Cell Structure and Orders of Magnitude

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Questions and Answers

What type of cells are animal and plant cells?

Both

Eukaryotic (correct)

Neither

Prokaryotic

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 ______.

chloroplasts Signup and view all the answers

What is the purpose of ribosomes in a cell?

Where protein synthesis occurs. Signup and view all the answers

Which structure helps regulate what enters and leaves the cell?

Cell membrane Signup and view all the answers

What process do stem cells undergo to become specialized?

Differentiation Signup and view all the answers

What is the maximum magnification of a light microscope?

x2000 Signup and view all the answers

Bacteria can multiply by ______.

binary fission Signup and view all the answers

Diffusion requires energy input.

False Signup and view all the answers

What does the zone of inhibition indicate in an antibiotic test?

The effectiveness of the antibiotic. Signup and view all the answers

Which of the following is a feature of xylem cells?

Transports water Signup and view all the answers

What type of tissue is responsible for gas exchange in plants?

Stomata Signup and view all the answers

What is the main purpose of having a thin membrane in biological systems?

Provides a short diffusion pathway. Signup and view all the answers

What type of solution causes animal cells to burst?

Hypotonic solution Signup and view all the answers

Osmosis uses energy to move water across cell membranes.

False Signup and view all the answers

Water moves from a _ solution to a _ solution during osmosis.

dilute, concentrated Signup and view all the answers

What is the effect of placing potato tubers in different concentrations of sugar solution?

Different volumes of water move in or out, affecting mass. Signup and view all the answers

Which process requires energy to move particles against their concentration gradient?

Active Transport Signup and view all the answers

What happens to plant cells in a hypertonic solution?

Water moves out, causing the cell to become soft and may lead to plasmolysis. Signup and view all the answers

Match the following terms with their definitions:

Isotonic = Equal concentration inside and outside the cell Hypotonic = Lower external concentration than inside the cell Hypertonic = Higher external concentration than inside the cell Turgor = Pressure that keeps plant cells rigid Signup and view all the answers

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

Definition: Undifferentiated cells that can divide to produce similar cells, with some differentiating for specific functions.
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.
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

Benefits:
- Potential to replace damaged tissues and organs.
- Use of unused embryos from fertility clinics reduces waste.
- Contributes to understanding differentiation processes.
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

Defined as the net movement of particles from high to low concentration; occurs passively without energy.
Small molecules (e.g., oxygen, glucose) can cross cell membranes; larger molecules (starch, proteins) cannot.
Examples in the Body:
- Oxygen diffuses from alveoli into blood; carbon dioxide is exhaled.
- Urea moves from liver cells to blood for kidney excretion.
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.
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.