Comp-CBSE-9-S-C5

Cells grow by dividing. The given picture shows one such growing cell ready to divide.

A. The number of daughter cells formed after the cell divides completely is ​ (a)  

B. The number of chromosomes received by each daughter cell is​ (b)  

Answer explanation

• A. Number of Cells: Cell division for growth (mitosis) is an equational division where one parent cell divides once to form two genetically identical daughter cells.

• B. Number of Chromosomes: The key is that during mitosis, the sister chromatids of each duplicated chromosome are pulled apart. Each daughter cell receives one copy of every chromosome.

  • The parent cell has 4 duplicated chromosomes.

  • After they split, each new daughter cell will receive 4 single-stranded chromosomes.

In an experiment, two beakers are set up. Beaker 1 contains a cell with a cell wall in a hypotonic solution. Beaker 2 contains a cell without a cell wall in the same hypotonic solution. What would be the most likely outcomes after 30 minutes?

• Cell in Beaker 1 bursts; Cell in Beaker 2 becomes turgid.

• Cell in Beaker 1 becomes turgid; Cell in Beaker 2 bursts.

• Both cells become turgid.

• Both cells burst.

Answer explanation

In a hypotonic solution, water enters both cells by osmosis.

• Beaker 1 (Cell with wall): The rigid cell wall prevents the cell from bursting. The cell swells and becomes turgid.

• Beaker 2 (Cell without a wall): No cell wall is present to resist the internal pressure. The cell continues to swell until it bursts.

Farmers use fertilizers rich in Nitrogen and Phosphorus. These elements are crucial for the synthesis of proteins and nucleic acids. Which cell organelle would be most active in utilizing these fertilizers for plant growth and repair?

• Chloroplast

• Vacuole

• Ribosome

• Lysosome

Answer explanation

While fertilizers provide the raw materials (Nitrogen for amino acids, Phosphorus for DNA/RNA), the ribosome is the primary organelle that directly utilizes these building blocks.

• Ribosomes are the sites of protein synthesis. They read genetic instructions from mRNA and assemble amino acids (which contain nitrogen) into proteins, which are essential for plant growth, enzyme function, and tissue repair.

In the given figure, mark the correct name for X and Y from the given options

Answer explanation

X represents the Endoplasmic Reticulum (ER).

The Endoplasmic Reticulum (ER) is a network of membrane-bound tubes and sheets inside the cell. It serves as a transportation system, connecting the nucleus to the cytoplasm and other organelles.

A cell functions like a highly efficient factory. If one of its organelles fails, it causes a specific problem. Match the correct consequence to the malfunctioning organelle.

• • Mitochondria

• • Material transport channels break down.

• • Endoplasmic Reticulum

• • Energy currency (ATP) not produced.

• • Lysosomes

• • Toxic waste and worn-out parts accumulate

• • Cell Wall

• • Proteins are synthesized but not modified and packaged.

• • Golgi Apparatus

• • The cell loses its shape and support.

Answer explanation

• Mitochondria: This is the "powerhouse of the cell." Its sole function is to produce ATP (energy). If it fails, energy production stops.

• Golgi Apparatus: This organelle acts as the cell's "post office," modifying, sorting, and packaging proteins. If it fails, proteins are made but cannot be processed correctly.

• Lysosomes: These are the cell's "stomachs" or "waste disposals," containing digestive enzymes to break down waste. If they fail, toxins and cellular debris build up.

• Endoplasmic Reticulum (ER): The ER is a network of transport channels. The Rough ER also has ribosomes for protein synthesis. If it fails, the cell's internal transport and synthesis system collapses.

• Cell Wall: This rigid outer layer (in plants, fungi, and bacteria) provides structural support and shape. If it breaks down, the cell loses its shape.

The diagram shows a single-celled organism with an irregular shape. A large food particle is positioned near the cell. The cell membrane is shown extending outward toward the particle, forming arm-like projections called pseudopodia that are beginning to surround the particle.

Click on the part of the cell where this process begins.

Answer explanation

Endocytosis is the process by which a cell engulfs external material, such as a food particle, by flexing its cell membrane inward to form a vesicle or vacuole inside the cell.

• How it works: The cell's flexible plasma membrane extends outward, surrounds the food particle, and pinches off, bringing the particle into the cytoplasm.

You are given two slides: one of a cheek cell and one of an onion peel. Which of the following structures would you observe in the onion peel cell but NOT in the cheek cell?

• Cell Membrane and Cytoplasm

• Nucleus and Mitochondria

• Cell Wall and Chloroplasts

• Ribosomes and Golgi Apparatus

Answer explanation

The onion peel is from a plant, while the cheek cell is from an animal. The key differences are:

• Cell Wall: A rigid outer layer made of cellulose that provides structure and support. It is present in onion (plant) cells but completely absent in cheek (animal) cells.

• Chloroplast: The organelle that performs photosynthesis. It is found in onion (plant) cells (specifically in the green parts, but the peel cells may have some or the potential for them) and is absent in cheek (animal) cells.

Structures like the cell membrane, cytoplasm, nucleus, and mitochondria are common to both cell types.

Various real-life observations are listed in Column I. Match each observation with the correct cellular process from Column II that is primarily responsible for it.

• Active Transport

• 1. An Amoeba extends its body to surround and engulf a food particle.

• Endocytosis

• 1. A plant cell, when placed in distilled water, becomes firm and swollen.

• Osmosis

• 1. Root hair cells in a plant absorb water and minerals from the soil.

Answer explanation

• 1. Endocytosis
  Explanation: The amoeba uses its flexible cell membrane to engulf the solid food particle, a process called endocytosis (specifically phagocytosis).

1. 2. Osmosis
   Explanation: Distilled water is a hypotonic solution. Water enters the plant cell via osmosis, making it turgid (firm and swollen).

2. 3. Active Transport
   Explanation: Root hairs need to absorb minerals from the soil even when their concentration is higher inside the root cell. This movement against the concentration gradient requires energy and is called active transport.

What property of the plasma membrane helps amoeba acquire food?

• It is flexible.

• It is selectively permeable.

• It is made up of proteins and lipids.

• It allows diffusion of some substances across it.

Answer explanation

The flexibility of the plasma membrane is the key property that allows an amoeba to acquire food.

Role of Flexibility: The fluid and flexible nature of the plasma membrane allows it to change shape, stretch, and fuse together to completely surround and engulf the food particle, forming an internal food vacuole.

A new single-celled organism is discovered. It is found to have a nucleoid, ribosomes, and a cell wall, but no other membrane-bound organelles. How should this organism be classified?

• Eukaryotic Plant Cell

• Eukaryotic Animal Cell

• Prokaryotic Cell

• Fungal Cell

Answer explanation

• The discovered organism has a nucleoid and no membrane-bound organelles; hence, it is definitely a prokaryote.

• Prokaryotic Cell: This type of cell (e.g., bacteria) is characterized by:

  • A nucleoid: A region where the genetic material (DNA) is located, but it is not surrounded by a nuclear membrane.

  • No membrane-bound organelles: It lacks organelles like a nucleus, mitochondria, chloroplasts, endoplasmic reticulum, or Golgi apparatus.

  • It has ribosomes (for protein synthesis) and often has a cell wall.

• Eukaryotic Cell: This type of cell (found in plants, animals, fungi, and protists) has a true nucleus enclosed by a membrane and contains various other membrane-bound organelles.