Science Biology Cell
THE FUNDAMENTAL UNIT OF LIFE
1.1 Discovery of cell - Robert Hooke discovered cell in 1665 with the help of a primitive
microscope. He made this observation from the cork which is a substance that comes
from the bark of a tree.
1.2 How to observe onion cell under microscope:
1) Take a small piece from an onion bulb and peel off the skin called epidermis from
the concave side of onion with the help of forceps. Put this layer immediately in a
watch glass containing water to prevent the peel from getting folded or
dehydrated.
2) Take a glass slide , put a drop of water on it and transfer a small piece of peel
from the watch glass to the slide. Make sure that the peel is perfectly flat on the
slide. You may need a thin camel hair paintbrush to transfer the peel.
3) Put a drop of safranin solution on piece followed by a coverslip. Avoid air bubbles
while placing the coverslip with the help of a mounting needle.
4) Observe this peel with the help of a compound microscope.
1.3 Structure of onion cells:
, 1
Similar structures are seen which are unlike in terms of shape and size but similar in
structure . They all share a cell wall,nucleus ,cell membrane and cytoplasm.
1.4 Cell theory
❖ Cells were first discovered by Robert Hooke in 1665.
❖ Van Leeuwenhoek observed free living cells in pond water for the first time .
(1674)
❖ Robert Brown in 1831 discovered the nucleus in the cell
❖ Purkinje (1839) coined the term protoplasm for the living substance in the cell.
❖ The cell theory : All the plants and animals are composed of cells and cell is the
basic unit of life was proposed by Schleiden (1838) and Schwann(1839).
❖ Virchow (1855) suggested all cells arise from pre existing cells.
❖ Electron microscope was discovered in 1940.
1.5 Difference between unicellular and multicellular organisms:
UNICELLULAR ORGANISMS MULTICELLULAR ORGANISMS
1) Cells which are composed of a Many single cells group together to
single cell are called unicellular perform different functions in a body
organisms. which is composed of many cells.
2) They are usually small and less They are usually big and more complex
complex and perform all functions and different organelles perform different
by their own. functions.
3) Example-Amoeba,Paramecium,Chl Example : Plants,animals
amydomonas,bacteria
1.6 Shape size relation with function:
The size and shapes of the cell are related to its function. Some cells like Amoeba have
changing shapes to perform all their functions. Some cells have a peculiar shape like
nerve cell which is long and branched to receive and transfer messages to control and
coordinate movement of different parts of body.
1.7 Division of Labour:
In multicellular cells , different types of cell organelles are present to perform various
functions of the cell . Like human body has a heart to pump blood and a stomach to
digest food. A cell is able to live and perform well because of these organelles They
THE FUNDAMENTAL UNIT OF LIFE
1.1 Discovery of cell - Robert Hooke discovered cell in 1665 with the help of a primitive
microscope. He made this observation from the cork which is a substance that comes
from the bark of a tree.
1.2 How to observe onion cell under microscope:
1) Take a small piece from an onion bulb and peel off the skin called epidermis from
the concave side of onion with the help of forceps. Put this layer immediately in a
watch glass containing water to prevent the peel from getting folded or
dehydrated.
2) Take a glass slide , put a drop of water on it and transfer a small piece of peel
from the watch glass to the slide. Make sure that the peel is perfectly flat on the
slide. You may need a thin camel hair paintbrush to transfer the peel.
3) Put a drop of safranin solution on piece followed by a coverslip. Avoid air bubbles
while placing the coverslip with the help of a mounting needle.
4) Observe this peel with the help of a compound microscope.
1.3 Structure of onion cells:
, 1
Similar structures are seen which are unlike in terms of shape and size but similar in
structure . They all share a cell wall,nucleus ,cell membrane and cytoplasm.
1.4 Cell theory
❖ Cells were first discovered by Robert Hooke in 1665.
❖ Van Leeuwenhoek observed free living cells in pond water for the first time .
(1674)
❖ Robert Brown in 1831 discovered the nucleus in the cell
❖ Purkinje (1839) coined the term protoplasm for the living substance in the cell.
❖ The cell theory : All the plants and animals are composed of cells and cell is the
basic unit of life was proposed by Schleiden (1838) and Schwann(1839).
❖ Virchow (1855) suggested all cells arise from pre existing cells.
❖ Electron microscope was discovered in 1940.
1.5 Difference between unicellular and multicellular organisms:
UNICELLULAR ORGANISMS MULTICELLULAR ORGANISMS
1) Cells which are composed of a Many single cells group together to
single cell are called unicellular perform different functions in a body
organisms. which is composed of many cells.
2) They are usually small and less They are usually big and more complex
complex and perform all functions and different organelles perform different
by their own. functions.
3) Example-Amoeba,Paramecium,Chl Example : Plants,animals
amydomonas,bacteria
1.6 Shape size relation with function:
The size and shapes of the cell are related to its function. Some cells like Amoeba have
changing shapes to perform all their functions. Some cells have a peculiar shape like
nerve cell which is long and branched to receive and transfer messages to control and
coordinate movement of different parts of body.
1.7 Division of Labour:
In multicellular cells , different types of cell organelles are present to perform various
functions of the cell . Like human body has a heart to pump blood and a stomach to
digest food. A cell is able to live and perform well because of these organelles They
