Class 9 Science

Tissue

  • Meristematic Tissue
  • Simple Permanent Tissue
  • Complex Permanent Tissue

Tissue: A groups of cells which is meant for a specific task is called tissue.

Tissue and Division of Labour

In complex organisms, different tasks are carried out by different organs and organ systems. This is necessary to ensure division of labour. In other words, it is necessary to ensure different parts of the body perform different tasks. Tissues are the first step towards division of labour in complex organisms.

In simple organisms, a cell or a small group of cell can be responsible for all the biological functions. In complex organisms, there is a need for more efficiency for different tasks.

Plant tissues are less complex

Plants have a sedentary life because they do not need to move in search of food or mate. So, plants may not need so many specialised tissues and much complexity.

Animal tissues are more complex

But an animal has to move in search of food and mate. So complex animals need more specialised tissues and complexity.

Plant Tissues

Plant tissues are of two main types, viz. meristematic tissue and permanent tissue.

Meristematic Tissue

Plant tissues in which cells keep on dividing are called meristematic tissue. Cells of meristematic tissue have dense cytoplasm and vacuoles are absent. Vacuoles are absent because these cells do not need to store substances. Meristematic tissues are present in those parts of plants which keep on growing. Meristematic tissues are classified on the basis of their location. They are of following types:

Meristematic Tissue
  1. Apical Meristem: Apical meristem is present on root apex, stem apex, leaf buds and flower buds. They are responsible for growth in length. Growth in length of a plant part is called primary growth.
  2. Lateral Meristem: Lateral meristem is present along the side of the stem. They are responsible for growth in girth. Growth in girth is called secondary growth.
  3. Intercalary Meristem: Intercalary meristem is present at the base of leaf or internodes. They are present on either side of the node.

Permanent Tissue

Once the cells of meristematic tissue divide to a certain extent, they become specialized for a particular function. This process of attaining specialisation is called differentiation. Once differentiation is accomplished, the cells lose their capability to divide and the tissue becomes permanent tissue. Permanent tissues are of two types, simple permanent tissue and complex permanent tissue.

Simple Permanent Tissue

Simple permanent tissue is composed of similar types of cells. Simple permanent tissues are of three types, viz. parenchyma, collenchyma and sclerenchyma.

Parenchyma

Parenchyma

The cells of parenchyma have thin cell wall. They are loosely packed, with lot of intercellular spaces between them. Parenchyma makes the largest portion of a plant body. Parenchyma mainly works as packing material in plant parts. The main function of parenchyma is to provide support and to store food. Parenchyma can be of special types, which are as follows:

  1. Chlorenchyma: In some plant parts, parenchyma has chlorophyll as well. In that case, parenchyma carries out photosynthesis. In this case, parenchyma termed as chlorenchyma.
  2. Aerenchyma: In aquatic plants, large air cavities are present in parenchyma. This provides buoyancy to the plant. In this case, parenchyma is known as aerenchyma.

Collenchyma

Collenchyma

The cell wall of collenchyma is thickened at corners. Intercellular spaces are very few. Collenchyma provides some degree of structural rigidity along with flexibility. Collenchyma is present in leaf stalk, and present just below the epidermis. Due to this, the leaf stalk can easily bend but does not break.

Sclerenchyma

Sclerenchyma

The cell wall in sclerenchyma is highly thickened all around. The cells are dead and intercellular space is absent. Sclerenchyma provides structural rigidity to plant parts. Bark is composed of sclerenchyma. Another example of sclerenchyma can be seen in the coconut husk. Hard covering of fruits and nuts are composed of sclerenchyma. While eating a pear, you will get a gritty feeling in your mouth. This comes due to sclerenchymatous tissue.

Stomata

The epidermis of leaves has small pores called stomata. A stoma is a composed of two guard cells which regulate the opening and closing of stoma. Stomata facilitates exchange of gases and transpiration.

Complex Permanent Tissue

Complex permanent tissue is composed of different types of cells. Complex permanent tissues are of two types, viz. xylem and phloem. Xylem and phloem together make the vascular bundle in plants.

Xylem

Xylem

Xylem is composed of trachieds, vessels, xylem parenchyma and xylem fibres. The cells of xylem are dead, except the cells of xylem parenchyma. Trachieds and vessels are tubular structures and thus they provide a channel for conduction of water and minerals. Xylem fibre provides structural support to the tissue. Xylem parenchyma stores food.

Phloem

Phloem is composed of sieve tubes, companion cells, phloem fibre and phloem parenchyma. Sieve tubes are tubular cells with perforated walls. Sieve tubes are the conducting elements of phloem. It means conduction or transportation of materials takes place through sieve tubes. Phloem is responsible for translocation of food in plants. The transport of food in phloem is a two way movement.

Quiz



See Answer

1: (b) Tissue, 2: (d) Vacuoles, 3: (c) Leaf bud, 4: (b) Lateral meristem, 5: (a) Xylem, 6: (b) Parenchyma, 7: (c) Water lily, 8: (d) Collenchyma, 9: (b) Sclerenchyma, 10: (c) Sclerenchyma, 11: (a) Parenchyma, 12: (d) Vascular Bundle, 13: (c) Sclerenchyma, 14: (b) Two, 15: (c) Both a and b, 16: (a) Xylem, 17: (b) Xylem, 18: (c) Both a and b, 19: (d) Phloem, 20: (c) Xylem parenchyma


Matter in Our Surroundings

Anything that has both mass and volume is called matter. You can also say that anything which has mass and which occupies space is called matter.

Is Matter Around Us Pure?

Elements and compounds are pure substances. All other substances are mixtures which means they are not pure substances.

Atoms and Molecules

Read about law of conservation of mass, law of constant proportions and Dalton's atomic theory.

Structure of Atoms

Atom is made of three particles; electron, proton and neutron. These particles are called fundamental particles of an atom or sub atomic particles.

Cell: The Fundamental Unit of Life

A cell is capable of independent existence and can carry out all the functions which are necessary for a living being.

Tissue

A groups of cells which is meant for a specific task is called tissue. Tissues are the first step towards division of labour in complex organisms.

Diversity in Living Organisms

Without proper classification, it would be impossible to study millions of organisms which exist on this earth.

Motion

If an object changes its position with respect to a reference point with elapse of time, the object is said to be in motion.

Force & Laws of Motion

Force has numerous effects. Force can set a stationary body in motion. Force can stop a moving body.

Gravitation

Earth attracts everything towards it by an unseen force of attraction. This force of attraction is known as gravitation or gravitation pull.

Work & Energy

When force is exerted on an object and object is displaced, work is said to be done. It means work is the product of force and displacement.

Sound

Sound is a type of energy. Sound travels in the form of wave from one place to another.

Why Do We Fall Ill

Health is a state of physical, mental and social well being. A condition in which the affected person is unable to carry out normal activities is termed as disease.

Natural Resources

Resources which are obtained from nature are called natural resources. Examples: Air, water, soil, wood, etc.

Improvement in Food Production

Food security is said to exist when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life.