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THE FUNDAMENTAL UNIT OF LIFE
TOPIC : CELL MEMBRANE ( PLASMA MEMBRANE)
The plasma membrane is a thin, flexible barrier that surrounds the outer boundary of all cells. It separates the
cell's internal environment from the external environment and controls the movement of substances in and out of
the cell. The plasma membrane is composed mainly of phospholipid molecules arranged in a double layer called
the phospholipid bilayer.
structure: The plasma membrane is primarily composed of phospholipids, which have a hydrophilic (water-
attracting) head and hydrophobic (water-repelling) tail. These phospholipids arrange themselves in a bilayer, with
the hydrophobic tails facing inward and the hydrophilic heads facing outward, towards the watery environments
inside and outside the cell.
Function: The main function of the plasma membrane is to regulate the passage of substances into and out of the
cell. It acts as a selectively permeable barrier, allowing some molecules to pass through while blocking others. This
selective permeability is crucial for maintaining the cell's internal environment and for communication with the
external environment.
Transport: Various mechanisms are involved in the movement of substances across the plasma membrane. These
include passive processes like diffusion and osmosis, where substances move from areas of high concentration to
areas of low concentration, and active transport, where energy is required to move substances against their
concentration gradient.
Cellular Communication: The plasma membrane contains proteins and receptors that allow cells to communicate
with each other and with the external environment. These proteins play roles in signal transduction, cell
recognition, and cell adhesion.
Cellular Structure: The plasma membrane gives cells their shape and structure, helping to maintain their integrity
and stability.
When a cell is placed in different types of solutions, such as hypotonic, hypertonic, and isotonic solutions, the
movement of water across the cell membrane will result in various effects on the cell.
Hypotonic Solution:
Definition: A hypotonic solution has a lower concentration of solutes (such as salts, sugars, etc.) compared to the
cytoplasm of the cell.
Effect on the Cell: In a hypotonic solution, water moves into the cell more rapidly than it moves out. This occurs
because water moves from an area of higher concentration (outside the cell) to an area of lower concentration
(inside the cell), across the selectively permeable membrane. As a result: The cell gains water and swells.
The cell membrane may expand and push against the cell wall (in plant cells) or become turgid.
In extreme cases, excessive water uptake can cause animal cells to burst (lyse), although plant cells are generally
protected by their rigid cell walls.
Hypertonic Solution:
Definition: A hypertonic solution has a higher concentration of solutes compared to the cytoplasm of the cell.
Effect on the Cell: In a hypertonic solution, water moves out of the cell more rapidly than it moves in. This occurs
because water moves from an area of higher concentration (inside the cell) to an area of lower concentration
(outside the cell), across the selectively permeable membrane. As a result:
The cell loses water and shrinks.
The cell membrane may pull away from the cell wall (in plant cells) and undergoes plasmolysis.
In extreme cases, excessive water loss can cause the cell to shrink and become shriveled (crenated) in animal cells.
Isotonic Solution:
Definition: An isotonic solution has the same concentration of solutes as the cytoplasm of the cell.
Effect on the Cell: In an isotonic solution, the concentration of water outside the cell is equal to the concentration
of water inside the cell. As a result:
There is no net movement of water into or out of the cell.
The cell maintains its normal shape and size.
There is no change in the turgidity of plant cells or the shape of animal cells.
In summary, the behavior of cells in different types of solutions is primarily determined by the movement of water
across the selectively permeable cell membrane, which in turn affects the cell's volume and shape.
MCQ
1. What is the main function of the plasma membrane in a cell?
a) Energy production
b) Regulation of cell shape
c) Selective permeability
d) Synthesis of proteins
Answer: c) Selective permeability
Which of the following is NOT a component of the plasma membrane?
a) Phospholipids
b) Proteins
c) Carbohydrates
d) DNA
Answer: d) DNA
Which term describes the property of the plasma membrane that allows it to allow certain substances to pass
while blocking others?
a) Selective permeability
b) Active transport
c) Osmosis
d) Endocytosis
Answer: a) Selective permeability
Which type of transport across the plasma membrane does not require energy expenditure by the cell?
a) Active transport
b) Passive transport
c) Facilitated diffusion
d) Exocytosis
Answer: b) Passive transport
The presence of which molecule on the outer surface of the plasma membrane is important for cell recognition?
a) DNA
b) RNA
c) Carbohydrates
d) Lipids
Answer: c) Carbohydrates
TOPIC : CELL WALL
The cell wall is a rigid, protective layer that surrounds the cell membrane of plant cells, fungi, algae, and
some bacteria. It is primarily composed of cellulose, a complex carbohydrate polymer, along with other
polysaccharides, proteins, and sometimes lignin.
Functions of the Cell Wall:
1. Structural Support: One of the primary functions of the cell wall is to provide structural support
and rigidity to the cell, helping it maintain its shape and withstand mechanical stress. This
structural support is crucial for the overall integrity and stability of plant tissues.
2. Protection: The cell wall acts as a protective barrier, shielding the cell from physical damage,
pathogens, and environmental stresses. It helps prevent the cell from bursting due to osmotic
pressure changes and provides defence against herbivores and pathogens.
3. Regulation of Water Balance: The cell wall regulates the movement of water into and out of the
cell, helping maintain the cell's internal water balance or turgor pressure. It prevents excessive
water uptake, which could lead to cell bursting, and provides structural support to cells in
hypotonic environments.
4. Cell Communication: The cell wall plays a role in cell-to-cell communication and signaling
processes. Plasmodesmata, microscopic channels that traverse the cell wall, allow for the
exchange of ions, molecules, and signalling molecules between adjacent plant cells, facilitating
coordination and communication within tissues.
5. Support for Growth: As plants grow, new cell wall material is synthesized and deposited, allowing
cells to expand and elongate. The cell wall provides a scaffold for cell growth and development,
determining the final shape and size of plant organs.
6. Differences Between Plant and Animal Cells:
While plant cells have cell walls, animal cells do not. Instead, animal cells have a flexible, lipid-
based plasma membrane that surrounds the cell. This structural difference contributes to the
distinct shapes and properties of plant and animal cells.
CYTOPLASM
The cytoplasm is a jelly-like substance that fills the interior of the cell, surrounding the nucleus and
organelles. It is a semi-fluid medium composed primarily of water, along with various dissolved
molecules, ions, and suspended particles.
Functions of the Cytoplasm:
1. Cellular Metabolism: The cytoplasm is the site of many cellular metabolic reactions, including
glycolysis, the initial stage of cellular respiration, which takes place in the cytoplasm. It also
houses enzymes involved in various biochemical pathways, such as protein synthesis and lipid
metabolism.
2. Support and Shape: The cytoplasm provides structural support to the cell and helps maintain its
shape. It fills the space between organelles and the cell membrane, providing a medium for
organelle movement and anchorage.
3. Transport: Within the cytoplasm, various molecules and organelles move through a process called
cytoplasmic streaming or cytoplasmic circulation. This movement helps distribute nutrients, ions,
and other substances throughout the cell, facilitating cellular functions and maintaining
homeostasis.
4. Storage: The cytoplasm serves as a storage site for various substances, including nutrients, ions,
and waste products. These stored materials can be utilized by the cell as needed for energy
production, biosynthesis, or other cellular processes.
5. Cellular Communication: The cytoplasm plays a role in cellular communication by housing
signaling molecules and components of signaling pathways. These molecules and pathways
enable cells to respond to external stimuli and coordinate cellular activities in response to
changing environmental conditions.
Structure of the Cytoplasm:
The cytoplasm consists of two main components:
 Cytosol: The liquid portion of the cytoplasm, where organelles are suspended. It is primarily
composed of water and dissolved molecules such as ions, sugars, amino acids, and proteins.
 Organelles: Various membrane-bound organelles, such as the endoplasmic reticulum, Golgi
apparatus, mitochondria, and lysosomes, are dispersed throughout the cytoplasm. These
organelles perform specific functions necessary for cellular processes.
PART 1 - CHAPTER 1 - CELL THE FUNDAMENTAL UNIT OF LIFE

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PART 1 - CHAPTER 1 - CELL THE FUNDAMENTAL UNIT OF LIFE

  • 1. THE FUNDAMENTAL UNIT OF LIFE TOPIC : CELL MEMBRANE ( PLASMA MEMBRANE) The plasma membrane is a thin, flexible barrier that surrounds the outer boundary of all cells. It separates the cell's internal environment from the external environment and controls the movement of substances in and out of the cell. The plasma membrane is composed mainly of phospholipid molecules arranged in a double layer called the phospholipid bilayer. structure: The plasma membrane is primarily composed of phospholipids, which have a hydrophilic (water- attracting) head and hydrophobic (water-repelling) tail. These phospholipids arrange themselves in a bilayer, with the hydrophobic tails facing inward and the hydrophilic heads facing outward, towards the watery environments inside and outside the cell. Function: The main function of the plasma membrane is to regulate the passage of substances into and out of the cell. It acts as a selectively permeable barrier, allowing some molecules to pass through while blocking others. This selective permeability is crucial for maintaining the cell's internal environment and for communication with the external environment. Transport: Various mechanisms are involved in the movement of substances across the plasma membrane. These include passive processes like diffusion and osmosis, where substances move from areas of high concentration to areas of low concentration, and active transport, where energy is required to move substances against their concentration gradient. Cellular Communication: The plasma membrane contains proteins and receptors that allow cells to communicate with each other and with the external environment. These proteins play roles in signal transduction, cell recognition, and cell adhesion. Cellular Structure: The plasma membrane gives cells their shape and structure, helping to maintain their integrity and stability. When a cell is placed in different types of solutions, such as hypotonic, hypertonic, and isotonic solutions, the movement of water across the cell membrane will result in various effects on the cell. Hypotonic Solution: Definition: A hypotonic solution has a lower concentration of solutes (such as salts, sugars, etc.) compared to the cytoplasm of the cell. Effect on the Cell: In a hypotonic solution, water moves into the cell more rapidly than it moves out. This occurs because water moves from an area of higher concentration (outside the cell) to an area of lower concentration (inside the cell), across the selectively permeable membrane. As a result: The cell gains water and swells. The cell membrane may expand and push against the cell wall (in plant cells) or become turgid. In extreme cases, excessive water uptake can cause animal cells to burst (lyse), although plant cells are generally protected by their rigid cell walls. Hypertonic Solution: Definition: A hypertonic solution has a higher concentration of solutes compared to the cytoplasm of the cell. Effect on the Cell: In a hypertonic solution, water moves out of the cell more rapidly than it moves in. This occurs because water moves from an area of higher concentration (inside the cell) to an area of lower concentration (outside the cell), across the selectively permeable membrane. As a result: The cell loses water and shrinks. The cell membrane may pull away from the cell wall (in plant cells) and undergoes plasmolysis. In extreme cases, excessive water loss can cause the cell to shrink and become shriveled (crenated) in animal cells. Isotonic Solution: Definition: An isotonic solution has the same concentration of solutes as the cytoplasm of the cell. Effect on the Cell: In an isotonic solution, the concentration of water outside the cell is equal to the concentration of water inside the cell. As a result: There is no net movement of water into or out of the cell. The cell maintains its normal shape and size. There is no change in the turgidity of plant cells or the shape of animal cells. In summary, the behavior of cells in different types of solutions is primarily determined by the movement of water across the selectively permeable cell membrane, which in turn affects the cell's volume and shape.
  • 2. MCQ 1. What is the main function of the plasma membrane in a cell? a) Energy production b) Regulation of cell shape c) Selective permeability d) Synthesis of proteins Answer: c) Selective permeability Which of the following is NOT a component of the plasma membrane? a) Phospholipids b) Proteins c) Carbohydrates d) DNA Answer: d) DNA Which term describes the property of the plasma membrane that allows it to allow certain substances to pass while blocking others? a) Selective permeability b) Active transport c) Osmosis d) Endocytosis Answer: a) Selective permeability Which type of transport across the plasma membrane does not require energy expenditure by the cell? a) Active transport b) Passive transport c) Facilitated diffusion d) Exocytosis Answer: b) Passive transport The presence of which molecule on the outer surface of the plasma membrane is important for cell recognition? a) DNA b) RNA c) Carbohydrates d) Lipids Answer: c) Carbohydrates TOPIC : CELL WALL The cell wall is a rigid, protective layer that surrounds the cell membrane of plant cells, fungi, algae, and some bacteria. It is primarily composed of cellulose, a complex carbohydrate polymer, along with other polysaccharides, proteins, and sometimes lignin. Functions of the Cell Wall: 1. Structural Support: One of the primary functions of the cell wall is to provide structural support and rigidity to the cell, helping it maintain its shape and withstand mechanical stress. This structural support is crucial for the overall integrity and stability of plant tissues.
  • 3. 2. Protection: The cell wall acts as a protective barrier, shielding the cell from physical damage, pathogens, and environmental stresses. It helps prevent the cell from bursting due to osmotic pressure changes and provides defence against herbivores and pathogens. 3. Regulation of Water Balance: The cell wall regulates the movement of water into and out of the cell, helping maintain the cell's internal water balance or turgor pressure. It prevents excessive water uptake, which could lead to cell bursting, and provides structural support to cells in hypotonic environments. 4. Cell Communication: The cell wall plays a role in cell-to-cell communication and signaling processes. Plasmodesmata, microscopic channels that traverse the cell wall, allow for the exchange of ions, molecules, and signalling molecules between adjacent plant cells, facilitating coordination and communication within tissues. 5. Support for Growth: As plants grow, new cell wall material is synthesized and deposited, allowing cells to expand and elongate. The cell wall provides a scaffold for cell growth and development, determining the final shape and size of plant organs. 6. Differences Between Plant and Animal Cells: While plant cells have cell walls, animal cells do not. Instead, animal cells have a flexible, lipid- based plasma membrane that surrounds the cell. This structural difference contributes to the distinct shapes and properties of plant and animal cells. CYTOPLASM The cytoplasm is a jelly-like substance that fills the interior of the cell, surrounding the nucleus and organelles. It is a semi-fluid medium composed primarily of water, along with various dissolved molecules, ions, and suspended particles. Functions of the Cytoplasm: 1. Cellular Metabolism: The cytoplasm is the site of many cellular metabolic reactions, including glycolysis, the initial stage of cellular respiration, which takes place in the cytoplasm. It also houses enzymes involved in various biochemical pathways, such as protein synthesis and lipid metabolism. 2. Support and Shape: The cytoplasm provides structural support to the cell and helps maintain its shape. It fills the space between organelles and the cell membrane, providing a medium for organelle movement and anchorage. 3. Transport: Within the cytoplasm, various molecules and organelles move through a process called cytoplasmic streaming or cytoplasmic circulation. This movement helps distribute nutrients, ions, and other substances throughout the cell, facilitating cellular functions and maintaining homeostasis. 4. Storage: The cytoplasm serves as a storage site for various substances, including nutrients, ions, and waste products. These stored materials can be utilized by the cell as needed for energy production, biosynthesis, or other cellular processes. 5. Cellular Communication: The cytoplasm plays a role in cellular communication by housing signaling molecules and components of signaling pathways. These molecules and pathways enable cells to respond to external stimuli and coordinate cellular activities in response to changing environmental conditions. Structure of the Cytoplasm: The cytoplasm consists of two main components:  Cytosol: The liquid portion of the cytoplasm, where organelles are suspended. It is primarily composed of water and dissolved molecules such as ions, sugars, amino acids, and proteins.  Organelles: Various membrane-bound organelles, such as the endoplasmic reticulum, Golgi apparatus, mitochondria, and lysosomes, are dispersed throughout the cytoplasm. These organelles perform specific functions necessary for cellular processes.