The rupture and fractionation do not usually occur in the water column in vessel/tracheids during the ascent of sap because of
lignified thick walls
cohesion and adhesion
weak gravitational pull
weak gravitational pull
B.
cohesion and adhesion
The Vertical conduction of water from root to aerial parts of the plant is called ascent of sap. The water molecules remain joined to each other due to a force of attraction called cohesion force. This attraction is due to the presence of hydrogen bonds between them. The magnitude of this force is very high, therefore, the continuous water column in the xylem cannot be broken easily due to the force of gravity or other obstructions offered by internal tissues in the upward movement of water. This adhesive property of water, ie, the attraction between the water molecules and the walls of xylem ensures the continuity of water column in xylem.
Due to transpiration water evaporates to outer atmosphere through stomata. As a result leaf cells develop low water potential and water from leaf veins moves into leaf cells. They xylem of the main stem. A pressure (pull) is thus, exerted by all the leaves on the stems, which is called transpiration pull. This is strong enough to pull up the column of water to a great height.
Which one of the following is linked to the discovery of Bordeaux mixture as a popular fungicide?
Bacterial leaf blight of rice
Downy mildew of grapes
Loose smut of wheat
Loose smut of wheat
The blood calcium level is lowered by the deficiency of
parathormone
thyroxine
calcitonin
calcitonin
Which one of the following is the correct difference between rod cells and cone cells of our retina?
|
Features |
Rod cells |
Cone cells |
|
Visual acuity |
High |
Low |
|
Features |
Rod cells |
Cone cells |
|
Visual Pigment contained |
Iodeosin |
Rhodopsin |
|
Features |
Rod cells |
Cone cells |
|
Overall function |
Vision in poor light |
Colour vision and detailed vision in bright light |
|
Features |
Rod cells |
Cone cells |
|
Overall function |
Vision in poor light |
Colour vision and detailed vision in bright light |
Which one of the followings in birds, indicates their reptilian ancestry?
Scales on their hind limbs
Four chambered heart
Two special chambers crop and gizzard in their digestive tract
Dry indehiscent single-seeded fruit formed from bicarpellary syncarpous inferior ovary is
Caryopsis
cypsela
Adiantum
Adiantum
The length of different internodes in a culm of sugarcane is variable because of
shoot apical meristem
position of axillary buds
size of leaf lamina at the node below each internode
size of leaf lamina at the node below each internode
The fleshy receptacle of syconus of fig encloses a number of
achenes
samaras
berries
berries
