Cell Structure & Functions- 1 - UPSC Sci Tech Free MCQ Test with solutions

The tissue composed of the living, thin-walled, polyhedral cell:
Explanation:
1. The tissue described in the question is a type of plant tissue.
2. It is composed of living cells that have thin walls and a polyhedral shape.
3. This tissue is responsible for various functions, such as storage, photosynthesis, and secretion.
4. The correct answer is parenchyma.
5. Parenchyma tissue is found in various parts of plants, including leaves, stems, roots, and fruits.
6. It is made up of relatively unspecialized cells that have thin cell walls and large intracellular spaces.
7. The cells of parenchyma tissue are often responsible for carrying out metabolic activities, such as photosynthesis in the case of parenchyma cells in leaves.
8. Parenchyma tissue can also be involved in storage functions, storing nutrients and water.
9. The thin walls and polyhedral shape of the cells allow for efficient exchange of gases and nutrients.
10. Overall, parenchyma tissue is an important and versatile tissue in plants, contributing to their growth, development, and survival.

Answer:
The single long part of a neuron is called the axon. The axon is responsible for transmitting electrical signals away from the neuron's cell body to other neurons, muscles, or glands. Here is a detailed explanation of each part of a neuron:
Dendrite:
- Dendrites are the short, branch-like extensions of a neuron that receive signals from other neurons or sensory receptors.
- They play a crucial role in collecting information from the external environment or other neurons and transmitting it to the cell body.
Axon:
- The axon is a long, slender extension of a neuron that carries electrical signals away from the cell body.
- It is covered by a fatty substance called myelin, which helps to insulate and speed up the transmission of signals.
- Axons can vary in length, with some reaching up to several feet in the human body.
Cell Body:
- Also known as the soma, the cell body is the main part of the neuron.
- It contains the nucleus, which houses the genetic material of the neuron, and other organelles necessary for its functioning.
- The cell body integrates incoming signals from dendrites and generates the electrical impulses that are transmitted through the axon.
Cytoplasm:
- The cytoplasm is the gel-like substance that fills the interior of the neuron.
- It contains various structures and molecules that are essential for the neuron's metabolic processes and the maintenance of its overall function.
In summary, while each part of a neuron plays a crucial role in its functioning, the single long part responsible for transmitting signals away from the cell body is the axon.

Cells with evenly thickened, hard, lignified walls are seen in sclerenchyma.
Sclerenchyma is a type of plant tissue that provides support and strength to the plant. It is characterized by thickened, hard, and lignified cell walls. These cell walls contain a substance called lignin, which makes them tough and rigid.
Key points:
- Sclerenchyma cells have evenly thickened cell walls, unlike other types of plant cells.
- The thickening of the cell walls is due to the deposition of lignin, a complex polymer.
- Lignified cell walls provide strength and support to the plant, allowing it to withstand mechanical stress.
- Sclerenchyma cells are dead at maturity and lack protoplasts.
- They are found in various parts of the plant, such as the stems, roots, and seed coats.
In contrast:
- Collenchyma cells have unevenly thickened cell walls and provide support to growing plant parts.
- Striated muscle cells are found in animals and have a completely different structure and function.
- Parenchyma cells are the most common type of plant cells and have thin cell walls. They are involved in various functions, such as photosynthesis and storage.
Overall, the presence of evenly thickened, hard, lignified walls is a characteristic feature of sclerenchyma cells in plants.

Answer:
The sclerenchyma can be identified by the thickness of its cell wall. The cell wall of sclerenchyma cells is significantly thicker than that of parenchyma cells.
Explanation:
To differentiate between parenchyma and sclerenchyma tissues, you need to examine the characteristics of the cell wall. The cell wall of sclerenchyma cells is composed of lignin, which makes it thick and rigid. On the other hand, the cell wall of parenchyma cells is thin and flexible.
Here are the key differences between parenchyma and sclerenchyma tissues:
Parenchyma tissue:
- Comprises living cells with thin and flexible cell walls.
- The cell walls contain cellulose.
- The cells have a large central vacuole.
- The cells are generally isodiametric (similar in size in all dimensions).
- The nucleus is located towards the center of the cell.
- Functions include storage, photosynthesis, and secretion.
Sclerenchyma tissue:
- Comprises dead cells with thick and rigid cell walls.
- The cell walls contain lignin.
- The cells have a small central vacuole or may lack a vacuole altogether.
- The cells are elongated and have tapering ends.
- The nucleus is typically located towards the periphery of the cell.
- Functions include support and protection.
In summary, the thickness of the cell wall is the key characteristic that can be used to identify sclerenchyma tissue in comparison to parenchyma tissue.

Explanation:
To answer this question, we need to understand the characteristics of different muscle types and identify which one fits the description of branched muscle fibers interconnected by oblique bridges.
A. Unstriated muscle fibers:
- Unstriated muscle fibers, also known as smooth muscle fibers, are found in the walls of hollow organs, such as the digestive tract and blood vessels.
- They are not branched and do not have oblique bridges. Therefore, option A is incorrect.
B. Striated muscle fibers:
- Striated muscle fibers, also known as skeletal muscle fibers, are responsible for voluntary movement and are attached to bones.
- They have a striped or striated appearance due to the arrangement of contractile proteins.
- However, striated muscle fibers are not branched and do not have oblique bridges. Therefore, option B is incorrect.
C. Cardiac muscle fibers:
- Cardiac muscle fibers make up the walls of the heart and are responsible for involuntary contractions.
- They are branched and interconnected by oblique bridges called intercalated discs.
- Cardiac muscle fibers fit the description mentioned in the question, so option C is correct.
D. Skeletal muscle fibers:
- Skeletal muscle fibers, as mentioned earlier, are striated and responsible for voluntary movement.
- However, they are not branched and do not have oblique bridges. Therefore, option D is incorrect.
In conclusion, the correct answer is option C: cardiac muscle fibers. They are branched muscle fibers interconnected by oblique bridges.

Plant cells with thickened walls at corners and non-lignified cell walls are seen in collenchyma.
Collenchyma cells are a type of ground tissue found in plants. They have a thickened primary cell wall, particularly at the corners, which provides support and flexibility to the plant. The cell walls of collenchyma cells are primarily made up of cellulose and pectin, and they lack lignin, which is responsible for the hardening and lignification of cell walls.
Here are the key characteristics of collenchyma cells:
1. Thickened walls at corners: The corners of collenchyma cells have extra layers of cell wall material, making them stronger and able to withstand mechanical stress.
2. Non-lignified cell walls: Unlike other types of cells, such as xylem cells, collenchyma cells do not contain lignin. This lack of lignification allows the cell walls to remain flexible and stretchable, contributing to the plant's ability to grow and adapt.
3. Support and flexibility: The primary function of collenchyma cells is to provide support to young and growing parts of the plant. The thickened cell walls at the corners and the absence of lignin allow them to provide structural support while still being flexible enough to accommodate growth.
In conclusion, cells with thickened walls at corners and non-lignified cell walls are characteristic of collenchyma cells in plants.

Answer:
Light and dark bands can be seen in:
- Striated muscles
Striated muscles, also known as skeletal muscles, display light and dark bands when viewed under a microscope. These bands are a result of the arrangement of contractile proteins within the muscle fibers. The light bands are called I bands and the dark bands are called A bands.
Explanation:
- Striated muscles are composed of long, multinucleated fibers that have a striped appearance when viewed under a microscope.
- The light and dark bands, also known as striations, are caused by the organization of the contractile proteins actin and myosin within the muscle fibers.
- The I bands contain actin filaments and are lighter in color, while the A bands contain overlapping actin and myosin filaments and are darker in color.
- The arrangement of these proteins allows for the sliding filament mechanism, which is responsible for muscle contraction.
- The presence of light and dark bands is a characteristic feature of striated muscles and can be observed in skeletal muscles, as well as cardiac muscles to a lesser extent.
- Smooth muscles, on the other hand, do not have the same organized arrangement of contractile proteins and therefore do not exhibit light and dark bands.
- Unstriated muscles, such as smooth muscles, lack the striations seen in striated muscles.
Therefore, the correct answer is B: striated muscles.