Eukaryotic cells contain membrane-bound organelles that perform specialized functions. The most important organelle is the nucleus, which houses the cell's DNA. Eukaryotic cells also have other organelles like mitochondria and chloroplasts. Eukaryotic cells are generally larger than prokaryotic cells, ranging from 10 to 100 micrometers in size. The endosymbiotic theory explains how eukaryotic cells originated from ancient symbiotic relationships between prokaryotic cells, with mitochondria and chloroplasts evolving from bacteria. This higher level of organizational complexity in eukaryotic cells allowed for the development of multicellular life.

1. eukaryotic cell
A cell that contains
membrane-bound
compartments in which
specific metabolic
activities take place. Most
important among these
compartments is the
nucleus, which houses the
eukaryotic cell's DNA. It is
this nucleus that gives the
eukaryote – literally, "true
Comparison of a typical eukaryotic cell with a typical prokaryotic cell (bacterium).
nucleus" – its name.
The drawing on the left highlights the internal structures of eukaryotic cells,
Eukaryotic organisms also
including the nucleus (light blue), the nucleolus (intermediate blue), mitochondria
have other specialized, (orange), and ribosomes (dark blue). The drawing on the right demonstrates how
membrane-bounded bacterial DNA is housed in a structure called the nucleoid (very light blue), as well
structures, called as other structures normally found in a prokaryotic cell, including the cell
organelles, which are membrane (black), the cell wall (intermediate blue), the capsule (orange),
small structures within ribosomes (dark blue), and a flagellum (also black).
cells that perform
dedicated functions.
Eukaryotic cells are
typically 10 to 100 micrometers across, or about 10 times the size of prokaryotic cells.
Origin of eukaryotic cells
The set of ideas most favored by biologists to explain how eukaryotic cells first came about is called the
endosymbiotic theory. This theory is able to account well for the fact that two of the organelles found in
eukaryotic cells, mitochondria and chloroplasts, have their own DNA that is completely distinct from the
DNA housed in the nucleus. According to the endosymbiotic theory, the eukaryotic cell evolved from a
symbiotic community of prokaryotic cells. Specifically, the mitochondria and the chloroplasts are what
remains of ancient symbiotic oxygen-breathing bacteria and cyanobacteria, respectively, whereas the
rest of the cell seems to be derived from an ancestral archaean prokaryote cell.
The origin of the eukaryotic cell was a milestone in the evolution of life. Although eukaryotes use the
same genetic code and metabolic processes as prokaryotes, their higher level of organizational

2. complexity has permitted the development of truly multicellular organisms. Without eukaryotes, the
world would lack mammals, birds, fish, invertebrates, fungi, plants, and complex single-celled organisms.
Comparison of eukaryotic and prokaryotic cells
feature eukaryotic cells prokaryotic cells
Found in "simple" organisms,
types of
Found in "complex" organisms, including all plants and animals including bacteria and
organism
cyanobacteria
Can specialize for certain functions, such as absorbing nutrients from food or
Usually exist as single, virtually
specialization transmitting nerve impulses; groups cells can form large, multicellular organs and
identical cells
organisms
Most animal cells are 10–30 micrometers across; most plant cells are 10–100
size Most are 1–10 micrometers across
micrometers across
Contain a nucleus and many other organelles, each surrounded by a membrane (the Lack a nucleus and other
nucleus
nucleus and mitochondrion have two membranes) membrane-encased organelles
nucleolus One (or more) present in each nucleus Absent
Simple duplex not associated with
DNA DNA always in combination with histone proteins histones (i.e. basic
proteins)Absent
spindle Present temporarily during mitosis and meiosis Absent
Complete nuclear fusion between gametes, with equal contributions from both Unidirectional transfer of genes
sexual system
genomes from donor to recipient
Present, but chemically different
cell wall Present in plant cells, but never contain muramic acid in many respects from eukaryotes
(e.g. presence of muramic acid)
internal Complex compartmentalization into endoplasmic reticulum, Golgi bodies, Usually simple and often
membranes lysosomes, etc transient, if present at all
ribosomes 80 S with subunits (60 S + 40 S) 70 S* with subunits (30 S + 50 S)
photosynthesis Complex chloroplasts (membrane-bounded organelles) Simple chromatophores
Virtually all forms are aerobic, though a few are faculatively anaerobic (e.g. yeasts);
respiration Simple chromatophores
and, uniquely, the trichomonads are obligate anerobes
electron Found on the inner membrane of special membrane-bound organelles: mitochondria
transport (oxidative phosphorylation) and chloroplasts (photophosphorylation). Virtually all
Localized on the cell membrane
system & ATP forms are aerobic, though a few are faculatively anaerobic (e.g. yeasts); and,
synthesis uniquely, the trichomonads are obligate anerobes

3. metabolic functions. For example, some
Prokaryotic Cells bacteria use sulfur instead of oxygen in their
Cells that lack a membrane-bound nucleus are metabolism.
called prokaryotes (from the Greek meaning
before nuclei). These cells have few internal
structures that are distinguishable under a
microscope. Cells in the monera kingdom such
as bacteria and cyanobacteria (also known as
Examples of Prokaryotic Cells
blue-green algae) are prokaryotes.
Prokaryotic cells differ significantly from
eukaryotic cells. They don't have a membrane-
bound nucleus and instead of having
chromosomal DNA, their genetic information is
in a circular loop called a plasmid. Bacterial cells
are very small, roughly the size of an animal
mitochondrion (about 1-2µm in diameter and
10 µm long). Prokaryotic cells feature three
major shapes: rod shaped, spherical, and spiral.
Instead of going through elaborate replication
processes like eukaryotes, bacterial cells divide
by binary fission.
Bacteria perform many important functions on
earth. They serve as decomposers, agents of
fermentation, and play an important role in our
own digestive system. Also, bacteria are
involved in many nutrient cycles such as the
nitrogen cycle, which restores nitrate into the
soil for plants. Unlike eukaryotic cells that
depend on oxygen for their metabolism,
prokaryotic cells enjoy a diverse array of

4. Plant cells are eukaryotic cells that differ in several key respects from the cells of other
eukaryotic organisms. Their distinctive features include:
A large central vacuole, a water-filled volume enclosed by a membrane known as the
tonoplast[1][2] maintains the cell's turgor, controls movement of molecules between the
cytosol and sap, stores useful material and digests waste proteins and organelles.
A cell wall composed of cellulose and hemicellulose, pectin and in many cases lignin, is
secreted by the protoplast on the outside of the cell membrane. This contrasts with the
cell walls of fungi (which are made of chitin), and of bacteria, which are made of
peptidoglycan.
Specialised cell–cell communication pathways known as plasmodesmata,[3] pores in the
primary cell wall through which the plasmalemma and endoplasmic reticulum[4] of
adjacent cells are continuous.
Plastids, the most notable being the chloroplasts, which contain chlorophyll a green
coloured pigment which is used for absorbing sunlight and is used by a plant to make its
own food in the process is known as photosynthesis. Other types of plastid are the
amyloplasts, specialized for starch storage, elaioplasts specialized for fat storage, and
chromoplasts specialized for synthesis and storage of pigments. As in mitochondria,
which have a genome encoding 37 genes,[5] plastids have their own genomes of about
100–120 unique genes[6] and, it is presumed, arose as prokaryotic endosymbionts living
in the cells of an early eukaryotic ancestor of the land plants and algae.[7]
Cell division by construction of a phragmoplast as a template for building a cell plate late
in cytokinesis is characteristic of land plants and a few groups of algae, notably the
Charophytes[8] and the Order Trentepohliales[9]
The sperm of bryophytes and pteridophytes have flagellae similar to those in
animals,[10][11] but higher plants, (including Gymnosperms and flowering plants) lack the
flagellae and centrioles[12] that are present in animal cells.

5. Animal Cell
Public Domain Image: National Human Genome Research Institute
Animal cells are eukaryotic cells, or cells with a membrane-bound nucleus. Unlike prokaryotic cells, DNA
in animal cells is housed within the nucleus. In addition to having a nucleus, animal cells also contain
other membrane-bound organelles, or tiny cellular structures, that carry out specific functions necessary
for normal cellular operation. Organelles have a wide range of responsibilities that include everything
from producing hormones and enzymes to providing energy for animal cells.
Animal Cells: Structures and Organelles
The following are examples of structures and organelles that can be found in typical animal cells:
Centrioles - organize the assembly of microtubules during cell division.
Cytoplasm - gel-like substance within the cell.
Endoplasmic Reticulum - extensive network of membranes composed of both regions with ribosomes
(rough ER) and regions without ribosomes (smooth ER).
Golgi Complex - responsible for manufacturing, storing and shipping certain cellular products.
Lysosomes - sacs of enzymes that digest cellular macromolecules such as nucleic acids.
Microtubules - hollow rods that function primarily to help support and shape the cell.
Mitochondria - power producers and the sites of cellular respiration.
Nucleus - membrane bound structure that contains the cell's hereditary information.
Nucleolus - structure within the nucleus that helps in the synthesis of ribosomes.
Nucleopore - tiny hole within the nuclear membrane that allows nucleic acids and proteins to move into
and out of the nucleus.
Ribosomes - consisting of RNA and proteins, ribosomes are responsible for protein assembly.
Animal cells contain other cell structures that are not depicted in the illustration above. Some of these
structures include the cytoskeleton, cilia and flagella and peroxisomes.

6. Parts of the Cell and Its Description
Cell Wall
A rigid layer of nonliving material that surrounds the sells of plants and some other organisms; helps to
protect and support the cell
Cell Membrane
Controls what substances come into and out of the cell
Nucleus
The cell's control center; it directs all of the cell's activities
Cytoplasm Contains
Contains a gel-like material and cell organelles
Mitochondria
Rod shaped cell structures that produce most of the energy needed to carry out the cell's functions
Endoplasmic Reticulum
A cell structure that forms a maze of passageways in which proteins and other materials are carried
from one part of the cell to another
Ribosome
A tony structure in the cytoplasm of a cell where proteins are made
Golgi Body
A structure in the cell that recieves proteins and other newly formed materials from the endoplasmic
reticulum, packages them, and distributes them to other parts of the cell
Chloroplast
A structure in the cells of plants and some other organisms that captures energy from sunlight and uses
it to produce food. (This is when the plant bends toward the light).
Vacuole
A water-filled sac inside a cell that acts as a stoarge area
Lysosome
A small round cell structure that contains chemicals that break down large food particles into smaller
ones
Organelle
A tiny sell structure that comes out a specific function within the cell

7. Cell Parts and Their Functions
Nucleus
- Large Oval body near the centre of the cell.
- The control centre for all activity.
- Surrounded by a nuclear membrane.
Nucleoplasm
- is the protoplasm in the nucleus.
- contains genetic material ---> CHROMOSOMES (DNA)
Nucleolus
- is found in the nucleus.
- contains more genetic information (RNA)
Cell Membrane
- the outer boundary of the cell.
- it separates the cell from other cells.
- it is porous ---> allows molecules to pass through.
Cell Wall ( Plant Cells Only )
- non living structure that surrounds the plant cell.
- protects + supports the cell.
- made up of a tough fibre called cellulose.
Cyto Plasm
- cell material outside the nucleus but within the cell membrane.
- clear thick fluid.
- contains structures called organelles.
Vacuoles
- are clear fluid sacs that act as storage areas for food, minerals, and waste.
- in plant cell the vacuoles are large and mostly filled with water. This gives the plant support.
- in animal cells the vacuoles are much smaller.
Mitochondria
- power house of the cell.
- centre of respiration of the cell.
- they release energy for cell functions.
Chloro Plasts ( Plant cells only )
- contains a green pigment known as chlorophyll which is important for photosynthesis.

8. Ribosomes
- tiny spherical bodies that help make proteins.
- found in the cyto plasm or attached to the endo plasmic reticulum.
Endo Plasmic Reticulum ( ER )
- systems of membranes throughout the cyto plasm.
- it connects the nuclear membrane to the cell membrane.
- passageway for material moving though the cell.
Golgi Bodies
- tube like structures that have tiny sacs at their ends.
- they help package protein.
Lysosomes
- " suicide sacs "
- small structures that contain enzymes which are used in digestion.
- if a lysosome were to burst it could destroy the cell.