NEET Important Chapter: Cell - The Unit of Life

Cell - The Unit of Life is a very important part of the NEET syllabus and this article will help you to get the insights and also one can refer to this for last-minute revision purposes. This chapter is an important component in Unit Structure and Function because it is the source of 2-3 questions per year. The chapter is entirely theoretical and requires thorough revision.

So, in this article, you’ll be studying about the cell, its discovery, the scientists involved, the kinds of cell, cell membrane, cell wall, and other major components of the cell. This synopsis of the chapter would be highly helpful to the student in order to gain the maximum marks. 

Important topics of Cell - The Unit of Life 

• Cell theory 

• Kinds of cell

• Cell Organelles

• Nucleus- Chromosomes

• Mitochondria

• Golgi Apparatus

Important Concepts of the Chapter

Cell

• A cell is known to be the most basic functional and structural unit of life. 

• Anton van Leeuwenhoek was the first person to see a cell and characterise it as a living organism. 

• A cell is considered a structure comprising organelles that perform essential processes in order for the cell to survive. Not all cells, however, are just the same.

Plants and animals have cells that are substantially different. The lack of cell walls in animal cells is among the most significant differences that exist. The egg or female ovum is the largest cell in the human body and is around 1 mm across. However, the granule cell, which is present in the human cerebellum and measures around 4.5 micrometres in diameter, is the smallest cell.

Cell Theory

• This scientific hypothesis stated that all living entities are made up of cells and that new cells are generated from pre-existing cells. 

• It was first postulated by Matthias Schleiden and Theodor Schwann. 

• Despite the fact that Schleiden and Schwann proposed the hypothesis, numerous renowned scientists have added to it, elevating it from a theory to a commonly acknowledged fact.

Types of Cells

Prokaryotic cells and Eukaryotic cells are the two different types of cells.

1. Prokaryotic Cells: Prokaryotic cells are unicellular microbes that are among the oldest living things on the planet. Because a typical prokaryotic cell is made up of only one membrane, all reactions take place in the cytoplasm. They can live on their own or in the guts of other animals, such as ruminants (cows and buffaloes).

2. Eukaryotic Cells: Eukaryotic cells, unlike prokaryotic cells, have a nucleus that is encased inside a membrane. Eukaryotic organisms are multicellular organisms that belong to the Eukaryota domain.
   
   

At the bottom of the article, students can find the difference and similarities between the two kinds of cells.

Cell Structure

• Cell Membrane: A structure which provides rigidity and protection to the cell and controls the movement of biomolecules in and out of the cell. Made up of phospholipid layers.

• Cell wall: It is the outermost layer found only in plant cells and is made up of cellulose, hemicellulose, and pectin. It provides stiffness and protects the plant cell from mechanical shocks and injuries.

• Cytoplasm: It is a jelly-like pool inside the cell membrane, carries cell organelles, and is the site for Biochemical reactions like glycolysis.

Cell Organelles

1. Nucleus: 

• It is the main component of a cell, carries DNA, and is responsible for growth and development.

2. Nucleolus: 

• Present inside the nucleus, site for ribosome synthesis, and also controls cellular reproduction.

3. Nuclear Membrane: 

• It is a membrane-enclosed nucleus and thus forms a barrier between the genetic material and other cell components.

4. Chromosomes: 

• Condensed chromatin fibre causes the formation of chromosomes. Chromosomes contain DNA and histones and determine the sex of an individual. 

• Humans carry 23 pairs of chromosomes. Two sister chromatids are attached by a structure called a centromere.

5. Centrosome: 

• Two cylindrical structures that take place in cell division.

6. Mitochondria: 

• This is a double-layered structure commonly called the powerhouse of the cell and synthesises ATP during cellular respiration. 

• Mitochondria carries cristae which are formed by the inward foldings of the inner membrane. 

• The mitochondrial matrix also contains DNA, along with RNA, ribosomes, and proteins.

7. Endoplasmic Reticulum: 

• Tubular structures seen in the proximity of the nucleus. Two types of ER are found in the cell - rough and smooth endoplasmic reticulum.

• RER is called so because of the presence of ribosomes on its surface. These structures are associated with protein synthesis.

• SER does not have ribosomes on its surface and is involved with lipid synthesis.

8. Ribosome: 

• Ribosomes are present on the surface of the endoplasmic reticulum and are called the protein factory of the cell. 

• Polyribosomes are formed when ribosomes get attached to mRNA.

9. Golgi Bodies: 

• These structures are responsible for the transportation of materials within the cytoplasm and carry Cisternae, which is the site for the modification and synthesis of various biomolecules. 

• Its functions include assorting the proteins (glycoproteins) and lipids (glycolipids) for secretion.

10. Lysosome: 

• Lysosome is also called as cell’s suicide bags, engulfs foreign particles and other metabolic wastes, helps in renewing the cells, and contains enzymatic secretions that break down organic matter.

11. Chloroplasts: 

• Double-layered structure found only in plants. 

• The structure bound by the inner membrane is called the stroma. 

• The stroma contains thylakoids; stacks of thylakoids grouped together are known as grana. 

• Chloroplasts contain chlorophyll and are the site for photosynthesis.

12. Vacuoles: 

• Centre for the storage of food, water, and other organic material.

13. Plastids: 

• Collective term given to chloroplast, chromoplast, and leucoplast and responsible for photosynthesis and the production and storage of metabolites. 

Differences Between Prokaryotic and Eukaryotic Cell

Similarities Between Prokaryotic Cell and Eukaryotic Cell

• Ribosomes are found in both cells and play a role in protein synthesis.

• DNA that is linked to genes can be found in both types of cells.

• In both, the cell wall is present.

• There are four sorts of main molecules that are found in both of them.

• In both cases, the process of DNA copying is comparable.

• Both share a few significant metabolic pathways.

• In both, the photosynthesis process is comparable.

• There are twenty standard amino acids in both cells.

• Both have the same genetic code.

• ATP is the energy source in both cells.

Solved Examples From the Chapter 

1. The cell wall of algae is made up of which substance?

(a) Protein

(b) Mannans

(c) Lipid

(d) all of the above

Ans: (b) Mannans

2. Match the Following:

Ans:

Cristae: The inner membrane of mitochondria folds inward to form cristae, a finger-like projection. It expands the absorption surface area.

Cisternae: A space between the membranes of flattened sacs of the Golgi apparatus and the endoplasmic reticulum, as well as between the two membranes of the nuclear envelope that contains fluid.

Thylakoids: Thylakoids are disc-shaped structures that are stacked to form grana. These include photosynthetic pigments and serve as a location for photosynthesis light reactions.

3. Name two cell organelles that are double membrane bound. 

Ans: Mitochondria and chloroplasts are the two organelles that are double-membrane bound.

4. Which of the following is not correct?

(a) Robert Brown discovered the cell.

(b) Schleiden and Schwann formulated the cell theory.

(c) Virchow explained that cells are formed from pre-existing cells.

(d) A unicellular organism carries out its life activities within a single cell.

Ans: Robert Brown discovered the cell. - It is a false statement.

The first person to see a cell was Robert Hook. He used a very primitive microscope and observed empty blocks like structure in the cork cells which were named as cells.

Solved Problems of Previous Year Question From the Chapter

1. When the Centromere is situated in the middle of two equal arms of chromosomes, the chromosome is referred to as:

1. Acrocentric

2. Sub-metacentric

3. Telocentric

4. Meta-centric

Ans: d. Meta-centric.

The chromosome is called Metacentric when the centromere lies in the centre of two equal arms of chromosomes.

Sub-metacentric chromosomes have the centromere located somewhat distant from the middle of the chromosome.

Acrocentric chromosomes are those in which the centromere is located relatively close to one end of the chromosome.

When the centromere is located at the end of the chromosome, it is referred to as telocentric.

2. The size of Pleuropneumonia-like Organism (PPLO) is:

1. 0.2 μm

2. 1-2 μm

3. 10-20 μm

4. 0.1 μm

Ans: d. 0.1 μm.

Key point to remember: With a diameter of 0.1 micrometres, PPLO is also known as mycoplasma. It's the tiniest cell ever found. 

3. The Golgi complex participates in

1. Activation of amino acid

2. Fatty acid breakdown

3. Respiration in Bacteria

4. Formation of secretory vesicles

Ans: d. Formation of Secretory Vesicles.

The Golgi complex is a membrane-bound organelle found solely in eukaryotic cells. It has a role in secretory vesicle production. 

Key Point to Remember: In bacteria, mesosomes perform respiration, ribosomes do amino acid activation as part of protein synthesis, and mitochondria perform fatty acid degradation via beta-oxidation.

4. The shorter and longer arms of submetacentric chromosomes are referred to as:

1. S-arm and l-arm, respectively.

2. q-arm and p-arm, respectively.

3. m-arm and n-arm, respectively.

4. p-arm and q-arm, respectively.

Ans: d. p-arm and q- arm, respectively.

Sub metacentric chromosome is Heterobrachial.

The small arm is referred to as the 'p' arm (p stands for petite/short) while the long arm is referred to as the 'q' arm.

Key Point to Remember: Human chromosomes have 2 arms - the p (short) arm and the q (long) arm, and both are separated by the centromere.  

Practice Questions

1. Which of the following is not true of a eukaryotic cell?

1. Cell wall is made up of peptidoglycans.

2. Mitochondria contain circular DNA.

3. It has 80S type of ribosome present in the cytoplasm.

4. Membrane-bound organelles are present.

Ans: a. Cell wall is made up of peptidoglycans.

Option a is incorrect as the cell wall is made up of cellulose in eukaryotic cells. The other options are true for eukaryotes, that is, mitochondria do carry circular DNA, the organelles present are membrane bound, which includes Golgi apparatus, chloroplasts etc., and the type of ribosome present in the cytoplasm is 80S. 

Point to Remember: The cell wall of prokaryotic cells is made up of peptidoglycan. 

2. The organelle common among prokaryotic and eukaryotic cells is 

1. Centrosome

2. Peroxisome

3. Ribosome

4. Glyoxysome

Ans: c. Ribosome.

There exist two different kinds of cells, namely, prokaryotes and eukaryotes.

The nucleus, endoplasmic reticulum, and mitochondria are membrane-bound organelles in eukaryotic cells; however, the ribosome is the only organelle that can be seen in both prokaryotic and eukaryotic cells.

Point to Remember: Eukaryotic ribosomes are much larger than Prokaryotic ones.

3. Identify the cell organelles labelled as A, B, C, and D. Mark the correct option w.r.t. organelle and its function.

1. A - Major site for synthesis of lipids.

2. B - Performs the function of packaging materials, to be delivered to only intracellular targets.

3. C - Sites of anaerobic respiration.

4. D - Main arena of cellular respiration.

Ans: d. D - Main arena of cellular respiration.

The correct labelling of the diagram has been given below.

A - Endoplasmic Reticulum, B - Golgi apparatus, C - Mitochondria, D - Cytoplasm.

So, the main arena of cellular respiration is Cytoplasm.

Point to Remember: Glycolysis of aerobic respiration takes place in the cytoplasm of the cell. Also, Anaerobic respiration occurs at the same location. 

Conclusion

The article has given crisp and concise content as per the Cell - The Unit of Life NEET notes. The questions added at the end are highly important from the exam point of view and thus the student can have a clearer understanding of the type of questions that might appear in the exam.