As students, we have heard the term cell numerous times. Can you recall any such incidents where you have heard the term? So, what is a cell? In short, all the living matter in the universe is composed of microscopic structures that are known as cells.
structure and function of a cell – Best Biology Notes for NEET Aspirants
What is a Cell?
In its most basic terms, a cell is the fundamental unit of life that is essential for an organism to develop and exist in its surroundings. Every living organism is made up of cells. Whether it is a plant, an animal, or a microorganism, cells provide structure and functions to their bodies.
It is observed that if we were to break an organism to its cellular level, the only independent constituent that we would find would be a living cell. This statement sums up why knowing the structure and functions of a cell is significant to understanding Biology as a whole subject.
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Facts About Cells
Before we proceed with understanding more about the structure and functions of a cell, let us quickly revise some fascinating facts about the fundamental unit of life.
- The study of cells and their relative functions is called cytology.
- A cell is an independent living component.
- Cells arise from pre-existing cells.
- Robert Hooke first discovered cells
- Anton Von Leeuwenhoek described a living cell.
- Robert Brown discovered the nucleus, which contains the genetic material of the cell.
- There are organisms made up of a single cell. They are called unicellular organisms.
- Organisms made up of many cells are called multi-cellular organisms.
- Even though cells are the fundamental unit of life, they have other components that perform various other biological functions.
- A group of cells working together form an organ. Thus, our body has multiple types of cells with different shapes and sizes.
- The number of cells in each organism varies.
- Cells also contain hereditary material.
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Types of Cells
As in a team, we see different members contributing to a mutual goal; the same happens with a group of cells. A group of similar cells works together to perform the same function. However, there are two main types of cells based on their cellular structure. They are-
- Prokaryotic cells (As bacterial cells)
- Eukaryotic cells (As animal and plant cells)
One can easily identify the type of cell by focusing on simple details. Let us cover quick notes based on the above types of cells.
|Do you face challenges while memorising the differences between a Prokaryotic and a Eukaryotic cell? Well, the solution is right below!|
- Organisms that have prokaryotic cells are generally known as prokaryotes.
- These cells are characterised by having no defined nucleus, i.e., the nucleus is not bound by a membrane.
- Prokaryotic cells are usually smaller in size as compared to eukaryotic cells.
- These cells also do not contain any membrane-bound organelle (chloroplast, vacuoles, plastids, mitochondria, etc.).
- All prokaryotic cells have cell walls except mycoplasma.
- Genetic material can either be DNA or RNA in the form of a single chromosome.
- For example, bacteria, cyanobacteria, and archaea.
- Organisms that have eukaryotic cells are generally called eukaryotes.
- These cells are characterised by having a defined nucleus with a membrane, i.e., a true nucleus.
- The cell size is comparatively larger.
- Cell organelles have membrane-bound structures.
- Eukaryotic animal cells only have cell membranes, while eukaryotic plant cells have a cell membrane and cell wall.
- The hereditary material is present in more than one chromosome.
- For example, fungi, protozoans, human cells, plant cells, and animal cells.
|A curious question – How do different structures of a cell function? Do you know the mechanism? If not, it’s time to read the points provided below!|
Cell Structures and Their Function
Before we talk about the organelles of a cell, let us go through the components that comprise a specific structure of the cell.
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- The cell membrane is a structure that gives rigidity and protection to the cell.
- It controls the movement of biomolecules in and out of the cell.
- It protects the cell and its organelles from the external environment.
- By nature, the cell membrane is semi-permeable. Meaning it only allows specific substances to pass through it.
- Membranes are composed of biomolecules that are arranged in a phospholipid bilayer.
- The membrane structure can easily be understood by the Fluid Mosaic Model, which Singer and Nicolson proposed.
|Curiously enough The fluid mosaic model explains the phospholipid bilayer of a cell membrane. According to this model, the fluid nature of lipids across the bilayer was explained.|
- The cell wall is a cell structure that is prominently associated with plant cells only.
- Biomolecules like cellulose, hemicellulose, and pectin form the cell wall.
- It is the outermost layer of plant cells that exclusively protects the plasma membrane and other cell components.
- It provides stiffness to the cell membrane.
- It protects the plant cell from mechanical shocks and injuries.
- Prokaryotic cells also have cell walls surrounding their cell membrane.
- The cytoplasm is a jellylike pool inside the cell membrane.
- All other cell organelles are suspended into the cytoplasm of the cell.
- Biochemical reactions like glycolysis take place within the cytoplasm.
Cell Organelles: Their Structure and Function
To thoroughly understand the structure and function of a cell, it is equally important to know about the constituents present inside it. Let us have a quick revision of cell components as they contribute to the overall performance of a cell.
- The nucleus is the main component of a cell.
- It contains DNA, which is a hereditary material.
- It transports signals to other components to further grow, mature, and carry on other life processes.
- The nucleus is a structure that provides protection to genetic material.
- The nucleolus is present inside the nucleus.
- It is the site for ribosome synthesis.
- It also controls cellular reproduction.
- The nucleus is enclosed by a nuclear membrane.
- The membrane forms a barrier between the genetic material and other cell components.
- Condensed chromatin fibre forms chromosomes.
- These are the structures that form during cell division that contain genetic material.
- Chromosomes contain DNA and histones.
- They determine the sex of an individual.
- Humans have 23 pairs of chromosomes.
- Two sister chromatids are attached by a structure called a centromere.
- This cell organelle takes part during cell division.
- It contains two cylindrical structures that are called centrioles (not present in plant cells).
- Universally known as the- Powerhouse of the Cell, mitochondria synthesises ATP during cellular respiration.
- It is a double membrane structure.
- The inner membrane forms inward foldings called cristae.
- Mitochondria produce cellular energy through aerobic respiration.
- The mitochondrial matrix also contains DNA, along with RNA, ribosomes, and proteins.
- These are tubular structures found in the proximity of the nucleus.
- Endoplasmic reticulum organises and synthesises selective molecules and sorts them to appropriate locations.
- There are two types of ER found in the cell- Rough endoplasmic reticulum and smooth endoplasmic reticulum.
- RER appears rough 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.
- They appear on the surface of the endoplasmic reticulum; ribosomes are called the protein factory of the cell.
- Polyribosomes are formed when ribosomes get attached with mRNA.
- While prokaryotic cells have the 70S (having subunits 50S and 30S) ribosomes, eukaryotic cells have 80S (having subunits- 60S and 40S) ribosomes.
- Also sometimes known as the Golgi apparatus, these structures are responsible for the transportation of materials within the cytoplasm.
- This cell organelle consists of various disc-shaped cisternae that are arranged parallel to each other.
- Their other function includes assorting the proteins (glycoproteins) and lipids (glycolipids) for secretion.
- Cisternae is the site for the modification and synthesis of various biomolecules.
- Lysosomes are regarded as cell’s suicide bags.
- They engulf foreign particles and prevent them from entering the cell. Thus, providing protection.
- Lysosomes also get rid of metabolic wastes.
- These structures help in renewing the cell.
- They contain enzymatic secretions, mostly hydrolytic enzymes (lipase, protease, etc.) that break down organic matter.
- Chloroplasts are only present inside the plant cells.
- Like mitochondria, they are also double-membrane structures.
- The structure bound by the inner membrane is called the stroma.
- The stroma contains thylakoids which are coin-like structures piled one above the other.
- Stacks of thylakoids grouped together are known as grana.
- Chloroplasts contain chlorophyll and are the site for photosynthesis.
- Genetic material is also observed stranded inside the stroma.
- Large vacuoles are primarily associated with plant cells, while animal cells have smaller ones.
- They are the centre for the storage of food, water, and other organic material.
- Vacuoles provide stiffness to the plant cell.
- Plastids are commonly found in plant cells.
- It is a collective term given to the following- chloroplast, chromoplast, and leucoplast.
|Do you have any doubts regarding the topic? If yes, check out the FAQs below as we might have covered your doubts!|
Frequently asked questions about- Cell Structure and Functions
1.What is the main function of a living cell?
Even though cells are the fundamental unit of life, there goes a lot inside a living cell. It is responsible for the following-
Synthesis of genetic material
Producing energy in the form of ATP
To grow and divide to replace old cells
For the development of a living organism
Helps in the reproduction of a new living organism
2. Are all living beings made up of cells?
Yes, all living beings are made up of cells. However, not all of them are made up of the same type of cells. Even different organs inside the human body have different types of cells.
3. What happens when a cell dies?
Apoptosis is the phenomenon of programmed cell death. When a cell dies on the external surface of the body, it is usually sloughed off. Whereas when a cell dies inside the body, it is ingested by phagocytic cells.
4. Are all cells alike?
Different cells are associated with different living beings. Even the cells throughout the bodies of a multicellular living organism are not alike. It means a single type of cell gives rise to a specific organ only. For example, neural cells make up the nervous system of human beings, and nephrons are the building units of the kidney.
5. What is cell biology?
Cell biology is the branch of science that deals with the structure, function, and nature of cells. It includes all the aspects of a cell, including its anatomy, cellular functions, signaling, reproduction, respiration, genetics, and cell death.
6. How is the cell the basic unit of life?
A cell is the basic unit of life because, being the smallest structure, it can live on its own. The independent behavior depicted by various cells explains why it is responsible for an organism to function.
7. Is the chapter- Cell Structure and Functions important for NEET?
The contents of the chapter- Cell Structure and Function, contribute to approximately 7% weightage in the NEET examination. Not only is this chapter easy, but it also can help students score high due to its interesting concepts.