The Fundamental Unit Of Life - Cell - Class 9 MCQ

Which cell evolved first?
Answer: Prokaryotic
Explanation:
To answer which cell evolved first, we need to consider the evolution of cells on Earth. Here is a detailed explanation:
1. Prokaryotic Cells:
- Prokaryotic cells are the simplest and most ancient forms of cells.
- They lack a nucleus and other membrane-bound organelles.
- Prokaryotic cells include bacteria and archaea.
- Archaea, a type of prokaryotic cell, are considered to be one of the oldest forms of life on Earth.
2. Eukaryotic Cells:
- Eukaryotic cells are more complex than prokaryotic cells.
- They have a nucleus and various membrane-bound organelles.
- Eukaryotic cells include cells found in plants, animals, fungi, and protists.
- The development of eukaryotic cells is believed to have occurred through endosymbiosis, where one prokaryotic cell engulfed another, leading to the formation of organelles like mitochondria and chloroplasts.
3. Plant Cells:
- Plant cells are a type of eukaryotic cell.
- They have additional features such as a cell wall, chloroplasts for photosynthesis, and a large central vacuole.
- Plant cells evolved from ancestral eukaryotic cells.
4. Archaebacteria:
- Archaebacteria, also known as archaea, are a type of prokaryotic cell.
- They are considered to be one of the oldest forms of life on Earth.
- Archaebacteria thrive in extreme environments such as hot springs, deep-sea hydrothermal vents, and salt pans.
In conclusion:
- Prokaryotic cells, including archaea, evolved first on Earth.
- Eukaryotic cells, which include plant cells, evolved later through endosymbiosis and other evolutionary processes.
- While plant cells are a type of eukaryotic cell, they are not the first cells to have evolved.

Cell volume shrinks in plasmolysis

Colorless plastids are known as leucoplasts.
Leucoplasts are a type of plastid found in plant cells that lack pigments. They are colorless and primarily involved in the synthesis and storage of various compounds. Here are some key points about leucoplasts:
- Definition: Leucoplasts are non-pigmented plastids that occur in plant cells and are responsible for storing and synthesizing various biomolecules.
- Lack of pigments: Unlike chloroplasts and chromoplasts, leucoplasts do not contain pigments such as chlorophyll or carotenoids, which give color to other plastids.
- Types of leucoplasts: There are several types of leucoplasts, each with specific functions:
- Amyloplasts: These leucoplasts are involved in storing starch and are commonly found in starchy organs such as tubers, roots, and seeds.
- Elaioplasts: Elaioplasts store lipids and are found in oil-rich tissues like seeds and fruits.
- Proteinoplasts: Proteinoplasts synthesize and store proteins, mainly found in protein-rich tissues like seeds.
- Aleuronoplasts: Aleuronoplasts are specialized leucoplasts found in the endosperm of cereals, responsible for storing proteins.
- Function: Leucoplasts play a crucial role in plant metabolism. They are involved in the synthesis of various biomolecules such as starch, lipids, and proteins. These plastids are also responsible for storing these compounds until they are needed by the plant.
- Development: Leucoplasts often originate from proplastids, which are undifferentiated plastids present in meristematic tissues. The development of leucoplasts is influenced by various factors, including environmental cues and plant hormones.
In conclusion, leucoplasts are colorless plastids found in plant cells that are involved in the synthesis and storage of various compounds. They lack pigments and have different types with specific functions, such as starch storage in amyloplasts and lipid storage in elaioplasts.

The barrier between the protoplasm and the outer environment in an animal cell is called the plasma membrane.
The plasma membrane, also known as the cell membrane, is a selectively permeable barrier that separates the internal environment of the cell from its external surroundings. It plays a crucial role in maintaining homeostasis and regulating the movement of substances in and out of the cell. Here are some key points about the plasma membrane:
- Structure: The plasma membrane is composed of a phospholipid bilayer with embedded proteins. The phospholipids have hydrophilic heads that face the watery environment both inside and outside the cell, and hydrophobic tails that face each other in the interior of the bilayer.
- Functions: The plasma membrane has several important functions, including:
- Regulating the passage of molecules: The plasma membrane is selectively permeable, allowing some substances to enter or leave the cell while restricting the movement of others.
- Maintaining cell shape: The plasma membrane provides structural support and helps maintain the shape of the cell.
- Cell signaling: The plasma membrane contains receptors that can detect and respond to signals from the external environment, allowing the cell to communicate with its surroundings.
- Cell adhesion: The plasma membrane plays a role in cell adhesion, allowing cells to stick together and form tissues.
- Transport mechanisms: The plasma membrane uses various transport mechanisms to control the movement of molecules across the membrane. These include passive processes like diffusion and osmosis, as well as active processes like active transport and endocytosis/exocytosis.
- Importance: The plasma membrane is essential for the survival and proper functioning of the cell. It creates a boundary between the cell and its environment, allowing the cell to maintain a stable internal environment and carry out its specific functions.
In conclusion, the barrier between the protoplasm and the outer environment in an animal cell is called the plasma membrane. It is a selectively permeable barrier that regulates the movement of substances in and out of the cell and plays a crucial role in maintaining cell homeostasis.

Introduction:
Mitochondria are membrane-bound organelles found in eukaryotic cells. They are often referred to as the "powerhouses" of the cell because they are responsible for producing the majority of the cell's energy in the form of adenosine triphosphate (ATP).
A. Aerobic Respiration:
Mitochondria are primarily involved in aerobic respiration, which is the process by which cells convert glucose and oxygen into carbon dioxide, water, and ATP. During aerobic respiration, mitochondria carry out several key steps, including the Krebs cycle and the electron transport chain.
B. Krebs Cycle of Aerobic Respiration:
The Krebs cycle, also known as the citric acid cycle or the tricarboxylic acid cycle, is a series of chemical reactions that occur in the mitochondria. It is an essential part of aerobic respiration and plays a crucial role in the breakdown of glucose and the production of ATP.
C. Glycolysis of Aerobic Respiration:
Glycolysis, the initial step of aerobic respiration, takes place outside the mitochondria in the cytoplasm. However, the end products of glycolysis, namely pyruvate, are transported into the mitochondria, where they enter the Krebs cycle.
D. Anaerobic Respiration:
Mitochondria are not directly involved in anaerobic respiration, which is a process that occurs in the absence of oxygen. Anaerobic respiration takes place in the cytoplasm and produces significantly less ATP compared to aerobic respiration.
Conclusion:
In conclusion, mitochondria are primarily involved in aerobic respiration, including the Krebs cycle of aerobic respiration. While they do not directly participate in glycolysis or anaerobic respiration, they play a crucial role in the overall process of energy production in the cell.