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BIOLOGY 3 Marks Question

PART - 2 - Unit V : CH - 17 Locomotion and Movement · Gujarat Board (GSEB) STD 11 Science (GSEB - English Medium). 3 questions.

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Question 13 Marks
Describe the structure of contractile proteins.
Answer
Contractile proteins consist of two primary types :
(i) Actin : Each actin (thin) filament is made of two 'F' (filamentous) actins helically wound to each other. Each ' $F$ ' actin is a polymer of monomeric ' $G$ ' (Globular) actins. Two filaments of another protein, tropomyosin also run close to the ' $F$ ' actins throughout its length. A complex protein troponin is distributed at regular intervals on the tropomyosin. In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments.
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(ii) Myosin : Each myosin (thick) filament is also a polymerised protein. Many monomeric proteins called Meromyosins constitute one thick filament. Each meromyosin has two important parts, a globular head with a short arm and a tail, the former being called the heavy meromyosin (HMM) and the latter, the light meromyosin (LMM).
The HMM component, i.e., the head and short arm projects outwards at regular distance and angle from each other from the surface of a polymerised myosin filament and is known as cross arm. The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.
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Question 23 Marks
What are muscular tissues? Describe their various types.
Answer
Muscular tissue is contractile tissue. Muscular tissues are formed by muscle cells. Muscle cells are elongated and slender, therefore they are also called muscle fibres. Within muscle fibres, many myofibrils are found. Due to the qualities of contractility and excitability in muscles, they are crucial for movement and mobility. They constitute approximately $40-50 \%$ of the entire human body weight.
Types of Muscles : Muscles can be classified into three types based on their structure and function-Skeletal Muscles, Cardiac Muscles, and Smooth Muscles.
1. Skeletal Muscles: These muscles are responsible for the movement of skeletal parts and aid in locomotion. They are connected to bones via tendons. They are also known as striated or voluntary muscles. They receive impulses from the voluntary nervous system, hence contracting according to one's will. Though these muscles contract rapidly, they tend to tire quickly. The majority of muscles in the body fall into this category and primarily assist in movement and changing physical postures.
2. Cardiac Muscles: These muscles are exclusively found in the heart. They are striated and involuntary muscles, controlled by the involuntary nervous system.
They possess the property of self-excitability and do not fatigue. These muscles are responsible for the contraction of the heart.
3. Smooth Muscles : Found in internal organs such as the digestive and circulatory systems. They are non-striated and involuntary muscles. They receive impulses from the autonomic nervous system. Their contraction is slow, leading to delayed fatigue. They play a major role in the movement of substances within lumens, for example, aiding digestion and transportation of gametes in the reproductive system. 
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Question 33 Marks
What are the functions of bones?
Answer
Functions of bones :
(1) Bones provide the body with structural support.
(2) Bone marrow in bones produces Red Blood Cells (RBCs).
(3) Bones serve as an attachment point for muscles.
(4) Bones give the body a definite shape.
(5) Bones protect soft organs from external impacts, such as the ribcage protecting the heart, lungs, and kidneys.
(6) Some small bones in the auditory system assist in hearing.
(7) Skeletal system assists in movement, locomotion, and other physical activities.
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