Human Biology: Cell Structure and Function

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Questions and Answers

What is the main function of the plasma membrane?

To isolate the interior of the cell from the external environment (correct)

To store genetic information

To produce energy for the cell

To synthesize proteins

What type of molecules can pass through the plasma membrane easily?

Large protein molecules

Small lipid-soluble molecules, such as oxygen and carbon dioxide (correct)

Water molecules with the help of aquaporins

Ionic compounds

What is the purpose of carbohydrates attached to lipids and proteins in the plasma membrane?

To increase the membrane's permeability

To form specialized sites for cell recognition (correct)

To regulate protein synthesis

To store energy for the cell

What is the composition of the phospholipid bilayer?

A sandwich of two layers of phospholipids with nonpolar tails facing inwards Signup and view all the answers

What is the function of integral proteins in the plasma membrane?

To span both layers of the phospholipid bilayer Signup and view all the answers

What is the cytoplasm composed of?

Water, enzymes, salts, and organelles Signup and view all the answers

What is the basic structural and functional unit of life?

Cell Signup and view all the answers

What is the nucleus in a cell?

A large organelle that may or may not be centrally located in the cytoplasm Signup and view all the answers

Which type of cell lacks a nucleus and membrane-bound organelles?

Prokaryotic cell Signup and view all the answers

What are inclusions in cells?

Metabolic by-products, storage forms of various nutrients and pigments Signup and view all the answers

What is the term for the study of the structure and function of cells?

Cytology Signup and view all the answers

What is the minimum size that can be observed using a light microscope?

200 nm Signup and view all the answers

What is the name of the region in prokaryotic cells where DNA is found?

Nucleoid Signup and view all the answers

What is the term for the living part of the cell?

Protoplasm Signup and view all the answers

What is the function of organelles in eukaryotic cells?

To perform specialized functions Signup and view all the answers

What is the shape of cubical cells?

Cube Signup and view all the answers

What is the main function of endocytosis?

To take in substances and materials from outside the cell Signup and view all the answers

Which type of endocytosis involves the ingestion of particles such as bacteria or dead cell remnants?

Phagocytosis Signup and view all the answers

What is the direction of movement of molecules during diffusion?

From an area of higher concentration to an area of lower concentration Signup and view all the answers

What type of molecules can easily diffuse through the plasma membrane?

Lipid-soluble molecules Signup and view all the answers

What is the function of transporter proteins in facilitated transport?

To bind to specific molecules for transport Signup and view all the answers

What is the direction of movement of molecules during facilitated transport?

From an area of higher concentration to an area of lower concentration Signup and view all the answers

What is the energy requirement for diffusion?

No energy requirement Signup and view all the answers

What is the purpose of receptor-mediated endocytosis?

To take in specific substances bound to receptors Signup and view all the answers

What is the main function of the Golgi complex in the cell?

To complete posttranslational modifications of proteins and package them for transport Signup and view all the answers

What is the primary function of lysosomes in the cell?

To break down and digest foreign substances and cellular waste Signup and view all the answers

What is the shape of mitochondria?

Oval-shaped Signup and view all the answers

What is the purpose of the cristae in the mitochondria?

To increase the surface area for energy production Signup and view all the answers

What is the term for the process by which cells break down and recycle their own components?

Autodigestion Signup and view all the answers

What is the type of transport that involves the movement of large molecules across the cell membrane using vesicles?

Bulk transport Signup and view all the answers

What is the process by which cells release substances into the extracellular environment?

Exocytosis Signup and view all the answers

What is the location of the Golgi complex in most cells?

Near the nucleus Signup and view all the answers

What is the primary difference between passive and active transport?

The requirement of energy expenditure Signup and view all the answers

What is the main function of pumps in active transport?

To move molecules against their concentration gradient Signup and view all the answers

What determines the direction of water diffusion during osmosis?

The concentration of solutes in the solution Signup and view all the answers

What is the result of a hypotonic solution on a cell?

The cell swells and eventually bursts Signup and view all the answers

What is the term used to describe the concentration of solutes in a solution?

Tonicity Signup and view all the answers

What is the role of a protein carrier in active transport?

To pump molecules against their concentration gradient Signup and view all the answers

What is the result of an isotonic solution on a cell?

The cell remains unchanged Signup and view all the answers

What is the net movement of water across a selectively permeable membrane called?

Osmosis Signup and view all the answers

Study Notes

Cell Structure and Function

All organisms are composed of one cell (unicellular) or more cells (multicellular)
Cells are the basic structural and functional units of life
Cytology is the branch of biology that deals with the structure and function of cells

Classification of Cells

Cells are classified into two groups: prokaryotes and eukaryotes
The primary difference between them is the presence or absence of a nucleus, a membrane-bound structure that houses the DNA
Prokaryotes:
- Unicellular microorganisms
- No nuclear membrane or other membrane-bound organelles
- DNA found in the central part of the cell (nucleoid)
- Have a cell wall like plants
- Examples: bacteria
Eukaryotes:
- Cells that contain a membrane-bound nucleus and other membrane-bound compartments called organelles
- Organelles have specialized functions
- Examples: animals, plants, and fungi

Cell Size and Shape

Cells vary in size and shape
Most cells are small and require a microscope to examine
Light microscope can see objects as small as 200 nm
Electron microscope can see objects as small as 0.2 nm
Different shapes of cells:
- Cube shape (e.g. cubical cells)
- Long column shape (e.g. goblet cell)
- Spindle shape (e.g. smooth muscle cells)
- Cells with long projections (e.g. nerve cells)

Protoplasm

The living part of the cell is called protoplasm
Protoplasm is composed of water, proteins, lipids, carbohydrates, and electrolytes
Protoplasm consists of two distinct regions:
1. Cytoplasm: lies outside the nucleus
2. Nucleoplasm: lies inside the nucleus
Cells also contain inclusions, which consist of metabolic by-products, storage forms of various nutrients, and pigments

Three Main Components of Cells

1. Plasma membrane: an outer membrane that separates the cell's interior from its surrounding environment
1. Cytoplasm: the fluid present in the cell and surrounded by the cell membrane, which contains water, enzymes, salts, and various organelles
1. Nucleus: a large organelle that may or may not be centrally located within the cytoplasm

Plasma Membrane Structure

Phospholipid bilayer: a "sandwich" made of two layers of phospholipids
Proteins: scattered throughout the plasma membrane, playing important roles in allowing substances to enter the cell
Carbohydrates: groups attached to some of the lipids (glycolipids) and proteins (glycoproteins)

Plasma Membrane Functions

The plasma membrane isolates the interior of the cell from the external environment (physical barrier)
The plasma membrane allows only certain molecules and ions to enter and exit the cytoplasm freely (selectively permeable)
Small lipid-soluble molecules, such as oxygen and carbon dioxide, can pass through the membrane easily
Small size of water molecules allows them to freely cross the membrane by using protein channels called aquaporins

Golgi Complex

Located near the nucleus in most cells
Consists of many smooth membranous saccules, some vesicular, others flattened, but all containing enzymes and proteins being processed
Functions:
- Completes posttranslational modifications of proteins produced in the RER
- Packages and addresses these proteins to their proper destinations

Lysosomes

Membranous sacs produced by the Golgi apparatus
Contain hydrolytic enzymes
Found in all cells of the body, but particularly numerous in white blood cells that engulf disease-causing microbes
Functions:
- Breaks down engulfed substances into simpler subunits
- Participates in autodigestion, breaking down parts of a cell

Mitochondria

Often called the powerhouses or energy factories of a cell
Responsible for making adenosine triphosphate (ATP), the cell's main energy-carrying molecule
Mitochondria are oval-shaped, double-membrane organelles:
- Outer membrane encloses the intermembrane space
- Inner membrane with many folds (cristae) enclosing a gel-like matrix
Abundant in cells or cytoplasmic regions where large amounts of energy are expended

Mechanisms of Transport across the Plasma Membrane

Bulk Transport (Vesicular Transport)

Cells use bulk transport to move large molecules, such as polysaccharides or polypeptides, across the membrane
Processes:
- Exocytosis: cells secrete substances, such as secretions or enzymes, packaged into vesicles
- Endocytosis: cells take in large molecules or other materials, including particles, liquids, and specific substances

Diffusion

Random movement of molecules from an area of higher concentration to an area of lower concentration, until they are equally distributed
Passive way for molecules to enter or exit a cell
Lipid-soluble material can easily slip through the hydrophobic lipid core of the membrane

Facilitated Transport

Many solutes do not simply diffuse across a plasma membrane
Transported by means of protein carriers within the membrane called a transporter
Binds only to a particular molecule, such as glucose
Passive transport, does not require energy to move substances down their concentration gradient

Active Transport

Moves molecules from an area of lower concentration to an area of higher concentration
Requires a protein carrier and uses energy to pump materials into the cell against the concentration gradient
Proteins involved in active transport are often called pumps
One type of pump moves sodium ions (Na+) to the outside and potassium ions (K+) to the inside of the cell

Osmosis

Special case of diffusion
Net movement of water across a selectively permeable membrane
Direction of water diffusion is determined by the tonicity of the solutions inside and outside the cell
Tonicity is based on dissolved particles, called solutes, within a solution
Three terms: hypotonic, isotonic, and hypertonic, relate the concentration of solutes inside a cell to the concentration of solutes in the fluid that contains the cells

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Description

Understand the basic structural and functional units of life, including unicellular and multicellular organisms, and the branch of biology that deals with cells, Cytology.