BIOLOGY 3 Marks Question

A neuron is a microscopic structure composed of three major parts, namely, cell body, dendrites and axon.
Cell Body. The cell body contains cytoplasm with typical cell organelles and certain granular bodies called Nissl's granules.
Dendrites. Short fibres which branch repeatedly and project out of the cell body also contain Nissl's granules and are called dendrites. These fibres transmit impulses towards the cell body.
Axon. The axon is a long fibre, the distal end of which is branched. Each branch terminates as a bulb-like structure called synaptic knob which possess synaptic vesicles containing chemicals called neurotransmitters. The axons transmit nerve impulses away from the cell body to a synapse or to a neuro-muscular junction.

i. Difference between Myogenic heart and Neurogenic heart:

Myogenic heart	Neurogenic heart
In the myogenic heart, the initiation of the   heartbeat beat is under muscular control.	Under nervous control. e.g. Insects,   Crustacea and Annelida.
e.g. Molluscs and vertebrates.	Insects, crustacea, and Annelida.

ii. Difference between Lymphatic capillaries and Blood capillaries:

Lymphatic capillaries	Blood capillaries
They are colourless.	They are red.
They convey lymph,	They convey blood.
They are wider than blood capillaries.	They are narrower than the lymphatic   capillaries

 

The labelled diagram of the human heart is given below:

A rubber band stretches and reverts back to its original position due to elasticity. However, when bubble gum stretches, but would not return to its original position, it is plasticity.
The meristematic cells are rich in protoplasm, possess large conspicuous nuclei. Their cell walls are primary in nature, thin, cellulosic, and elastic with abundant plasmodesmatal connections.
However. plants follow different pathways in response to the environment or phases of life to form different kinds of structures. This ability is called plasticity.

Features which make mammals as dominant and successful animals are as follows:
i. The presence of an insulating and protective hairy exoskeleton.
ii. They are warm-blooded so have a high rate of metabolism.
iii. They are viviparous animals and show placentation and intrauterine development which increases the chances for survival of young ones.
iv. They show a high degree of parental care.
v. They have more developed hearing efficiency due to the presence of pinna, three ear-ossicles and coiled cochlea in the ear.
vi. They are able to speak through indicative/verbal language.
vii. They have a good power of learning due to the presence of a more developed brain.