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Plants are unique among eukaryotic organisms in that their cells are made up of membrane-enclosed nuclei and organelles that enable them to produce their own food. The green pigment chlorophyll allows plants to use sunlight to convert carbon dioxide and water into carbohydrates, chemicals, and sugars that can be used as food. Plant cells have also maintained a unique defensive structure passed on by prokaryotic ancestors. Both simple plant cells share the same motif as normal eukaryote cells, but lack flagella and centrioles as animal cells (Gunning and Steer). The plant cells also do have specialized components which include central vacuole, rigid cell wall, chloroplasts, and plasmodesmata.
The cell wall is a very rigid and tough layer which bounds plant cells. Its main role is to supply the needed firmness against mechanical stress. The cell also provides the cell with the restricted plasticity that stops the cell from bursting as a result of the turgor pressure. Also, given that the cell walls are well cutinized, they are able to stop water loss and help with communication between the cells. The following list provides some of the other functions of the cell wall (Stille, 13);
Helps in osmotic-regulation
Provide structural support
Give the cell a definite structure and shape
Aids in the diffusion of gases out and in of the cell
Separate the interior of the cell from the external environment
The plant has a cell wall made up of three layers which includes middle lamella, primary cell wall and secondary cell wall. Even though all plants cells have the primary and the middle lamella, not all of contain the secondary cell wall. The middle lamella has polysaccharides referred to as pectins, which assist in cell adhesion by assisting the cell walls of the adjacent cells to bind together. The primary cell wall is made up of cellulose microfibrils that are present within the gel-like matrix of the hemicelluloses fibres. The secondary cell wall is formed when primary cell wall stopped growing or dividing. It supports and strengthens the cell.
The chloroplasts are the cellular organelles found in green plants and some of the eukaryotic organisms (Stille 6). Its roles main role is to carry out the process of photosynthesis by absorbing and converting it into sugar and also producing free energy that is kept in the form of NADPH and ATP through the process photosynthesis. This is the plant component that is found in higher plants and are generally planoconvex or biconvex shaped. Different plants have different shapes of the chloroplasts and they vary from filamntous saucer-shaped, spheroid shaped or ovoid or discoid shaped (Wise and Hoober). The chloroplasts are vesicular and they have a colorless center. Some of them have a shape of a club, i.e. thin middle zone and the ends which are full of chlorophyll, hence making them swell. The average size of the chloroplasts varies from plant to plant, but the average size is 1-3 Âµ in thickness and 4-6 Âµ in diameter. They also have a double membrane bound organelles, made up of the inner membrane and the outer membrane.
The following are the major functions of the chloroplasts
Making food for the plant through the process of photosynthesis
Helping in the light reaction process which takes place on the membrane of thylakoids
It also uses the potential energy of the hydrogen ions to produce energy
It produces NADPH2 molecules and also oxygen through the photolysis of the water
Vacuoles are the storage bubbles that are found in the cells. They are responsible for storing food and other types of nutrients a cell requires to survive. In addition, vacuoles store water and even waste products in order for the rest of the cell to be protected from any form of contaminations. In storing water, the vacuoles maintain an interior hydrostatic force of the plant cell. The pressure within the plant cells generated by vacuoles make the plant to be able to hold its flowers and leaves(Gunning and Steer). And eventually those waste products would be sent out of the cell. The vacuole structure is a bit fairly simple. It has a membrane that surrounds a collection of fluids. The fluids has waste products or nutrients. Plants also use vacuoles in storing water. The tiny water bags assist in supporting the plant.
Vacuoles have an acidic pH internally, which allows it to denature the misfolded proteins which are transferred to vacuole from the cytoplasm. The structure of the vacuole in most cases complements its functions. Most of the mature and grown plant cells have one large vacuole which is bounded by structures called tonoplast. It is an active and a vibrant membrane of the plant cell structure. The vacuole also contains vacuole sap which has different digestive enzymes which are able to destroy the cell. The tonoplast also assist in maintaining the turgor pressure which helps in support the leaves and flowers to the plant.
The Bryophytes are non non-vascular plants which produce an embryo. Its life history includes a dominant Gametophytes or haploid stage. These types of plants are ancient and diverse group of the non-vascular plants. They are made up of three taxonomic groups; liverworts (Marchatiophyta), hornworts (Anthocerotophyta) and mosses (Bryophyta) which have managed to evolve separately. The bryophytes are not considered to have facilitated the rise to the vascular plants, but they are seen as the earliest land plants. Just like the other land plants, Bryophytes have evolved from green algal ancestors, which are related to Charophytess. The majority of the bryophytes have creeping or erect stems and small leaves, but the hornworts and liverworts have flat thallus and with no leaves (Cummings and Larry). Globally, there are almost ten thousand species of mosses, seven thousand species of liverwort and two hundred species of hornworts. On the other hand, Charophyceae is a particular class of the charophyte green algae. Some of the botanists include chlorophyte and Charophyceae in the plant kingdom. Charophyceae is found within the Streptophyta class, and at present Charophyceae is treated under the division of the Charophyta, with Charophyta being the distinct division. Most of the Charophyceae such as Spirogyra are living in freshwater habitats, but some also live in moist soil in the terrestrial habitats. Unlike Bryophytes, Charophyceae is able to live as colonies, single cells, or unbranched or branched filaments and they come in various shapes.
The distinguishing characteristics of Bryophytes and charyophyceae include lifestyle; Charophytes have a two-stage life cycle, which involves a haploid stage and antheridia stage. On the other hand Bryophytes have its stages dominated by gametophyte stage, and that it Sporophytes are not branched and they lack vascular tissues, while the Charophytes has vascular tissues. The other characteristics which make Bryophytes different from Charophytes with regard to life cycle include;
The gametophyte is the dominant generation
The sporophyte is dependent, smaller on the gametophyte but it is still multicellular
The fertilization process is dependent on the free water carrying sperm from the antheridia to the archegonia
The bryophytes zygote and the second embryo are retained on the gametophyte, later the bryophyte embryo develops into the multicellular 2n sporophyte. The tissues of the bryophytes gametophyte and sporophytes are produced by the apical meristem.
The other Difference between Algae (Charyophyceae) and the Mosses (Bryophytes)
The phylum of algae is Phaeophyta, Rhodophyta or Chlorophyta of the kingdom Protoctista, while the mosses fit into the class Musci of the Phylum Bryophyta.
Algae has nobody differiation into stems, roots and roots while mosses have some kind of differentiation into leaves and stems.
Rhizoids fix Mosses on to the ground by the while algae are fixed to the substratum by holdfast
There is no alteration of the population in the algae, but there is alteration of population in mosses
There are no unicellular mosses, but there are unicellular algae
Bryophytes gametangia always have an outer layer made up of sterile jacket cells, which the Charyophyceae do not have.
The Charophytes are existing group of the green algae, which most closely relate to the land plants. Around five hundred million years ago, Charophytes ancestors are believed to emerge onto the land and gave rise to the terrestrial plants. The recent biochemical, molecular and the cell-biology based research has shown that some of the extant Charophytes do have remarkable similarities to the terrestrial plants (Cummings and Larry). The land plants and the Charophytess share some enzymes that the rest of the green algae lack. These types of enzymes assist the cell in holding organic products which it does not want to lose. They are present in the peroxisomes of the charaphytes and the plants, but not in the algae.
Also, proteins which prepare cellulose in both land plants and the Charophytess are assembled in circles, but in the other algae, they are positioned in lines. The cell division of plants is more similar to the Charophytess cell division than that of the other algal cell division. The shape of the sperm of the land plants is more like the sperms of the Charophytes than of the other algae. In addition, some of the Charophytess have a protein in their own cell walls, referred to as sporopollenin which were present in the earliest land plants (Shmoop University). The Charophytess also have DNA, which is closer to the land plants than the other green algae. In summary some of the traits which plants have in common with the Charophytes includes; rings of the cellulose tasked with the synthesis of protein, the structure of the flagellated sperm and the formation of the phragmoplast during the process of cell division. A comparison of both chloroplasts and nuclear genes indicate that Charophytes are the closest living relatives of the terrestrial plants. It is these observations which provide good evidence that the plants and the Charophytess share one common ancestor.
Cummings, Robert J. and Larry Jon. Friesen. Plant Diversity. Hawaii: Kailua Kona, 2017.
Gunning, Brian E. S. and Martin W. Steer. Plant Cell Biology: Structure and Function. New
York: Jones & Bartlett Learning, 2006.
Shmoop University. Plant Evolution and Diversity. 2016,
http://www.shmoop.com/plant-evolution-diversity/plant-predecessors.html, Accessed 3 February 2017
Stille, Darlene R. Plant Cells: The Building Blocks of Plants. Washington: Capstone Publishers,
Wise, Robert R. and J. Kenneth Hoober. The Structure and Function of Plastids. London:
Springer Science & Business Media, 2007.
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