Life, as we know it, took billions of years to evolve. From the very first precursor of life to the multitude of multicellular organisms that we see around us today, the most basic unit of all these is the cell.
Introduction to Fundamental Unit of Life
All About Cells
Cells are the basic structural and functional unit of life. Cell was discovered by Robert Hooke. A number of cells can work together to form tissues and organs.
Cellular respiration is the process by which the food releases energy in the mitochondria. Cells absorb glucose from the food and burn it to produce energy.
Structural Organization of Cells
Prokaryotic & Eukaryotic cells
Two types of cell; Prokaryotic and Eukaryotic cells. Prokaryotic cells are primitive and lack well defined nucleus. Eukaryotic cells are more advanced and have well defined nucleus.
Cell structure in Eukaryotic cells
Eukaryotic cells have the most well defined structure. These cells have cell membrane, membrane bound cell organelles and a well defined nucleus. The nucleus has its own membrane called nuclear membrane.
- Cell membrane is the outer covering of a cell.
- It is made up of phospho-lipid bilayer membrane.
- It is selectively permeable in nature.
- The structure of cell membrane is best described by the fluid mosaic model.
The movement of molecules from a region of their high concentration to a region of their lower concentration is known as diffusion.
Osmosis in selectively permeable membrane
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, hypotonic solutions, hypertonic solutions
- 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 higher concentration of solute compared to the surrounding fluid and thus push water out of cell, shrinking it.
Cell walls in plants
Plant cells are different from animals cells due to the presence of cell wall. Cell wall is made of cellulose and gives a rigid structure to the plant cell.
Endocytosis is the invagination of cell membrane, followed by pinching off forming a membrane bound vesicle. This is commonly seen in Amoeba.
Nucleus in cells
Nucleus is the processing unit of the cell. It is a double membrane bound organelle which contains the genetic material for inheritance.
Cytoplasm is the fluid found inside the cell. It gives the structure to the cell and houses different organelles of the cell.
Organelles are structures present in the cytoplasm of the cell that help in several functions of the cell.
Smooth ER do not have ribosomes and thus are not involved in protein synthesis. They are however involved in the lipid metabolism and detoxifying poisonous molecules.
Golgi Apparatus is also called the post office of the cell. They package and transport the proteins across the cytoplasm.
Mitochondria are also called power plant of the cell. They generate ATP via the electron transport chain. They also have a DNA called mtDNA, which makes them semi-autonomous organelle.
Comparison between plant & animal cells
Question from The Fundamental Unit Of Life Class 9 Notes
- How does a plant cell differ from an animal cell?
- Differentiate between a eukaryotic cell and a prokaryotic cell.
- What would be the outcome in a scenario where a rupture occurs in the plasma membrane?
- Define osmosis.
- How does an amoeba acquire food?
- Growth and repair require which type of cell division?