The chapter contain detail descriptions regarding structures and functions of different cell organelles of plant and animal cells which is helpful to UG and PG students of Science. Cell is the basic unit of structure and function in all living organisms. The basic constituents of plant and animal cells are the same, viz nucleic acid, proteins, carbohydrates, lipids and various inorganic substances They organized in the same fundamental manner. The shape of plant cell is rectangular and that of animal cell is round with irregular appearance. Cell organelles various membrane bound structures that are found within a cell such as nucleus, plastids, mitochondria, endoplasmic reticulum etc.

1. CELL ORGANELLES
Prepared and Delivered by:-
Dr. M. H. Sapovadiya
Assistant Research Scientist
Dept. of Genetics and Plant Breeding
CoA, Junagadh Agricultural University, Junagadh (Gujarat)

2. CELL ORGANELLES

3. CELL ULTRASTRUCTURE
 Cell is the basic unit of structure and function in all living
organisms.
 The basic constituents of plant and animal cells are the same,
viz., nucleic acid, proteins, carbohydrates, lipids and various
inorganic substances.
 They organized in the same fundamental manner.
 The shape of plant cell is rectangular and that of animal cell is
round with irregular appearance.
 Cell organelles: various membrane bound structures that are
found within a cell such as nucleus, plastids, mitochondria,
endoplasmic reticulum, etc.,

4. CELL
Non-living inclusions (Cell wall) Living materials (Protoplast)
Nucleus Cytoplasm
1. Nuclear membrane 1. Plasma-membrane
2. Nucleoplasm 2. Endoplasmic reticulum
3. Chromatin 3. Ribosomes
4. Nucleolus 4. Golgi body
5. Vacuoles
6. Mitochondria
7. Plastids
8. Lysosomes
9. Centrosomes
10. Microtubules

5. Plant Cell

6. CELL WALL
 It is the outermost part of the cell and is always non-living
(Rigid and Strong) but it is produced and nourished by
living protoplasm.
 The cell wall is found only in plants and absent in animals.
 Multilayered viz., middle lamella, primary cell wall
(dispersed arrangement) and secondary cell wall (parallel
arrangement of cellulose fibrils).
Functions:
1. To protect inner parts of cell.
2. To give a definite shape of the cell.
3. To provide mechanical support.

8. MIDDLE LAMELLA
 A specialized region associated with the cell
walls of plants, and sometimes considered an
additional component of them, is the middle
lamella.
 The middle lamella cements together the
primary walls of two contiguous cells.
 The middle lamella is mainly composed of a
pectic compound which mostly appears to be
calcium pectate.

9. PRIMARY CELL WALL
 The main chemical components of the primary plant
cell wall include cellulose in the form of organized
microfibrils, a complex carbohydrate made up of
several thousand glucose molecules linked end to
end.
 In addition, the cell wall contains two groups of
branched polysaccharides, the pectins and cross-
linking glycans.
 It is soft, elastic, transparent and readily permeable
to water.

10. SECONDARY CELL WALL
 The secondary plant cell wall, which is often
deposited inside the primary cell wall as a cell
matures, sometimes has a composition nearly
identical to that of the earlier-developed wall.
 More commonly, however, additional substances,
especially lignin, are found in the secondary wall.
➢ It gives sufficient rigidity and strength to the plant
body.
➢ It is permeable to water and solutes.
➢ Lignin also makes plant cell walls less vulnerable to
attack by fungi or bacteria.
 Cutin, suberin, and other waxy materials that are
sometimes found in plant cell walls.

11. PLASMA LEMMA OR PLAMA MEMBRANE
 The membrane enclosing cytoplasm of a cell is
known as plasma lemma or plasma membrane.
 It presents both in plant and animal cell
 Composed of lipids and proteins
Functions:
1. It regulates the passage in and out of the cell
2. It acts as a selectively permeable membrane
3. It checks the entry of toxic elements from out side
into the cytoplasm
4. It permits only passage for molecules like minerals
into the cell and restricts their outward movement

12. FLUID MOSAIC MODEL
 The plasma membrane is composed of a double layer
(bilayer) of lipids (phospholipids).
 Phospholipids are characteristically hydrophilic ("water-
loving") at their phosphate ends and hydrophobic ("water-
fearing") along their lipid tail regions.
 In each layer of a plasma membrane, the hydrophobic lipid
tails are oriented inwards and the hydrophilic
phosphate groups are aligned so they face outwards,
either toward the aqueous cytosol of the cell or the
outside environment.
 Within the phospholipid bilayer of the plasma
membrane, many diverse proteins (glycoprotein) are
embedded, while other proteins simply adhere to the
surfaces of the bilayer.

13. PLASMODESMATA
• Plasmodesmata (singular, plasmodesma) are small channels
that directly connect the cytoplasm of neighboring plant
cells to each other, establishing living bridges between cells.
• The plasmodesmata, which penetrate both the primary and
secondary cell walls allow certain molecules to pass directly
from one cell to another and are important in cellular
communication.

14. CYTOPLASM
 Part of plant cells outside the nucleus (and
outside the large vacuole of plant cells) is called
cytoplasm.
Cytoplasmic inclusions (Non-living):
 These are not metabolic active parts but they are storage
sites of end product
 It includes oil drops, yolk granules, pigments, starch
granules etc.
Cytoplsmic organelles:
 Organells are membrane bounded, living structures
 They performed important activities like biosynthesis,
metabolic and respiratory

15. ENDOPLASMIC RETICULUM (E.R.)
 The term E. R. was first used by Porter in 1948 to describe a fine
reticulum in the endoplasmic cells.
 Endoplasmic means "within the cytoplasm", and reticulum means "little
net".
 The ER is an extensive membranous network within the cytoplasm.
 It is thread or tube like- floating in cytoplasm on which ribosomes are
attached.

16. ENDOPLASMIC RETICULUM (E.R.)
Two Types:
1. Smooth E. R.: also known as agranular ER
o Outer and inner surfaces are regular and they do not have
attached ribosome, no protein synthesis.
o Contain more lipid than rough ER.
2. Rough E. R.: also known as granular ER
o Outer and inner membrane found attached with ribosomes
o Rough ER is well developed in those cell which is actively involved
in protein synthesis.
Rough and Smooth ER change into each other as per needs of cells.

17. FUNCTIONS: ER
The ER functions as a packaging system. It does not work
alone. The ER works closely with the Golgi apparatus,
ribosomes, RNAs, mRNA and tRNA.
1. Rough ER plays important role in the synthesis and
packaging of proteins.
2. Smooth ER acts as a storage organelle.
3. ER acts as inter-cellular transport system for various
substances.
4. ER provides passage for mRNA from nucleus to the
cytoplasm.

18. RIBOSOMES (RIBOZYMES)
 Small round particles in a cell made up of RNA and
protein that are primarily involved in the assembly of
proteins by translating messenger RNA are called
Ribosomes.
 However, though they are generally described as
organelles, it is important to note that ribosomes are
not bound by a membrane and are much smaller than
other organelles.
 Ribosomes are mainly found bound to the
endoplasmic reticulum and the nuclear envelope, as
well as freely scattered throughout the cytoplasm.
 The ribosomes in a eukaryotic cell generally have a
Svedberg value of 80S and are comprised of 40s and
60s subunits. Prokaryotic cells, on the other hand,
contain 70S ribosomes, each of which consists of a 30s
and a 50s subunit.

20. GOLGI APPARATUS
 The Golgi apparatus (GA), also called Golgi body
or Golgi complex and found universally in both
plant and animal cells, is typically comprised of
a series of five to eight cup-shaped, membrane-
covered sacs called cisternae that look
something like a stack of deflated balloons.
 Golgi complex was first describing by Camillo Golgi in
1822 in nerve cells of cat and owl.

21. FUNCTION OF GOLGI COMPLEX:
1. Packaging of food materials such as proteins, lipids and
phospholipids for transport to other cells.
2. It secrete many granules and lysosomes (originated from
golgi bodies).
3. The golgi apparatus also protects against cell destruction
known as apoptosis

22. LYSOSOMES
 Cell organelles with large number of digestive enzymes
which are used primarily for digestion and removal of
excess or worn-out organelles, food particles and engulfed
viruses or bacteria.
 The term Lysosome was first used by Dave in 1955.
 Lysosomes are membrane bound organelles that are found
mainly in the animal cells.
 Greek word 'lysis' means destruction or dissolution and
'soma' means body.
 In plant cell they are bounded storage granules and
contain hydrolytic digestive enzymes.

23. LYSOSOMES
Function:
1. Digestion of intracellular substances and foreign
particles, which comes in the cell by pinocytosis
and phagocytosis. Thus lysosomes act as a disposal
system of the cell.
2. To repair the damage to the plasma membrane.
3. Lysosomes are also involved in programmes cell
death, or autolysis. This is the reason why
lysosomes are often called as 'suicide sacs'

24. MITOCHONDRIA
 A spherical or rod shaped organelle in the cytoplasm of
nearly all eukaryotic cells, containing genetic material and
many enzymes important for cell metabolism, including those
responsible for the conversion of food to usable energy is
called mitochondria (Singular-mitochondrion)
 Randomly distributed throughout cytoplasm
 They are bounded by two membranes of lipo-proteins
 They arise by fission of pre-existing mitochondria, on an
average cell may have 200-800 mitochondria
 Mitochondria are semi-autonomus, self reproducing
organelles because they contain their own genome.

26. MITOCHONDRIA
Function:
1. It involved in respiration, oxidation of food (carbohydrates,
amino acids and fatty acids) and metabolism of energy
(powerhouse of cell).
2. They contain circular DNA molecules and ribosomes so
they are capable of synthesis of certain proteins.
3. Since they contain DNA, they contribute to heredity by way
of cytoplasmic inheritance.
4. Mitochondria help the cells to maintain proper
concentration of calcium ions within the various
compartments of the cell by serving as storage tanks of
calcium ions.

27. PLASTIDS
 Plastids are highly specialized living protoplasmic
bodies of the cytoplasm
 Plastids are major organelles found in plants and
algae.
 Plastids often contain pigments used in photosynthesis,
and the types of pigments present can change or
determine the cell's color.
 Plastids are found in the cytoplasm of plant cells only.

28. TYPES OF PLASTIDS

29.  Leucoplasts (Amyloplast, Elaioplasts, Etioplasts and
Proteinoplasts):
✓ Colourless plastid-absent of pigment.
✓ Occurs in plant cell-not exposed to light such as root and seeds.
✓ Function: Store protein (Proteinoplasts) and lipids
(Elaioplasts), Sugar convert into starch (Amyloplast),
precursor pigment for chlorophyll production (Etioplasts).
 Chromoplasts:
✓ They contain pigments of different colour – yellow, orange and
red.
✓ Present in petals of flowers and fruits.
✓ Function: to attract agents of pollination and in fruit to attract
agents of dispersal.
 Chloroplasts:
✓ They are green in coloured due to chlorophyll,
✓ Found in plant parts which are exposed to the light
✓ Function: Photosynthesis
TYPES OF PLASTIDS

31. NUCLEUS AND IT’S STRUCTURE
Nucleus:
 The nucleus was first discovered by Robert Brown in 1833,
since nucleus contains chromosomes of genes is called as
controlling center of the cell.
 Usually spherical or oval shape.
 Larger in active cell than in resting cells.
 Store house of almost all the genetic information.
 It consists of four structures:
1. Nuclear membrane
2. Nucleoplasm (karyolimph)
3. Nuclear reticulum (chromatin)
4. Nucleous

33. 1. NUCLEAR MEMBRANE
 Nucleus is enclosed by two membranes of lipo-proteins,
which separated nucleus from cytoplasm and membranes
are not continuous but they are broken at several places is
known as nuclear pores
 Space between two nuclear membrane is known as peri
nuclear space
 Outer membrane is attached with ER on which ribosomes
are present
Function:
1. It facilitates and regulates nucleo-cytoplasmic interaction
2. The nuclear pores regulate the exchange of micro
molecules i.e. protein, r-RNA, m-RNA etc.

34. 2. Nucleoplasm:
The watery substances in higher nucleolus and chromatin are
present which is surrounded by nuclear membrane is called
Nucleoplasm or Nuclear sap or Karyolymph
It is shapeless contains dissolved phosphorus ribose sugar proteins
nucleotides and had nucleic acids
3. Nucleolus:
In higher organisms, every cell nucleus has a spherical, darkly
stained colloidal body, which can be easily seen and generally
disappear during cell division
It is associated with a particular nucleolar organizing chromosome
Chemically, it is composed of large amount of ribosomal proteins
and ribosomal RNA
Functions:
1. Biogenesis of ribosomes
2. Stores all proteins of ribosomes
3. Provide energy for nuclear activities

35. 4. NUCLEAR RETICULUM (CHROMATIN FIBERS)
 Nucleoplasm contains many thread like, coiled and much
elongated structures
 During cell division – mitosis and meiosis – chromatin fibers
becomes thick ribbon like structure which are known as
chromosomes
Function:
1. Chromatin fibers are the basic unit
2. They are also fundamental basis of inheritance since
they contain the genetic material
On the basis of stainability Cohn (1964) classified chromatin in
two parts:
Heterochromatin
Euchromatin

36. CYTOPLASMIC VACUOLES
 Vacuoles are storage bubbles found in cells.
 Small or large sized liquid filled structure.
 Found in both animal and plant cell but more in number
and large size in plant cell.
 The vacuoles of plant cells are bounded by single, semi-
permiable membrane known as tonoplast.

37. CYTOPLASMIC VACUOLES
Function:
1. Storage and transmission of the materials and
maintenance of internal pressure
2. It contains water, phenol, alkloids, pigment salts and other
secretary products

38. MICROTUBULES
 Microtubules are straight, hollow, tubular cylinders which make
up the cytoskeleton.
 They are responsible for structural support and transport of the
cell.
 Complex structure made up of 13 individual protofilaments
arrange to form hallow cylinder
 Transportation of small molecules produce fibres during cell
division

43. PLANT CELL VERSUS ANIMAL CELL
SN Particulars Plant cell Animal cell
1. Cell wall Present Absent
2. Plasma membrane Cell wall & cell
membrane
Cell membrane only
3. Plastids Present Absent
4. Ribosome Present Present
5. Mitochondria Present Present
6. Golgi apparatus Present Present
7. Endoplasmic reticulum Present Present
8. Lysosomes Usually absent Present
9. Nucleus Present Present
10. Vacuole Very large Very small
11. Centrioles Lower plants only Present
12. Microtubules Present Present
13. Cytoplasm Present Present
14. Cell shape Rectangular
(Fixed)
Round (Irregular)