Plant Cell & Animal Cell | Additional Study Material for NEET PDF Download

The cell is the basic unit of life in all organisms. Like humans and animals, plants are also composed of several cells. The plant cell is surrounded by a cell wall which is involved in providing shape to the plant cell.  Apart from the cell wall, there are other organelles that are associated with different cellular activities.
Let us have a detailed look at the plant cell, its structure and functions of different plant cell organelles.

Plant Cell Definition

“Plant cells are eukaryotic cells with a true nucleus along with specialized structures called organelles that carry out certain specific functions.”

What is a Plant Cell?

Plant cells are eukaryotic cells that vary in several fundamental factors from other eukaryotic organisms. Both plant and animal cells contain nucleus along with similar organelles. One of the distinctive aspects of a plant cell is the presence of a cell wall outside the cell membrane.

Plant Cell Diagram

The plant cell is rectangular and comparatively larger than the animal cell. Even though plant and animal cells are eukaryotic and share a few cell organelles, plant cells are quite distinct when compared to animal cells as they perform different functions. Some of these differences can be clearly understood when the cells are examined under an electron microscope.
Plant Cell Diagram showing different cell organelles

Plant Cell Structure

Just like different organs within the body, plant cell structure includes various components known as cell organelles that perform different functions to sustain itself.  These organelles include:

Cell Wall

• Cell wall was discovered by Robert–Hooke.
• Outer most but dead boundary of plant cell is cell wall.
• Bacteria is included in plants because they have cell wall.

• Middle lamella consist of Ca & Mg pectates (Plant cement). Amount of Ca is more.
• Fruits become soft and juicy due to dissolved middle lamella.
• Cellulose is the main constituent of cell wall but in addition to cellulose – Hemicellulose, Cutin, Pectin, Lignin, Suberin are also present in cell wall.
• Cell wall worked as frame or protective layer of cell.
• Cellulose microfibrils and macrofibrils are arranged in layers to form skeleton of cell wall. In between these layers, other substances like pectin, hemicellulose may be present. These form matrix of cell wall.
• Network of cellulose fiber forms skeleton of cell wall. 35-100 cellulose chain = 1 micelle. 20 micelle = 1 Microfibril 250 micro fibril = 1 Macrofibril in cell wall.
• Middle lamella is cement material between two adjacent cells in multi cellular plants or outermost layer of cell wall. (primary wall is considered as outermost layer in a cell)
• Martinez and palamo (1970) discovered cell-coat in animal cells, which is known as Glycocalyx. [Made by sialic acid, mucin and hyaluronic acid (animal cement)].
• Cell wall materials (Cellulose, Hemicellulose, Pectin, lignin) are synthesized in plant golgi bodies or dictyosomes. Material of lipid nature (cutin and suberin) are synthesized in sphaerosome.

Formation of cell wall occurs by two methods

• Intussusception: This is a deposition of wall material in the form of fine grains.
• Apposition: Deposition of layers.
• Primary wall is formed mainly by intussusception, while secondary wall formed by both methods. Growth of already formed cell wall take place only by intussusception.
• A Special protein called expansin helps in growth of cell wall by loosing the cellulose microfibril and addition of new cell wall material takes place in the space. Thus expansin is called as "cell wall loosening factor".

Specialisation of cell wall

• Lignification: Lignin (coniferyl alcohol) is a cellulose derivative carbohydrate which  deposits on walls of sclerenchyma,vessels and tracheids.
• Excess of lignin decreases the economic importance of pulp.
• PITS
  Pits are formed in lignified cell wall. Deposition of lignin occurs throughout the cell wall leaving some small thin walled areas called pits. Pits are generally formed in pairs on the wall of adjacent cells. Two pits of a pair are seperated by a thin membrane called pit membrane (completely permeable) (earliar composed of middle lamella and primary wall). But, after some time primary wall may be dissolved. There are two types of pit pairs
  (i) Simple pits - When diameter of a pit cavity is uniform throughout its length then such type of pits are called simple pits.
  (ii) Bordered pits - When diameter of pit cavity increases from inside to outside then such pits are called Bordered pits. In such pits, pit membrane have a thickening, composed of suberin called Torus. Torus functions like a valve to regulate the flow of materials.
  Pits occur in sclerenchyma, vessels and tracheids.  Tracheids in gymnosperms have maximum number of bordered pits.
• Suberisation : Suberisation occurs on cork and casparian strips of endodermal cells. Suberin is a highly impermeable material. It is water tight and air tight material. So suberisation also leads to death of cell. Maximum suberisation occurs in middle lamella. It reduces the transpiration rate in plants.
• Cutinisation: Cutin - is also hydrophobic, waxy substance. Cutinisation is the deposition of cutin on cell walls of leaf epidermis. It reduces the transpiration rate in plants.
• Cuticularisation: Deposition of cutin on the surface of leaf. It leads to formation of cuticle.
• Mucilage deposition: Mucilage deposits on the surface of hydrophytes.
• Deposition of silica: Occurs on the Leaves of grasses, Equisetum, Atropa, Diatoms, rice. 

Cell membrane

It is the semi-permeable membrane that is present within the cell wall. It is composed of a thin layer of protein and fat.
The cell membrane plays an important role in regulating the entry and exit of specific substances within the cell.
For instance, cell membrane keeps toxins from entering inside, while nutrients and essential minerals are transported across.

Nucleus

The nucleus is a membrane-bound structure that is present only in eukaryotic cells. The vital function of a nucleus is to store DNA or hereditary information required for cell division, metabolism and growth.

• Nucleolus: It manufactures cell’s protein-producing structures and ribosomes.
• Nucleopore: Nuclear membrane is perforated with holes called nucleopore that allows proteins and nucleic acids to pass through.

Plastids

They are membrane-bound organelles that have their own DNA. They are necessary to store starch, to carry out the process of photosynthesis. It is also used in the synthesis of many molecules, which form the building blocks of the cell. Some of the vital types of plastids and their functions are stated below:

Leucoplasts 

• They are found in non-photosynthetic tissues of plants. They are used for the storage of protein, lipid and starch.

Chloroplasts 

• It is an elongated organelle enclosed by phospholipid membrane. The chloroplast is shaped like a disc and the stroma is the fluid within the chloroplast that comprises a circular DNA. Each chloroplast contains a green coloured pigment called chlorophyll required for the process of photosynthesis. The chlorophyll absorbs light energy from the sun and uses it to transform carbon dioxide and water into glucose.

Chromoplasts 

• They are heterogeneous, coloured plastid which is responsible for pigment synthesis and for storage in photosynthetic eukaryotic organisms. Chromoplasts have red, orange and yellow coloured pigments which provide colour to all ripe fruits and flowers.

Chromoplasts 

They are heterogeneous, coloured plastid which is responsible for pigment synthesis and for storage in photosynthetic eukaryotic organisms. Chromoplasts have red, orange and yellow coloured pigments which provide colour to all ripe fruits and flowers.

Golgi Apparatus 

They are found in all eukaryotic cells which are involved in distributing synthesized macromolecules to various parts of the cell.

Ribosomes 

They are the smallest membrane-bound organelles which comprise RNA and protein. They are the sites for protein synthesis, hence, also referred to as the protein factories of the cell.

Mitochondria 

They are the double-membraned organelles found in the cytoplasm of all eukaryotic cells. They provide energy by breaking down carbohydrate and sugar molecules, hence they are also referred to as the “Powerhouse of the cell.”

Lysosome 

Lysosomes are called suicidal bags as they hold digestive enzymes in an enclosed membrane. They perform the function of cellular waste disposal by digesting worn-out organelles, food particles and foreign bodies in the cell.

Plant Cell Types 

Cells of a matured and higher plant become specialized to perform certain vital functions that are essential for their survival. Few plant cells are involved in the transportation of nutrients and water, while others for storing food. The specialized plant cells include parenchyma cells, sclerenchyma cells, collenchyma cells, xylem cells and phloem cells. Following are some of the different types of plant cells:

Collenchyma Cells 

They are hard or rigid cells, which play a primary role in providing support to the plants when there is restraining growth in a plant due to lack of hardening agent in primary walls.

Sclerenchyma Cells 

These cells are more rigid compared to collenchyma cells and this is because of the presence of a hardening agent. These cells are usually found in all plant roots and mainly involved in providing support to the plants.

Parenchyma Cells 

Parenchyma cells play a significant role in all plants. They are the living cells of plants, which are involved in the production of leaves. They are also involved in the exchange of gases, production of food, storage of organic products and cell metabolism. These cells are typically more flexible than others because they are thinner.

Xylem Cells 

Xylem cells are the transport cells in vascular plants. They help in the transport of water and minerals from the roots to the leaves and other parts of the plants.

Phloem Cells 

Phloem cells are other transport cells in vascular plants. They transport food prepared by the leaves to different parts of the plants.

Plant Cell Functions 

Plant cells are the building blocks of plants. Photosynthesis is the major function performed by plant cells. Photosynthesis occurs in the chloroplasts of the plant cell. It is the process of preparing food by the plants, by utilizing sunlight, carbon dioxide and water. Energy is produced in the form of ATP in the process. A few plant cells help in the transport of water and nutrients from the roots and leaves to different parts of the plants.

Animal Cell

We are aware of the fact that the cell is the structural and fundamental unit of life. It is also the smallest and the most basic biological unit of living organisms. On the basis of the cellular organization, cells are further classified as eukaryotic and prokaryotic. Plant cells and animal cells fall under the eukaryotic category.

Animal Cell Definition

“An animal cell is a type of eukaryotic cell that lacks a cell wall and has a true, membrane-bound nucleus along with other cellular organelles.”

Explanation

Animal cells range in size from a few microscopic microns to few millimetres. The largest known animal cell is the ostrich egg, which can stretch over 5.1 inches across and weighs about 1.4 kilograms. This is in stark contrast to the neuron in the human body, which is just 100 microns across.
The shape of animal cells also varies, with some being flat, others oval or rod-shaped. There are also more intriguing shapes such as curved, spherical, concave and rectangular. Most of the cells are microscopic in size and can only be seen under the microscope.
As stated before, animal cells are eukaryotic cells with a membrane-bound nucleus. Furthermore, these cells exhibit the presence of DNA inside the nucleus. They also comprise other membrane-bound organelles and cellular structures which carry out specific functions necessary for a cell to function properly.

Animal Cell Diagram

The diagram given below depicts the structural organization of the animal cell. The various cell organelles present in an animal cell are clearly marked in the animal cell diagram provided below.
Animal cell diagram detailing the various organelles

Though this animal cell diagram is not representative of any one particular type of cell, it provides insight into the primary organelles and the intricate internal structure of most animal cells. Furthermore, it is easy to distinguish between a plant and animal cell diagram just by inspecting the presence or absence of a cell wall.

Animal Cell Structure

Animal cells are generally smaller than plant cells. Another defining characteristic is its irregular shape. This is due to the absence of a cell wall. But animal cells share other cellular organelles with plant cells as both have evolved from eukaryotic cells.

A typical animal cell comprises the following cell organelles:

➤ Cell Membrane 

• A thin semipermeable membrane layer of protein and fats surrounding the cell. Its primary role is to protect the cell from its surrounding. Also, it controls the entry and exit of nutrients and other microscopic entities into the cell.

➤ Nuclear Membrane 

• It is a double-membrane structure that surrounds the nucleus. It is also referred to as the nuclear envelope.

➤ Nucleus 

• It is an organelle that contains several other sub-organelles such as nucleolus, nucleosomes and chromatins. It also contains DNA and other genetic materials.

➤ Centrosome 

• It is a small organelle found near to the nucleus which has a thick centre with radiating tubules. The centrosomes are where microtubules are produced.

➤ Lysosome (Cell Vesicles) 

• They are round organelles surrounded by a membrane and comprising digestive enzymes which help in digestion, excretion and in the cell renewal process.

➤ Cytoplasm 

• A jelly-like material which contains all the cell organelles, enclosed within the cell membrane. The substance found within the cell nucleus, contained by the nuclear membrane is called the nucleoplasm. 

➤ Golgi Apparatus 

• A flat, smooth layered, sac-like organelle which is located near the nucleus and involved in manufacturing, storing, packing and transporting the particles throughout the cell.

➤ Mitochondrion 

• They are spherical or rod-shaped organelles with a double membrane. They are the powerhouse of a cell as they play an important role in releasing energy.

➤ Ribosome 

• They are small organelles made up of RNA-rich cytoplasmic granules, and they are the sites of protein synthesis.

➤ Endoplasmic Reticulum (ER) 

• This cellular organelle is composed of a thin, winding network of membranous sacs originating from the nucleus.

➤ Vacuole 

• A membrane-bound organelle present inside a cell involved in maintaining shape and storing water, food, wastes, etc.

➤ Nucleopore 

• They are tiny holes present in the nuclear membrane which are involved in the movement of nucleic acids and proteins within the cell.

Animal Cell Types

There are numerous types of animal cells, each designed to serve specific functions. The most common types of animal cells are:

➤ Skin Cells 

• Melanocytes, keratinocytes, Merkel cells and Langerhans cells

➤ Muscle Cells 

• Myocyte, Myosatellite cells, Tendon cells, Cardiac muscle cells

➤ Blood Cells 

• Leukocytes, erythrocytes, platelet

➤ Nerve Cells 

• Schwann cell, glial cells etc

➤ Fat Cells 

• Adipocytes

Points to Note About Animal Cell

The cell is the structural and functional unit of life. These cells differ in their shapes, sizes and their structure as they have to fulfil specific functions. Plant cells and animal cells share some common features as both are eukaryotic cells. However, they differ as animals need to adapt to a more active and non-sedentary lifestyle. Furthermore, animals need to acquire their own food, therefore, they do not possess any of the specialized cell organelles such as chloroplasts.

Difference Between Plant cell and Animal cell

The cell is the fundamental unit of life. All the life activities are carried out by cells. The organisms are classified based on the number of cells present in them. Unicellular organisms are single-celled, while multicellular organisms have a large number of cells. Unicellular organisms are believed to be one of the earliest forms of life on earth. Eventually, more complex multicellular organisms evolved from these unicellular life forms over the aeons.
Multicellular organisms have specialized cells with complicated cell organelles, which unicellular organisms typically lack. In an ecosystem, plants have the role of producers while animals have taken the role of consumers. Hence, their daily activities and functions vary, so do their cell structure. Cell structure and organelles vary in plants and animals, and they are primarily classified based on their function. The difference in their cell composition is the reason behind the difference between plants and animals, their structure and functions.
Each cell organelle has a particular function to perform. Some of the cell organelles are present in both plant cell and the animal cell, while others are unique to just one. Most of the earth’s higher organisms are eukaryotes, including all plant and animals. Hence, these cells share some similarities typically associated with eukaryotes. For example, all eukaryotic cells consist of a nucleus, plasma membrane, cytoplasm,  peroxisomes, mitochondria, ribosomes and other cell organelles.

Differences Between Plant Cell and Animal Cell

Diagram showing the Difference between Plant cell and Animal cell

As stated above, both plant and animal cells share a few common cell organelles, as both are eukaryotes. The function of all these organelles is said to be very much similar. However, the major differences between the plant and animal cells, which significantly reflect the difference in the functions of each cell.

The major differences between the plant cell and animal cell are mentioned below:

Conclusion

Both plant and animal cells comprise membrane-bound organelles, such as endoplasmic reticulum, mitochondria, the nucleus, Golgi apparatus, peroxisomes, lysosomes. They also have similar membranes, such as cytoskeletal elements and cytosol. The plant cell can also be larger than the animal cell. The normal range of the animal cell varies from about 10 – 30 micrometres and that of plant cell range between 10 – 100 micrometres.