fundamental unit of life

• in 1665, robert Hooke saw the cork that remled the structure of a honey comb and observed it under a self made microscope and saw that it had small box compartments 1000 times smaller than the cork. he called these cells
• the term 'cell' derived from the Latin word that means cella, meaning little room or hallow space.
• All living organisms are composed of tiny living organisms of tiny living units called cells.
• living organism that consists of one cell is called unicellular. ex. bacteria, amoeba, Chlamydomonas, paramecium, euglena
• majority of the organisms are multicellular and visible without microscope. eg. most fungi, plants and animals
• all cells thus come from pre-existing cells
• the shape and size of cells are related to the specific function they perform
• basic function of cells:

  1. a division of labour in multicellular organisms. eg. human beings
  2. each cell has got specific components within it known as cell organelles. they have different function, eg. clean up waste material
• all cells are found to have the same organelles, no matter what their function is or what organism they are found in.
• three features of a cell are: plasma membrane, nucleus and cytoplasm
• cell or plasma membrane:

  1. the outer covering of each cell, forming a boundary of the cytoplasm.
  2. it allows the entry or exit of some materials in and out of the cell.
  3. it is also called a selectively permeable membrane
• certain substances like carbon dioxide and oxygen move across the cell membrane by a process called diffusion

  
  

  a region of higher concentration move to a region where its concentration is low
• certain substances with water molecules move across the plasma membrane is by the process of osmosis
• types of solution of osmosis

  1. hypertonic (hyper=higher): the solution outside the cell has more concentration than the cell sap. exosmosis will take place and the cell will shrink (go in-more, go out-less)
  2. hypotonic (hypo=lower): the solution outside the cell is less concentrated than the cell sap. endomosis will take place and cells will swell up. (go in-less, go out-more)
  3. isotonic (iso=same): the solution outside the cell will be the same as the cell sap. there will be no change in cell size.
• important points of plama membrame:

  1. unicellular freshwater organisms and most plant cells tend to gain water through osmosis
  2. plasma membrane is flexible and made up of organic molecules called lipids and proteins
  3. plasma membrane can only be seen through an electron microscope
  4. the plasma membrane also enables the cell to engulf materials from the external environment. this process is known as endocytosis. eg. ameoba
• the cell wall is a rigid non-living wall outside the plasma membrane and is mainly composed of cellulose.
• when a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell, which is called plasmolysis
• only living cells can absorb water by osmosis, not dead cells.
• cell walls allow the cell of fungi, plants and bacteria to withstand hypotonic solution without bursting
• cell walls function:

  1. provides structural strength, rigidity and definite shape to the cell
  2. it helps in transport of various substances across it
• the membrane-enclosed organelle within a cell that contains chromosomes is called a nucles.
• nuclear membrane separates the nucleus from the cytoplasm. mainly made up of proteins and lipids. it is a doubled layer covering the nucleus.
• the nucleus contains chromosomes which are visible as rod-shaped structures only when the cell is about to divide.
• chromosomes are composed of DNA and proteins and are found in the nucleus of a cell.
• DNA (deoxyribo nucleic acid) contains information for constructing and organising cells. functional segments of DNA are genes
• when the cells are not dividing, DNA is present as parts of chromatin material.

  chromatin material is visible as an entangled mass of thread.

  when the cell is about to divide, the chromatin gets divided into chromosomes
• undefined nuclear region containing only nucleic acids is called a nucleoid
• Prokaryotic cell:

  • 1-10μm
  • lack nuclear membrane
  • no membrane-bound organells
  • chromosomes are single
  • eg, bacteria, archaea
• Eukaryotic cell:

  • 5-100μm
  • having a nuclear membrane
  • membrane-bound organelles within the cell
  • chromosomes are more than one
  • eg, animals, plants
• the chlorophyll is photosynthetic prokaryotic bacteria is associated with membranous vesicles but not with plastids as in eukaryotic cells

  • Chlorophyll is a green pigment that helps with photosynthesis (turning sunlight into energy)
  • Prokaryotic bacteria are simple, single-celled organisms, like some types of bacteria.
  • In these bacteria, chlorophyll is found inside small sacs called membranous vesicles.
  • Unlike eukaryotic cells (such as plant cells), these bacteria don’t have plastids (special structures like chloroplasts) where chlorophyll is usually stored in more complex organisms.
• Cytoplasm is the liquid that fills the inside of a cell. it is the fluid content inside the plasma membrane, which contains many specialised cell organelles.

  virsuses do not show the characteristics of life because they lack any membrane until they enter a host cell and use its cell components to multiply
• Cell organelles

  • An organelle is a subcellular structure that has one or more specific jobs to perform in the cell
  • some examples are: i. endoplasmic reticulum. ii. Golgi apparatus iii. lysosomes iv. mitochondria v. plastids vi. vacuoles
• i. endoplasmic reticulum (ER)

  there are two types of ER

  1. rough endoplasmic reticulum (RER)
  2. smooth endoplasmic reticulum (SER)
• RER:

  1. have ribosomes attached to the membrane (makes it look rough)
  2. mainly synthesise proteins
  3. develop from the nuclear envelope

  SER:

  1. does not have ribosomes over the membrane
  2. mainly synthesise lipids
  3. develop from RER
• functions of ER:

  1. synthesis of proteins,
  2. lipid synthesis,
  3. protein transport
  4. SER helps in detoxifying poisons and drugs
• ii.Golgi apparatus

  • first discovered by Camillo Golgi
  • consist of smooth, flattened, membrane-bound sac-like structures called Cisterns
  • Cisterns are stacked above the other in parallel rows
  • is surrounded by vesicles which are discharged from Cisterns.
• functions of Golgi apparatus:

  1. it packages materials synthesized in the cell and transports these out of the cell
  2. it is involved in the formation of lysosomes
  3. in some cases, complex sugars are made from simple sugar in the organelle
• iii. lysosomes (digestive/suicidal bags)

  1. membrane-bounded sacs filled with digestive enzymes. (these enzymes are made by RER)
  2. it is a waste disposal system of cell
  3. lysosomes containing a powerful enzymes capable of breaking down the materials. hence the name digestive.
  4. when the cell is damaged, it may burst and enzymes digest the cell, that's why it's known as suicidal bags.
• functions of lysosomes:

  1. it is capable of breaking down all organic materials
  2. they destroy foreign bodies such as bacteria etc
  3. they help keep clean the cell by digesting foreign bodies, eat worn-out cell organelles and remove dead cells
• iv. mitochondria

  1. the powerhouse of the cell.
  2. have to the membrane covering
  3. the outer membrane is porous and the inner is deeply folded
  4. the energy needed for various chemical activities needed for life is released by mito in the form of ATP (adenosine triphosphate-known as the energy currency of cell) molecule.
  5. have their own DNA which means they can make their own protein,