BIO lessons 7,8,9

Homeostasis + Communication + Nutrient Processing + Gas Exchange + Movement

What is homeostasis, and why is it important?

Homeostasis is the maintenance of a stable internal environment despite changes outside the body. It is essential because cells function best within a narrow range of conditions.

How does negative feedback help maintain homeostasis?

Negative feedback detects a change from the normal set point and produces a response that reverses the change, returning the body to normal.

How does the body respond if body temperature becomes too high?

Sweating and vasodilation increase heat loss, lowering body temperature back to its normal set point.

How does the body respond if body temperature becomes too low?

Shivering produces heat, while vasoconstriction reduces heat loss to help restore normal body temperature.

Why is negative feedback called 'negative'?

Because it opposes or reverses the original change rather than increasing it.

What is positive feedback?

Positive feedback amplifies the original change instead of reversing it and continues until a specific process is completed.

Why is positive feedback less common than negative feedback?

Because it does not maintain stability—it drives a process to completion instead.

What are two examples of positive feedback?

Labor contractions during childbirth and blood clotting.

What are the two main types of digestion?

Mechanical digestion (physical breakdown) and chemical digestion (enzymatic breakdown of food molecules).

What is the purpose of mechanical digestion?

To physically break food into smaller pieces, increasing surface area for enzymes.

What is the purpose of chemical digestion?

To use enzymes to break macromolecules into nutrients small enough to be absorbed.

Where does digestion begin, and what enzyme starts it?

Digestion begins in the mouth, where salivary amylase starts breaking down starch.

What happens to food in the stomach?

Gastric acid and pepsin begin protein digestion while the stomach churns food into chyme.

What is chyme?

The partially digested mixture of food and stomach secretions that enters the small intestine.

Why is the small intestine the main site of digestion and absorption?

Because most chemical digestion occurs there, and nutrients are absorbed through its lining.

What digestive enzymes does the pancreas release into the small intestine?

Proteases, lipases, and amylase.

Why does the pancreas release bicarbonate into the small intestine?

To neutralize the acidic chyme coming from the stomach.

What is the function of bile?

Bile emulsifies fats, breaking them into smaller droplets that lipase can digest more efficiently.

Where is bile produced and where is it stored?

Produced by the liver and stored in the gallbladder.

Why do the villi and microvilli of the small intestine increase nutrient absorption?

They greatly increase the surface area available for absorption.

What is gas exchange?

The process of taking oxygen into the body and removing carbon dioxide.

What pathway does air follow through the respiratory system?

Nose → trachea → bronchi → bronchioles → alveoli.

Where does gas exchange occur?

In the alveoli of the lungs.

Why are alveoli surrounded by many capillaries?

To allow efficient exchange of oxygen and carbon dioxide between air and blood.

How does oxygen move from the lungs into the blood?

Oxygen diffuses from the alveoli into nearby capillaries down its concentration gradient.

How does carbon dioxide leave the blood?

Carbon dioxide diffuses from the blood into the alveoli to be exhaled.

What carries most oxygen in the blood?

Hemoglobin inside red blood cells.

How many oxygen molecules can one hemoglobin molecule carry?

Four oxygen molecules.

Which factors affect hemoglobin's ability to hold oxygen?

pH, temperature, and carbon dioxide concentration.

Why does hemoglobin release more oxygen in active tissues?

Active tissues have higher CO₂, higher temperature, and lower pH, causing hemoglobin to release oxygen more easily.

What type of muscle is responsible for voluntary movement?

Skeletal muscle.

What is the sliding filament model?

Muscle contraction occurs when actin and myosin filaments slide past one another, shortening the sarcomere.

Do actin and myosin filaments become shorter during contraction?

No. They slide past each other while maintaining the same length.

What is the sarcomere?

The basic contractile unit of skeletal muscle.

What triggers muscle contraction?

A nerve impulse causes the sarcoplasmic reticulum to release calcium ions.

What is the role of calcium during muscle contraction?

Calcium binds to troponin, changing its shape and exposing binding sites on actin.

What happens after calcium exposes the binding sites on actin?

Myosin attaches to actin, allowing cross-bridge cycling and muscle contraction.

What is water balance in biology?

Water balance refers to the regulation of the amount of water in an organism, ensuring that internal conditions remain stable even when external conditions change.

Why is water balance important for organisms?

Water balance is crucial for cellular functions, as water is vital for biochemical reactions, nutrient transport, and temperature regulation.

What is osmoregulation?

Osmoregulation is the process by which organisms regulate the water and electrolyte balance in their bodies, maintaining osmotic pressure.

Which organ is primarily responsible for osmoregulation in mammals?

The kidneys are the primary organ for osmoregulation, filtering blood to create urine while retaining necessary water and salts.

How do gills assist in water balance for fish?

Gills help fish regulate ion concentrations in aquatic environments, facilitating osmoregulation.

What are aquaporins?

Aquaporins are specialized channel proteins in cell membranes that facilitate the transport of water molecules in and out of cells, playing a crucial role in osmotic balance.

Which hormones are involved in regulating water balance?

Hormones such as antidiuretic hormone (ADH) and aldosterone play significant roles in water balance.

How does antidiuretic hormone (ADH) regulate water balance?

ADH increases the permeability of the kidney tubules to water, promoting reabsorption and reducing urine output when water is in short supply.

What role does aldosterone play in water balance?

Aldosterone helps regulate sodium and potassium levels, influencing water retention as sodium levels affect osmotic pressures.

How does water balance relate to thermoregulation?

Water balance is essential for regulating body temperature, as evaporation of water through sweating or respiration helps cool the body.

How do organisms adapt to maintain homeostasis regarding water balance?

Organisms employ various structures and mechanisms such as kidneys, gills, hormonal regulation, and aquaporins to maintain homeostasis and ensure survival.