Fundamental Unit Of Life - Practice Test, Class 9 Science - Class 9 MCQ

Main Constituent of Cell Wall:
The main constituent of the cell wall is cellulose.
Explanation:
Cell wall is a rigid structure that surrounds the cell membrane of plant cells, bacteria, fungi, and some protists. It provides support and protection to the cell. The main constituent of the cell wall varies in different organisms, but in the case of plant cells, it is primarily composed of cellulose.
Cellulose:
- Cellulose is a complex carbohydrate and a polymer of glucose molecules.
- It is made up of long chains of glucose molecules linked together by beta-1,4-glycosidic bonds.
- These chains are arranged in a parallel manner, forming microfibrils.
- The microfibrils are then cross-linked and embedded in a matrix of other polysaccharides, proteins, and lignin, which provide additional strength and support to the cell wall.
Other Constituents of the Cell Wall:
While cellulose is the main constituent of the cell wall, there are other components present as well, depending on the organism:
- In addition to cellulose, plant cell walls may also contain hemicellulose, pectin, lignin, and proteins.
- Bacterial cell walls are composed of peptidoglycan.
- Fungal cell walls can vary and may contain chitin, glucans, and proteins.
Conclusion:
The main constituent of the cell wall is cellulose, a complex carbohydrate made up of long chains of glucose molecules. In addition to cellulose, other components such as hemicellulose, pectin, lignin, proteins, peptidoglycan, chitin, and glucans may also be present in the cell wall depending on the organism.

Organelle Present in Onion Cells but not in Human Cheek Cells: Cell Wall
The cell wall is a rigid structure that surrounds the cell membrane in plant cells and some other organisms. It provides support and protection to the cell. While both onion cells and human cheek cells have a cell membrane, only onion cells have a cell wall. Here is a detailed explanation:
Onion Cells:
- Onion cells are plant cells, and plants have a cell wall as a distinctive feature.
- The cell wall is made up of cellulose, a complex carbohydrate.
- It is located outside the cell membrane and provides rigidity to the cell.
- The cell wall allows the cell to maintain its shape and protect it from external stresses.
Human Cheek Cells:
- Human cheek cells are animal cells and do not have a cell wall.
- Animal cells only have a cell membrane that acts as a selective barrier.
- The cell membrane controls the movement of substances into and out of the cell.
Importance of Cell Wall:
- The cell wall provides strength and structural support to plant cells.
- It helps plants maintain their shape and stand upright.
- The cell wall also protects the cell from mechanical damage and pathogens.
- In addition, the cell wall allows plants to withstand osmotic pressure changes.
Conclusion:
The cell wall is present in onion cells but not in human cheek cells. The presence of a cell wall is a characteristic feature of plant cells and provides various functions such as support, protection, and regulation of osmotic pressure.

Father of Biology
The person known as the "father of biology" is Aristotle. He is considered to be one of the most influential thinkers and scholars in the field of biology. Here is a detailed explanation of why Aristotle is given this title:
Aristotle's Contributions to Biology:
- Aristotle was one of the first philosophers to systematically study and classify living organisms. He categorized and described a wide range of animals and plants, laying the foundation for the field of taxonomy.
- He conducted detailed anatomical studies on various species, making observations and documenting their structures and functions.
- Aristotle also proposed the theory of spontaneous generation, which suggested that life could arise spontaneously from non-living matter. Although this theory has since been disproven, it was a significant contribution to the study of biology at the time.
- He emphasized the importance of observation and empirical evidence in understanding the natural world, setting the stage for the scientific method.
- Aristotle's works, such as "History of Animals" and "On the Parts of Animals," were influential in shaping the study of biology for centuries to come.
Other Options:
- Camillo Golgi was an Italian physician and biologist known for his work on the structure of the nervous system. He is not considered the father of biology.
- Rudolf Virchow was a German physician and pathologist who made significant contributions to the understanding of diseases and cell biology. While he is often referred to as the "father of modern pathology," he is not considered the father of biology.
- Matthias Schleiden was a German botanist who co-founded the cell theory. While his work was important in the field of biology, he is not considered the father of biology.
In conclusion, Aristotle is widely recognized as the father of biology due to his significant contributions to the study of living organisms and his influence on the development of biological thought.

White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells.

The Thickness of Cell Membrane:
The cell membrane is a crucial component of all cells. It is a thin, flexible barrier that surrounds the cell and separates the internal environment from the external environment. The thickness of the cell membrane has been studied extensively, and it is generally agreed upon that the range falls between 7-10 nanometers.
Explanation:
To provide a detailed solution, let's break down the key points:
1. Cell Membrane:
- The cell membrane, also known as the plasma membrane, is a phospholipid bilayer with embedded proteins.
- It plays a vital role in maintaining the integrity of the cell, regulating the movement of substances in and out of the cell, and facilitating cellular communication.
2. Thickness of Cell Membrane:
- The exact thickness of the cell membrane may vary slightly depending on the cell type and conditions.
- Studies and research have consistently measured the thickness of the cell membrane in the range of 7-10 nanometers.
3. Range of Thickness:
- Option A: 7-9 nanometers - This option falls within the generally accepted range for the thickness of the cell membrane.
- Option B: 6-10 nanometers - This option also falls within the accepted range for the cell membrane thickness.
- Option C: 7-10 nanometers - This option is correct as it encompasses the known range of the cell membrane thickness.
- Option D: 6-9 nanometers - This option is close to the accepted range but does not include the upper limit of 10 nanometers.
Therefore, the correct answer is Option C: 7-10 nanometers.

Cell organelle found only in Plant is: Plastids
Plastids are a group of organelles found only in plant cells. They are responsible for various functions related to energy production and storage, as well as the synthesis and storage of important molecules.
Explanation:
Plastids are unique to plant cells and are not found in animal cells. They are double-membrane organelles that are involved in a variety of essential plant cell processes. Here are some key points about plastids:
- Plastids are involved in photosynthesis, which is the process by which plants convert sunlight into energy. Chloroplasts, a type of plastid, contain chlorophyll, a pigment that captures sunlight and facilitates the synthesis of glucose.
- Besides chloroplasts, other types of plastids include chromoplasts and leucoplasts. Chromoplasts contain pigments such as carotenoids, which give fruits and flowers their vibrant colors. Leucoplasts, on the other hand, are responsible for storing starches, oils, and proteins.
- Plastids have their own DNA, which is separate from the DNA found in the cell nucleus. This DNA encodes some of the proteins necessary for plastid function and replication.
- Plastids can divide and multiply within a cell, allowing for the growth and development of plant tissues.
- Additionally, plastids can differentiate into different forms depending on the needs of the plant. For example, in root cells, they can develop into amyloplasts, which are specialized for starch storage.
In conclusion, plastids are a distinct organelle found only in plant cells. They play a crucial role in photosynthesis, pigmentation, and the storage of essential molecules. Their presence is one of the key features that differentiate plant cells from animal cells.

Function of centriole:
Centrioles are small, cylindrical structures found in animal cells. They play a crucial role in cell division and the formation of the spindle fibers. Here's a detailed explanation of the function of centrioles:
1. Formation of spindle fibers:
- Centrioles are involved in the formation of spindle fibers during cell division. Spindle fibers are responsible for separating the chromosomes and ensuring equal distribution of genetic material to the daughter cells.
- Centrioles are found in pairs called centrosomes. These centrosomes migrate to opposite ends of the cell and form the spindle apparatus, which consists of microtubules.
- The microtubules extend from the centrioles and attach to the chromosomes, allowing for their movement and separation during cell division.
2. Cell division initiation:
- Centrioles are also involved in the initiation of cell division. They are responsible for organizing the microtubule network necessary for cell division to occur.
- During the cell cycle, the centrioles replicate, and each pair moves to opposite ends of the cell. This ensures that each daughter cell receives a complete set of centrioles to initiate cell division.
In summary, the function of centrioles is primarily related to cell division and the formation of spindle fibers. They play a crucial role in ensuring the accurate distribution of genetic material to the daughter cells.

The cell organelle that is not bounded by a membrane is the Ribosome. Here's a detailed explanation:
Ribosome:
- Ribosomes are small, spherical organelles found in both prokaryotic and eukaryotic cells.
- They are responsible for protein synthesis and are involved in the translation of mRNA into proteins.
- Ribosomes can be found freely floating in the cytoplasm or attached to the endoplasmic reticulum (ER).
- Unlike other organelles, ribosomes do not have a membrane surrounding them.
Other cell organelles:
- Lysosome: Lysosomes are membrane-bound organelles that contain digestive enzymes. They are involved in breaking down waste materials and cellular debris.
- ER (Endoplasmic Reticulum): The ER is an extensive network of membrane-bound tubules and sacs. It plays a role in protein synthesis, lipid metabolism, and detoxification.
- Nucleus: The nucleus is a membrane-bound organelle that contains the cell's genetic material, DNA. It is the control center of the cell and governs cellular activities.
Therefore, out of the given options, the correct answer is A: Ribosome.

The process that requires energy provided by ATP is: Active transport
Explanation:
Active transport is a process that requires energy in the form of ATP (adenosine triphosphate) to move molecules or ions against their concentration gradient across a cell membrane. This process is essential for maintaining proper cellular function and homeostasis.
Here is a detailed explanation of active transport:
1. Definition: Active transport is the movement of substances from an area of lower concentration to an area of higher concentration, against the concentration gradient. This movement requires the expenditure of energy.
2. ATP as an energy source: ATP is a molecule that provides energy for cellular processes. When ATP is hydrolyzed to ADP (adenosine diphosphate) and inorganic phosphate (Pi), energy is released. This energy is utilized by specific proteins called transporters or pumps to actively move substances across the cell membrane.
3. Role of transport proteins: Transport proteins embedded in the cell membrane act as molecular pumps. These proteins undergo conformational changes fueled by ATP hydrolysis, allowing them to bind to specific molecules or ions on one side of the membrane and transport them to the other side.
4. Types of active transport: There are different types of active transport mechanisms, such as primary active transport and secondary active transport.
- Primary active transport: In primary active transport, ATP directly provides the energy needed to transport molecules or ions. An example of this is the sodium-potassium pump, which actively transports sodium ions out of the cell and potassium ions into the cell.
- Secondary active transport: In secondary active transport, the energy stored in the electrochemical gradient of one molecule or ion is used to transport another molecule or ion against its concentration gradient. This process indirectly relies on ATP. An example is the sodium-glucose cotransporter, which uses the energy from the sodium gradient to transport glucose against its concentration gradient.
5. Importance of active transport: Active transport is essential for various physiological processes, including nutrient absorption, ion balance, nerve impulse transmission, muscle contraction, and cellular signaling. It allows cells to maintain proper concentrations of molecules or ions inside and outside the cell, enabling them to function optimally.
In summary, active transport is a process that requires ATP as an energy source to move molecules or ions against their concentration gradient across the cell membrane. This process is vital for maintaining cellular homeostasis and carrying out essential physiological functions.

The largest cell in the human body is the ovum, or female egg cell. It is about 0.1 millimeters in diameter, which is about the same size as a strand of hair. 

The power house of a cell is the mitochondrion.
Explanation:
Mitochondrion:
- The mitochondrion is an organelle found in most eukaryotic cells.
- It is often referred to as the "powerhouse" of the cell because it generates most of the cell's supply of adenosine triphosphate (ATP), which is used as a source of chemical energy.
- The process through which ATP is produced is called cellular respiration, and it takes place within the mitochondria.
- Mitochondria have their own DNA and can reproduce themselves, suggesting that they were once independent organisms that were engulfed by ancestral eukaryotic cells.
- They have a highly folded inner membrane called the cristae, which provides a large surface area for the chemical reactions involved in ATP production.
- The outer membrane of the mitochondrion acts as a barrier, separating the contents of the mitochondrion from the rest of the cell.
Other organelles mentioned:
- Chloroplast: This organelle is found in plant cells and is responsible for photosynthesis, not energy production.
- Golgi apparatus: This organelle is involved in processing, packaging, and sorting proteins for transport within the cell or for secretion.
- Nucleolus: This organelle is found within the nucleus of a cell and is involved in the production of ribosomes, not energy production.
Therefore, the correct answer is B: Mitochondrion.

The number of lenses in a compound light microscope is 2.
Explanation:
- A compound light microscope consists of multiple lenses that work together to magnify the specimen.
- The two main lenses in a compound light microscope are the objective lens and the eyepiece lens.
- The objective lens is located near the specimen and produces a magnified image of the specimen.
- The eyepiece lens, also known as the ocular lens, is located at the top of the microscope and further magnifies the image produced by the objective lens.
- The combination of these two lenses allows for greater magnification and resolution of the specimen.
- Therefore, the correct answer is A: 2 lenses.

Answer:
Mitochondria are found:
- In all types of living cells: Mitochondria are present in both animal and plant cells, as well as in other eukaryotic cells.
Key Points:
- Mitochondria are double-membraned organelles found in the cytoplasm of cells. They are often referred to as the "powerhouse" of the cell because they are responsible for generating most of the cell's energy in the form of ATP (adenosine triphosphate).
- Mitochondria have their own DNA and can replicate independently of the cell.
- Mitochondria are believed to have originated from ancient bacteria that were engulfed by ancestral eukaryotic cells through a process called endosymbiosis.
- While mitochondria are most commonly associated with cellular respiration and energy production, they also have other important functions, such as regulating cell death pathways and calcium signaling.
- In addition to animal and plant cells, mitochondria can also be found in other eukaryotic organisms, such as fungi and protists. However, they are not present in prokaryotic cells, such as bacteria and archaea.
Conclusion:
Mitochondria are found in all types of living cells, including animal cells, plant cells, and other eukaryotic cells. They play a crucial role in energy production and have various other functions in cellular processes.

The organelle considered as a "suicide bag" is Lysosomes.
Lysosomes are membrane-bound organelles found in animal cells. They contain various enzymes that are responsible for breaking down waste materials and cellular debris through a process called autophagy. However, if the lysosomes malfunction or rupture, they can release their digestive enzymes into the cytoplasm, leading to cell death. This process is often referred to as "programmed cell death" or apoptosis.
Key points:
- Lysosomes are membrane-bound organelles.
- They contain enzymes responsible for breaking down waste materials and cellular debris.
- Lysosomes can undergo a process called autophagy, where they digest and recycle cellular components.
- If lysosomes malfunction or rupture, they can release their enzymes into the cytoplasm, leading to cell death.
- This process is known as apoptosis or "programmed cell death."
- Due to their ability to cause cell death, lysosomes are sometimes referred to as "suicide bags" of the cell.

Plasma membrane is selectively permeable membrane ... morewhich allow the substance to come inside and outside to the cell according to use and it also help the cell organelles to leave in the cytoplasm with other cell membrane plasma membrane also give support and rigidity to the cell.

Ribosomes are the center for protein synthesis.
Explanation:
- Ribosomes are small, spherical organelles found in all living cells.
- They are responsible for the synthesis of proteins, which are essential for the structure, function, and regulation of cells.
- Protein synthesis is a complex process that involves the translation of genetic information from DNA to RNA and then to proteins.
- Ribosomes play a crucial role in this process by acting as the site of protein synthesis.
- They consist of two subunits, a large subunit, and a small subunit, which come together to form a functional ribosome.
- Ribosomes can be found in the cytoplasm of prokaryotic cells and in both the cytoplasm and the endoplasmic reticulum of eukaryotic cells.
- They are composed of ribosomal RNA (rRNA) and proteins, with the rRNA being responsible for catalyzing the formation of peptide bonds during protein synthesis.
- Ribosomes function by reading the genetic code carried by messenger RNA (mRNA) and using this information to assemble amino acids into a polypeptide chain, which will eventually fold into a functional protein.
- This process occurs in a series of steps, including initiation, elongation, and termination, and is essential for the growth, development, and maintenance of cells.
- In summary, ribosomes are the center for protein synthesis, playing a critical role in the production of proteins necessary for cellular function.

Cell Secretion is done by -

• Plastids: Plastids are responsible for various functions in plant cells, but they are not directly involved in cell secretion.


• ER (Endoplasmic Reticulum): The ER is involved in the synthesis, folding, and modification of proteins. It plays a crucial role in the secretion of proteins.


• Golgi Apparatus: The Golgi apparatus is responsible for modifying, sorting, and packaging proteins for secretion or transport to other parts of the cell.


• Nucleolus: The nucleolus is involved in the synthesis of ribosomes and does not directly participate in cell secretion.

Therefore, the correct answer is C: Golgi apparatus.
The Golgi apparatus plays a vital role in the secretion of various molecules from the cell. Here is a detailed explanation of how the Golgi apparatus is involved in cell secretion:
1. Protein Synthesis: Proteins are synthesized in the ribosomes present on the rough endoplasmic reticulum (ER).
2. Transport to the Golgi Apparatus: The newly synthesized proteins are transported from the ER to the Golgi apparatus in small vesicles.
3. Modification and Sorting: Within the Golgi apparatus, the proteins undergo various modifications, such as folding, glycosylation (attachment of sugar molecules), and addition of other functional groups. These modifications help in the proper folding and functionality of the proteins.
4. Packaging into Vesicles: The Golgi apparatus sorts the modified proteins and packages them into specialized vesicles called secretory vesicles. These vesicles contain the proteins that are destined for secretion.
5. Transport to the Cell Membrane: The secretory vesicles are then transported towards the cell membrane, where they fuse with the membrane and release their contents to the outside of the cell through a process called exocytosis.
6. Other Secretory Pathways: Besides protein secretion, the Golgi apparatus is also involved in the secretion of other molecules, such as lipids and carbohydrates, through similar processes of modification, sorting, and packaging.
In conclusion, the Golgi apparatus is responsible for modifying and packaging various molecules, including proteins, for secretion from the cell. It plays a crucial role in maintaining cellular homeostasis and communication with the external environment.

Eukaryotic cell means:
- A eukaryotic cell is a type of cell that has a true nucleus enclosed within a membrane.
- It is characterized by having membrane-bound organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus.
- Eukaryotic cells are typically larger and more complex than prokaryotic cells.
- They can be found in plants, animals, fungi, and protists.
- The nucleus in a eukaryotic cell contains the DNA, which is organized into multiple linear chromosomes.
- Eukaryotic cells undergo mitosis and meiosis for cell division.
- These cells are capable of performing various specialized functions due to their complex internal structure.
- Eukaryotic cells are involved in processes such as protein synthesis, energy production, and cellular communication.
- They have a cytoskeleton that provides structural support and helps with cell movement.
- Eukaryotic cells have a flexible cell membrane that regulates the exchange of materials with the external environment.
- Examples of eukaryotic cells include human skin cells, plant leaf cells, and yeast cells.
In conclusion, a eukaryotic cell refers to a cell with a true nucleus and membrane-bound organelles, and it is larger and more complex compared to prokaryotic cells.

Mitochondria:
- Cristae and Oxysomes are associated with mitochondria.
- Cristae are the folds in the inner membrane of the mitochondria that increase the surface area for chemical reactions.
- Oxysomes are the protein complexes located on the cristae that are involved in the electron transport chain and ATP synthesis.
Plastids, Golgi apparatus, and Plasma membrane:
- Plastids are organelles found in plant cells that are involved in processes like photosynthesis and storage of pigments.
- The Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids for transport within the cell.
- The plasma membrane is the outer boundary of the cell that controls the flow of substances in and out of the cell.
Conclusion:
- Based on the given information, it is clear that Cristae and Oxysomes are associated with mitochondria.

Intercellular Connections of Plant Cells
The intercellular connections of plant cells are called plasmodesmata. Plasmodesmata are small channels that allow for communication and transport between adjacent plant cells. These connections play a crucial role in various cellular processes, including nutrient and signal exchange, as well as the coordination of growth and development within the plant.
Key Points:
- Intercellular connections in plant cells are called plasmodesmata.
- Plasmodesmata are small channels that connect adjacent plant cells.
- These connections allow for the exchange of nutrients and signals between cells.
- Plasmodesmata play a vital role in coordinating growth and development within the plant.
- They are involved in the transport of water, ions, sugars, hormones, and other molecules between cells.
- Plasmodesmata also contribute to the defense mechanisms of plants by facilitating the movement of defense signals and molecules.
Overall, plasmodesmata serve as a vital communication network within plant tissues, enabling the coordination and integration of various cellular processes. By allowing for the exchange of molecules and information between cells, these intercellular connections play a crucial role in the overall function and development of plants.