In a Chromosome apart from primary constriction, secondary constrictions occur. The nucleoli develop from secondary constrictions and such secondary constrictions are called nucleolar organizer regions.

Magnification:
1. The optical increase in the size of an image is called magnification. It is calculated by the following formula.
2. Magnification = \(\frac { size\ of\ image\ seen\ with\ the\ microscope }{ size\ of\ the\ image\ seen\ with\ normal\ eye } \)

1. Transmission Electron Microscope (TEM).
2. Scanning Electron Microscope (SEM).

(i) Corti first observed protoplasm Felix Dujardin (1835) observed a living juice in animal cell and called it "Sarcode". Purkinje (1839) coined the term protoplasm for sap inside a plant cell. Hugo Van Mohl (1846) indicated importance of protoplasm.
(ii) Max Schultze (1861) established similarity between Protoplasm and Sarcode and O. Hertwig (1892) proposed a theory which later called the 'protoplasm theory' Huxley (1868) proposed protoplasm as a "physical basis of life".

(i) A beam of electrons passes through the specimen to form an image. It provides two-dimensional image.
(ii) The magnification is 1-3 lakhs times and resolving power is 2 - 10 Å.

1. Photosynthesis.
2. Light reactions takes place in granum.
3. Dark reactions take place in stroma.
4. Chloroplast is involved in photorespiration.

S.No	Chromoplasts	Leucoplasts
1.	Coloured Plastids.	Colourless Plastids store food materials
2.	Eg: Chloroplast Occurs in green algae and higher plants Pigments chlorophyll a and b	Eg: Amyloplast - Stores - Starch.

1. Telocentric (Terminal centromere).
2. Acrocentric (terminal centromere capped by Telomere).
3. Sub-metacentric (centromere subterminal).
4. Metacentric (centromere median).

S.No	70s Ribosomes	80s Ribosomes
1.	They have 30S small subunit and 50S large subunit	They have 40S small subunit and 60S large subunit
2.	Found in Prokaryotes.	Found in Eukaryotes.
3.	16S rRNA in small subunit.	18S rRNA in small subunit.

S.no Prokaryotes Eukaryotes 1 It is unicellular It is unicellular and Multicellular 2 Many prokaryotes contain a single circular chromosome Eukaryotes contain multiple linear chromosomes 3 Prokaryotic chromosomes are condensed in the nucleoid via DNA supercoiling Eukaryotic chromosomes are condensed in membrane-bound nucleus via histones 4 In prokaryotes transcription and translation occur simultaneously in the cytoplasm In eukaryotes transcription occurs in nucleus and translation occurs in cytoplasm 5 Most prokaryotes contain only one copy of each gene that is they are haploid Most eukaryotes contain two copies of each gene that is they are diploid 6 Extrachromosomal DNA (i.e.) plasmids are present Eg: Bacteria Plasmids are absent. Eg: Plant cell, Animal cell

Cell wall is the outermost protective cover of cell. It was first observed by Robert Hooke. In plants it is made up of cellulose, hemicellulose, pectin, lignin, cutin, suberin and silica. In a plant cell wall shows three distinct regions (a) Primary wall (b) Secondary wall (c) Middle lamellae
(a) Primary wall:
(i) It is the first layer inner to middle lamellae, primarily consisting of loose network of cellulose microfibrils in a gel matrix.
(ii) It is thin, elastic and extensible. In most plants the microfibrils are made up of cellulose oriented differently based on shape and thickness of the wall.
(iii) The matrix of the primary wall is composed of hemicellulose, pectin, glycoprotein and water.
(iv) Hemicellulose binds the microfibrils with matrix and glycoproteins control the orientation of microfibrils while pectin serves as filling material of the matrix.
(v) Cells such as parenchyma and meristems have only primary wall.

  Plant Cell Wall
b. Secondary wall :
(i) Secondary wall is laid during maturation. It plays a key role in determining the shape of a cell. It is thick, inelastic and is made up of cellulose and lignin.
(ii) The secondary wall is divided into three sub layers termed as SI' S2 and S3 where the cellulose microfibrils are compactly arranged with different orientation forming a laminated structure and the cell wall strength is increased.
c. Middle lamellae:
(i) It is the outermost layer made up of calcium and magnesium pectate, deposited at the time of cytokinesis.
(ii) It is a thin amorphous layer which cements two adjacent cells. It is optically inactive (isotropic).
(iii) Plasmodesmata and Pits: Plasmodesmata act as a channel between the protoplasm of adjacent cells through which many substances pass through.
(iv) Moreover, at few regions the secondary wall layer is laid unevenly whereas the primary wall and middle lamellae are laid continuously such regions are called pits
(v) The pits of adjacent cells are opposite to each other. Each pit has a pit chamber and a pit membrane.
(vi) The pit membrane has many minute pores and thus they are permeable. The pits are of two types namely simple and bordered pit.

1.Protoplasm is translucent, odourless and polyphasic fluid
2. It is a crystal colloid solution which is a mixture of chemical substances forming crystalloid i.e. true solution (sugars, salts, acids, bases) and others forming colloidal solution (Proteins and lipids).
3. The pH of the protoplasm is around 6.8, contain 90% water (10% in dormant seeds).
4. Protoplasm is neither a good nor a bad conductor of electricity. It forms a delimiting membrane on coming in contact with water and solidifies when heated.
5. Cohesiveness: Particles or molecules of protoplasm are adhered with each other by forces, such as Van der Waal's bonds, that hold long chains of molecules together. This property varies with the strength of these forces.
6. Contractility: The contractility of protoplasm is important for the absorption and removal of water especially stomatal operations.
7. Surface tension: The proteins and lipids of the protoplasm have less surface tension, hence they are found at the surface forming the membrane. On the other hand the chemical substances (NaCl) have high surface tension, so they occur in deeper parts of the cell protoplasm.

Ultrastructure of Plant Cell

S.No Plant cell Animal cell 1.  Usually they are larger than animal cells Usually smaller than plant cells 2. Cell wall present in addition to plasma membrane and consists of middle lamellae, primary and secondary walls Cell wall absent. 3.  Plasmodesmata present.  Plasmodesmata absent. 4.  Chloroplast present. Chloroplast absent. 5.  Vacuole large and Permanent. Vacuole small and temporary. 6.  Tonoplast present around vacuole.  Tonoplast absent 7.  Centrioles absent except motile cells of lower plants.  Centrioles present 8.  Nucleus present along the periphery of the cell  Nucleus at the centre of the cell 9.  Lysosomes are rare  Lysosomes present. 10.  Storage material is starch grains.  Storage material is a glycogen granules.