Cell : The Unit of Life - Class 11 Biology - Chapter 8 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - Cell : The Unit of Life | NCERT | Biology | Class 11
__________ are organisms that have cell organelles and a well-defined nucleus.
A. Bacteria
B. Prokaryotes
C. Eukaryotes
The correct option is C. Eukaryotes.
Eukaryotes are organisms characterized by having well-defined nuclei and membrane-bound organelles such as mitochondria, Golgi apparatus, and endoplasmic reticulum. Examples of eukaryotes include diverse living organisms like amoeba, fungi, plants, and animals.
A student looking through a light microscope saw this cell in cytokinesis. This cell is most likely from:
A) a plant
B) a virus
C) an animal
D) a bacterium
Correct Answer: C) an animal
Cytokinesis refers to the process wherein a cell's cytoplasm divides, following nuclear division. This event marks a critical phase in the cell cycle.
For animal cells, cytokinesis occurs through a process called cleavage furrow formation. This involves the pinching of the cell membrane, initiating from the cell's periphery towards the center, eventually splitting the cell into two daughter cells.
Plant cells differ in that they possess a rigid cell wall, and cytokinesis is conducted via the formation of a cell plate beginning at the center of the cell and expanding outward. This plate ultimately develops into a new cell wall dividing the two daughter cells.
Virus and bacteria lack the structural components (like a cell wall in plants or a cleavage mechanism in animal cells) required for the processes observed in cytokinesis. Moreover, viruses do not undergo cell division, as they replicate by hijacking host cellular machinery.
Therefore, the observed characteristics of cytokinesis suggest the cell described by the student is from an animal.
Which ones do not have cellular structure?
A. PPLO
B. Rickettsia
C. Viruses
D. Archaebacteria
The correct answer is C. Viruses.
Viruses are unique as they lack a cellular structure, making them acellular. Unlike other options listed which all consist of cells, viruses consist only of genetic material (DNA or RNA) enclosed in a protein coat and do not have the cellular machinery found in living cells.
Sieve tube is
A) enucleated
B) nucleated
C) multinucleated
D) dead cells
Correct Answer: A) enucleated
Explanation: Sieve tube cells are elongated living cells, which are organized longitudinally and function closely with companion cells. During their development, sieve tube cells undergo progressive changes leading to the loss of several organelles including the nucleus, Golgi bodies, ribosomes, and the tonoplast. By maturity, these cells retain a functioning plasma membrane, and possess modified mitochondria, plastids, and smooth endoplasmic reticulum, but are without a nucleus, making them enucleated.
The operations within sieve tubes are managed by the nucleus of the associated companion cell.
Which of the following organelle is called the 'suicide bags' of the cell?
A. Mitochondria
B. Lysosomes
C. Golgi apparatus
D. None of the above
The correct option is B. Lysosomes
Lysosomes are often referred to as the 'suicide bags' of the cell. They are filled with digestive enzymes that help in breaking down waste materials, invading substances, and cellular debris. Crucially, these organelles can also lead to the self-destruction of cells by releasing their protein-digesting enzymes, which directly contributes to their nickname.
A battery may have one or more than one cell connected in series.
A) True
B) False
The correct option is A) True.
The definition of a battery can vary among different sources. According to some sources, a battery is an arrangement of multiple cells connected in series. However, standard books and reliable definitions clarify that a battery may consist of one or more cells connected in series. Therefore, it's possible for a single cell to function as a battery. Here, we adhere to the definition provided in standard textbooks, which recognizes that both one cell and multiple cells connected in series qualify as a battery. This supports the true statement regarding the structure of a battery.
Muscle cells do not have:
(A) nucleus
(B) chloroplasts
(C) cell membrane
(D) nucleolus
The correct answer is (B) chloroplasts.
Muscle cells are a type of animal cells, and it is important to understand that plastids such as chloroplasts are exclusive to plant cells. Therefore, animal cells, including muscle cells, do not contain chloroplasts.
With respect to cells, which of the following is a characteristic of living things?
A) Size of the cell
B) Organization of the cells
C) Presence of a cellular structure
D) Number of cells present
The correct answer is C) Presence of a cellular structure.
The presence of a cellular structure is a fundamental characteristic of living things. This criterion is essential as all living things, regardless of the variety in the number of cells they possess, must have at least some form of cellular organization. However, attributes like the organization and size of the cell, or the number of cells present, do not fundamentally define whether or not an entity is considered living. This makes option C the best choice among the given options.
Choose the statement which is true for Kingdom Protista:
A. The organisms belonging to this kingdom are prokaryotes.
B. The organisms belonging to this kingdom are unicellular eukaryotes.
C. The organisms belonging to this kingdom are multicellular eukaryotes.
D. The organisms belonging to this kingdom do not have mitochondria.
The correct option is B. The organisms belonging to this kingdom are unicellular eukaryotes.
Kingdom Protista primarily consists of unicellular eukaryotes. This group includes organisms that exhibit characteristics similar to plants, animals, and fungi but are predominantly unicellular. These organisms possess a true nucleus and membrane-bound organelles, which are defining features of eukaryotic cells.
Meristematic cells are characterized by:
A. thin cell walls and large intercellular spaces
B. thin cell walls and no intercellular spaces
C. thick cell walls and large intercellular spaces
D. thick cell walls and no intercellular spaces
The correct answer is B. thin cell walls and no intercellular spaces.
Meristematic cells are specialized structures located in regions of the plant where growth is actively taking place, such as the roots and shoot apices, as well as along the lateral axis in mature plants. These cells are crucial as they continually divide to produce new cells contributing to plant growth.
Characteristics of meristematic cells include thin cell walls, which facilitate easier and more frequent cell division, dense cytoplasm, and a prominent nucleus. Significantly, these cells do not have intercellular spaces; this means they are tightly packed together, which is optimal for synchronized cell division and growth activities.
Which among the following is absent in eukaryotes?
A. Mesosomes
B. Plasma membrane
C. Cell wall
D. Nucleus
The correct option is A. Mesosomes
Mesosomes are specialized structures formed by the invagination of the plasma membrane into the cell. These extensions contain respiratory enzymes and are primarily found in prokaryotic cells. Eukaryotic cells do not have mesosomes.
Both plasma membranes and cell walls are present in eukaryotic and prokaryotic cells, though it is noteworthy that animal cells, which are eukaryotic, do not possess cell walls.
A well-defined nucleus, characterized by the presence of a nuclear membrane, is a hallmark of eukaryotic cells. In contrast, prokaryotic cells feature a nucleoid, which is an irregular region that contains DNA but lacks a nuclear membrane.
A cell is able to survive when:
A Nucleus may be removed, but cytoplasm is intact.
B Cytoplasm may be removed, but nucleus is intact.
C Both cytoplasm and nucleus are intact.
D Cytoplasm is lost, but nucleus and cell membrane are intact.
The correct answer is C: Both cytoplasm and nucleus are intact.
For a cell to survive and properly function, it is essential that both the cytoplasm and the nucleus are intact. The cytoplasm of a cell houses various organelles that are crucial for cellular activities like energy production, while the nucleus contains genetic material (DNA) necessary for controlling cell growth, metabolism, and reproduction. Thus, the presence of both structures is vital for the cell's continuity and functionality.
"What is meant by cell sap?"
Cell sap refers to the fluid content that is found within the vacuoles of plant cells. This solution is composed of various substances including sugars, amino acids, waste substances like tannins, and mineral salts. These components are crucial for the storage and regulation of essential compounds within the plant.
A student was looking at a cell under a microscope. He noted down his observations:
A. A well-defined nucleus. B. Large ribosomes. C. A cell wall.
From which of the following is the cell likely taken from?
A. Euglena
B. Banana leaf
C. Mycoplasma
D. Human cheek cells
The correct answer is B. Banana leaf.
The observations noted by the student, such as a well-defined nucleus and large ribosomes, indicate that the cell is eukaryotic, as prokaryotic cells typically lack a well-defined nucleus and do not have large ribosomes. The key distinguishing feature here is the presence of a cell wall, which is characteristic of plant cells, not animal cells.
Plant cells are surrounded by a cell wall for extra protection and structural support, a feature absent in animal cells. Given the options and the observed characteristics of the cell, the most likely source of the cell is a banana leaf, which is part of a plant. Hence, option B is correct.
Cell organelles are suspended in the $\qquad$ of the cell.
A) nucleus
B) plasma membrane
C) cytoplasm
D) vacuole
The correct answer is C) cytoplasm.
Cytoplasm is a jelly-like substance within a cell where various organelles such as the endoplasmic reticulum, mitochondria, and Golgi complex are embedded. These organelles are suspended in the cytoplasm and carry out specialized functions crucial for the cell's operations.
Which of these are characteristics of all monerans? (i) Cell wall made of cellulose (ii) Heterotrophic (iii) Nerve cells (iv) Prokaryotic (v) Unicellular
A i and ii
B i, ii, and iv
C ii and iv
D iv and v
The correct answer is D (iv and v).
Monerans, which comprise groups like bacteria, archaea, actinomycetes, and cyanobacteria, feature varying characteristics. Notably, their cell walls are comprised of peptidoglycan rather than cellulose. Additionally, while some monerans are heterotrophic, others have the capability to be autotrophic, indicating a diversity in their nutritional processes.
Nerve cells are distinctly associated with animals, and are not a characteristic of monerans. A defining trait of all monerans is that they are prokaryotic, which means they lack a defined nucleus and other complex cell structures found in eukaryotes. Lastly, monerans are fundamentally unicellular; even though some may form colonies, each organism operates as a single cell. Thus, the attributes (iv) Prokaryotic and (v) Unicellular correctly describe characteristics inherent to all monerans.
Plasma membrane is made up of
A) Carbohydrate layer
B) Silicon layer
C) Cholesterol layer
D) Phospholipid layer.
The correct answer is D) Phospholipid layer.
The plasma membrane is primarily composed of phospholipids, which are organized into a phospholipid bilayer. Each phospholipid molecule features a hydrophilic head (water-loving) and hydrophobic tails (water-hating). Within the bilayer, the hydrophobic tails face inward, shielded from water, while the hydrophilic heads are exposed outward towards the cytoplasm or the external environment of the cell. This arrangement is crucial for the selective permeability and fluid nature of the cell membrane.
What do we call the slug-like phase of the cellular slime mold life cycle?
A) Plasmodium
B) Pseudoplasmodium
C) Sporangium
D) Macrocyst
The correct answer is B) Pseudoplasmodium.
Pseudoplasmodium is a stage in the lifecycle of cellular slime molds where haploid amoeboid cells aggregate and form a multicellular structure that resembles a slug. This structure is not a true multicellular organism as it is composed of individual cells that can function independently. In this slug-like phase, known as Pseudoplasmodium, the cells come together to migrate as a unit before forming a stalked fruiting body.
Plasmodium, on the other hand, refers to a different structure, typically a multinucleate and acellular mass observed in the life cycles of Myxomycetes, which is involved in feeding.
Sporangium is a structure involved in spore production, and is not related to the slug-like phase of cellular slime molds.
Macrocyst happens during the sexual reproduction phase of slime molds and involves the aggregation of many amoeba cells to form a large cell.
Building material for the cell wall is carried through the:
A. Endocytosis
B. Exocytosis
C. Phagocytosis
D. Pinocytosis
The correct answer is B. Exocytosis.
Exocytosis is critical in plant cells, facilitating the delivery of proteins, wall polysaccharides, and additional membrane materials that are essential for growth and function. This process involves the fusion of secretory vesicles with the plasma membrane, hence providing the building materials necessary for the construction and maintenance of the cell wall and for enhancing cell-to-cell communications.
"The term 'Cell' was coined by:
A) Robert Brown
B) Robert Hooke
C) Robert Koch
D) Robert Edwards"
The correct answer is B) Robert Hooke.
Robert Hooke coined the term "cell," which is derived from the Latin word for a small compartment. He chose this term after observing the structure of a cork slice under a microscope. The boxlike shapes reminded him of the cells, or rooms, that monks lived in within a monastery. Consequently, he described the cork as being composed of these cells.
The cytoplasm of a cell consists of a nucleus and organelles like mitochondria and vacuoles.
A) True
B) False
The correct answer is B) False.
Cytoplasm is defined as the semifluid substance within a cell that is enclosed by the cell membrane but external to the nucleus. It does not include the nucleus itself; instead, cytoplasm surrounds the nucleus. This area of the cell contains various organelles such as mitochondria, chloroplasts (in plant cells), and vacuoles. Thus, stating that the cytoplasm consists of a nucleus is incorrect.
Which of the following statements about vacuoles is correct?
A. Plant and animal cells have the same number of vacuoles.
B. Vacuoles are absent in a plant cell.
C. The vacuoles in a plant cell are smaller and more in number than in animal cells.
D. Vacuoles in a plant cell are larger than those in an animal cell.
The correct answer is option D.
Vacuoles in a plant cell are generally larger than those found in animal cells. This is a key difference as vacuoles play various roles such as storing nutrients and waste products, and in plant cells, they also help in maintaining cell rigidity by controlling turgor pressure.
Lysosomes are absent in which animal cells?
A. Erythrocytes
B. Plasma cells
C. Nerve cells
D. Muscle cells
The correct answer is A. Erythrocytes.
Erythrocytes, also known as red blood cells, lack several cellular structures including lysosomes, endoplasmic reticulum, Golgi apparatus, and a nucleus. This adaptation helps to maximize space for hemoglobin, enhancing their oxygen-carrying capacity.
Select the wrong statement from the following:
A. The chloroplasts are generally much larger than mitochondria.
B. Both chloroplasts and mitochondria contain an inner and an outer membrane.
C. Both chloroplasts and mitochondria have smooth inner membrane.
D. Both chloroplasts and mitochondria contain their own DNA.
Option C is the incorrect statement.
In statement C, it states that both chloroplasts and mitochondria have smooth inner membranes, which is not accurate. Let’s analyze each statement:
Statement A: Chloroplasts are generally much larger than mitochondria. This is true. Chloroplasts are usually around 10 micrometers long, while mitochondria typically measure about 1 micrometer in length.
Statement B: Both chloroplasts and mitochondria contain an inner and an outer membrane. This statement is true as both organelles are double-membraned.
Statement C: As mentioned, the inner membrane of mitochondria is not smooth but contains many infoldings known as cristae which increase the surface area for ATP synthesis. In contrast, chloroplasts have a smooth inner membrane.
Statement D: Both organelles contain their own DNA, which supports their semi-autonomous nature, allowing them to synthesize some of the proteins they need. Thus, statement D is true.
In conclusion, the incorrect statement, according to the information provided and cellular structure facts, is option C.
Is a ribosome an organelle that does not have a membrane?
A Ribosome
B Vacuole
C Mitochondria
D Chloroplast
The correct answer is A) Ribosome.
Ribosomes are unique among cellular structures as they are not enclosed by a membrane. They can exist freely within the cell's cytoplasm or be attached to the rough endoplasmic reticulum. Their main role within the cell is protein synthesis.
"Disintegration of the cell is required when the product of interest is:
A. intracellular
B. intercellular
C. extracellular."
The correct answer is A. intracellular.
Cell disintegration is essential when the target product is located inside the cells (intracellular). This process enables the extraction of such products while preserving their structure and biological activity.
Raj observed a cell under a microscope. He could see a cell wall, a distinct vacuole, along with some other cell organelles. Which type of cell did he observe?
A. Plant cell
B. Animal cell
C. Human cell
D. Viral cell
The correct answer is A. Plant cell.
Key reasons for Raj observing a plant cell include the presence of a cell wall and a distinct vacuole, which are typical characteristics not found in animal, human, or viral cells. These features help in identifying it distinctly as a plant cell.
Give reasons for the following: (I) The cells of meristematic tissue have dense cytoplasm, thin walls, and prominent nuclei. (II) Vacuoles are absent in the cells of the tissue.
(I) Meristematic tissue is crucial for plant growth as it consists of cells that are in a constant state of division. To facilitate this rapid cell division, the cells are densely packed with dense cytoplasm and prominent nuclei, which are essential for the cell division process. The thin cell walls of these cells are an adaptation that allows for easier and faster cell division.
(II) The cells in meristematic tissue typically lack vacuoles. This characteristic can be attributed to their primary function, which is cell division. Vacuoles, which are common in mature plant cells, are primarily for storage and maintaining cell turgidity, functions that are not required in actively dividing cells. Consequently, the absence of vacuoles in meristematic cells ensures that there is more space available for the dense cytoplasm and large nucleus necessary for the division process.
What is Endoplasmic Reticulum (ER)? Mention its types.
The Endoplasmic Reticulum (ER) is a crucial cell organelle characterized by its extensive, interconnected network of membrane-bound tubes and sheets, which include structures such as cisternae, vesicles, and tubules. The ER plays a key role in transporting materials throughout the cell. It is categorized into two types:
Rough Endoplasmic Reticulum (RER): This type is coated with ribosomes and is primarily involved in protein synthesis.
Smooth Endoplasmic Reticulum (SER): Unlike the RER, the SER does not have ribosomes on its surface and is chiefly involved in lipid synthesis.
Amoeba has no specific shape.
A) True
B) False
The correct option is A) True.
Amoebas do not possess a specific shape like many bacteria and other organisms. These microorganisms are characterized by their irregular shape, which they can alter as needed. This flexibility facilitates their movement, feeding, reproduction, and excretion processes.
The cell's "garbage disposals" are the:
A. Lysosomes
B. Peroxisomes
C. Mitochondria
D. Vacuoles
The correct option is A. Lysosomes
Lysosomes are often referred to as the cell's "garbage disposals" because they digest unwanted materials in the cytoplasm. This includes waste products from outside the cell and obsolete components from inside the cell.
Given below is a list of characteristics about Amoeba and WBCs. With reference to the statements, choose the correct option.
Amoeba WBC
Statement 1: Both Amoeba and WBCs use pseudopodia for locomotion. Statement 2: Both Amoeba and WBCs are capable of independent existence. Statement 3: Both Amoeba and WBCs can change their shapes. Statement 4: Both Amoeba and WBCs have a cell membrane.
A) Statement 1 is incorrect.
B) Statement 1 and 2 are incorrect.
C) Statement 1, 2, 3, and 4 are incorrect.
D) None of the above
The correct answer is B. Statement 1 and Statement 2 are incorrect.
Statement 1 claims that both Amoeba and WBCs use pseudopodia for locomotion. However, this is not entirely accurate. While Amoeba does use pseudopodia for locomotion as well as for engulfing food, WBCs use pseudopodia primarily for the process called phagocytosis (to engulf pathogens), not for locomotion. Hence, this statement is incorrect.
Statement 2 asserts that both Amoeba and WBCs are capable of independent existence. This is incorrect because while Amoeba, a unicellular organism, can exist independently, WBCs cannot. White blood cells (WBCs) are part of the cellular components of blood in multicellular organisms and depend on the organism for their survival and function.
Statement 3 and 4 are correct as both Amoeba and WBCs can change their shapes and possess a cell membrane. Thus, these statements do not contribute to the error in the options provided.
Every human being starts with just one cell.
A) True
B) False
The correct answer is:
A) True
Every human being begins as a single cell, which is called a zygote. This cell undergoes numerous divisions and differentiations, eventually forming tissues, organs, and the entire human body. An average adult possesses approximately 1 trillion cells in their body.
Plasma membrane is made up of:
A) cellulose
B) silicon
C) chitin
D) phospholipids
The correct answer is D) phospholipids.
The plasma membrane is primarily made up of phospholipids, which form a structure known as the phospholipid bilayer. Each phospholipid molecule is composed of a hydrophilic head and two hydrophobic tails.
The hydrophobic tails face inward, away from water, while the hydrophilic heads face outward towards the water-rich environments of the cytoplasm and the extracellular fluid. This arrangement is critical for the membrane's function in protecting and enclosing the cell.
Glucose partially breaks down into lactic acid in:
A) Yeasts
B) Muscle cells
C) All cells
D) Plant cells
The correct answer is B) Muscle cells.
Muscle cells undergo a process called anaerobic respiration when oxygen levels are low. In this process, glucose is partially broken down into lactic acid. This biochemical pathway helps in generating energy, albeit less efficiently than aerobic respiration.
Most abundant organelles of the cell are:
A. Mitochondria
B. Plastids
C. Ribosomes
D. Microbodies
The correct answer is C. Ribosomes.
Ribosomes are the most abundant organelles in a cell. These structures are crucial for protein synthesis, facilitating the assembly of amino acids into proteins based on the genetic instructions carried by mRNA.
Which organelle is called the "post office of the cell"?
A) Golgi apparatus
B) Endoplasmic reticulum
C) Ribosome
D) Peroxisome
The correct answer is A) Golgi apparatus.
The Golgi apparatus is often referred to as the "post office of the cell". This organelle plays a crucial role in packaging, modifying, and transporting proteins throughout the cell to where they are needed.
The number of chromosomes in the majority of human cells is:
The majority of human cells, which are called somatic cells (such as skin, heart, and brain cells), contain a total of 46 chromosomes. This comprises 23 pairs. However, it's important to note that human gametes (sex cells like sperm and eggs) contain only 23 chromosomes, which is half the number present in somatic cells.
Which of the following cells secrete a waxy, water-resistant layer on their outer surface?
A Guard cells
B Epidermal cells
C Companion cells
D Cork cells
The correct answer is B Epidermal cells.
Epidermal cells in the aerial parts of plants are known for secreting a waxy, water-resistant layer on their outer surface. This layer plays a crucial role in protecting the plant from excessive water loss and environmental damage.
Which cell organelle is known as "suicidal bag"?
A. Ribosome
B. Centrosome
C. Lysosome
D. Peroxisome
To answer this, let’s consider each option:
Ribosomes are not the correct answer. They function as the site of protein synthesis in the cell, and do not have characteristics related to a "suicidal bag."
Centrosomes are also incorrect. They are involved in the process of cell division and play no role analogous to a "suicidal bag."
Lysosomes are the correct answer. They are known as "suicidal bags" because they contain digestive enzymes that can break down cellular components. If a lysosome bursts, these enzymes can digest and destroy the cell itself, which is why they are termed as such.
Peroxisomes, lastly, are not the right choice either. They are involved in fatty acid metabolism and do not have the characteristics of a "suicidal bag."
Therefore, the organelle known as the "suicidal bag" is: C. Lysosome.
Which is a prokaryotic cell amongst the following?
A. Amoeba
B. Bacteria
C. Yeast
D. Volvox
Prokaryotic cells are characterized by their simplicity in structural organization. They lack membrane-bound organelles such as the nucleus, mitochondria, chloroplasts, and other complex organelles. Instead, their genetic material (DNA and RNA) is present in a region of the cytoplasm without a surrounding membrane, often referred to as the nucleoid.
Now, breaking down the options:
Amoeba is a eukaryotic organism, characterized by a well-defined nucleus and the presence of other complex organelles.
Bacteria are classic examples of prokaryotic organisms, as they exhibit all the features mentioned for prokaryotes.
Yeast is a single-celled fungi which, despite its simplicity, is classified as a eukaryotic organism because it has a nucleus enclosed within a membrane.
Volvox is a colonial green algae with a complex structure that includes chloroplasts for photosynthesis, classifying it as eukaryotic.
Hence, the correct answer to the question is: Option B. Bacteria.
Cristae are associated with:
A) Nucleus
B) Chloroplast
C) Cell Wall
D) Mitochondria
Cristae are structures associated with mitochondria. They are folds found in the inner membrane of mitochondria. These folds significantly increase the surface area of the inner membrane, which plays a crucial role in cellular respiration. The increased surface area provided by the cristae allows for a higher rate of ATP synthesis, crucial for energy production within the cell.
To further elaborate:
Mitochondria are described as the "powerhouse of the cell" because they generate most of the cell's supply of ATP, used as a source of chemical energy.
The inner membrane of the mitochondria, where the cristae are located, contains enzymes and structures critical for electron transport and chemiosmosis, processes central to ATP production.
Given this information, the correct answer to the relationship of cristae is: D) Mitochondria.
Lipoprotein is found in:
A Cell membrane
B Nucleus
C Cytoplasm
D Cell wall
Lipoproteins are primarily found in the cell membrane where they play a crucial role. Essentially, lipoproteins can be described as droplets of fats that are surrounded by a single layer of molecules, including numerous cholesterol molecules. These structures are critical as they help in the structural integrity and functionality of the cell membrane, allowing for various molecules to enter and exit the cell efficiently.
Given this understanding, we can determine that the correct answer is:
A) Cell membrane
Lipoproteins are not present in the nucleus, cytoplasm, or cell wall, making options B, C, and D incorrect for this question.
Cell organelles are embedded in:
A. Cytoplasmic membrane
B. Mucin
C. Protoplasm
D. Cytoplasm.
Cytoplasm: This is a jelly-like substance that surrounds and supports the organelles inside the cell. It is found between the cell membrane (also known as the plasma membrane) and the nucleus. Essentially, the cytoplasm provides a medium for chemical reactions to occur and acts as a cushion to protect the organelles within the cell.
Cytoplasmic Membrane: This term is another name for the cell membrane and it surrounds the cytoplasm, providing the cell with structure and regulating the movement of substances in and out of the cell. It does not embed the organelles.
Protoplasm: A more inclusive term, protoplasm refers to all the contents within the cell membrane, including both the cytoplasm and the nucleus. It isn't specific to where organelles are embedded but rather encompasses the entire internal content of the cell.
Mucin: Mucin is not directly related to cell structure in the context of this question. It is a protein that constitutes mucus, primarily found in the respiratory and digestive tracts.
Hence, cytoplasm is the environment where cell organelles such as mitochondria, chloroplasts, and the endoplasmic reticulum are embedded, making option D the correct answer.
Ribosomes are granules formed of:
A. Only mRNA
B. Only Proteins
C. rRNA + Proteins
D. Only DNA
Ribosomes are essential cellular organelles known for their role in protein synthesis. They are not composed solely of RNA or proteins, nor are they formed from DNA. Instead, ribosomes are complex structures composed of both ribosomal RNA (rRNA) and proteins.
This composition facilitates their primary function translation, which is the process of converting the genetic information carried by messenger RNA (mRNA) into a sequence of amino acids, thereby synthesizing proteins. This synthesis takes place within the ribosomes.
Based on the given options, the best answer to the question "Ribosomes are granules formed of:" is:
C. rRNA + Proteins
This option correctly identifies the two main components that make up ribosomes, highlighting their crucial role in the process of translation and protein manufacturing within the cell.
Cell organelles essential for photorespiration are:
A Ribosome
B Dictyosome
C Peroxisomes
D Glyoxisome
Photorespiration is the process in plants that leads to the loss of fixed carbon dioxide. Initiated within the chloroplast, photorespiration is significantly influenced by the presence of sunlight and involves multiple organelles.
One crucial organelle in this process is the peroxisome. Specifically, peroxisomes help facilitate a number of reactions within the photorespiration process, ensuring it proceeds effectively.
The other options provided, namely:
A) Ribosomes, which are primarily the protein factories of the cell responsible for protein synthesis.
B) Dictyosomes, or Golgi apparatus, which are involved in processing and packaging biomolecules.
D) Glyoxysomes, which are specialized peroxisomes found in seedlings and are mainly concerned with lipid conversion rather than photorespiration.
From these options, peroxisomes are the correct answer — denoted as option C — as they are directly involved in the photorespiration pathway. The involvement of peroxisomes makes them fundamental in managing the reactions that maintain metabolic balance when photorespiration occurs. Thus, the answer to the question regarding which cell organelle is essential for photorespiration is:
C) Peroxisomes.
Kreb's cycle is found in which part of the cell?
A. Mitochondria
B. Cell membrane
C. Golgi body
D. Nucleus
The Krebs cycle, also known as the tricarboxylic acid (TCA) cycle or citric acid cycle, plays a crucial role in cellular energy production. It is a series of enzyme-catalyzed chemical reactions, which are of great importance in all aerobic organisms. This cycle metabolizes acetyl coenzyme A produced from carbohydrates, fats, and proteins into carbon dioxide and water, thus generating a substantial amount of ATP (adenosine triphosphate), which is the energy currency of the cell.
The Krebs cycle takes place within a specific compartment of the cell known as the mitochondrial matrix. This area is enclosed by the inner mitochondrial membrane, within the mitochondrion, which itself is characterized by a double-membrane structure. The release of energy stored in acetyl coenzyme A is critical for the production of ATP as well as for the generation of building blocks used in several other biosynthetic pathways.
Given the options provided: A. Mitochondria B. Cell membrane C. Golgi body D. Nucleus
The correct answer is Option A: Mitochondria. This is because the mitochondrial matrix is the exclusive site where the Krebs cycle occurs, fundamental to energy synthesis in cells.
DNA of Eukaryotes has:
A. Fatty acid
B. Cholesterol
C. Histone
D. All of the above
The DNA in eukaryotes is complex and involves various components in its organization and structure. Eukaryotic DNA is not free-floating within the nucleus but is instead structured around proteins called histones. This organization forms something known as a chromosome.
A. Fatty acid: This component is not related to the structural organization of eukaryotic DNA.
B. Cholesterol: Cholesterol is a type of lipid found in cell membranes, not directly involved with DNA structure.
C. Histone: Histones are basic (positively charged) proteins that strongly interact with the negatively charged DNA to form a complex called chromatin. This interaction facilitates the supercoiling of DNA, making it compact enough to fit within the nucleus of the cell.
From the options provided, the correct answer is:
C. Histone
Histones play a crucial role in the organization and function of DNA in eukaryotic cells by forming the structural framework that DNA wraps around, thus ensuring both stability and accessibility of the DNA for processes like transcription and replication.
Which of the following is/are correct statement(s)?
A Synthesis of urea takes place in liver.
B Eukaryotes have mitochondria.
C Virus is prokaryote.
D Both A and B.
The correct statements among the provided options are:
Option A: The synthesis of urea takes place in the liver. The liver is not only the largest gland in the body but also plays a crucial role in various metabolic processes including the synthesis of urea. This statement is correct.
Option B: Eukaryotes have mitochondria. Mitochondria are known as the powerhouse of the cell because they are responsible for energy production. They are double-membraned and present in most eukaryotic cells, where they help synthesize energy. This statement is correct.
Option C: Viruses are classified as prokaryotes. This statement is incorrect. Viruses are non-cellular entities that do not possess characteristics of prokaryotic or eukaryotic cells; they lack cellular structures and mechanisms of their own and depend completely on the host cell's machinery for reproduction.
Given these explanations, Option D, which states both A and B are correct, is the right answer. Therefore, the summary is:
A is correct: Synthesis of urea occurs in the liver.
B is correct: Eukaryotes have mitochondria.
C is incorrect: Viruses are not prokaryotic as they are non-cellular.
D is correct: Both A and B are true statements.
Based on this analysis, Option D "Both A and B" is the correct answer.
Which cell organelle is known as the "powerhouse of the cell"?
A. Mitochondria
B. Lysosome
C. Golgi apparatus
D. Endoplasmic reticulum.
The correct answer to the question "Which cell organelle is known as the 'powerhouse of the cell'?" is A. Mitochondria.
Mitochondria are often referred to as the powerhouse of the cell. They play a crucial role in cellular respiration, during which they help to produce ATP (adenosine triphosphate), which is the primary energy currency of the cell. This process is integral for supplying the necessary energy for various cellular functions.
Other options provided are:
B. Lysosome: Known as the cell's "suicidal bags", lysosomes are involved in breaking down waste materials and cellular debris.
C. Golgi apparatus: This organelle is involved in the packaging and dispatch of protein products produced in the cell.
D. Endoplasmic reticulum: It plays a key role in both protein synthesis and the production of lipids (fats).
Therefore, the mitochondria's distinct function in energy production makes them the "powerhouse of the cell."
In a cell, which cell organelle other than the nucleus contains DNA?
A. Lysosome
B. Golgi bodies
C. Endoplasmic reticulum
D. Mitochondria.
Lysosomes are often referred to as "suicidal bags" and are involved in the breakdown of cell components. They do not contain DNA.
Golgi bodies are involved in the packaging and distribution of proteins, and also do not contain DNA.
Endoplasmic reticulum (ER) is primarily involved in the synthesis of proteins and lipids. Like the previous options, it does not contain DNA.
However, the correct answer is:
Mitochondria (Option D). Mitochondria are unique among cell organelles in that they have their own DNA. This organelle is often described as semi-autonomous or kind of "self-operating" because it can produce some of its own structural proteins. This characteristic allows it to somewhat function independently within the cell, and it plays a critical role in cellular energy production.
Therefore, among the given options, mitochondria is the correct answer as it contains its own DNA, contributing crucially to both its functions and inheritance patterns in cell biology.
Which cell organelle is called "suicide bags"?
A. Centrosome
B. Chromosome
C. Lysosome
D. Mesosome.
The cell organelle which is often referred to as "suicide bags" is the lysosome. The reason lysosomes are given this nickname relates to their key function within the cell.
Lysosomes are filled with hydrolytic enzymes which are capable of breaking down various biomolecules in the cell, including proteins, nucleic acids, and lipids. This ability is essential for cellular waste disposal and the recycling of cellular components. However, these enzymes can also lead to the self-destruction of the cell if they are released internally in an uncontrolled manner. This can happen during certain cell injuries or when the cell is supposed to die in a controlled manner known as apoptosis. Thus, due to their role in potentially 'killing' the cell, lysosomes are dubbed as "suicide bags."
In summary, the correct answer to the question is:
C. Lysosome
Which one of the following statements about cell organelles and their function is correct?
Mitochondria are associated with anaerobic respiration.
Lysosomes are important in membrane biogenesis.
Smooth endoplasmic reticulum is involved in protein synthesis.
Golgi bodies are involved in packaging and dispatching of materials.
The correct answer from the provided options is that Golgi bodies are involved in the packaging and dispatching of materials.
Let's clarify why this statement is accurate and why the other choices are incorrect:
Mitochondria are incorrectly linked with anaerobic respiration in the question. In fact, mitochondria are the site of aerobic respiration where they utilize oxygen to produce ATP (Adenosine Triphosphate) during cellular respiration.
Smooth endoplasmic reticulum (SER) does not participate in protein synthesis. Instead, the SER is primarily involved in the synthesis and storage of lipids, including steroids. Protein synthesis mainly occurs in the ribosomes and the rough endoplasmic reticulum.
Lysosomes are referred to as ‘suicidal bags' of the cell due to their function involving digestion of cellular waste with hydrolytic enzymes. They are not involved in membrane biogenesis, which is the responsibility of the endoplasmic reticulum, using proteins and lipids that they synthesize.
Golgi bodies, however, are correctly described as being involved in the packaging and dispatching of materials. The Golgi apparatus modifies, sorts, and packages proteins and lipids for storage or transport out of the cell. These materials can be packaged into vesicles that transport them to their target locations.
Thus, the statement about Golgi bodies accurately matches the function of this cell organelle.
Second most abundant component inside the cell is:
Water
Nucleic acids
Proteins
Carbohydrates
The correct option is C: Proteins.
Here's a breakdown of the composition by percentage of the total cellular mass:
Water: 70-90%
Proteins: 10-15%
Carbohydrates: 3%
Lipids: 2%
Nucleic acids: 5-7%
Ions: 1%
Which of the following is not a characteristic of prokaryotes?
Option 1) DNA
Option 2) cell membrane
Option 3) cell wall
Option 4) endoplasmic reticulum
The correct answer is option 4) endoplasmic reticulum.
Prokaryotic cells lack membrane-bound organelles, which includes structures like the endoplasmic reticulum (ER). Below are the key characteristics of prokaryotes:
DNA: Present in the nucleoid region.
Cell membrane: Present and essential for cellular processes.
Cell wall: Typically present, supporting the cell structure.
Prokaryotic cells do not have:
A true nucleus enclosed by a membrane.
Membrane-bound organelles such as mitochondria, the Golgi apparatus, or the endoplasmic reticulum (ER).
Ribosomes in prokaryotes facilitate protein synthesis, composed of two subunits: large and small. This lack of membrane-bound organelles distinctly separates them from eukaryotic cells.
Which one of the following options contains structures that distinguish a nerve cell from other types of cell?
Option 1) Nucleus and mitochondria
Option 2) Perikaryon and dendrites
Option 3) Vacuoles and cytoskeletal fibres
Option 4) Flagellum and medullary sheath
The correct option is B: Perikaryon and dendrites.
Neurons are the structural and functional units of the nervous system. Let's break down the unique features of nerve cells:
Cell Body or Perikaryon: This contains cytoplasm with typical cell organelles and special granular bodies known as Nissl's granules.
Dendrites: These are short, highly branched fibres originating from the cell body. They play a critical role in transmitting nerve impulses towards the cell body.
Perikaryon and dendrites are distinct to nerve cells, differentiating them from other cell types, making this the correct answer.
In contrast:
Nucleus, mitochondria, vacuoles, and cytoskeletal fibres are found in nearly all cell types, so they do not distinguish nerve cells.
While a medullary sheath is unique to nerve cells, a flagellum is not present in nerve cells. Therefore, this option is incorrect.
Nuclear membrane is absent in
A. Volvox
B. Nostoc
C. Penicillium
D. Agaricus
The correct option is B. Nostoc.
Nostoc is categorized under cyanobacteria, which are prokaryotic organisms. This means that they do not have a nuclear membrane. In contrast:
Volvox is a green algae and is a eukaryotic organism, which possesses a nuclear membrane.
Penicillium and Agaricus are both fungi, also eukaryotic in nature, thus having nuclear membranes.
Thus, the absence of a nuclear membrane is a characteristic feature of prokaryotic cells like Nostoc.
The free surface of which of the following epithelia cannot have cilia?
A. Cuboidal
B. Columnar
C. Squamous
D. None of the above
The correct option is C: Squamous
Simple epithelial tissue composed of flattened cells with irregular boundaries is known as squamous epithelium.
Cilia are hair-like structures that can be present on the surface of cuboidal and columnar epithelia. When cilia are present on these types of epithelia, they are referred to as ciliated epithelium. However, cilia are absent in squamous epithelium.
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Which of the following is not correct?
(a) Robert Brown discovered the cell.
(b) Schleiden and Schwann formulated the cell theory.
(c) Virchow explained that cells are formed from pre-existing cells.
(d) A unicellular organism carries out its life activities within a single cell.
The incorrect statement is:
(a) Robert Brown discovered the cell.
Robert Brown is known for describing the nucleus in 1831, but it was Robert Hooke who discovered the cell in 1665.
New cells generate from
(a) bacterial fermentation
(b) regeneration of old cells
(c) pre-existing cells
(d) abiotic materials
The correct answer is (c) pre-existing cells.
New cells are formed from pre-existing cells, as explained by Rudolf Virchow's modification of the cell theory.
Match the following
Column I | Column II |
---|---|
(a) Cristae | (i) Flat membranous sacs in stroma |
(b) Cisternae | (ii) Infoldings in mitochondria |
(c) Thylakoids | (iii) Disc-shaped sacs in Golgi apparatus |
Column I | Column II |
---|---|
(a) Cristae | (ii) Infoldings in mitochondria |
(b) Cisternae | (iii) Disc-shaped sacs in Golgi apparatus |
(c) Thylakoids | (i) Flat membranous sacs in stroma |
Which of the following is correct:
(a) Cells of all living organisms have a nucleus.
(b) Both animal and plant cells have a well defined cell wall.
(c) In prokaryotes, there are no membrane bound organelles.
(d) Cells are formed de novo from abiotic materials.
(c) In prokaryotes, there are no membrane bound organelles.
This statement is correct. Prokaryotic cells do not have membrane-bound organelles such as a nucleus, mitochondria, or ER, which are found in eukaryotic cells.
What is a mesosome in a prokaryotic cell? Mention the functions that it performs.
A mesosome in a prokaryotic cell is a specialized differentiated form of the cell membrane characterized by invaginations or infoldings. These extensions can be in the form of vesicles, tubules, and lamellae.
Functions of Mesosomes:
Cell Wall Formation: They participate in the formation of the cell wall.
DNA Replication and Distribution: Mesosomes play a role in the replication of DNA and its distribution to the daughter cells during cell division.
Respiration: They help in cellular respiration.
Secretion Processes: Mesosomes participate in secretion activities of the cell.
Surface Area Increase: They increase the surface area of the plasma membrane, enhancing various enzymatic activities.
In essence, mesosomes are involved in vital processes such as cell wall formation, DNA replication, respiration, and secretion in prokaryotic cells.
How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?
Neutral solutes move across the plasma membrane by the process of simple diffusion along the concentration gradient, i.e., from an area of higher concentration to an area of lower concentration.
Polar molecules, however, cannot pass through the nonpolar lipid bilayer in the same way. Instead, they require a carrier protein of the membrane to facilitate their transport across the membrane. This process is known as facilitated diffusion.
In cases where molecules or ions need to be transported against their concentration gradient (from lower to higher concentration), the process is energy dependent and is called active transport. This process utilises ATP (e.g., the $\mathrm{Na}^{+}/\mathrm{K}^{+}$ pump).
Key Points:
Neutral solutes: Moved by simple diffusion.
Polar molecules: Moved by facilitated diffusion using carrier proteins.
Active transport: Requires energy (ATP) to move substances against their concentration gradient.
Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.
Two cell organelles that are double membrane bound are mitochondria and chloroplasts.
Characteristics and Functions
1. Mitochondria:
Characteristics:
Sausage-shaped or cylindrical.
Diameter: 0.2-1.0 µm; Length: 1.0-4.1 µm.
Outer Membrane: Smooth and forms the continuous boundary.
Inner Membrane: Forms infoldings called cristae to increase surface area.
Contains matrix filled with enzymes, DNA, RNA, and ribosomes (70S).
Functions:
Sites of aerobic respiration.
Produce cellular energy in the form of ATP, hence called the "powerhouses" of the cell.
Involved in cellular processes such as the regulation of the metabolic rate and apoptosis.
Labelled Diagram of Mitochondrion:
2. Chloroplasts:
Characteristics:
Found in plant cells and euglenoides.
Lens-shaped, oval, spherical, discoid or ribbon-like.
Length: 5-10 µm; Width: 2-4 µm.
Outer and Inner Membranes: Enclose the stroma.
Stroma: Contains thylakoids, enzymes, DNA, and ribosomes (70S).
Thylakoids: Arranged in stacks called grana.
Functions:
Sites of photosynthesis.
Capture light energy to convert into chemical energy (synthesis of carbohydrates).
Produce oxygen as a byproduct of photosynthesis.
Labelled Diagram of Chloroplast:
What are the characteristics of prokaryotic cells?
Prokaryotic cells have several distinctive characteristics:
Size: They are generally smaller than eukaryotic cells.
Lack of a Well-defined Nucleus: The genetic material in prokaryotic cells is not enveloped by a nuclear membrane.
Genetic Material: The DNA is typically a single circular chromosome. In addition to genomic DNA, many bacteria also possess small circular DNA called plasmids.
Cell Wall: Most prokaryotic cells have a rigid cell wall. The cell wall provides structural support and shapes the cell.
Cell Envelope: The cell envelope consists of the outermost glycocalyx, the cell wall, and the plasma membrane.
No Membrane-bound Organelles: Unlike eukaryotic cells, prokaryotic cells lack membrane-bound organelles like mitochondria, chloroplasts, and the endoplasmic reticulum.
Ribosomes: They possess 70S ribosomes, which are smaller than the 80S ribosomes found in eukaryotes.
Motility Structures: Some prokaryotes have flagella for movement, which are structurally different from eukaryotic flagella.
Surface Structures: Prokaryotic cells may have surface structures such as pili and fimbriae which help in attachment but do not play a role in motility.
Reproduction: Prokaryotes typically reproduce asexually through binary fission.
These characteristics provide a fundamental structural and functional simplicity compared to eukaryotic cells.
Multicellular organisms have division of labour. Explain.
In multicellular organisms, there is a concept known as division of labour, where cells differentiate and specialize to perform distinct functions. Here's an explanation:
Cell Specialization: Different cells in a multicellular organism become specialized to perform specific tasks. For example, nerve cells (neurons) transmit signals, muscle cells contract to enable movement, and red blood cells transport oxygen.
Organelles and Functions: Within each cell, different organelles have specific functions. For instance, mitochondria produce energy (ATP), ribosomes synthesize proteins, and the Golgi apparatus packages and distributes proteins.
Tissues, Organs, and Systems: Specialized cells group together to form tissues (e.g., muscle tissue, nervous tissue). Tissues combine to form organs (e.g., the heart, lungs). Organs work together in systems (e.g., the circulatory system, respiratory system) to perform complex functions required for the organism's survival.
Cell is the basic unit of life. Discuss in brief.
A cell is considered the basic unit of life because it is the smallest structural and functional unit capable of performing life processes. Here are some key points to understand why the cell is fundamental:
Structural Basis: All living organisms are either unicellular (consisting of a single cell) or multicellular (composed of many cells). Each cell is encased by a cell membrane that separates it from the external environment.
Functional Unit: Cells perform necessary functions such as metabolism, growth, and reproduction. They carry out complex processes like protein synthesis, energy production, and signal transduction.
Cell Theory: Formulated by Schleiden and Schwann, and later refined by Rudolf Virchow, this theory states:
All living organisms are composed of cells and products of cells.
All cells arise from pre-existing cells.
Types of Cells: There are two primary types:
Prokaryotic cells: Lack a true nucleus and membrane-bound organelles (e.g., bacteria).
Eukaryotic cells: Have a membrane-bound nucleus and various organelles (e.g., plant and animal cells).
Diversity and Specialization: Cells vary widely in size, shape, and function. For example, nerve cells are long and specialized for signal transmission, while red blood cells are biconcave to efficiently carry oxygen.
In summary, the cell's ability to independently perform life processes and its role as the building block of all living organisms underscore its status as the basic unit of life.
What are nuclear pores? State their function.
Nuclear pores are minute openings in the nuclear envelope, formed by the fusion of its two membranes.
Functions:
Facilitating transport: They serve as passages through which RNA and protein molecules move in both directions between the nucleus and the cytoplasm.
Nuclear pores are crucial for the exchange of materials necessary for various cellular processes, including gene expression and protein synthesis.
Both lysosomes and vacuoles are endomembrane structures, yet they differ in terms of their functions. Comment.
Lysosomes and vacuoles are both part of the endomembrane system, but they have distinct functions:
Lysosomes:
Function: Mainly involved in digestion and breakdown of macromolecules.
Composition: Contains various hydrolytic enzymes (lipases, proteases, carbohydrases).
Role: Active in digesting damaged cell parts or foreign particles.
Vacuoles:
Function: Primarily involved in storage and maintenance of turgor pressure.
Composition: Can store water, sap, excretory products, and other materials.
Role: Important for osmoregulation in some organisms (e.g., contractile vacuole in Amoeba), and for containing food particles in the form of food vacuoles.
Summary
While lysosomes specialize in breakdown and recycling of cellular components, vacuoles mainly focus on storage and maintaining cellular homeostasis.
Describe the structure of the following with the help of labelled diagrams.
(i) Nucleus
(ii) Centrosome
(i) Nucleus
The nucleus is a membrane-bound organelle that contains the cell's genetic material. Here's a labelled diagram of the nucleus:
Key components of the nucleus:
Nuclear Envelope: Double membrane with nuclear pores facilitating molecule exchange.
Nucleoplasm: Semi-fluid matrix inside the nucleus.
Chromatin: DNA-protein complex appearing as fibers in the nucleoplasm.
Nucleolus: Site of ribosomal RNA (rRNA) synthesis.
(ii) Centrosome
A centrosome is an organelle that contains a pair of centrioles and is crucial for cell division. Here's a labelled diagram of the centrosome and centrioles:
Key components of the centrosome:
Centrioles: Cylindrical structures made up of nine triplets of microtubules.
Pericentriolar Material: Amorphous matrix around centrioles assisting in microtubule nucleation.
Together, the centrosome and centrioles play an essential role in the organization of microtubules and formation of the spindle apparatus during cell division.
What is a centromere? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.
A centromere is a primary constriction on a chromosome where two chromatids are held together. It is a critical structure for proper chromosome segregation during cell division. Kinetochores, disc-shaped protein structures, are present on either side of the centromere and attach to spindle fibers during cell division.
The position of the centromere forms the basis for the classification of chromosomes into four types:
Metacentric chromosome: The centromere is situated in the middle, forming two equal arms.
Sub-metacentric chromosome: The centromere is slightly away from the middle, creating one shorter arm and one longer arm.
Acrocentric chromosome: The centromere is close to one end, resulting in one very short arm and one very long arm.
Telocentric chromosome: The centromere is at the terminal end, with no short arm.
Diagram Showing Types of Chromosomes Based on Centromere Position
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Cell: The Unit of Life - Comprehensive Class 11 Notes
Introduction to Cell: The Unit of Life
Cells are the fundamental units of life, forming the basic building blocks of all organisms. They play a crucial role in biological functions and understanding them is paramount for students of biology.
Cell Theory
Cell theory signifies the unity of living organisms and states that:
All living organisms are composed of cells and products of cells.
All cells arise from pre-existing cells.
This theory was developed by scientists Schleiden and Schwann and was later expanded by Rudolf Virchow.
Types of Cells
There are two primary types of cells: Prokaryotic and Eukaryotic.
Prokaryotic Cells
Prokaryotic cells, such as bacteria, do not possess a membrane-bound nucleus. These cells have simpler structures but accomplish complex functions.
Eukaryotic Cells
Eukaryotic cells, found in protists, fungi, plants, and animals, have a membrane-bound nucleus and various other organelles.
Cell Components and Functions
Prokaryotic Cells
Cell Envelope and Its ModificationsThe cell envelope consists of the outer glycocalyx, a cell wall, and a plasma membrane. This complex structure provides protection and structural support.
Ribosomes and Inclusion BodiesProkaryotic ribosomes are sites of protein synthesis.
Eukaryotic Cells
Plasma MembraneThe plasma membrane is a selectively permeable barrier composed of a lipid bilayer with embedded proteins. It helps in transport, communication, and structural integrity.
NucleusThe nucleus contains genetic material (DNA) and controls cellular activities. It is surrounded by a nuclear envelope with pores for material exchange.
graph TD;
A[Nucleus] --> |Contains DNA| B[Genetic Information]
A --> |Controls| C[Cellular Activities]
MitochondriaKnown as the powerhouses of the cell, mitochondria generate ATP through aerobic respiration.
PlastidsPlastids, such as chloroplasts, are found in plant cells. Chloroplasts contain chlorophyll and are crucial for photosynthesis.
graph LR;
A[Chloroplasts] --> |Trap Light Energy| B[Photosynthesis]
RibosomesRibosomes, found free in the cytoplasm or attached to ER, are pivotal in protein synthesis.
Endoplasmic Reticulum (ER)Rough ER: Studded with ribosomes, it synthesizes proteins. Smooth ER: Involved in lipid synthesis.
Golgi ApparatusThis organelle modifies, sorts, and packages proteins and lipids for transport.
LysosomesLysosomes contain hydrolytic enzymes necessary for intracellular digestion.
VacuolesVacuoles are storage organelles; plant cells have a large central vacuole for storing nutrients and waste products.
CytoskeletonThe cytoskeleton consists of microtubules, microfilaments, and intermediate filaments, providing mechanical support and enabling motility.
graph BT;
A[Cytoskeleton] --> |Support| B[Cell Shape]
A --> |Enable| C[Motility]
Cilia and FlagellaCilia and flagella are hair-like structures that aid in cell movement and fluid transport.
Centrosomes and CentriolesCentrosomes contain centrioles that help in the formation of spindle fibres during cell division.
MicrobodiesMicrobodies like peroxisomes contain enzymes for specific metabolic pathways in both plant and animal cells.
Differences Between Plant and Animal Cells
Plant Cells: Have a cell wall, chloroplasts, and a large central vacuole.
Animal Cells: Lack cell walls and chloroplasts but possess centrioles and lysosomes.
graph LR;
PlantCells -->|"Cell Wall"| CellExternalStructure
PlantCells -->|Chloroplasts| Photosynthesis
PlantCells -->|"Large Vacuole"| Storage
AnimalCells -->|Centrioles| Cell_Division
AnimalCells -->|Lysosomes| Digestion
Summary
Understanding the structure and function of cells is fundamental for grasping the complexities of life. Cells, as the smallest units of life, display immense diversity in form and function but share common features that underscore the unity of living systems. Through studying cells, we uncover the intricate processes that sustain life and gain insights into the molecular underpinnings of health and disease.
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