LIVING CELLS

 LIVING CELLS

Introduction:

The living cell (from Latin cella, meaning "small room") is the basic structural, functional, and biological unit

of all known organisms.

✓ A cell is the smallest or basic unit of life. Living cells are often called the "building blocks of life".

✓ The study of cells is called cell biology, cellular biology, or cytology.

✓ Cells consist of cytoplasm enclosed within a membrane.

✓ Organisms can be classified as unicellular (consisting of a single cell such as bacteria)

or multicellular (including plants and animals).

✓ Most unicellular organisms are classed as microorganisms.

✓ The number of cells in plants and animals varies from species to species; it has been estimated that

humans contain somewhere around 40 trillion (4×1013) cells. The human brain accounts for around 80

billion of these cells.

✓ Cells were discovered by Robert Hooke in 1665, who named them for their resemblance to cells

inhabited by Christian monks in a monastery. Cell theory, first developed in 1839 by Matthias Jakob

Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that

cells are the fundamental unit of structure and function in all living organisms, and that all cells come

from pre-existing cells.

Cell Structure:

✓ Cells are of two types: eukaryotic, which contain a nucleus, and prokaryotic, which do not.

Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or

multicellular.

✓ Organelles are parts of the cell which are adapted and/or specialized for carrying out one or more vital

functions, analogous to the organs of the human body (such as the heart, lung, and kidney, with each

organ performing a different function).

✓ Both eukaryotic and prokaryotic cells have organelles, but prokaryotic organelles are generally simpler

and are not membrane-bound.

✓ Cell nucleus:

• A cell's information center, the cell nucleus is the most conspicuous organelle found in a

eukaryotic cell. It houses the cell's chromosomes, and is the place where almost all DNA

replication and RNA synthesis (transcription) occur.

• The nucleus is spherical and separated from the cytoplasm by a double membrane called the

nuclear envelope.

• In prokaryotes, DNA processing takes place in the cytoplasm.

• The nucleus controls the life activities in the cell.

• It is also responsible for cell division.

✓ Mitochondria: generate energy for the cell.

• Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in

the cytoplasm of all eukaryotic cells.

• Respiration occurs in the cell mitochondria.

✓ Chloroplasts can only be found in plants and algae, and they capture the sun's energy to make

carbohydrates through photosynthesis.

✓ Vacuoles:

• They are often described as liquid filled space and are surrounded by a membrane.

• Some cells, most notably Amoeba, have contractile vacuoles, which can pump water out of the

cell if there is too much water.

• The vacuoles of plant cells and fungal cells are usually larger than those of animal cells.

• Vacuoles store waste products and in plant cells, store water.

✓ Cell wall:

• Different types of cell have cell walls made up of different materials; plant cell walls are

primarily made up of cellulose, fungi cell walls are made up of chitin and bacteria cell walls

are made up of peptidoglycan.

• The cell wall acts to protect the cell mechanically and chemically from its environment, and is

an additional layer of protection to the cell membrane.

• It also gives shape to the plant cell.

✓ Cell Membrane

• The cell membrane is a biological membrane that separates the interior of all cells from the

outside environment.

• The cell membrane surrounds the cytoplasm of living cells, physically separating the

intracellular components from the extracellular environment.

• The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell.

• The cell membrane is selectively permeable and able to regulate what enters and exits the cell,

thus facilitating the transport of materials needed for survival.

✓ Cytoplasm

• The cytoplasm is the fluid present in the cell enclosed within the cell membrane that comprises

water and enzymes, salts, and various organelles.

• The cytoplasm is about 80% water and usually colorless.

• The cytoplasm is responsible for holding the components of the cell and protects them from

damage. It stores the molecules required for cellular processes and is also responsible for

giving the cell its shape.