Plant - Growth & Development Test 6

Auxins are the phytohormones present in plants which has several important roles to play in plant life. It is usually seen at the tip of  shoots, at the meristematic region.

The effect of gravity on the plant can be demonstrated using an apparatus called as clinostat. The clinostat has a rotating pot like container mounted on an axial rod. A potted plant is fitted horizontally on the clinostat and is slowly rotated at about four rotations per hour. By this, the effect of gravity is completely eliminated, as all the sides of the plant are equally stimulated by gravity. If the rotation of the clinostat is stopped for a considerable period of time, then the tip of the stem is observed to curve and grow upwards. This proves that the stem tip is negatively geotropic.
Thus, the correct answer is option C.

A general rule of thumb is that 1% more light will give similar percentage increase in plant growth, resulting in a 1% higher yield. All plants require light and CO2 for photosynthesis.
Photomorphogenesis relies on various photo pigments to sense and respond to light colors, which range from ultraviolet to near- infrared and include all the colors of the rainbow that humans see as reflected light.
 

See , Pinus tree has pyramid like shape....in simple words... Elder branches are larger than younger branches, so its looks like a cone...this pattern is called excurrent habit....this is due to..apical dominance in plant, auxin produced in the apical meristem inhibits axillary buds near the apical meristem from developing into actively growing shoots.. so this type of pattern developsso option Band the ..most.. important thing is that it helps in the..wind pollination.

Auxin is a group of several natural (and artificial) plant hormones; the most common and physiologically important auxin is indoleacetic acid (IAA). Some manufactured, or synthetic, auxins have structures similar to that of IAA. The synthetic auxin naphthalene acetic acid stimulates root development on stem cuttings and is used for asexual propagation, particularly of woody plants with horticultural importance.
Thus, the correct answer is option A.

Auxin is a plant hormone that plays important role in phototropism, growth movement in response to light. It promotes cell elongation. It is unequally distributed in the plant cells. It is transported towards the shady side and thus present in higher concentration. However, less auxin is transported towards the illuminated side. Due to this, the plant to grow more on the shaded side and bend in the direction of the light source. It shows phototropic response where faster cell elongation is seen on the shaded side than on the illuminated side. 

Phototropism was first studied by Charles Darwin in 1880 in Canary Grass and oat coleoptiles. Later on F.W. Went in 1923, suggested the involvement of auxins in this phenomenon. Experimental approach to demonstrate positive phototropism in shoot tips is a darkened black box. The black box is having a small window at one side. A well-watered potted plant is placed inside the box. The is referred to as a phototropic chamber or heliotropic chamber. The window is kept closed for about 24 hours and the plant shows normal growth. If the window is kept opened, it is found after two days, that the shoot tip bends and grows towards light proving that it is positively phototropic.

Auxins are weakly acidic growth hormones having an unsaturated ring structure and capable of promoting cell elongation, especially of shoots. ... The movement of auxins is basipetal in stem ie, from apex to base and acropetal in roots ie, from tip towards shoot. This type of movement is called polar movement.

Auxins are plant hormones and essential for the development of the plant as these play an important role in plant growth through cell elongation. On a molecular level, auxins are compounds with an aromatic ring and a carboxylic acid group and its chemical structure is indole -3-acetic acid (C₁₀H₉NO₂).

Ethylene is a fruit ripening hormone. It also induces femaleness in plants. Auxins are the hormones responsible for cell elongation in plants. High auxin concentration increases the synthesis of ethylene and hence help to promote femaleness in dioecious plants. Thus the correct answer is option A.

NAA prevents the fall of fruits.
NAA (Naphthalene acetic acid) is a synthetic auxin. It is produced artificially. It inhibits the abscission. It prevents the formation of a layer called an abscission layer which is formed between the organs like fruits, flowers, etc. and the stem.  It is a layer of dead cells which causes fruit fall. As NAA prevents the formation of this layer, so it prevents the fall of fruits.

In artificial ripening of banana, uncontrolled application of ethylene gas may cause over ripening of banana. It can be prevented from over-ripening by dipping in ascorbic acid solution.

Weedicides or herbicides are weed killers or pesticides used to control weeds in agricultural farms. AMO 1618  or (2-isopropyl-5-methyl-4-trimethylammonium chloride)-phenyl-1-piperidine carboxylate is an  inhibitor of gibberellin biosynthesis which leads to retarded germination. Higher concentrations will lead to  reduced sensitivity of seeds.

Agent orange refers generally to all the phenoxy weedicide sprayed that contain dioxin. Dioxin is a toxic substance causing cancer and genetic damage. It is so called from the colour of the identifying strip in which it was stored.

Phytotron is a experimental setup of green house which is used to study interaction between plant and environment it is used for controlled experiments.

Cytokinin causes delay of senescence called Richmond Lang effect. It checks disappearance of chlorophyll and degradation of protein synthesis in leaves.
Senescense of leaves leads to yellowing and finally leads to the fall from the plant.  If a young excised leaf is kept in water, it slowly changes its color to yellow and dies.  If such leaves are provided with cytokinin, the yellowing is significantly delayed and such an effect is called Richmond and Langs effect; named after the discoverers.

Florigen is a hypothetical flower-inducing growth hormone. It is produced in response to a specific period of day length typical of a plant. Florigen is considered to be the same in all the flowering plants.It induces only flowering. It is neither a growth promoter nor a growth inhibitor.

Thus, the correct answer is option C.

Option A is correct.. amides and ureas inhibit photo sytem 2 DCMU(3-(3,4-dichlorophenyl)-1,1-dimethylurea) or Diuron.

Auxin are growth promoting phytohormones. They promote growth in extremely minute quantities. At higher concentration, they are harmful and may kill the plant. The exact mechanism by which this effect is caused is not known, but it is believed that higher concentration of auxins increases growth promotion to such an extent that plant is killed, i.e., plant grows to meet its end.

Thus, the correct answer is option B.

Auxin is a growth promoter, generally produced by the growing apex of stem and root of the plants.

Auxins, help to initiate rooting in stem cuttings, an application widely used for plant propagation. Auxins promote flowering, e.g., in pineapples. Auxins also help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits.