CBSE – 9th Standard Science

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Class 9 Chapter 6 – Tissues

Tissues

  • Cells specializing particular function is carried out by a cluster of cells at a definite place in the body. This cluster of cells is called as tissues.
  • Blood, phloem and muscle are all examples of tissues.
  • A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue.

PLANT TISSUES

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  • Based on the dividing capacity of the tissues, various plant tissues can be classified as meristematic tissue and permanent tissue.
  • Depending on the region where tissues are present, meristematic tissues are classified as apical, lateral and intercalary.

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  • Apical meristem is present at the growing tips of stems and roots and increases the length of the stem and the root.
  • The girth of the stem or root increases due to lateral meristem.
  • Intercalary meristem is the meristem at the base of the leaves or internodes on
  • The process of taking up a permanent shape, size, and a function is called differentiation.
  • Cells of meristematic tissue differentiate to form different types of permanent tissue.
  • A few layers of cells form the basic packing tissue.
  • This tissue is parenchyma, a type of permanent tissue. It consists of relatively unspecialized cells with thin cell walls.
  • This tissue provides support to plants and also stores food.
  • In some situations, it contains chlorophyll and performs photosynthesis, and then it is called
  • In aquatic plants, large air cavities are present in parenchyma to give buoyancy to the plants to help them float. Such a parenchyma type is called
  • The parenchyma of stems and roots also stores nutrients and water.

COLLENCHYMA

  • The flexibility in plants is due to another permanent tissue, collenchyma.
  • It allows easy bending in various parts of a plant without breaking.
  • It also provides mechanical support to plants.
  • The cells of this tissue are living, elongated and irregularly thickened at the corners.
  • There is very little intercellular space.

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SCLERENCHYMA

  • Yet another type of permanent tissue is sclerenchyma.
  • It is the tissue which makes the plant hard and stiff.
  • The cells of this tissue are dead.
  • They are long and narrow as the walls are thickened due to lignin.
  • The epidermis is usually made of a single layer of cells.
  • The entire surface of a plant has this outer covering of epidermis. It protects all the parts of the plant.
  • Epidermal cells on the aerial parts of the plant often secrete a waxy, water-resistant layer on their outer surface which aids in protection against loss of water, mechanical injury and invasion by parasitic fungi.
  • Most epidermal cells are relatively flat. Often their outer and side walls are thicker than the inner wall

STOMATA

  • We can observe small pores here and there in the epidermis of the leaf. These pores are called stomata.
  • Stomata are enclosed by two kidney-shaped cells called guard cells.
  • They are necessary for exchanging gases with the atmosphere.
  • Transpiration also takes place through stomata.
  • Epidermal cells of the roots, whose function is water absorption, commonly bear long hair-like parts that greatly increase the total absorptive surface area.
  • Cells of cork have a chemical called suberin in their walls that makes them impervious to gases and water.

XYLEM

  • Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres. The cells have thick walls, and many of them are dead cells.
  • Tracheids and vessels are tubular structures. This allows them to transport water and minerals vertically.
  • The parenchyma stores food and helps in the sideways conduction of water. Fibres are mainly supportive in function.

PHLOEM

  • Phloem is made up of four types of elements sieve tubes, companion cells, phloem fibers and the phloem parenchyma.
  • Sieve tubes are tubular cells with perforated walls.
  • Phloem is unlike xylem in that materials can move in both directions in it. Phloem transports food from leaves to other parts of the plant.

ANIMAL TISSUES

  • For movement of our body parts we have specialized cells called muscle cells.
  • The contraction and relaxation of these cells result in movement.
  • Blood is a type of connective tissue, and muscle forms muscular tissue.

EPITHELIAL TISSUES

  • The covering or protective tissues in the animal body are epithelial tissues. Epithelium covers most organs and cavities within the body.
  • It also forms a barrier to keep different body systems separate.
  • The skin, the lining of the mouth, the lining of blood vessels, lung alveoli etc. are all made of epithelial tissue.
  • Epithelial tissue cells are tightly packed and form a continuous sheet.

CONNECTIVE TISSUE

  • The cells of connective tissue are loosely spaced and embedded in an intercellular matrix.
  • The matrix may be jelly like, fluid, dense or rigid.
  • Bone is another example of a connective tissue.

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  • Another type of connective tissue is cartilage, has widely spaced cells.
  • Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx.
  • 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.
  • Fat storing adipose tissue is found below the skin and between internal organs. The cells of this tissue are filled with fat globules.

MUSCULAR TISSUES

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  • Muscular tissue consists of elongated cells, also called muscle fibers. This tissue is responsible for movement in our body.
  • Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.
  • Muscles present in our limbs move when we want them to, and stop when we so decide. Such muscles are called voluntary muscles.
  • The muscles of the heart show rhythmic contraction and relaxation throughout life. These involuntary muscles are called cardiac muscles.
  • Heart muscle cells are cylindrical, branched and uninucleate.

NERVOUS TISSUES

  • The brain, spinal cord and nerves are all composed of the nervous tissue.
  • The cells of this tissue are called nerve cells or neurons.
  • A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise.
  • Each neuron has a single long part, called the axon.
  • And many short, branched parts called dendrites.
  • Many nerve fibres bound together by connective tissue make up a nerve.