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Eukaryotic Cells

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Eukaryotic Cells

A eukaryotic cell is a compartmentalised cell that contains organelles such as a nucleus and mitochondria.

There are four main types of eukaryotic cells: plant, animal, fungi and protist cells. In this article, we will mainly cover animal and plant cells. Unlike prokaryotes which do not have a nucleus, all eukaryotes have a nucleus.

Differences between prokaryotic and eukaryotic cells

As mentioned, the main differences between eukaryotic cells and prokaryotic cells are that eukaryotes have a nucleus. Instead of a nucleus, prokaryotes have loose chromosomes that contain DNA information. Bacteria and other cells can also contain plasmids - small, circular DNA. Interestingly, these are separate from the main chromosome and will replicate independently. Almost like a mind of its own! Plasmids often provide a genetic advantage - this is where antibiotic resistance can occur. In addition, cells can exchange these plasmids via bacterial conjugation. Prokaryotes are "smart" with their adaptations.

Bacterial conjugation: DNA plasmids are transferred between two bacteria via a pilus (hair-like appendage).

Below you will find a table showing the differences between eukaryotic and prokaryotic cells, also known as the ultrastructure or the composition of eukaryotic cells.

Table 1. Summary of differences between prokaryotic and eukaryotic cells.

Prokaryotic cells

Eukaryotic cells
Size
1-2 μm
Up to 100 μm
Compartmentalisation
No
Membranes that separate different organelles of the cell
DNA
Circular, in the cytoplasm, no histones
Linear, in the nucleus, packed with histones
Cell membrane
Lipid bilayer
Lipid bilayer
Cell wall
Yes
Yes
Nucleus
No
Yes
Endoplasmic reticulum
No
Yes
Golgi apparatus
No
Yes
Lysosomes & Peroxisomes
No
Yes
Mitochondria
No
Yes
Vacuole
No
Some
Ribosomes
Yes
Yes
Plastids
No
Yes
Plasmids
Yes
No
Flagella
Some
Some
Yes
Yes

Eukaryotic cell

As you already know, eukaryotic cells are "defined" by the presence of a nucleus. A nuclear membrane surrounds the nucleus. The nucleus contains the cell's genetic information - which is contained within the chromosomes; however, mitochondria and chloroplasts have their own DNA.

Typical eukaryotic cell size

The size of eukaryotic cells varies quite a bit. Eukaryotic cells are usually bigger than prokaryotic cells ranging from 10–100 µm, making them up to 1000 times bigger than prokaryotic cells. When referencing cell size, we are referring to the diameter. Animal cells are usually up to 30µm, while plant cells can reach 100µm.

Cell's nucleus

Let's take a closer look at the nucleus, cell nuclei store cell's DNA and control cell's activities. The nucleus is enclosed by a double nuclear membrane continuous with the endoplasmic reticulum. Inside the nucleus, a nucleolus plays a key role in the transcription and processing of rRNA (ribosomal RNA).

See our article on cell structure to learn more about different organelles in cells.

The nucleus is the most noticeable feature in a microscope because it is the biggest, approximately 10-20 micrometres.

Structural adaptations of the nucleus

  • The nuclear envelope is the double membrane surrounding the nucleus. The outer part of the membrane is directly attached to the endoplasmic reticulum.

  • The nuclear pores act as a passageway for larger molecules, such as the messenger RNA (mRNA). There are 3000 nuclear pores in a nucleus, each with an approximate diameter of 40 to 100 nm.

  • The chromosomes are composed of DNA bound to proteins called histones

  • A nucleoplasm is similar to a cell's cytoplasm. It is a jelly-like liquid surrounding the nucleolus

  • Within the nucleus, the nucleolus is where ribosomal RNA is produced. The nucleolus is also where ribosomes are assembled. Cells can have more than one nucleus.

Figure 1

Plant and animal cells

Below you will find a diagram of two eukaryotic cells - one is a plant, and the other is an animal cell. Note the difference in structures of these two cells.

Example differences between plant and animal cells:

  • Size: Animal cells tend to be smaller than plant cells.
  • Shape: Due to a cell wall in plant cells, they tend to be a cube or a rectangle in shape. Animal cells do not have cell walls and thus appear in irregular shapes.
  • Cilia: Cilia, microtubules that help with cell movement, are found in animal cells but not in plant cells.
  • Plastids: Plant cells have chloroplasts which are essential for photosynthesis.
  • Lysosomes: A membrane-bound organelle containing digestive enzymes are usually only present in animal cells. Lysosomes break down excess or old/worn down cell parts. Vacuole in plant cells takes care of this.
  • Vacuole: The plant contains a large vacuole that takes up most of the space in the cell. It has many functions, but the primary function is to maintain the hydrostatic pressure of the cell. Animal cells can also contain vacuoles; however, they are much smaller and mainly help isolate waste from the cell.

Table 2. Summary of the main differences between animal and plant cells.

Plant Cell

Animal cell

Size

10 - 100 micrometres

10 - 30micrometres

Shape

regular

irregular

Nucleus

yes

yes

Mitochondria

yes

yes

Ribosomes

yes

yes

Golgi Apparatus

yes

yes

Cytoskeleton

yes

yes

Cell membrane

yes

yes

Endoplasmic reticulum

yes

yes

Center vacuole

yes

no

Chloroplasts

yes

no

Cell wall

yes

no

Vacuoleyesyes, but smaller and different function
Cilianoyes

Figure 2

Figure 3

Shape and size of a cell

The animal cell is depicted as round. However, we know that the membrane around animal cells is fluid and mostly made of phospholipids, meaning that the shape of the animal cell is irregular. A plant cell has a more restricted shape similar to a cube/rectangle due to the presence of a cell wall.

Figure 4

Plant organelles

Let's take a look at what A level biology can teach us about plant organelles.

Chloroplasts

Chloroplasts represent another notable distinction between a plant and animal cell. Similar to mitochondria, they have their own DNA and ribosomes. Both mitochondria and chloroplasts are found in plant cells.

Chloroplasts are sites where photosynthesis occurs. The chloroplast has the following structural features:

  • Chloroplast envelope: Like the nuclear envelope, chloroplasts have a double membrane.

  • Grana: stacks of disc-like structures found inside the chloroplasts. These discs are called thylakoids. This is where chlorophyll is found, which is the pigment that gives plants their green colour. It is also the photosynthetic pigment of plant cells.

  • Stroma: is the place where the second part of photosynthesis takes place. In this fluid-filled space, there are a lot of enzymes. These are needed to synthesise sugars.

Vacuoles

While some animal cells can have multiple small vacuoles, the single vacuole in plant cells is much larger and can take up as much as 90% of a plant cell.

The vacuole in animal cells can store and digest substances.

In plants, the vacuole has multiple functions:

  • Water storage: A plant's ability to store water is crucial to surviving times of drought and makes it susceptible to forces such as osmosis, which takes water from the cell when in a salty environment and lets it into the cell when in pure water (distilled water).

Xerophytes are plants adapted to dry habitats. Xerophytes possess a series of adaptations that help them survive in these conditions. This involves thick waxy cuticles to prevent water loss, increased water storage, rolling of the leaves and others.

  • pH level regulation: Plant enzymes have a very broad pH range, ranging from 3.0 to 10.0. This range is achieved by the vacuole, which pumps protons (H+ or H3O+) into the cytoplasm, which lowers the pH in the plant cell, making it acidic.
  • Turgor maintenance: As mentioned before, the size of the vacuole is controlled by osmosis. When the plant cell has reached its maximum water storage capacity, it is called turgid.

Turgor: the pressure caused by the fluid in the cell and is regulated by the vacuole.

Imagine a crunchy piece of salad; this is high turgor pressure; when the pressure is low, the salad gets soft and limp. This phenomenon happens when there is not enough fluid in the cell, up to 90% found in the vacuole. Putting a soggy piece of salad in water can make it crunchy again by elevating the turgor.

Cell wall

Plant cells have cell walls. The cell wall of plants consists of cellulose. The cell wall is vital for tensile strength and protection against osmotic stress, i.e., it does not allow the cell to burst.

Prokaryotes, fungi and some protists also have cell walls; however, they have different structural components.

  • Protists such as algae have polymers (substances consisting of large molecules) similar to cellulose in plants.
  • Fungi cell walls contain chitin.
  • Prokaryote cell walls are made up of peptidoglycan.

Additionally, the cell wall is responsible for water movement throughout the plant through plasmodesmata (membrane-lined pores that connect adjacent cells). Water can move through symplast and apoplast pathways. Symplast pathways occur through the cell wall, while apoplast through the cytoplasm.

Types of specialised eukaryotic cells

As previously mentioned, plant cells and animal cells are both eukaryotic cells. While they seem like very different organisms at first glance, they have some similarities. The most profound is the presence of specialised cells that have similar characteristics. For example, the skin cells of an animal and epidermal cells of a plant are, in both cases, the outermost layer that protects the underlying structures.

All stem cells can develop into any specialised cell. An early embryo contains these types of cells, which differentiate into different cells in the body. When the embryo is fully developed, stem cells can still be found in the human body in small numbers.

You have probably heard about stem cells from bone marrow. Stem cells in the bone marrow can differentiate into red blood cells, white blood cells and platelets. Adult stem cells have also been previously found in the brain, blood vessels, skeletal muscle, heart and even teeth.

Stem cells in a plant can be found in meristems of the plant, which are located in roots and shoots.

Here is a list of plant and animal cell types for you to compare. We will first look at types of plant cells and then cat types of animal cells in direct comparison.

Examples of specialised animal cells

  • Skin cells: Outer layer for protection.

  • Blood cells: Oxygen transport and essential for the immune system.

  • Muscle cells: For strength and movement.

  • Fat cells: For energy storage and source.

  • Nerve cells: Present in the whole body to send and receive signals from and to the brain.

  • Reproductive cells: Sperm and ovum (egg cells) are needed to produce offspring.

Cells can often differentiate further. For example, above mentioned blood cells can differentiate into white blood cells of various types and red blood cells.

Examples of specialised plant cells

  • Parenchyma cells: For synthesis and storage of materials.

  • Collenchyma cells: Shock absorbing also have a support function in young plants.

  • Sclerenchyma cells: Structural support.

  • Xylem cells: Cells for structural support and transportation of water within the plant. When the water in the mesophyll cells evaporates (plant leaves), it is replaced by water transported by the xylem cells.

  • Phloem cells: Transportation of nutrients.

  • Reproductive cells: For the production of offspring (plants often have both male and female produce cells that together produce seeds).

  • Epidermal cell: Tightly packed cells that make up the outer layer of a plant, similar to our skin making up our body's outer, protective layer. Root hair cells are a type of epidermal cell in the root region. They exchange material with the outside world and absorb water and minerals.

Specialisation and organisation of cells

Eukaryotes are mostly multicellular organisms (with some exceptions, including phytoplankton, zooplankton, yeast and others).

The first step in understanding how multicellular structures work is to understand single cells and their organelles. As each organelle performs a specific function, a cell's type can be determined by the number and the size of the organelles found inside. An example would be cells with many mitochondria, which metabolise a lot of ATP for energy - like muscle cells.

Multicellular organisms require cells to perform specific tasks. Cells are tailored to achieve this by having a specific structure and set of organelles. Despite the fact that all cells have the same DNA sequence at the start, only specific genes are expressed in specific cells. For example, muscle cells have a different gene expression than skin cells.

Some cells lose their ability to multiply after differentiating. Others, however, keep that ability and are able to regenerate tissue if there was a lesion, for example. As in the more general statement "all cells come from another cell" that applies to unicellular organisms, all cells within a multicellular organism come from another cell.

Cells can be grouped into tissues where they perform a similar function, such as muscular tissue. Organs are constructed from groups of tissues. For example, the heart is composed of various tissues, such as muscle and epithelial tissue. Organ systems are made up of organs that work together, such as the cardiovascular system, which is made up of the heart and blood vessels.

Eukaryotic Cells - Key takeaways

  • A eukaryotic cell is a compartmentalised cell that contains organelles such as a nucleus and mitochondria.
  • Animal and plant cells are both eukaryotic; however, they have organelles found in one but not the other, such as cell walls and chloroplasts in plants.
  • Stem cells can differentiate into any cell. They can be found in meristems of plants and embryonic cells in animals. Adult stem cells have a more limited capability of differentiation.
  • Cells organise into groups, tissues, organs and organ systems to carry out an organism's function.

Frequently Asked Questions about Eukaryotic Cells

Prokaryotes do not have a nucleus, eukaryotic cells have a nucleus and membrane bound organelles

Animal cells 10-30 micrometers, Plant cells 10-100 micrometers

Yes all eukaryotic cells have a nucleus, even if they are unicellular organisms, they are still considered eukaryotes if they have a nucleus 


A cell with membrane bound organelles and membrane bound organelles. They are more complex than prokaryotic cells. They are most commonly found in multicellular organism, such as plants or animals.

Eukaryotic cells can form multicellular organisms in which the cells adapt to do specific functions.

Animals, plants, fungi, protists

Final Eukaryotic Cells Quiz

Question

What main types of eukaryotic cells are there?

 

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Answer

 Animal, Plant, Funghi, Protist

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Question

What organelle gives eukaryotes their name?


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Answer

The nucleus

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Question

What organelles do plant cells have that animal cells do not?

Chloroplasts, cell wall, center vacuole

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Answer

Chloroplasts, cell wall, center vacuole

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Question

What organelle is responsible for photosynthesis?


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Answer

Chloroplasts

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Question

What organelles can produce energy sources?


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Answer

Chloroplasts and mitochondria 

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Question

What is the main function of animal vacuoles?


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Answer

 Storage of substances 

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Question

What are the functions of plant vacuoles?


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Answer

Regulate PH, control size, control turgor 

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Question

Which cell can be bigger, animal or plant?


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Answer

Plant cells can be up to 100 micrometers big, animal cells however can only be up to 30 micrometers.

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Question


What is the cell wall in plants made of?


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Answer

Cellulose, a polysaccharide

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Question

What feature do plant cells and prokaryotic cells share?


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Answer

They both have cell wall

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Question

What plant cells are similar to animal skin cells?


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Answer

Epidermal cells in plants have a similar function to skin cells in animals.

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Question


What type of specialised animal cells are there?


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Answer

Skin cells, muscle cells, nerve cells, fat cells, blood cells and the two different reproductive cells

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Question

What do many specialised cells together form?

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Answer

Specialised cells together form tissues, such as muscle tissue.

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Question

What are plant stem cells also called?


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Answer

Meristematic cells

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Question

What gives a plant cell its rectangular shape?

 

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Answer

The stable cell wall 

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