MSBSHSE Class 8 Science Chapter 10 Cell and Cell Organelles Important

Q1. Who am I?

a. I am ATP producing factory.

b. I am single layered, but maintain cellular osmotic pressure.

c. I support the cell, but I am not cell wall. I have a body resembling net.

d. I am chemical factory of the cell.

e. Leaves are green because of me.

Answer a: Mitochondria –Mitochondria are membrane-bound organelles present in the cytoplasm of all eukaryotic cells, that produces adinosine triphosphate (ATP), the main energy molecule used by the cell.

Answer b: Vacuole –Vacuoles are membrane-bound cell organelles present in the cytoplasm and filled with a watery fluid containing various substances.

Answer c: Endoplasmic reticulum –Endoplasmic Reticulum is a complex network of tubular membranes exclusively present in the cytoplasm of the eukaryotic cell.

Answer d: Chloroplasts –Chloroplast is an organelle that contains the photosynthetic pigment chlorophyll that captures sunlight and converts it into useful energy, thereby, releasing oxygen from water.

Answer e: Chlorophyll –Pigment imparting green colour to plants.

Q2. What would have happened? If …….

a. RBCs had mitochondria.

b. There had been no difference between mitochondria and plastids.

c. Genes had been absent on the chromosomes.

d. Plasma membrane had not been selectively permeable.

e. Plants lacked anthocyanin.

Answer a: Mitochondria are absent in RBCs. Due to this, the oxygen which is carried by them is not used for themselves.

Answer b: Mitochondria and plastids are the cell organelles present in eukaryotes. Mitochondria are found in all the eukaryotic cells, including plants and animals, whereas plastids are found only in plant cells.

Answer c: A gene is a basic unit of hereditary. So, if genes are absent on the chromosomes, then the offspring fails to look like the parent. Absence of genes will prevent the baby from looking like the parent as the gene is the unit which transfers the characteristics from the parent to the child. It is made up of DNA and is present within a nucleus.

Answer d: If Plasma membrane had not been selectively permeable then any substance can enter the cell which can harm the balance between the cell content and outside environment.

Answer e: In food, the main sources of anthocyanins are berries, such as blackberries, grapes , blueberries etc, and some vegetables such as egg-plants and avocado. If plants lacked anthocyanin, they died.

Q3. Who is odd man among us? Give reason.

a. Nucleolus, mitochondria, plastids, endoplasmic reticulum

b. DNA, Ribosomes, Chlorophyll

Answer a: Plastids because they are not found in animal cells, only found in plant cells.

Answer b: Chlorophyll is odd as DNA and ribosome are found in animals but chlorophyll is found in plants.

Q4. Give functions.

a. Plasma membrane

b. Cytoplasm

c. Lysosome

d. Vacuole

e. Nucleus

Answer a: Following are the important plasma membrane function:

• The plasma membrane forms a barrier between the cell organelles from the outside environment.
• It allows only certain molecules to pass through it.
• It facilitates communication and signalling between the cells.

Answer b: One of the major functions of cytoplasm is to enable cells to maintain their turgidity, which enables the cells to hold their shape. Other functions of cytoplasm are as follows:

• The jelly-like fluid of the cytoplasm is composed of salt and water and is present within the membrane of the cells and embeds all of the parts of the cells and organelles.
• The cytoplasm is home to many activities of the cell as it contains molecules, enzymes that are crucial in the breakdown of the waste.
• The cytoplasm also assists in metabolic activities.
• Cytoplasm provides shape to the cell. It fills up the cells, thus enabling the organelles to remain in their position. The cells, without cytoplasm, would deflate and substances will not permeate easily from one to the other organelle.
• A part of the cytoplasm, the cytosol has no organelles. Rather, the cytosol is enclosed by matrix boundaries that fill up the cell section which does not hold the organelles.

Answer c: The key function of lysosomes is digestion and removal of waste. Cellular debris or foreign particles are pulled into the cell through the process of endocytosis. The process of endocytosis happens when the cell membrane falls in on itself (invagination), creating a vacuole or a pouch around the external contents and then bringing those contents into the cell. On the other hand, discarded wastes and other substances originating from within the cell are digested by the process of autophagocytosis or autophagy. The process of autophagy involves disassembly or degradation of the cellular components through a natural, regulated mechanism.

Answer d: The important functions of vacuole include:

Storage –A vacuole stores salts, minerals, pigments and proteins within the cell. The solution that fills a vacuole is known as the cell sap. The vacuole is also filled with protons from the cytosol that helps in maintaining an acidic environment within the cell. A large number of lipids are also stored within the vacuoles.

Turgor Pressure –The vacuoles are completely filled with water and exert force on the cell wall. This is known as turgor pressure. It provides shape to the cell and helps it to withstand extreme conditions.

Endocytosis and Exocytosis –The substances are taken in by a vacuole through endocytosis and excreted through exocytosis. These substances are stored in the cells, separated from the cytosol. Lysosomes are vesicles that intake food and digest it. This is endocytosis and it varies in different cells.

Answer e: Following are the important nucleus function:

• It contains the cell’s hereditary information and controls the cell’s growth and reproduction.
• The nucleus has been clearly explained as a membrane-bound structure that comprises the genetic material of a cell.
• It is not just a storage compartment for DNA, but also happens to be the home of some essential cellular processes.
• First and foremost, it is possible to duplicate one’s DNA in the nucleus. This process has been named DNA Replication and creates an identical copy of the DNA.
• Creating two identical copies of the host or body is the first step in cell division, where each new cell will get its own set of instructions.
• Secondly, the nucleus is the spot of transcription. Transcription is the process of creating different types of RNA from DNA. Transcription would be a lot like making copies of individual pages of the human body’s instructions that can then be passed out and read by the rest of the cell.
• The central rule of biology states that DNA is copied into RNA, which is then turned into protein.

Q5. Who gives me the colour?  (Select the correct option).

Red tomato	Chlorophyll
Green leaf	Carotene
Carrot	Anthocyanin
Violet	Lycopene

Answer:

Red tomato	Lycopene
Green leaf	Chlorophyll
Carrot	Carotene
Violet	Anthocyanin

Q6. How many types of cells are found in living organisms?

Answer: Cells are similar to factories with different labourers and departments that work towards a common objective. Various types of cells perform different functions. Based on cellular structure, there are two types of cells:

• Prokaryotes
• Eukaryotes

Prokaryotic Cells

• Prokaryotic cells have no nucleus. Instead, some prokaryotes such as bacteria have a region within the cell where the genetic material is freely suspended. This region is called the nucleoid.
• They all are single-celled microorganisms. Examples include archaea, bacteria, and cyanobacteria.
• The cell size ranges from 0.1 to 0.5 µm in diameter.
• The hereditary material can either be DNA or RNA.
• Prokaryotes reproduce by binary fission, a form of sexual reproduction.

Eukaryotic Cells

• Eukaryotic cells are characterised by a true nucleus.
• The size of the cells ranges between 10–100 µm in diameter.
• This broad category involves plants, fungi, protozoans, and animals.
• The plasma membrane is responsible for monitoring the transport of nutrients and electrolytes in and out of the cells. It is also responsible for cell to cell communication.
• They reproduce sexually as well as asexually.
• There are some contrasting features between plant and animal cells. For eg., the plant cell contains chloroplast, central vacuoles, and other plastids, whereas the animal cells do not.

Q7. Which instrument had you used to observe cells?

Answer: A microscope is an optical instrument used to observe objects that are invisible to the naked eye. It is used to view and study cell structure.

Q8. Describe the structure of the cell?

Answer: The cell structure comprises individual components with specific functions essential to carry out life’s processes. These components include- cell wall, cell membrane, cytoplasm, nucleus, and cell organelles. Read on to explore more insights on cell structure and function.

Cell Membrane

• The cell membrane supports and protects the cell. It controls the movement of substances in and out of the cells. It separates the cell from the external environment. The cell membrane is present in all the cells.
• The cell membrane is the outer covering of a cell within which all other organelles, such as the cytoplasm and nucleus, are enclosed. It is also referred to as the plasma membrane.
• By structure, it is a porous membrane (with pores) which permit the movement of selective substances in and out of the cell. Besides this, the cell membrane also protects the cellular component from damage and leakage.
• It forms the wall-like structure between two cells as well as between the cell and its surroundings.
• Plants are immobile, so their cell structures are well-adapted to protect them from external factors. The cell wall helps to reinforce this function.

Cell Wall

• The cell wall is the most prominent part of the plant cell structure. It is made up of cellulose, hemicellulose and pectin.
• The cell wall is present exclusively in plant cells. It protects the plasma membrane and other cellular components. The cell wall is also the outermost layer of plant cells.
• It is a rigid and stiff structure surrounding the cell membrane.
• It provides shape and support to the cells and protects them from mechanical shocks and injuries.

Cytoplasm

• The cytoplasm is a thick, clear, jelly-like substance present inside the cell membrane.
• Most of the chemical reactions within a cell take place in this cytoplasm.
• The cell organelles such as endoplasmic reticulum, vacuoles, mitochondria, ribosomes, are suspended in this cytoplasm.

Nucleus

• The nucleus contains the hereditary material of the cell, the DNA.
• It sends signals to the cells to grow, mature, divide and die.
• The nucleus is surrounded by the nuclear envelope that separates the DNA from the rest of the cell.
• The nucleus protects the DNA and is an integral component of a plant cell structure.

Q9. Explain the characteristics of the cell?

Answer: Following are the various essential characteristics of cells:

• Cells provide structure and support to the body of an organism.
• The cell interior is organised into different individual organelles surrounded by a separate membrane.
• The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth.
• Every cell has one nucleus and membrane-bound organelles in the cytoplasm.
• Mitochondria, a double membrane-bound organelle is mainly responsible for the energy transactions, vital for the survival of the cell.
• Lysosomes digest unwanted materials in the cell.
• Endoplasmic reticulum plays a significant role in the internal organisation of the cell by synthesising selective molecules and processing, directing and sorting them to their appropriate locations.

Q10. Define cell.

Answer: A cell is the structural and fundamental unit of life. Cells are complex, and their components perform various functions in an organism. They are of different shapes and sizes, pretty much like bricks of the buildings. Our body is made up of cells of different shapes and sizes. Cells are the lowest level of organisation in every life form. From organism to organism, the count of cells may vary. Humans have the number of cells compared to that of bacteria.

Cells comprise several cell organelles that perform specialised functions to carry out life processes. Every organelle has a specific structure. The hereditary material of the organisms is also present in the cells.

Q11. What is cytoplasm?

Answer: The fluid that fills up the cells is referred to as the cytoplasm. It encompasses the cytosol with filaments, ions, proteins, and macromolecular structures and also other organelles suspended in the cytosol. The cytoplasm of the eukaryotic cells associates with the cell contents except for the nucleus. But in prokaryotic cells, as they do not possess a defined nuclear membrane, the cytoplasm possesses the genetic material of the cell. The cells, in comparison to the eukaryotes, are smaller and have an uncomplicated arrangement of the cytoplasm.

Q12. What is cell organelles?

Answer: An organelle is a specialized subunit having a specific function within the cell. They are ‘organs of the cell.’ Each organelle has its own lipoprotein membrane. Except nucleus and chloroplast, all other organelles can be seen only with an electron microscope.

Q13. What are the functions of Endoplasmic Reticulum?

Answer: The functions of Endoplasmic Reticulum are:

• It is the framework that supports cell.
• Conduction of proteins.
• Toxins that have entered the body through food, air and water are made water soluble by ER and then flushed out of the body.

Q14. Explain Golgi Complex.

Answer: It is made up of 5-8 hollow Fusing vesicles and flat sacs placed parallel to each other.

These sacs are called ‘cisternae’ and are filled with different enzymes. The proteins coming from ER are enclosed in vesicles, which come towards golgi complex via cytoplasm. They fuse with the formation face of the golgi membranes and empty their contents in the cisternae.

As they pass through the cisternae, they are chemically modified with the help of enzymes. They are again packed in the vesicles. These vesicles exit from the maturation face. Thus, cisternae work like a packing department that packs and distributes substances.

Q15. What are the functions of Golgi Complex?

Answer: The functions of Golgi Complex are as follows:

• Golgi complex is the secretory organ of the cell.
• It modifies, sorts and packs materials synthesized in the cell (enzymes, mucus, proteins, pigments etc.) and dispatches them to various targets like plasma membrane, lysosome etc.
• It produces vacuoles and secretory vesicles.
• It helps in the formation of cell wall, plasma membrane and lysosomes.

Q16. Explain the functions of mitochondria?

Answer: The functions of mitochondria are:

• To produce energy-rich compound- ATP.
• Synthesis of proteins, carbohydrates, lipids etc. by using the energy in ATP.

Q17. List the types of Plastids?

Answer: There are different types of plastids with their specialized functions. Among which few are mainly classified based on the presence or absence of the Biological pigments and their stages of development.

• Chloroplasts
• Chromoplasts
• Gerontoplasts
• Leucoplasts

Q18. What is nucleus?

Answer: A nucleus is defined as a double-membraned eukaryotic cell organelle that contains the genetic material. The nucleus is found only in eukaryotes and is the defining characteristic feature of eukaryotic cells. However, some cells, such as RBCs do not possess a nucleus, though they originate from a eukaryotic organism.

Q19. Write the difference between Mitochondria and Plastids.

Answer: The difference between Mitochondria and Plastids

Mitochondria	Plastids
Found in all eukaryotic cells	Found only in plant cells
Produces ATP	Produces glucose and stores it as starch
The main function is cell respiration	Main organelle for photosynthesis
Smaller in size	Comparatively larger in size
Pigments are absent	Pigments are present

Q20. Define vacuole.

Answer: The term “vacuole” means “empty space”. They help in the storage and disposal of various substances. They can store food or other nutrients required by a cell to survive. They also store waste products and prevent the entire cell from contamination. The vacuoles in plant cells are larger than those in the animal cells. The plant vacuoles occupy more than 80% of the volume of the cell. The vacuoles may be one or more in number.

Q21. Define Endocytosis and Exocytosis.

Answer: Endocytosis is defined as the process of trapping a particle or substance from the external environment by engulfing it. Endocytosis is of two types viz phagocytosis, also known as cellular eating and pinocytosis, also referred to as cellular drinking.

Exocytosis, on the other hand, is described as the process of fusing vesicles with the plasma membrane to release their contents to the external environment of the cell.

Q22. Difference between Cell Membrane and Plasma Membrane.

Answer: Following are the important differences between cell membrane and plasma membrane:

Cell Membrane	Plasma Membrane
It surrounds the entire components of the cell.	It surrounds only the cell organelles.
It regulates the tonicity of the cell.	It does not regulate the tonicity of the cell.
Cell membrane can be transformed to stimulate movement and feeding in organisms such as Paramaecium.	Plasma membrane cannot be modified.
It contains initial receptors for signal transduction and is the first step in cell signalling.	It is not the first step in cell signalling. However, it is involved in the process.
Always protects the cell from bacteria and viruses.	Does not always protect the cell from outside invaders.
Plays an important role in cytokinesis during cell division.	Does not play a key role in cytokinesis during cell division.
Cilia are present and are involved in feeding and movement.	Cilia are absent.
Is a target for antimicrobials.	Is not a target for antimicrobials.

Q23. What is osmosis?

Answer: Osmosis is a process by which the molecules of a solvent pass from a solution of low concentration to a solution of high concentration through a semipermeable membrane.

Osmosis is of two types: Endosmosis and Exosmosis.

Q24. Define structure of plasma membrane.

Answer: Protein molecules are embedded in two layers of phospholipids. Plasma membrane is said to be a selectively permeable membrane as it allows some substances to enter the cell, while prevents other substances. Due to this property, useful molecules of water, salt and oxygen enter the cell and CO₂ exits the cell. If any changes occur outside the cell, the cellular environment does not change due to plasma membrane. This condition is called homeostasis.

Q25. Write the difference between Eukaryotic cells and Prokaryotic cells.

Answer: The differences between Eukaryotic cell Prokaryotic cell are:

	Prokaryotes	Eukaryotes
Type of Cell	Always unicellular	Unicellular and multi-cellular
Cell size	Ranges in size from 0.2 μm – 2.0 μm in diameter	Size ranges from 10 μm – 100 μm in diameter
Cell wall	Usually present; chemically complex in nature	When present, chemically simple in nature
Nucleus	Absent	Present
Ribosomes	Present. Smaller in size and spherical in shape	Present. Comparatively larger in size and linear in shape
DNA arrangement	Circular	Linear
Mitochondria	Absent	Present
Cytoplasm	Present, but cell organelles absent	Present, cell organelles present
Endoplasmic reticulum	Absent	Present
Plasmids	Present	Very rarely found in eukaryotes
Ribosome	Small ribosomes	Large ribosomes
Lysosome	Lysosomes and centrosomes are absent	Lysosomes and centrosomes are present
Cell division	Through binary fission	Through mitosis
Flagella	The flagella are smaller in size	The flagella are larger in size
Reproduction	Asexual	Both asexual and sexual
Example	Bacteria and Archaea	Plant and Animal cell