SBI4U – Grade 12 AP Biology – Homoeostasis Test


Thanks, Bairavi Sripalan!


Homeostasis Lab Transpiration & Circulatory

Main Ideas

Regulatory System

– An attempt to control internal environment

– Monitor (receptor) – detects when body it outside its normal limits

– Coordinating Centre (Nervous System) – relays info to a regulator that the body is outside its normal limits

– Regulator ( Hormones) – reacts to return body to its optimal condition

– Negative Feedback – body responds in such a way to reverse the direction of change

– Positive Feedback – change occurs in some variable that response is to amplify that change even more in the same direction



3 functions of the kidneys


– Occurs in the bowman’s capsule, squeezes blood to filter it

– Moves through afferent arteriole into glomerulus

– Not all materials can pass through only dissolved solutes



– Transfer of essential solutes and H2O from nephrons back into blood

– Via active and passive transport

– Occurs until threshold level is reached



-Excess NaCl is excreted with urine

– Creates osmotic gradient that draws water from the nephron

– As waster is reabsorbed solutes become more concentrated


Immune System

– Recognizes foreign bodies

– Responds with the production of immune cells and proteins

– Innate Immunity – present before any exposure to pathogens and are effective from the time of birth, consists of external barriers plus internal cellular & chemical defences’ ex. Skin mucus, secretions. Internal defences: Phagocytic cells, antimicrobial proteins, inflammatory response, natural killer cells



– Acquired Immunity – develops after exposure to agents such as microbes, toxins and other foreign substances ex. Antibodies, hummoral response, cytotoxic, lymphocytes defend against infection in body cells, cell mediated response

– Lymphocytes è thymus è t-cells

– Lymphocytes è bone marrow è b-cells

– B-cell receptors – bind to specific, intact antigens

– Made up of two identical: heavy chains and light chains

– The tips of the chains forms a constant region, which contains a variable reigion becase it’s amino acid sequence varies extensively from one b cell to another

– Acquired immunity has three important properties , has receptor diversity, a lack of reactivity against host cells and immunological memory


Circulation & Gas Exchange

– Open and closed circulatory system


Blood Pressure – how fast blood flows through veins

– Aldosterone increases Na+ reabsorption in nephron, this increases osmotic gradient thus more water moves out of the nephron



– Controls hormones, secretes chemical signals to Local Regulator, Hormones, Pheromones, Neurohormones and Neurotransmitters


Local Regulators

– Chemical signals that travel over short distances by diffusion

– Paracrine – signal acts on cells near the secreting cell

– Autocrine – act on the secreting cell itself



-contact target cells at synapses

At synapses – neurons often secrete chemical signals called neurotransmitters that diffuse a short distance to bind the receptors on the target cell

Neurotransmitters play a role in sensation, memory, cognition and movement

Neurohormones – class of hormones that originate from neurons in the brain and diffuse through the bloodstream

Pheromones – chemical signals that are released from the body

– Used to communicate with other individuals in the species



– Marks trails to food sources, warn off predators and attract potential mates



The same hormones may have different effects on target cells

Insulin and glucagon (cycles)

Neurons, Synapses & Signalling

– 2 main parts – CNS (central nervous system)

– – PNS ( peripheral nervous system)

– Process information in three stages

– Sensory input, integration and motor output

– Animals have complex nervous systems which consists of

– CNS where integration takes place; brain and nerves

– PNS brings info into and out of CNS

– Ion pumps and channels maintain the resting potential of a neuron

– Every cell has a voltage across its plasma called a membrane called membrane potential

– Messages are transmitted as changes in membrane potential

– Formation of the Resting potential

– Sodium Potassium pump è channel protein that makes Na+ and K+ using ATP

– Concentration gradients rep chemical potential energy

– Most Voltage-gated channels are closed, some K+ are open

– When action potential is generated, voltage-gated Na+ open first that allows Na+ to flow into the cell

– During the rising phase the threshold is crossed and membrane potential is increased

– During the falling phase, voltage-gated Na+ channels become inactivated, voltage-gate K+ channels open and K+ flow out of the cell

– The undershot, the membrane permeability to K+ is at first higher than at rest, then the voltage-gated K+ channels close and resting potential is restored.



Male hormones – testosterone and andorsterone

Produced in interstitial cells between seminiforous cells

Testosterone stimulates: muscles, facial hair, sperm, growth of larynx, increases secretion of bodily oils

Female hormones

Ovaries contain fibrous tissue called follicles

Primary oocyte – matures in ovum

Granulosa cells- source of nutrients for oocyte

Follicles divide into primary and secondary

Menstrual Cycle

Approximately 28 days

1. Flow Phase – shedding of endometrium days 1-5

2. Follicular Phase when follicles develop, high estrogen levels, day 6-13 and ovulation on day 14 (LH/FSH surge)

3. Luteal Phase – when egg leaves the scar, corpus luteum present


In the luteal phase, estrogen levels decline

Corpus Luteum

– Secretes both estrogen and progesterone

– Prepares for embryo and inhibits ovulation


If not fertilized corpus luteum degrades, estrogen and progesterone levels decline and then stimulates small contractions and begins shedding of the lining