This document summarizes key aspects of cell biology. It defines the cell and compares prokaryotic and eukaryotic cells. It describes several important cell organelles - plastids, the nucleus, mitochondria, the Golgi apparatus, and the endoplasmic reticulum. It also summarizes the cell theory, which states that cells are the fundamental unit of life and that new cells are produced from existing cells.

1. XI E
Biology
Spandan B.
Summer Holiday Homework

2.  Cell- Definition
 Comparison of the types of cells (prokaryotic and
eukaryotic)
 Generalized Cell
 Cell Organelles
 Plastids
 Nucleus
 Mitochondria
 Golgi bodies
 Endoplasmic reticulum
 Acknowledgements

3. Cell – Definition
 The cell is the basic structural, functional and biological unit of
all known living organisms.
 It is the smallest unit of life that is classified as a living thing,
except virus, and is often called the building block of life.
 It consists of a protoplasm enclosed within a membrane.
 Organisms can be classified as unicellular (consisting of a
single cell; including most bacteria) or multicellular
(including plants and animals).
 While the number of cells in plants and animals varies from
species to species, humans contain about 100 trillion (1014)
cells.
 Most plant and animal cells are between 1 and
100 micrometres and therefore are visible only under the
microscope.
 Cells are of two types –
 Prokaryotic
 Eukaryotic

4. Comparison of features of
prokaryotic and eukaryotic cells
Prokaryotes
Eukaryotes
Typical organisms bacteria, archaea fungi, plants, animals
Typical size ~ 1–5 µm ~ 10–100 µm
Type of nucleus no real nucleus
nucleus with double
membrane
DNA Single chromosome Multiple chromosomes
Cytoplasmatic structure very few organelles Multiple organelles
Cell movement flagella made of flagellin
flagella
and cilia containing microt
ubules
Mitochondria none one to several thousand
Chloroplasts none in algae and plants
Organization usually single cells
Single celled as well as
multicellular
Cell division
Binary fission (simple
division)
Mitosis(fission or budding)

6.  In biology, cell theory is a scientific theory that describes the properties
of cells, the basic unit of structure in every living thing.
 The observations of Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow and
others led to the development of the cell theory.
 The generally accepted parts of modern cell theory include:
 All known living things are made up of one or more cells.
 All living cells arise from pre-existing cells by division.
 The cell is the fundamental unit of structure and function in all living
organisms.
 The activity of an organism depends on the total activity of independent
cells.
 Energy flow (metabolism and biochemistry) occurs within cells.
 Cells contain hereditary information (DNA) which is passed from cell to cell
during cell division.
 All cells are basically the same in chemical composition in organisms of
similar species.
 The cell theory holds true for all living things, no matter how big or small.

7. PLASTIDS
 Plastids are major organelles found in the cells
of plants and algae.
 They are the site of manufacture and storage of
important chemical compounds used by the cell.
 Plastids often contain pigments used
in photosynthesis and the types of pigments
present can change or determine the cell's
color.
 They possess a circular double-stranded DNA
molecule.

8. NUCLEUS
The nucleus is a membrane-enclosed organelle found in eukaryotic cells.
It contains most of the cell's genetic
material, organized as multiple long
linear DNA molecules.
The function of the nucleus is to maintain
the integrity of these genes and to control
the activities of the cell by
regulating gene expression.
The nucleus is, therefore, the control center of the cell.

9. MITOCHONDRIA
 Mitochondria is a membrane-
enclosed organelle found in
most eukaryotic cells.
 These organelles range from
0.5 to 1.0 micrometer (μm) in
diameter.
 Mitochondria are sometimes
described as "cellular power
plants" because they generate
most of the cell's supply
of adenosine
triphosphate (ATP),

10. GOLGI APPARATUS
 The Golgi apparatus is an organelle found in
most eukaryotic cells.
 It was identified in 1897 by the Italian
physician Camillo Golgi and named after him in
1898.
 Part of the cellular endomembrane system, the
Golgi apparatus packages proteins inside the
cell before they are sent to their destination; it is
particularly important in the processing of
proteins for secretion.

11. ENDOPLASMIC RETICULUM
 The endoplasmic reticulum (ER) is an organelle of cells in eukaryotic
organisms that forms an interconnected network of membrane vesicles.
 According to the structure the endoplasmic reticulum is classified into
two types –
 rough endoplasmic reticulum (RER)
 smooth endoplasmic reticulum (SER).
 The rough endoplasmic reticulum is studded with ribosomes on
the cytosolic face. These are the sites of protein synthesis.
 The rough endoplasmic reticulum is predominantly found
in hepatocytes where protein synthesis occurs actively.
 The smooth endoplasmic reticulum is a smooth network without the
ribosomes. The smooth endoplasmic reticulum is concerned with lipid
metabolism, carbohydrate metabolism and detoxification.
 The smooth endoplasmic reticulum is abundantly found in mammalian
liver and gonad cells.

12. ACKNOWLEDGEMENTS
 Wikipedia contributors. "Endoplasmic reticulum." Wikipedia, The Free
Encyclopedia. Wikipedia, The Free Encyclopedia, 5 Jun. 2013. Web. 7
Jun. 2013.
 Wikipedia contributors. "Golgi Apparatus." Wikipedia, The Free
Encyclopedia. Wikipedia, The Free Encyclopedia, 17 May. 2009. Web. 7
Jun. 2013.
 Wikipedia contributors. "Plastids." Wikipedia, The Free Encyclopedia.
Wikipedia, The Free Encyclopedia, 17 Dec. 2004. Web. 7 Jun. 2013.
 Wikipedia contributors. "Cell." Wikipedia, The Free Encyclopedia.
Wikipedia, The Free Encyclopedia, 14 May. 2013. Web. 7 Jun. 2013.
 Wikipedia contributors. "Cell Theory." Wikipedia, The Free Encyclopedia.
Wikipedia, The Free Encyclopedia, 2 Oct. 2007. Web. 7 Jun. 2013.