Biology Chapter: The Cell and Plasma Membrane
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Biology Chapter: The Cell and Plasma Membrane

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Which part of the plasma membrane is responsible for providing receptor sites for various chemicals?

  • Glycolipids (correct)
  • Phospholipids
  • Cholesterol
  • Proteins (correct)
  • What is the main structural component of the plasma membrane that forms a barrier separating the internal cell parts from the external environment?

  • Glycolipids
  • Phospholipid bilayer (correct)
  • Carbohydrates
  • Cholesterol
  • What is the primary function of ribosomes in the cell?

  • Cell division
  • Lipid storage
  • Protein synthesis (correct)
  • Energy production
  • What role does cholesterol play in the plasma membrane?

    <p>It stabilizes the membrane.</p> Signup and view all the answers

    How does the rough endoplasmic reticulum differ from the smooth endoplasmic reticulum?

    <p>Rough ER has a ribosome-studded surface, while smooth ER does not.</p> Signup and view all the answers

    Which of the following correctly describes the arrangement of phospholipids in the plasma membrane?

    <p>Two parallel rows with heads facing toward the water.</p> Signup and view all the answers

    Which of the following is NOT a function of the endoplasmic reticulum?

    <p>Energy production</p> Signup and view all the answers

    What role do mitochondria play in cellular activity?

    <p>Energy production</p> Signup and view all the answers

    Which function of the plasma membrane involves controlling the movement of substances in and out of the cell?

    <p>Mediating entrance and exit of substances</p> Signup and view all the answers

    Which of the following is NOT a component of the plasma membrane?

    <p>Nucleic acids</p> Signup and view all the answers

    What component of the Golgi complex is critical for the delivery of proteins?

    <p>Cisternae</p> Signup and view all the answers

    What type of molecule is primarily responsible for the flexibility of the plasma membrane?

    <p>Phospholipids</p> Signup and view all the answers

    Which structure within a cell is primarily involved in the removal of debris?

    <p>Lysosomes</p> Signup and view all the answers

    What is melanin primarily responsible for in the human body?

    <p>Protecting against UV light</p> Signup and view all the answers

    Where are glycolipids primarily located within the plasma membrane?

    <p>On the outer surface</p> Signup and view all the answers

    Which of the following best describes the composition of mitochondria?

    <p>Two membranes with inner folds</p> Signup and view all the answers

    What does selective permeability of the plasma membrane refer to?

    <p>The membrane permits some substances to pass more easily than others.</p> Signup and view all the answers

    Which factors contribute to the selective permeability of the plasma membrane?

    <p>Size of molecules, solubility in lipids, charge on ions, presence of carrier molecules.</p> Signup and view all the answers

    What primarily determines the ease with which an ion can pass through the plasma membrane?

    <p>The charge of the ion in relation to the membrane.</p> Signup and view all the answers

    What is the primary composition of the cytoplasm?

    <p>Water, proteins, carbohydrates, lipids, and inorganic substances.</p> Signup and view all the answers

    Which of the following is NOT a function of the cytoplasm?

    <p>Transport of nutrients outside the cell.</p> Signup and view all the answers

    What is the primary role of the nucleus within a cell?

    <p>Control center for cell functions and genetic material management.</p> Signup and view all the answers

    Ribosomes are primarily composed of which type of RNA?

    <p>Ribosomal RNA (rRNA).</p> Signup and view all the answers

    Which of the following best describes the role of organelles?

    <p>They execute various specialized functions necessary for cell growth, maintenance, repair, and control.</p> Signup and view all the answers

    What is the main purpose of the sodium-potassium pump in cellular processes?

    <p>To create an electrical potential across the membrane</p> Signup and view all the answers

    During which type of endocytosis does the cell membrane form pseudopodia to engulf large particles?

    <p>Phagocytosis</p> Signup and view all the answers

    Which process enables the cell to export substances by enclosing them in vesicles that fuse with the membrane?

    <p>Exocytosis</p> Signup and view all the answers

    What type of solution would cause a cell to swell due to an influx of water?

    <p>Hypotonic solution</p> Signup and view all the answers

    What is required for active transport mechanisms to function efficiently?

    <p>Energy in the form of ATP</p> Signup and view all the answers

    Which effect does a hypertonic solution have on a cell?

    <p>It causes the cell to lose water and shrink.</p> Signup and view all the answers

    Which of the following processes is classified as active transport?

    <p>Endocytosis</p> Signup and view all the answers

    What characterizes exocytosis?

    <p>Substances move out of the cell.</p> Signup and view all the answers

    In what situation does an isotonic solution affect a cell?

    <p>It maintains the cell's size as water moves equally in and out.</p> Signup and view all the answers

    Which of the following best describes a hypotonic solution's effect on a cell?

    <p>It causes the cell to swell and potentially burst.</p> Signup and view all the answers

    What is the main function of active transport mechanisms in cells?

    <p>Moving substances against their concentration gradient.</p> Signup and view all the answers

    Which situation requires the cell to engage in endocytosis?

    <p>Uptake of nutrients.</p> Signup and view all the answers

    Which statement about facilitated diffusion is true?

    <p>It requires carrier proteins to assist larger molecules.</p> Signup and view all the answers

    What occurs to a cell placed in a hypertonic solution?

    <p>The cell shrinks due to water moving out.</p> Signup and view all the answers

    Which characteristic defines a hypotonic solution?

    <p>It has a lower concentration of solutes than the cell.</p> Signup and view all the answers

    What is the primary effect of placing a cell in an isotonic solution?

    <p>The cell will maintain its size and shape.</p> Signup and view all the answers

    What process describes the movement of water across a selectively permeable membrane?

    <p>Osmosis</p> Signup and view all the answers

    How does active transport differ from passive transport mechanisms like osmosis?

    <p>Active transport requires energy input.</p> Signup and view all the answers

    What is the role of hydrostatic pressure in the process of filtration?

    <p>It drives the movement of solvent and solutes.</p> Signup and view all the answers

    What happens when a cell is placed in a hypotonic solution?

    <p>Water enters the cell more quickly than it can exit.</p> Signup and view all the answers

    What distinguishes dialysis from osmosis?

    <p>Dialysis separates larger solute molecules from smaller ones.</p> Signup and view all the answers

    Study Notes

    The Cell

    • Is the basic, living, structural and functional unit of the body
    • Can be divided into 4 main parts:
      • Plasma (cell) Membrane
      • Cytoplasm
      • Organelles
      • Inclusions

    Plasma Membrane

    • Separates cell’s internal parts from the extracellular fluid and the external environment
    • Is an exceedingly thin structure (6.5–10 nm in thickness).
    • Is composed of:
      • Phospholipids
      • Proteins
      • Cholesterol
      • Glycolipids
      • Water
      • Carbohydrates
      • Ions
    • Phospholipids are arranged in two parallel rows forming a lipid bilayer, and consist of a hydrophilic head-group and 2 long hydrophobic hydrocarbon chains
    • Glycolipids are always located on the outer surface of the plasma membrane and have an oligosaccharide in the hydrophilic head projecting like hair into the surroundings
    • Proteins are the main functional elements embedded in the lipid matrix, some extend through the whole membrane while others are anchored in the outer or inner layer
    • Cholesterol molecules are almost equal in number to the phospholipids and are interspersed among the phospholipids, they stabilize the cell membrane

    Functions of the Plasma Membrane

    • Flexible boundary that encloses the cellular contents and separates them from the external environment
    • Facilitates contact with other body cells or with foreign cells or substances
    • Provides receptors for chemicals such as hormones, neurotransmitters, enzymes, nutrients and antibodies
    • Mediates the entrance and exit of certain substances and restricts the passage of other substances

    Plasma Membrane Permeability

    • Is the selective permeability of the plasma membrane
    • Is due to:
      • Size of molecules
      • Solubility in lipids
      • Charge on ions
      • Presence of carrier molecules

    Cytoplasm

    • Is the substance inside the cell’s plasma membrane and external to the nucleus
    • Is the matrix or ground substance of the cell
    • Is a thick, semitransparent, elastic fluid containing the cytoskeleton
    • Consists of:
      • Water (75-90% of cytoplasm)
      • Proteins
      • Carbohydrates
      • Lipids
      • Inorganic substances

    Functions of the Cytoplasm

    • Site of synthesis of new substances
    • Site where chemicals are packaged for transport to other parts of the cell
    • Facilitates the excretion of waste materials

    Organelles

    • Are specialised portions of the cell that assume roles in:
      • Growth
      • Maintenance
      • Repair
      • Control
    • Include:
      • Nucleus
      • Ribosomes
      • Endoplasmic Reticulum
      • Golgi Complex
      • Mitochondria
      • Lysosomes
      • Centrosome and Centrioles

    Nucleus

    • Is usually round or oval
    • Is the largest structure in the cell
    • Is the “control centre” of the cell
    • Is separated from the cytoplasm by a nuclear membrane, which contains several small pores
    • Contains the genetic material DNA as well as RNA that controls protein synthesis

    Ribosomes

    • Are tiny granules consisting of a type of RNA called ribosomal RNA (rRNA)
    • May be found on the rough endoplasmic reticulum or scattered within the cytoplasm
    • Are the sites of protein synthesis

    Endoplasmic Reticulum

    • Consists of a system of parallel membranes surrounding a network of channels
    • Is continuous with the nuclear membrane
    • There are 2 types of ER:
      • GRANULAR (rough) ER dotted with ribosomes
      • AGRANULAR (smooth) ER without ribosomes

    Functions of ER

    • Provides a surface area for chemical reactions to occur
    • Acts as a transport channel through which various substances may pass from one part of the cell to another
    • Serves as a storage site for synthesised molecules
    • Plays a role in the packaging of molecules together with the Golgi Complex.

    Golgi Complex

    • Usually situated near the nucleus
    • Is made up of four to eight flattened membranous sacs stacked upon one another

    Functions of the Golgi Complex

    • To process, sort and deliver proteins to various parts of the cell.
    • Lipid packaging and secretion.

    Mitochondria

    • Are sausage-shaped structures scattered throughout the cytoplasm
    • Each mitochondrion consists of two membranes:
      • The outer membrane – smooth
      • The inner membrane – folded upon itself forming cristae that provide a very large surface area where chemical reactions can take place.
    • Provide energy for the cell by producing ATP

    ATP Production

    • Glucose
      • ↓ GLYCOLYSIS
      • Pyruvic Acid + fatty acids & amino acids
      • Acetyl-CoA
      • Krebs' Cycle
      • ADP  ATP

    Lysosomes

    • Are small spherical structures dispersed throughout the cytoplasm
    • Contain powerful digestive enzymes
    • Their function is to remove the debris from within the cell

    Centrosome & Centrioles

    • The centrosome is a dense area of the cytoplasm located near the nucleus
    • It contains a pair of cylindrical structures called centrioles
    • These play a part in spindle formation during cell division

    Cell Inclusions

    • Examples include:
      • Melanin: a pigment stored in cells of the skin, hair and eyes which protects the body by screening out harmful ultraviolet rays from the sun
      • Glycogen: a polysaccharide stored in the liver, skeletal muscle cells and the vaginal mucosa which is broken down by the liver into glucose.

    Passive Processes

    • Diffusion is the net movement of molecules or ions from an area of higher to lower concentration.
      • This occurs until equilibrium is reached, where movement is equal in both directions.
      • The difference between high and low concentrations is called the concentration gradient.
      • Substances can diffuse through the cell membrane in two ways:
        • By dissolving in the lipid bilayer and diffusing through it, such as oxygen, carbon dioxide, fatty acids, and alcohol.
        • By diffusing through channels within the integral proteins of the membrane, such as water and ions like sodium, potassium, and chloride.

    Facilitated Diffusion

    • Facilitated diffusion is the movement of larger molecules across a selectively permeable membrane with the help of integral proteins acting as carriers.
      • Large molecules like glucose are not soluble in lipids and cannot diffuse through the membrane on their own.
      • They combine with a carrier to become soluble in the phospholipid bilayer of the membrane.
      • This allows glucose to pass through the membrane from a high concentration to a lower concentration.
      • No energy is used in this process.

    Osmosis

    • Osmosis is the net movement of water molecules across a selectively permeable membrane from an area of higher to lower water concentration.
      • This happens until equilibrium is reached.
      • Water molecules pass through channels in integral proteins within the membrane.
      • The passage of water through a selectively permeable membrane generates osmotic pressure.
      • Osmotic pressure is the pressure required to prevent the movement of pure water into a solution containing solutes when separated by a selectively permeable membrane.
      • Higher solute concentration leads to higher osmotic pressure.
      • Osmotic pressure is crucial for water movement between body compartments.

    Isotonic, Hypotonic, and Hypertonic Solutions

    • Isotonic Solutions: These have the same total concentration of water molecules and solute molecules on both sides of the cell membrane.
    • Hypotonic Solutions: These have a lower concentration of solutes and therefore a lower concentration of water. Water molecules enter the cell faster than they leave, causing the cell to swell.
    • Hypertonic Solutions: These have a higher concentration of solutes and a lower concentration of water. Water molecules leave the cell faster than they enter, causing the cell to shrink.

    Filtration

    • Filtration is the movement of solvents like water and solutes like glucose across a selectively permeable membrane due to gravity or hydrostatic pressure.
      • This occurs from a higher to lower pressure area.
      • Most small to medium-sized molecules can be forced through the cell membrane.
      • Example: Filtration occurs in the kidneys where blood pressure forces water and small molecules through tiny blood vessels into kidney tubules.
      • Protein molecules are retained, while harmful substances like urea are eliminated.

    Dialysis

    • Dialysis is the diffusion of solute particles across a selectively permeable membrane where small molecules are separated from larger ones.

    Active Processes

    • Active transport is the movement of substances, usually ions, across a selectively permeable membrane from a lower to higher concentration.
      • This requires energy expenditure in the form of ATP.
      • It involves interaction with integral proteins in the membrane.

    Active Transport of Sodium and Potassium (Sodium-Potassium Pump)

    • This mechanism actively transports sodium from inside the cell to the outside and potassium from the outside to the inside.
      • Present in all cell membranes, it uses ATP as its energy source.
      • It typically transports 3 sodium ions to the outside for every 2 potassium ions transported to the inside.
      • This creates an electrical potential across the membrane with negativity inside and positivity outside.
      • The sodium-potassium pump is an electrogenic pump.

    Endocytosis

    • Endocytosis is the movement of large molecules and particles through plasma membranes where the membrane surrounds the substance, encloses it, and brings it into the cell.
      • Two types of endocytosis:
        • Phagocytosis: The cytoplasm extends outwards to form pseudopodia, which surround the object, enclose it within the cell membrane, and form a phagocytic vesicle. This vesicle then detaches from the cell membrane, and its contents are digested.
        • Pinocytosis: The engulfed material is liquid instead of solid. A small droplet of extracellular fluid is attracted to the cell membrane, which folds around it and forms a pinocytic vesicle. This vesicle then detaches from the cell membrane and travels into the cell.

    Exocytosis

    • Exocytosis is the export of substances from the cell by reverse endocytosis.
      • Commonly occurs in secretory cells.

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