Biology Notes “Cell Theory” For Railway ALP/Technician & RRB Group D 2018 Exam
Short Notes on Biology for Railway ALP/Technician 2018 & RRB Group D Exam 2018
In continuation to the Short Notes on Biology ,today we will be covering “Cell Theory” from the Biology part of the General Science section. Around 5-8 questions from this topic are asked from this topic in every exam. Thus, the post is very helpful for the upcoming SSC & Railway Exams 2018.
WHAT IS CELL
The basic unit of structure and function in living organisms is the cell.
Robert Hooke – Discovered and coined the term cell in 1665
Robert Brown – Discovered Cell Nucleus in 1831
Schleiden and Schwann – Presented The cell theory, that all the plants and animals are composed of cells and that the cell is the basic unit of life.
TWO TYPES OF CELL
Prokaryotes and Eukaryotes
Differences between a Prokaryotic and a Eukaryotic cell
Prokaryotic Cell:
1. Nuclear membrane is absent in prokaryotic cell.
2. Chromosomes are single in prokaryotic cell.
3. DNA is naked.
4. Nucleolus is absent in prokaryotic cell.
5. Mitochondria is absent. Respiratory and photosynthetic enzymes present in plasma-membrane.
6. Endoplasmic reticulum is absent in prokaryotic cell.
7. Ribosomes – 70S type/size, made up of 5OS and 30S sub-units. All ribosomes are free in cytoplasm.
8. In prokaryotic cell, chloroplast is absent. However, present in blue-green algae is associated with lamellae. These lamellae are not enclosed by membrane.
9. Golgi bodies are absent in prokaryotic cell.
10. Lysosome is absent in prokaryotic cell.
11. Cell-Wall is thin. Non cellulosic, contains amino sugars and muramic acid.
12. Cytoplasmic streaming or Amoeboid movement does not occur in prokaryotic cell.
13. Division of cell is amitosis or direct.
Eukaryotic Cell:
1. Nuclear membrane is present in eukaryotic cell.
2. In eukaryotic cell, chromosomes are many in number.
3. DNA is combined with proteins.
4. Nucleolus is present in eukaryotic cell.
5. Mitochondria is present in cytoplasm of eukaryotic cell.
6. Endoplasmic reticulum is present in eukaryotic cell.
7. Ribosomes – 80S type/size. In plants these dissociate into 60S and 40S sub-units. Most of the ribosomes attached to endoplasmic reticulum. Some ribosomes are free in the cytoplasm.
8. All green plants have typical chloroplasts which have grana.
9. Golgi bodies are present in eukaryotic cell.
10. Lysosome are present in eukaryotic cell.
11. Cell-Wall is thick, cellulosic, does not contain amino and muramic acid.
12. Cytoplasmic streaming or Amoeboid movement may occur in eukaryotic cell.
13. Division of cell is indirect. Mitosis and Meiosis.
Cell Organelles
Plasma Membrane or Cell Membrane
Cell membrane is also called the plasma membrane.
- It can be observed only through an electron microscope.
- Plasma membrane is the outermost covering of the cell that separates the contents of the cell from its external environment
- The plasma membrane is flexible and is made up of organic molecules called lipids and proteins
Cell Wall
Cell wall is absent in animals.
- Plant cells, in addition to the plasma membrane, have another rigid outer covering called the cell wall. The cell wall lies outside the plasma membrane.
- The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance and provides structural strength to plants.
Cytoplasm
It is the jelly-like substance present between the cell membrane and the nucleus.
The cytoplasm is the fluid content inside the plasma membrane.
Nucleus
It is generally spherical and located in the centre of the cell.
Nucleus is separated from the cytoplasm by a double layered membrane called the nuclear membrane.
Nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring.
The entire content of a living cell is known as protoplasm [cytoplasm + nucleus]. It includes the cytoplasm and the nucleus. Protoplasm is called the living substance of the cell.
Chromosomes
Chromosomes contain information for inheritance of features from parents to next generation in the form of DNA (deoxyribo nucleic acid) molecules.
Chromosomes are composed of DNA and Protein.
DNA molecules contain the information necessary for constructing and organizing cells. Functional segments of dna are called genes
Nucleoid
In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the absence of a nuclear membrane. Such an undefined nuclear region containing only nucleic acids is called a nucleoid.
Vacuoles
Empty structure in the cytoplasm is called vacuole. It could be single and big as in an onion cell (plant cell).
Large vacuoles are common in plant cells. Vacuoles in animal cells are much smaller.
Vacuoles are storage sacs for solid or liquid contents
Endoplasmic Reticulum (ER)
It is responsible for protein and lipid synthesis. There are two types of endoplasmic reticulum: rough and smooth.
The rough endoplasmic reticulum has ribosomes present and is responsible for the synthesis of proteins.
The smooth endoplasmic reticulum does not have ribosomes present and is responsible for the synthesis of lipids.
In addition to protein synthesis, the endoplasmic reticulum is also used to modify proteins.
Ribosome
The ribosome is a large complex of RNA and protein molecules
Golgi Apparatus or Golgi Complex
The primary function of the Golgi apparatus is to process and package the macromolecules such as proteins and lipids that are synthesized by the cell.
The golgi apparatus is also involved in the formation of lysosomes.
Lysosomes
Lysosomes are a kind of waste disposal system of the cell.
Lysosomes are also known as the ‘suicide bags’ of a cell.
Lysosomes help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles because they contain powerful digestive enzymes capable of breaking down all organic material.
Mitochondria
Mitochondria are known as the powerhouse of the cell.
The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine Triphosphate) molecules.
ATP is known as the energy currency of the cell.
Plastids
Plastids are present only in plant cells. There are two types of plastids – chromoplasts (coloured plastids) and leucoplasts (white or colourless plastids).
Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules are stored.
Green coloured plastids are called chloroplasts. They provide green colour to the leaves.
Chloroplasts are important for photosynthesis in plants