How the nervous and endocrine systems detect and respond to change and keep the body's internal conditions steady, then how reproduction makes offspring. Concept tutorials with a live response-pathway and body-temperature board.
Stimulus–response pathways, nerves and hormones, and negative feedback (AC9S9U01).
A stimulus is any change the body detects, outside it or inside it. Every response follows the same pathway: stimulus, receptor, command centre, effector, response.
The central nervous system (brain and spinal cord) is the command centre: sensory neurons carry impulses in from receptors, motor neurons carry them out to effectors. Reflexes go through the spinal cord without waiting for the brain.
The body runs the same stimulus–receptor–command centre–effector pathway in two ways. The nervous system sends electrical signals along nerves: fast, short and to one place. The endocrine system sends hormones from glands in the blood: slower, longer-lasting and to target organs anywhere.
The nervous system sends fast, short-lived electrical impulses along nerves to one place. The endocrine system releases hormones into the blood: slower, longer-lasting, and they reach every cell but act only on target cells.
Homeostasis keeps internal conditions near a set point by negative feedback: a change away from the set point is detected, and the response reverses it. Body temperature is controlled by the hypothalamus through sweating, shivering and blood flow.
A few quick questions on tracing a negative feedback loop in two examples, and finding which part has failed in a disorder. Taught in class; use this to check yourself.
Gametes, and why sexual reproduction makes varied offspring while asexual reproduction makes clones (AC9S9U02).
Gametes (sperm and egg, or the nuclei in pollen and ovules) carry half the usual number of chromosomes, so fertilisation restores the full set. Each is specialised: sperm to swim and get in, the egg to feed the embryo and let only one sperm in.
In sexual reproduction each offspring gets a random half of each parent's genes, so offspring vary. In asexual reproduction one parent makes genetically identical clones. Variation helps a population survive change; asexual reproduction is fast and needs no partner.
A few quick questions on reproductive structures, asexual reproduction, and comparing the two strategies. Taught in class; use this to check yourself.
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