BRAINCAKEChemical Control
Revision notes for Chemical Control in Edexcel Biology B (9BI0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- HomeostasisHomeostasis is the maintenance of a constant internal environment within narrow limits, despite changes in the external or internal environment.…
- Feedback SystemsHomeostatic control relies on feedback systems.
- Negative FeedbackNegative feedback is a mechanism in which a change from the set point triggers a response that reverses the change, bringing the variable back…
- Positive FeedbackPositive feedback is a mechanism in which a change triggers a response that increases the change, so the variable moves even further from its…
- Chemical ControlMammals coordinate their responses in two ways: the nervous system and the endocrine (hormonal) system.
- Endocrine GlandsEndocrine glands are groups of secretory cells that release hormones directly into the blood.
- Hormone Release SystemEndocrine glands release hormones in response to three main types of stimulus.
- Pituitary GlandThe pituitary gland is a pea-sized gland at the base of the brain, attached to the hypothalamus by a stalk.
- Second Messenger SystemPeptide hormones, and amine hormones such as adrenaline, are water soluble and cannot cross the cell surface membrane.
- Plant StimuliPlants cannot move from place to place, so they must respond to changes in their environment to survive.
- Plant ResponsesPlant responses can be grouped into tropisms and nastic responses.
- Plant GrowthUnlike animals, plants keep growing throughout their lives, but only in particular regions called meristems.
- AuxinsAuxins are a group of plant growth regulators.
- How Auxins WorkAuxin causes cell elongation by a mechanism described by the acid growth hypothesis.
- GibberellinsGibberellins (GA) are plant growth regulators made in young leaves, shoot tips, roots and seeds.
- CytokininsCytokinins are plant growth regulators that promote cell division.
- Synergy and AntagonismPlant growth regulators rarely act alone.
- Apical DominanceApical dominance is the inhibition of the growth of lateral (side) buds by the apical bud at the tip of the shoot.
- Sensory Systems in PlantsAlthough plants have no nervous system or sense organs, they have sensitive receptor molecules and cells that detect stimuli.
- PhytochromesPhytochrome is a blue-green photoreceptor pigment found in small amounts in plant cells.
- PhotoperiodismPhotoperiodism is the response of an organism to changes in the photoperiod, the relative lengths of day and night.
- Long Day PlantsLong day plants flower when the days are long and the nights are shorter than a critical length.
- Short Day PlantsShort day plants flower when the nights are longer than a critical length, in other words when they receive a long, uninterrupted dark period.
- Day Neutral PlantsDay neutral plants are plants whose flowering is not controlled by photoperiod.
- Signal DetectionFlowering in long day and short day plants is controlled by photoperiod, but which part of the plant detects it?
- DiscoveryThe pigment that detects light for flowering and germination is phytochrome.
- PhotomorphogenesisPhotomorphogenesis is the control of plant growth and development by light, independent of photosynthesis.
- Germination and PhotomorphogenesisMany small seeds, such as lettuce, need light to germinate.
- Phytochromes, Photomorphogenesis and TropismsPhytochrome exists in two interconvertible forms: Pr + red light (660 nm) → Pfr Pfr + far-red light (730 nm) → Pr Pfr → Pr slowly in darkness…
- Phytochrome as a Transcription FactorPhytochrome causes long-lasting changes in the plant, such as greening, by changing which genes are expressed.
On the specification
- 9.1 Homeostasis
- 9.2 Chemical control in mammals
- 9.3 Chemical control in plants