Class 9

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

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JAC Board Class 9th Science Chapter 7 Notes Diversity in Living Organisms

→ Biodiversity: The word ‘biodiversity’ is used to define the diversity of life forms. Biodiversity is a word more often used to refer to the variety of life forms found in a particular geographic region.

→ Diversity: Diversity of life forms in a geographic region provides stability in that region.

→ Taxonomy: It is a branch of biology . which deals with identification, nomenclature and classification of organisms. Carolus Linnaeus is called the father of taxonomy.

→ Classification: The method of arranging organisms into groups or sets on the basis of similarities and differences is called classification.

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

→ Importance of Classification
a. It makes the study of a wide variety of organisms easy and systematic.
b. It helps to understand how the different organisms have evolved with time.
c. It helps to understand the inter-relationships among different groups of organisms.
d. It forms a base for the study of other biological sciences, like biogeography.

→ Classification of organisms by Aristotle: Greek philosopher, Aristotle first classified the animals based on their place of residence, i.e., whether they lived on land, in water or in the air. However, this was not an appropriate way to group organisms as animals living in the same habitat can have very different characteristics.

→ Later, all the living organisms were identified and categorised on the basis of their body structure and function. The idea of evolution was first described by Charles Darwin in 1859 in his book ‘The Origin of Species.’

→ Basis of Classification: There are certain features or properties used for the classification of living organisms which are known as characteristics. Organisms with same characteristics are placed in same groups.

→ The major characteristics considered for classification of all organisms into five major kingdoms are:
a. Type of cellular organisation
i. Prokaryotes: The organisms which have cells without well defined nucleus are called prokaryotes.
ii. Eukaryotes: The organisms which have cells with well defined nucleus are called eukaryotes. Presence of nucleus and membrane bound organelles give better efficiency to the cells.

b. Body organisations
i. Unicellular: The organisms made up of a single cell alone are termed as unicellular organisms. In them, the single cell is responsible for carrying out all the necessary functions to maintain life.
ii. Multicellular: The organisms made up of more than one cell are called multicellular organisms. Because of more number of cells, there can be some division of labour to gain more efficiency.

c. Mode of obtaining food
i. Autotrophs: Organisms producing their own food are called autotrophs. All green plants are examples of autotrophs. They have a pigment called chlorophyll, which facilitates photosynthesis.
ii. Heterotrophs: Organisms who are dependent on either plants or animals are called heterotrophs. They do not have chlorophyll. All animals, fimgi, various bacteria and protozoa belong to this group.

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

→ Hierarchy of Classification:
Linnaeus proposed a classification system that arranged organisms into taxonomic groups at different levels according to the characteristics they have. The groups or the levels from top to bottom are:
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 1
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 2
→ Nomenclature: An organism can have different names in different languages. This creates confusion in naming the organism. So, a scientific name is needed which is accepted globally. Binomial system of nomenclature given by Carolus Linnaeus is used for naming different organisms.

→ Following are some conventions in writing the scientific names:
a. Genus should be written first, followed by the name of the species.
b. First letter of the genus should be capital and that of the species should be in small letter.
c. When printed, the name should be written in italics and if hand written, the genus and the species should be underlined separately.
For example – Homo sapien for human, Panthera tigris for tiger.

→ Classification System
a. Two Kingdom Classification: Carolus Linnaeus in 1758 classified the living organisms into two groups, viz., plants and animals.
b. Five Kingdom Classification: Whittaker in 1959, further classified the organisms into five kingdoms,viz. Monera, Protista, Fungi, Plantae and Animalia.

→ Carl Woese in 1977 further divided kingdom Monera into Archaebacteria (or Archaea) and Eubacteria (or Bacteria).

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

→ Kingdom Monera
a. Prokaryotic, unicellular.
b. Can be autotrophic or heterotrophic.
c. May or may not have a cell wall.
d. Examples: Anabaena and bacteria (heterotrophic), Cyanobacteria or blue green algae (autotrophic).
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 3

→ Kingdom Protista
a. Eukaryotic, unicellular.
b. Can be autotrophic or heterotrophic.
c. Have cilia, flagella or pseudopodia for locomotion.
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d. Examples: Plant like – unicellular algae, diatoms; Animal like – protozoans (Amoeba, Paramecium, Euglena); Fungi like – slime moulds and water moulds.

→ Kingdom Fungi
a. Heterotrophic, eukaryotic organisms.
b. Saprophytic. They use.decaying organic materials as food.
c. Some fungi live in a symbiotic relationship with cyanobacteria. They are called lichens. The algal part provides food and the fungal part provides minerals and substratum.
d. Cell wall is made up of chitin.
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e. Examples: Mushrooms (Agaricus), green mould (Penicillium), smut (Aspergillus).

→ Kingdom Plantae:
a. Multicellular, eukaryotic.
b. Autotrophs, use chlorophyll for photosynthesis.
c. Cellulosic cell wall present.

→ Kingdom Animalia:
a. The organisms of Animalia include all organisms which are multicellular, eukaryotic and without cell wall.
b. Organisms of kingdom Animalia are heterotrophs.

→ Classification of Kingdom Plantae
Based upon body differentiation, types of vascular tissues (xylem or phloem), reproductive structures (seeds or spores) and type of seeds, (covered or naked), kingdom plantae is divided into the following divisions:

→ Division 1: Thallophyta
a. The plants of thallophyta do not have well differentiated body.
b. The plants in thallophyta are known as algae and they are predominantly aquatic.
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c. Examples: Spirogyra, Ulothrix, Cladophora, Chara, etc.

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

→ Division 2: Bryophyta
a. The plants of this group are called amphibians of plant kingdom.
b. Though not distinctly developed, plant body can be differentiated to form stem and leaf like-structures.
c. Examples: Moss (Funaria) and Marchantia.
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→ Division 3: Pteridophyta
a. Plants of Pteridophyta have defined roots, stems and leaves.
b. These plants have specialised tissues that transport water and other materials from one part to another part of the plant.
c. Examples: Marsilea, fem and horse-tails.
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d. The similarity among the thallophytes, the bryophytes and the pteridophytes is that all of them have naked embryos, which are known as spores.
e. The plants of these groups are known as ‘cryptogams’, which means ‘hidden reproductive organs’.

→ Division 4: Gymnosperms
a. The plants of this group bear naked seeds and are usually perennial, evergreen and woody.
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b. Examples: Pine, Cycas and Deodar.

→ Division 5: Angiosperms
a. This word is made from two Greek words: angio- meaning covered and sperma- meaning seed.
b. The seeds develop inside an organ which is modified to become a fruit. These are also called flowering plants.
c. Plant embryo in seeds has structures called cotyledons. Cotyledons are called ‘seed leaves’ because in many instances they emerge out and become green when the seed germinates.
d. The angiosperms are divided into two groups on the basis of the number of cotyledons present in the seed:

  • Monocots (Monocotyledonous): These seeds have a single cotyledon. E.g., onion.
  • Dicot (Dicotyledonous): These seeds have two cotyledons. E.g., musturd.

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 10

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

→ Classification of Kingdom Animalia
Based on the extent and type of the body design differentiation, Animal kingdom is classified into the following phyla:

→ Phylum Porifera
a. Cellular level of organisation.
b. Non-motile animals.
c. Holes on the entire body surface which lead to a canal system for circulation of water and food.
d. Hard outside layer known as skeleton.
e. Examples: Sponges (Spongilla, Sycon).
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 11

→ Phylum Coelenterata
a. Tissue level of organisation.
b. No coelom.
c. Radial symmetry’, diploblastic.
d. Hollow gut, move from one place to another.
e. Examples: Hydra, sea-anemone, jelly fish, corals.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 12

→ Phylum Platyhelminthes
a. Well-developed organs.
b. No coelom.
c. Known as flatworms.
d. Bilateral symmetry, triploblastic.
e. Free living or parasitic.
f. Digestive cavity has a single opening for ingestion and egestion.
g. Examples: Planaria, liverfluke, tape worm, etc.
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→ Phylum Nematoda
a. Cylindrical body.
b. No well-developed body (i.e., no real organ).
c. False coelom.
d. Bilateral symmetry, triploblastic.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 14
e. Many are parasitic worms living inside human body and can cause various diseases, like filarial worms cause elephantiasis, round worms and pin worms living in human intestine cause infection.
f. Examples: Ascaris, Wuchereria.

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

→ Phylum Annelida
a. Found everywhere including fresh water, marine water as well as on land.
b. Bilaterally symmetrical and triploblastic body.
c. True body cavity present.
d. Segmented (segments specialised for different functions).
e. Extensive organ differentiation.
f. Examples: Earthworm, Nereis, leeches.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 15

→ Phylum Arthropoda
a. The largest group of animals.
b. Open circulatory system.
c. Generally known as insects.
d. Bilateral, triploblastic.
e. Segmented, sometimes fused.
f. Jointed appendages like feet, antenna.
g. Examples: Prawns, butterflies, houseflies, spiders, scorpions, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 16

→ Phylum Mollusca
a. Coelom present.
b. Triploblastic, bilateral symmetry.
c. Soft bodies, sometimes covered with shell.
d. Generally not segmented.
e. No appendages present.
f. Kidney-like organs for excretion.
g. Examples: Chiton, Octopus, Pila, Unio.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 17

→ Phylum Echinodermata
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a. Spiny skinned.
b. Free-living marine organisms.
c. Triploblastic with coelom present.
d. Skeleton of calcium carbonate.
e. Water vascular system for locomotion.
f. Bilateral symmetry before birth.
g. Examples: Starfish, sea cucumber,
feather star, etc.

→ Phylum Hemichordata
a. Small group of marine animals.
b. Cylindrical, bilateral symmetry, triploblastic.
c. Coelom present.
d. Gills for respiration.
e. Examples: Balanoglossus.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 19

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

→ Phylum Chordata
a. Bilateral symmetry, triploblastic.
b. Coelom present.
c. Notochord present.
d. Gills presented at some phase of life.
e. Dorsal nerve chord.
f. Post-anal tail present at some stage of life, e.g., in human beings during embryonic stages.

Phylum chordata is further subdivided into three sub-phyla, namely, urochordata, cephalochordata and vertebrata. Urochordata and cephalochordata are together called as Protochordata.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 20
a. Protochordata

  • Bilaterally symmetrical, triploblastic.
  • Coelom present.
  • Marine.
  • Examples: Herdmania, Amphioxus,

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 21

b. Vertebrata

  • Notochord is replaced by vertebral column
  • Two, three, four chambered heart. Examples: Human (4 chambered), frog (3 chambered), fishes (2 chambered).
  • Organ for excretion, e.g., kidney, is present.
  • Paired appendages.

→ Classification of Vertebrata
The organisms of this kingdom have a true vertebral column and an internal skeletal structure. Vertebrates are further classified into the following classes:

Cyclostomata:
a. Jawless vertebrates.
b. Elongated body.
c. Circular mouth, slimy skin, scaleless.
d. Ectoparasites or borers of other vorebebrates.
e. Example: Petromyzon, Myxine (Hagfish).
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 22

Pisces:
a. The organisms of this group are typically different types of fishes.
b. Fishes can live only in water.
c. The skin of fishes is covered with scales/plates.
d. Fishes use oxygen dissolved in water to breathe with the help of the gills.
e. The tail of a fish helps in its movements.
f. Fishes are cold-blooded organisms and their hearts have only two chambers.
g. Fishes lay eggs (oviparous).
h. Examples: Rohu, Catla, Scoliodon, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 23

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

Amphibia:
a. The organisms of Amphibia have mucus glands in the skin, and they have three- chambered heart.
b. Amphibians can live in water as well as on land.
c. These organisms respire through either gills or lungs.
d. They lay eggs.
e. Examples: Salamander, toad, frog, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 24

Reptilia:
a. The organisms of Reptilia are cold blooded. They cannot maintain a constant body temperature.
b. They have three-chambered heart, except crocodiles which have four- chambered heart.
c. These organisms lay eggs with tough coverings (oviparous).
d. They have scales.
e. Examples: King cobra, turtle, chameleon, lizard, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 25

Aves:
a. Aves are warm-blooded.
b. These organisms lay eggs.
c. Most of the Aves have feathers.
d. Four-chambered heart is present.
e. They have hollow bones which help them to fly.
f. Examples: Pigeon, crow, etc.
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Mammalia
a. The organisms of Mammalia are warmblooded and they have four-chambered heart.
b. Mammalia are typically characterised for their mammary glands.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 27
c. Mammary glands produce milk to nourish the young ones.
d. Most of the mammals give birth to young ones. However, a few mammals, such as the Platypus and the Echidna, lay eggs.
e. Skin of mammals has hair along with sweat and oil glands.
f. Examples: Human, bat, cat, whale, etc.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 6 Tissues

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JAC Board Class 9th Science Chapter 6 Notes Tissues

→ A group of cells having a common origin and similar function are termed as tissues.

→ Plant tissues: They are primarily classified into two groups:
a. Meristematic tissues
b. Permanent tissues

Meristematic tissues: They are capable of dividing continuously to produce new cells. The meristematic tissues are present only at the growing regions such as shoot tip. root tip and at the base of intemodes and leaves.
JAC Class 9 Science Notes Chapter 6 Tissues 1
Depending on the area where they are present, meristematic tissues are classified as apical, lateral and intercalary. Meristematic tissues are very active, have dense cytoplasm, thin cellulosic walls and prominent nuclei. They lack vacuoles.

JAC Class 9 Science Notes Chapter 6 Tissues

Permanent tissues: Formed from meristematic tissues, the cells in the tissue lose the ability to divide. They have differentiated and attained a permanent shape suitable for their functions. Permanent tissues are divided into two categories. Simple permanent tissues: Tissues which are made up of only one type of cells are called simple tissues.

Parenchyma, collenchyma and sclerenchyma are examples of simple tissues,
a. Parenchyma: Composed of unspecialised cells with relatively thin cell walls, large intercellular space, present in soft parts of the plant. Their main function is storage.
JAC Class 9 Science Notes Chapter 6 Tissues 2

b. Collenchyma: It is composed of living and elongated cells with cell walls and irregularly thickened at the comers. There is very little intercellular space. It provides mechanical support and elasticity to plant. It helps in bending of leaves and stems.

c. Sclerenchyma: It is composed of long, narrow and thick-walled cells. This tissue is made up of dead cells, and there are no intercellular spaces. Sclerenchyma cells are dead. They are present in seeds, nuts, husk of coconut- fibre of jute, etc.
JAC Class 9 Science Notes Chapter 6 Tissues 3

JAC Class 9 Science Notes Chapter 6 Tissues

→ Complex permanent tissues: Made up of more than one type of cells (conducting tissues).
a. Xylem: It is composed of tracheids, vessels, xylem parenchyma and xylem fibres. Xylem conducts water and dissolves minerals from roots to all parts of the plant. Except xylem parenchyma, xylem cells are dead cells.
JAC Class 9 Science Notes Chapter 6 Tissues 4
b. Phloem: It conducts food from the green leaves/parts to other parts of the plant. It is composed of four elements-sieve tubes, companion cells, phloem parenchyma and phloem fibres. Except phloem fibres, phloem cells are living cells.
JAC Class 9 Science Notes Chapter 6 Tissues 5

→ Animal tissues: Animal tissues are of four types in higher animals including human beings.
JAC Class 9 Science Notes Chapter 6 Tissues 6
a. Epithelial tissues: They are present for the covering of the external surfaces, internal cavities and organs of the animal body. Various types of epithelial tissues are:

  • Squamous epithelium in the lining of mouth and oesophagus.
  • Cuboidal epithelium in the lining of kidney tubules and salivary glands.
  • Columnar epithelium in the intestine and columnar epithelium with cilia in the lining of respiratory tract.
  • Glandular epithelium in the glands aids in a special function as gland cells, which can secrete at the epithelial surface.

b. Muscular tissues: They are made up of muscle cells, called muscle fibres. There are three types of muscle fibres:

  • Striated muscles (skeletal muscles or voluntary muscles): Cells are cylindrical, unbranched and multinucleate.
  • Smooth muscles (involuntary muscles): Cells are long, spindle-shaped and possess a single nucleus.
  • Cardiac muscles (involuntary muscles): Cells are cylindrical, branched and uninucleate.

c. Connective tissues: They connect various tissues and organs. They provide support to different parts of the body by forming packaging around different organs of the body. The different types of connective tissues in our body are bone, cartilage, tendon, ligament and blood.

d. Nervous tissues: The tissue responds to stimuli. The brain, spinal cord and nerves are composed of nervous tissues or neurons. A neuron consists of cell body, cytoplasm, nucleus, dendrite, axon and nerve ending. The neuron impulse allows us to move our muscles when we want to respond to stimuli.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life

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JAC Board Class 9th Science Chapter 5 Notes The Fundamental Unit of Life

→ All organisms consist of tiny building blocks which are known as cells. The term ‘cell’ was coined by Robert Hooke from the Latin word ‘cella’ which means a Tittle room’.

→ Cell is the basic structural and functional unit of all organisms. Cell is the lowest level of organisation that is ‘alive’.

→ Cell theory states that: All living organisms are composed of cells. Cell is the fundamental unit of life. All new cells arise from pre-existing cells.

→ Shape and size of cells: Cells vary in shape and size. They may be oval, spherical, rectangular, spindle shaped or totally irregular like the nerve cell. The size of cells also varies in different animals and plants. Most of the cells are very small in size, like red blood cells (RBCs), while some cells are fairly large, like nerve cells. Average size of a cell varies from 0.5 to 20 pm.

→ Cell Structure: Cell is a compound of same basic constituents.
1. Plasma membrane: Plasma membrane is the covering of the cell that separates the contents of the cell from its external environment. It is the living part of a cell. It is a very thin, delicate, elastic and selectively permeable membrane. As it is a selectively permeable membrane, it allows the flow of certain selected substances in and out of the cell. The plasma membrane is flexible and is made up of organic molecules called lipids and proteins. The flexibility of cell membrane also enables the cell to engulf food and other materials from its external environment. Such process is known as endocytosis. It is observed in Amoeba.

JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life

→ Transport of Substances through Plasma Membrane: Substances can pass through plasma membrane by two processes: diffusion and osmosis.
a. Diffusion: It is the process of movement of substances from their higher concentration to their lower concentration. During respiration, CO2 is given out as a waste product and accumulates in higher concentration inside the cell as compared to the outside medium. Due to the difference in concentration inside and outside the cell, CO2 starts moving out of the cell.

b. Osmosis: The movement of water moleculas through a selectively permeable membrane is called osmosis. Osmosis is the movement of water from a region of higher water concentration, through a semi-permeable membrane, to a region of lower water concentration.

→ If the medium surrounding the cell has a higher water concentration than the cell, the cell will gain water by osmosis. Such a solution is known as a hypotonic solution.
JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 1

  • If the medium has exactly the same water concentration as the cell, there will be no net movement of water across the cell membrane. Such a solution is known as an isotonic solution.
  • If the medium has a lower water concentration than the cell, it will lose water by osmosis. Such a solution is known as hypertonic solution.

→ Cell wall: Cell wall is a non-living, thick and freely permeable covering made up of cellulose. It is available in eukaryotic plant cells and in prokaryotic cells as well. It determines the shape of the cells. It protects the plasma membrane. It prevents desiccation or dryness in cells. It helps in the transport of various substances in and out of the cell.

→ Nucleus: Nucleus is covered by a double¬layered membrane. The fluid inside the nucleus is called nucleoplasm. Nucleus consists of chromosomes which are important for the functioning of a cell. Chromosomes consist of genes which are the carriers of genetic information. Nucleus controls all the metabolic activities of the cell. It is the storehouse of genes. Without nucleus, cell can neither survive nor show specialised activities.

→ Type of cells: The cells can be categorised in two types:

  • Prokaryotic cell: In some organisms, DNA and RNA (genetic substances) are bound by a membrane. This membrane bound nucleus is termed as true nucleus. Prokaryotic cells are the cells in which true nucleus and membrane bound organelles are absent. They are primitive and incomplete cells. Prokaryotes are always unicellular organisms. Bacteria and blue-green algae are examples of prokaryotes.
  • Eukaryotic cell: Eukaryotic cells are the cells in which true nucleus and membrane bound organelles are present. They are advanced and complete cells. Eukaryotes include all living organisms (both unicellular and multicellular) except bacteria and blue green algae.

JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 2

JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life

→ Protoplasm: It is a jelly-like, viscous, colourless semi-fluid substance present in various cell organelles in colloidal form. Protoplasm consists of two parts:

  • Cytoplasm: It is that part of protoplasm which surrounds the nucleus. It contains the various cell organelles.
  • Nucleoplasm: It is that part of protoplasm which is located inside the nucleus.

Protoplasm stores vital chemicals like amino acids, proteins, sugar, etc. It is the site of some metabolic reactions.
JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 3

→ Cell organelles: These are small membrane bound structures suspended in the cytoplasm. They perform lots of chemical activities to support the structure and functioning of a cell. Some cell organelles are described below:
1. Endoplasmic Reticulum: Endoplasmic reticulum is a mesh-like structure which is composed of numerous tubes. It extends from the plasma membrane to the nuclear membrane. There are two types of endoplasmic reticulum, viz, smooth ER (synthesises lipids, detoxify drugs) and rough ER (synthesises proteins). Rough ER has ribosomes on its surface which give it the characteristic rough appearance.
It serves as the transport channel in the cell. Substances are transported from cell membrane to cytoplasm and to nucleus and vice-versa. ER also serves the role of packing many substances in the cell. It helps in the formation of plasma membrane and Golgi-bodies. Smooth ER helps in synthesis and transport of lipids.
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2. Golgi body: The Golgi apparatus, first described by Camillo Golgi, consists of a system of membrane-bound vesicles arranged approximately parallel to each other in stacks called cistemae. The materials synthesised near the ER are packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus. The Golgi bodies store, modify, pack and dispatch the substances. They help in the formation of lysosomes.
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3. Lysosomes: Lysosomes are small sac-like structures. They are derived from Golgi complex. Lysosomes contain digestive enzymes. They are found in eukaryotic cells, mostly in animals. Lysosomes help in digestion of foreign substances and wom-out cell organelles. They provide protection against bacteria and vims. They help to keep the cell clean. During the distribution in cellular metabolism, e.g., when they get damaged, lysosomes may burst and the enzymes digest their own cell. Therefore, lysosomes are also known as suicidal bags of a cell.

4. Ribosomes: These are extremely small, dense and round bodies interspersed in the cytoplasm. Ribosomes are made up of ribonucleic acid (RNA) and proteins. In prokaryotic cell, ribosomes are of 70 S type. In eukaryotic cells, ribosomes are of 80 S type. Ribosome is responsible for protein synthesis. They are not membrane bound.

5. Mitochondria: Mitochondria are small sausage-shaped organelles. It is a double-membrane structure. Outer membrane is smooth whereas inner membrane is projected into numerous finger-like structures called cristae. Mitochondria contain their own DNA and ribosomes. They provide energy for the vital activities of living cells. They produce energy due to chemical reactions, in the form of ATPs (Adenosine Triphosphate – energy currency of the cell). Therefore, it is called ‘powerhouse of the cell’.
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6. Centrosome and centrioles: Centrosome is found only in eukaryotic animal cells. It is not bounded by any membrane but consists of centrioles. Centrioles are hollow cylindrical structures arranged at right angle to each other and are made up of microtubules. Centrioles help in cell division and also help in the formation of cilia and flagella.

7. Plastids: Plastids are present in most of the plant cells and absent in animal cells. They are usually spherical or discoidal in shape. These are double membrane bound organelles. Plastids also have their own DNA and ribosomes. Plastids are of three types:

  1. Chloroplast: They are green coloured plastids containing chlorophyll. Chloroplasts manufacture food by the process of photosynthesis.
  2. Chromoplast: They are colourful plastids. They provide colour to flowers and fruits.
  3. Leucoplast: They are colourless plastids. They help in the storage of various substances like starch, proteins and fats.

JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life

8. Vacuoles: Vacuoles are fluid filled chambers and are often seen in many cells. Vacuoles are very large in plant cells. A plant cell usually has a single but large central vacuole. Such a vacuole fills almost the entire space inside the cell. Vacuoles are much smaller and few in number in animal cells.
Cell division: A cell divides by one of the following two processes:
i. Mitosis: Each cell divides into two daughter cells and each new cell has same number of chromosomes as the mother cell.
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ii. Meiosis: Each cell divides into four daughter cells, each having half the number of chromosomes as the mother cell.
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JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 4 Structure of the Atom

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JAC Board Class 9th Science Chapter 4 Notes Structure of the Atom

→ Atoms are made up of three fundamental particles or sub-atomic particles called electrons, protons and neutrons. Protons and neutrons of an atom are almost of same mass. The mass of proton is approximately 2000 times as that of an electron.

→ Electron (e): These negatively charged particles were discovered by J.J.Thomson in 1897. In the experiment, a gas at low pressure was taken in a discharge tube made up of glass.
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 1

→ At the ends of the discharge tube, two electrodes were placed, connected to a battery for high voltage supply. The electrode connected to the negative end was known as cathode and that to the positive end as anode.

→ A stream of negatively charged particles was observed coming out of the cathode towards the anode. These particles were called electrons. The collection of negatively charged particles emitted from the cathode in the discharge tube are called cathode rays.

JAC Class 9 Science Notes Chapter 4 Structure of the Atom

→ Proton (p+): In 1886, Goldstein observed in the same experiment, with different situation that, anode emitted positive particles which were called protons.

→ Canal rays: The positively charged radiations produced in the discharge tube from anode are called canal rays.

→ Difference between electron and proton:

Electron Proton
Its mass is negligible. Its mass is 1 unit.
Charge is negative. Charge is positive.
J.J Thomson discovered it. E. Goldstein discovered it.

→ Neutron (n): These neutrally charged particles were discovered by James Chadwick in 1932. Neutrons are present in atoms of all elements except hydrogen.

→ The structure of an atom:
1. Thomson’s Model of an atom: An atom is a positively charged sphere and the electrons are embedded in it. The magnitude of positive and negative charge is same inside an atom, so the atom is electrically neutral.
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 2
2. Rutherford’s α-particle scattering experiment’: α-particles are doubly charged helium ions. Since they have a mass of 4 u, the fast moving α-particles have a considerable amount of energy. A thin gold foil with thickness of about 1000 atoms was taken. A lot of fast moving α-particles were bombarded on this thin gold foil. After passing through the foil, α-particles hit the screen.
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 3

Following are the observations and inferences made:

Observation Inference
a. Most of the α-particles pass through the foil without getting deflected. a. Most of the space inside the atom is empty.
b. Some particles were deflected by small angles. b. Positive charge of the atom occupies very little space.
c. One out of 12,000 particles rebound back. c. All the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

Rutherford, on the basis of this experiment, suggested ‘the nuclear model of an atom’. According to the nuclear model of an atom:
a. Most of the space inside the atom is empty.
b. At the centre of an atom, a small, heavy, positively charged nucleus is present.
c. Electrons revolve around the nucleus.
d. Total positive charge in nucleus is the same as total negative charge on all electrons of the atom as atom has net zero charge.

JAC Class 9 Science Notes Chapter 4 Structure of the Atom

→ Drawback of Rutherford’s model of an atom: If any charged particle undergoes accelerated motion, it must radiate energy. Therefore, if a charged body (e;) rotates around another charged body (nucleus), it will radiate energy. Due to energy loss through the radiation, speed of electrons will decrease and eventually jt will fall into the nucleus. But such collapse does not occur and atoms are found to be quite stable.

3. Bohr’s Model of Atom: In 1913, Neils Bohr overcame the limitations of Rutherford’s model and proposed a model of atomic structure.
Following are the postulates:
a. Electrons revolve around a centrally located heavy, small and positively charged nucleus in certain discrete orbits.
b. While revolving in discrete orbits, electrons do not radiate energy.
c. These discrete orbits or shells are called energy levels. These orbits or shells are represented by the letters K, L, M, N …
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 4
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 5
→ Distribution of Electrons in Different Orbits: Distribution of electrons in different orbits (shells) is given by Bohr and Bury:
a. Maximum number of electrons present in a shell is given by 2n2 (n = shell number).
For example,
n = 1 (K shell). 2n2 = 2 (1)2 = 2 electrons
b. The maximum number of electrons that can be accommodated in the outermost orbit is 8.
c. Electrons are not accommodated in a given shell, unless the inner shells are completely filled.

→ Atomic Number: The number of protons present in the nucleus of an atom is called its atomic number. It is denoted by Z.

→ Mass Number: Mass number is equal to the number of nucleons present inside the nucleus of an atom. It means, it is the sum of the total number of protons and neutrons of an atom. It is denoted by the letter A.
‘Mass number of element = Number of protons + Number of neutrons’
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 6

→ Isotopes: Isotopes are atoms of same element having same number of protons but different number of neutrons. Isotopes have similar chemical properties but different physical properties.
For example: 126C, 146C

→ Uses of Isotopes:
a. An isotope of uranium (23592C) is used in nuclear power plants to generate electricity.
b. An isotope of cobalt is used in treatment of cancer.
c. An isotope of iodine is used in treatment of goitre.
Isobars: Atoms of different elements having same mass number but different atomic numbers are called isobars.
For example: 4020Ca, 4018Ar

→ Valency: The electrons in the last shell of the atom are called valence electrons. These govern the chemical properties of elements. The number of valence electrons that take part in a chemical reaction is called valency of the atoms.
For example, hydrogen has only one electron in its outermost orbit, thus it requires one more electron to fill its outermost orbit (K shell). For this, hydrogen atom shares one electron with another hydrogen atom and forms Hr

→ When an electron from a higher energy level falls in an orbit of lower energy level, the difference in energy is radiated in the form of electromagnetic radiation or light. This explains why different atoms on heating or under other conditions emit light of different colours.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 3 Atoms and Molecules

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JAC Board Class 9th Science Chapter 3 Notes Atoms and Molecules

→ In 430 B.C., Democritus postulated that matter is made up of very small particles calLed “Atomos’ which means ‘indivisible’. Later, Antoine Lavoisier, from his experimental observations, established the laws of chemical combinations.

→ The Law of Conservation of Mass: This law of conservation of mass states that, the total mass of reactants is equal to the total mass of products.
For example:
A + B → C + D
(Reactants) → (Products)
Total mass of reactants = Total mass of products

→ Law of Definite Proportions: According to the law of definite proportions, in a chemical substance, the elements are always present in definite proportion by mass. For example. in water, the ratio of the mass of hydrogen to the mass of oxygen is always 1: 8.

→ After a series of experiments, Dalton concluded that all matter must be composed of tiny particles, which cannot be further divided. He called them atoms.

JAC Class 9 Science Notes Chapter 3 Atoms and Molecules

→ “The smallest particle of an element is called an atom.”
Atomic radius is measured in nanometer (nm).
1nm = 1 × 109m
1 m = 109nm
Atomic radii of hydrogen atom 1 × 10-10 m

→ Dalton’s Postulates:

  • Matter is made up of atoms.
  • Atoms are indivisible and indestructible.
  • Atoms of a given element are identical in mass and in properties.
  • Compounds are formed by a combination of two or more same or different kinds of atoms and a chemical reaction is a rearrangement of atoms.
  • Atoms of different elements have different masses and chemical properties.
  • Atoms combine in the ratio of small whole numbers to form compounds.
  • The relative number and kind of atoms are constant in a given compound.

→ Elements and symbols: Dalton proposed a scheme of notation to represent elements.
JAC Class 9 Science Notes Chapter 3 Atoms and Molecules 1

→ Symbols for some elements as proposed by Dalton Symbols of some common elements

Name of the element Latin name Symbol
Hydrogen – H
Helium – He
Carbon – C
Copper Cuprum Cu
Cobalt – Co
Chloride – Cl
Cadmium – Cd
Boron – B
Barium – Ba
Bromine – Br
Bismuth – Bi
Sodium Natrium ‘ Na
Potassium Kalium K
Iron Ferrum Fe
Gold Aurum Au
Silver Argentum Ag
Mercury Hydrargyrum Hg

→ Molecule: A molecule is a group of two or more atoms that are chemically bonded together and form the smallest part of an element or a compound. This can exist independently and shows all the properties of that substance.

JAC Class 9 Science Notes Chapter 3 Atoms and Molecules

→ Atomicity: The number of atoms constituting a molecule is referred to as its atomicity. Molecules of an element constitute same type of atoms. They may be monoatomic, diatomic or polyatomic.

Name of the element Atomicity Molecular formula
Helium Monoatomic He
Neon Monoatomic Ne
Argon Monoatomic Ar
Krypton Monoatomic Kr
Xenon Monoatomic Xe
Radon Monoatomic Rn
Hydrogen Diatomic H2
Chlorine Diatomic Cl2
Nitrogen Diatomic N2
Phosphorus Polyatomic (Tetra) P4
Sulphur Polyatomic (Octa) S8

→ Ion: Ion is a charged particle and can be positively or negatively charged. A positively charged particle in a molecule is called cation, for example, Na+, Ca2+. An anion is a negatively charged particle in a molecule, for example, F–, Cl–.

→ Valency: The combining capacity of an element is known as valency. The combining capacity of the atoms to form molecules either with same or different elements is defined as valency. Valency is used to find out the number of atoms of an element that will combine with the atom of another element to form a chemical compound.

Every atom wants to become stable. To do so, it may lose, gain or share electrons.
a. If an atom consists of 1,2 or 3 electrons in its valance shell, then its valency is 1, 2 or 3 respectively, and it will lose 1, 2 or 3 electrons respectively.
b. If an atom consists of 5, 6 or 7 electrons in the outermost shell, then it will gain 3, 2 or 1 electron respectively, and its valency will be 3, 2 or 1 respectively.
c. If an atom has 4 electrons in the outermost shell, then it will share these electrons and hence its valency will be 4.
d. If an atom has 8 electrons in the outermost shell, then its valency is 0.
JAC Class 9 Science Notes Chapter 3 Atoms and Molecules 2

→ Variable valency: Some elements show more than one valency, hence, termed as variable valency elements.
For example:
Iron shows
valency II – Fe2+ (Ferrous ion)
valency III – Fe3+ (Ferric ion)

Copper shows
valency I – Cu+ (Cuprous ion)
valency II – Cu2+ (Cupric ion)

JAC Class 9 Science Notes Chapter 3 Atoms and Molecules

→ Chemical Formulae: The chemical formula of a compound is a symbolic representation of its composition.
Rule 1: Cross multiply the valency of elements to form a compound.
JAC Class 9 Science Notes Chapter 3 Atoms and Molecules 3

Rule 2: If compound consists of both metal and non-metal, then metal is written first. For example: In calcium chloride (CaCl2) and zinc sulphide (ZnS), Calcium and Zinc are metals, so they are written first, whereas chloride and sulphide are non-metals.

Rule 3: If a compound is formed with polyatomic ions, then polyatomic ions are written in brackets.
For example: In aluminium sulphate [Al2(SO4)3], the polyatomic sulphate ion, SO42- is enclosed in a bracket before writing the subscript 3.
Here, the bracket with a subscript 3 indicates that three sulphate groups (SO42-) are joined to two aluminium atoms.

Note: Compounds made up of a metal and a non-metal are called salts or ionic compounds. All the above examples are of salts.

→ Mole Concept: The quantity of a substance is expressed in terms of mole. 1 mole is also defined as the amount of substance which contains 6.022 × 1023 units (Avogadro’s number denoted by NA).
For example 1 mole of oxygen atoms represents 6.022 × 1023 atoms of oxygen and 5 moles of oxygen atoms contain 5 × 6.022 × 1023 atoms of oxygen.

→ Molar Mass: The mass of 1 mole of a substance is called molar mass. Atomic mass or molecular mass in gram is equal to molar mass.
For example: Atomic mass of Fe is 56 u. Molar mass of Fe is 56 g.
Atomic mass of H2O is 18 u. Molar mass of H2O is 18 g.
Number of moles = \(\frac{\text { Given mass }}{\text { Molar mass }}\)

For example, number of moles in 122 g of iron will be
\(\frac{\text { Given mass }}{\text { Molar mass }}=\frac{112}{56}\) = 2 × 6.022 × 1023 atoms.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 2 Is Matter Around Us Pure

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JAC Board Class 9th Science Chapter 2 Notes Is Matter Around Us Pure

→ A pure substance consists of a single type of particles.

→ A mixture has more than one substance (element / compound) mixed in any proportion.

→ Mixtures can be separated into pure substances by appropriate separation techniques.

→ A solution is a homogeneous mixture of two or more substances. The major component of a solution is known as the solvent and the minor one is the solute. For example, sugar dissolved in water or alloy of copper and zinc or ethyl alcohol in water.

  • Mass percentage of a solution
    = \(\frac{\text { Mass of solute }}{\text { Mass of solution }}\) × 100
  • Volume percentage of a solution
    = \(\frac{\text { Mass of solute }}{\text { Mass of solution }}\) × 100

→ Materials which are insoluble in a solvent and have particles which are visible to naked eyes form a suspension. A suspension is a heterogeneous mixture.

→ When solids are dispersed in liquids to form a heterogeneous mixture or an opaque medium, it is called suspension.

JAC Class 9 Science Notes Chapter 2 Is Matter Around Us Pure

→ Colloidal solutions are heterogeneous mixtures where particles of 1 × 109 to 1 × 10-6 m diameter, called dispersed phase, are distributed uniformly in a solvent, called dispersing medium.

→ Difference between true solutions, suspension and colloidal solutions.

True Solution ColloidalSolution Suspension
It is a homogeneous mixture of solute and solvent. It appears to be homogeneous but actually it is a heterogeneous mixture of dispersed phase and dispersing medium. It is a heterogeneous mixture.
The solute particles are very small, i.e., less than 109 m in diameter. The solute particles are between 109 and 106 m in diameter. The solute particles are quite large, i.e., larger than 106 m in diameter.
Particles of true solution are not visible to naked eye. Particles are not visible to naked eye but can be seen with ultra­microscope. Particles are big enough to be seen by naked eye.
The entire solution passes through filter paper. The particles can pass through ordinary filter paper. The particles cannot pass through filter paper.
The solute particles do not show Tyndall effect. The particles show Tyndall effect. The particles may or may not show Tyndall effect.
The particles do not settle down. The particles do not settle down. The particles may settle due to gravity.

→ Different Types of Colloids
JAC Class 9 Science Notes Chapter 2 Is Matter Around Us Pure 1

→ Separation of a mixture can be done by hand-picking, sieving, winnowing, sedimentation, decantation, filtration, evaporation, distillation, fractional distillation, centrifugation, crystallisation and chromatography.

→ A physical change brings about a change in the state of matter without change in the composition or chemical nature of the substance.

→ A chemical change brings about a change in chemical properties of matter because one or more substances are transformed into a new substance.

→ Pure substances can be elements or compounds.

→ An element is a form of matter which cannot be broken down by chemical reactions into simpler substances.

JAC Class 9 Science Notes Chapter 2 Is Matter Around Us Pure

→ A compound is a substance composed of two or more different types of elements, chemically combined in a fixed proportion.

→ Properties of a compound are different from its constituent elements whereas a mixture shows the properties of its constituting elements or compounds.
JAC Class 9 Science Notes Chapter 2 Is Matter Around Us Pure 2

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 1 Matter in Our Surroundings

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JAC Board Class 9th Science Chapter 1 Notes Matter in Our Surroundings

→Matter: Everything in this universe is made up of material which is called matter. Matter is anything that has mass and occupies space. Matter is made up of lots of tiny particles.

→ Characteristics of particles of matter:
a. Particles of matter have space between them.
b. Particles of matter are continuously moving.
c. Particles of matter attract each other. Matter exists in three different states, viz., solid, liquic and gas.

Solid Liquids Gas
1. Strong intermolecular force of attraction. 1. Weak intermolecular force of attraction. 1. Very weak intermolecular force of attraction.
2. Very less intermolecular space. 2. Large intermolecular space. 2. Very large intermolecular space.
3. Have definite shape and volume. 3. No definite shape but definite volume. 3. No definite shape and volume.
4. High density, high melting and boiling points. 4. Density is lower, low melting and boiling points. 4. Density is very low.
5. Solids cannot be compressed. 5. Liquids can be compressed. 5. Gases are highly compressible.
6. Solids cannot flow. 6. Liquids can flow. 6. Gases can flow.

→ Matter can change its state from solid to liquid and from liquid to gas and vice-versa.
JAC Class 9 Science Notes Chapter 1 Matter in Our Surroundings 2

→ Effect of Temperature: On increasing temperature, the particles gain energy and start vibrating with greater energy. Due to increased kinetic energy, the particles overcome the force of attraction and a new state is obtained.

→ Melting Point: It is the temperature at which a solid becomes a liquid at atmospheric pressure. Boiling Point: It is the temperature at which a liquid changes into its vapour form at atmospheric pressure.

JAC Class 9 Science Notes Chapter 1 Matter in Our Surroundings

→ Latent Heat of Fusion: The amount of heat energy required to change 1 kg of a solid into liquid at its melting point is called the latent heat of fusion of the solid.

→ Latent Heat of Vaporisation: The amount of heat energy required to change 1 kg of a liquid into vapour at atmospheric pressure, at its boiling point is called the latent heat of vaporisation of the liquid.

→ Sublimation: It is the change of state directly from solid to gas or vice-versa without going through the liquid state. Evaporation: It is a surface phenomenon in which a liquid changes into vapour/gas below its boiling point. It results in lowering of temperature, i.e., cooling is caused when evaporation takes place.

→ Factors affecting Evaporation: An increase in surface area increases the rate of evaporation. An increase in temperature increases the rate of evaporation. A decrease in humidity increases the rate of evaporation. An increase in wind speed increases the rate of evaporation.

→ Some measurable quantities and their units:

Quantity SI Unit A Symbol
Temperature kelvin K
Length metre m
Mass kilogram kg
Weight newton N
Volume cubic metre m3
Density kilogram per cubic metre kg/m3
Pressure v pascal Pa

JAC Class 9 Science Notes

JAC Class 9 Science Notes in Hindi & English Jharkhand Board

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JAC Jharkhand Board Class 9th Science Notes in Hindi & English Medium

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JAC Class 9 Science Important Questions and Answers in Hindi & English Jharkhand Board

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JAC Jharkhand Board Class 9th Science Important Questions in Hindi & English Medium

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JAC Class 9 Science Solutions in Hindi & English Jharkhand Board

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JAC Jharkhand Board Class 9th Science Solutions in Hindi & English Medium

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