9.1 Chemical Control In Mammals And Plants Flashcards
What is homeostasis?
The maintenance of a state of dynamic equilibrium in the body, despite changes in the external or internal conditions within a narrow range
Describe the negative feedback system.
Provides a way of maintaining a condition such as the conc of a substance within a narrow range - a change in conditions is registered by receptors and as a result effectors are stimulated to restore equilibrium
Describe the positive feedback system.
Where effectors work to increase an effect that has a triggered response
E.g., birth/labour
What are hormones?
Organic chemicals produced in endocrine glands and released into the blood and carried through the transport system to parts of the body where they bring about changes, which may be widespread or very targeted - usually either proteins, or steroids
What are endocrine glands?
They produce hormones - they do not have duct - they release hormones directly into the bloodstream
What are exocrine glands?
They produce chemicals (e.g enzymes) and release them along small tubes or ducts
Explain the mode of action of adrenaline.
It’s a secondary messenger model:
1. Hormone-receptor complex forms
2. Conformational change to receptor activates Glycoprotein
3. Activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP)
4. cAMP activates protein kinase A pathway
5. Results in glycogenolysis
Explain the mode of action of oestrogen.
- Steroid hormone diffuses through cell membrane
- Forms hormone-receptor complex with ER alpha receptor in the cytoplasm
- Complex enters the nucleus & acts as transcription factor
Name 3 groups of plant growth factors.
Auxins
Gibberellins
Cytokinins
What is the function of auxin?
Involved in trophic responses e.g. IAA
Controls cell elongation
Suppresses lateral buds to maintain apical dominance
It promotes root growth e.g in rooting powders
Explain how auxins and cytokinins control the growth of lateral buds.
Auxin is released from the terminal bud
And diffuses down the stem to inhibit cytokinin action
The cytokinin stimulates lateral shoot growth
And is produced from base of shoot
How do auxins cause cell elongation?
- IAA causes active transport H+ ions into cell wall
- Disruption to H-bonds between cellulose molecules and action of expansions make cell more permeable to water
- Cells with higher turgor pressure elongate faster
List the functions of gibberellins.
Stimulate:
1. Germination
2. Elongation at cell internodes
3. Fruit growth
4. Rapid growth/flowering
How is germination stimulated?
- Seed absorbs water, activating embryo to secrete gibberellins
- Gibberellins diffuse to aleurone layer, which produces amylase
- Amylase diffuses to endosperm layer to hydrolyse starch
- Hexose sugars act as respiratory substrate to produce ATP as ‘energy currency’
List the functions of cytokinins.
- Stimulate development of lateral buds by promoting cell division at apical meristems
- Promote leaf abscission synergistically with ethene
Name the 2 ways plants growth hormones interact.
- Synergistically to achieve same effect
- Antagonistically with inverse effects
What is positive phototropism?
Plants growing and bending towards the light source controlled by IAA
IAA diffuses to other cells and will diffuse towards shaded side of the shoot resulting in a higher concentration of IAA there
What is negative phototropism?
Usually in roots - bending away from the light
IAA inhibits cell elongation causing root cells to elongate more on the lighter side
What is negative gravitropism?
Causes shoots/plant to bend upwards
IAA will diffuse from the upper side to the lower side of a shoot so if the plant is on its side it will bend upwards
What is positive gravitropism?
Root bends down towards gravity
IAA moves to lower side of roots
What is Phytochrome?
Plant photoreceptor
1. Pr absorbs red light
2. Pfr absorbs far-red light
State the time of day when each form of Phytochrome is most abundant.
In darkness: Pr abundant
In sunlight: Pfr abundant
Ratio of Pr:Pfr enables plant to detect how long days are
How does Phytochrome control flowering?
Pr absorbs red light and converts to Pfr
This stimulates flowering which signifies that light intensity is high enough for photosynthesis
What are long and short day plants?
Long day: flower when sunlight hours exceed a critical value
Short day: flower when darkness hours exceed a critical value
What is photomorphogenesis?
Pattern of plant growth and development determined by light intensity
How does Phytochrome control photomorphogenesis?
Transition from Pr to Pfr controls: localisation of proteins within cells, transcription of certain genes and phosphorylation of proteins
Therefore affects: germination, circadian rhythm and flowering
