Homeostasis Study Guide (Chapter 5, Cengage Biology Honors)

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Feedback Loops

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Positive vs. Negative Feedback Loops

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Graphic by Tanisha Kurani

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Feedback Loop Examples

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Example	Information
Blood Clotting	Group of blood cells, platelets, and protein clumped together over a wound to stop bleedingNegative loopBleeding (input) is stopped by clot (output), reverses direction of blood
Ice-Albedo	Albedo - Amount of sunlight or radiation reflected by a surface Positive loopIce is highly reflective, it reflects some sunlight back to space, heating the ocean up and melting more and more ice.
Body Temperature	Receptors are stimulated by a discrepancy from the normal 98.6 degrees F and send a signal to control centerControl center decides whether to vasodilate (cool down) or vasoconstrict (heat up) and sends a signal to effectors w/ decisionEffectors execute the decision w/ sweat glands or muscle contractionNegative loopThe body loses or retains heat to stabilize yourself to a particular temperature
Labor/Giving Birth	More pressure on cervix stimulates receptor cells that releases oxytocinOxytocin goes back to cervix and simulates contractionsPositive loop - Contractions go back to more pressure on the cervix until baby is born
Fruit Ripening	Acidic levels rise and amount of simple sugars increase, activating fruit ripening enzymesEnzymes cause the ripened fruit to ripen more fruit
Guard Cells/Stomata	Guard cells = 2 epidermal cells that open and close stomatal poresStomata = Tiny substance essential to photosynthesis, made up of guard cellsTakes in CO2, releases O2 Stomata must open to release water, but when it opens, leads to water going in and needing to refillNegative loop

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Transport

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Factors that influence diffusion:

1. Concentration

2. Temperature

3. Size

4. Charge

5. Pressure

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Concentration

• Concentration gradient - adjacent regions with different concentrations

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When a cell goes through passive transport or diffusion, it tries to travel from a high concentration gradient to a low concentration gradient.

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KEY VOCAB:

• Solute: The thing being dissolved

• Solvent: The thing dissolving the solute

• Solution: The product once it’s dissolved

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Passive Transport

• Diffusion - The movement of atoms/molecules from an area of high concentration to low concentration

• Osmosis - Diffusion relating to water

• Facilitated diffusion - Diffusion where molecules pass through protein channel

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• Turgor Pressure - Plants fill themselves with water to preserve structure

  • If it loses that water, it stops pushing and becomes soft

• Osmotic Pressure - The amount of turgor needed to stop osmosis

• Plasmolysis - Cell membrane pulling away from cell wall (opposite of turgor)

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Active Transport

Active transport moves against the concentration gradient (low to high) and requires energy.

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• Protein pump - A pump that moves molecules across the membrane

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Endocytosis	Exocytosis
Into the cell - uses cell membrane  to engulf materials  \n Phagocytosis - The cell eats the particles and uses them for stuffPinocytosis - The cell drinks up the particles and uses it for stuffReceptor-Mediated - The cell uses receptors to target specific molecules	Fuses with cell

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Examples

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Bioenergetics

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Energy - The ability to do work

Entropy - Unusable dispersed energy

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Laws of Thermodynamics

1. First Law of Thermodynamics: Energy cannot be created or destroyed

2. Second Law of Thermodynamics: Energy tends to disperse spontaneously, always increasing entropy in a system

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Potential vs. Kinetic Energy, Endergonic Exergonic

• Potential energy - Energy that is stored in a fixed position or motion

  • Chemical energy - form of potential energy due to arrangement of atoms within the molecules

• Kinetic energy - Energy of motion

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Metabolic Control + Enzymes

• Most enzymes not only have an active site, but also an Allosteric Regulation

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Allosteric Regulation - Cofactors/Coenzymes bind to atom and change active site of enzymes

• Allosteric Activation - Changes shape of active site so enzyme is turned on and works

• Allosteric Inhibition - Changes shape of active site so the enzyme is turned off and doesn’t work

  

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Coenzyme - Allows redox reactions to proceed

• Ex: ATP - provides activation energy to start reactions whenever needed

  • Breaks bonds between 2nd and 3rd phosphate groups, giving off the potential energy, can spend and refill
  • Stores (Endergonic) and releases (Exergonic)

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Feedback Inhibition - Final product of a process decreases/stops the process once the product is made

• Negative loop

  

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Electron Transfer Chains and Redox Reactions

Metabolic reactions may be Redox reactions, Redox reactions transfer electrons between atoms.

• REMEMBER: The electron that has a charge is being reduced

  

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Electron Transfer Chains - Can be formed with many Redox reactions over and over, releases energy in small amounts (slow) and fuels many reactions in a cell