1.) Compare and contrast the structure of a generalized plant cell, animal cell, and prokaryotic cell. Which features are common to all cells? Which are specific to just prokaryotes, or just plants, or just animals?.

1.    1.)  Compare and contrast the structure of a generalized plant cell, animal cell, and prokaryotic cell. Which features are common to all cells? Which are specific to just prokaryotes, or just plants, or just animals?

A) 

A

Prokaryotic Cells

Prokaryotes were the first organism to evolve on this planet and still retain the simplest cell structure. Prokaryotic cells are generally small, unicellular and are very common. They can be found anywhere – in soil, water, skin, intestines etc. Bacteria are also prokaryotic cells. Thus, theoretically, bacteria are living on our skin as well as in our intestines. It is also important to note that prokaryotic cells do not contain a nucleus.

There are many parts of prokaryotic cells:

• Cell Wall: A layer of peptidoglycan that surrounds the cell and thus protects the cell. The cell wall is always present, and also helps to maintain the cell’s shape and prevent the cell from bursting open.
• Plasma Membrane: The plasma membrane is similar to a cell wall, but much thinner. It is essentially composed of phospholipids, which are pushed up against the inside of the cell wall. The importance of the plasma membrane is that it controls the entry and exit of substances in the cell. Thus, it is partially permeable in order to allow things to travel through it. It also can pump substances in or out with the use of active transport, as well as produce ATP (energy) by aerobic cell respiration.
• Pili: Pili are protein filaments that stick out from the cell wall – they can be pulled out or pulled in by a ratchet mechanism. They are used for cell adhesion as well as when bacteria stick together to form aggregations of cells. Pili also have a communication benefit allowing two cells to exchange DNA during a process called conjugation.
• Ribosomes: Ribosomes are created from RNA, and have the task of synthesizing proteins. They are rather small structures, and are smaller in prokaryotic cells than in eukaryotic cells. They float in the middle of the cell, in the cytoplasm.
• Cytoplasm: The cytoplasm is a fluid the fills the space that the plasma membrane surrounds. It is mainly composed of water but also contains many dissolved substances. The cytoplasm contain many enzymes for the cell as well as the ribosomes – however, it does not contain any membrane-bound organelles. The cytoplasm carries out the chemical reactions of metabolism.
• Nucleoid: A region of the cytoplasm that contains the DNA of the cell, similar to a nucleus. However, unlike a nucleus, the DNA is circular and naked. Additionally, the nucleiod is stain less densely than the rest of the cytoplasm because there are fewer ribosomes and less protein in it. (The total amount of DNA in a prokaryote is much smaller than in eukaryotes).
• Flagella: The flagella are structures protruding from the cell wall, although the base of the organelle is within the cell wall. Using energy, the flagella can be rotated, to ‘propel’ the cell from one place to another. The flagella in prokaryotic cells are solid and inflexible.

Eukaryotic Cells 

Eukaryotic cells have much more complicated structure when compared to prokaryotic cells. Unlike prokaryotes, eukaryotes do have a nucleus, as well as many other organelles in their cytoplasm with a single or double membranes. Different organelles have different functions that they do for the cell.

There are six important organelles in eukaryotic cells:

• Nucleus: the nucleus in eukaryotes is very important. It is where all the genetic material of the cell is kept – that is to say where DNA is replicated/transcribed as well as where mRNA is modified. The nuclear membrane of the nucleus is also doubled, and contain large amounts of chromatin (uncoiled chromosomes). Often times, these chromatin are present at the edge of the nucleus, thus leaving a densely stained area.
• Rough Endoplasmic Reticulum: The rough endoplasmic reticulum (rER) consists of cisternae which are flattened membrane sac; synthesizes protein through its ribosomes, which are then carried by small membrane sacs (vesicles), which carry the protein to the Golgi apparatus.
• Golgi Apparatus:  Like rER, the golgi apparatus consists of cisternae. However, these cisternae are not as long, are often curved, do not have ribosomes attached and have many vesicles nearby (unlike rER). The main job of the golgi apparatus is to process the proteins brought by the rER and then carry these to the plasma membrane for secretion.
• Lysosomes: Formed from Golgi vesicles, which are spherical with a single membrane. Lysosomes contain high levels of protein; these appear densely stained in electron micrographs. Lysosomes also contain digestive enzymes, which can break down ingested food; organelles; the whole cell.
• Mitochondria: Mitochondria are very important for the cell as they produce ATP (energy) through aerobic cell respiration (can use fat to make ATP). It also has a double membrane; creates structures called cristae; has fluid within called the matrix. The general shape is spherical or ovoid.
• Free ribosomes: Being roughly 20 nm in diameter, free ribosomes synthesize protein, releasing it to work on various parts of the cell (cytoplasm, as enzymes, etc.). They appear as dark granules in the cytoplasm and do not possess a membrane. They are created in the region of the nucleus called the nucleolus.

This is a table comparing the similarities and differences between prokaryotic and eukaryotic cells:

Not only can prokaryotes and eukaryotes be compared, so can animal and plant cells. This is a table comparing plant and animal cells:

A,)

EXAMPLE

Difference between Plant and Animal cells

The differences between Plant and animal cells are as follows

Characteristic	Plant cells	Animal cells
Plastids	Yes	No
Cell wall	Yes	No
Large central vacuole	Yes	No
Centrosome and Centrioles	No	Yes
Glyoxysomes	Yes	No

a.

	Animal cell		Plant cell
i.	Animal cells are smaller in size.	i.	Plant cells are comparatively larger.
ii.	They lack a cell wall.	ii.	Cell wall is the outermost structure in a plant cell.
iii.	They lack plastids except Euglena.	iii.	Plastids are present in all plant cells.
iv.	Many vacuoles are present and they are smaller in size.	iv.	They have a single large central vacuole.
v.	They have centrioles.	v.	They lack centrioles.

b.

Characteristics	Prokaryotes	Eukaryotes
Size of the cell	Cells are small in size.	Cells vary in size and are generally larger than those in prokaryotes.
Nucleus	No nucleus with a nuclear membrane is present.	There is a well-defined nucleus with a nuclear membrane.
Membrane-enclosed organelles	Organelles having a membrane around them (e.g., mitochondria, plastids) are absent.	Membrane-enclosed organelles are present.
Cell wall	Cell wall is usually present. It is composed of peptidoglycan.	Cell wall is usually present in plant cells. It is composed of cellulose.
Genetic material	The genetic material is present as nucleoid, i.e., a properly defined nucleus is absent.	The genetic material is present inside the well-defined nucleus.

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 can be 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, and so does their cell structure. Cell structure and organelles vary in plants and animals, and are primarily classified based on their function. The difference in their cell composition is the reason behind the difference between plant and animal cells.

Each cell organelle has a particular function to perform. Some of the cell organelles are present in both plant cells and animal cells, while others are unique to just one of them. Most of the earth’s higher organisms are eukaryotes, including all plants 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.

Also Read: Cells

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, there are major differences between plant and animal cells.

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

Plant Cell	Animal Cell
Cell Shape
Square or rectangular in shape	Irregular or round in shape
Cell Wall
Present	Absent
Plasma/Cell Membrane
Present	Present
Endoplasmic Reticulum
Present	Present
Nucleus
Present and lies on one side of the cell	Present and lies in the centre of the cell
Lysosomes
Present but are very rare	Present
Golgi Apparatus
Present	Present
Cytoplasm
Present	Present
Ribosomes
Present	Present
Plastids
Present	Absent
Vacuoles
Few large or a single, centrally positioned vacuole	Usually small and numerous
Cilia
Absent	Present in most of the animal cells
Mitochondria
Present but fewer in number	Present and are numerous
Mode of Nutrition
Primarily autotrophic	Heterotrophic

Conclusion

Both plant and animal cells comprise membrane-bound organelles, such as endoplasmic reticulum, mitochondria, the nucleus, Golgi apparatus, and lysosomes. 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 micro

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 can be 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, and so does their cell structure. Cell structure and organelles vary in plants and animals, and are primarily classified based on their function. The difference in their cell composition is the reason behind the difference between plant and animal cells.

Each cell organelle has a particular function to perform. Some of the cell organelles are present in both plant cells and animal cells, while others are unique to just one of them. Most of the earth’s higher organisms are eukaryotes, including all plants 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.

Also Read: Cells

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, there are major differences between plant and animal cells.

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

Plant Cell	Animal Cell
Cell Shape
Square or rectangular in shape	Irregular or round in shape
Cell Wall
Present	Absent
Plasma/Cell Membrane
Present	Present
Endoplasmic Reticulum
Present	Present
Nucleus
Present and lies on one side of the cell	Present and lies in the centre of the cell
Lysosomes
Present but are very rare	Present
Golgi Apparatus
Present	Present
Cytoplasm
Present	Present
Ribosomes
Present	Present
Plastids
Present	Absent
Vacuoles
Few large or a single, centrally positioned vacuole	Usually small and numerous
Cilia
Absent	Present in most of the animal cells
Mitochondria
Present but fewer in number	Present and are numerous
Mode of Nutrition
Primarily autotrophic	Heterotrophic

Conclusion

Both plant and animal cells comprise membrane-bound organelles, such as endoplasmic reticulum, mitochondria, the nucleus, Golgi apparatus, and lysosomes. 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.