Animal Cell Labeled diagram in which we will learn about the structure of an animal cell and their work accordingly. Animal cell includes the Cell membrane, nucleus, mitochondria, endoplasmic reticulum, ribosomes, Golgi apparatus, lysosomes, centrioles, vacuoles, cytoplasm, cytoskeleton.

• The scientific study of cells is called Cytology.
• Cells are the basic unit of life, responsible for the structure and function of all living organisms.
• The first dead cell was discovered by Robert Hooke in 1665. He observed cork cells under a microscope and coined the term “cell”.
• The first living cell was discovered by Anton van Leeuwenhoek in 1674. He used a self-made microscope to observe bacteria, protozoa, and sperm cells.
• Robert Brown discovered the cell nucleus.
• Swanson is known as the Father of Modern Cell Biology.
• A.K. Sharma is known as the Father of Indian Cytology.
• The smallest cell is Mycoplasma (PPLO).
• The longest human cell is a nerve cell.
• The largest human cell is the ovum (egg cell).
• The smallest human cell is the sperm cell.

• The shape and function of cells vary greatly.
• Cells can change their shape and function according to the body’s needs.
• Red Blood Cells (RBCs) are the most abundant cells in the human body.
• White Blood Cells (WBCs) can change their shape as part of the immune response.

Parts of a Cell

1. Protoplasm (Living Substance)

• First described by Purkinje, protoplasm is a gel-like substance found inside cells.
• It includes all cell contents enclosed within the plasma membrane.
• It is made up of 80% water and is essential for life processes.
• It has two major components:
  1. Cytoplasm (Cell fluid)
  2. Nucleoplasm (Fluid inside the nucleus)

2. Cell Wall

• The cell wall is a rigid structure found in plant cells and some microorganisms.
• It provides shape, support, and protection to the cell.
• The outermost layer of a plant cell is the cell wall.
• In bacteria, the outermost layer is called the “capsule”.
• The cell wall of fungi is made of chitin.
• The cell wall of plants is primarily composed of cellulose, calcium carbonate (CaCO₃), and gallactans.

3. Cell Membrane (कोशिका झिल्ली)

• The cell membrane is present in both plant and animal cells.
• In prokaryotic cells, the outer membrane is the cell wall, while the inner membrane is the plasma membrane.
• The cell membrane forms a protective boundary around the cell.
• It has a semi-permeable function, meaning it regulates what enters and exits the cell.
• The cell membrane is bi-layered (double-layered) and composed mainly of lipids and proteins.
• It helps in cellular communication and nutrient exchange.
• Some substances can pass through the membrane easily, while others require transport mechanisms.

4. Mitochondria (Powerhouse of the Cell)

• Discovered by Altmann, mitochondria have their own DNA.
• They generate energy (ATP), which is why they are called the powerhouse of the cell.
• Mitochondria are self-replicating and can function independently.
• They perform 70-80% of the cell’s energy-related activities.
• After the nucleus, mitochondria are the second-largest organelles in the cell.
• Their structure is similar to bacterial cells, supporting the endosymbiotic theory.

5. Endoplasmic Reticulum (ER) – अंतर प्रद्रव्य जालिका

• The ER is a network of membranes connected to the cell membrane and nuclear membrane.
• It provides structural support and facilitates intracellular transport.
• It is of two types:
  • Smooth ER (SER) – Helps in lipid synthesis.
  • Rough ER (RER) – Has ribosomes on its surface and is responsible for protein synthesis.
• The Rough ER is more stable near the nuclear membrane, while the Smooth ER is less stable near the plasma membrane.

6. Ribosomes (Protein Factories of the Cell)

• Ribosomes are the smallest organelles in a cell.
• They are responsible for protein synthesis, making them factories of the cell.
• First discovered by Palade.
• Ribosomes are found in all living cells, making them a universal cellular component.
• A single cell can contain millions of ribosomes.
• There are two types of ribosomes:
• The 70S ribosome consists of 50S and 30S subunits.
  • 70S Ribosomes (found in prokaryotic cells)
  • It is lighter and is found in prokaryotic cells.
• The 80S ribosome consists of 60S and 40S subunits.
  • 80S Ribosomes (found in eukaryotic cells)
  • It is heavy and is found in eukaryotic cells.
  • S = Sedimentation Coefficient (Sedimentation coefficient/sedimentation rate).

7. Golgi Body / Golgi Apparatus

• The Golgi body is an organelle that packages and processes proteins and lipids inside the cell.
• It plays a role in protein transport by working with RNA, as t-RNA helps transfer protein molecules.
• Discovered by Camillo Golgi in 1898.
• It is also called the “Dictyosome” in plant cells.
• The Golgi body is involved in the formation of lysosomes and storage of vacuoles.
• It is the main organelle for secretion in the cell.

8. Centrosome (Centrioles) – तारककाय

• The centrosome helps in cell division.
• It is absent in plant cells, which is why plant cells divide using a “cell plate” instead of centrioles.
• Discovered by Van Beneden (1883) and named by Theodor Boveri (1888).
• It is present near the nucleus in animal cells.

9. Lysosome (Lysosome) – लाइसोसोम

• Lysosomes are responsible for intracellular digestion.
• They contain hydrolytic enzymes that break down waste and damaged cell parts.
• If a damaged organelle inside the cell is no longer functional, the lysosome digests it.
• If the entire cell is damaged, lysosomes cause cell death by digesting the entire cell—this is why they are called “suicidal bags”.
• Lysosome is also called the “Bag,” “Atom Bomb,” “Scavenger of the Cell”, or “Disposal Bag.”
• It was discovered by Christian de Duve.
• Lysosomes are not found inside RBCs. Therefore, after RBCs die, they are broken down in the spleen.
• This is why the spleen is called the “graveyard of RBCs.”

10. Nucleus (केंद्रक)

• It was discovered by Robert Brown.
• It controls the cell, so it is called the “brain of the cell.”
• It contains 80% protein.
• The nucleus is the largest organelle in any cell.

Note:

• In humans, RBCs (Red Blood Cells) are called “brain-less cells” because they do not have a nucleus.
• Mature plant cells are also called “brain-less cells” because their nucleus is inactive.
• The study of the nucleus is called Karyology.

Parts of the Nucleus:

a. Nuclear Membrane (केंद्रक झिल्ली)

• The double-layered membrane of the nucleus.
• It is made of Lipoproteins.
• It contains pores that allow the exchange of materials between the nucleus and cytoplasm.

b. Nucleoplasm (केंद्रक द्रव)

• The fluid-like substance inside the nucleus.
• It contains RNA, proteins, and enzymes.

c. Nucleolus (केंद्रिका)

• It is the smallest part of the nucleus.
• It is involved in protein synthesis.

d. Chromatin (क्रोमैटिन)

• It appears as a network of threads inside the nucleus.
• It contains DNA, which is the genetic material.

Vacuoles (रसधानी)

• The empty space in any cell is called a vacuole.
• In emergency situations, vacuoles store water, minerals, and nutrients.
• They are smaller in animals but larger in plants.
• Vacuoles were first observed in protozoa by Spallanzani.
• The term “vacuole” was given by Dujardin.
• Vacuoles in plant cells were first observed by Schwann.
• Vacuoles have a membrane called Tonoplast.
• Vacuoles function as storage sacs for solid and liquid substances.

Parts of Cells

Prokaryotic Cell

• Not all organelles are found in these cells; they are also called primitive cells.
• They contain a cell membrane and ribosomes (70S) but lack other organelles.

Eukaryotic Cell

• These are fully developed cells.
• All cell organelles are present in them.
• They contain ribosomes (80S).
• Plant cells are square-shaped, and their largest organelle is the plastid.
• They have large vacuoles.
• Centrioles are found in animal cells.
• Animal cells are round, and their largest organelle is the nucleus.