Topic 9.1 Chemical control in mammals and plants Flashcards
Define homeostasis
the maintenance of a state of dynamic equilibrium in the body, despite changes in the external or internal conditions
Define sensors/receptors
specialised cells that are sensitive to specific changes in the environment
Define effectors
systems (usually muscles or glands) that either work to reverse, increase or decrease changes in a biological system
What needs to be controlled in the body?
- pH levels: so that structures of protein molecules remain stable (enzymes function at their optimum activity and structure of cell membranes maintained)
- core temperature: to maintain optimum activity for enzymes and integrity of the membranes
- water potential: to avoid osmotic effects which could damage or destroy the cells
What are the two types of communication in a feedback system?
- by hormones (chemical messages)
- by nerve impulses (electrical messages)
What are the majority of feedback system in a mammal?
negative feedback systems
Define negative feedback systems
they provide a way of maintaining a condition, such as the concentration of a substance, within a narrow range. A change in conditions is registered by receptors and as a result effectors are stimulated to restore the equilibrium
Define positive feedback systems
where effectors work to increase an effect that has triggered a response e.g. labour
Define hormones
organic chemicals produced in endocrine glands and released in the blood and carried through the transport system to parts of the body where they bring about changes, may be widespread or very targeted. hormones are usually proteins, parts of proteins or steroids
What are endocrine glands?
produce hormones, do not have ducts and they release hormones directly into the bloodstream
Define exocrine glands
produce chemicals e.g. enzymes and release them along small tubes or ducts
What stimuli affect plants?
-light- presence or absence, direction of light, intensity and length of daily exposure
-gravity
-water
temperature
-sometimes to touch and chemicals
Define tropisms
plant growth responses to environmental cues
What are the 3 stages of plant growth?
- division
- assimilation
- elongation
Which regions of a plant are most sensitive to plant growth substances?
- cell elongation: making it easier for the cellulose cell wall to be stretched
- cell division: increasing the number of divisions that occur
Define auxins
plant hormones that act as powerful growth stimulants and involved in apical dominance, stem and root growth, and tropic responses to unilateral light
Where are auxins produced?
auxins are produced in the shoots and diffuse away from the tip towards the roots
Define gibberellins
plant hormones that act as growth regulators, particularly in the internodes of stems by stimulating the elongation of growing cells; also promote the growth of fruit and involved in breaking dormancy in seeds and in germination. produce amylase which breaks down starch stores
Define cytokinins
plant hormones that promote cell division in the apical meristems and the cambium through interactions with auxins. they promote lateral bud development, which can overcome apical dominance, and work synergistically with ethene in the abscission (shedding) of leaves, flowers and fruits
Name 3 groups of plant growth factors
- auxins
- gibberellins
- cytokinins
List the functions of auxins
- involved in trophic responses
- control cell elongation
- suppress lateral buds to maintain apical dominance
- promote root growth
How do auxins cause cell elongation?
- IAA causes active transport of H+ ions into cell wall
- disruption to H-bonds between cellulose molecules and action of expansins make cell more permeable to water
- cells with higher turgor pressure elongate faster
List the functions of gibberellins
they stimulate…
- germination
- elongation at cell internodes
- fruit growth
- rapid growth/flowering
Define the pituitary gland
a small gland in the brain that has an anterior and a posterior lobe, it produces and releases secretions that affect the activity of most of the other endocrine glands in the body
What is the hypothalamus?
a small area of the brain directly above the pituitary gland that controls the activities of the pituitary gland and coordinates the autonomic (unconscious) nervous system
Give an example of a function of the hypothalamus
monitors the blood levels of a number of metabolites and hormones
How is germination stimulated?
- seed absorbs water, activating embryo to release gibberellins
- gibberellins diffuse to aleurone layer, which produces amylase
- amylase diffuses into endosperm and breaks down food stores to provide embryo with materials for respiration and growth
- enzymes produced in response to gibberellin digest the endosperm, products released from endosperm are used by embryo to make new cells and germinate
List the function of cytokinins
- stimulate development of lateral buds by promoting cell division at apical meristem
- promote leaf abscission synergistically with ethene
Define abscission
the shedding of leaves, flower parts or fruits from a plant after the formation of an abscission zone across the stem attaching the organ to the plant
Name the 2 ways plant growth hormones interact
- synergistically: to achieve the same effect e.g. auxins and gibberellins
- antagonistically: with inverse effects e.g. auxins (suppress lateral buds) and cytokinis (stimulate lateral buds)
Define phytochrome
a plant pigment that reacts with different types of light and affects the responses of the plant
What are the two types of phytochrome?
Pr - absorbs red light (biologically inactive)
Pfr - absorbs far red light (biologically active)
What happens to Pr in the light?
It is converted into Pfr
What are the effects of Pr and Pfr on germination?
Pfr: stimulates germination
Pr: inhibits germination ( a flash of red light produces biologically active Pfr, which triggers germination)
Which type of light stimulates germination?
red light
Which type of light inhibits germination?
far red light
State the time of day in which each phytochrome is most abundant
in the daylight: Pfr most abundant
in the darkness: Pr most abundant
How does phytochrome control flowering?
Pr absorbs red light and converts to Pfr, which stimulates flowering
What are the typical characteristics of etoilation?
- rapid stem lengthening but little thickening (seedling grows as tall as possible as fast as possible to reach the light)
- little root growth
- no leaf growth
- no chlorophyll
Which photochrome does a seed only contain?
Pr
Why is it important that the core temperature remains stable?
to maintain a stable rate of enzyme controlled reactions
- temp too low= insufficient kinetic energy for enzyme and substrate molecules
- temp too high= enzymes denature
Why is it important that blood pH remains stable?
maintain stable rate of enzyme-controlled reactions + optimum conditions for other proteins + structure of cell membranes is maintained
acidic pH= H+ ions interact with the H bonds + ionic bonds in tertiary structure of enzymes –> changes active site
Why is it important that blood water potential remains stable?
prevent osmotic lysis
Outline the general stages involved in negative feedback
receptors detect deviation –> coordination centre (by hormones or nervous system –> corrective mechanism by effector –> receptors detect that conditions have returned to normal
What is the difference between an endocrine and exocrine gland?
endocrine glands produce hormones and do not have ducts, hormones are released directly into the bloodstream. exocrine glands produce chemicals e.g. enzymes and release along small tubes or ducts
Define etiolated
describes the form of plants grown in the dark, with long internodes, thin stems, small or unformed leaves and white or pale yellow in colour
Do short day plants want Pfr above or below the threshold?
below the threshold so they have a longer length of darkness
Do long day plants want Pfr above or below the threshold?
above a threshold which is why they have a shorted length of darkness so not all the Pfr is converted
