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INTERMEDIATE BIOLOGY NOTES
CELL
- A cell is the fundamental, structural and functional unit of all living organisms
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- Anton Von Leeuwenhoek: First observed and described a live cell
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Q) Development of electron microscope helped in cell study because resolving power of
electron microscope is much higher than light microscope
Q) Electron microscope has high resolution power because of very low wavelength of electron
beam
Q)Under microscope we should use light with min wavelength (eg among option
blue,green,yellow and red we should choose blue)
CELL THEORY
- Matthias Schleiden (1838) observed that all plants are composed of different kinds of cells
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-He also found that plant cells have cell wall
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-Schleiden & Schwann formulated the cell theory
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-He modified the cell theory
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(ii) All cells arise from pre-existing cells
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This keeps the cell in ‘living state’
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- Cells differ in size, shape and activities
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3 µm in length)
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o Longest cells: E
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Nerve cell
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o Human RBCs are about 7
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- Based on the functions, shape of cells may be disc-like, polygonal, columnar, cuboid, thread
like, or irregular
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- They have no membrane bound nucleus and organelles
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- They are generally smaller and multiply more rapidly than the eukaryotic cells
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E
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Bacteria have 4 basic shapes: Bacillus, Coccus, Vibrio and
Spirillum
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0001mm
Q) Organelles can be separated from cell homogenate through diffential centrifugation
CELL ORGANELLES IN PROKARYOTIC CELL
1) Cell Envelope
- It is a chemically complex protective covering
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a)Glycocalyx:
-Outer layer
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-It may be a slime layer (loose
sheath) or capsule (thick & tough)
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-Seen in all prokaryotes except
mycoplasma
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Q)Bacterial cell wall is made up of peptidoglycan
Q)Mycoplasma is wall less microorganism

c)Plasma membrane
- Inner layer
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-This is structurally similar to that of the eukaryotes
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o Gram negative: They do not retain the gram stain
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-It includes vesicles, tubules & lamellae
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o In DNA (chromosome) replication
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o In respiration and secretion processes
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- Chromatophores are pigment-containing membranous infoldings in some prokaryotes (e
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cyanobacteria)
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- Many bacteria have small circular DNA (plasmid) outside the genomic DNA
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g
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Q) Prokaryotic cell does not have nuclear membrane
Q) Chromosome in bacterial cell can be 1-3 in no and are always circular
4)FLAGELLA
- These are thin filamentous extensions from the cell wall of motile bacteria
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- Bacterial flagellum has 3 parts – filament, hook and basal body
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Q)Motile bacteria are able to move by flagella
Q)Cyanobacteria lacks flagellated cells
4) PILLI AND FIBRIAE

- These are surface structures that have no role in motility
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Pilus) are elongated tubular structures made of a special protein (pilin)
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- In some bacteria, they help to attach the bacteria to rocks in streams and to the host tissues
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- They are about 15 nm by 20 nm in size
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-They together form 70S prokaryotic ribosomes
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- Function: Ribosomes are the site of translation (protein
synthesis)
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-Ribosomes translate the mRNA into proteins
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- E
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phosphate granules, cyanophycean granules and glycogen granules, gas vacuoles etc
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- They have well organized membrane bound nucleus and organelles
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- Their genetic material is organized into chromosomes
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Q) Inclusion bodies are not bound by any membrane
Q) Inclusion bodies lie free in cytoplasm
Q) Inclusion bodies represent reserve material in cytoplasm
Q) Inclusion bodies have no role in ingestion of food
Q)eg of inclusion bodies are Glycogen granules, phosphate granules,cyanophycean granules
CELL ORGANELLES IN EUKARYOTIC CELL
1)CELL MEMBRANE
- Chemical studies on human RBCs show that cell membrane is composed of a lipid bilayer,
protein & carbohydrate
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-So the non-polar tail of saturated hydrocarbons is protected from the aqueous environment
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-E
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In human RBC, membrane has 52% protein and 40% lipids
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o Peripheral proteins: Lie on the surface of membrane
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According to
this, the quasifluid nature of lipid enables lateral movement of proteins
within the overall bilayer
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Q)Plasma membrane is made up of protein,lipids and carbohydrates
Q)Latest model for plasma membrane is fluid mosaic model
Q)Fluid mosaic model was given by Singer and Nicolson
Q) According to fluid mosaic model,plasma membrane is composed of phospholipids, extrinsic
and intrinsic proteins
Q)In fluid mosaic model phospholipids form a bimolecular layer in middle part
Q)Lipid layer can sometimes flip flop but protein can travel or be embedded in lipid bilayer but
never undergo flip flop movement in lipid bilayer
Q)Proline Is not a constituent of Cell membrane

Functions:
o Transport of the molecules
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o Due to the fluid nature, the plasma membrane can help in cell growth, formation of
intercellular junctions,secretion, endocytosis, cell division etc
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Passive transport:
-It is the movement of molecules across
the membrane along the concentration gradient (i
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, from higher concentration to the lower)
without the expenditure
of energy
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Simple diffusion:
-It is the movement of neutral solutes
across the membrane
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Osmosis:
-It is the movement of water by diffusion across the membrane
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-So they require membrane carrier protein for transport
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Active transport:
-It is the movement of molecules across
the membrane against the concentration gradient (i
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from lower to the higher concentration)
with the expenditure of

energy (ATP is utilized)
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g
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Q)Active and passive transport differ in passive transport is along concentration gradient while
active transport is due to metabolic energy
Q)Cell recognition and adhesion occurs due to glycoproteins and glycolipd present in cell
membrane
2)CELL WALL
- It is a non-living rigid structure found outer to the plasma membrane of fungi and plants
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-In other plants, it consists of
cellulose, hemicellulose, pectins and proteins
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-It gradually diminishes as the cell matures andthe secondary wall is formed on the inner side
(towards membrane)
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-Cell wall and middle lamellae may be traversed by plasmodesmata
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Q)Desmo
Q)Middle lamella is mainly composed of calcium pectate
Q) Element necessary for middle lamella is Ca
Functions:
a
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b
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c
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d
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Q) Plasmodesmata are connections between adjacent cells
Q)Plasmodesmata forms transport channel between adjacent cells
Q) Desmosomes are concerned with cell adherence
Q)Cell wall shows complete permeability
3) ENDOMEMBRANE SYSTEM
- It is a group of membranous organelles having coordinated functions
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Q) ENDOMEMBRANE SYSTEM includes ENDOPLASMIC RETICULUM, GOLGI
APPARATUS,LYSOSOMES and VACUOLES
A) ENDOPLASMIC RETICULUM
- These are a network of tiny tubular structures scattered in the cytoplasm
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- Endoplasmic reticulum is 2 types:

a
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-RER is frequently observed
in the cells actively involved in protein synthesis and secretion
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Q) RIBOSOMES are attached to surface of rough ENDOPLASMIC RETICULUM
Q)ROUGH ENDOPLASMIC RETICULUM is involved in protein folding, protein glycosylation
and clevage of signal peptide
Q) ENDOPLASMIC RETICULUM is concerned with glycosylation of proteins
Q) ENDOPLASMIC RETICULUM is involved in modification and outing of newly synthesized
proteins to their destination
b
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-SER is the major site for synthesis of lipid
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Q) RIBOSOMES are absent in smooth ENDOPLASMIC RETICULUM
Q) Smooth ENDOPLASMIC RETICULUM is site for lipid synthesis
B)GOLGI APPARATUS
- Densely stained reticular structures near the nucleus
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- They consist of flat, discshaped sacs (cisternae) of 0
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0 µm diameter
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- Cisternae are concentrically arranged with convex cis (forming) face and concave trans
(maturing) face
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Q) GOLGI APPARATUS is organelle located near nucleus and contains a collection of flattened
membrane bound cisternae
Q) GOLGI APPARATUS is absent in bacteria and blue green algae
Q)Other name of GOLGI BODY is apparato reticolare
#Function of Golgi apparatus:
o Secretes materialsto intra-cellular targets or outside the cell
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-This is why Golgi apparatus remains in close association with the
endoplasmic reticulum
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o Formation of glycoproteins and glycolipids
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- Lysosomal vesicles contain almost all types of hydrolytic enzymes (hydrolases– lipases,
proteases, carbohydrases)
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They digest carbohydrates,proteins, lipids and nucleic acids
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- It contains water, sap, excretory product and other materials not useful for the cell
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- In plant cells, the vacuoles can occupy up to 90% of the volume of the cell
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-Hence their concentration is higher in the vacuole than in the cytoplasm
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- In many cells (e
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protists), food vacuoles are formed by engulfing the food particles
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- Number, shape and size of mitochondria per cell are variable depending on the physiological
activity
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2-1
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5 µm) and
length 1
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1 µm
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- It divides lumen into 2 aqueous compartments, i
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, the outer compartment and the inner
compartment (matrix)
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-They increase the
surface area
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- Matrix possesses a circular DNA, a few RNA molecules,ribosomes (70S) and components for
protein synthesis
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-They produce energy in the form of ATP
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5
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- Large sized
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- They contain some pigments
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Chloroplasts:
- Contain chlorophyll and carotenoid pigments
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b
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-This gives a yellow, orange or red colour
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Leucoplasts:
-These are colourless plastids of varied
shapes and sizes with stored nutrients
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E
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potato
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§ Aleuroplasts: Store proteins
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- These are lensshaped,oval,spherical,discoid or ribbon-like organelles
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Width: 2-4 µm
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g
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- Inner membrane of chloroplast is less permeable
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-It contains many organized flattened
membranous sacs called thylakoids
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- Chlorophyll pigments are present in the thylakoids
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- There are flat membranous tubules called the stroma lamellae connecting the thylakoids of the
different grana
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- The ribosomes of the chloroplasts are smaller (70S) than the cytoplasmic ribosomes (80S)
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- It is first observed by George Palade (1953)
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-They
together form 80S
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- It provides mechanical support, motility, maintenance of the shape of the cell etc
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- CILIA
Small structures which work like oars
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- Flagella: Longer
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-Flagella of prokaryotes and eukaryotes are structurally different
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-Their core (axoneme) has many microtubules running parallel to the long axis
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-This is called 9+2 array
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- It is connected to one of the
tubules of each peripheral doublet by a radial spoke
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-The peripheral doublets are also
interconnected by linkers
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B) CENTROSOMES AND CENTRIOLES
- Centrosome is an organelle usually containing two nonmembrane bound cylindrical structures
called centrioles
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- The centrioles lie perpendicular to each other
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-Each of the peripheral fibril is a triplet
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- The central part of the centriole is also proteinaceous and called the hub, which is connected
with tubules of the peripheral triplets by radial spokes made of protein
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8) NUCLEUS

Nucleus was first described by Robert Brown (1831)
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Some cells have more than one
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E
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mammalian RBC and sieve tube cells of vascular plants
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-It is a barrier between the materials present in nucleus &
cytoplasm
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-Nuclear envelope has minute pores formed by the fusion of its two membranes
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o Nuclear matrix (nucleoplasm)
o Chromatin:
-A network of nucleoprotein fibres
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- During cell division, chromatins
condense to form chromosomes
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- It is continuous with the nucleoplasm
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Chromosomes:
- A human cell has 2 m long thread of DNA
distributed among its 46 (23 pairs)
chromosomes
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-On the sides of centromere, disc shaped structures called kinetochores are present
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o Sub-metacentric chromosome: Centromere is nearer to one end forming one shorter arm and
one longer arm
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o Telocentric chromosome: Terminal centromere
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-It is called satellite
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- Present in both plant and animal cells

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