Questions and Answers
What type of cells are animal and plant cells?
What is the function of the nucleus in a cell?
Contains DNA coding for proteins needed to build new cells.
Bacterial cells have a nucleus.
False
In plant cells, photosynthesis takes place in the ______.
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What is the purpose of ribosomes in a cell?
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Which structure helps regulate what enters and leaves the cell?
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What process do stem cells undergo to become specialized?
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What is the maximum magnification of a light microscope?
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Bacteria can multiply by ______.
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Diffusion requires energy input.
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What does the zone of inhibition indicate in an antibiotic test?
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Which of the following is a feature of xylem cells?
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What type of tissue is responsible for gas exchange in plants?
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What is the main purpose of having a thin membrane in biological systems?
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What type of solution causes animal cells to burst?
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Osmosis uses energy to move water across cell membranes.
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Water moves from a _______ solution to a _______ solution during osmosis.
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What is the effect of placing potato tubers in different concentrations of sugar solution?
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Which process requires energy to move particles against their concentration gradient?
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What happens to plant cells in a hypertonic solution?
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Match the following terms with their definitions:
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Study Notes
Cell Structure
- All living organisms consist of cells categorized as prokaryotic or eukaryotic.
- Eukaryotic cells, found in animals and plants, contain organelles: cell membrane, cytoplasm, and nucleus with DNA.
- Prokaryotic cells, like bacteria, are smaller and include a cell wall, cell membrane, cytoplasm, a single circular DNA strand, and plasmids.
Orders of Magnitude
- Understanding size comparisons through orders of magnitude:
- 10 times larger = 10¹
- 1000 times larger = 10³
- 10 times smaller = 10⁻¹
- Measurement prefixes:
- Centi: 0.01
- Milli: 0.001
- Micro: 0.000001
- Nano: 0.000000001
Subcellular Structures
- Each organelle has a specific function:
- Nucleus: Contains DNA, surrounded by a nuclear membrane.
- Cytoplasm: Site of chemical reactions, contains enzymes and organelles.
- Cell Membrane: Regulates entry and exit of substances.
- Mitochondria: Location for aerobic respiration, energy production.
- Ribosomes: Site of protein synthesis, associated with rough endoplasmic reticulum.
- Plant cell-specific organelles:
- Chloroplasts: Site of photosynthesis, contains chlorophyll.
- Permanent Vacuole: Contains cell sap, maintains rigidity.
- Cell Wall: Composed of cellulose, provides structural strength.
Bacterial Cell Structure
- Bacterial cells lack a nucleus; their genetic material floats in the cytoplasm in a circular DNA strand.
- Cell wall composition differs (peptidoglycan).
Cell Specialization
- Cells differentiate to acquire new structures for specific functions; this can occur at different life stages.
- Examples of animal specialized cells:
- Sperm Cells: Adapted for mobility, contain enzymes for fertilization.
- Nerve Cells: Long axons for signal transmission, numerous mitochondria for energy.
- Muscle Cells: Contains specialized proteins for contraction, high energy needs met by mitochondria.
- Examples of plant specialized cells:
- Root Hair Cells: Increased surface area for water and nutrient absorption.
- Xylem Cells: Hollow structure for efficient water transport, strengthened by lignin.
- Phloem Cells: Transports products of photosynthesis; relies on companion cells for energy sources.
Cell Differentiation
- Stem cells can differentiate into specialized cells, shaped by gene expression changes.
- Most animal cells differentiate early and lose plasticity; plant cells retain ongoing differentiation capacity.
Microscopy
- Light microscopes: invented by Robert Hooke in 1665, maximum magnification approximately x2000, resolution of 200nm.
- Electron microscopes: Developed in the 1930s, capable of magnifications up to x2,000,000 and higher resolution (10nm to 0.2nm).
- Standard calculations in microscopy:
- Magnification = eyepiece lens x objective lens.
- Size of object = size of image / magnification.
Culturing Microorganisms
- Microorganisms are grown in nutrient-rich media, either in nutrient broth or on agar plates.
- Steps for agar culture involve sterilization to avoid contamination, and controlled incubation at 25 degrees Celsius for safety.
- Colony calculations post-culturing utilize binary fission; the formula for population growth incorporates mean division time.
- Antibiotic effectiveness tested by measuring clear zones of inhibition around discs soaked in different antibiotics.
Cell Division and Genetics
- Chromosomes in the nucleus carry DNA; humans have 23 pairs (46 total).
- Gene: A segment of DNA coding for proteins that influence characteristics.
- Mitosis is the stage in the cell cycle where cell division occurs, enabling growth and repair.### Cell Division
- Interphase: Stage of cell growth; includes organelle increase, protein synthesis, DNA replication (forming 'X' shape), and energy store enhancement.
- Mitosis: Chromosomes align at the cell equator; cell fibers pull chromosomes apart to opposite ends.
- Cytokinesis: Cytoplasm and cell membranes divide, resulting in two identical daughter cells.
- Importance: Mitosis is essential for growth, development, and repair of damaged cells in multicellular organisms. It is also crucial for asexual reproduction.
Stem Cells
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Definition: Undifferentiated cells that can divide to produce similar cells, with some differentiating for specific functions.
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Types of Stem Cells:
- Embryonic Stem Cells: Formed from the fusion of egg and sperm; can differentiate into any cell type. Useful in medical research for conditions like diabetes, Alzheimer’s, and spinal cord injuries.
- Adult Stem Cells: Located in bone marrow; primarily generate blood cells.
- Plant Meristems: Found in root and shoot tips; can differentiate into any plant cell throughout the plant's life, crucial for cloning plants.
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Therapeutic Cloning: Involves creating an embryo with a patient's genes to harvest stem cells for tailored tissue or organ replacement, minimizing rejection risk.
Stem Cell Research: Benefits vs. Problems
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Benefits:
- Potential to replace damaged tissues and organs.
- Use of unused embryos from fertility clinics reduces waste.
- Contributes to understanding differentiation processes.
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Problems:
- Limited understanding of differentiation controls.
- Ethical concerns related to embryo destruction.
- Risk of transferring infections from contaminated stem cells.
- Argument that resources could be better used in other medical fields.
Transport in Cells
Diffusion
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Defined as the net movement of particles from high to low concentration; occurs passively without energy.
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Small molecules (e.g., oxygen, glucose) can cross cell membranes; larger molecules (starch, proteins) cannot.
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Examples in the Body:
- Oxygen diffuses from alveoli into blood; carbon dioxide is exhaled.
- Urea moves from liver cells to blood for kidney excretion.
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Factors Affecting Rate:
- Concentration gradient: Larger differences speed up diffusion.
- Temperature: Higher temperatures increase particle movement.
- Surface area: Increased surface area leads to faster diffusion.
Osmosis
- The movement of water across a partially permeable membrane from a less concentrated to a more concentrated solution.
- Water moves from an area of high water potential to low; it's passive and does not require energy.
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Effects on Cells:
- In animals, a dilute external solution can cause cells to burst; a concentrated solution can make them shrivel.
- In plants, a dilute solution causes turgor pressure in vacuoles, providing rigidity; a concentrated solution can lead to plasmolysis (cell death).
Active Transport
- The process of moving substances against their concentration gradient, requiring energy.
- Occurs in root hairs for water and mineral ion uptake from soil.
- Also happens in the gut, where glucose and amino acids move into the bloodstream from digested food, even in lower concentrations.
Adaptations for Efficient Transport
- Large Surface Area: Facilitates faster particle movement; e.g., alveoli in lungs, villi in the small intestine, leaf structures.
- Thin Membrane: Shortens diffusion pathway; e.g., thin walls of alveoli and villi.
- Efficient Blood Supply: Maintains steep concentration gradients, enhancing diffusion; e.g., constant blood flow in lungs and countercurrent flow in fish gills.
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Description
Learn about the differences between prokaryotic and eukaryotic cells, and understand size comparisons through orders of magnitude. Discover the components of cells and their relative sizes.
