RBSE Solutions Class 11 Biology Chapter 7 Cell Wall and Cell Membrane

RBSE Class 11 Biology Chapter 7 Multiple Choice Objective Questions

Question 1. Middle Lamella is made up of-
(a) Lignin
(b) Pectin
(c) Pectates of Ca & Mg
(d) Cellulose
Answer: (c) Pectates of Ca & Mg
In simple words: The middle lamella is like the glue between plant cells, and it is mainly made of substances called pectates, specifically those combined with calcium and magnesium.

🎯 Exam Tip: Remember that the middle lamella is primarily composed of pectin compounds, which help in binding adjacent plant cells together.

Question 2. The most abundant substance in cell wall is-
(a) Protein
(b) Fat
(c) Carbohydrates
(d) Nucleic acids
Answer: (c) Carbohydrates
In simple words: The main building material for plant cell walls is carbohydrates, especially a type called cellulose.

🎯 Exam Tip: Cellulose, a complex carbohydrate, forms the primary structural component of plant cell walls, providing strength and rigidity.

Question 4. One molecule of cellulose consists of-
(a) 3000 glucose molecules
(b) 30,000 glucose molecules
(c) 30,000 fructose molecules
(d) 30,000 galactose molecules
Answer: (a) 3000 glucose molecules
In simple words: A single molecule of cellulose is made up of about 3000 smaller glucose molecules joined together in a long chain.

🎯 Exam Tip: Understand that cellulose is a polymer, meaning it's a large molecule made of many repeating smaller units (monomers), which in this case are glucose units.

Question 5. Simple pits are found in-
(a) Sclerenchyma
(b) Collenchyma
(c) Sieve tubes
(d) Tracheids
Answer: (c) Sieve tubes
In simple words: Simple pits, which are small, unthickened areas in cell walls, are often seen in sieve tubes, which are part of plant transport systems.

🎯 Exam Tip: Distinguish between simple pits and bordered pits, noting their structural differences and the types of cells where each is typically found.

RBSE Class 11 Biology Chapter 7 Very Short Answer Questions

Question 1. Who propounded unit membrane concept?
Answer: Robertson (1958).
In simple words: The idea of the unit membrane was proposed by Robertson in the year 1958.

🎯 Exam Tip: When asked for the discoverer of a concept, always include the name and the year if available for a complete answer.

Question 2. Cell wall is made up of what?
Answer: Polysaccharides (Chitin, cellulose, pectin).
In simple words: Cell walls are built from complex sugars called polysaccharides, like chitin in fungi and cellulose or pectin in plants.

🎯 Exam Tip: Remember that the exact composition of the cell wall can vary between different organisms, such as plants, fungi, and bacteria.

Question 3. Where the lignin is found in the cell wall?
Answer: Lignin is found as a hard substance deposited in the secondary cell wall, making it strong and rigid. It is common in woody plants.
In simple words: Lignin is found in the cell wall, mainly in the secondary wall, where it helps to make the plant stiff and woody.

🎯 Exam Tip: Lignin is crucial for providing mechanical support and waterproofing in plant tissues, especially in xylem vessels.

RBSE Class 11 Biology Chapter 7 Short Answer Questions

Question 4. What is the thickness of cell membrane?
Answer: The cell membrane has a thickness of about 75 Angstroms (which is typically between 70 to 80 Angstroms).
In simple words: The cell membrane is very thin, usually around 75 Angstroms thick.

🎯 Exam Tip: Knowing the approximate thickness of the cell membrane helps in understanding its delicate structure and functions.

Question 5. What is endocytosis?
Answer: Endocytosis is the process where a cell takes in substances from its surroundings by wrapping its cell membrane around them to form a vesicle inside the cytoplasm.
In simple words: Endocytosis is when a cell brings things from outside into its cytoplasm.

🎯 Exam Tip: Distinguish endocytosis from exocytosis, which is the process of expelling substances from the cell.

Question 1. What are pits ? Give their types.
Answer: Pits are thin, unthickened areas in the cell walls of some plant cells, like parenchyma, sclerenchyma, sieve plates, vessels, and tracheids. These areas allow substances to pass through the otherwise thick cell wall. There are mainly two types of pits:
(A) Simple pits – These pits are found between the cell walls of nearby cells, such as sieve tubes and parenchyma cells. They are typically round and cylindrical. Simple pits help in the exchange of water and dissolved substances across the membrane. Their diameter stays the same, and the pit cavity widens towards the inside of the cell.
(B) Bordered pit – These pits are more complex than simple pits. In bordered pits, the secondary cell wall forms a border that overhangs the pit cavity, making the pit opening narrower than the actual pit diameter. Sometimes, the pit opening is lenticular (lens-shaped). A bordered pit also has an oval thickening in the middle of its pit membrane, which is called a torus. The pit membrane is flexible.
In simple words: Pits are thin spots in plant cell walls that let things pass through. Simple pits are basic openings, while bordered pits have a special rim and a central thickening called a torus.

🎯 Exam Tip: Focus on the structural differences and the presence or absence of a secondary wall border and torus to distinguish between simple and bordered pits.

Question 2. What is plasmodesmata ?
Answer: Plasmodesmata are tiny channels or connections that pass through the cell walls of adjacent plant cells, connecting their cytoplasm directly. They allow molecules and communication signals to move between individual plant cells, creating a continuous cytoplasmic network called the symplast.
In simple words: Plasmodesmata are small bridges between plant cells that allow their internal parts to connect and share materials.

🎯 Exam Tip: Understand that plasmodesmata are vital for intercellular communication and transport in plants, forming the symplastic pathway.

Question 3. What do you mean by phagocytosis and pinocytosis.
Answer: Phagocytosis and pinocytosis are both forms of endocytosis, processes where cells engulf substances from their external environment.
Phagocytosis: This is when a cell takes in large solid particles or whole cells by extending its plasma membrane to surround them, forming a phagosome. It is often called "cell eating."
Pinocytosis: This is when a cell takes in liquids and small dissolved molecules by forming small vesicles from its plasma membrane. It is often referred to as "cell drinking."
In simple words: Phagocytosis is how cells "eat" large solid particles, while pinocytosis is how cells "drink" liquids and small dissolved substances.

🎯 Exam Tip: The key difference between phagocytosis and pinocytosis lies in the size and nature (solid vs. liquid) of the particles being engulfed by the cell.

RBSE Class 11 Biology Chapter 7 Essay Type Questions

Question 4. Explain unit membrane concept of cell membrane.
Answer: Robertson (1958) proposed the unit membrane concept. According to this model, every cell membrane, as well as the membranes of organelles inside the cell, shares a similar basic structure. It is described as a single unit membrane consisting of three distinct layers. These layers include two protein layers (one on each side) and one phospholipid layer in the middle. The total thickness of this unit membrane is approximately 75 Angstroms, typically ranging from 70 to 80 Angstroms.
In simple words: Robertson's unit membrane idea says that all cell membranes look alike, with three layers: two protein layers outside and one fat layer inside, measuring about 75 Angstroms thick.

🎯 Exam Tip: Note the key components (proteins, phospholipids) and their arrangement in the unit membrane model, along with its approximate thickness.

Question 5. What are thickenings?
Answer: Thickenings refer to the process where additional layers are added to the cell wall, specifically during the formation of the secondary wall on the inner side of the primary wall. The type of thickening that occurs depends on the specific function and nature of the cell wall. These thickenings are formed due to the deposition of hard substances, which can include lignin, cellulose, hemicelluloses, and suberin. This process makes the cell wall stronger and more rigid.
In simple words: Thickenings are extra layers that make cell walls stronger by adding hard materials like lignin and cellulose, usually on the inside of the first wall.

🎯 Exam Tip: Identify the main substances involved in cell wall thickening and understand that this process provides mechanical strength to plant cells.

Question 6. Give two functions of cell wall.
Answer: The cell wall plays several important roles in plant cells. Here are two of its functions:
(i) It provides definite shape & size to the cell.
(ii) It provides mechanical support to the cell.
In simple words: The cell wall helps a plant cell keep its shape and size, and it also gives the cell strong support.

🎯 Exam Tip: Remember that the rigid cell wall protects the plant cell from mechanical stress and prevents excessive water uptake by maintaining turgor pressure.

Question 7. Give two functions of cell membrane.
Answer: The cell membrane is crucial for the cell's survival and interaction with its environment. Here are two of its functions:
(i) It provides shape & size to the cells.
(ii) It protects the cell organelles.
In simple words: The cell membrane gives cells their basic shape and size, and it also keeps the parts inside the cell safe.

🎯 Exam Tip: Beyond shape and protection, emphasize that the cell membrane is selectively permeable, controlling what enters and exits the cell.

Question 1. Explain structure of cell wall. Give suitable diagram.
Answer: The plant cell wall is a tough outer covering that gives plant cells their definite shape. Its structure and what it's made of can differ depending on its specific functions. For example, the cell wall in fungi is primarily made of polysaccharides like chitin, while in algae, it consists of cellulose and pectin.
Structurally, the cell wall is made of two main parts:
(A) Fibrils: These are made of cellulose. A single cellulose molecule contains about 3000 glucose molecules. About 100 cellulose molecules combine to form a micelle, and 20 micelles then form a microfibril. Approximately 250 microfibrils come together to create one macrofibril, which has a diameter of 250 Angstroms. Fibrils are not present in the primary cell wall but are found in parallel arrangements in the secondary cell wall. A matrix fills the spaces between these fibrils.
(B) Matrix: This is a non-crystalline, jelly-like substance found between the primary and secondary cell walls. It contains water, glycoproteins, pectin, and hemi-cellulose. It might also have gum, resin, tannin, wax, and silica. In some places, plant cell walls lack a cellulose layer, forming tiny openings called primary pits.
The primary pits of adjacent plant cells allow the formation of plasmodesmata. Plasmodesmata are pores or channels that connect the cytoplasm of neighboring plant cells, enabling the passage of molecules and communication signals. Water and small-molecular-weight substances can freely move through these plasmodesmata, creating a continuous cytoplasmic system called the symplast. In contrast, the space outside the plasma membrane, called the apoplasm, allows materials to diffuse freely but is interrupted by structures like casparian strips in roots, air spaces between cells, and the plant cuticle.