Cell The Structural And Functional Unit Of Life Class 10 ICSE Notes
- Introduction:
Cell are the most basic structuralunit of life on earth.they have the ability to perform all the functions required for survilal of life. Cells have abilty to devide and are of microscopic in nature.
1.1 Cells – basics
- Cells are the building blocks of living things.
- Cells are the structural and functional building blocks of life.
- The chemical and metabolic processes of all cells are similler.
- Pre-existing cells give rise to new cells.
1.2 Numbers:
- On the basis of no cells can be classified as:
a.) Unicellular – Organisms comprising of a single cell. E.g. prokaryotes like bacteria, amoeba.
b.) Multicellular -Organisms comprising of many cell functioning together in harmoney. E.g mammels, fishes, plants ets.
1.3 Size:
- Cells are found in a number of different sizes. Cells can be as small as a bacteria to as large as a birds egg.
- The lagest cell known till date is the ostrich egg and the longest cell is the nerve cell.
1.4 Shape:
- The shape of the cell is directly related to its function.
- Circulr and biconcave shape of red blood cellsfeciletate oxygen transport whereas WBC havean irregular amoeboid shape helpingthem to tavell easily through blood vessels.
- Some other shapes are concave, bean shaped, elongated etc.
- Essential cell parts:
- The cell has many organelles but the most important are the plasma membrane, the cytoplasm, the neucleus
1.) Cell membrane
- The outermost covering of a cell which serves as a barrier for entry or exit of substances in a cell.
- The membrane is made up of lippoproteins , is living and responsible for maintaing rigity, flexiblity and shape ofcell
a.) Cellwall: It is present in plant cells surrounding the plasma membrane. It is different from the plasma membrane asthecell wall is dead, freely permiable, very ridgidas it is made up of cellulose.
2.) Cytoplasm
- It is the fluid matrix of the cell,which is the site of several cell organelle, enzyme catalysis etc.
- Cytosol: it is a liquid medium expect the cell organelles.
3.) Nucleus:
- It is a double membrane bound structure which stoes genetic material in them.
- The nucleoplasm – the semi solid matrix of nucleus
- The genetic material is in form of chromatin fiber which gets condenced during cell division.
1.5 Fine structure of cell – The organelles:
a.) Cell wall –
1.) Outermost, rigid, freely permiable outermost cell wall in plants.
2.) It provids the cells with protection
b.) Cell membrane –
1.) it seperates the cell component from the environment.
2.) it is selectively permiable for entry and exit solutes through them.
3.) the membrane is thin, living, dynamic and living.
c.) Cytoplasm–
1.) It is the cell’s fluid matrix, which is the location of various cell organelles, enzyme catalysis, and so on.
2.) Cytosol: a liquid medium that contains the cell organelles.
d.) Endoplasmic reticulum –
1.) It is the network of tubules involved in generation and transport of proteins and fats
2.) It spreads across the cell forming a supportive frame, as it is continuous with the nuclear membrane and the plasma membrane.
3.) Smooth and rough endoplasmic reticulum arethetwo types of er foundin cells.
e.) Mitochondria-
1.) These organelle with variable shapes and are responsible for production of energy of the cell in the process of aerobic respiration
2.) It is site of prodution of respiratory enzymes
f.) Golgi apparatus-
1.) They are bag like strutures which are usedto produce enzymes and hormones.
2.) In animal cells they help in formation of the sperms acrosomal vessicle.
g.) Ribosome-
1.) It is responsible for translation which are associted with endoplasmic reticulum or may be prsent in the cytoplasm
2.) Ribosomes are made up of RNA, they are arranged in small speheres which are quit dense
h.) Centrosome:
1.) They are present on animal cells only and comprise of centrioles ,located near the nucleus.
2.) They are involved in the synthesis of spindle fibers and cell cycle regulation.
i.) Plastids:
1.) These are pigment (mostly chlorophyll ) containing bodies, arranged in stacks called thallakoids
2.) The different kinds of plastids include chloroplast, chromoplast and leucoplast.
j.) Nucleus
1.) It is the cells organizing center which also stores genetic information in form of DNA which formsthe chromosomes.
2.) It is necessary for cell survival.
Also see: This Chapter all Solution Selina book
k.) Nucleolus-
1.) Produces ribosomal RNA, also involved in ribosomal assembly.
l.) Chromatin fiber-
1.) DNA Fibers are associated with proteins, which form condenced structure in resting state.
2.) DNA carries genetic information.
m.) Vacuoles-
1.) These are water sacs, covered with tonoplast.
2.) Apart from water they store food, pigments, waste products.
3.) They provide cell with turgidity.
n.) Granules-
1.) Small crystals or droplets present in cytoplasm which are used as cell food.
1.6 Microscopic examination of onion peel:
1) Epidermal cells form the cells in onion peel.
2) Prepration of wet mount to study cell morphology:
- Cut the onion in 4 pieces, then remove a scale from the leaf.
- As the onion bulb is fleshey, one has to remove a small layer from inner side of the peel
- The next step is to mount the onion peel on the slide in a drop of water. Coveritwith acoverslip.
- This slide can be observed in low power.
- One can perorm staining of the peel with help of iodine or eosine
- Ovservation after staining: nucleus is seen towards one end near the cell wall.
1.7 The nucleus- key to the life of cell
- To prove the importance of nucleus experiment was performedon amoeba cells
-case 1: amoeba devides to reproduce – in this there isdivision of nucleus and it is distributed equally in daughter cells
– case 2: removal of nucleus – the cell does not survive
-case 3: addition of nucleus to the cell which was devoide is added with nucleus – the cell survives
- Conclusion: The nucleus is most important part of a cell, which when lost the cell can not survive.