Vascular tissue - class-XII

• Phloem is also called as bast. 
• These tissues in plants conduct foods made in the leaves to all other parts of the plant. 
• Phloem is composed of various specialized cells called sieve tubes, companion cells, phloem fibers, and phloem parenchyma cells.
• Hence, Phloem is a food synthesizing tissue.

Phloem is responsible for transport of food and minerals. Food synthesized in photosynthetic parts is translocated to nonphotosynthetic parts through the phloem. Phloem translocates organic substances and inorganic solutes first from leaves to all other parts of the plant and storage organs. Storage organs re-export organic nutrients to those parts which require the same as newly formed leaves and fruits i.e., it is bidirectional.

Minerals are absorbed by plants - (B) In Ionic form.

The food manufactured in the leaves is translocated upwards and downwards. And to all the parts of the plant through its phloem. The phloem conducts some other substances like amino acids. The conducting cells of the phloem are cylindrical cells known as sieve tubes. These partitions are known as sieve plates. Sieve elements are the food conducting cells of many phloem tissues. Sieve elements in angiosperms are the sieve tubes, while in gymnosperms and pteridophytes, these are sieve cells.

So, the correct answer is option B.

In plants, phloem tissues perform the function of  conduction of food.

• Phloem is the vascular tissue responsible for the transport of sugars from source tissues (e.g., photosynthetic leaf cells) to sink tissues (e.g., non-photosynthetic root cells or developing flowers). 
• Other molecules such as proteins and mRNAs are also transported throughout the plant via phloem. Phloem is composed of several cell types including sclerenchyma, parenchyma, sieve elements and companion cells. 
• The sieve element and companion cell are found closely associated with each other in what is referred to as the sieve element/companion cell complex. One or more companion cells may be associated with a single sieve element. 

In-plant food is transported through the phloem.

Xylem is a type of vascular tissue in plants that transports water and solutes from the roots to the leaves. Phloem is the vascular tissue in plants which conducts sugars and other metabolic products (food) upward and downwards from the leaves.
Thus, the correct answer is option B.

• Vascular tissues make up the organs that transport water, minerals, and food throughout the plant. Vascular tissue can be divided into two functional units. Xylem transports water and minerals from root to shoot. 
• Phloem transports nutrients (such as sugar and amino acids) from leaves and other production sites to roots, flowers, stems, and other tissues.

Phloem transports synthesized food from the leaves to the rest of the plant body. The transport of water, nutrients, and other substances from one part of a plant to another is called as translocation. The medium of transport in plants is water. 

Xylem conducts water and minerals to different parts of the body which can be used for photosynthetic reaction and for several metabolic processes.
Phloem is responsible for transporting sugars, proteins and other organic molecules in plants. It is a vascular tissue in land plants primarily responsible for the distribution of sugars and nutrients manufactures in the shoot.

Phloem tissue is responsible for translocation, which is the transport of soluble organic substances, e.g., sugar. The substances travel along sieve elements, but other types of cells are also present: the companion cells, parenchyma cells, and fibres.

The food manufactured in the leaves is translocated upwards, downwards and laterally to all parts of the plant through the phloem. The phloem also conducts some other substances such as amino acids. The conducting cells of the phloem are cylindrical cells called sieve tubes, which have sieve like partitions at both ends. These partitions are called as sieve plates. 

Phloem is responsible for transport of food and minerals. Food synthesized in photosynthetic parts is translocated to non-photosynthetic parts through phloem. Food is transported in multi-directional fashion.

Xylem tissues include tracheids, vessels, fibres and parenchyma and serve in the ascent of sap/water and minerals. Phloem tissues is a composed of four elements namely, sieve elements, companion cell, phloem fibres and phloem parenchyma and serve in translocation of organic nutrients. Transfer RNA (tRNA) serve as carrier RNA and transports amino acids from cell pool to the mRNA bound to the ribosome where the protein is being synthesized. Haemoglobin molecule contains four polypeptide chains and four heme prosthetic groups. It serves as a carrier of oxygen gas. 

Phloem is a vascular tissue in land plants primarily responsible for the distribution of sugars and nutrients manufactured in the leaves of the plants by the process of photosynthesis.

Phloem tissue is responsible for translocation, which is the transport of soluble organic substances, for example, sugar. The substances travel along sieve elements, but other types of cells are also present: the companion cells, parenchyma cells, and fibers.

a) Passage cells often occur in the endodermis.

b) Stomata are cells in the epidermis of leaves. It is also called accessory or subsidiary cells.

c) Sieve tubes are related to companion cells and both are portions of plant phloem.

d) Lenticels are spongy openings in the periderm. It helps in gaseous exchange.

e) Mesophyll of a leaf comprises palisade cells that work in the absorption of light for photosynthesis.

Thus the answer is matching "A−4, B−5, C−1, D−2, E−3".

The correct option is C.

The sieve tubes are the conducting vessels in the phloem tissue. These are the long tube like cells which have perforated transverse plates. These are the cells which are responsible for the conduction of food. The sucrose is the main sugar which is the form of carbohydrate stored in the plants. The sugar is transported through the phloem vessels from the source end (leaves) to sink end (roots). 

Collenchyma tissue is elastic, extensible and have capacity to expand.

In ringing experiment, the bark ring is scraped away which also removes the phloem causing xylem exposure. In this experiment, sugar moves downwards in the stem but the movement is stopped by the ring. As as result sugar bulge forms above the ring. This suggest that sugar transports down in the stem in the phloem.

Loading of phloem is a process of loading carbon into the phloem for transport to different sinks in a plant. Sinks include metabolism, growth, storage and other processes or organ that need carbon solutes to persist.

The radioactive tracer is a chemical compound used to determine the atoms and molecules by the virtue of radioactive decay. The age of a tree, transportation of solute through phloem etc is seen through the use of radioactive of carbon. 

Tracheids and vessels both have pits but vessels have an opening which connects single individual vessel elements to form a single tube. These end openings are called perforation plates. Tracheids are imperforate, have pit pairs on common walls.

Positive root pressure pushes up the water. 

Vessels are multicellular with wide lumen. They are made up of vessel  elements lying one above the other. The wall of vessels is hard but not thick having wide lumen. Whereas tracheids are unicellular with narrow lumen. 

The primary function of the epidermis in plants is to provide a protective barrier against water loss, mechanical injury, and pathogen entry.

Ringing/Girdling experiments demonstrate that phloem is responsible for translocation of food because phloem is present outside to xylem so when a ring of bark is removed from a woody plant, the woody xylem part remains intact, water and nutrient reaches the leaves. After the preparation of the photosynthate, it is not transported to other parts below the girdle since the phloem part is removed. This experiment shows that the phloem tissue aids food transport.

Xylem flow is unidirectional and phloem flow is bidirectional because xylem transport water from soil to leaves and phloem transfers the food.

Starch and sucrose are more efficient forms in which the energy can be stored when compared to glucose. The starch is not soluble in water. Hence, the sucrose which is soluble in water is the form which is used for transport. This structural form increases the efficient energy transfer. Sucrose is not as reactive as glucose. This helps to prevent the chemical reactions which can convert the sucrose while transport. 

Spring is considered as the flowering season. This is the period when there is growth of the floral buds which are formed at the apex of the vegetative shoots. Generally, there is a flow of sugar from the source (leaves) to sink end (roots). Due to the increase in the activity in the apex regions of the plant, there is consumption of food in the leaves. Hence, the food to the flower buds is supplied by the roots. 

The parenchyma cells in the phloem tissue are known as phloem parenchyma. There are different types of phloem parenchyma cells, companion cells, albuminous and other parenchyma cells. The transfer cells are a type of companion cells. These are the cells which have folded cell wall surface. This helps to increase the transfer of the sugar in the lateral sides. They also help in scavenging the solutes which require ATP to move across the membranes. 

The sugar molecules are transported by the conducting cells in the phloem tissue in the form of sucrose. These sugar molecules are transported from the source end to the sink end. The source end is the region where the sugar is present in high concentrations. The sugar needs to be moved in the sieve elements in the source end by the process of sieve elements. Energy needs to be spent to move the sugar molecules in the form of ATP. The sugar molecules are transported through osmosis and removed from the sieve cells in the sink end by active transport. 

Sugars are synthesized as glucose and fructose, translocated as sucrose and stored as starch for long-term storage in plants. Translocation of organic nutrients from the region of source or supply to the region of utilization is mostly in the form of sucrose. Sucrose is water soluble and more efficient in energy storage as compared to the glucose and fructose as well as glucose is more reactive and hence, phloem transports sugar in the form of sucrose.

In plant transport system no heart, no blood, and no other circulatory system, but plants do need a transport system to move food, water, and minerals around. They use two different systems then xylem moves water and solutes from the roots to the leaves and phloem moves food substances from leaves to the rest of the plant, then phloem is the transporting system of food to the plants.

Xylem is the chief water and nutrients conducting tissues of the plants. These xylem tissues form the part of vascular tissues. These conduct water and nutrients from the roots to the top of the plants i.e. to the stem and the leaves. Along with acting as a conducting tissue, xylem also provides the mechanical strength to the plant parts.

Osmosis is the process of flow of fluid from higher to lower concentration through the semi-permeable membrane. The wall of xylem vessels behaves as the semi-permeable membrane so diffusion of water from one xylem vessel to another xylem vessel can be called the phenomenon of osmosis.