Class 9 Chapter 6 – 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.
- 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.
- 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.
- 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.
- 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
- 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 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 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.
- 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.
- 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.
- 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.
- 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 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.
- 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.
- Chapter 1 – Matter in our surroundings
- Chapter 2 – Is matter around us pure
- Class 9 chapter 3 – Atoms & Molecules
- Class 9 Chapter 4 – Structure of the Atom
- Class 9 Chapter 5 – The fundamental unit of life
- Class 9 Chapter 6 – Tissues
- Class 9 Chapter 7 – Diversity in living organisms
- Class 9 Chapter 8 – Motion
- Class 9 Chapter 9 – Force and laws of motion
- Class 9 Chapter 10 – Gravitation
- Class 9 Chapter 11 – Work & Energy
- Class 9 Chapter 12 – Sound
- Class 9 Chapter 13 – Why do we fall ill
- Class 9 Chapter 14 – Natural Resources
- Class 9 Question Bank Chapter 1 – Matter in our surrounding
- Class 9 Question Bank Chapter 2 – Is matter around us pure
- Class 9 Question Bank Chapter 3 – Atoms and molecules
- Class 9 Question Bank Chapter 4 – Structure of the Atom
- Class 9 Question Bank Chapter 5 – The fundamental unit of life
- Class 9 Question Bank Chapter 6 – Tissues
- Class 9 Question Bank Chapter 7 – Diversity in living Organism
- Class 9 Question Bank Chapter 8 – Motion
- Class 9 Question Bank Chapter 9 – Force and laws of Motion
- Class 9 Question Bank Chapter 10 – Gravitation
- Class 9 Question Bank Chapter 11 – Work and energy
- Class 9 Question Bank Chapter 12 – Sound
- Class 9 Question Bank Chapter 13 – Why do we fall ill
- Class 9 Question Bank Chapter 14 – Natural Resources