Unit 1 – Topic 3: Cellular Energy

Catabolism vs. Anabolism

Cellular metabolism consists of two complementary processes: catabolism and anabolism.

• Catabolism: The breakdown of complex molecules into simpler ones, releasing energy. Example: Cellular respiration.

• Anabolism: The synthesis of complex molecules from simpler ones, requiring energy input. Example: Protein synthesis.

• Comparison: Catabolic reactions provide the energy (often in the form of ATP) needed for anabolic reactions.

ATP as the Energy Coupler

Adenosine triphosphate (ATP) is the primary energy carrier in cells. It allows energy from catabolic reactions to be used in anabolic reactions.

• ATP stores energy in its high-energy phosphate bonds.

• When ATP is hydrolyzed to ADP and inorganic phosphate (), energy is released for cellular work.

• Catabolic reactions regenerate ATP from ADP and .

Aerobic Respiration

Aerobic respiration is the process by which cells convert glucose and oxygen into ATP, carbon dioxide, and water.

• Glycolysis: Occurs in the cytoplasm. Inputs: glucose; Outputs: 2 pyruvate, 2 ATP, 2 NADH.

• Krebs Cycle (Citric Acid Cycle): Occurs in the mitochondrial matrix. Inputs: acetyl-CoA; Outputs: CO2, NADH, FADH2, 2 ATP per glucose.

• Electron Transport Chain (ETC): Occurs in the inner mitochondrial membrane. Inputs: NADH, FADH2, O2; Outputs: H2O, ~32 ATP per glucose.

Aerobic vs. Anaerobic Respiration

• Aerobic respiration: Requires oxygen, produces more ATP (up to 36-38 ATP per glucose).

• Anaerobic respiration (fermentation): Does not require oxygen, produces less ATP (2 ATP per glucose), and results in byproducts like lactic acid or ethanol.

Unit 2 – Topic 1: Homeostasis

Sensory Receptors and Their Stimuli

Sensory receptors detect changes in the environment (stimuli) and initiate signals to maintain homeostasis.

• Types of receptors:

  • Mechanoreceptors: Detect pressure, touch, sound.

  • Photoreceptors: Detect light (e.g., in the eye).

  • Chemoreceptors: Detect chemicals (e.g., taste, smell).

  • Thermoreceptors: Detect temperature changes.

  • Nociceptors: Detect pain.

Structure and Function of Nerve Cells

Neurons are specialized cells that transmit nerve impulses.

• Structure: Dendrites (receive signals), cell body (contains nucleus), axon (transmits signals), synaptic terminals (communicate with other cells).

• Function: Conduct electrical impulses and communicate via neurotransmitters.

Types of Neurons

• Sensory neurons: Carry signals from receptors to the central nervous system (CNS).

• Interneurons: Connect neurons within the CNS.

• Motor neurons: Carry signals from the CNS to effectors (muscles or glands).

Coordination of Homeostasis: Nervous and Endocrine Systems

The nervous and endocrine systems coordinate responses to internal and external stimuli using negative feedback mechanisms.

• Nervous system: Fast, electrical signals; immediate responses.

• Endocrine system: Slower, chemical signals (hormones); longer-lasting effects.

• Negative feedback: A process that counteracts changes from a set point to maintain stability (e.g., body temperature, blood glucose).

Transmission of Nerve Impulses

Nerve impulses are transmitted as action potentials along neurons and across synapses.

• Action potential: A rapid change in membrane potential that travels along the axon.

• Synaptic transmission: Neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic cell.

Hormonal Signaling

Hormones relay messages to target cells via the circulatory or lymphatic system.

• Only cells with specific receptors respond to a given hormone.

• The number of receptors determines a cell’s sensitivity to the hormone.

Feedback-Control Diagrams

Feedback-control diagrams illustrate the components of homeostatic regulation.

• Components: Stimulus, receptor, control center, effector, communication pathway.

• Used to analyze physiological responses (e.g., temperature regulation, blood glucose control).

Thermoregulation and Osmoregulation

Thermoregulation in Humans

Humans maintain a stable internal temperature through various mechanisms.

• Sweating: Evaporative cooling to reduce body temperature.

• Shivering: Muscle activity generates heat.

• Vasodilation: Blood vessels widen to increase heat loss.

• Vasoconstriction: Blood vessels narrow to reduce heat loss.

Thermoregulatory Mechanisms in Endotherms

• Structural: Insulation (fur, fat), body size/shape.

• Behavioral: Seeking shade, basking in sun.

• Physiological: Sweating, panting, shivering.

Osmoregulation in Humans

Osmoregulation maintains water and solute balance in the body.

• Antidiuretic hormone (ADH): Regulates water reabsorption in the kidneys.

• Kidney: Filters blood, reabsorbs water, excretes waste as urine.

• Feedback diagrams illustrate the role of ADH in response to dehydration or overhydration.

Research Investigation and Assessment

• Students plan and develop research questions, find evidence, and analyze data as part of their assessment.

• Key skills: rationale development, analysis, evaluation, and scientific communication.