Unit 4: The Cell. As the building blocks of all living organisms, cells are not only the foundation of life but also the key to unraveling the mysteries of biological processes. From the tiniest microorganisms to the most complex multicellular organisms, the cell stands as a testament to the remarkable intricacy of nature’s design.
In these notes, we will delve into the inner workings of the cell, exploring its structures, functions, and the astonishing diversity it encompasses. Our voyage will traverse the realms of cell theory, cell membrane dynamics, organelle functionality, cellular energy production, and cellular reproduction. With each concept uncovered, we will piece together the puzzle of life itself.
Unit 4 Biology of 1st Year Short Answers Questions
What is the cell defined as?
The cell is defined as the structural and functional unit of life, capable of carrying out all activities of life.
Who first discovered cells and how?
Robert Hooke discovered cells by studying thin sections of cork under his self-made compound microscope and observing minute compartments that he termed as cells.
How did Robert Hooke describe cells in his discovery?
Robert Hooke described cells as minute honeycomb-like compartments bounded by thick walls.
- 1st Year Biology Unit No.1 Introduction Notes
- 1st Year Biology Unit No. 2 Biological Molecules Notes
- 1st Year Biology Unit No. 3 Enzymes Notes
- 1st Year Biology Unit No. 5 Variety of Life Notes
- 1st Year Biology Unit No. 6 Kingdom Prokaryotae Notes
Who introduced the concept that all living beings originate from or consist of cells?
Lorenz Oken, a German scientist, introduced the concept that all living beings originate from or consist of vesicles or cells.
What did Jean Baptist de-Lamarck suggest about the importance of cellular tissue in living beings?
Jean Baptist de-Lamarck suggested that no body can have life if its constituent parts are not cellular tissue or are not formed by cellular tissue.
What significant discovery did Robert Brown make in 1831 regarding cells?
Robert Brown discovered the presence of the nucleus in the cell, which changed the previous idea of the cell as an empty space.
Who formulated the Cell Theory, and what are its basic components?
Theodor Schwann, a German zoologist, and Matthias Schleiden, a German botanist, formulated the Cell Theory. They identified three basic components of the cell: the nucleus, cytoplasm, and plasma membrane.
What is the significance of the Cell Theory?
The Cell Theory established that all living organisms are composed of cells and cell products. It revolutionized the understanding of life’s fundamental unit and structure.
What additional structure did Theodor Schwann and Matthias Schleiden identify in plant cells?
They identified the cell wall as an additional structure present only in plant cells, which is not found in animal cells.
How did the Cell Theory contribute to the understanding of living organisms?
The Cell Theory helped establish that cells are the basic building blocks of complex multicellular organisms and that all life processes occur within cells.
What are the salient features of Cell Theory?
The salient features of Cell Theory are: (1) All organisms are composed of one or more cells. (2) All cells arise from pre-existing cells. (3) Cell is the basic structural as well as functional unit for all organisms.
What is the role of cells in living organisms?
Cells are the basic units of structure and function in living organisms. They work together in multicellular organisms, with different cells specialized for various functions.
How does division of labor occur among cells in multicellular organisms?
In multicellular organisms, cells specialize for different functions, leading to a division of labor. Each type of cell performs a specific role that contributes to the overall function of the organism.
Provide examples of specialized functions carried out by different types of animal cells.
Examples of specialized functions in animal cells include muscle cells contracting and relaxing, nerve cells transmitting impulses, gland cells secreting substances, and red blood cells carrying oxygen.
What functions do plant cells perform in a multicellular organism?
In plants, different types of cells have distinct roles. For instance, xylem cells conduct water and minerals, phloem cells transport food, sclerenchymatous cells provide support, and chlorenchymatous cells perform photosynthesis.
What is the common plan of organization among plant and animal cells?
Despite their structural and functional diversity, both plant and animal cells share a common plan of organization, which is the basis of the Cell Theory. They are the fundamental units of life and play vital roles in the functioning of organisms.
What are the two types of microscopes used to study the structure of a cell?
Light microscope and electron microscope.
How is cell fractionation performed, and what is its purpose?
Cell fractionation involves homogenizing or disrupting tissues to separate cellular components for detailed study. It helps isolate organelles and study their functions.
What is the principle behind density gradient centrifugation during cell fractionation?
Different cellular components separate into distinct layers based on their size, weight, and density in a centrifuge.
When might ultracentrifugation be used in cell fractionation?
Ultracentrifugation is used for separating cellular components that require high speeds for effective separation.
What are the three basic components of a cell?
Plasma membrane (cell wall in plant cells), cytoplasm with cell organelles, and nucleus with nuclear or chromatin material.
How do cells of animals and plants differ from those of bacteria in terms of nucleus and complexity?
Cells of animals and plants have a distinct nucleus enclosed by a membrane and are complex, known as eukaryotic. Bacteria lack a definite nucleus and are prokaryotic.
How are eukaryotic cell sizes measured, and what is the size of one nanometer?
Eukaryotic cell sizes are measured in micrometers (nm), where 1 nm is equal to 0.000001 meter or 1 x 10^-6 of a meter.
What has modern technology enabled scientists to study in cells?
Modern technology has made it possible to study various components of the cell, including its organelles, structure, and function in detail.
What is the plasma membrane’s primary function?
It serves as a barrier between the cell’s contents and its environment, controlling the passage of selective substances.
How is the plasma membrane of plant cells different from other cells?
In most plant cells, the plasma membrane is covered by a cell wall.
What is the chemical composition of the cell membrane?
The cell membrane is composed of lipids and proteins, with proteins making up 60-80% and lipids making up 20-40%. Carbohydrates are also present in small quantities.
What is the basic structure proposed earlier for the cell membrane?
The basic structure proposed was a lipid bilayer sandwiched between inner and outer layers of protein, called the unit membrane.
What is the Fluid Mosaic Model?
The Fluid Mosaic Model describes the cell membrane as having proteins embedded in the lipid bilayer in a mosaic pattern. It’s the currently accepted model for the cell membrane’s structure.
How do substances cross the cell membrane through transport?
Substances cross the cell membrane through active and passive transport, utilizing charged pores. Lipid-soluble substances cross more easily.
What does it mean for the cell membrane to be differentially permeable or selectively permeable?
The cell membrane allows only certain substances to pass through, maintaining a definite gradient. Lipid-soluble substances cross more easily than charged particles.
What is the term for the movement of substances from low to high concentration?
Active transport refers to the movement of substances against the concentration gradient, requiring energy provided by ATP.
How do animal cells take in materials through the cell membrane?
In some animal cells, materials are taken in through endocytosis, which involves infolding of the membrane to form vacuoles. This can be phagocytosis for solid particles or pinocytosis for liquid material.
What role does the cell membrane play in nerve cells (neurons)?
In nerve cells, the cell membrane transmits nerve impulses throughout the body, contributing to coordination.
What is the outermost boundary in most plant cells?
The cell wall.
How does the cell wall of plant cells differ from that of prokaryotes?
The cell wall of plant cells differs in structure and chemical composition from that of prokaryotes.
How many main layers compose the plant cell wall?
The plant cell wall is composed of three main layers: the primary wall, secondary wall, and middle lamella.
What is the first layer to be formed between the primary walls of neighboring plant cells?
The middle lamella is the first layer to be formed between the primary walls of neighboring plant cells.
What are the primary components of the primary wall?
The primary wall is composed of cellulose, along with some deposition of pectin and hemicelluloses.
How are cellulose molecules arranged in the primary wall?
Cellulose molecules are arranged in a criss-cross arrangement.
What develops in newly growing plant cells and is considered a true wall?
The primary wall develops in newly growing cells and is considered a true wall.
What composes the secondary wall and where is it formed?
The secondary wall is composed of inorganic salts, silica, waxes, cutin, lignin, etc. It is formed on the inner surface of the primary wall.
What is the strengthening material in the prokaryotic cell wall?
The strengthening material in the prokaryotic cell wall is peptidoglycan or murein.
What does the fungal cell wall contain?
The fungal cell wall contains chitin.
What role does the cell wall play in terms of cell shape and rigidity?
The cell wall provides a definite shape to the cell and keeps it rigid.
Does the cell wall act as a barrier to materials passing through it?
No, the cell wall does not act as a barrier to the materials passing through it.
What are the two main components that collectively form protoplasm?
Nucleus and cytoplasm.
What is the soluble part of the cytoplasm called?
Cytosol.
What is the chemical composition of cytosol in terms of water content?
About 90% water.
What types of solutions can be formed by molecules and ions in the cytosol?
Small molecules and ions can form true solutions, while some large molecules form colloidal solutions.
What are the two possible forms of colloidal solutions in the cytosol?
Colloidal solutions can be a sol (non-viscous) or a gel (viscous).
What is the primary function of the cytoplasm?
The main function of the cytoplasm is to store vital chemicals and serve as a site for metabolic processes such as glycolysis.
Name some cell organelles found in the cytoplasm.
Endoplasmic reticulum, mitochondria, Golgi complex, plastids, ribosomes, lysosomes, and centriole.
How do free-floating cell organelles like mitochondria move within the cytoplasm?
They move due to cytoplasmic streaming movements.
What is cytoplasmic streaming?
Cytoplasmic streaming is an active mass movement of the cytoplasm that causes the movement of organelles like mitochondria within the cell.
What is the Endoplasmic Reticulum (ER)?
The Endoplasmic Reticulum is a network of channels within the cytoplasm of cells, often connected to the plasma membrane and in contact with the nuclear membrane.
What are the two morphological forms of Endoplasmic Reticulum?
The two forms of Endoplasmic Reticulum are the rough ER (RER), which has attached ribosomes, and the smooth ER (SER), which lacks ribosomes.
What is the function of rough ER (RER)?
The rough ER is involved in the synthesis of proteins. It synthesizes proteins that can be stored in the cytoplasm or exported out of the cell.
What is the function of smooth ER (SER)?
The smooth ER is involved in the metabolism of various molecules, particularly lipids. It also helps in detoxifying harmful drugs and is involved in the transmission of impulses in certain cells.
What is the structural difference between RER and SER?
RER has attached ribosomes on its surface, giving it a rough appearance. SER lacks ribosomes and has a smooth surface.
What are cisternae in the context of the ER?
Cisternae are spherical or tubular membranes that separate the material present in the ER channels from the cytoplasmic materials.
What is the composition of eukaryotic ribosomes?
Eukaryotic ribosomes are composed of both ribosomal RNA (rRNA) and protein, making them ribonucleo-protein particles.
How are ribosomes attached to messenger RNA (mRNA)?
Ribosomes are attached to mRNA through the small ribosomal subunit. A group of ribosomes attached to mRNA is known as a polysome.
Where are new ribosomes assembled, and how are they transported to the cytoplasm?
New ribosomes are assembled in the nucleolus of the nucleus and then transported to the cytoplasm via the nuclear membrane’s pores.
What is the role of the nucleolus in ribosome synthesis?
The nucleolus is the factory for ribosome assembly, producing new ribosomes that are essential for protein synthesis.
Who discovered the Golgi apparatus and in what year?
Golgi discovered the Golgi apparatus in 1898.
What are the main components of the Golgi apparatus?
The Golgi apparatus consists of stacks of membrane-bound sacs called cisternae, along with associated vesicles forming the Golgi complex.
What is the function of the forming face of the Golgi apparatus?
The forming face is where blebs from the tips of the smooth endoplasmic reticulum (SER) fuse with Golgi cisternae.
What is the maturation face of the Golgi apparatus responsible for?
The maturation face is where cisternae break up into vesicles, including secretory granules (transport vesicles).
How does the Golgi apparatus contribute to protein modification?
The Golgi apparatus modifies proteins and lipids by adding carbohydrates, converting them into glycoproteins or glycolipids.
What is the role of the Golgi complex in cell secretions?
The Golgi complex is involved in the processing and packaging of products formed within the cell (such as enzymes synthesized on ribosomes), converting them into finished products for export.
How do proteins synthesized on ribosomes reach the Golgi apparatus?
Proteins synthesized on ribosomes are transported to the Golgi apparatus through the endoplasmic reticulum (ER) before being further processed.
What is the significance of the Golgi apparatus in digestion?
In mammals, the Golgi apparatus plays a role in the formation of granules containing enzymes used for digestion, such as those produced by the pancreas.
How are cisternae stacks within the Golgi apparatus formed?
Cisternae stacks within the Golgi apparatus are continuously formed by the fusion of vesicles, which are likely derived from the budding of the smooth endoplasmic reticulum (SER).
What are the two main faces of the Golgi apparatus and their functions?
The Golgi apparatus has a forming face (outer convex surface) where vesicles from the SER fuse, and a maturation face (inner concave surface) where cisternae break up into vesicles, including secretory granules.
What are lysosomes and what makes them different from other organelles?
Lysosomes are cytoplasmic organelles found in most eukaryotic cells. They are unique due to their morphology and function.
Who first isolated lysosomes as a separate component and in what year?
Lysosomes were first isolated as a separate component by De Duve in 1949.
What process occurs when a foreign object enters a cell and is engulfed by a lysosome?
The process is called phagocytosis, which is the cell’s eating process. The lysosome breaks down the foreign object into digestible pieces.
What is the primary function of lysosomes?
Lysosomes contain enzymes that digest various components, including phagocytosed food particles and old cell parts, through processes like phagocytosis and autophagy.
What are primary lysosomes and how are they formed?
Primary lysosomes are formed when enzymes synthesized on the rough endoplasmic reticulum (RER) are processed in the Golgi apparatus and bud off as Golgi vesicles.
What is the role of secondary lysosomes or digestive vacuoles?
Secondary lysosomes, also known as digestive vacuoles, are formed when primary lysosomes fuse with phagocytic vacuoles, enabling the lysosomal enzymes to digest the contents of the vacuole.
What is autophagy and how do lysosomes play a role in it?
Autophagy is the process of cells digesting their own old or worn-out parts. Lysosomes are involved in autophagy by digesting these cellular components, allowing for renewal and recycling of materials.
How are lysosomes related to extra cellular digestion?
Lysosomes release enzymes for extracellular digestion, aiding in breaking down substances outside the cell.
What are storage diseases and how are they related to lysosomal enzymes?
Storage diseases are congenital disorders caused by the accumulation of certain substances within cells due to a mutation affecting specific lysosomal enzymes responsible for their degradation.
Can you provide an example of a storage disease and its impact?
Tay-Sach’s disease is an example of a storage disease. It is caused by the absence of an enzyme involved in lipid catabolism, leading to the accumulation of lipids in brain cells and resulting in mental retardation.
What were the particles isolated by De Duve and coworkers in 1965 enriched with?
Oxidative enzymes such as peroxidase, catalase, and glycolic acid oxidase.
Why was the name “peroxisome” given to the organelle?
Because peroxisomes are specifically involved in the formation and decomposition of hydrogen peroxide in the cell.
What is the size of peroxisomes?
Approximately 0.5 nm in diameter.
Besides animal and plant cells, where else have peroxisomes been found?
Protozoa, yeast, and many cell types of higher plants.
What are glyoxysomes, and where are they most abundant?
Glyoxysomes are organelles found in plants that contain glycolic acid oxidase, catalase, and enzymes not found in animal cells. They are most abundant in plant seedlings.
What is the primary activity of glyoxysomes in germinating plant seedlings?
The conversion of stored fatty acids to carbohydrates through the glyoxylate cycle.
In which type of seeds are glyoxysomes responsible for the breakdown of fatty acids to succinate?
Seeds rich in lipids such as castor bean and soybeans.
When is the organelle known as a glyoxysome present, and when is it absent?
Present during the germination of lipid-rich seeds and absent in lipid-poor seeds like peas.
Where are vacuoles particularly large and abundant?
Plant cells.
What is the main function of vacuoles in plant cells?
To expand the cell without diluting its cytoplasm and to store water, cell products, and metabolic intermediates.
How do vacuoles contribute to the support and rigidity of plant cells?
The plant vacuole provides turgor, which supports individual plant cells and contributes to the rigidity of leaves and young plant parts.
What are the three main components of the cytoskeletal fabric found in the cytosol?
Microtubules, microfilaments, and intermediate filaments.
Name some of the main proteins present in the cytoskeleton.
Tubulin (in microtubules), actin, myosin, tropomyosin, and others.
What are cilia, flagella, basal bodies, and centrioles derived from?
Special assemblies of microtubules.
What cellular movements are facilitated by microfilaments?
Cyclosis and amoeboid movements.
What is the function of intermediate filaments?
They determine cell shape and integrate cellular compartments.
What is the primary role of microtubules during mitosis?
They are involved in the assembly and disassembly of the spindle structure.
What protein makes up microtubules?
Tubulin.
How are microfilaments connected to the cell’s plasma membrane?
They are linked to the inner face of the plasma membrane.
What is the diameter range of intermediate filaments?
Intermediate filaments have a diameter between that of microtubules and microfilaments.
Where are centrioles typically located in cells?
Near the exterior surface of the nucleus.
How many microtubules are present in each cross section of a centriole?
Each centriole consists of a cylindrical array of nine microtubules.
What role do centrioles play in cell division?
They are involved in the location of furrowing during cell division and in the formation of the spindle.
Are centrioles present in higher plants?
No, centrioles are absent in higher plants.
How do centrioles duplicate before cell division?
They duplicate and one pair migrates to the opposite side of the nucleus.
What is the arrangement of centrioles in relation to each other?
They are usually placed at a right angle to each other.
What is the main function of mitochondria in eukaryotic cells?
Mitochondria are involved in the manufacture and supply of energy to the cell.
Why are mitochondria often referred to as the “powerhouses of the cell”?
Mitochondria generate energy for the cell through various metabolic processes.
How do mitochondria appear under a compound microscope?
Under a compound microscope, mitochondria can appear as vesicles, rods, or filaments.
What is the structure of a mitochondrion’s outer and inner membranes?
A mitochondrion is bound by two membranes: the outer membrane is smooth, while the inner membrane forms infoldings called cristae.
What are the infoldings of the inner mitochondrial membrane called, and what purpose do they serve?
The infoldings of the inner mitochondrial membrane are called cristae. They increase the surface area for metabolic reactions.
What components can be found in the mitochondrial matrix?
The mitochondrial matrix contains enzymes, coenzymes, organic and inorganic salts, and other molecules necessary for metabolic processes.
What important metabolic processes occur within the mitochondria?
Mitochondria are involved in processes like the Krebs cycle, aerobic respiration, and fatty acid metabolism.
How is ATP (adenosine triphosphate) generated in mitochondria, and what role does it play?
ATP is generated through metabolic processes within mitochondria. It serves as an energy-rich compound that fuels cellular activities.
What is the significance of the presence of ribosomes and DNA in mitochondria?
The presence of ribosomes and DNA suggests that mitochondria can synthesize some of their own proteins and are capable of self-replication.
How does the number and size of mitochondria in a cell relate to its physiological activity?
The size and number of mitochondria vary based on the physiological activity of the cell. More active cells often have more and larger mitochondria.
Describe the structure and location of F1 particles within mitochondria.
F1 particles are small knob-like structures located on the inner surface of cristae in the mitochondrial matrix.
What is the role of mitochondria in the regeneration of energy?
Mitochondria regenerate spent energy, in the form of ADP (adenosine diphosphate), back into ATP, effectively replenishing the cell’s energy supply.
What are plastids?
Plastids are membrane-bound, mostly pigment-containing bodies found in cells. They are present in plant cells.
How many main types of plastids are there?
A2: There are three main types of plastids: chloroplasts, chromoplasts, and leucoplasts.
What is the primary function of chloroplasts?
Chloroplasts contain chlorophyll, a green pigment, which absorbs light energy and helps in the manufacture of food through photosynthesis.
How does the structure of a chloroplast appear under a light microscope?
Under a light microscope, chloroplasts appear as heterogeneous structures with small granules known as grana embedded in a matrix.
What are the three main components of a chloroplast as seen under an electron microscope?
The three main components of a chloroplast under an electron microscope are the envelope, the stroma, and the thylakoid.
What is the function of the stroma in a chloroplast?
The stroma is a fluid-filled region that surrounds the thylakoids. It contains proteins, ribosomes, DNA, and is where CO2 is fixed to produce sugars through photosynthesis.
What are the structures that make up a granum?
A granum is composed of flattened vesicles called thylakoids, stacked on top of each other like coins.
What is the role of chlorophyll in the chloroplast?
Chlorophyll molecules are arranged on the layers of thylakoids within the granum and are responsible for trapping sunlight energy for photosynthesis.
Which plastid type imparts colors to plant parts other than green?
Chromoplasts are responsible for imparting colors to plant parts other than green, such as petals and ripened fruit.
Where are leucoplasts typically found and what is their function?
Leucoplasts are colorless plastids found in underground parts of plants. They serve as storage organelles for food materials.
Who reported the presence of the cell nucleus in 1831?
Robert Brown.
How is the nucleus of a cell usually described in relation to the surrounding cytoplasm?
Slightly darker than the surrounding cytoplasm.
What is the main function of the nucleus within a cell?
To control the life and activities of the cell.
How does the position of the nucleus differ in animal cells compared to plant cells?
In animal cells, it generally occupies the central space, while in plant cells it is pushed towards the periphery due to the presence of a large vacuole.
What is the term for cells with one nucleus? And what about cells with two nuclei?
Mononucleate for cells with one nucleus; Binucleate for cells with two nuclei.
When is the nucleus of a cell visible?
The nucleus is only visible when the cell is in a non-dividing stage.
What replaces the chromatin material in the nucleus during cell division?
Chromosomes replace the chromatin material during cell division.
What is the chemical composition of the nucleus?
DNA, RNA, and proteins, including enzymes.
What are the components of the nucleus?
Nuclear membrane, nucleoli, nucleoplasm, and chromosomes.
What is the purpose of the nuclear pores?
Nuclear pores allow the exchange of materials between the nucleus and the cytoplasm.
What is the main function of the nucleolus?
The nucleolus is where ribosomes are assembled and then exported to the cytoplasm via nuclear pores.
What is a centromere, and what is its role during cell division?
The centromere is the place on the chromosome where spindle fibers are attached during cell division.
Where is the genetic information necessary to control the cell’s activities located?
The genetic information is located on the chromosomes in the form of genes.
How many chromosomes are found in a human cell?
Each human cell contains 46 chromosomes.
What is the difference between diploid and haploid chromosome numbers?
Diploid chromosome number (2n) is present in normal body cells, while haploid chromosome number (n) is present in germ cells.
What are the main differences between prokaryotic and eukaryotic cells?
Answer: The main differences between prokaryotic and eukaryotic cells are based on the structure of their nuclei. Eukaryotic cells have a well-defined nucleus enclosed in a double nuclear membrane, while prokaryotic cells lack a nuclear membrane, and their genetic material (DNA) is directly submerged in the cytoplasm.
What are the main differences between prokaryotic and eukaryotic cells?
Answer: The main differences between prokaryotic and eukaryotic cells are based on their nucleus structure. Eukaryotic cells have a well-defined nucleus with double nuclear membranes, enclosing genetic material (chromosomes or DNA). In contrast, prokaryotic cells lack a nuclear membrane, and their genetic material is directly present in the cytoplasm.
What are prokaryotes and eukaryotes?
Answer: Organisms possessing prokaryotic cells are called Prokaryotes. These include bacteria and blue-green algae. Organisms possessing eukaryotic cells are called Eukaryotes, which encompass animals, plants, fungi, and protists.
Which membrane-bound structures are absent in prokaryotic cells compared to eukaryotic cells?
Answer: Prokaryotic cells lack various membrane-bound structures present in eukaryotic cells, including mitochondria, endoplasmic reticulum, chloroplasts, and Golgi apparatus.
How is genetic material organized in prokaryotic and eukaryotic cells?
Answer: In prokaryotic cells, genetic material (DNA) is present in the cytoplasm without a nuclear membrane. In eukaryotic cells, genetic material is enclosed within a distinct nucleus, surrounded by double nuclear membranes.
What is the main method of cell division in prokaryotic cells, and how does it differ from eukaryotic cell division?
Answer: Prokaryotic cells divide through binary fission, a process where the cell splits into two identical daughter cells. Eukaryotic cells, on the other hand, divide through mitosis (for somatic cells) or meiosis (for reproductive cells), involving complex steps to ensure proper distribution of genetic material.
What is the main structural component of the cell wall in prokaryotic cells?
Answer: The main structural component of the cell wall in prokaryotic cells is peptidoglycan or murein, which is composed of polysaccharide chains covalently bound to shorter chains of amino acids.
How do the ribosomes in prokaryotic cells differ from those in eukaryotic cells?
Answer: Prokaryotic cells have smaller ribosomes known as 70S ribosomes, while eukaryotic cells possess larger ribosomes called 80S ribosomes.
Which type of cells are considered more primitive in terms of evolution, prokaryotic or eukaryotic cells?
Answer: Prokaryotic cells were initially considered more primitive due to their simpler structure. However, this view has evolved, and both prokaryotic and eukaryotic cells have their own evolutionary significance and complexity.
What is the composition of the cell wall in plant cells, and how does it differ from the cell wall in prokaryotic cells?
Answer: The cell wall in plant cells is primarily composed of cellulose. It differs from the cell wall in prokaryotic cells, which is made up of peptidoglycan or murein.
Question: Describe various movements involved in the transport of materials across the cell membrane.
Various movements across the cell membrane include passive diffusion, facilitated diffusion, active transport, endocytosis, and exocytosis.
Question: State various structural modiications in a cell involved in secretions.
Structural modifications for secretions in cells include the development of Golgi apparatus, endoplasmic reticulum, secretory vesicles, and specialized secretory granules.
Question: List the processes blocked by mitochondrial failure in a cell.
Mitochondrial failure in a cell can block processes such as oxidative phosphorylation, ATP production, and cellular respiration.
Question: What will happen if a chromosome loses its centromere?
Loss of a chromosome’s centromere can lead to improper segregation during cell division, potentially causing genetic instability and aneuploidy.
Question: How does autophagy help in converting a tadpole larva into an adult amphibian?
Autophagy helps convert a tadpole larva into an adult amphibian by breaking down and recycling unnecessary or damaged cellular components during metamorphosis.
Question: Is there any similarity between bacterial and plant cell wall?
Both bacterial and plant cells have cell walls. Bacterial cell walls are composed of peptidoglycan, while plant cell walls are primarily made of cellulose, hemicellulose, and other components.
1st Year Biology Unit 4 Long Questions
Question: Compare structure and function of chloroplasts and mitochondria.
Answer: Chloroplasts
Structure: Chloroplasts are double-membraned organelles found in plant cells and some protists. They have an outer membrane and an inner membrane that enclose the stroma, a semi-fluid matrix. Within the stroma, there are stacks of thylakoid membranes called grana. The thylakoid membranes contain chlorophyll and other pigments involved in photosynthesis.
Function: Chloroplasts are responsible for photosynthesis, the process by which plants and some other organisms convert light energy into chemical energy stored in glucose. They capture light energy, convert it into chemical energy, and use this energy to synthesize glucose from carbon dioxide and water. Oxygen is also produced as a byproduct.
Mitochondria
Structure: Mitochondria are double-membraned organelles found in most eukaryotic cells. They consist of an outer membrane and an inner membrane that encloses the mitochondrial matrix. The inner membrane is folded into structures called cristae, which increase its surface area.
Function: Mitochondria are often referred to as the “powerhouses” of the cell because they are responsible for cellular respiration. They generate ATP (adenosine triphosphate), a molecule that stores and releases energy for cellular activities. Mitochondria break down glucose and other molecules to produce ATP through a series of biochemical reactions.
Question: State ‘Cell Theory’ and discuss its emergence.
Answer: Cell Theory and its Emergence
Cell Theory: The cell theory is a fundamental concept in biology that states:
All living organisms are composed of one or more cells.
The cell is the basic unit of structure, function, and organization in all organisms.
Cells arise from pre-existing cells through cell division.
Emergence of the Cell Theory:
In the 17th century, the development of microscopes allowed scientists like Robert Hooke to observe cells in cork and Antonie van Leeuwenhoek to discover microorganisms.
In the mid-19th century, Matthias Schleiden, Theodor Schwann, and Rudolf Virchow contributed to the formulation of the cell theory.
Schleiden (1838) concluded that plants are made up of cells.
Schwann (1839) extended this idea to animals.
Virchow (1855) proposed that cells arise from pre-existing cells through division.
The work of these scientists helped establish the concept that cells are the fundamental units of life and that all organisms are composed of cells.
Question: Write notes on : (a) Cytoskeleton (b) Peroxisomes & Glyoxysomes
Answer: (a) Cytoskeleton: The cytoskeleton is a network of protein filaments and tubules that provide structural support, shape, and organization to the cell. It also plays a crucial role in cell movement, intracellular transport, and cell division. The cytoskeleton is composed of three main components:
Microtubules: Hollow tubules made of tubulin proteins. They are involved in maintaining cell shape, cell division, and serving as tracks for intracellular transport.
Microfilaments (Actin filaments): Thin fibers made of actin proteins. They contribute to cell shape, muscle contraction, cell division, and cell movement.
Intermediate filaments: Intermediate-sized filaments that provide mechanical support to the cell and help anchor organelles.
(b) Peroxisomes & Glyoxysomes:
Peroxisomes: Peroxisomes are membrane-bound organelles containing enzymes that are involved in various metabolic processes, including breaking down fatty acids and detoxifying harmful substances. They play a role in lipid metabolism and the production of hydrogen peroxide.
Glyoxysomes: Glyoxysomes are specialized peroxisomes found in plant cells, particularly in germinating seeds. They are involved in the conversion of stored lipids into carbohydrates, providing energy for seedling growth. This process is known as glyoxylate cycle.
Question: What might happen if some lysosomal enzymes are absent? Explain with examples.
Answer: When certain lysosomal enzymes are absent or deficient, it can lead to a group of disorders known as lysosomal storage diseases (LSDs). Lysosomal enzymes are responsible for breaking down various molecules within cells, and when they are not functional, these molecules accumulate within the lysosomes, leading to cellular dysfunction and tissue damage. The exact manifestations of each LSD depend on which specific enzyme is deficient and which molecules accumulate. Here are a few examples:
Gaucher’s Disease: This disease is caused by a deficiency of the enzyme glucocerebrosidase. Without this enzyme, a lipid called glucocerebroside cannot be broken down properly. This leads to its accumulation within lysosomes, primarily in macrophages (a type of immune cell). The accumulation can result in enlargement of the liver and spleen, anemia, and bone abnormalities.
Tay-Sachs Disease: Tay-Sachs is caused by a deficiency of the enzyme hexosaminidase A. This enzyme is responsible for breaking down a lipid called GM2 ganglioside. Without functional hexosaminidase A, GM2 ganglioside accumulates in nerve cells, particularly in the brain. This leads to progressive neurological deterioration, developmental regression, and early death in affected individuals.
Pompe Disease: Pompe disease is characterized by a deficiency of the enzyme acid alpha-glucosidase (also known as acid maltase). This enzyme is responsible for breaking down glycogen, a complex sugar molecule, into glucose. Without this enzyme, glycogen accumulates in lysosomes, particularly in muscle cells. This leads to muscle weakness, respiratory difficulties, and heart problems.
Fabry Disease: Fabry disease results from a deficiency of the enzyme alpha-galactosidase A. This enzyme normally breaks down a lipid called globotriaosylceramide (Gb3). Without it, Gb3 accumulates in various cells, including blood vessel lining cells and nerve cells. This can lead to kidney dysfunction, skin rashes, cardiovascular complications, and neuropathic pain.
Niemann-Pick Disease: Niemann-Pick disease comes in several types, but they are all characterized by the accumulation of sphingolipids, particularly sphingomyelin, due to enzyme deficiencies. The type and severity of symptoms depend on the specific enzyme deficiency. Common features include liver and spleen enlargement, lung and nervous system problems.