Untitled Flashcards Set

Diffusion

• Definition: Movement of particles from an area of higher concentration to an area of lower concentration.

• How It Works:

• Molecules in a solution move constantly and collide with each other, spreading out randomly.

• This random motion drives diffusion until the concentration of particles is equal in all areas.

• Key Points:

• Passive process (no energy needed).

• Happens naturally due to molecular motion.

• Equilibrium: When concentrations on both sides of a membrane are equal, but molecules continue to move in both directions at equal rates (no net change).

• Example: Sugar in tea spreads from where it’s concentrated (sugar crystals) to where it’s less concentrated (tea).

Facilitated Diffusion

• Definition: The movement of molecules across the cell membrane through protein channels, allowing substances that cannot diffuse directly to pass.

• Why It’s Needed:

• The cell membrane is made of a lipid bilayer, which small, uncharged molecules can pass through easily.

• Larger or charged molecules (e.g., glucose or ions like Cl-) need help from protein carriers.

• How It Works:

• Proteins act as channels or carriers to “facilitate” the diffusion of specific molecules.

• Molecules still move from high concentration to low concentration.

• Key Points:

• Faster than regular diffusion.

• Highly specific to the molecules it allows through.

• Passive process (does not use energy).

• Example: Glucose passing through protein carriers in red blood cells.

Osmosis

• Definition: Diffusion of water across a selectively permeable membrane, facilitated by special proteins called aquaporins.

• How It Works:

• Water moves from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration).

• The membrane allows water to pass but not solute molecules.

• Key Points:

• Special case of facilitated diffusion (water uses aquaporins).

• Passive process (no energy required).

• Effects on Cells:

• Isotonic: Solute concentration is the same inside and outside; water moves equally in both directions.

• Hypertonic: Higher solute concentration outside → water exits the cell → cell shrinks.

• Hypotonic: Lower solute concentration outside → water enters the cell → cell swells.

Osmotic Pressure

• Definition: The force caused by differences in solute concentration, which drives the movement of water across the membrane.

• Key Effects:

• Animal cells in hypertonic solutions shrink due to water loss.

• Animal cells in hypotonic solutions swell and may burst if too much water enters.

• Plant cells resist bursting due to rigid cell walls but may swell or shrink depending on the solution.

Active Transport

• Definition: Movement of materials against the concentration gradient (low → high concentration), requiring energy (ATP).

• Key Characteristics:

• Opposite of diffusion; works “uphill” against natural flow.

• Uses transport proteins or changes in cell membrane shape.

• Types of Active Transport:

• Protein Pumps: Transport ions or small molecules across the membrane (e.g., sodium-potassium pump).

• Endocytosis: The process of taking material into the cell by forming a vesicle:

• Phagocytosis (“cell eating”): Engulfing large particles or cells (e.g., white blood cells consuming bacteria).

• Pinocytosis (“cell drinking”): Taking in liquid by forming small vesicles.

• Exocytosis: Releasing materials from the cell by fusing vesicles with the cell membrane (e.g., removal of waste or water).

Comparison: Passive vs. Active Transport

• Passive Transport:

• Includes diffusion, facilitated diffusion, and osmosis.

• No energy required.

• Moves substances from high to low concentration.

• Active Transport:

• Includes protein pumps, endocytosis, and exocytosis.

• Requires energy (ATP).

• Moves substances from low to high concentration.

The Cell as an Organism

Basic Unit of Life

• What are cells?

• Cells are the smallest living units that perform all life processes.

• Unicellular organisms consist of one cell that does everything needed to live.

• In terms of numbers, unicellular organisms dominate Earth.

Unicellular Organisms

• Examples of Unicellular Life:

• Prokaryotes:

• Bacteria: Live in diverse environments (soil, water, air, human body).

• Extremely adaptable due to their simple structure.

• Question: How can bacteria survive in extreme environments like hot springs or deep-sea vents?

• Eukaryotes:

• Include amoebas, algae, and yeasts.

• Yeasts: Break down nutrients and help make food (e.g., bread, beer).

• Question: Why do yeast cells play a crucial role in ecosystems and food production?

• How do unicellular organisms survive?

• Must maintain homeostasis:

• Keep stable conditions inside despite external changes.

• Example: A pond-dwelling amoeba absorbs water while balancing mineral levels.

• Perform all life processes:

• Grow, transform energy (e.g., through photosynthesis or cellular respiration), reproduce, and respond to environmental changes.

Multicellular Life

What makes multicellular life different?

• Multicellular organisms consist of specialized, interdependent cells that work together like a team.

• Example: Think of a baseball team where each player (cell) has a specific role but works toward a shared goal.

• Guiding Question: Why can’t the cells in your body survive alone like a bacterium can?

Cell Specialization

• How do cells specialize?

• All multicellular organisms begin as a single cell (zygote).

• Through cell differentiation, cells develop specialized roles.

• Examples:

• Animal cells:

• Red blood cells transport oxygen and remove carbon dioxide.

• Nerve cells (neurons) carry electrical impulses to communicate between body parts.

• Plant cells:

• Leaf cells contain chloroplasts for photosynthesis.

• Root cells absorb water with tiny hair-like projections.

• How does specialization help?

• Each specialized cell type contributes to maintaining homeostasis for the entire organism.

• Example: Without red blood cells delivering oxygen, muscle cells couldn’t produce energy efficiently.

Homeostasis: Unicellular vs. Multicellular Organisms

• Unicellular Organisms:

• Each cell must do everything itself.

• Example: A bacterium adjusts its behavior directly to changes in its surroundings (like moving toward food or away from toxins).

• Multicellular Organisms:

• Cells are interdependent and communicate to maintain balance.

• Example: When your body temperature rises, sweat glands (specialized cells) release sweat to cool you down.

• Guiding Question:

• What advantages do multicellular organisms have over unicellular ones when it comes to homeostasis?

Energy Needs and Mitochondria

• Why do cells need energy?

• To perform functions like movement, transport of materials, and maintaining internal balance.

• Energy comes from mitochondria through cellular respiration (glucose → ATP).

• Distribution of Mitochondria:

• Cells with high energy demands have more mitochondria.

• Examples:

• Heart cells (left ventricle): Pump blood continuously, so they need a lot of energy.

• Pituitary gland cells: Perform hormone regulation, so they need less energy.

• Question:

• Why might a defective mitochondria be more harmful to heart cells than skin cells?

Levels of Organization in Multicellular Organisms

1. Cells: Basic units of life.

• Example: A nerve cell (neuron).

2. Tissues: Groups of similar cells performing a shared function.

• Example: Nerve tissue sends signals throughout the body.

3. Organs: Structures made of different tissues working together.

• Example: The brain contains nerve, blood vessel, and connective tissues.

4. Organ Systems: Groups of organs working for a specific purpose.

• Example: The nervous system (brain, spinal cord, nerves) controls body functions.

• Question:

• Why does organizing into systems make multicellular organisms more efficient?

Cellular Communication

• How do cells communicate?

• Through chemical signals passed between cells.

• These signals can:

• Speed up or slow down cell activity.

• Cause dramatic changes (e.g., activating a response to injury).

• Examples:

• Nerve cells use electrical impulses and chemicals to send messages rapidly.

• Cellular junctions: Neighboring cells connect to pass signals or hold tissues together.

• Tight junctions: Prevent leaks (e.g., in skin).

• Communication junctions: Share chemical messages (e.g., in the heart).

• Why is this important?

• Cellular communication ensures coordination and response to changes, keeping the organism alive.

• Example: Your optic nerve transmits visual information from your eyes to your brain in milliseconds.

• Question:

• What might happen if cells in your body couldn’t communicate effectively?

Graph Analysis: Mitochondria in Mouse Cells

• Observations:

• Heart (left ventricle) has the highest percentage of mitochondria, indicating its high energy need.

• The pituitary gland has the lowest percentage.

• Conclusion:

• Uneven distribution of mitochondria reflects the specific energy needs of different tissues.

• Guiding Question:

• How do mitochondria ensure that energy is distributed efficiently across different cell types?

Key Connections to Remember

• Homeostasis: Maintained differently in unicellular vs. multicellular organisms.

• Specialization: Leads to efficiency but also dependence on other cells in multicellular organisms.

• Energy Needs: Tissues with higher energy demands rely more on mitochondria.

Unicellular Organisms

Q: How can bacteria survive in extreme environments?

• Adaptable: Use heat-resistant enzymes (thermophiles) or pressure-resistant membranes (barophiles).

• Metabolize unique substances like sulfur or methane.

Q: Why are yeasts important?

• Ecosystems: Recycle nutrients by breaking down organic material.

• Food: Ferment sugars for bread (CO₂) and alcohol production.

Multicellular Life

Q: Why can’t body cells survive alone?

• Specialized cells depend on others for nutrients, oxygen, and waste removal.

Homeostasis

Q: How does homeostasis differ between unicellular and multicellular organisms?

• Unicellular: Directly interact with the environment, limiting flexibility.

• Multicellular: Use specialized systems (e.g., sweat glands or blood vessels) for better control.

Energy Needs and Mitochondria

Q: Why is defective mitochondria worse for heart cells?

• Heart cells need constant energy for pumping; skin cells need less and can regenerate.

Levels of Organization

Q: Why are systems efficient in multicellular organisms?

• Division of labor: Cells, tissues, organs, and systems specialize to perform tasks together.

Cellular Communication

Q: What happens if cells can’t communicate?

• Miscommunication leads to problems like immune failure, uncontrolled cell growth (cancer), or paralysis.

Graph Analysis: Mitochondria in Mouse Cells

Q: How is energy distributed across cell types?

• High-energy cells (heart, brain) have more mitochondria; low-energy cells (glands) have fewer.

This version is concise but keeps the core points. Let me know if you’d like further edits!

• Mitochondrial density directly correlates with the metabolic demands of the cell type, influencing overall energy production efficiency.