Class 9 Science Chapter 5 The Fundamental Unit Of Life

Key Concept: Mitosis

b) Growth and repair

[Solution Description]

The primary purpose of mitosis in multicellular organisms is growth and repair. During mitosis, a single mother cell divides to produce two genetically identical daughter cells, each containing the same number of chromosomes as the mother cell. This ensures that the organism can grow by increasing the number of cells and repair damaged tissues by replacing old or dead cells.

Key Concept: Discovery of the electron microscope

c) Electron microscope

[Solution Description]

The electron microscope was invented in 1940, which provided a much higher magnification and resolution compared to light microscopes. This allowed scientists to observe the complex structure of cells and their organelles in detail.

Key Concept: Cell Theory

c) Theodor Schwann

[Solution Description] Theodor Schwann, in collaboration with Schleiden, proposed that all animals are composed of cells as part of the cell theory in 1838-39.

Key Concept: Nucleus

b) Nucleus

[Solution Description]

The nucleus is the darkly coloured, spherical or oval, dot-like structure near the centre of each cell. It contains chromosomes which carry DNA, responsible for inheritance of characters.

Key Concept: Term protoplasm

d) Purkinje

[Solution Description]

The term ‘protoplasm’ for the fluid substance of the cell was coined by Purkinje in the year 1839. This term is fundamental in understanding the composition of cells.

Key Concept: Unicellular vs Multicellular Organisms

c) They consist of a single cell performing all life functions

[Solution Description]

Unicellular organisms, such as Chlamydomonas, Paramoecium, and bacteria, consist of a single cell that performs all life functions. They are different from multicellular organisms, which are composed of many cells. Unicellular organisms can live independently and carry out all necessary processes for survival within a single cell.

Key Concept: Mitochondria

b) Energy production

[Solution Description]

Mitochondria are known as the powerhouses of the cell because they generate energy in the form of ATP (Adenosine triphosphate) molecules. ATP is used by the cell for various chemical activities needed for life, including making new chemical compounds and performing mechanical work.

Key Concept: Purkinje’s term “protoplasm”

d) Purkinje

[Solution Description]

Purkinje, in 1839, introduced the term ‘protoplasm’ to refer to the fluid substance of the cell. This was a significant contribution to the understanding of cell biology.

Key Concept: Virchow’s expansion of Cell Theory

c) 1855

[Solution Description]

Virchow expanded the cell theory in 1855 by proposing that all cells arise from pre-existing cells. This year marks an important milestone in the history of cell biology.

Key Concept: Terminology

b) A little room

[Solution Description]

The syllabus states that the word “cell” is derived from Latin and means ‘a little room’. This term was used by Robert Hooke to describe the compartments he observed in cork.

Key Concept: Lysosomes Role

c) They digest the cell’s own components when damaged

[Solution Description]

Lysosomes are called ‘suicide bags’ because if the cell gets damaged or there is a disturbance in cellular metabolism, lysosomes may burst and release their digestive enzymes. These enzymes can then digest the cell’s own components, leading to cell death.

Key Concept: Golgi Apparatus, ER, Lysosomes

c) Golgi apparatus; formation of lysosomes

[Solution Description]

The Golgi apparatus is responsible for modifying, packaging, and dispatching proteins synthesized near the ER. It also plays a role in the formation of lysosomes, which are involved in cellular digestion.

Key Concept: Cell Organelles

c) Each organelle performs a specific function vital for the cell’s survival

[Solution Description]

Cell organelles are essential because they perform specific functions that keep the cell alive and operational. For instance, mitochondria produce energy, ribosomes synthesize proteins, and lysosomes remove waste. Without these organelles, the cell would not be able to carry out its basic functions necessary for survival.

Key Concept: Leeuwenhoek’s discovery, Pond water observation

c) It marked the first observation of single-celled organisms

[Solution Description]

Leeuwenhoek’s discovery of free-living cells in pond water was significant because it was the first time that microorganisms were observed and documented. This discovery laid the foundation for the field of microbiology and expanded our understanding of life at the microscopic level.

Key Concept: Plastids, DNA & Ribosomes

d) Plastids have their own DNA and ribosomes.

[Solution Description]

Plastids have their own DNA and ribosomes, which is a key feature supporting the endosymbiotic theory. This theory suggests that plastids originated from free-living prokaryotic organisms that were engulfed by ancestral eukaryotic cells.

Key Concept: Chromatin Material

c) It organizes into chromosomes

[Solution Description]

Chromatin material, which consists of DNA and proteins, is typically found as an entangled mass of thread-like structures in a non-dividing cell. When the cell prepares to divide, this chromatin material condenses and organizes into distinct structures called chromosomes. This condensation is necessary for the accurate segregation of genetic material during cell division.

Key Concept: Cell Wall, Plasmolysis

c) The cell will shrink and collapse due to loss of water

[Solution Description]

The cell wall provides structural support and prevents the cell from bursting in hypotonic solutions. In a hypertonic solution, water moves out of the cell, causing plasmolysis. However, if the cell wall is removed, the cell loses its structural integrity. Without the cell wall, the plasma membrane will shrink away more significantly, leading to cell collapse or death.

Key Concept: Diffusion, Osmosis, Plasma Membrane

b) $CO_2$ molecules will move out of the cell

[Solution Description]

The movement of substances like $CO_2$ across the plasma membrane occurs through diffusion. Diffusion is the process where molecules move from a region of higher concentration to a region of lower concentration. In this case, since the concentration of $CO_2$ is higher inside the cell than outside, $CO_2$ molecules will move out of the cell until equilibrium is reached.

Key Concept: Vacuoles, Storage of Substances

c) Lipids

[Solution Description]

Vacuoles in plant cells store substances such as amino acids, sugars, organic acids, and proteins. However, lipids are primarily stored in other organelles like lipid droplets, not vacuoles. Therefore, lipids are not typically stored in vacuoles.

Key Concept: Concept: Advancements in Microscopy

c) Electron Microscope

[Solution Description]

The discovery of the electron microscope in 1940 allowed scientists to observe and understand the complex structure of cells and their organelles in much greater detail compared to earlier light microscopes.

Key Concept: Cell Theory

c) Purkinje

[Solution Description]

The term ‘protoplasm’ was coined by Purkinje in 1839 to describe the fluid substance of the cell. This term is significant in the study of cell biology.

Key Concept: Discovery of Cells

d) Robert Brown

[Solution Description] Robert Brown discovered the nucleus in the cell in 1831. This was a significant discovery in the field of cell biology.

Key Concept: Plastids, Chloroplasts, Photosynthesis

d) Chloroplasts containing chlorophyll

[Solution Description]

Chloroplasts are the organelles in plant cells that capture light energy and convert it into chemical energy through photosynthesis. The pigment chlorophyll, present in chloroplasts, is essential for absorbing light energy. Therefore, the correct answer is chloroplasts containing chlorophyll.

Key Concept: Mitochondria DNA

b) Presence of their own DNA and ribosomes

[Solution Description]

Mitochondria have their own DNA and ribosomes, which enable them to produce some of their own proteins independently of the cell’s nucleus. This is a unique characteristic that supports the endosymbiotic theory of mitochondrial origin.

Key Concept: Unicellular Organisms

d) Amoeba

[Solution Description]

Amoeba is a unicellular organism, meaning it consists of only one cell and can perform all life functions independently.

Key Concept: Endoplasmic Reticulum, Membrane Biogenesis

d) Membrane biogenesis

[Solution Description] The rough endoplasmic reticulum (RER) has ribosomes attached to its surface, which are essential for protein synthesis. These proteins are then transported to various parts of the cell or used in membrane biogenesis. If ribosomes cannot attach to the RER, the synthesis of proteins specifically destined for the membrane or secretion would be disrupted. This would directly affect membrane biogenesis, as these proteins are crucial components of the cell membrane.

Key Concept: Membrane Significance

d) Viruses lack membranes and depend on host cells for multiplication

[Solution Description]

Viruses lack any membranes and hence do not exhibit characteristics of life until they enter a living body and use its cell machinery to multiply. The absence of membranes means viruses cannot carry out metabolic processes independently. They rely on host cells for replication and other life functions.