What are Living Organisms
Made Up of?
living organisms are made of cells. cells are capable of independent existence and performing the essential function of life. viruses are non cellular because they lack cell like structures.
robert hook first observe cork cells under microscope in 1665
leeuwenhook first oberves single celled organism in 1674
pasteur discovered microbial fermentation in 1856
pasteur disapproved spontaneous generation in 1862
koch determine causative agents for many bacterial infection during period of 1876-1906.
smallest cell: mycoplasma (PPLO- pleuro pneumonia like organism, about 10 micrometer in size)
longest cells: nerve cell
largest cell: ostrich cell
What is a Cell Made Up of? What is the Structural Organisation of a Cell?
protoplasm: nucleus+ cell membrane +cytoplasm
cytoplasm: all content except nucleus (contain organalles)
nucloplasm: nucleus+ its content
cytosol : fluid where cytoplasm suspended.
PLASMA MEMBRANE OR CELL
MEMBRANE
outer most boundary of cell, regulate trafficking, selectable permeable, electrically charged, potential difference across membrane (membrane potential), highly dynamic structure, fluid structure.
MODELS
1. OVERTON MODEL: plasma membrane is made of lipid. lipid soluble component crosses plasma membrane. doesn't explain how ions are transported.
2. GORTER AND GRENDEL MODEL: bilayer plasma membrane, failed to explain ion transport
used RBC to explain the model
3. DANIELLI AND DAVSON METHOD: plasma membrane= lipid + protein
trilaminar model/ sandwich model
failed to explain the function of plasma membrane.
4. ROBERTSON MODEL: unit membrane, plasma membrane= bilayer lipid + protein on both sides
structure of plasma membrane = 75 angstrom (20A+ 35A+20A)
5. SINGER AND NICOLSON MODEL: protein embedded in bilayer , fluid mosaic model.
TRANSPORT ACCROSS PLASMA MEMBARNE
Diffusion
The movement of molecules from a region of their high concentration to a region of their lower concentration is known as diffusion. E.g. carbon dioxide and oxygen move across the cell membrane by diffusion.
Osmosis
Osmosis is the movement of water across a semi-permeable membrane. Osmosis is a selective process since the membrane does not allow all molecules to pass through it. Water is usually the only free flowing molecule across this membrane.
Isotonic solutions are those which have the same solute and pH concentration as the surrounding body fluid or the cytoplasm.
Hypotonic solutions contain lesser amount of solute concentration compared to the surrounding fluid and can force the cell to rupture due to excess input of water into the cell.
Hypertonic solutions contain a higher concentration of solute compared to the surrounding fluid and thus push water out of the cell, shrinking it.
CELL WALL
major constituent of plant and bacterial cell.
it is a structural layer that surrounds same type of cells, situated outside the cell. it can be tough, flexible and gives rigid protection and support to the cell. cell wall is non living structure formed of living protoplast (cell without cell wall- protoplast).
there are mainly three types of cell wall
1. bacterial cell wall: composed of peptidoglycan, provide shape, and resistance to osmotic pressure, regulate transport of substances
2. plant cell wall: composed of polysaccharide (cellulose), lipid and mineral deposits, act cement between two cells. it gives a rigid structure to the plant cell. It provides structural support to plants. E.g. Cell wall enables the cells to withstand hypotonic solution without bursting.
3. fungal cell wall: made of chitin, glucan and protein which protects against osmotic lysis , act as molecular sieve, binding site for enzymes.
NUCLEUS
The nucleus is the processing unit of the cell. It is a double membrane-bound organelle which contains the genetic material for inheritance. The nuclear membrane contains pores that allow the transfer of materials from the nucleus to the cytoplasm. The nucleus is the brain of the cell as it controls various functions such as cell division, reproduction, inheritance, etc. The nucleus contains genetic material, i.e. chromosomes that contain DNA. DNA carry information for inheritance from parents to offspring. Prokaryotes lack a well-defined nucleus and the genetic material is present in a region known as the nucleoid.
chromosomes
Chromosomes are the genetic material present in the nucleus. It contains DNA with associated proteins. They are present as threads called chromatin. During the growth phase of the cell, the chromatin condenses into a much thicker structure called a chromosome. Human cells contain 23 pairs of chromosomes (46 in total).
Chromatin
Chromatin is a thread-like structure which serves as the genetic material present inside the nucleus of the cell. It is made up of DNA and protein molecules. DNA contains the hereditary information needed for the structure and function of the organism.
CELLULAR ORGANELLES
Endoplasmic Reticulum:
largest single membrane bound intracellular compartment
extensive network of closed and flattened membrane structures.
closed compartment is called ER lumen.
found in almost all eukaryotic cells except mature RBC, ova, embryonic cells, prokaryotic cells.
ER appears to arise from outer envelop of nucleus by out folding or from plasma by in folding
SER seems to arise from RER by detachment of ribosomes.
ER can be classified into
1. RER: Rough ER are the ones that have ribosomes on them. The ribosome is made up of nucleic acids and proteins. They are the site of protein synthesis. The Rough ER is also involved in the modification and folding of proteins.
2.SER: Smooth ER do not have ribosomes and thus are not involved in protein synthesis. They are, however, involved in lipid metabolism and detoxifying of poisonous molecules.
FUNCTION:
mechanical support and distribution of cytoplasm
surface area for chemical reaction
interacellular transport system
storage of synthesized molecule
proteins synthesised in RER, lipid synthesis in SER
detoxification
GOLGI APPARATUS
occur in all eukaryotic cells except male gametes of bryophyta, pteridophyta, mature sieve tubes, fungal cells, matures sperms and RBCs and prokaryotes. Golgi Apparatus is also called the post office of the cell. They package and transport the proteins across the cytoplasm. it can be subcategorised into
1. cis golgi: entry area to golgi apparatus follows transitional element (towards ER)
2. golgi stack:cisternae of stack )
3. trans golgi: directly connects to trans cisternae (towards plasma membrane)
If there were no Golgi bodies, the proteins in cells would float around without direction. Other cells and organs in the body would not function properly without the products that the Golgi body normally sends.
FUNCTION
LYSOSOMES
single membrane bound organelle
unique in composition
contain digestive enzyme
same role played by vacoule in plant cell
found in animal cell
discovered by Chritian De Duve in 1955, suicidal bags, abundant in cells related to enzymatic reaction.
it help in attacking foreign object
FUCTIONS:
MITOCHONDRIA
first observed by Koliker in 1850 as granular structure in straited muscles.Mitochondria are also called the powerhouse of a cell. They generate ATP (energy currency of cell) via the electron transport chain. They also have a DNA called mtDNA, which makes them a semi-autonomous organelle. Mitochondria can make their own proteins.
mitochondria are the power house of the cell, if there is no mitochondria in a cell then there would be no or very less energy in the cell. Cell would not be able to function properly that may ultimately result in cell death or death of an whole organism.
FUNCTION
PLASTIDS
Found in plants for storage
chief power factory of plant
can be classified as
1. Etioplast: not exposed to light, found in angiospermsgrown in dark. normal chloroplast can be converted into etioplast in absence of light
2. chloroplast: responsible for photosynthesis, filled with a pigment called chlorophyll in thylakoids.
3. chromoplast: contain caretenoid pigment allow different colours of flower and fruits to attract pollinator
4. leucoplast:non pigmented organelle , non photosynthetic, storage sheds. it is of three types
a. Amyloplast store starch
b. protenoplast store protein
c. Elioplast store fats and oils
VACUOLE
Membrane bound organelle, acidic in nature, share some property with lysosome hold large amount of food and water, fluid filled space enclosed by membrane, exists temporarily in animal cells
FUNCTIONS
stores water and food temporarily.
store waste material, so rest of cell is protected from contamination.
CELL DIVISION
The process by which new cells are made is called cell division.
There are two main types of cell division: mitosis and meiosis.
The process of cell division by which most of the cells divide for growth is called mitosis. each cell called mother cell divides to form two identical daughter cell. The daughter cells have the same number of chromosomes as mother cell. It helps in growth and repair of tissues in organisms.
Specific cells of reproductive organs or tissues in animals and plants divide to form gametes. They divide by a different process called meiosis which involves two consecutive divisions. When a cell divides by meiosis it produces four new cells instead of just two.
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