Tissue Class 9 Science Chapter 6 Notes

Tissue Class 9 Science Chapter 6 Notes are available here. These notes are prepared by the subject experts of our team.

Tissue Class 9 Science Chapter 6 Notes

• All living organisms are made of cells.
• In unicellular organisms, a single cell performs all basic functions.
• Example: In Amoeba, a single cell handles movement, food intake, gaseous exchange, and excretion.
• Multicellular organisms have millions of specialized cells for specific functions.
• Specialized functions are carried out efficiently by different groups of cells.
• In humans:
• Muscle cells contract and relax for movement.
• Nerve cells carry messages.
• Blood transports oxygen, food, hormones, and waste.
• In plants, vascular tissues conduct food and water throughout the plant.
• Multicellular organisms exhibit division of labor, with specialized cells grouped into tissues.
• Tissues are clusters of similar cells that perform a particular function efficiently.
• Examples of tissues: blood, phloem, muscle.

Are Plants and Animals Made of Same Types of Tissues?

• Plants and animals have different structures and functions.
• Plants are stationary and have a large quantity of supportive tissue, generally with dead cells, to stay upright.
• Animals move to find food, mates, and shelter, consuming more energy, and most of their tissues are living.
• Growth patterns differ:
• Plant growth is limited to certain regions with specific tissues that divide throughout life (meristematic tissue), while other tissues are permanent.
• Animal cell growth is more uniform without distinct regions for dividing and non-dividing cells.
• In complex animals, the structural organization of organs and organ systems is more specialized and localized than in complex plants.
• This difference reflects the distinct modes of life and feeding methods of plants and animals.
• Plants are adapted for sedentary existence, while animals are adapted for active locomotion.
• These adaptations contribute to differences in organ system design between plants and animals.
• The concept of tissues will be discussed in detail with reference to complex animal and plant bodies.

Meristematic Tissue (Plants Tissue)

• Plant growth occurs only in specific regions.
• Dividing tissue, or meristematic tissue, is located at these points.
• Meristematic tissues are classified based on their location: apical, lateral, and intercalary.
• New cells produced by meristematic tissue initially resemble meristem cells.
• As new cells grow and mature, they differentiate into components of other tissues.
• Apical meristem is located at the growing tips of stems and roots, increasing their length.
• Lateral meristem (cambium) increases the girth of the stem or root.
• Intercalary meristem is located near the node in some plants.
• Meristematic tissue cells are very active, with dense cytoplasm, thin cellulose walls, and prominent nuclei.
• Meristematic cells lack vacuoles.

Permanent Tissue (Plants Tissue)

• Cells formed by meristematic tissue take up a specific role and lose the ability to divide.
• These cells form permanent tissue.
• The process of taking up a permanent shape, size, and function is called differentiation.
• Differentiation results in the development of various types of permanent tissues.

Simple Permanent Tissue (Plants Tissue)

• A few layers of cells beneath the epidermis are usually simple permanent tissue.
• Parenchyma is the most common type of simple permanent tissue.
• Parenchyma consists of relatively unspecialized cells with thin cell walls.
• Parenchyma cells are living and usually loosely arranged, with large intercellular spaces.
• Parenchyma tissue generally stores food.
• When parenchyma contains chlorophyll and performs photosynthesis, it is called chlorenchyma.
• In aquatic plants, parenchyma with large air cavities that help them float is called aerenchyma.
• Collenchyma is another permanent tissue that provides flexibility and mechanical support in plants.
• Collenchyma allows bending of plant parts like tendrils and stems of climbers without breaking.
• Collenchyma is found in leaf stalks below the epidermis.
• Collenchyma cells are living, elongated, and irregularly thickened at the corners with very little intercellular space.
• Sclerenchyma is a type of permanent tissue that makes plants hard and stiff.
• Examples include the husk of a coconut, which is made of sclerenchymatous tissue.
• Cells of sclerenchyma tissue are dead, with long and narrow cells having thickened walls due to lignin.
• Often, these walls are so thick that there is no internal space inside the cell.
• Sclerenchyma tissue is found in stems, around vascular bundles, in leaf veins, and in the hard covering of seeds and nuts.
• It provides strength and structural support to plant parts.
• The outermost layer of cells in plants is called the epidermis.
• Epidermis is typically a single layer of cells.
• In plants from dry habitats, the epidermis may be thicker to protect against water loss.
• Epidermis covers the entire surface of the plant, providing protection.
• Epidermal cells on aerial parts often secrete a waxy, water-resistant layer for further protection.
• Epidermal tissue forms a continuous layer without intercellular spaces due to its protective role.
• Most epidermal cells are relatively flat, with thicker outer and side walls compared to the inner wall.
• Small pores in the leaf epidermis are called stomata, which are necessary for gas exchange with the atmosphere.
• Stomata are enclosed by two kidney-shaped cells called guard cells.
• Transpiration, the loss of water in the form of water vapor, occurs through stomata.
• Epidermal cells of roots have long hair-like structures that increase the total absorptive surface area for water absorption.
• Some desert plants have an epidermis with a thick waxy coating of cutin on its outer surface, providing waterproofing.
• The outer layer of a branch of a tree differs from the outer layer of a young stem.
• As plants age, a secondary meristem in the cortex forms layers of cork cells.
• Cork cells are dead, compactly arranged, and lack intercellular spaces.
• Cork cells contain suberin in their walls, making them impermeable to gases and water.
• Some desert plants have an epidermis with a thick waxy coating of cutin on its outer surface, providing waterproofing.
• The outer layer of a branch of a tree differs from the outer layer of a young stem.
• As plants age, a secondary meristem in the cortex forms layers of cork cells.
• Cork cells are dead, compactly arranged, and lack intercellular spaces.
• Cork cells contain suberin in their walls, making them impermeable to gases and water.

Complex Permanent Tissue (Plants Tissue)

• Simple permanent tissues are made of one type of cells that look alike.
• Complex tissues are made of more than one type of cells that coordinate to perform a common function.
• Examples of complex tissues are xylem and phloem.
• Xylem and phloem are conducting tissues and form a vascular bundle.
• Vascular tissue is a distinctive feature of complex plants, essential for their survival in terrestrial environments.
• Xylem consists of tracheids, vessels, xylem parenchyma, and xylem fibers.
• Tracheids and vessels have thick walls and are often dead when mature.
• Tracheids and vessels are tubular structures that transport water and minerals vertically.
• Xylem parenchyma stores food.
• Xylem fibers provide support.
• Phloem is made up of sieve cells, sieve tubes, companion cells, phloem fibers, and phloem parenchyma.
• Sieve tubes are tubular cells with perforated walls.
• Phloem transports food from leaves to other parts of the plant.
• All phloem cells, except phloem fibers, are living cells.

Animal Tissues

• Muscle cells are specialized cells responsible for movement through contraction and relaxation.
• During breathing, inhaled oxygen is absorbed in the lungs and transported to body cells through blood.
• Cells need oxygen for functions related to mitochondria.
• Blood carries oxygen and food to cells and collects wastes for disposal in the liver and kidneys.
• Blood and muscle are examples of tissues in the body.
• Different types of animal tissues include epithelial tissue, connective tissue, muscular tissue, and nervous tissue.
• Blood is a type of connective tissue, while muscle forms muscular tissue.

Epithelial Tissue (Animal Tissues)

• Epithelial tissues are the covering or protective tissues in the animal body.
• Epithelium covers most organs and cavities and forms barriers to keep body systems separate.
• Examples of epithelial tissue locations: skin, lining of the mouth, lining of blood vessels, lung alveoli, and kidney tubules.
• Epithelial tissue cells are tightly packed, forming a continuous sheet with minimal cementing material and almost no intercellular spaces.
• Anything entering or leaving the body must cross at least one layer of epithelium.
• The permeability of epithelial cells regulates the exchange of materials between the body and the external environment and between different body parts.
• All epithelium is usually separated from underlying tissue by an extracellular fibrous basement membrane.
• Different epithelia have structures that correlate with their functions.
• Simple squamous epithelium: found in cells lining blood vessels or lung alveoli for substance transportation through a selectively permeable surface.
• Simple squamous epithelial cells are thin, flat, and form a delicate lining.
• The esophagus and lining of the mouth are covered with squamous epithelium.
• The skin, made of squamous epithelium, protects the body.
• Skin epithelial cells are arranged in multiple layers to prevent wear and tear, called stratified squamous epithelium.
• Tall epithelial cells are present where absorption and secretion occur, such as in the inner lining of the intestine.
• Columnar epithelium facilitates movement across the epithelial barrier.
• In the respiratory tract, columnar epithelial tissue has cilia, which are hair-like projections on the outer surfaces of epithelial cells.
• Cilia can move to push mucus forward and clear it.
• This type of epithelium is called ciliated columnar epithelium.
• Cuboidal epithelium, consisting of cube-shaped cells, forms the lining of kidney tubules and ducts of salivary glands.
• Cuboidal epithelium provides mechanical support.
• Epithelial cells can specialize as gland cells, which secrete substances at the epithelial surface.
• When a portion of epithelial tissue folds inward, it forms a multicellular gland, called glandular epithelium.

Connective Tissue (Animal Tissues)

• Blood is a type of connective tissue.
• Connective tissue cells are loosely spaced and embedded in an intercellular matrix.
• The matrix can be jelly-like, fluid, dense, or rigid.
• The nature of the matrix varies according to the function of the specific connective tissue.
• Blood has a fluid matrix called plasma.
• Red blood corpuscles (RBCs), white blood corpuscles (WBCs), and platelets are suspended in the plasma.
• Plasma contains proteins, salts, and hormones.
• Blood flows and transports gases, digested food, hormones, and waste materials to different parts of the body.
• Bone is a type of connective tissue.
• It forms the framework that supports the body.
• Bone anchors muscles and supports the main organs.
• It is a strong and nonflexible tissue.
• Bone cells are embedded in a hard matrix composed of calcium and phosphorus compounds.
• Ligaments are a type of connective tissue that connects bones to each other.
• Ligaments are very elastic and have considerable strength.
• Ligaments contain very little matrix.
• Tendons are another type of connective tissue that connects muscles to bones.
• Tendons are fibrous tissue with great strength but limited flexibility.
• Cartilage is another type of connective tissue with widely spaced cells.
• The solid matrix of cartilage is composed of proteins and sugars.
• Cartilage smoothens bone surfaces at joints and is found in the nose, ear, trachea, and larynx.
• Cartilage is flexible enough to fold (as in the ears) but provides less flexibility compared to bones in the arms.
• Areolar connective tissue is found between the skin and muscles, around blood vessels and nerves, and in the bone marrow.
• Areolar tissue fills spaces inside organs, supports internal organs, and aids in tissue repair.
• Fat-storing adipose tissue is found below the skin and between internal organs.
• Adipose tissue cells are filled with fat globules for fat storage and insulation purposes.

Muscular Tissue (Animal Tissues)

• Muscular tissue consists of elongated cells known as muscle fibers.
• Muscular tissue is responsible for movement in the body.
• Muscles contain contractile proteins that contract and relax to facilitate movement.
• Voluntary muscles, also known as skeletal muscles, can be moved by conscious will.
• These muscles are attached to bones and aid in body movement.
• Under the microscope, skeletal muscles show alternating light and dark bands or striations.
• Skeletal muscles are also called striated muscles because of these striations.
• Cells of skeletal muscle tissue are long, cylindrical, unbranched, and multinucleate.
• Involuntary movements like the movement of food in the alimentary canal and the contraction of blood vessels are controlled by smooth muscles.
• Smooth muscles are also found in the iris of the eye, ureters, and bronchi of the lungs.
• Cells of smooth muscles are long, spindle-shaped, and have pointed ends.
• Smooth muscles are uninucleate (having a single nucleus).
• They are called unstriated muscles because they lack the alternating light and dark bands (striations) seen in skeletal muscles.
• The muscles of the heart exhibit rhythmic contraction and relaxation throughout life.
• These involuntary muscles are known as cardiac muscles.
• Cardiac muscle cells are cylindrical, branched, and uninucleate.

Nervous Tissue (Animal Tissues)

• Nervous tissue is specialized for responding to and transmitting stimuli rapidly within the body.
• The brain, spinal cord, and nerves are composed of nervous tissue.
• Cells of nervous tissue are called nerve cells or neurons.
• Neurons consist of a cell body with a nucleus and cytoplasm, from which arise long thin hair-like parts called axons and short, branched parts called dendrites.
• A neuron can be up to a meter long.
• Nerve fibers bound together by connective tissue make up a nerve.
• The signal passing along the nerve fiber is called a nerve impulse.
• Nerve impulses enable muscle movement.
• The functional combination of nerve and muscle tissue is essential for animal movement in response to stimuli.