When you were little you might have liked plants. You liked how they could grow and change and you liked how independent they were. Later in school you might have seen a plant cell under the microscope and were amazed.
The cells of a plant are like miniature factories, building a variety of fabrics to keep the plant alive. One of these substances is called chlorophyll, and it is responsible for absorbing sunlight and converting it into energy.
Plant Cell – Definition
One plant cell (also called eucytes) is, like the animal cell, a eukaryotic cell. Plant cells have a nucleus, unlike prokaryotes, which do not have a nucleus.
The plant cell contains several organelles surrounded by membranes. The organelles are integrated into the basic plasma (also cytoplasm or cell plasma) of the cell. Not all of the individual organelles of the cell are enveloped by membranes, but are free in the basic plasma of the cell. These include the organelles of the cytoskeleton and ribosomes.
Organelles are not organs. Unlike organelles, organs are made up of many cells while organelles are components of a cell!
Plant cell model – structure and components
The following cell organelles can be distinguished:
cytoplasm
The cytoplasm consists of 70% water and 20% protein. It has a consistency similar to a gel due to the high concentration of proteins and protein complexes. The cytoplasm is involved in the vast network of synthesis and degradation of substances, often involving organelles. Furthermore, it is the space of the biosynthesis of ribosomes, the breakdown of glucose, the oxidative cycle of pentose phosphates and the synthesis of many amino acids. It is therefore the most important reaction space for metabolites and ions.
If you centrifuge all sedimentable components of the cytoplasm, you get the cytosol!
cell wall
the cell wall is a characteristic of plant cells which does not contain animal cells. The cell wall has the following functions: protecting the cell, maintaining its shape, preventing excessive inflow of water. In general, the cell wall also opposes gravity.
Compared to a cell membrane, the cell wall is much stronger. The general structure of the cell wall is the same from plant to plant, but its chemical composition can occasionally differ.
Polysaccharide cellulose microfibrils are components of the cell wall of a plant. These are formed by the cellulose synthesizing enzymes and are separated from cells into the extracellular space. There, the cellulose molecules are embedded in a so-called matrix, i.e. a space between the cells that consists of polysaccharides and proteins.
A young plant cell first builds a relatively thin and flexible wall called the primary cell wall. A so-called middle lamella is located between the primary cell walls of neighboring cells. The middle lamella is a thin layer rich in sticky (binding) pectin-class polysaccharides. To a certain extent, the middle lamella holds the neighboring cells together.
As the cell matures and stops growing, it strengthens the cell wall. Some types of plant cell have an additional secondary cell wall located between the plasma membrane and the primary cell wall. The secondary cell wall has a strong and durable matrix because it is stacked in multiple layers. Thus the cell has its firm hold and protection, which is ensured by the cell wall.
For example, wood consists mainly of secondary cell walls. That is why it is extremely stable and does not lose its shape easily.
cellulose
Natural materials, like cellulose, are the main components of the plant’s supporting structure, the cell wall. In addition, carbon is stored in the cellulose.
A molecule of cellulose is an unbranched polysaccharide derived from glucose. The glucose molecule is formed during photosynthesis using the carbon dioxide that has been absorbed. That is why CO₂ is stored in the cellulose. When plants die, they are decomposed by fungi and various bacteria. Cellulose is then broken down into water and carbon dioxide, and energy is released.
cell membrane
the cell membrane consists of a lipid bilayer and various proteins that are located on or in the cell membrane.
The phospholipids of the cell membrane each have a polar, hydrophilic head (water-soluble) and a non-polar, hydrophobic tail (water-repellent).
nucleus
in the nucleus A plant cell contains all of the plant’s genetic information, the chromosomes. The nucleus varies in size depending on the plant species and is surrounded by a nuclear envelope, a double membrane, so that its contents are protected from the cytoplasm.
The cell nucleus also contains the nucleoli, which are essential for the biosynthesis of the ribosomes.
The cell nucleus is interspersed with several nuclear pores. Many nuclear pores form a so-called nuclear pore complex, which plays an important role in regulating the entry and exit of RNAs and some proteins. The nuclear pores are often referred to as so-called «customs stations» because they control the traffic of the cell nucleus.
In addition, the interior of the cell nucleus is lined by so-called nuclear lamina, which represent a network-like meshwork of protein filaments. The nuclear lamina are responsible for keeping the structure and shape of the nucleus stable and protected. The cell nucleus forms a so-called continuum with the ER.
mitochondrion
So-called mitochondria are located in cells that consume a lot of energy.
mitochondria are small cell organelles of cell respiration that are found in the cytoplasm and are surrounded by a double membrane layer. They absorb oxygen and combine energy from the oxidation of nutrient molecules, such as sugars, to produce almost all of the ATP that drives cell activities.
Mitochondria are comparable in size to small bacteria. Similar to bacteria, the mitochondria also have their own genome in the form of a circular DNA molecule. They also have their own ribosomes. The ribosomes are not the same ones that are otherwise found in eukaryotic cells. This is about prokaryotic 70S ribosomes. They also have their own transport RNAs (tRNA).
Today it is generally known that the «ancestors» of today’s mitochondria were eubacteria. The free-living eubacteria processed oxygen. The eubacteria were probably taken up by an anaerobic progenitor cell that cannot utilize oxygen itself. The bacterium escaped digestion by phagocytosis for unknown reasons and evolved in symbiosis with the cell. In exchange for providing energy in the form of ATP, which they made available to the host, the bacteria received nourishment and protection from the cell.
This partnership between a primitive anaerobic predatory eukaryotic cell and an aerobic bacterial cell is thought to have evolved about 1.5 billion years ago when the atmosphere began to oxidize.
plastids
plastids are characteristic organelles of plants. In principle, chloroplasts or chromoplasts that contain pigment can be distinguished from non-pigmented leukoplasts.
In addition to the generally lenticular chloroplasts of higher plants, there are other forms and types of plastids common in plant organs such as the flowers and fruits of vegetative plants. In most cases, a cell contains only one type of plastid.
Chromoplasts synthesize and store red, yellow, and orange pigments in the cells of flowers and fruits. The chloroplasts contain all the pigments including the green pigment chlorophyll. Leucoplasts are non-pigmented organelles that store substances, such as amyloplast, which stores starch.
chloroplasts
chloroplasts Like mitochondria, they are membrane-enclosed organelles found in many eukaryotic cells, especially in the cells of algae and plants. Photosynthesis is carried out in the chloroplasts by converting the sun’s light energy into chemical energy.
You can find more information in the article Photosynthesis by !
Like mitochondria, chloroplasts have their own genome and most likely evolved from symbiotic photosynthetic bacteria taken up by a mitochondrial-containing eukaryotic cell. In addition, the chloroplasts are surrounded by two membranes.
A chloroplast consists of an outer membrane, an inner membrane, thylakoids, ribosomes, grana and a nucleoid. The thylakoid describes the inner membrane system in which the light reaction of photosynthesis takes place. ATP (adenosine triphosphate) and NADPH are formed here. The grana arise from the overlaps of the thylakoids. This means that a granum consists of a stack of thylakoids. There is a particularly high pigment content in a granule. In addition, there are several copies of the plastid DNA in a compact form in the so-called nucleoid.
A eukaryotic cell that has chloroplasts no longer needs to consume other cells for sustenance – it has chloroplasts it inherited for sustenance. Instead of having to search for food now, they have built a dense protective cell around themselves. Plants are autotrophic organisms (≠ heterotrophy) because they are able to absorb inorganic substances and produce organic substances from them. However, they require energy for this process. Plants are so-called photoautotrophic organisms because they need light as an energy source.
Like animal cells, fungi have mitochondria but no chloroplasts. Unlike animal cells, they have a strong cell wall that severely restricts their movement and phagocytosis. Fungi are believed to be scavengers, feeding on nutrient molecules secreted by other cells or released when dead cells are broken down.
ribosomes
ribosomes are complex organelles formed from ribosomal ribonucleic acids (rRNA) and various proteins and consist of two subunits.
The ribosomes are responsible for protein biosynthesis within a cell. Cells that perform many protein biosynthetic processes have a higher number of ribosomes than cells that do not perform many protein biosynthetic processes.
Ribosomes can be free or bound in a cell. This means that they are either free in the cytoplasm or attached to the outer surface of the endoplasmic reticulum (ER) or a nuclear envelope. These ribosomes are structurally identical. However, the resulting proteins of the two types have slightly different functions: Proteins that are formed on free ribosomes, such as enzymes, can…