Featured post

What If the Earth Stopped Spinning for 5 Seconds?

-
 Imagine if the Earth, spinning at a staggering 1,600 km/h at the equator, suddenly stopped for just 5 seconds and then resumed. While this might seem like a brief pause, the consequences would be catastrophic. Here's a look at what would happen and why this hypothetical scenario is so terrifying. 1. The Power of Inertia When the Earth spins, everything on its surface—including the air, water, and you—is moving along with it. If the planet suddenly stopped, inertia would cause everything to continue moving at the same speed. What You’d Experience: You’d be flung forward at the speed of the Earth’s rotation, which could feel like a supersonic crash. Impact on Structures: Buildings, vehicles, and even oceans would be thrust forward, resulting in unimaginable destruction. 2. Catastrophic Weather Events The atmosphere wouldn’t stop spinning instantly. Winds traveling at thousands of kilometers per hour would ravage the planet, causing storms far worse than any hurricane we’ve experie
Post a Comment

THE FUNDAMENTAL UNIT OF LIFE

-

 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. 



Comments

Post a Comment

Popular posts from this blog

TISSUES

-
Image
 All living organisms are made up of cells. Unicellular organisms consist of a single cell that performs all basic functions. In multicellular organisms, there are millions of specialized cells. Specialized cells in multicellular organisms carry out specific functions efficiently. Different groups of cells are responsible for different specialized functions. Muscle cells in humans contract and relax for movement, nerve cells carry messages, and blood transports oxygen, food, hormones, and waste materials. In plants, vascular tissues conduct food and water throughout the plant. Multi-cellular organisms exhibit division of labor, where specific functions are carried out by clusters of cells in a definite place in the body. These clusters of cells are called tissues. Tissues are arranged and designed to maximize efficiency in performing their functions. Examples of tissues include blood, phloem, and muscle. A tissue is formed by a group of cells that are similar in structure and/or work t
Read more

CELL STRUCTURE AND FUNCTION NCERT HIGHLIGHTS

-
 Cell Structure and Functions: Cytology, the Science of Cells: Let's begin with cytology, which is the scientific study of cells. It delves into the form, structure, and composition of these tiny units of life. The Cell: Life's Building Block: A cell is the fundamental structural and functional unit of life. Think of it as the building block of living organisms. In unicellular organisms like amoeba and bacteria, a single cell performs all essential life functions. Cell Theory Founders: Back in the day, Anton Von Leeuwenhoek was the first to observe and describe live cells under a microscope. Later, Robert Brown discovered something crucial, the nucleus. Cell Theory, the Bedrock of Biology: In the mid-19th century, Matthias Schleiden and Theodore Schwann put forth the cell theory. It stated that all living organisms are made up of cells and their products. Furthermore, they emphasized that all cells come from pre-existing cells. This theory was later refined by Rudolf Virchow.
Read more