Plant Transport and Physiology

• Monocots have scattered vascular bundles, while dicots have a continuous ring arrangement of vascular bundles. In a dicot stem, after a few years of growth, phloem is present as a single continuous layer or sheet on the outer side as a constituent of bark. 
• It can be easily removed because it is present as a continuous sheet. In a similar manner phloem cannot be removed in a monocot stem, because of the scattered arrangement, some of the vascular bundles might be present near the surface and some embedded deep inside. 
• Removing phloem from each of the bundles individually is not possible. The girdling experiment is used to identify the tissue through which food is conducted. In this experiment, a ring of phloem is removed from the woody plant. 
• Hence girdling experiments cannot be performed on a monocot stem-like sugarcane.

The primary cause of heat buildup in cities is insolation i.e. absorption of solar radiation by roads and buildings. Storage of this heat by building material results in subsequent re-radiation. Due to transpiration of plant surface, its temperature does not rise 4-5 degree above the ambient and sometimes is cooler. This then translates into the cooling of the environment. Hence rooftop gardening reduces the overall heat absorption of the building which then reduces energy consumption. Thus the correct answer is option A.

Transpiration is the biological process by which plants release water vapor into the atmosphere through their leaves.

The root nodule bacterium is microaerobic in the sense that it requires oxygen but the high concentration of oxygen is detrimental to nitrogen-fixing enzyme system. Here leghaemoglobin proves beneficial, it absorbs or binds oxygen so that there is no free oxygen left in the nodule and then carries micro-amounts of oxygen to the nodule bacteroids. Thus the correct answer is option B.

The Pressure flow hypothesis often regarded as mass flow hypothesis explains best about the movement of Plant sap through phloem .The concept was proposed by E.Munch . The transpiration of water from leaves and other part of plant body produces negative pressure inside transport vessels causing root to absorb large amount of water along with ions to maintain the continuity of column of water . 

The mineral salts are absorbed into the symplasm, i.e., cytoplasm of root cells. There are special specific mineral transporters present in the plasma membrane of cells, which absorb the minerals from soil solution by transporting them across the membrane from soil solution to the cytoplasm of root cells. This way minerals can be absorbed irrespective of or against the concentration gradient of minerals. The minerals are present in the soil solution at very low concentrations and are usually absorbed against the concentration gradient with the help of specific carriers.

Soil respiration refers to the production of carbon dioxide when soil organisms respire. They include roots and other microbiota. Roots continuously respire and liberate significant quantities of CO2. The CO2, when dissolved in soil water, produces carbonic acid.  Immediately they ionize into H+ and bicarbonate ions. Thus during respiration in plant root carbonic acid is formed. Thus the correct answer is option C.

Plant root cells contain relatively large quantities of organic cations and anions that do not diffuse through cell membranes. These organic ions could act as non-diffusible ions and may bind inorganic ions by electrostatic attraction. Thus ions are absorbed to the surface of roots electrostatically.

The contact exchange theory posits that ions adsorbed on the surface of soil particles are exchanged directly with ions on the surface of root hairs through contact.

The contact exchange theory of mineral absorption was proposed by researchers Jenny and Overstreet in the 1930s.

A) Blue-green algae

From the region of maturation in roots, the epidermis develops a special unicellular hair like structure known as root hairs that help to increase the surface area of root to maximize the absorption of water and minerals.

Plants can absorb nitrate or nitrite from the soil via their root hairs. If nitrate is absorbed, it is first reduced to nitrite ions and Ammonium ions for incorporation into various compounds.

The external protective layer in dicot root is called as epiblema or piliferous layer. The cells of epidermis extend into unicellular root hairs. In the root cap there is no root hair present. In absence of root hairs water absorption is not possible. So, the correct answer is option B.