Ø Plants are unique among the eukaryotes, organisms where cells have membrane enclosed nuclei and organelles because they can manufacture their own food. Chlorophyll which gives green colour to plants, enable them to use sunlight to convert water and carbon-dioxide into C6H12O6 and O2.
Ø Plants cells have number of specialized structure including cell wall, centriole vacuole, plasmodesmata and chloroplasts.
Plant cell structure can be explained as follows:
I. Nucleus: It carries genetic information which inherits the physical traits from one generation to another. It has dark stained nucleolus responsible for protein formation which is enclosed in double membrane. Nuclear membrane protects the nucleus from physical damage.
II. Nucleolus: It produces ribosomes which move out of nucleus and take positions on the RER.
III. Cytoplasm: It is jelly like structure in which cell organelles are embedded and suspended. The main function is to keep all constituents of cell intact. It is occupied with proteins that control cell metabolism including signal transduction pathway, glycolysis, intracellular receptors and transcription factors.
IV. Cell membrane: It is made up of cellulosic fibres and proteins. Its main function is to transport material through cells.
V. Cell Wall: It provides definite structure, rigidity and protection to cells. It gives different shapes to cells like oval, elongated, round and rectangular. It is composed primarily of protein called cellulose.
VI. Plastids: Plants prepare their own food with a unique process called photosynthesis. Most common plastids is chloroplast which contains chlorophyll pigment which provides green colour to plants.
VII. Mitochondria: It is the largest cell organelle. It is also known a power house or engine house of the cell. These organelles provide energy required for cellular activities by breaking down complex carbohydrates prepared during photosynthesis.
VIII. Ribosome: It is the main site of protein synthesis, it is rich in RNA. These organelles could be bound to E.R. which is known as bound ribosome or found free floating in cytoplasm known as free ribosome.
IX. Endoplasmic Reticulum (ER): It is the second largest cell organelle. It forms a series of interconnected flattened tubular sacs. There are two types of ER, RER and SER. RER, mainly responsible for holding out proteins formed in the ribosomes and in transportation.
X. Golgi apparatus: Proteins formed and bound by ER need to be processed so as to perform normal function. This function is performed by golgi complex. Dictyosomes associated with ER release protein chains after processing.
XI. Vacuoles: Plant cell is characterized by larger and lesser number of vacuoles manly responsible for maintaining fullness of cell. Its main function is to store ions, sugars and secondary metabolites.
· All living things are made up of cells. It is multicellular eukaryotic cell surrounded by plasma membrane and it contains the nucleus and membrane bound organelles.
· Animal cell are of various size and have irregular shapes. Size ranges between 1-100µm.
· Animal cell lack cell wall, vacuole and plastids. `
Animal Cell Structure:
Animal cell structure can be explained as follows:
I. Cell membrane: All living cells have plasma membrane that encloses their contents. This membrane also regulates the passage of molecules. Cell membrane is semi permeable allowing some substances to pass into the cell and blocking others.
II. Centriole: It is small barrel shaped tube composed of proteins. It is located in the cytoplasm. Centriole made up of bundles of microtubules. Main function of centriole is to help in cell division and in the spatial arrangement of structure within the cells. It is essential for the development of cilia and flagella. They are self replicating organelles.
III. Cilia and flagella: They are the extensions of cell membrane that are lined with cytoskeleton. Flagella are generally much longer than cilia. Flagella are whip like structure, which is primarily responsible for cell movement. Cilia are short hair like structure moving back and forth across outside of cell.
IV. Nucleus: It is highly specialized organelle that serves as the information processing and administrative centre of the cell. It stores cell hereditary material and coordinates the cell’s activities which include growth, intermediary metabolism, protein synthesis and reproduction.
V. Peroxisomes: It is enzyme containing structure that help to detoxify alcohol from bile acid and break down fats or found in cytoplasm. Peroxisomes are roughly spherical and bound by single membrane.
VI. Centrosome: It is also known as microtubule organizing centre. Centrosome is a small body near the nucleus which has dense centre and radiating tubules.
VII. Cytoplasm: It is jelly like material outside the cell nucleus in which organelles are located.
VIII. Golgi apparatus: It is flattened layered sac like organelle. It produces membrane that surrounds cytoplasm. Golgi body packages proteins and carbohydrates into membrane bound vesciles for export from the cell.
IX. Lysosomes: It is round organelle surrounded by vesicle and contains digestive enzymes. Lysosomes contain hydrolytic enzymes help in digestion of cell contents.
X. Mitochondria: It is spherical to rod shaped organelle with double membrane. Its inner membrane is folded many times forming series of projection called cristae. Mitochondrion is responsible for generating energy in the form of ATP. It is the site of respiration, where glucose and oxygen are changed into energy.
XI. Endoplasmic Reticulum: There are two types of ER found in cell: RER and SER. In RER ribosomes attached to the surfaces of ER, where proteins and lipids are produced within cell and also concerned with transport of these materials within cell. SER, where there are no ribosomes attached to the surface of ER.
Prokaryotes are primitive organisms as their name suggest where all cell oragnelles are not well developed while eukaryotes are developed organisms with well defined cell organelles
Organisms are composed of cells which have some special structures that help them to perform some special functions. These structures are known as cell organelles. Such organelles are nucleus, ER, golgi body, lysosome, chloroplast, mitochondria.
Cell theory states that all living organisms are made up of cells. It is the basic unit of life. According to Rudolf virchow that "omnis cellulae e cellulae".