Eukaryotic Cells

Eukaryotic cells have a nucleus enclosed within the nuclear membrane and form large and complex organisms. Protozoa, fungi, plants, and animals, all have eukaryotic cells. They are classified under the kingdom Eukaryota.

They have the ability to maintain different environments in a single cell that allows them to carry out various metabolic reactions. This helps them grow many times larger than the prokaryotic cells.

Characteristics of Eukaryotic Cells

The characteristics of eukaryotic cells are as follows:

  1. Eukaryotic cells have the nucleus enclosed within the nuclear membrane.

  2. The nucleus has mitochondria.

  3. Flagella and cilia are the locomotory organs in a eukaryotic cell.

  4. A cell wall is the outermost layer of the eukaryotic cells.

  5. The cells divide by a process called mitosis.

  6. The eukaryotic cells contain a cytoskeletal structure.

  7. The nucleus contains a single, linear DNA, which carries all the genetic information.

Eukaryotic Cell Structure

The eukaryotic cell structure comprises of the following:

Plasma Membrane

The plasma membrane separates the cell from the outside environment.

It comprises certain embedded proteins which help in the exchange of substances in and out of the cell.

Cell Wall

A cell wall is a rigid structure present outside the plant cell. It is, however, absent in animal cells.

It provides shape to the cell and helps in cell-to-cell interaction.

It is a protective layer that protects the cell from any injury or pathogen attacks.

It is composed of cellulose, hemicellulose, pectins, proteins, etc.

Cytoskeleton

The cytoskeleton is present inside the cytoplasm which consists of microfilaments, microtubules, and fibres to provide perfect shape to the cell, anchor the organelles, and stimulate the cell movement.

Endoplasmic Reticulum

It is a network of small, tubular structures that divides the cell surface into two parts: luminal and extraluminal.

Endoplasmic Reticulum is of two types:

  • Rough Endoplasmic Reticulum which contains ribosomes.

  • Smooth Endoplasmic Reticulum that lacks ribosomes and is therefore smooth.

Nucleus

The nucleoplasm enclosed within the nucleus contains DNA and proteins.

The nuclear envelop consists of two layers- the outer membrane and the inner membrane. Both the membranes are permeable to ions, molecules, and RNA material.

Ribosome production also takes place inside the nucleus.

Golgi Apparatus

It is made up of flat disc-shaped structures called cisternae.

It is absent in red blood cells of humans and sieve cells of plants.

They are arranged parallel and concentrically near the nucleus.

It is an important site for the formation of glycoproteins and glycolipids.

Ribosomes

These are the main site for protein synthesis.

They are composed of proteins and ribonucleic acids.

Mitochondria

These are also known as “powerhouse of cells” because they produce energy.

It consists of an outer membrane and an inner membrane. The inner membrane is divided into folds called cristae.

They help in the regulation of cell metabolism.

Lysosomes

They are known as “suicidal bags” because they possess hydrolytic enzymes to digest protein, lipids, carbohydrates and nucleic acids.

Plastids

These are double-membraned structures and are found only in plant cells. These are of three types:

  • Chloroplast that contains chlorophyll and is involved in photosynthesis.

  • Chromoplast that contains a pigment called carotene that provides the plants yellow, red, or orange colours.

  • Leucoplasts that are colourless and store oil, fats, carbohydrates, or proteins.

Eukaryotic Cell Diagram

Eukaryotic cell diagram mentioned below depicts different cell organelles present in eukaryotic cells. The nucleus, endoplasmic reticulum, cytoplasm, mitochondria, ribosomes, lysosomes are clearly mentioned in the diagram.

Eukaryotic Cell Diagram

Eukaryotic Cell Diagram illustrated above shows the presence of a true nucleus.

Eukaryotic Cell Cycle

The eukaryotic cells divide during the cell cycle. The cell passes through different stages during the cycle. There are various checkpoints between each stage.

Quiescence (G0)

This is known as the resting phase and the cell does not divide during this stage. The cell cycle starts at this stage. The cells of the liver, kidney, neurons and stomach all reach this stage and can remain there for longer periods. Many cells do not enter this stage and divide indefinitely throughout their life.

Interphase

In this stage, the cells grow and take in nutrients to prepare them for the division. It consists of three

checkpoints:

Gap 1 (G1) – Here the cell enlarges. The proteins also increase.

Synthesis (S) – DNA replication takes place in this phase.

Gap 2 (G2) – Ther cells enlarge further to undergo mitotic division.

Mitosis

Mitosis involves the following stages:

  • Prophase

  • Prometaphase

  • Metaphase

  • Anaphase

  • Telophase

  • Cytokinesis

On division, each daughter cell is an exact replica of the original cell.

Examples of Eukaryotic Cells

Eukaryotic cells are exclusively found in plants, animals, fungi, protozoa and other complex organisms. The examples of eukaryotic cells are mentioned below:

Plant Cells

The cell wall is made up of cellulose which provides support to the plant. It has a large vacuole which maintains the turgor pressure. The plant cell contains chloroplast which aids in the process of photosynthesis.

Fungal Cells

The cell wall is made of chitin. Some fungi have holes known as septa which allow the organelles and cytoplasm to pass through them.

Animal Cells

These do not have cell walls, instead, they have a cell membrane. That is why animals have varied shapes. They have the ability to perform phagocytosis and pinocytosis.

Protozoa

Protozoans are unicellular organisms. Some protozoa have cilia for locomotion. A thin layer called pellicle provides supports to the cell.

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