Tissues in Action Class 9 PPT & Notes (Ch 3) Free Download

A tissue is a group of cells that are similar in structure and work together to perform a specific function. In a unicellular organism such as amoeba, one cell does all the jobs. In a multicellular organism the work is shared, so different tissues do different jobs. This sharing of work is called division of labour, and it makes the complex life processes of an organism more efficient.

Because their ways of life are different, plants and animals have different kinds of tissues. The next sections take plant tissues first, then animal tissues, and finally the system of bones, muscles and joints that lets the human body move.

Plants grow in three ways:

• Length: roots grow deeper and stems grow taller
• Girth: stems become thicker over time
• Regrowth: grass grows back after mowing, and new branches appear after pruning

Cells that divide actively form a special tissue called meristematic tissue.

• Cells are small, with thin cell walls
• A large, prominent nucleus, which controls the rapid cell division
• Dense cytoplasm with many organelles, so the metabolic activity is high
• Cells are tightly packed, with no intercellular space
• Vacuoles are absent, because vacuoles store water, which would slow down division

Compare this with a parenchyma cell, which is large and has a big central vacuole.

All three work together: length + girth + branching = complete plant growth. At a root tip the cells are arranged in zones. The root cap protects the tip, the apical meristem is the zone of cell division, then comes the zone of elongation where cells increase in size, and then the zone of maturation where permanent tissues form.

Two onions are kept in two jars of water, Jar A and Jar B. On day 3 the root tips of Jar B are cut off by 1 cm, while Jar A is left untouched.

• Observation: the roots of Jar A keep growing; the roots of Jar B stop growing
• Conclusion: roots grow only from their tips (the apical meristem)
• Root tips contain actively dividing cells, which can be confirmed by observing mitosis

On a graph of root length against days (1 to 7), both lines rise together till day 3. Then the Jar B line goes flat, while the Jar A line keeps rising. The key learning: the growth region is only at the root tip.

The lateral meristem (cambium) divides actively and produces xylem on the inside and phloem on the outside. It adds one new ring each year. Scientists count annual rings to estimate the age of a tree. A wide ring means a good growth year; a narrow ring means a drought or an unfavourable year.

Both the number of annual rings and the diameter increase with age, and this increase in girth is the work of the lateral meristem.

• Node: the point on a stem where a leaf or branch arises
• Internode: the part of the stem between two consecutive nodes
• The intercalary meristem lies at the base of the internode (or just above the node) and helps the internode elongate
• When the tip of a stem is cut, the stem stops growing in length, but new branches grow from the nodes
• Grass grows back after mowing because of the intercalary meristem at the base of its nodes

Meristematic cells keep dividing and adding new cells. Some of the new cells stay meristematic, while others lose the ability to divide. A cell that loses this ability becomes specialised for a specific job such as support, storage or transport. This process is called differentiation, and the result is permanent tissue. Permanent tissues are either simple (one type of cell) or complex (more than one type of cell).

T.S. means transverse section, a cross-cut view of the stem seen under a microscope. From the outside to the inside:

• Epidermis: the outermost layer, a single layer of flat rectangular cells
• Ground tissue: parenchyma, collenchyma and sclerenchyma
• Vascular bundles: xylem on the inside, phloem on the outside, and lateral meristem between them

• The epidermis is the outermost, single layer of flat, tightly packed rectangular cells
• It protects the plant from mechanical injury, water loss and microorganisms
• It is covered by a waxy layer called the cuticle (made of cutin)
• Root hair is a projection of an epidermal cell; it increases the surface area for absorbing water and minerals from the soil
• Stomata are pores in the leaf epidermis used for gas exchange and transpiration

• Each stoma is surrounded by a pair of guard cells, which control its opening and closing
• CO₂ enters and O₂ leaves through open stomata (gaseous exchange)
• Transpiration is the evaporation of water vapour through the stomata
• Transpiration creates a pull in the xylem, which helps water rise upward against gravity

• Parenchyma: loosely packed living cells with a large central vacuole. In green parts it carries out photosynthesis and is called chlorenchyma. In aquatic plants it has large air cavities and is called aerenchyma, which helps the plant float
• Collenchyma: living cells with a nucleus and a vacuole (smaller than in parenchyma). Pectin works like rubber and gives flexibility, so stems and tendrils can bend without breaking, like a fresh twig or a leaf stalk
• Sclerenchyma: long, narrow cells with tapered ends that interlock with neighbouring fibres. Lignin makes the walls extremely hard and strong, so they resist pulling forces. Sclerenchyma fibres such as jute, flax and hemp are commercially important

• Xylem transports water and minerals from the roots upward, and also gives mechanical strength
• It has four components: tracheids, vessels, xylem parenchyma and xylem fibres
• Tracheids are elongated with tapered ends and are found in all vascular plants. Vessels are cylindrical, wider and joined end to end, so water moves faster (in angiosperms)
• Tracheids, vessels and xylem fibres are dead cells with thick walls
• Xylem parenchyma is the only living component of xylem; it stores food and helps lateral water movement
• Water path: root hair → cortex → xylem → stem → leaves

• Phloem transports food (sucrose) from the leaves to all parts of the plant, in both directions (up and down)
• It is mostly made of living cells, unlike xylem
• Four components: sieve tubes, companion cells, phloem parenchyma and phloem fibres
• Sieve tubes are long tubular living cells whose perforated end walls are called sieve plates
• Companion cells are specialised parenchyma cells that regulate the loading and unloading of sugars
• Phloem parenchyma stores resins, tannins and latex; phloem fibres give mechanical strength

Xylem and phloem together are called vascular tissue (complex permanent tissue). They form the vascular bundles in stems, roots and leaves.

• Dermal tissue system: the epidermis, the outer covering that protects the plant
• Ground tissue system: parenchyma, collenchyma and sclerenchyma, which make up the main body
• Vascular tissue system: xylem and phloem, which conduct water and food

Animal cells group together to form tissues with a structure that suits their function. There are four main types: epithelial, connective, muscular and nervous. Animal tissues allow movement, sensing, protection and transport. Unlike plants, animals have no meristematic tissue; their growth is spread through the body.

• It forms the outer covering of the body (skin) and lines internal organs such as the mouth, lungs, blood vessels, intestines and kidney tubules
• Cells are closely packed with very little intercellular space
• This tight packing prevents the entry of germs and reduces water loss
• It also helps in absorption, secretion and movement of substances

Connective tissue connects and supports other tissues and organs. Its unique feature is that the cells are embedded in an intercellular matrix, and the matrix decides the nature of the tissue (fluid, solid or fibrous). Blood, bone, cartilage, tendon and ligament are all connective tissues.

• Touch your elbow gently: a hard, rigid structure is bone (strength and protection)
• Press your ear or nose gently: it is soft and flexible and returns to shape, so it is cartilage (cushioning)
• Wiggle your fingers and feel your forearm: the movement you feel is the tendon connecting muscle to bone
• Move your leg up from a sitting position: the knee does not go beyond a limit because of the ligament

Cardiac muscle cells are joined at intercalated discs, which allow synchronised contraction. All three muscle types use ATP energy for contraction. Muscles often work in antagonistic pairs: one muscle contracts while its partner relaxes, for example the biceps and the triceps.

Nervous tissue is the body's control and communication network. The brain is the main control centre, and all muscles, voluntary and involuntary, receive instructions from nervous tissue. Example: you touch something hot, a nerve signal goes to the brain, and the brain signals the hand to withdraw.

• Neuron: the nerve cell, the basic structural and functional unit of nervous tissue
• Cell body: contains the nucleus and controls the metabolism of the cell
• Dendrites: short, branching projections that receive signals from other neurons
• Axon: one long fibre that carries the impulse away from the cell body
• Axon terminals: the branching ends that pass the signal on to the next neuron or to a muscle

The musculoskeletal system is made of bones, muscles, joints, cartilage, tendons and ligaments. Muscles pull on bones to produce movement, so the bones act as levers. The system helps us stand upright, move, keep our posture and protect delicate organs, and it works under the control of the nervous system. An adult skeleton is about 12 to 15% of the total body weight.

Adult males have about 40 to 50% muscle mass and adult females about 30 to 40%. Bone mass is about 12 to 15% of total body weight in both. To estimate your own bone and muscle weight, multiply your weight by these percentages, and compare with your classmates to find a class average. Age, gender, ethnicity, nutrition and exercise all affect bone and muscle mass.

• The skeleton is a framework of 206 bones that gives shape, strength and protection
• Skull: a hard case of flat bones that protects the brain, eyes and ears
• Vertebral column (backbone): 33 vertebrae that support the upright posture. Cartilage discs between the vertebrae act as cushions and allow bending and twisting
• Rib cage: 12 pairs of ribs and the sternum (breastbone), which protect the heart and lungs

The ribs attach to the spine at the back and to the sternum at the front. They are joined to the sternum by flexible cartilage, which lets the rib cage move while we breathe. During inhalation the rib cage expands, the space in the chest increases and air enters the lungs. During exhalation the rib cage contracts, the space decreases and air is pushed out.

In a young plant the outer protective layer is a single-layered epidermis. As the plant ages, cells below the epidermis begin to divide as a lateral meristem. These cells form the cork cambium (a secondary lateral meristem), which produces cork cells: dead, compact cells that are impermeable to water and gases. Cork cells pile up to form the bark of an old tree, which replaces the epidermis.

Bone marrow is the soft tissue inside the cavity of long bones. It contains stem cells, special undifferentiated cells that can divide and differentiate. Stem cells produce all types of blood cells: RBCs, WBCs and platelets. In a bone marrow transplant, stem cells from a healthy donor are given to a patient with a blood disease such as leukaemia (blood cancer) or thalassaemia (a blood disorder).

In 1958 F.C. Steward grew single phloem cells from a carrot root into complete plants. Totipotency is the ability of a single mature cell to develop into a complete organism. The cells first dedifferentiated (regained the ability to divide) into an undifferentiated mass, and then redifferentiated to form roots, a shoot and a whole plant in a nutrient medium. This is similar to the way a zygote develops into a complete human being.

Conclusion: the phloem cells of a carrot keep their full development potential, and light, air and a liquid medium together give the best growth.

Crown gall disease causes tumour-like swellings on plant stems. It is caused by the bacterium Agrobacterium tumefaciens and produces rapid growth, like cancer in animals. Scientists studied how this bacterium transfers its DNA into plant cells. Today Agrobacterium is used as a tool in the genetic engineering of crops.

• B.G.L. Swamy: a renowned botanist from Karnataka, known for work on plant morphology and anatomy. His Kannada science book Hasuru Honnu blends science, satire and culture in a botanical excursion in the Western Ghats, and won the Kendra Sahitya Akademi Award in 1978
• Sipra Guha Mukherjee and S.C. Maheshwari: a breakthrough in plant tissue culture. They grew a complete plant from anther culture (pollen cells) on an artificial nutrient medium under controlled laboratory conditions, which contributed greatly to crop improvement

Yoga is an ancient Indian practice of postures (asanas), breathing and meditation. Surya Namaskar has 12 sequential poses that activate all the major muscles and joints. Its benefits include better flexibility, posture and breathing, less stress, and protection against lifestyle diseases. 21 June is celebrated worldwide as International Yoga Day.

• Meristematic: apical (length), lateral (girth), intercalary (regrowth after cutting)
• Simple permanent: parenchyma (storage), collenchyma (flexible support), sclerenchyma (hard support)
• Complex permanent: xylem (water and minerals, upward), phloem (food, both directions)
• Epidermis: protective outer layer with cuticle, stomata and root hairs
• Tissue systems: dermal, ground and vascular

• Epithelial: tightly packed cells forming the outer covering and organ linings; five types (exchange, protection, secretion, sensory, absorption)
• Connective: blood (liquid matrix), bone (hard matrix), cartilage (jelly-like matrix), tendon, ligament
• Muscular: skeletal (voluntary, striated), smooth (involuntary, unstriated), cardiac (branched, only in the heart)
• Nervous: neurons with dendrites (receive), cell body (process) and axon (transmit)
• Musculoskeletal system: bones, muscles and joints working under the control of the nervous system

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