We are providing you with class 9th biology chapter 1 The fundamental unit of life along with the ncert solutions to help the students to clear their doubts regarding the subject. Students find difficulty in mugging up the terms and concepts so, we have provided short and detailed notes so that they can get the gist of the lesson. Here you can get the summary of the lesson, the fundamental unit of life along with the solutions of ncert.
The Fundamental Unit Of Life Class 9: Facts to remember
Robert Hooke in 1665 discovered the smallest functional unit of life and named it cell. He discovered through a self-built microscope and saw little rooms in a cork. The cell can independently perform all the necessary functions and is considered the basic unit of life.
There are two types of cells:
- Animal cell
- Plant cell
The Basic Structure Of A Cell
1. Plasma/Cell membrane
This is the outermost covering and separates the inner contents from the external environment. It only allows some materials to move in and out of the cell membrane. That is why it is called the selectively permeable membrane.
Gases like co2 and o2 can move in and out through a process called diffusion of gases. The movement of water molecules through such a selectively permeable membrane from high to low concentration. It is called osmosis.
If the medium surrounding the cell has the same level, there will be no movement at all. Such a solution would be called an isotonic solution.
If the medium has a lower water concentration then the cell will lose water by osmosis. Such a solution would be called a hypertonic solution.
The plasma membrane is made up of lipids and proteins and it is flexible enough to make the cell large and can engulf food easily. This type of movement can be seen in Amoeba and it is called endocytosis
2. Cell wall (Protective wall)
Plant cells have another wall to protect themselves and this is a very rigid covering. This is called a cell wall and lies outside the plasma membrane. It is made up of cellulose and provides structural strength to the plants.
When a living plant loses water through osmosis there is shrinkage of all the contents and this is called plasmolysis.
3. Nucleus (Brain of a cell)
The nucleus has a double-layered called nuclear membrane. It has pores that allow the transfer of materials from inside to outside; cytoplasm.
The nucleus contains rod-shaped structures that contain information for an inheritance; chromosomes. Chromosomes contain information for an inheritance to transfer from one to the next generation. Chromosomes are composed of DNA and protein. Functional segments of DNA are called genes. The nucleus plays a central role in cellular reproduction.
In some organisms like bacteria, the nuclear material is not enclosed by a nuclear membrane and membrane-bound cell organelle is absent. Such nuclei are called nuclei and such cells are known as prokaryotic cells. Such cells have single chromosomes.
Cells having a well-defined nucleus and having membrane-bound cell organelle is termed as a eukaryotic cell. Such cells have more than one chromosome.
The cytoplasm is the fluid content inside the plasma membrane along with some specialized cell organelles that can perform some specific functions.
5. Cell Organelles
Cell organelles are required to keep their contents separate from the external environment. Different components of the cell perform different functions and these are called cell organelles.
- Endoplasmic Reticulum (ER) (Channels, Network for transport)
The ER is a large network of membrane-bound tubes and sheets. It looks like long tubules or round or oblong bags.
There are two types of ER-Rough endoplasmic reticulum [RER] and smooth endoplasmic reticulum [SER]. RER has particles called ribosomes attached to its surface. The ribosomes Endoplasmic Reticulum are the sites of protein manufacture.
The SER helps in the manufacture of fat molecules, or lipids, important for cell function. Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis. Some other proteins and lipids function as enzymes and hormones.
One important function of ER is to serve as channels for the transport of materials between various regions of the cytoplasm and nucleus.
2. Golgi Apparatus (Packaging)
The Golgi apparatus, first described by Camillo Golgi, consists of a system of membrane-bound vesicles arranged approximately, parallel to each other in stacks called cisterns.
The material synthesized near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus. Its functions include the storage, modification, and packages of products in vesicles. In some cases, complex sugar may be made from simple sugar in the Golgi apparatus. It is also involved in the formation of lysosomes.
3. Lysosomes [Suicidal bags] (Cleanliness of cell)
Lysosomes are a kind of waste disposal bag to get rid of the waste materials to help the cell clean by digesting any foreign material. Foreign materials include bacterias, food wella s some cell organelles in broken pieces.
Lysosomes end up breaking it into pieces and may burst. The enzymes digest their own cells. That is why it is known as suicidal bags.
4. Mitochondria (Powerhouse, Energy provider)
These are known as powerhouses of the cell as the energy required by the cell is fulfilled by the chemical activities in the form of ATP. ATP (adenosine triphosphate) is also known as the energy currency of the cell.
Mitochondria has two membranes:
- The outer membrane is porous
- The inner membrane is deeply folded
5. Plastids: Plastids are present only in plant cells. There are two types of plastids: chromoplasts and leucoplasts.
Chromoplasts are the colored plastids present in leaves, flowers, and fruits. Plastids containing the pigment chlorophyll are known as chloroplasts. They are important for photosynthesis in plants.
Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll. Leucoplasts are found primarily in organelles in which materials such as starch, oils, and protein granules are stored.
The internal organization of the plastids consists of numerous membrane layers embedded in a material called the stroma. Plastids are similar to mitochondria in external structure. Plastids have their own DNA and ribosomes.
6. Vacuoles (Storage): Vacuoles are storage sacs for solid or liquid contents. Vacuoles are small-sized in animal cells while plant cells have very large vacuoles [50% to 90% cell volume].
In-plant cells, vacuoles are full of cell sap and provide turgidity and rigidity to the cell. In Amoeba, the food vacuole contains the food items that are consumed and contractile vacuoles expel excess water and some wastes from the cell.
NCERT Solutions For Class 9 The Fundamental Unit Of Life
Q1. Who discovered cells, and how?
Robert Hooke discovered the cell in 1665 through his self-designed microscope and examined a thin slice of cork that resembled a honeycomb. To these small compartments, he named cells.
Q2. Why is the cell called the structural and functional unit of life?
A cell is the basic structural and functional unit because it is capable of conducting all the necessary activities.
Q3. How do substances like C02 and water move in and out of the cell? Discuss.
CO2 moves by diffusion and H2O moves by osmosis through the cell membrane.
Q4. Why is the plasma membrane called a selectively permeable membrane?
It is called a selectively permeable membrane because it allows the entry and exit of some substances, not all.
Q5. Fill in the gaps in the following table illustrating the differences between prokaryotic and eukaryotic cells.
Q6. Can you name the two organelles we have studied that contain their own genetic material?
The two organelles which have their own genetic material are:
- Mitochondria 2. Plastids
Q7. If the organization of a cell is destroyed due to some physical or chemical influence, what will happen?
The cell will not be able to revive and lysosomes will digest it.
Q8. Why are lysosomes known as suicide hags?
Lysosomes burst and the enzymes can digest their own cell that is why they are called the suicidal bags. Question 4. Where are proteins synthesized inside the cell?
Q9. Make a comparison and write down ways in which plant cells are also different from animal cells.
Q10. How is a prokaryotic cell different from a eukaryotic cell?
In some organisms like bacteria, the nuclear material is not enclosed by a nuclear membrane, and membrane-bound cell organelle is absent. Such nuclei are called nuclei and such cells are known as prokaryotic cells. Such cells have single chromosomes.
Cells having well-defined nuclei and having membrane-bound cell organelle is termed as a eukaryotic cell. Such cells have more than one chromosome.
Q11. What would happen if the plasma membrane ruptures or breaks down?
If the plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out.
Q12. What would happen to the life of a cell if there was no Golgi apparatus?
If there were no Golgi bodies, packaging and dispatching of materials synthesized by the cell will be stocked.
Q13. Which organelle is known as the powerhouse of the cell? Why?
Answer: Mitochondria is known as the powerhouse of the cell because it releases the energy required for different activities of life in the form of ATP.
Q14. Where do the lipids and proteins constituting the cell membrane get synthesized?
Lipids and proteins are synthesized in ER [Endoplasmic Reticulum].
Q15. How does Amoeba obtain its food?
Amoeba takes their food by the cell membrane which forms the food vacuole.
Q16. What is osmosis?
Osmosis is the process of movement of water molecules from a region of higher water concentration through a semipermeable membrane to a region of lower water concentration.
Q17. Carry out the following osmosis experiment:
Take four peeled potato halves and scoop each one out to make potato cups, one of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water.
(a) Keep cup A empty
(b) Put one teaspoon sugar in cup B
(c) Put one teaspoon salt in cup C ‘
(d) Put one teaspoon sugar in the boiled potato cup D
Keep these for two hours. Then observe the four potato cups and answer the following:
(i) Explain why water gathers in the hollowed portion of B and C.
(ii) Why is potato A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed-out portions of A and D.
- Water gathers in B and C because in both situations there is a difference in the concentration of water in the trough and water in the cup of Potato. Hence, osmosis takes place as the potato cells act as a semipermeable membrane.
- Potato A is necessary for this experiment for comparison, it acts as a control.
- Water does not gather in the hollowed-out portions of A and D. As a cup of A does not have a change in the concentration for water to flow. For osmosis to occur one of the concentrations should be higher than the other.
Conclusion: In cup D, the cells are dead and hence the semi-permeable membrane does not exist for the flow of water and no osmosis takes place.
In a nutshell, we have provided the short and detailed summary of class 9th social science chapter The Fundamental Unit Of Life along with the ncert solutions to help the students to clear their doubts and they would be able to memorize the notes. We have also provided important diagrams to clear the conceptual knowledge as well as the basics of biological terms.