• Dutch brothers- Francis Janssan discovered compound microscope in 1950.
• Robert Hooke (1665) coined the name ‘cell’. He published hisina a book by name ‘Micrographia’.
• Marcello Malphi (1672) described the cells as ‘utricles’.
• Antony Von Leeuwenhoek (1674) for the first time discovered Protozoans, Bacteria, Sperm cells and R.B.C.
• Purkinjie (1830) coined the term Protoplasm.
• Robert Brown (1831) coined the name Nucelus to the thick structure present at the centre of the cell.
• Dujardin (1836) noticed the importance of cell Organelle and referred the nucleus as ‘Sarcode’.
• Schleden (1838) proposed cell theory in plants. He reported that all plants are made up of cells.
• Schwann (1838) proposed cell theory in animals. He repotred that all animals are made up of cells. He also proposed that tissues are formed my cells and cells are the functional units of an oraganism.
• Schleiden and Schwann belived that new cells arise from non-living substances.
• Robert Remark and Rudolf Virchw reported that new cells arise from pre-existing cells.
• Knoll and Ruska (1932) discovered electron microscope and opened new era in cell biology.
STRUCTURE OF AN ANIMAL CELL
Cells are the structural and functional units of living organisms. The shape and size of the cells exhibit a lot of diversity. Shape of the cell basically depends on the state of its physiological activity and other mechanical factors.
The smallest cells being erythrocytes, Sperm cells etc., (8mm). The biggest cell being the egg of an Ostrich (175 mm).
Robert hoek was the first to examine a cell in a piece of corck under microscope. He used the term cell in his book ‘micrographia. Study of cells is called ‘cytology’.
A typical animal cell has three main components. They are – 1) Plasma membrane
and 3) Nucleus.
1) Plasma membrane.
B. Endoplasmic Reticulum.
C. Golgi Apparatus.
A. Nuclear envelop
1. Plasma membrane :
1. Plasma membrane surrounds the cell and forms the outer boundary of the cell.
2. Plasmalemma is made up f phospholipid bilayer and Proteins.
3. The membrane Protiens include peripheral proteins and intrinsic proteins.
4. Plasma membrane helps in the maintenance of cellular homeostasis.
5. Plasma membrane seperates the inside of the cell from the outside.
6. It is selectively permeable and regulates the movement of materials into and out of the cell.
7. Molecules move across the Plasma membrane by simple diffusion, facilitated diffusion, Osmosis, Filtration, active transport, exocytosis and by three types of Endocytosis, i.e,
• Pinocytosis- cell drinking
• Phagocytosis- cell eating
8. The Plasma membrane participates actively in the ingestion of food particles or foreign substances by the process of ‘endocytosis’.
9. In Secondary cells the secretions are passed outside the cell with the help of plasma membrane by the process called ‘exocytosis’.
2. Cytoplasm :
1. Cytoplasm is the portion of the protoplasm present outside the nucleus and inside the plasma membrane.
2. Cytoplasm is a homogeneous mixture. It is a colloidal substance.
3. It contains 90% of water and 10% oragnic and inorganic substances.
4. The fluid portion of the cytoplasm is called CYTOSOL
5. Non living substances like metabolic products suspended in the cytoplasm are referred as dentplasts or meta plasts or paraplasts or trophoplasm. The reserve food present in the trophoplasm is referred as ‘ergastic substance’.
6. Living active substances present in the cytoplasm are referred as cytoplasmic organelle or cyto membrane system. They are –
A) Endo Plasmic Reticulum (EPR) :
1. The endoplasmic reticulum is a net work of membrane bound cisternae and tubules.
2. The endoplasmic reticulum is continous from the outer membrane of the nuclear envelope to the plasma membrane.
3. EPR establishes connection inbetween erternal and internal environment of the cell.
4. Within the cell EPR forms a connection in between the cytoplasm and nucleoplasm.
5. It provides mechanical support to the cell. So it is refered as ‘Cytoskeleton’
6. It acts as Intracellular transport system. It permits the substances to enter into the cell and allows secretory and excretory substances to leave the cell.
7. There are two types of EPR they are-
A) Rough EPR : With attached Ribosomes. It is the site for Proteins synthesis.
B) Smooth EPR : Without attached Ribosomes. It is the site for lipid production, detoxificaton
B) Golgi Apparatus :
1. It is located at a fixed position just above the nucelus.
2. It is most abundant in Secretory cell. E.g: Pancreatic cells.
3. It is mainly useful in Secretion, processing and storing the protiens.
4. The Golgi complex is composed of three morphological forms. Namely
5. Transition vesicles formed from the ER fuse with Golgi apparatus at the cis-face.
6. In the Golgi apparatus the protiens are concentrated, modified and are packaged int secretory vesicles. Secretery vesicles are released into the cytoplasm from the trans-face of the Golgi apparatus.
7. When these vesicles reach the plasma membrane, they fuse with it and release their contents to the outside of the cell by exocytosis.
C) Mitochondria :
1. Mitochondria are the semiautonomous, self-replicating organelles.
2. Mitochondria are the hollow sac like structures present in Eukaryotes except in mammalian RBC
3. Mitochondria will have Ribosomes, electron transport system, oxidative enzymes and small amount of circular DNA.
4. Mitochondria supply energy necessory for various metobolic activities of the cells. Hence referred as ‘Power house’ of the cell.
5. Mitochondria are double membrane bound organelle. The inner membrane is infolded to form critae.The innermembrane encloses introchordinal matrix. The matrix contains 705 ribosmes, circular DNA, and the enzymes involved in Kreb’s cyte. The inner membrane contains the enzymes of the electron transport chain and the ATP synthose