Control and Coordination-5 Flashcards
what are the limitations of electrical impulses
Electrical impulses are an excellent means for transferring information. Firstly, they will reach only
those cells that are connected by nervous tissue, not each and every cell
in the animal body. Secondly, once an electrical impulse is generated in
a cell and transmitted, the cell will take some time to reset its mechanisms
before it can generate and transmit a new impulse. In other words, cells
cannot continually create and transmit electrical impulses. It is thus no
wonder that most multicellular organisms use another means of
communication between cells, namely, chemical communication.
how do animals communicate chemically
If, instead of generating an electrical impulse, stimulated cells release
a chemical compound, this compound would diffuse all around the
original cell. If other cells around have the means to detect this compound
using special molecules on their surfaces, then they would be able to
recognise information, and even transmit it.
iwhat are plant hormones
These are organic compounds produced in low concentrations by a particular plant part) source) which is transported to another part where it acts( target). They diffuse to the area of action. Different plant hormones help to coordinate growth, development and responses to the environment.
name the different hormones
- Plant growth hormones
i) Auxin
ii) Gibberellins
iii) Cytokinin
-Plant growth inhibitor
i) Abscisic acid
ii) Ethylene
what are auxins?
Auxins are the plant hormones that are produced in plant tips and promote cell elongation and growth of terminal buds and fruit formation. These are produced in stem, buds and root tips, particularly in the apical meristem of root/shoot.
how do auxins promote phototropism
Auxins are distrubuted uniformly when all parts of the plant receive equal sunlight. However, when the plant is kept near the window, one part of the plant will receive more sunlight than the other. In this case, auxins prefer to be in the shaded region so they diffuse to the part of the plant which is away from the sunlight. The concentration of auxins here causes this part of the plant to grow more faster/longer than the part of the plant near the sunlight. hense the plant appears to bend towards the sunlight.
What is plant hormone gibberellins
Gibberellins are plant hormones that promote stem growth, seed germination and leaf expansion.They occur in a low concentration n vegetative tissues but high concentration in the germinating seeds. They help stimulate the break down of stored energy in seeds and allow for germination and sprouting of leaves. These are important for the growth and develpment of plant thorugh flowering and seed germination by inducing cell division and elongation.
what are plant hormone cytokinins
Cytokinins promote cell division, and cell differentiation
and it is natural then that they are present in greater concentration in
areas of rapid cell division, such as fruits and seeds.it delays ageing of leaves, promotes opening of stomata and fruit growth
what is abscisic acid?
It is a plant hormone which inhibits growth. Its effects include wilting of leaves. It produced under abiotic stress conditions. For example during drought stress conditions, it suppresses shoot growth and promotes root growth. It plays a role in closing of stomata during water stress. It also plays a role in senescence and abscission layer formation. It helps maintain dormancy of embryo and falling down of ripened fruits.
what is ethylene
It is a gaseous plant hormone that helps in the ripening fruit. It usually produced under stress, senencence or ripening. Its main function if to cause ripening of fruits. Excess ethylene can lead to the dropping of fruits and leaves.
