GSEB Solutions for Class 9 Science and Technology – The Fundamental Unit of Life: The Cell (English Medium)
B. Nerve cell
A single nerve cell can be as long as 100cm in length.
A. Robert Hooke
Robert Hooke observed a honeycomb like structure while observing a slice of bottle cork under his microscope. He named this structure, a cell.
Mitochondrion is the site of ATP synthesis in a cell. Thus, it is called as the powerhouse of the cell.
Lysosomes contain digestive enzymes that are capable of disrupting the cell and its organelles. Thus, lysosomes are called as suicide bags.
Lysosomes are formed from Golgi apparatus which are also single membrane bound organelles.
Plastids are organelles that contain food or pigment and are absent in animal cells.
Prokaryotes do not have a well defined nucleus and also, do not have membrane bound organelles.
Tonoplast is a membrane that surrounds the vacuole that stores food and separates it from the surrounding cytoplasm.
Chromosomes are present in the nucleoplasm present in the nucleus in animal cells. Thus, cells devoid of nucleus also lack in chromosomes.
Two characteristics of a prokaryotic cell are:
- Nucleus is not developed.
- Membrane bound organelles are absent.
Robert Brown discovered nucleus and describes its characteristics in plant cells in the 19th century.
Watson and Crick discovered the double helical structure of the DNA molecule. However, DNA was first discovered by Friedrich Miescher in the 19th century.
Two major cell organelles of a Eukaryotic cell are
- Golgi body
Chief function of the following organelles are
- Mitochondria – synthesis of ATP
- Lysosomes – intracellular digestion
- Golgi body – storage and synthesis of proteins
- Ribosomes – storage and synthesis of proteins
- Chloroplast – photosynthesis
When a cell is placed in sugar or salt solution, and the concentration of water outside the cell is less than the concentration of water inside the cell, the water moves out of the cell by the process of osmosis. As a result, the cell shrinks. This phenomenon shown by a cell is known as plasmolysis.
The two main functions of the cell wall are
- To provide mechanical strength to the cell.
- To maintain the shape of the cell.
The English scientist Robert Hooke discovered the cell while observing a layer of a bottle cork under his primary microscope.
CO2 moves in and out of the cell through simple diffusion as cell membrane is permeable to carbon dioxide gas.
Water moves in and out of the cell, across the cell membrane through osmosis.
Plasma membrane is a thin, living, delicate membrane that surrounds the cytoplasm. It allows the easy passage of only a few selective materials in and out of the cell into the environment. Hence, it is called as a selectively permeable membrane.
Lysosome contains digestive enzymes. During disturbance in the cell, the digestive enzymes are released in the cytoplasm of the cell that destroy the cells and all its cell organelles. Thus, lysosome is known as a suicide bag.
Mitochondria are the cell organelle known as the powerhouse of the cell.
Cellular respiration takes place in the mitochondria of the cell. It transforms carbohydrates and lipids from the cells to carbon dioxide and water. During this process of oxidation, it releases free energy that is used for the synthesis of ATP.
Thus, as synthesis of ATP takes place in mitochondria, it is known as the power house of the cell.
When two solutions of different concentrations are separated by a semi-permeable membrane then the solute moves from a lower concentration to a higher concentration. This movement of a solute is called osmosis.