Plant Cell Structure

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 construction motif as the normal eukaryote cell, but lack lysosomes, flagella, and centrioles (Gunning and Steer). The plant cells also do have a number of specialized components which include central vacuole, rigid cell wall, chloroplasts and plasmodesmata.

Cell Wall

It is a very rigid and tough layer which bounds plant cells. Its main role is to provide the needed rigidity or protection against mechanical stress and infection. The cell also provides the cell with the limited 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 in communication between the cells. The following list provides some of the other functions of the cell wall;

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 outer environment

Cell Wall Structure

The cell wall of a plant is made up of three layers. From the outermost layer, the layers are identified as the middle lamella, primary cell wall and secondary cell wall. While all plants cells have the primary and middle lamella, not all have the secondary cell wall. The middle lamella is the outer cell wall that 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 contained within the gel-like matrix of the hemicelluloses fibres and the pectin polysaccharides. The secondary cell wall is formed when the primary cell wall stopped growing or dividing. It supports and strengthens the cell.

Chloroplasts

The chloroplasts are the cellular organelles found in green plants and some of the eukaryotic organisms. Its roles main role is to carry out the process of photosynthesis by absorbing and converting it into sugar molecules and also producing free energy that is stored in the form of NADPH and ATP through photosynthesis.

Chloroplast Structure

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. 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 µ in thickness and 4-6 µ in diameter. They also have a double membrane bound organelles, made up of the inner membrane and the outer membrane.

Chloroplasts Function

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

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 internal hydrostatic pressure of the plant cell. By providing pressure within the plant cells, vacuoles make the plant to be able to support its flowers and leaves. 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, this allows it to denature the misfolded proteins which are transferred to the 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 surrounded by a structure called tonoplast. It is a very active and a dynamic 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.

Distinguishing Characteristics of the Bryophytes Compared

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. Globally, there are almost ten thousand species of mosses, seven thousand species of liverwort and two hundred species of hornworts.

Difference between Chlorophyta and Bryophyta

All the organisms are grouped into five main kingdoms, which include Monera, Fungi, Plantae, Animalia and Protoctista.

The distinguishing characteristics of Bryophytes and charyophyceae

Character Bryophyta Charyophyceae Protonema Filamentous, forming a lot of buds Globose, forming only one bud also Gametophyte form Has a leafy shoot Only simple thallus Arrangement of leaves The leaves are arranged in spirals Has no leaves Form of the leaf The leaves are undivided Has no leaves Special Organelles Has no organelles Single plastids which have pyrenoids Water conducting cells It is present in both sporophytes and gametophytes It is absent Stomates It is present in the sporophyte capsule It is present in both gametophyte and sporophyte Capsule Complex with the operculum, neck and theca of the fixed size They are undifferentiated and horn shaped and they are growing continuously from the basal meristem Seta Photosynthetic and emergent from the gametophyte early in the development Absent Gametangial position Apical clusters Sunken in the thallus and scattered

Key features of the Bryophytes Life cycle

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 other Difference Between Algae (Charyophyceae) and Mosses (Bryophytes)

The algae belong to the phylum Phaeophyta, Rhodophyta or Chlorophyta of the kingdom Protoctista, whereas the mosses belong to the class Musci of the Phylum Bryophyta of the kingdom Plantae.

Algae have no body differiation into stems, roots and roots while mosses have some kind of differentiation into leaves and stems.

Mosses are fixed to the ground by the rhizoids 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

The reasons Charyophytes are thought to be the ancestors of the plants

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. The land plants and the Charophytess share some enzymes that the other green algae do not have. These enzymes assist the cell to hold onto organic products which it does not want to lose. The enzymes are found in the peroxisomes of the charaphytes and the land plants, but not on the other algae. Also, the proteins which make cellulose in both land plants and the Charophytess are arranged in circles, but in the other algae, they are arranged 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. 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 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.

Works Cited

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. 3 February 2017 .

Stille, Darlene R. Plant Cells: The Building Blocks of Plants. Washington: Capstone Publishers, 2006.

Wise, Robert R. and J. Kenneth Hoober. The Structure and Function of Plastids. London: Springer Science & Business Media, 2007.