Structure of a plant cell - class-X

Pectic substances are a group of polysaccharides in plant cell walls and some mucilages, which are endowed with multifunctional properties, such as the control of cell wall integrity and porosity. Methylene blue is used to indicate whether the cells are dead or alive.

The Eukaryotic cells, in addition to the nucleus, have many membrane-bound organelles like the mitochondria, endoplasmic reticulum, Golgi bodies etc. Such membrane-bound organelles are absent in the Prokaryotic cells

In the plant cell, plasma membrane and cell wall both are present, both act as a barrier between protoplasm and the outer environment.

• A plant cell has a cell wall and single central vacuole.
• Plant cells are eukaryotic cells that differ in several key aspects from the cells of other eukaryotic organisms. 
• Their distinctive features include:
• A large central vacuole
• A cell wall composed of cellulose and hemicellulose
• Specialized cell-to-cell communication pathways known as plasmodesmata

Plant cells sometimes form mineral crystals. Calcium carbonate occurs as a mass of crystals around a cellulose core to form cystolith (eg, leaf of Banyan). In several plants, calcium oxalate forms needle-like raphides, prismatic crystals, star-shaped sphaeraphides or Druses or powdery mass named as crystal sand.

Plants are made up of water, organic and inorganic substances. Water makes the majority of the volume of the plant cell. Water comprises of 80-90 percent of the plant's total weight. Water is used to support the cell structure, for metabolic functions, to carry the nutrients and for photosynthesis. 

A most abundant compound in living organisms protoplasm is water. Plants contain even more water than animals do- most of them are anywhere from 90 to 95% water. In plants, about 85% of the fresh weight of leaves can be water. Each water molecule is made up of two hydrogen and one oxygen atom. Hence, hydrogen is the most abundant element in a plant body.

Plant cell is covered by a cellulosic cell wall. The cell wall is dead at maturity but grows when immature to permit cell elongation. Intussusception is growth by deposition of new materials between existing components of cell walls. Cell elongation occurs through intussusception. In apposition, new wall layers are laid. Growth of wall in new cells occurs through apposition.

The cell wall is a protective outer covering of the cell. It is mostly present in plant cells. It is not present in the animal cell. It supports the contents of the cell and protects from pathogen attack and wear and tear. It is made of cellulose. Cellulose is a natural polymer made of smaller sugar units. It gives remarkable strength to the wood. 

Cellulose is a structural polysaccharide found in the cell walls of plants.

Plant and animal cells have several differences and similarities. For example, animal cells do not have a cell wall or chloroplasts but plant cells do. Animal cells are round and irregular in shape while plant cells have fixed, rectangular shapes.

The main difference between an animal cell and a plant cell is that plant cells have a cell wall, which the animal cells lack. The cell wall which is made up of cellulose gives the plant cell rigidity resulting in a fixed, rectangular shape. Animal cells lack the rigidity hence, they tend to have a round and irregular shape. Animal cells tend to vary greatly in appearance. The cell wall allows high pressure to build inside of the plant cell without bursting. Due to this, the plant cell is able to accept large amounts of liquid through osmosis without bursting. Animal cells, which only have a thin membrane restricting access to the cell, tend to burst if they absorb too much extra water.

Cellulose forms an integral part of the cell wall which provides strength and rigidity to the cell. It helps to maintain the structural integrity of a particular cell. Cellulose is a complex polysaccharide which is made up of β(1→4) linked D-glucose units.

The plant cell contains three different types of cell organelles which have two membranes. The chloroplast, mitochondria and the nucleus are the organelles which are surrounded by double membranous structures. The chloroplast is involved in photosynthesis, mitochondria performs respiration and the nucleus controls the activity of the other organelles. 

Cellulose forms an integral part of the cell wall which provides strength and rigidity to the cell. It helps to maintain the structural integrity of a particular cell. Cellulose is a complex polysaccharide which is made up of β(1→4) linked D-glucose units.

Vacuoles are found in almost all the cells. A plant cell usually has a large central sap vacuole. Most mature plant cells have one large vacuole that typically occupies more than 30% of the cell's volume, and that can occupy as much as 80% of the volume for certain cell types and conditions. Another important characteristic of a plant cell is the presence of a cellulosic cell wall. The plant cell wall is dead at maturity and is rigid. Hence, cell wall provides support and maintains the shape of a plant cell.

Plant cells have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. As a result, the plant cells become “turgid” when they swell up and become turgid.

• Plant cells store fat in sphaerosome.
  
• Spherosomes or oleosomes can be defined as small cellular organelles found in plant cells that are enclosed by a single membrane. 
  
• It is mainly responsible for the storage and synthesis of lipid. 
  
• They are obtained from the endoplasmic reticulum and are surrounded by a phospholipid monolayer.
  
• So, the correct answer is 'Sphaerosome'.
  

• A plant cell having more than two nuclei is known as coenocyte.
  
• Coenocyte refers to a multinucleate condition of the cell (algae, fungi or plant) which occurs due to the multiple nuclear divisions which are not followed by cytokinesis.
  
• So, the correct answer is 'Coenocyte'.

Centrosomes are organelles involved in cell division and are typically found in animal cells, but they are absent in the cells of higher plants.

Cellulose is found in plant cell walls (a-ii), Chitinase breaks down chitin in fungal walls (b-iv), Lysozyme breaks down bacterial cell walls (c-i), and Protease breaks down proteins (d-iii).

DNA is found in the nucleus (chromosomes), as well as in semi-autonomous organelles like chloroplasts and mitochondria, which contain their own circular DNA. Ribosomes are composed of RNA and proteins, not DNA.

Pure water is a hypotonic solution that causes endosmosis. The water diffuses into the cell causing the cytoplasm to build up pressure against the wall. This pressure is called turgor pressure that causes rigidity of the cell and the cell does not burst. This turgor pressure is responsible for the enlargement and extension of the cells during growth.

Cell wall is the outer rigid protective and supportive covering of plant cells, fungi and some protists. Cell membrane is covering of protoplasm which occurs inside the cell wall. In plants the cell wall is made of cellulose.

Basal body is also known as kinetosome. This is a short cylinder like a centriole, consists of nine triplet microtubules; it organizes assembly of the axoneme microtubules.
Animal cells posses centrioles and basal bodies, which are involved in cell division. 
Centrioles are cylindrical organelles that help in cell division. Basal bodies are formed from centrioles. 
Microtubules are filamentous structures formed from centrioles, which are involved in chromosomal separation during cell division. Nine triplets microtubules together form basal body. 
Plant cells do not possess centriole. Hence, it does not possess basal bodies formed from centrioles. 

Vacuoles are like storage bubbles which are found mostly in plant cells. They occupy most of the portion of plant cells. These are used for storage of food or water. They also store toxic metabolic by-products or end products of plant cells. Such vacuoles are thrown out of the cell by exocytosis. Osmotic pressure and turgidity are maintained by vacuoles due to the presence of cell sap. 

Centrosomes are the cellular organelles which are involved in the formation of centrioles. The centrioles are the centres for the formation of the microtubules required for the spindle fibres formation during cell division. The aster is the star-like formation around the centriole. This is the region from where the spindle fibres get distributed in all the sides. The centrioles and aster are present in the animal cells and absent in the plant cells. Thus, the correct answer is option A. 

The cellulosic cell wall provides structural shape (a), protection (b), and mechanical strength to withstand environmental stressors (c). While it is involved in some signaling, option (d) is less standard than the primary structural roles listed in (a, b, c).