Summary IGCSE Biology Triple Notes (Structure and Function in Living Organisms) EDEXCEL
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IGCSE BIOLOGY
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Hi! This revision guide covers the second topic of the Edexcel Triple Science Biology Specification: The Structure and Function of Living Organisms. It includes the subtopics: Homeostasis and Thermoregulation, Photosynthesis, Co-ordination and Response, Respiration and Gas Exchange, Blood and the H...
IGCSE Biology Triple Science Notes
Structure and Function in Living Organisms
Contents:
Homeostasis and Thermoregulation
Photosynthesis
Co-ordination and Response
Respiration and Gas Exchange
Blood and the Heart
Kidneys
The Eye
Digestion
, Homeostasis is the maintenance of a constant internal environment. The body needs to be
kept at a temperature of about 37 degrees celsius for enzymes involved in bodily processes
to function properly. If the body temperature is too low, it causes hypothermia. If it is too high,
the body has heat stroke. Both result in death. Constant body temperature is maintained by
negative feedback, which means a change occurs in opposite directions to bring it back to
normal. When the body is too hit then heat-sensitive receptors in the thermoregulatory
centre of the brain (hypothalamus) detect this by measuring blood temperature. To lose heat,
the body produces sweat, thus taking away heat energy when it evaporates. Blood vessels
at the surface of the skin become narrower to reduce heat lost through radiation, which is
called vasoconstriction. When it is cold, we shiver, increasing the rate of respiration in our
muscles to produce heat. Body hairs stand on end, trapping layers of air against the skin to
insulate the body and reduce heat loss.
During photosynthesis, light energy is absorbed by chlorophyll, a substance found in
chloroplasts. This energy is used to convert carbon dioxide from the air and water from the
soil into simple sugars called glucose. Oxygen is also produced and released as a gas. The
main limiting factors of photosynthesis in a plant are light, carbon dioxide and temperature.
A tropism is the plant's response to a directional stimulus. Some of these are:
● Phototropism
○ Light
○ The positive response to shoots
○ The negative response of roots
● Geotropism
○ Gravity
○ The positive response to roots
○ The negative response of shoots
● Hydrotropism
○ Water
○ The positive response of root
○ The negative response to shoots
Plant stems bend towards light because auxins concentrate on the sides furthest from light
causing cell elongation.
Nervous System:
● Ears
○ Sound energy
○ Kinetic energy
● Eyes
○ Light energy
● Nose/Tongue
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