metals.

Sodium, Magnesium, Calcium, etc are obtained by electrolysis of their molten chlorides.

At cathode   Na⁺ + e^- à Na

At anode      2Cl^- à Cl₂ + 2e^-

Refining of metals

This is the final step to get the purest form of metal by removing all the impurities.

Electrolytic refining is the method widely used for this.

 Corrosion

Corrosion is the deterioration of a metal as a result of chemical reactions between it and the surrounding environment.

Both the type of metal and the environmental conditions, particularly gases that are in contact with the metal, determine the form and rate of deterioration.   

 

§  Silver articles become black. This is because silver reacts with the sulphur in the air and forms coating of silver sulphide.

§  Green coat is formed on copper articles. Copper reacts with moist carbon dioxide and forms a greenish coat of copper carbonate.

§  Iron articles rusts. Iron when exposed to moist air forms a brown flaky substance called rust.

 

Prevention of corrosion

Rusting is prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys.

Galvanisation – Articles are coated with thin layer of Zinc.

Alloy – This is the homogeneous mixture of two or more metals or a metal and a non-metal.

Steel = Iron + Nickel + Chromium + carbon (very less)

Brass = Copper + Zinc

Bronze = Copper + Tin

Solder = Lead + Tin (low MP. Used for welding)

Amalgam – An Alloy in which one metal is mercury

 Note – Pure gold is very soft and not suitable for making jewellery.

Addition of 2 parts of copper (or silver) to 22 parts of gold makes it hard.