Model Paper 6 — NEET STD 11 Science — Question

Mechanism of muscle contraction is best explained by the sliding filament theory which states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments. Organise sequence of contraction and choose correct option :
(i) Action potential spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm.
(ii) This pulls the attached actin filaments towards the centre of A-band.
(iii) Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.
(iv) Increase in Ca⁺⁺ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin.
(v) Signal sent by the central nervous system (CNS) via a motor neuron.
(vi) The Z-line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction.
(vii) A neural signal reaching neuromuscular junction releases a neurotransmitter (Acetyl choline) which generates an action potential in the sarcolemma.

Sweat produced by sweat glands is a watery fluid which contain

The nitrogen fixing symbiotic organism present in Azolla is

Which one of the following statements is not correct?

An increase in pulmonary volume decreases the intra pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into lungs. i.e.........

Bilaterally symmetrical but acoelomate animal is

All of them are characters of reptiles except