NCERT Solution Class 11th Biology Chapter – 8 Structural Organisation in Animals Notes

NCERT Solution Class 11th Biology Chapter – 8 Structural Organisation in Animals

NCERT Solution Class 11th Biology Chapter – 8 Structural Organisation in Animals

?Chapter – 8?

✍Structural Organisation in Animals✍

?Notes?

 All organisms are composed of cells.

Some are composed of a single cell and called unicellular organisms while others, like us, are composed of many cells and called multicellular organisms.

The cell is the fundamental structural and functional unit of all living organisms.

Unicellular organisms explain that a cell is capable of independently existing and of performing the essential functions of life.

Robert Hooke was the first person to describe the cell in 1865 when he used a microscope built by him to examine a thin slice of cork.

In 1831, Robert Brown made an important discovery when he reported the presence of a small sphere in the cells of the orchid root. This rounded body which later came to be called the ‘nucleus’ was thought to be of common occurrence in the cells.

In 1838, Matthias Schleiden, a German Botanist, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the different tissues of the plant.

Same time, Theodore Schwann (1839), a British Zoologist, also studied different types of animal cells. He observed the nuclei in these cells had a thin outer layer which is today known as the ‘plasma membrane’.

Schwann proposed the hypothesis that the bodies of animals and ( plants are composed of cells and products of cells.

Schleiden and Schwann combined their views and formulated the cell theory.

In 1855 when Rudolf Virchow first explained that cells divided and new cells are formed the pre-existing cells.

Cell theory as understood today is:

1. all living organisms are composed of cells and products of cells,
2. all cells arise from pre-existing cells.

A typical cell consists of a cell membrane, nucleus, and cytoplasm. Plant cells have a cell wall.

Cells are specialized to perform different functions and their shape and size may vary accordingly.

Cells are not only the building blocks of an organism but also the functional unit of life.

Cells vary in their shape, size, and activities/functions. Based on the presence or absence of a membrane-bound nucleus and other organelles, cells and hence organisms can be named eukaryotic or prokaryotic.

A typical eukaryotic cell consists of a cell membrane, nucleus, and cytoplasm.

Plant cells have a cell wall outside the cell membrane.

The plasma membrane is selectively permeable and facilitates the transport of several molecules. The endomembrane system includes ER, Golgi complex, lysosomes, and/vacuoles.

All the cell organelles perform different but specific functions. Centrosome and centriole form the basal body of cilia and flagella that facilitate locomotion.

In animal cells, centrioles also form spindle apparatus during cell division. The nucleus contains nucleoli and chromatin networks. It not only controls the activities of organelles but also plays a major role in heredity.

The endoplasmic reticulum contains tubules or cisternae. They are of two types: rough and smooth.

The Golgi body is a membranous organelle composed of flattened sacs. The secretions of cells are packed in them and transported from the cell.

Lysosomes are single membrane structures containing enzymes for the digestion of all types of macromolecules. Ribosomes are involved in protein synthesis.

Plastids are pigments containing organelles found in plant cells only. In-plant cells, chloroplasts are responsible for trapping light energy essential for photosynthesis.

The nucleus is enclosed by a nuclear envelope, a double membrane structure with nuclear pores. The inner membrane encloses the nucleoplasm and the chromatin material.

Cellular – A honeycomb-like structure with an empty compartment which Hooke called ‘cellular- a Latin word for a small room.

Plasma membrane – The nuclei in these cells had a thin outer layer which is today known as the ‘plasma membrane.

Organelles – Certain cellular functions are associated with different types of distinct structures called organelles present in the cytoplasm.

Peptidoglycan – The cell wall is rigid because of the presence of special macromolecules called peptidoglycan.

Polyribosomes – The ribosomes are the site of protein synthesis. Several ribosomes may attach to a single mRNA and form a chain called polyri¬bosomes or polysomes.

Pilin – The pills are elongate tubular structures made of a special protein called pinin.

Cell wall – The plant cells possess a conspicuous thick layer of cellulose covering the cell membrane called the cell wall.

Passive transport – Many molecules can move passively across the membrane without any requirement of energy called passive transport.

Endomembrane System – Each of the membranous organelles is distinct in terms of their structure and function but many of these are considered together as a part of the so-called Endomembrane system because their functions are coordinated.

Endoplasmic Reticulum (ER) – The electron microscopic study of the variety of eukaryotic cells revealed the presence of a network or reticulum of the tiny tubular structure scattered in the cytoplasm and hence, called the Endoplasmic Reticulum.

Exocytosis – The hydrolytic enzymes present in the phagosomes partially digest the engulfed material a residual body is formed, which is usually eliminated from the cell by a process called exocytosis.

Turgor pressure – Vacuoles also exert a hydrostatic pressure called the turgor pressure that gives mechanical support to the cell.

Matrix – Each mitochondrion is a double membrane-bound structure with the outer membrane and the inner membrane dividing its lumen distinctly into two aqueous compartments i.e. the outer compartment and the inner compartment called the matrix.

Hub – The central part of the centriole is also, proteinaceous called the hub.

Nucleus – The eukaryotic cells usually possess a large-sized, almost centrally located, and densely stained organelle containing the genetic material called the nucleus.

Histones – The biochemical analysis of the isolated chromatin has revealed that it contains DNA and some basic protein called histones.

Kinetochore –  Every chromosome essentially has a primary constriction of the centromere on the sides of which disc-shaped structures called the kinetochore.