NCERT Solutions For Class 9 Science Chapter 6 Tissues

A tissue is a group of similar cells that work together to perform a specific function.  In multicellular organisms, cells are specialized, and these specialized cells are organized into tissues. This organization helps the body work more efficiently.

Examples:

• In plants, xylem tissue transports water.
• In animals, muscle tissue helps in movement.

In multicellular organisms, tissues are very useful because they:

1. Divide Work (Division of Labour): Different tissues perform different functions, making the body work more efficiently.
2. Increase Efficiency: Specialized cells in tissues can do their jobs better than general cells.
3. Allow Organ Formation:Tissues group together to form organs, which perform complex functions.
4. Help in Growth and Repair:Some tissues (like meristematic in plants) help in growth, while others help in healing injuries.

Types of simple tissues:

• Parenchyma
• Collenchyma
• Sclerenchyma

These are simple permanent tissues found in plants. They are made of only one type of cell and help in functions like storage, support, and strength.

Apical meristem is found at the tips of roots and shoots in plants.

It is responsible for the increase in length of the plant, also called primary growth.

The husk of coconut is made up of sclerenchyma tissue.
This tissue is made of dead cells with thick walls and provides strength and protection.

The constituents of phloem are:

• Sieve tubes
• Companion cells
• Phloem fibres
• Phloem parenchyma

Phloem helps in transporting food from the leaves to other parts of the plant.

The tissue responsible for movement in our body is muscular tissue. Muscular tissue is made up of muscle cells (muscle fibers) that have the ability to contract and relax. This property helps in the movement of body parts.

There are three types of muscular tissue:

1. Skeletal muscles – Attached to bones; help in voluntary movements like walking or lifting.
2. Smooth muscles – Found in internal organs like the stomach and intestines; work involuntarily.
3. Cardiac muscles – Found only in the heart; responsible for pumping blood and also work involuntarily.

Together, these muscles allow us to move, digest food, breathe, and circulate blood.

A neuron has a cell body with many short branches called dendrites and one long branch called an axon. The cell body contains the nucleus.
Dendrites receive messages, and the axon carries messages away to other neurons or muscles. Neurons are long and branched, which helps them carry signals quickly through the body.

Features of cardiac muscles-

1. Cardiac muscles are involuntary – they work without our control.
2. They are found only in the walls of the heart.
3. The muscle cells are branched, striated (striped), and have one nucleus.

Functions of areolar tissue:

1. Connects different tissues and organs together.
2. Fills space inside organs and acts as a packing tissue.
3. Supports and strengthens internal organs.
4. Helps in repair of tissues after injury.
5. Defends the body by destroying germs (contains white blood cells).

Xylem tissue is made up of four types of elements:

1. Tracheids
2. Vessels
3. Xylem fibres
4. Xylem parenchyma

These parts help in carrying water and minerals from the roots to the rest of the plant and also give support.

Difference between simple and complex tissues in plants:

1. Simple tissues are made up of only one type of cell.
   Complex tissues are made up of more than one type of cell working together.
2. Simple tissues mainly help in support, storage, and photosynthesis.
   Complex tissues help in transport of water, food, and minerals.
3. Examples of simple tissues: Parenchyma, Collenchyma, Sclerenchyma
   Examples of complex tissues: Xylem, Phloem

Difference between Parenchyma, Collenchyma, and Sclerenchyma based on their cell wall:

1. Parenchyma: - Cell wall is thin and made of cellulose.
2. Collenchyma: - Cell wall is unevenly thickened, especially at corners, and contains cellulose and pectin.
3. Sclerenchyma: - Cell wall is thick and lignified (contains lignin), making it very hard and rigid.

Functions of stomata:

1. Exchange of gases– Stomata allow oxygen and carbon dioxide to move in and out of the leaf.
2. Transpiration – Stomata help in the loss of excess water from the plant as water vapor.
3. Maintains water balance – By opening and closing, stomata control water loss and help the plant stay hydrated.

The specific function of cardiac muscle is to pump blood throughout the body by rhythmic contraction and relaxation.

These muscles are found only in the walls of the heart and work involuntarily, meaning they function without our conscious effort. Cardiac muscles contract in a coordinated way to ensure a continuous flow of blood, supplying oxygen and nutrients to all body parts and removing waste materials.

Their unique structure allows them to work tirelessly throughout a person's life without getting fatigued.

Difference between Striated, Unstriated, and Cardiac Muscles (Based on structure and location in the body)

1. Striated Muscles (Skeletal Muscles)

• Structure: Long, cylindrical, multinucleated, and have light and dark bands (striations).
• Location: Attached to bones (arms, legs, etc.).
• Control: Voluntary (under our control).

2. Unstriated Muscles (Smooth Muscles)

• Structure: Spindle-shaped, single nucleus, no striations (smooth appearance).
• Location: Found in walls of internal organs like stomach, intestines, blood vessels, and bladder.
• Control: Involuntary (not under our control).

3. Cardiac Muscles

• Structure: Cylindrical, branched, single nucleus, with faint striations.
• Location: Found only in the walls of the heart.
• Control: Involuntary (work automatically without rest).

(a) Epithelial tissue – forms the inner lining of our mouth.
(b) Tendon – connects muscle to bone in humans.
(c) Phloem – transports food in plants.
(d) Adipose tissue – stores fat in our body.
(e) Blood – connective tissue with a fluid matrix.
(f) Nervous tissue – present in the brain.

Here is the identification of the type of tissue in each case:

1. Skin: Epithelial tissue
2. Bark of tree: Protective tissue
3. Bone: Connective tissue
4. Lining of kidney tubule: Cuboidal epithelial tissue
5. Vascular bundle: Complex permanent tissue (xylem and phloem)

Parenchyma tissue is present in the following regions:

1. Cortex and pith of stems and roots
2. Mesophyll of leaves (palisade and spongy layers)
3. Flesh of fruits
4. Seeds (for storage)
5. Xylem and phloem (as xylem and phloem parenchyma)

The epidermis in plants plays a vital protective role. Its main functions include:

1. Protection: It forms the outermost layer of cells, protecting the plant from mechanical injury, pathogens, and excessive water loss.
2. Water regulation: It has a waxy coating called the cuticle that reduces water loss by evaporation.
3. Gas exchange: It contains stomata, which are small pores that regulate the exchange of gases (like oxygen and carbon dioxide) and also control water loss through transpiration.
4. Absorption (in roots): In root regions, epidermal cells have extensions called root hairs that help absorb water and minerals from the soil.

Cork acts as a protective tissue in plants by forming a tough outer covering on stems and roots. The cells of cork are dead and have walls coated with a waxy substance called suberin, which makes them waterproof and resistant to gases. This helps prevent water loss, protects against mechanical injury, stops the entry of harmful microbes, and provides insulation from extreme temperatures.