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Questions and Answers
What did Robert Hooke observe?
What did Robert Hooke observe?
Cells in cork
What did Anton van Leeuwenhoek observe?
What did Anton van Leeuwenhoek observe?
Living cells (animalcules)
Who is credited with the discovery of the nucleus?
Who is credited with the discovery of the nucleus?
Which of these statements is NOT part of the Cell Theory?
Which of these statements is NOT part of the Cell Theory?
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Prokaryotic cells have membrane-bound organelles.
Prokaryotic cells have membrane-bound organelles.
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Which of these is NOT an example of a eukaryotic cell?
Which of these is NOT an example of a eukaryotic cell?
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What is the role of the plasma membrane?
What is the role of the plasma membrane?
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Which of the following is NOT a characteristic of all cells?
Which of the following is NOT a characteristic of all cells?
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What is one reason why cells are so small?
What is one reason why cells are so small?
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What is the function of ribosomes?
What is the function of ribosomes?
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Where are ribosomes found in prokaryotic cells?
Where are ribosomes found in prokaryotic cells?
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What is the function of the endomembrane system?
What is the function of the endomembrane system?
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Name the two main types of endoplasmic reticulum.
Name the two main types of endoplasmic reticulum.
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What is the function of the Golgi apparatus?
What is the function of the Golgi apparatus?
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Lysosomes are responsible for breaking down cellular waste products.
Lysosomes are responsible for breaking down cellular waste products.
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What is the function of mitochondria?
What is the function of mitochondria?
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What is the function of chloroplasts?
What is the function of chloroplasts?
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Mitochondria and chloroplasts are believed to have originated from prokaryotic cells.
Mitochondria and chloroplasts are believed to have originated from prokaryotic cells.
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What is the function of the cytoskeleton?
What is the function of the cytoskeleton?
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Which of the following is NOT a component of the cytoskeleton?
Which of the following is NOT a component of the cytoskeleton?
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Which type of cytoskeletal element is involved in cell division?
Which type of cytoskeletal element is involved in cell division?
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Match the following types of cell junctions with their corresponding function.
Match the following types of cell junctions with their corresponding function.
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Plant cell walls are made primarily of cellulose.
Plant cell walls are made primarily of cellulose.
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Which type of cell junction is found in plant cells?
Which type of cell junction is found in plant cells?
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Which of the following is NOT a characteristic of a prokaryotic cell?
Which of the following is NOT a characteristic of a prokaryotic cell?
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Prokaryotic cells are generally larger and more complex than eukaryotic cells.
Prokaryotic cells are generally larger and more complex than eukaryotic cells.
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Which of the following processes involves the programmed death of cells?
Which of the following processes involves the programmed death of cells?
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What is the process called when a cell engulfs and digests material from its surroundings?
What is the process called when a cell engulfs and digests material from its surroundings?
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Which of the following is NOT a function of the cell wall in plants?
Which of the following is NOT a function of the cell wall in plants?
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Study Notes
Cell Structure and Function
- Cells are the smallest unit of life
- Knowledge of cell structure improves with technological advances
- Cells need to be small or have increased surface area for efficient metabolic activity
- Membranes create compartments within cells
- The endomembrane system is a group of related organelles
- Endosymbiotic theory proposes that mitochondria and chloroplasts evolved from prokaryotic cells
- Prokaryotic and eukaryotic cells differ in their structure and organisation
Cell Theory
- Every organism is composed of one or more cells
- The cell is the smallest unit with life processes
- Continuity of life arises from cell growth and division
Prokaryotic vs Eukaryotic Cells
-
Prokaryotic Cells:
- Lack membrane-bound organelles
- Contain ribosomes in the cytosol
- DNA is in a region called the nucleoid
- Have external structures like cell walls or capsules
- Eubacteria and archaea are examples
-
Eukaryotic Cells:
- Contain membrane-bound organelles
- Organelles perform specific functions in the cytosol
- DNA is in the nucleus
- Some have cell walls
- Examples include animal, plant, fungi and protists
All Cells
- Smallest unit of life
- Can survive independently or have the potential to
- Highly organized for metabolic processes
- Sense and respond to their environment
- Have the potential to reproduce
Cell Membranes
- Main component is a lipid bilayer
- Provides cells with fluid properties
- Composed of two layers of phospholipids (hydrophilic heads and hydrophobic tails)
Cell Size
- Most cells are small to maintain a good surface area-to-volume ratio
- Cell volume determines metabolic activity
- Surface area determines the number of substances that can enter or leave the cell
Ribosomes
- Translate nucleotide sequences of messenger RNA into polypeptide chains (protein synthesis)
- Not membrane-bound organelles in eukaryotes
- In eukaryotes, they can be free in the cytoplasm, attached to the endoplasmic reticulum, or inside mitochondria and chloroplasts
- In prokaryotic cells, they float freely in the cytoplasm
- Composed of ribosomal RNA
Microscopes
-
Light Microscopes:
- Create detailed images of small objects
- Can be simple or compound
- Wavelength limitations restrict the resolution to roughly 200 nm.
-
Electron Microscopes:
- Use streams of accelerated electrons instead of light
- Focus electrons using magnets instead of lenses
- Can resolve structures down to much smaller scales
Eukaryotic Cells Overview
- Contain a nucleus and other organelles
Organelles
- Internal membrane-bound structures for specific functions
- Benefit from compartmentalisation.
Animal Cell Features
- Include specific organelles discussed earlier
Plant Cell Features
- Include specific organelles discussed earlier
Nucleus
- Keeps eukaryotic DNA separate from cytoplasmic activities
- Makes it easier to organise DNA and copy before cell division
Nuclear Envelope
- Double membrane enclosing the nucleus
- Innermost surface has DNA attachment sites
Endomembrane System
- Group of related organelles assembling lipids and modifying polypeptide chains
- Sorting and shipping of products to various destinations
Endoplasmic Reticulum
- Part of the endomembrane system
- Rough ER: Modifies polypeptide chains
- Smooth ER: Manufactures lipids, metabolizes carbohydrates and detoxifies
Golgi Body
- Receives proteins from the RER
- Further modifies, packages, sorts and adds carbohydrates to proteins
- Site of polysaccharide synthesis in plant cells
- Packages finished products for shipment to final destinations
Vesicles
- Membranous sacs that transport materials within cells
- Examples: lysosomes, transport vesicles, peroxisomes
Dynamic Cell Membranes
- Constantly being formed, recycled, and degraded
Mitochondria
- "Powerhouses" of the cell producing ATP
- Double membrane: inner membrane houses the ATP-making machinery
Chloroplasts
- Convert sunlight energy into organic sugars through photosynthesis
- Contain DNA and ribosomes
Mitochondrial/Chloroplast Origin (Endosymbiotic Theory)
- Resemble bacteria
- Have their own DNA and ribosomes
- Divide on their own
- Likely evolved from prokaryotes engulfed but not digested
Specialized Plant Organelles
- Plastids (e.g., chloroplasts, amyloplasts, chromoplasts).
- Central vacuole
Other Plastids
- Chromoplasts: No chlorophyll, abundant carotenoids, pigments in fruits and flowers
- Leucoplasts/Amyloplasts: No pigments, store starch
Apoptosis
- Programmed cell death
- Involves a sequence of events leading to cell destruction
- Cell fragments are engulfed by other cells
- Caused by enzymes called caspases
Autophagy
- Self-eating process where cells recycle their own components
Cytoskeleton
- Present in all eukaryotic cells
- Supports cell shape and internal organisation
- Enables movement of organelles and in some cases, cell motility
Cytoskeletal Elements
- Microtubules, microfilaments, intermediate filaments
Microtubules
- Largest cytoskeletal components
- Composed of tubulin
- Involved in shape, motility and cell division
Microfilaments
- Thinnest cytoskeletal components
- Composed of actin
- Involved in cell movement, shape and maintenance
Intermediate Filaments
- Only in animal cells of certain tissues
- Most stable cytoskeletal elements
Motor Proteins
- Kinesins and dyneins move along microtubules
- Myosins move along microfilaments
Flagella and Cilia
- Structures for cell motility
- 9 + 2 internal structure
Plant Cell Walls
- Secondary cell wall (3 layers): Cellulose and lignin
- Provides support, restricts volume and acts as barrier to infections
Plant Cuticle
- Secretions and waxes accumulate at the plant cell surface
- Semitransparent
- Restricts water loss
Matrices Between Animal Cells
- Hold cells together in tissues
- Contribute to physical properties (e.g., cartilage, skin)
- Filter materials
- Orient cell movement during growth and repair
Plant Cell Junctions (Plasmodesmata)
- Plasma membranes of adjacent cells are continuous
- Water and solutes pass freely between plant cells
Animal Cell Junctions
- Tight Junctions: Anchor cells to form tissues and block materials from passing through the space between cells
- Desmosomes: Anchor cells together in tissues that stretch
- Gap Junctions: Allow communication between cells
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