Atom And Molecule

Atom

An atom is the smallest unit into which matter can be divided without the release of electrically charged particles.

It also is the smallest unit of matter that has the characteristic properties of a chemical element.

The atom is the basic building block of all matter.

Atoms are very small, they are smaller than anything that we can imagine or compare with.

More than millions of atoms when stacked would make a layer barely as thick as a sheet of paper.

Most of the atom is empty space.

The rest consists of a positively charged nucleus of protons and neutrons surrounded by a cloud of negatively charged electrons.

 

Atomic mass

Atomic mass is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element.

Atomic mass indicates the size of an atom.

Although the mass is the sum of all the protons, neutrons and electrons in an atom.

Molecule

A molecule is in general a group of two or more atoms that are chemically bonded together, that is tightly held together by attractive forces.

A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance.

Atoms of the same element or of different elements can join together to form molecules.

 

Ion

Compounds composed of metals and non-metals contains charged species. The charged species are known as Ions.

An ion is a charged particle and can be negatively or positively charged.

Negatively charged ion is called an ‘anion’ and the positively charged ion, a ‘cation’.

A group of atoms carrying a charge is known as a polyatomic ion.

Types of Plant tissues and Plant tissues

 Types of Plant tissues:

 

(1) Meristematic tissue: Meristematic tissues are group of cells, which have the ability to divide.

This tissue consists of small, cubodial densely packed cells, which keeps on dividing to form new cells.

These tissues are capable of stretching, enlarging and differentiate into other types of tissues as they mature.

Meristematic tissues give rise to permanent tissues.

 

There are three types of meristem based on the origin of meristematic cells :- Apical meristem, Lateral meristem and Intercalary meristem.

(a) Apical meristem is the region at the tip of the plant body. Thus, apical meristem helps in the increase in the height of the plant.

(b) Lateral meristem is a meristem located parallel to the sides of a stem or root, responsible for the thickening of the stem or root by the addition of secondary growth.

(c) Intercalary meristem is a meristem developing between regions of mature or permanent tissue (as at the base of the grass leaf).

 

(2) Permanent tissues:The tissues, which are derived from the Meristematic tissues, are called as permanent tissues.

They are the tissues, which have lost their ability to divide as they have attained their mature form.

Permanent tissues may be classified into three main groups:Simple,Complex and Special tissues.

(a) Simple Tissue:

Simple tissues are homogeneous and composed of structurally and functionally similar cells.

These are of three types:

(i) Parenchyma:

Parenchyma is the most common tissue which is morphologically and physiologically simple and unspecialized. These cells are found in epidermis, cortex, pericycle, pith etc. They are responsible for photosynthesis, storage of food, secretion etc.

(ii) Collenchyma:

Collenchyma are living tissues composed of more or less elongated cells and often have some chloroplast to carry on photosynthesis. It is generally situated below the epidermis.

(iii) Sclerenchyma:

Cells are long, thick-walled and lignified with tapering ends. These are fibre like in appearance and also known as sclerenchymatous fibre. These are dead cells and perform mechanical function.

(b) Complex tissue:

The complex tissues are composed of different types of cells performing diverse functions.

These  are of two types xylem and phloem:

(i) Xylem: Xylem is the one of the two types of transport tissue in vascular plants.The basic function of Xylem is transport water from roots to shoots and leaves,but it also transport some nutrients.

(ii) Phloem: It is the living tissue that transports the soluble organic compounds made during photosynthesis.

 

(c) Special tissue:

Special tissues are structurally modified and specially organized for secretary function.

These are of two types:

(i) Laticiferous tissue: These are specialized tube like structures known as laticiferous ducts found in many angiosperms.

These ducts are filled with white or yellow latex. Laticiferous ducts are of two types: Latex cells as found in madar and Latex vessels as found in rubber, papaya etc.

 

(ii) Glandular tissue: It consists of different types of glands which are formed by single cell or group of cells. These secrete resin, oil, mucilage, tannin, gums etc.

 

Tissue-Explanation and its Types

 Tissue

A group of cells that are similar in structure and work together to achieve a particular function is called tissue.

Or you can say a group of cells having common origin, similar structure and performing a definite function is called a tissue.

Organs are formed by the functional grouping together of multiple tissue.

All living organisms are made of cells.

In Unicellular organisms, a single cell performs all basic functions.

For example: Amoeba

In Amoeba, a single cell carries out movement,intake of food and respiratory gases, respiration and excretion.

But in Multi-cellular organisms there are millions of cells.Most of these are specialized to carry out a few functions. Each specialized function is taken up by a different group of cells.

Since these cells carry out only a particular function,they do it very efficiently. In human beings muscle cells contract and relax to cause movement,nerve cells carry messages, blood flows to transport oxygen,food,hormone and waste materials and so on.

In plants, vascular tissues conduct food and water from one part of the plant to other parts. So multi-cellular organisms show division of labor.

Cells specializing in one function are often group together in the body. This means that a particular function is carried out by a cluster of cells,called a tissue,is arranged and designed so as to give the highest possible efficiency of function.

Blood,phloem and muscles are all example of tissues.

Is there any difference between Plant and Animal tissue?

There are noticeable difference between plant tissues and animal tissues.

Plants are fixed they don’t move from one place to other which provides them structural strength.Most of these tissues are dead,since dead cells provide mechanical strength as easily as live ones and need less maintenance. The growth in plants are limited in certain regions.

On the other hand animals move around in search of food etc. They consume more energy as compare to plants.Most of there tissues are living. Cell growth in animals is more uniform.

Plant tissue

They are grouped into two basic types.

Meristematic tissues: Meristematic tissues are group of cells, which have the ability to divide.

This tissue consists of small, cubodial densely packed cells, which keeps on dividing to form new cells. These tissues are capable of stretching, enlarging and differentiate into other types of tissues as they mature. Meristematic tissues give rise to permanent tissues.

Permanent tissues:The tissues, which are derived from the Meristematic tissues, are called as permanent tissues.

They are the tissues, which have lost their ability to divide as they have attained their mature form.

Animal tissue

They are grouped into four basic types.

Epithelial tissue: Covers body surfaces and lines body cavities

Muscular tissues: Enables movement of structures within the body and movement of the entire person/animal

Connective tissues: Binds and Supports body parts

Nervous tissue: Enables responses to stimuli and coordinates bodily functions.

Metals and Non-Metals (important questions)

Metals and Non-Metals (important questions)

Q1. Give examples of five elements that are metallic.

Ans. Copper, iron, gold, silver and aluminium.

Q2. Give examples of five elements that are non-metallic.

Ans. Sulphur, phosphorus, carbon, hydrogen, oxygen, chlorine and bromine.

Q3. How do metals and non-metals combine?

Ans. Metals and non-metals combine by transference of electrons from metals to non-metals.

Q4. What is an ionic bond ?

Ans: The electrostatic attraction between the cation and anion is called the ionic bond.

Q5. Hydrogen is not a metal, yet it is placed in the activity series of metals. why ?

Ans. Like metals, hydrogen can lose an electron to form positive ion (H+).

Q6. Why is H2 gas not evolved when a metal is treated with nitric acid.

Ans. Nitric acid is a strong oxidising agent. It oxidises the H2 produced to water and itself gets reduced to some oxide of nitrogen, i.e. nitrous oxide (N2O), nitric oxide (NO).

Q7. Name two metals other than silver and gold which are not attacked even by steam.

Ans. Lead and copper.

Q8. What are minerals ?

Ans. The elementary state or the compounds in form of which the metals occur in nature, associated with impurities of gangue, etc. are called minerals.

Q9. What is an ‘ore’ ?

Ans. The mineral from which metal can be extracted conveniently and economically is called an ore.

Q10. What do you understand by ‘thermite reaction’ ?

Ans. The reduction of metal oxide to metal using aluminium as the reducing agent is called thermite reaction or aluminothermy.

Q11. Why aluminium does not occur in native state ?

Ans. Aluminium, being a reactive metal, combines with oxygen readily to form alumina.

Q12. What is the composition of stainless steel ?

Ans. Iron (74%), chromium (18%) and nickel (8%).

Q13. Name the metals which are usually alloyed with gold to make it harder.

Ans. Copper and silver.

Q14. What is meant by 22 carat gold ?

Ans. An alloy consisting of 22 parts by weight of pure gold and 2 parts by weight of copper or silver is called 22 carat gold.

Q15. Why is pure gold not suitable for making ornaments ?

Ans. Because, pure gold is soft and ductile.

Q16. Name a metal which is used for galvanising iron ?

Ans. Zinc.

Q17. Why is an iron grill painted frequently ?

Ans. To protect it from rusting.

Q18. Name two metals which are highly resistant to corrosion.

Ans. Platinum and gold.

Q19. The corrosion of iron is called…   .

Ans. Rusting.

Q20. The process of depositing a thin layer of zinc on iron articles is called  …….. .

Ans. Galvanisation.

Q21. State conditions for rusting of iron.

Ans. Presence of moisture and air.

Q22. Metals generally occur in solid state. Name and write the symbol of a metal that exists in liquid state at room temperature.

Ans. Mercury (Hg).

Q23. Alloy are used in electrical heating devices rather than pure metals. Give one reason.

Ans. Alloys generally have lower melting points than the constituent metals. Therefore, in case short – circuiting occurs, the alloy melts, electrical connection is broken and fire are avoided.