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CBSE NOTES CLASS 9 SCIENCE CHAPTER 6

TISSUES

Tissue

Difference in Body Structure of Unicellular and Multi Cellular Organism

Difference between Plants & Animal Tissues

Plant Tissues

Types of Plant Tissues

Meristematic tissues or Meristems

The Apical Meristem

The Lateral Meristem

The Intercalary Meristem

Permanent plant tissues

Simple permanent plant tissues

Parenchyma

Chlorenchyma

Aerenchyma

Collenchyma

Sclerenchyma

Epidermal Tissue

Stomata and guard cells

Complex Permanent Tissues

Xylem

Phloem

Animal Tissues

Epithelial tissue

Simple Squamous Epithelium

Stratified Squamous Epithelium

Columnar Epithelium

Ciliated Epithelium

Cuboidal Epithelium

Glandular epithelium

Connective Tissue

Bone

Cartilage

Tendons

Ligaments

Blood

Lymph

Areolar Connective Tissue

Adipose Connective Tissue

Muscular Tissues

Striated muscles / skeletal muscles / voluntary muscles

Unstriated muscles / smooth muscles / involuntary muscles

Cardiac Muscles

Nervous Tissue

Neurons

CBSE NOTES CLASS 9 SCIENCE CHAPTER 6

TISSUES

Tissue

A group of cells that are similar in structure and/or work together to achieve a particular function form a tissue.

Difference in Body Structure of Unicellular and Multi Cellular Organism

In unicellular organisms, a single cell performs all the basic functions of life, like movement, respiration, digestion, reproduction, etc.

For example, 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 cells are specialised to carry out a few functions. Each specialised function is taken up by a different group of cells. Since these cells carry out only a particular function, they do it very efficiently.

For example in human beings, muscle cells contract and relax to cause movement; nerve cells carry messages; blood flows to transport oxygen, food, hormones and waste material and so on.

In plants, vascular tissues conduct food and water from one part of the plant to other parts.

Thus, multi-cellular organisms show division of labour between different types of cells. The tissues are arranged and designed so as to give the highest possible efficiency of function.

Difference between Plants & Animal Tissues

1. Motion

Plants are stationary or fixed – they don’t move. Most of the tissues in plants are supportive, which provide them with structural strength. Most of these tissues are dead. Since dead cells can provide mechanical strength as easily as live ones, and need less maintenance.

Animals on the other hand move around in search of food, mates and shelter. They consume more energy as compared to plants. Most of the tissues they contain are living.

2. Pattern of Growth.

The growth in plants is limited to certain regions. There are some tissues in plants that divide throughout their life. These tissues are localised in certain regions.

Cell growth in animals is more uniform. So, there is no such demarcation of dividing and non-dividing regions in animals

3. Structural organisation of organs and systems

The structural organisation of organs and organ systems is far more specialised and localised in complex animals than even in very complex plants.

PLANT TISSUES

Types of Plant Tissues

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1. Meristematic tissues or Meristems

The Meristems are the tissues having the capabilities of cell division. These are found on regions of the plant where growth takes place.

The cells of meristems are undifferentiated. New cells produced by meristem are initially like those of meristem itself, but as they grow and mature, their characteristics slowly change and they become differentiated as components of other tissues.

Types of Meristems

(a) The Apical Meristem is present at the growing tip of the stem and roots and increases the length.

(b) The Lateral Meristem is present at the lateral side of stem and roots (cambium) and increases the girth.

(c) The Intercalary Meristem is present at internodes or base of the leaves and increases the length between the nodes.

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The cells of meristematic tissue are very active and hence they have dense cytoplasm, thin cellulose walls and prominent nuclei. They lack vacuoles.

The vacuoles causes hindrance in cell division as it is full of cell sap to provide turgidity and rigidity to the cell. They also do not have any waste material to store so vacuoles are usually absent in the meristematic cells.

2. Permanent tissues

When the cells formed by meristematic tissue take up specific roles and lose the ability to divide, they form a permanent tissue.

The process of taking up a permanent shape, size, and function is called differentiation. Cells of meristematic tissue differentiate to form different types of permanent tissue.

There are two types such permanent tissues.

(A) Simple permanent tissues

Tissues which are made of only one type of cells, which look like each other, are called simple permanent tissues.

(i) Parenchyma

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(ii) Collenchyma

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(iii) Sclerenchyma

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(iv) Epidermal Tissue

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CO2 and water are required for photosynthesis and O2 is given out during day. O2 is taken in and CO2 is given out during respiration.

(B) Complex Permanent Tissues

(i) Xylem

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(ii) Phloem

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ANIMAL TISSUES

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(i) Epithelial tissue

Epithelium covers the outer body and most organs and cavities within the body. It forms a barrier to keep different body systems separate.

Examples: The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue.

Simple Squamous Epithelium is extremely thin and flat and forms a delicate lining.

Examples - oesophagus and the lining of the mouth.

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Stratified Squamous Epithelium is arranged in pattern of layers to prevent wear and tear.

Example - skin, which protects the body, is made of stratified squamous epithelium.

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Columnar Epithelium consists of tall column like cells. The Columnar cells help in absorption and secretion.

Example – inner lining of the intestine.

Ciliated Epithelium: If the columnar epithelium also has cilia, hair-like projections on the outer surfaces of epithelial cells, it is called Ciliated Epithelium. The cilia can move, and their movement pushes the mucus forward to clear it.

Example – lining of the respiratory tract

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Cuboidal Epithelium (with cube-shaped cells) forms the lining of kidney tubules and ducts of salivary glands, where it provides mechanical support.

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Glandular epithelium: Epithelial cells which can secrete substances at the epithelial surface are called gland cells. When a portion of the epithelial tissue folds inward, a multicellular gland is formed which is called glandular epithelium.

(ii) Connective Tissue

Tissues that connect, support, bind, or separate other tissues or organs. It has two parts – matrix and the cells embedded in the matrix.

(a) Bone

Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds. It is a strong and nonflexible tissue.

It forms the framework that supports the body. It also anchors the muscles and supports the main organs of the body.

(b) Cartilage

The cartilage is a connective tissue with solid matrix composed of proteins and sugars. The cells are widely spaced. It is highly flexible.

Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx.

(c) Tendons

Tendons connect bones to muscles tissue. Tendons are fibrous tissue with great strength but limited flexibility.

(d) Ligaments

Two bones can be connected to each other by a type of connective tissue called the ligament. This tissue is very elastic. It has considerable strength. Ligaments contain very little matrix.

(e) Blood

Blood has a fluid (liquid) matrix called plasma, in which red blood cells (RBCs), white blood cells (WBCs) and platelets are suspended. The plasma contains proteins, salts and hormones. Blood flows and transports gases, digested food, hormones and waste materials to different parts of the body.

(f) Lymph

The lymph is formed when the interstitial fluid (the fluid which lies in the intercellular spaces of all body tissues) is collected through lymph capillaries. It is then transported through larger lymphatic vessels to lymph nodes, where it is cleaned by lymphocytes. This blood then is poured into the viens and mixes back with the blood.

(g) Areolar Connective Tissue

Areolar connective tissue is found between the skin and muscles, around blood vessels and nerves and in the bone marrow. It fills the space inside the organs, supports internal organs and helps in repair of tissues.

(h) Adipose Connective Tissue

Adipose tissue is found below the skin and between internal organs. The cells of this tissue are filled with fat globules. Storage of fats also lets it act as an insulator.

(iii) Muscular Tissues

Muscular tissue consists of elongated cells, also called muscle fibres. This tissue is responsible for movement in our body. Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.

Striated muscles/skeletal muscles /voluntary muscles

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The muscles, which can be moved by conscious will, are called voluntary muscles. For example muscles present in our limbs move when we want them to, and stop when we so decide.

These muscles are also called skeletal muscles as they are mostly attached to bones and help in body movement.

They have alternate dark and light bands. The cells of this tissue are long, cylindrical, unbranched and multinucleate (having many nuclei).

Unstriated muscles/smooth muscles /involuntary muscles

The muscles that contract and relax without conscious control are called involuntary muscles.
They are called smooth muscles or unstriatiated (dark bands/ light bands are absent).

Examples – Muscles in the alimentary canal, uterus, Iris of an eye.

The cells are long with pointed ends (spindle-shaped) and uninucleate (having a single nucleus).

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Cardiac Muscles

The involuntary muscles of heart are called cardiac muscles. Heart muscle cells are cylindrical, branched and uninucleate.

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Nervous Tissue

Cells of the nervous tissue are highly specialised for being stimulated and then transmitting the stimulus very rapidly from one place to another within the body.

The brain, spinal cord and nerves are composed of the nervous tissue.

Neuron -The cells of nervous tissue are called nerve cells or neurons.

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A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise.

The long part is called the axon and short, branched parts are called dendrites. The dendrites receive nerve impulses from the receptors and the axon transmits impulses away from the cell body. The neuron is terminated in nerve endings, which transmit the message using chemicals.

An individual nerve cell may be up to a metre long.

Many nerve fibres bound together by connective tissue make up a nerve.