Revision: Basic Biology >> Tissues : Plant and Animal Tissues Biology (English Medium) ICSE Class 9 CISCE

A tissue, in biology, is defined as a group of cells that have a similar structure and perform a specific function. The word tissue originates from French, which means "to weave."

• Cells that perform a particular function always live in a group. This group of cells is called a tissue.
• For example, blood, phloem, muscle, etc. are examples of tissues.

A group of similar cells which perform a specific function.
example: Muscular tissue in animals.

A tissue is a group of cells that are similar in structure and are organized together to perform a specific task.

The tissue is a group of cells of similar structure and function.

Vascular tissue is the complex plant tissue in higher plants that are composed of xylem and phloem and is concerned with conducting water, minerals, and organic food throughout the plant body.

A group of similar cells, along with intercellular substances which perform a specific function, is called a tissue.

Meristematic tissue is a group of cells that constantly divide and produce cells indefinitely throughout the life of the plant.

Permanent tissue refers to a group of cells which temporarily or permanently cease to divide and thus assume permanent form and function

The population of all plant and animal species living in a particular area constitutes a biotic community.

All the members or individuals of a particular species living in a particular area constitute its population.

The zone on the earth in which all living beings exist is termed as the biosphere.

A group of living organisms that can breed among themselves constitute a species.

The epithelial cells are connected to each other laterally as well as to the basement membrane by junctional complexes called cell junctions.

The tissue which connects various tissues together in any organ is called connective tissue.

An organ is a group of tissues that work together to perform a specific function or set of functions in the body.

The heart, lungs, liver, and kidneys are examples, each playing a vital role in maintaining the body's overall health and function.

The cells that constitute nervous tissue are called neurons or nerve cells.

• Anatomy = Study of Internal Structure - Plant anatomy is the study of the internal structure of plants, which includes the organisation and structure of tissues.
• Basic Unit = Cell - The basic unit of plants is the cell. Cells are organised into Tissues → Organs (organisational hierarchy).
• Tissue Definition - A tissue is a group of similar cells having a common origin that perform a specific function together.
• Monocots vs. Dicots - Anatomical (internal structural) differences exist between monocots and dicots, so it's important to know them separately.
• Internal Structure Adapts - The internal structures of plants adapt according to their environment (e.g., water availability, climate), and structural similarities exist in both external and internal morphology of organisms.

• Meristematic tissue consists of cells that can divide and is restricted to specialised regions of the plant.
• Apical meristem is found at the root and shoot tips, is a primary meristem and increases the length of the plant.
• Intercalary meristem is found between mature tissues, is a primary meristem and helps form branches and flowers.
• Lateral meristem is found in mature regions, is a secondary meristem and is responsible for secondary growth (e.g. vascular cambium, cork cambium).
• Axillary bud is present in the axils of leaves and is responsible for forming branches or flowers.

• Parenchyma has thin-walled cells with intercellular spaces; the cell wall is made of cellulose. It performs photosynthesis, storage and secretion.
• Collenchyma is made of living, closely packed cells that are thickened at corners due to the deposition of cellulose and pectin. It provides mechanical support to young stems and petioles.
• Sclerenchyma is made of dead cells with thick, lignified walls and has two types of cells: fibres and sclereids.

Xylem

• Xylem consists of tracheids, vessels, xylem fibres and xylem parenchyma. It conducts water and minerals from roots to other parts of the plant.
• In stems (endarch), protoxylem is towards the centre and metaxylem towards the periphery. In roots (exarch), protoxylem is towards the periphery and metaxylem towards the centre.

Phloem

• Phloem consists of sieve tube elements, companion cells, phloem fibres and phloem parenchyma. It transports food from leaves to various parts of the plant.
• Mature sieve tube elements lack a nucleus, so their functions are controlled by the nucleus of companion cells.
• Protophloem has narrow sieve tubes (first formed), and metaphloem has bigger sieve tubes (later formed).

• Epithelial tissue has a free surface that faces either body fluids or the external environment, and its cells are tightly packed with very little intercellular space.
• Simple epithelium consists of a single layer of cells and mainly performs functions like lining, secretion, and absorption.
• Squamous epithelium is made of thin, flat cells and helps in diffusion, while cuboidal epithelium has cube-shaped cells and is involved in secretion and absorption.
• Columnar epithelium consists of tall cells that help in secretion and absorption, and ciliated epithelium contains cilia that move substances like mucus in a specific direction.
• Glandular epithelium is specialised for secretion and may be unicellular (goblet cells) or multicellular (such as salivary glands).
• Exocrine glands release their products through ducts, whereas endocrine glands secrete hormones directly into body fluids.
• Compound epithelium has multiple layers of cells and mainly provides protection, while cell junctions (tight, adhering, and gap junctions) help in preventing leakage, holding cells together, and communication between cells.

• Connective tissue is the most abundant tissue in the animal body, linking and supporting other tissues. Its cells (except in blood) secrete collagen or elastin fibres for strength, elasticity and flexibility.
• Loose connective tissue includes areolar tissue (supports epithelium; has fibroblasts, macrophages and mast cells) and adipose tissue (stores fat); both are found beneath the skin.
• Dense regular tissue has parallel collagen fibres; tendons connect muscle to bone, and ligaments connect bone to bone.
• Dense irregular tissue has collagen fibres oriented differently and is present in the skin.
• Specialised connective tissue includes cartilage (chondrocytes + collagen fibres) and bone (calcium salts + collagen fibres with osteocytes in lacunae).

• Muscle fibres are composed of fine fibrils called myofibrils and bring about movement and locomotion.
• Skeletal muscles are long, cylindrical, multinucleated, striated fibres closely attached to skeletal bones (voluntary).
• Smooth muscles are spindle-shaped, uninucleated, non-striated fibres found in the walls of internal organs like blood vessels, stomach and intestine (involuntary).
• Cardiac muscles are short, cylindrical, uninucleated fibres found only in the heart wall, with intercalated discs for communication between cells.