Which of the following is the functional unit of a myofibril?
a. sarcomere
b. myofilament
c. sarcolemma
d. endomysium

Sarcomere

Explanation:

Myofibril is the unit of the muscle cell. The myofibril is rod like in structure and developed by the process of myogenesis in embryo.

Sarcomere is the basic structural unit of the skeletal muscles and shows striations under the microscope. Sarcomere consists of thick and thin filaments of actin and myosin. Different bands like A- band , H-Band, I-Band and Z- line is visible in the sarcomere.

Thus, the correct answer is option (A).

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.