All questions of Cells and organisms for Grade 6 Exam

The cell was first discovered and named by Robert Hooke in 1665. He remarked that it looked strangely similar to cellula or small rooms which monks inhabited, thus deriving the name. However what Hooke actually saw was the dead cell walls of plant cells (cork) as it appeared under the microscope.

It's fission in which single cell divide and form two daughter cells....Fission this process of reproduction characteristically seen in unicellular organisms...

Option c

And nucleus because it controls the cell

**Explanation:**

**Introduction:**
Ostrich eggs are the largest eggs produced by any living bird species. They are laid by female ostriches, which are flightless birds native to Africa. Ostrich eggs are known for their large size and unique characteristics.

**Visual Appearance:**
Ostrich eggs are indeed visible to the naked eye due to their size. They are about 15-18 centimeters in length and weigh around 1.4 kilograms on average. This makes them the largest eggs produced by any bird species. The size of an ostrich egg is approximately equal to 24 chicken eggs.

**Shell Structure:**
The shell of an ostrich egg is extremely thick and sturdy. It is composed of multiple layers, including a hard outer layer and a porous inner layer. The outer layer protects the egg from external damage, while the inner layer allows for gas exchange during incubation.

**Cellular Composition:**
Like all eggs, an ostrich egg contains cells within it. However, it is important to note that the cells present in an ostrich egg are not visible to the naked eye. The cells are microscopic in size and require magnification, such as a microscope, to be seen.

**Misinterpretation:**
The question seems to imply that the ostrich egg itself is a single cell visible to the naked eye. However, this is a misinterpretation. The ostrich egg is a structure produced by the female ostrich's reproductive system, which contains multiple cells within it. These cells are not individually visible without the aid of magnification.

**Conclusion:**
In conclusion, the statement that an ostrich egg is a cell visible to the naked eye is false. While the egg itself is visible due to its large size, it is composed of multiple cells that are not individually visible without magnification. Ostrich eggs are fascinating structures worth studying, but their cellular composition requires the use of scientific tools to observe at a microscopic level.

Because a hen's whole egg is a cell, which you call yolk.
hope it helps
Tirtha Yeole
legends group

Because microscope is nachine help in view very tiny object.

The correct answer is B

Amoeba is an example of a multicellular organism.
Explanation:
- Amoeba is a type of single-celled organism known as a protist.
- It belongs to the group of organisms called unicellular organisms, which means they are composed of a single cell.
- Multicellular organisms, on the other hand, are composed of multiple cells that work together to form tissues, organs, and organ systems.
- Examples of multicellular organisms include animals, plants, and fungi.
- Amoeba, being a single-celled organism, does not fit into the category of multicellular organisms.
- It lives as a single cell and carries out all its necessary functions within that single cell.
- Amoeba reproduces asexually by a process called binary fission, where one cell divides into two identical daughter cells.
- It does not have specialized cells or tissues like multicellular organisms do.
- Therefore, the statement that Amoeba is an example of a multicellular organism is false.

Plasma membrane is a bilayered membrane

The plasma membrane is a crucial component of all living cells. It acts as a barrier that separates the inside of the cell from the external environment. The plasma membrane is composed of a bilayer of phospholipids, making it a bilayered membrane.

Structure of the plasma membrane:
The plasma membrane is made up of different types of molecules arranged in a specific manner. It has a unique structure that allows it to perform its functions effectively. The main components of the plasma membrane include:

1. Phospholipids: The phospholipids form the basic structure of the plasma membrane. They are composed of a hydrophilic (water-loving) head and two hydrophobic (water-repelling) tails. These phospholipids are arranged in a bilayer with the hydrophilic heads facing the outer and inner sides of the membrane and the hydrophobic tails sandwiched in between.

2. Proteins: Proteins are embedded in the phospholipid bilayer. They serve various functions such as transport of molecules, cell signaling, and structural support. Some proteins span the entire width of the membrane (integral proteins), while others are attached to one side of the membrane (peripheral proteins).

3. Cholesterol: Cholesterol molecules are interspersed within the phospholipid bilayer. They help stabilize the structure of the membrane and regulate its fluidity.

4. Glycolipids and Glycoproteins: These molecules are present on the outer surface of the plasma membrane. They play a role in cell recognition and communication.

Functions of the plasma membrane:
The plasma membrane has several important functions, including:

1. Selective permeability: The plasma membrane regulates the movement of substances in and out of the cell. It allows certain molecules to pass through while preventing the entry of others.

2. Cell signaling: Proteins present on the plasma membrane transmit signals from the external environment to the interior of the cell, allowing the cell to respond to its surroundings.

3. Cell adhesion: The plasma membrane proteins help cells adhere to each other, forming tissues and organs.

4. Protection: The plasma membrane acts as a physical barrier, protecting the cell from harmful substances and maintaining its internal environment.

In conclusion, the plasma membrane is a bilayered membrane composed of phospholipids, proteins, cholesterol, glycolipids, and glycoproteins. Its structure and composition enable it to perform its vital functions in maintaining cell integrity, regulating molecular transport, and facilitating cell signaling.

The tissue composed of the living, thin-walled, polyhedral cell is called parenchyma

Parenchyma is a type of tissue that is made up of living cells with thin cell walls. lt is a simple permanent tissue that makes up a large part of plant-soil tissues. parenchyma is non-vascular and is made up of cells that are basic, living, and undifferentiated. These cells are modified to perform various functions

Explanation:

The living substance of a cell is collectively known as protoplasm. It is a complex, highly organized and colloidal substance that constitutes the living matter of a cell. Protoplasm is found in all living cells, whether they are plant or animal cells.

Protoplasm is composed of two major components:

1. Nucleoplasm: It is the protoplasmic material that makes up the nucleus of a cell. It contains the genetic material of the cell in the form of DNA (deoxyribonucleic acid).

2. Cytoplasm: It is the protoplasmic material that surrounds the nucleus and fills the entire cell. It is composed of various organelles, such as mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles.

Functions of Protoplasm:

1. It provides a medium for all the metabolic activities of a cell.

2. It gives shape and form to a cell.

3. It helps in the movement of materials within a cell.

4. It is responsible for the growth and reproduction of a cell.

5. It helps in the maintenance of the internal environment of a cell.

Conclusion:

In conclusion, the living substance of a cell is known as protoplasm, which is composed of nucleoplasm and cytoplasm. Protoplasm is responsible for all the metabolic activities of a cell and is essential for the growth and reproduction of a cell.

Characteristic feature of a nerve cell:

A nerve cell, also known as a neuron, is the fundamental unit of the nervous system. It is responsible for transmitting and receiving signals within the body. When viewed under a microscope, a nerve cell exhibits several characteristic features. The correct feature out of the given options is option 'B', which describes a nerve cell as having a cell body with branched cytoplasmic extensions at one end and a long projection at the other end.

Explanation:

1. Cell body:
The cell body, also called the soma, is the main part of a nerve cell. It contains the nucleus, which controls the cell's activities, and other organelles necessary for its functioning. The cell body is typically oval in shape, which is why option 'A' might seem like a plausible answer. However, the correct option 'B' provides a more accurate description.

2. Branched cytoplasmic extensions:
At one end of the cell body, nerve cells have branched cytoplasmic extensions called dendrites. These structures receive signals from other nerve cells or sensory receptors and transmit them towards the cell body. Dendrites increase the surface area available for receiving signals, allowing the nerve cell to gather information from its surroundings.

3. Long projection:
At the other end of the cell body, nerve cells have a long projection called an axon. This structure is responsible for transmitting signals away from the cell body and towards other nerve cells or target cells, such as muscles or glands. The axon can vary in length, with some reaching several feet in the human body.

4. Function of nerve cells:
Nerve cells play a crucial role in the transmission of electrical signals, known as nerve impulses or action potentials. These signals allow communication between different parts of the nervous system and facilitate the coordination of various bodily functions. The branched dendrites receive incoming signals, which are then integrated in the cell body. If the resulting signal is strong enough, it is transmitted down the axon as a nerve impulse.

Conclusion:

The correct characteristic feature of a nerve cell, as observed under a microscope, is a cell body with branched cytoplasmic extensions at one end (dendrites) and a long projection at the other end (axon). These features enable nerve cells to transmit and receive signals, allowing for communication within the nervous system.

Explanation:

Striated muscles refer to the muscles that have a striped appearance under a microscope. These muscles are composed of repeating units called sarcomeres, which give rise to the characteristic light and dark bands.

Light and dark bands can be seen in striated muscles due to the arrangement of two types of protein filaments within the sarcomeres: actin and myosin.

Actin filaments are thin filaments that are attached to specialized structures called Z-lines. They appear lighter under a microscope.

Myosin filaments are thick filaments that are located between the actin filaments. They appear darker under a microscope.

Key Points:
- Light and dark bands are seen in striated muscles.
- Striated muscles have a striped appearance under a microscope.
- These muscles are composed of repeating units called sarcomeres.
- Sarcomeres contain actin and myosin filaments.
- Actin filaments are thin and attached to Z-lines, appearing lighter.
- Myosin filaments are thick and located between actin filaments, appearing darker.

Conclusion:

In conclusion, light and dark bands can be seen in striated muscles. These bands are a result of the arrangement of actin and myosin filaments within the sarcomeres of the muscle fibers. The light bands correspond to actin filaments, while the dark bands correspond to myosin filaments. This characteristic striped appearance is unique to striated muscles and can be observed under a microscope.

Parenchyma:
Parenchyma cells are simple, unspecialized plant cells that make up the bulk of the plant body. They have thin, flexible primary cell walls that are usually not lignified. The primary function of parenchyma cells is to carry out various metabolic activities such as photosynthesis, storage, and secretion. They are typically found in the outer layers of stems, roots, leaves, and fruits.

Aerenchyma:
Aerenchyma is a specialized type of parenchyma tissue that contains air spaces. These air spaces provide buoyancy to the plant and enable efficient oxygen transport to submerged plant parts. Aerenchyma cells have thin cell walls to facilitate the movement of gases.

Epidermal cells:
Epidermal cells are the outermost layer of cells in plants. They form a protective covering over the plant surface and help reduce water loss through the process of transpiration. Epidermal cells have a thick cuticle layer on their outer surface and often have specialized structures such as trichomes and stomata. The cell walls of epidermal cells are typically thin and flexible.

Collenchyma:
Collenchyma cells are elongated cells with irregularly thickened primary cell walls. These thickened walls are most prominent at the corners of the cells, providing structural support to young and growing plant parts. Collenchyma cells are usually found below the epidermis, in regions of the plant that require flexibility and tensile strength. The cell walls of collenchyma cells are non-lignified, allowing them to stretch and expand as the plant grows.

Correct answer:
In the given question, the correct answer is option 'B' - Collenchyma. Collenchyma cells have thickened walls at the corners and non-lignified cell walls, which provide structural support and flexibility to the plant. These characteristics are not observed in parenchyma, aerenchyma, or epidermal cells.

Single celled organisms only have one cell and hence they are also called unicellular(uni means one and cellular means cell)

Identification of Sclerenchyma Tissue

Sclerenchyma tissue is a type of plant tissue that provides mechanical support and protection to the plant. It is composed of cells that have thick, lignified cell walls. The correct answer to identify sclerenchyma tissue among the given options is option 'D', which pertains to the thickness of the cell wall.

Explanation:

1. Parenchyma Tissue:
- Parenchyma tissue is one of the three types of simple plant tissues, along with collenchyma and sclerenchyma.
- It is composed of loosely packed cells with thin cell walls, which are usually alive at maturity.
- The cells of parenchyma tissue have a prominent nucleus, which can be located anywhere within the cell.
- Parenchyma cells are usually isodiametric in shape, meaning they have a similar length, width, and height.
- These cells are involved in various functions, such as photosynthesis, storage of nutrients, and gas exchange.

2. Sclerenchyma Tissue:
- Sclerenchyma tissue is another type of simple plant tissue that provides mechanical support and protection to the plant.
- Unlike parenchyma cells, sclerenchyma cells have thick, lignified cell walls, which provide rigidity and strength.
- The cell walls of sclerenchyma cells are impregnated with a substance called lignin, making them harder and more rigid.
- Due to the presence of lignin, sclerenchyma cells are usually dead at maturity.
- The cells of sclerenchyma tissue are elongated and have tapered ends.
- The nucleus is generally absent in mature sclerenchyma cells, as it degenerates during cell maturation.
- The primary function of sclerenchyma tissue is to provide mechanical support to the plant, especially in areas where rigidity is required, such as the stem and branches.

Conclusion:

In conclusion, the correct way to identify sclerenchyma tissue among the given options is by observing the thickness of the cell wall. Sclerenchyma cells have thick, lignified cell walls, which distinguish them from other types of plant tissues. The position or absence of the nucleus, the size of the cell, or the location of the nucleus are not reliable indicators for identifying sclerenchyma tissue.

Answer:

Explanation:
The correct answer to the question is option B: Group of cells. Here's a detailed explanation of why tissue is a group of cells:
1. Tissue definition: Tissue refers to a group or collection of similar cells that work together to perform a specific function in the body.
2. Cell definition: A cell is the basic structural and functional unit of all living organisms. It is the smallest unit of life and can carry out various functions necessary for the survival and functioning of an organism.
3. Tissue composition: Tissues are composed of a group of cells that are similar in structure and function. These cells are organized and work together to perform a specific task or function in the body.
4. Types of tissues: There are four main types of tissues in the human body: epithelial tissue, connective tissue, muscle tissue, and nervous tissue. Each type of tissue is composed of specific cells that have specialized functions.
5. Functions of tissues: Tissues play a vital role in maintaining the structure and function of organs and systems in the body. They provide support, protection, and coordination of various activities.
In conclusion, tissue is a group of cells that work together to perform a specific function in the body. It is an essential component of the human body and is responsible for the proper functioning of organs and systems.

Answer:

The correct answer is option 'B' - sclerenchyma.

Sclerenchyma is a type of plant tissue that provides mechanical support and protection to the plant. It is characterized by cells with evenly thickened, hard, and lignified walls. These walls are made up of a substance called lignin, which makes them rigid and tough.

Characteristics of Sclerenchyma Cells:
- Evenly thickened walls: Sclerenchyma cells have walls that are uniformly thickened throughout. This thickening provides strength and support to the plant.
- Hard and lignified walls: The walls of sclerenchyma cells are hardened and reinforced with lignin. Lignin is a complex polymer that adds rigidity and resistance to these cells.
- Lack of protoplasts: Mature sclerenchyma cells are dead and lack protoplasts, which are the living contents of plant cells. The absence of protoplasts allows the cells to be fully filled with lignin, making them rigid and inelastic.
- Lack of intercellular spaces: Sclerenchyma cells are closely packed together, leaving little to no intercellular spaces. This arrangement further enhances their strength and support.

Functions of Sclerenchyma Cells:
- Mechanical support: The thickened and lignified walls of sclerenchyma cells provide strength and support to the plant. They enable the plant to stand upright and resist mechanical stress, such as wind or gravity.
- Protection: Sclerenchyma cells can also act as a protective barrier. For example, in the case of seed coats, the hard and tough sclerenchyma cells prevent damage to the developing embryo.
- Conductivity: In some plants, sclerenchyma cells can also aid in the transport of water and nutrients. They may form specialized structures, such as fibers or sclereids, that facilitate the movement of fluids within the plant.

Examples of Sclerenchyma Cells:
- Fibers: Sclerenchyma fibers are long, slender cells that are commonly found in the stems, leaves, and vascular tissues of plants. They provide structural support and are responsible for the strength and flexibility of plant parts.
- Sclereids: Sclereids, also known as stone cells, are compact and irregularly shaped sclerenchyma cells. They are found in various plant organs, such as the seed coats of nuts and the gritty texture of pears. Sclereids provide mechanical protection and can also contribute to the dispersal of seeds.

In conclusion, cells with evenly thickened, hard, and lignified walls are characteristic of sclerenchyma tissue. These cells provide mechanical support, protection, and sometimes even aid in the transport of fluids within the plant.

Cyanobacteria are prokaryotic cells that lack membrane-bound organelles and nuclei. Their common name is blue-green algae because of their blue-green color brought on by their pigment phycocyanin. Most algae are considered plants, but blue-green algae are bacteria.

Animal don't require it

Cardiac Muscle Fibres:

- Cardiac muscle fibres are branched and interconnected by oblique bridges.
- These muscle fibres are found in the walls of the heart.
- Cardiac muscle is a special type of muscle tissue that is responsible for the contraction of the heart, allowing it to pump blood throughout the body.

Structure and Function of Cardiac Muscle Fibres:
- Cardiac muscle fibres are striated, meaning they have a striped appearance when viewed under a microscope.
- The striations are due to the arrangement of contractile proteins within the muscle fibres.
- These proteins, called actin and myosin, are responsible for the contraction of the muscle.
- The branched nature of cardiac muscle fibres allows for coordinated contractions, ensuring that the heart beats as a whole rather than individual segments.

Intercalated Discs:
- One unique feature of cardiac muscle fibres is the presence of intercalated discs.
- Intercalated discs are specialized cell junctions that connect adjacent cardiac muscle cells.
- They contain gap junctions, which allow for the rapid transmission of electrical signals between cells.
- This allows for the coordinated contraction of the entire heart, ensuring that all the chambers contract in sync.

Function of Cardiac Muscle Fibres:
- Cardiac muscle fibres contract rhythmically and involuntarily, allowing the heart to pump blood.
- The contraction of cardiac muscle is regulated by electrical signals that originate in the sinoatrial (SA) node, often referred to as the "natural pacemaker" of the heart.
- These electrical signals spread rapidly through the intercalated discs, causing the muscle fibres to contract in a coordinated manner.
- The contraction and relaxation of cardiac muscle fibres allow the heart to pump blood efficiently throughout the body.

Conclusion:
- In conclusion, branched muscle fibres interconnected by oblique bridges are cardiac muscle fibres.
- These muscle fibres are striated, and their unique structure allows for coordinated contractions and efficient pumping of blood by the heart.

Neurons and their Parts

Neurons are specialized cells in the nervous system that transmit information through electrical and chemical signals. They have various components that enable them to perform their functions. One of these components is a single long part called the axon.

The Axon: The Long Part of a Neuron

The axon is a long, slender projection that extends from the cell body of a neuron. It is responsible for transmitting electrical impulses, known as action potentials, away from the cell body and toward other neurons or target cells. The axon is the primary conduit for communication between neurons, allowing for the transmission of information across the nervous system.

Structure of an Axon

The axon is composed of specialized structures that facilitate its function. These structures include:

1. Axon Hillock: This is the region where the axon originates from the cell body. It plays a crucial role in generating and initiating action potentials.

2. Axon Terminal: At the end of the axon, there are small branches called axon terminals or terminal buttons. These structures contain synaptic vesicles filled with neurotransmitters, which are released into the synapse to communicate with the next neuron or target cell.

3. Myelin Sheath: In some neurons, the axon is surrounded by a protective covering called the myelin sheath. This sheath is made up of specialized cells called Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system. The myelin sheath acts as an insulator, allowing for faster transmission of electrical signals along the axon.

Function of the Axon

The axon plays a vital role in transmitting information between neurons. When an electrical impulse, or action potential, reaches the axon hillock, it triggers a chain reaction that propels the action potential down the length of the axon. This process is known as axonal conduction.

The axon terminals at the end of the axon form synapses with other neurons or target cells. When an action potential reaches the axon terminal, it triggers the release of neurotransmitters from synaptic vesicles. These neurotransmitters then bind to receptors on the receiving neuron or target cell, transmitting the information across the synapse.

In Conclusion

In summary, each neuron has a single long part called the axon. This structure is responsible for transmitting electrical impulses away from the cell body and towards other neurons or target cells. The axon plays a critical role in facilitating communication within the nervous system and is composed of specialized structures such as the axon hillock, axon terminals, and myelin sheath.

The function unit of the life is called cell.

Chloroplast is found in the:


There are four options given and we need to determine which one is correct.
A: Plant cell only
- Chloroplasts are specialized organelles found in plant cells.
- They are responsible for photosynthesis, the process by which plants convert sunlight into energy.
B: Animal cell only
- Animal cells do not contain chloroplasts.
- They obtain energy through other means such as cellular respiration.
C: Both of these
- This option is not correct because chloroplasts are only found in plant cells, not animal cells.
D: None of these.
- This option is also not correct because chloroplasts are indeed found in plant cells.
Conclusion:
- The correct answer is A: Plant cell only.
- Chloroplasts are unique to plant cells and play a crucial role in the process of photosynthesis.

The shape of striated muscle cells is cylindrical.

Striated muscle cells, also known as muscle fibers, are a type of muscle cell found in skeletal and cardiac muscles. They are characterized by their unique appearance under a microscope, which is due to the presence of alternating light and dark bands called striations.

Explanation:
The shape of striated muscle cells is cylindrical, which means they have a long and cylindrical shape. This shape is essential for their function in generating force and movement in the body.

Importance of Cylindrical Shape:
The cylindrical shape of striated muscle cells has several important implications for their function:

1. Force Generation: The cylindrical shape allows for a large number of contractile proteins, called myofibrils, to be packed within each muscle fiber. This arrangement maximizes the force-generating capacity of the muscle cell, enabling it to contract with significant force.

2. Alignment of Sarcomeres: Sarcomeres are the basic units of muscle contraction and are arranged in series along the length of the muscle fiber. The cylindrical shape of the muscle fiber ensures that the sarcomeres are aligned in parallel, allowing for efficient force transmission along the length of the muscle.

3. Optimal Length-Tension Relationship: The cylindrical shape of the muscle fiber also allows for the optimal length-tension relationship, which is crucial for generating maximum force. When a muscle fiber is at its resting length, the actin and myosin filaments within the sarcomeres can form the most cross-bridges, leading to optimal force production.

4. Efficient Energy Metabolism: The cylindrical shape of muscle fibers also facilitates efficient energy metabolism. The cytoplasm of the muscle fiber, called the sarcoplasm, contains numerous mitochondria that provide energy in the form of ATP for muscle contraction. The cylindrical shape allows for a large surface area-to-volume ratio, ensuring efficient exchange of nutrients and waste products with the surrounding blood vessels.

In conclusion, the cylindrical shape of striated muscle cells is essential for their function in generating force and movement in the body. This shape allows for efficient force generation, alignment of sarcomeres, optimal length-tension relationship, and efficient energy metabolism.