BRAINCAKEChemical Control
Revision notes for Chemical Control in Edexcel Biology (9BI0). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- 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.