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Questions and Answers
Which statement accurately reflects the contributions of Matthias Schleiden and Theodor Schwann?
What is the main difference between unicellular and multicellular organisms regarding reproduction?
According to the cell theory, which of the following statements is NOT true?
What role do cells play in multicellular organisms?
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Which of the following statements regarding the sizes of cells is accurate?
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What is a key characteristic that distinguishes prokaryotic cells from eukaryotic cells?
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Which of the following is true about bacteria?
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What is the role of ribosomes in prokaryotic cells?
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Which structure is found outside the plasma membrane of prokaryotic cells?
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Which of the following best describes eukaryotic cells?
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What is the function of the glycocalyx in bacterial cells?
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What distinguishes archaea from bacteria?
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Which of the following is NOT a component of a typical bacterial cell?
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What is the primary function of cytosol in eukaryotic cells?
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Which structural feature is common to both flagella and cilia?
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What distinguishes smooth endoplasmic reticulum (SER) from rough endoplasmic reticulum (RER)?
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What is the main role of the Golgi apparatus in a eukaryotic cell?
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Which organelles are considered semiautonomous?
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Which of the following statements about vacuoles is true?
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What role does the nuclear envelope play in the cell?
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Which component primarily aids in maintaining the shape of eukaryotic cells?
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How do lysosomes contribute to cellular function?
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What is unique about peroxisomes compared to other organelles?
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Which structure forms the outer boundary of a eukaryotic cell?
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What is a primary function of mitochondria in eukaryotic cells?
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What type of movement do actin filaments facilitate in the cytoskeleton?
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How do vesicles communicate within the endomembrane system?
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Study Notes
The Cell
- Matthias Schleiden, in the 1830s, stated that all plants are composed of cells.
- Theodor Schwann stated that all animals are composed of cells.
Organisms and Cells
- Unicellular organisms are widespread.
- Plants and animals, including humans, are multicellular.
- The cell is the fundamental structural and functional building block of organisms; it is the smallest unit of life.
Examples of Cells
- Examples of cells: Amoeba Proteus, plant stem, bacteria, red blood cell, nerve cell.
Cell Theory
- Cells reproduce; when a cell reaches a certain size, it divides.
- Unicellular organisms reproduce through cell division.
- Multicellular organisms grow by cell division.
- Cells play a role in the reproduction of multicellular organisms, ensuring cell continuity across generations.
Cell Theory Statements
- All living organisms are composed of one or more cells.
- Cells are the smallest units of living organisms.
- New cells arise only from pre-existing cells.
Types of Cells
- Two main cell types: prokaryotic and eukaryotic.
Prokaryotic Cells
- Prokaryotes lack a membrane-bound nucleus.
- Prokaryotes are simpler and smaller than eukaryotes.
- They are prevalent in air, water, soil, and even within human bodies.
- Prokaryotes are divided into:
- Bacteria: Abundant and mostly non-harmful.
- Archaea: Less common, often found in extreme environments.
Typical Bacterial Cell
- Average size of bacteria is 1.1 to 1.5 micrometers in width and 2 to 6 micrometers in length
- Bacteria are characterized by:
- Plasma membrane: Acts as a barrier.
- Cytoplasm: The interior region enclosed by the plasma membrane.
- Nucleoid: Region containing genetic material (DNA).
- Ribosomes: Involved in protein synthesis.
- Structures outside of the plasma membrane:
- Cell wall: Provides support and protection.
- Glycocalyx: Traps water and offers protection.
- Appendages:
- Pili: For attachment.
- Flagella: For locomotion.
Eukaryotic Cells
- Eukaryotic organisms include protists, fungi, plants, and animals.
- Eukaryotes have a membrane-bound nucleus that houses DNA.
- They are compartmentalized, containing specialized structures called organelles that perform specific functions.
- Like prokaryotes, eukaryotes have a plasma membrane that separates the cell's contents from the environment and regulates passage of materials.
- Shape, size, and organization of eukaryotic cells vary considerably across species and even among different cell types within a species.
Cytosol
- Cytosol is the region within a eukaryotic cell, outside of the organelles and inside the plasma membrane.
- Cytoplasm encompasses everything within the plasma membrane, including cytosol, the endomembrane system, and semiautonomous organelles.
- Cytosol is the central coordinating region for numerous metabolic activities in eukaryotic cells.
- Metabolism includes:
- Catabolism: Breakdown of molecules into smaller components.
- Anabolism: Synthesis of cellular molecules and macromolecules.
Cytoskeleton
- Network of protein filaments extending from the nucleus to the plasma membrane in eukaryotic cells, maintaining cell shape and facilitating movement.
- Three types of filaments:
- Microtubules: Dynamic instability, organized at the centrosome (microtubule-organizing center) in animal cells.
- Intermediate filaments: More stable than microtubules and actin filaments, with less dynamic polymerization and depolymerization.
- Actin filaments: Also called microfilaments, involved in various cellular processes like cell movement.
Flagella and Cilia
- Flagella and cilia are involved in cell movement.
- Flagella are typically longer than cilia and found singly or in pairs.
- Cilia are generally shorter than flagella and cover part or all of a cell's surface.
- Both structures share the same internal organization: microtubules, dynein, and axoneme.
- Movement involves a bending wave, initiated at the base and progressing towards the tip.
Endomembrane System
- A network of membranes that enclose the nucleus, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, and the plasma membrane.
- These structures cooperate and communicate through transport vesicles.
- Plant cells lack lysosomes.
Nuclear Envelope
- Double-membrane structure surrounding the nucleus.
- The outer membrane is continuous with the ER membrane.
- Nuclear pores provide passageways for materials to enter and exit the nucleus.
- The nucleus' contents are not part of the endomembrane system.
Nucleus
- Contains chromosomes, composed of DNA and protein (chromatin).
- Primarily responsible for the protection, organization, and expression of the genetic material.
- Ribosome assembly takes place in the nucleolus.
Endoplasmic Reticulum (ER)
- Intricate network of membranes forming flattened, fluid-filled tubules or cisternae.
- The ER membrane encloses a single compartment called the ER lumen.
- Types:
- Rough endoplasmic reticulum (rough ER): Studded with ribosomes, involved in protein synthesis and sorting.
- Smooth endoplasmic reticulum (smooth ER): Lacks ribosomes, involved in detoxification, carbohydrate metabolism, calcium balance, and synthesis/modification of lipids.
Golgi Apparatus
- Also known as the Golgi body, Golgi complex, or simply Golgi.
- Stack of flattened, membrane-bound compartments, not continuous with the ER.
- Vesicles facilitate transport of materials between stacks.
- Functions:
- Secretion
- Processing
- Protein sorting
Lysosomes
- Contain acid hydrolases, enzymes that catalyze hydrolysis.
- Possess various acid hydrolases to break down proteins, carbohydrates, nucleic acids, and lipids.
- Autophagy involves the recycling of worn-out organelles through endocytosis.
Vacuoles
- Vacuole functions vary widely across cell types and environmental conditions.
- Types:
- Central vacuoles in plants: Storage and support.
- Contractile vacuoles in protists: Expelling excess water.
- Phagocytic vacuoles in protists and white blood cells: Degradation.
Plasma Membrane
- Boundary between the cell and the extracellular environment.
- Controls the passage of materials into and out of the cell (selectively permeable).
- Cell signaling through receptors.
- Cell adhesion.
Semiautonomous Organelles
- Can grow and divide to reproduce themselves but are not entirely independent.
- Require other cellular components for their internal structures.
- Examples:
- Mitochondria
- Chloroplasts
- Peroxisomes
Mitochondria
- Possess outer and inner membranes, creating an intermembrane space and a mitochondrial matrix.
- Primary function is to produce energy in the form of ATP.
- Also involved in the synthesis, modification, and breakdown of various cellular molecules.
- Can generate heat in brown fat cells.
Chloroplasts
- Responsible for photosynthesis: capturing light energy and using it to synthesize organic molecules like glucose.
- Found in nearly all plants and algae.
- Have outer and inner membranes with an intermembrane space.
- Third membrane, the thylakoid membrane, forms flattened tubules that stack into a granum (plural, grana).
Peroxisomes
- Small organelles present in all eukaryotic cells.
- Catalyze certain chemical reactions, typically involving the breakdown of molecules by removing hydrogen or adding oxygen.
- Reactions produce hydrogen peroxide (H2O2).
- Catalase in peroxisomes breaks down H2O2 without generating harmful free radicals.
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