Biology
The Cell
:
- The Cell is the basic structural and functional unit of all known livingorganisms. It is the smallest unit of life and is often called the building block of life.
- The branch of biology which deals with the study of cell, is called Cytology.
- Robert Hooke coined the term cell, The first living cell was discovered by Leeuwenhoek.
These are of
two types
1.
Prokaryotic Cells Pro=primitive,
karyos=nucleus) These are
primitive cells, lacking a well defined
nucleus and most of the other
cell organelles, e.g, bacterial
cell.
2.
Eukaryotic Cells (Eu
= true, karyos= nucleus) These have a well defined nucleus and membrane bound
cellorganelles. These are present in unicellular and multicellular plant and animal
cells.
Differences
between Prokaryotic and Eukaryotic Cell
Prokaryotic Cell Eukaryotic Cell
- Simplest and primitive in nature. Developed and Comparatively complex in nature.
- Lacks nuclear envelope. Nucleus is present with elaborate nuclear envelope
- Membrane bound cell organellels are absent. Membrance bound cellorganelles are present.
- Single naked chromosome present. Many chromosomses are present.
- Cell division is direct. Cell division occures by mitosis meiosis.
- These are present only in plant cells and are of three types- chloroplasts green), leucoplasts (white), and chromoplasts (of various colours except green). Chloroplast is the site of photosynthesis as it contains chlorophyll, while leucoplasts are storage plastids. Chloroplast is called the kitchen of the cell.
- The red colour of tomatoes is due to the presence of lycopene pigment, i.e., chromophore.
- The color of carrot is due to carotene Pigment.
- It has cell wall Cell wall is usually absent
- Plastids are found.Plastids are usually absent
- Centrioles and centrosomes are absent Centrioles and centrosomes are found in all clls.
- A bIg vacuole is present. Vacuole is absent or very small in size.
- DNA was discovered by JamesD Watson and Francis Crick, Who got Nobel Prize tor this discovery It is a long polymer made from repeating units called nucleotides.
- Each nucleotide consists of avnucleoside (i.e. nitrogenous base and deoxyribose sugar) and a phosphate group, joined together by phosphodiester bonds.
- Is It has four bases, i.e. adenine, e, Cytosihe and thymilne.
- Adenine and guanine are the purine bases, cytosine and thymine are Pyrimidine bases.
Parts of Cell and their Functions :
cell consists of cell wall and protoplasm.
Protoplasm of Cell :
It is the living fluid matter present inside the plasma
membrane. The fluid present outside the nuclear membrane is called cytoplasm
and the fluid present inside the nuclear membrane is called nucleoplasm.
Deutoplasm is the non-living matter of the cell.
Cell Wall :
It is present in plant cells, bacteria, fungi, algae and
some archaea. It is composed of cellulose in plants and chitin in fungi. It is
non-living. Its main function is to provide shape and rigidity to the cell.
Plasma Membrane :
The cell is enclosed by a thin membrane called the cell
membrane or Plasmalemma. It is composed of proteins and phospholipid
molecules. It is elastic, living far various substances.
Mitochondria
It was discovered by R Altman in 1880 and the term
mitochondria was coined by Carl Benda.
It is bounded by a double membrane. The inner membrane has many
folds, called the cristae. Fluid (called matrix) is present on interior, which
contains many enzymes and coenzymes. It 1s a seml- autonomouss (can form its
own copies) organelle and is called power house of the cell because in it,
stepwise oxidation of fuel Occurs which results in release of chemical energy
This energy is stored in the form of ATP.
Plastids :
Endoplasmic Reticulum :
It was discovered by KR
Porter These are allow membranous System having ribosomes (thus called
Rough ER) or no ribosomes (tnus called smooth ER).
Ribosomes :
Ribosomes were discovered by GE Palade.These are
minute, non-membranous particles,composed of RNA and protein. 70 S type of-ribosomes
are found in prokaryotes, while 80 S type in eukaryotes. These are the site of
protein synthesis.
Lysosomes :
Lysosomes were discovered by de Duve. These are
polymorphic organelles having hydrolytic enzymes. These enzymes function at
(acidic) pH5. These are sometimes called suicidal bags of the cell.
Lysosome helps in Carcinogenesis, i.e, conversion of a
normal cell into cancerous cell.
Centrosome :
It was discovered by T Boveri. It is composed of two
set of centrioles and participate in the formation of mitotic spindle during
cell division.
Vacuoles :
These are non-living reservoir, bounded by a membrane Called
tonoplast. Pigment anthocyanin is present in the cell vacuole, which provide
colour to flowers. It stores toxic metabolic waste and helps in osmoregulation.
Nucleus :
It was discovered by Robert Brown. It contains nucleoplasm,
nucleolus and chromatin material. Nucleolus is rich in protein and RNA All this
material is covered up by a nuclear membrane Chromatin is the controlling of
cell as it form chromosomes.
Chromosome :
Chromosome is thread-like structure, found in the nucleus.
Bead-like structures found on chromosome are called genes, which are made up of
DNA and are the carrier of genetic information from generation to generation.
Chromosomes are units of inheritance. In some viruses e.g retrovirus, RNA is
the genetic material.
Differences between Plant and Animal Cell
Plant Cell Animal Cell
Nucleic Acids :
These contain the genetic instructions used in the
development and functioning of all known living organisms.
These are of two types: DNA and RNA.
Deoxyribonucleic Acid (DNA) :
Ribonucleic Acid (RNA) :
- It is also made up of a long chain of nucleotides.
- Each nucleotide Consists of a nitrogenous base, a ribose sugar, and a phosphate group.
- It contains uracil in place of thymine.
. RNA is of three types-
- mRNA (messenger RNA)
- rRNA (ribosomal RNA)
- tRNA (transfer RNA)
These three RNA's take part in protein synthesis.
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