Biology Chapter: The Cell and Plasma Membrane

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Questions and Answers

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?

It stabilizes the membrane. Signup and view all the answers

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

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

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

Two parallel rows with heads facing toward the water. Signup and view all the answers

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

Energy production Signup and view all the answers

What role do mitochondria play in cellular activity?

Energy production Signup and view all the answers

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

Mediating entrance and exit of substances Signup and view all the answers

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

Nucleic acids Signup and view all the answers

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

Cisternae Signup and view all the answers

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

Phospholipids Signup and view all the answers

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

Lysosomes Signup and view all the answers

What is melanin primarily responsible for in the human body?

Protecting against UV light Signup and view all the answers

Where are glycolipids primarily located within the plasma membrane?

On the outer surface Signup and view all the answers

Which of the following best describes the composition of mitochondria?

Two membranes with inner folds Signup and view all the answers

What does selective permeability of the plasma membrane refer to?

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

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

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

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

The charge of the ion in relation to the membrane. Signup and view all the answers

What is the primary composition of the cytoplasm?

Water, proteins, carbohydrates, lipids, and inorganic substances. Signup and view all the answers

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

Transport of nutrients outside the cell. Signup and view all the answers

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

Control center for cell functions and genetic material management. Signup and view all the answers

Ribosomes are primarily composed of which type of RNA?

Ribosomal RNA (rRNA). Signup and view all the answers

Which of the following best describes the role of organelles?

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

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

To create an electrical potential across the membrane Signup and view all the answers

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

Phagocytosis Signup and view all the answers

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

Exocytosis Signup and view all the answers

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

Hypotonic solution Signup and view all the answers

What is required for active transport mechanisms to function efficiently?

Energy in the form of ATP Signup and view all the answers

Which effect does a hypertonic solution have on a cell?

It causes the cell to lose water and shrink. Signup and view all the answers

Which of the following processes is classified as active transport?

Endocytosis Signup and view all the answers

What characterizes exocytosis?

Substances move out of the cell. Signup and view all the answers

In what situation does an isotonic solution affect a cell?

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

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

It causes the cell to swell and potentially burst. Signup and view all the answers

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

Moving substances against their concentration gradient. Signup and view all the answers

Which situation requires the cell to engage in endocytosis?

Uptake of nutrients. Signup and view all the answers

Which statement about facilitated diffusion is true?

It requires carrier proteins to assist larger molecules. Signup and view all the answers

What occurs to a cell placed in a hypertonic solution?

The cell shrinks due to water moving out. Signup and view all the answers

Which characteristic defines a hypotonic solution?

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

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

The cell will maintain its size and shape. Signup and view all the answers

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

Osmosis Signup and view all the answers

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

Active transport requires energy input. Signup and view all the answers

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

It drives the movement of solvent and solutes. Signup and view all the answers

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

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

What distinguishes dialysis from osmosis?

Dialysis separates larger solute molecules from smaller ones. 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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Description

Explore the fundamental unit of life in this quiz focused on the cell's structure and the plasma membrane. Discover how different components like phospholipids and proteins contribute to the cell's functionality. Test your understanding of cellular organization and membrane composition.