Cell Transport and Homeostasis

Cell Transport

• Students will analyze the relationship between structures and functions of living cells.
• They'll investigate the role of cellular transport (active, passive, osmosis) in homeostasis.

Homeostasis

• Homeostasis is an organism's need to stay stable by regulating internal conditions.
• It's a dynamic equilibrium, meaning things stay within a range, not always the same.
• Examples of regulated factors include pH, temperature, and blood sugar.
• Organisms respond to stimuli (changes in the environment) to maintain homeostasis.
• Response is a change within the organism in reaction to a stimulus.

Feedback Mechanisms

• Feedback mechanisms help maintain homeostasis.
• They use system output to signal and change input, stabilizing or amplifying the system response.
• Feedback can be positive or negative.

Positive Feedback

• In a positive feedback loop, the output intensifies the response, creating a cycle of increasing effect.
• Examples include childbirth (hormones, contractions, pressure), and fruit ripening (ethylene signaling).

Negative Feedback

• In a negative feedback loop, the output causes a counter-response, returning the system to a set point (stabilization).
• Examples include body temperature regulation, water concentration (osmoregulation), and blood sugar regulation.

Cell Membrane

• Homeostasis is regulated at a cellular level, with the cell membrane controlling the movement of substances into and out of the cell.
• Cell membranes are selectively permeable, meaning they are picky about what can pass through.
  • Small, nonpolar, and/or neutral molecules pass easily
  • Large and/or polar molecules pass less easily.

Types of Cell Transport

• Active transport requires energy (ATP) to move substances against the concentration gradient (low to high).

  • Examples: molecular pumps, exocytosis, and endocytosis.

• Passive transport does not require energy. Substances move down the concentration gradient (high to low). Types include:

  • Simple diffusion – substances move directly across the membrane; examples: O2 and CO2
  • Facilitated diffusion – substances use transport proteins to move across the membrane; examples: glucose and calcium.
  • Osmosis – the passive transport of water across a membrane from high water concentration to low concentration.
  • Water moves in three types of solutions
    • Hypertonic - Water concentration is lower outside the cell, water leaves the cell, causing cells to shrivel
    • Hypotonic - Water concentration is higher outside the cell, water moves into the cell, causing cells to swell
    • Isotonic - Equal water concentration between inside and outside of the cell.

• Endocytosis – Taking large particles into the cell using vesicles

• Exocytosis – Exporting materials out of the cell using vesicles.

• Phagocytosis – "cell eating," engulfing solids

• Pinocytosis – "cell drinking," engulfing liquids

Summary

• A chart summarizing the type of transport, examples of substances moved, and how it maintains homeostasis is also provided.