Plant Cells

2021-05-17 15:45:19
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Plant cells are considered to be eukaryotic as the DNA is enclosed in a membrane-bound nucleus. The major distinguishing feature of plant cells is the cell wall that occurs outside the cell membrane CITATION Bru15 \l 1033 (Bruce & Johnson, 2015). The plant cell is further composed of membrane-bound organelles that carry out particular functions for normal cell operation and survival. The organelles have different responsibilities, from producing enzymes and hormones to providing energy for the plant.

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Cell wall

A cell wall is a layer that is rigid that surrounds the cell and found outside the cell membrane. The cell wall contains protein, cellulose, and polysaccharides. The cell wall provides protection and tensile strength against osmotic and mechanical stress CITATION Eld10 \l 1033 (Solomon, Berg, & Martin, 2010). It enables plant cells to have turgor pressure, which is the pressure of the contents of the cell against the cell wall. Cell walls are made of cellulose that has microfibrils that are embedded in polysaccharides. The cell wall further has lignin and suberin that provide strength and prevent water from penetrating respectively.

Chloroplast

Chloroplasts are essential to plant cells part. Plant cells have about 50 chloroplasts, and the number vary based on the function and type of the cell CITATION Bru15 \l 1033 (Bruce & Johnson, 2015). Chloroplasts are disc-like and capture the sun energy assist during the photosynthesis. Chloroplasts are enclosed by an outer and inner phospholipid layer with an intermembrane space. Within the chloroplast is a fluid called stroma that contains DNA molecules. The stroma further has ribosomes, thylakoids, and sub-organelles for photosynthesis CITATION Bru15 \l 1033 (Bruce & Johnson, 2015). The thylakoid discs are arranged in stacks referred to as grana. Within the thylakoid membrane is where the photosynthesis takes place. The thylakoid membrane has light absorbing pigments like carotenoids and chlorophyll that absorb light energy wavelengths CITATION Eld10 \l 1033 (Solomon, Berg, & Martin, 2010). This converts light energy into chemical energy.

Cytoplasm

Cytoplasm is included all the cell contents enclosed by the cell membrane. It is jelly-like and consists enzymes, salts, water and organelles CITATION Bru15 \l 1033 (Bruce & Johnson, 2015). It has a gel like texture and a clear appearance in color. Cytoplasm is essential in dissolving cellular waste and moving materials within the cell.

Endoplasmic Reticulum (ER)

ER involve a network of canals and sacks filled with fluid CITATION Eld10 \l 1033 (Solomon, Berg, & Martin, 2010). They manufacture and transport chemical compounds to be used outside and within the cell. Thus, they carry materials around the cell, it is the cells transport system. The ER is made up of the smooth and rough ER. The rough ER has a rough appearance because it is lined with ribosomes. However, the Smooth ER has no ribosomes and smooth in appearance. The smooth ER synthesizes lipids while the rough ER transports proteins.

Golgi Apparatus

These are stacks that are flattened and look like pancakes CITATION Eld10 \l 1033 (Solomon, Berg, & Martin, 2010). They modify fats and proteins build ups in the ER and prepares them to be exported outside the cell. Thus, it is sometimes referred to as post office of the cell or the packaging organelle as it plays the role of transporting proteins CITATION Bru15 \l 1033 (Bruce & Johnson, 2015).

Mitochondria

The mitochondrion is oblong shaped and occurs in the cytoplasm of plant cells CITATION Bru15 \l 1033 (Bruce & Johnson, 2015). They break down sugar and carbohydrates to provide energy. The mitochondrion is referred to as a powerhouse of the cell. It is important in respiration in the cell.

Nucleus

It is a specialized organelle in the cell that is round and dark, surrounded by a double membrane referred to as nuclear envelope CITATION Bru15 \l 1033 (Bruce & Johnson, 2015). The nuclear envelope has pores that are selectively permeable. The nucleus has DNA on the special strands called chromosomes. The nucleus coordinates the activities of the cell and include cell division, protein synthesis, intermediary metabolism, and growth. Therefore, it is the control center of the cell for reproduction and metabolism.

Plasma Membrane

Plant cells have a plasma membrane, which encloses the content of the cell. It is a bi-lipid membranous layer composed of carbohydrates and proteins. It is also the inner membrane that protects the cell and is surrounded by a cell wall. The plasma membrane is flexible and able to move away and close to the cell wall CITATION Eld10 \l 1033 (Solomon, Berg, & Martin, 2010). The plasma membrane is permeable and controls the movement of molecules out and inside the cell. It also synthesizes and assembles the components of the cell wall. It also provides stability and protects the cells.

Question 2

Primary Growth

Primary growth is the division of cells at the tip of stems and roots CITATION Mic00 \l 1033 (Kent, 2000). As a result, primary tissues are formed leading to primary growth by apical meristems. Primary growth involves the growth of the length of a plant either below or above the ground. Above the ground is the shoot system owing to a small region called the shoot apical meristem. Below the ground is the shoot system due to a small region called the root apical meristem. Apical meristem is essential in cell division or mitosis in the shoot system as opposed to the root system. The growth and elongation of both shoot and root occur because of subsequent elongation of cells and repeated cell division resulting from apical meristems.

Below is the structure of the root tip and leaf primordia

CITATION And05 \l 1033 (Lack & Evans, 2005)

CITATION And05 \l 1033 (Lack & Evans, 2005)Apical meristems occur in the tips of roots behind the root cap and stems. The tissues in plants that lead to primary growth are referred to as primary tissues. During growth, the apical meristems grow and continue dividing by adding more cells to the leaf primordia and root tip. The elongation of stem and root leads to a primary body of the plant. The root and stem apical meristems have delicate cells that must be protected. The root apical meristem is protected by the root cap while the shoot apical meristem is protected through hypocotyl or epicotyl tissues as the seedling emerges from the soil, thus reducing the force on the root tip CITATION Mic00 \l 1033 (Kent, 2000). In monocots, there is coleoptile that forms a protective layer around the shoot. The apical meristem provides embryonic tissue systems referred to as primary meristems: the protoderm forming the epidermis, cortex, procambium that produces the primary phloem and xylem and the ground meristems that comprises parenchyma cells CITATION Mic00 \l 1033 (Kent, 2000). In monocots like corn, intercalary meristems lead to a lengthening of the internode. The elongation of the stem usually takes place after a short period.

Question 3

Secondary Growth

The growth that begins after primary growth is known as secondary growth. Secondary growth is essential in the development of a plant body. Because of the evolution of secondary development and growth, vascular plants form trunks that are thick and treelike. Secondary growth permanent tissues like secondary cortex, xylem, and phloem. Thus, secondary growth is essential in increasing the girth of a body of a plant.

CITATION Bru15 \l 1033 (Bruce & Johnson, 2015)In the woody, stems bark are made of CITATION Mic00 \l 1033 (Kent, 2000) lateral meristems and cork cambium that have cork cells and vascular cambium that produce vascular tissues. Secondary xylem develops into the wood, and the xylem occurs at the outer surface of the wood. In woody plants, young shoots and roots continue developing like in primary growth. The development of stems and roots from primary to secondary growth results from Cambia: cork cambium and vascular cambium. They arise from the primary tissues and are not similar to stem and root. In the root system, between the primary phloem and xylem forms the vascular cambium in the stele. This forms vascular root cambium surrounding the root xylem. In stem system, between the primary phloem and xylem forms the vascular cambium making the tissues be dictyostelic stem CITATION Mic00 \l 1033 (Kent, 2000). In the root and stem, the vascular cambium leads to a tube. As a result of elongation, stem to root axis elongate leading to the development of more cambium. Thus, as the vascular cambium continue dividing cells are formed leading to secondary xylem and phloem, growth at the bark. In dicots, the secondary growth takes place in the cortex and stele CITATION Mic00 \l 1033 (Kent, 2000). The processes take place simultaneously but result from different meristematic tissues. Vascular cambium initiate stele while cortex initiates cork cambium.

Question 4

Water Movement

The transport system in plants involve passages that are tube like and made of vascular tissue. The vascular tissues are phloem and xylem. Water in the root hairs is absorbed through osmosis. The vascular systems run through the stem from the roots and finally to the leaves. Thus, water is transported to the leaves through xylem tubes. Through, transpiration, a plant can lose water at the surface of the leaf. This is the primary cause of the movement of water in the xylem tubes. Transpiration creates a negative pressure or tension on the surface of the leaf, and this is based on the pressure deficit of the vapor that may be high at low relative humidity or low at high relative humidity. Water from is pulled through tension. During the night, the stomata are closed causing transpiration to end; the water is held at the leaf and stem by cohesion forces of water molecules and through adhesion of water molecules to the walls of tracheids, vessels, and xylem. This is called the cohesion-tension theory that describes the manner in which water can move through the xylem vessel. Within the leaf, water occurring on the mesophyll surface makes the microfibrils saturate on the primary cell wall. There are many intercellular air spaces in the leaf that assist in exchanging carbon dioxide and oxygen that is essential during photosynthesis. Thus, the water is evaporated because the intracellular airspaces are exposed leading to a decrease in the mesophyll cells. The reduction of the mesophyll cells causes more water tension leading to an increase in pulling water in the xylem. The tracheid and vessels are adapted to contain the pressure changes. Through cavitation, the sizes and number of gas bubbles are reduced between the vessels. The gas bubbles can reduce or stop the continuous flow of water up the plant. The more the tension required in pulling water in a continuous column, the taller the tree.

Question 5

Food Movement

The manner in which food moves in plants is different from water movement. Food is made by a process called photosynthesis which has to be distributed the plant parts to provide enough energy for growth and maintenance. Food thus moves from where it is made to the sink where it is utilized. The vascular tissue that is responsible for transport of food in the plant is phloem. The phloem is composed of sieve tubes and has lost most cell organelles unlike the xylem (Boundless, 2016). The phloem has companion cells with a nucleus. The sieve tubes and companion cells have pores thus providing cellular functions and support by making protein. The sieve tubes have continuous cell column, and sieve plates separate them allowing sap and sugars to flow (Boundless, 2016). The figure below is a phloem having sieve tubes.

(Boundless, 2016)

The sap and sugars are transported differently from water as...

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