Flashcards in F215: Responding To The Environment Deck (92)
What is a tropism?
A directional growth response in which the direction of the response is determined by the direction of the external stimulus.
Describe types of tropisms.
Phototropism - shots grow towards light to enable photosynthesis.
Geotropism - roots grow towards the pull Of gravity to anchor it in soil.
Chemotropism - ?
Thigmotropism - shoots of climbing plants wind around other plants or solid structures for support.
What is a positive and negative tropic response?
If a plant responds towards a stimulus it is a positive tropic response, and vice versa.
How can hormones move around plants?
Mass flow in the phloem sap or xylem vessels.
What are meristems?
Particular places in the plant where there are groups of cells capable of dividing for growth.
The cell wall around a plant cell limits the cells ability to divide ad expand.
What are the types of meristems?
Apical meristems - located at the tips of roots and shoots, and are responsible for their length.
Lateral bud meristems - found in the buds, can give rise to side shoots.
Lateral meristems - found in a cylinder near the outside of roots and shoots, responsible for their width.
Some plants have intercalary meristems between nodes, responsible for length.
Describe different types of plant hormones and their effects.
Auxins - promote cell elongation, inhibit growth of side shoots and leaf fall.
Cytokinins - promote cell division.
Gibberellins - promote seed germination and growth of stems.
Abscisic acid - inhibits seed germination and growth, causes aromas to close when there is low water.
Ethene - promotes fruit ripening.
Describe the process of phototropism.
Auxins are responsible for cell elongation.
When light shines on a shoot it causes auxins to be transported to the shaded side, where they then promote elongation of cells and the shoot bends towards the light.
When light is coming evenly from both sides the auxins are pushed down the shoot and the shoot grows vertically.
Cytokines stop the leaves of deciduous trees senescing by making sure the leaf acts as a sink for phloem transport. So the leaf has a good supply of nutrients.
When cytokinin production drops, that supply of nutrients swindles and senescence begins, this is usually followed by leaves being shed.
What is apical dominance?
When the growing apical bud at the tip of the shoot inhibits growth of lateral buds further down the shoot.
Auxins prevent lateral buds from growing.
The tip Is the source of auxins, so when removed auxin concentration drops and lateral buds grow.
What other two hormones are involved in apical dominance?
Abscisic acid inhibits bud growth.
When the tip is removed the A acid conc drop and the bus starts to grow.
Cytokinins promote bud growth.
Override apical dominance.
When the tip is removed cytokinins spreads evenly around the plant, opposed to just going to the shoot apex, and this promoted bud growth.
Describe commercial uses of auxins.
Dipping the end of a cutting in rooting powder before planting it encourages root growth.
The rooting powder contains auxins.
Treating un pollinated flowers with auxin can promote growth of seedless fruit by promoting ovule growth.
Herbicides: artificial auxins used to kill weeds, they are transported in the phloem to all parts of the plant, and cannot be broken down by the plants enzymes.
They promote shoot growth so much the stem cannot support itself and it crumbles and dies.
Describe the commercial use of gibberellins in fruit production.
Delay senescence in citrus fruits, so they can be left longer unpicked or in shops.
Act with cytokines to elongate apples shape.
Elongate the stalk of grapes allowing them to be less compact, and grow fully unrestricted.
Describe brewing in relation to gibberellins.
Adding gibberellins can speed up the process.
The genes for amylase production are switched off by gibberellins, which break starch into maltose.
Describe gibberellins in relation to sugar production.
Spraying sugar came with gibberellins stimulates growth between the nodes, making the stems elongate.
This makes more storage room for sugar available.
Describe plant breeding and gibberellins.
Conifer plants take a very long time to selectively breed due to only becoming reproductively active at a very late stage.
Gibberellins induce seed formation in young trees.
Some plants are biennial and only flower in their second year of life.
Gibberellins induce seed production in the first year.
Spraying plants with gibberellin synthesis inhibitors can keep flowers short and stocky.
Prevents lodging, when stems bend over because do the water collected, making them hard to harvest.
Describe the commercial use of cytokines.
Delay leaf senescence, and also prevent yellowing of lettuce leaves once they have been picked.
Used in tissue culture to mass produce plants, they promote bud and shoot growth.
Describe the commercial uses of Ethene.
It Is a gas and cannot be sprayed directly.
Speeds up ripening of fruits like apples, tomatoes and citrus fruits.
Promotes fruit drop in cotton, cherry and walnut.
Promotes female sex expression in cucumbers, increasing yield and reducing chances of self pollination (which makes them bitter).
Promotes lateral growth in some plants, yielding compact flowering stems.
In storage or to increase shelf life Ethene is restricted by low oxygen and temperatures or by Ethene inhibitors like silver salts.
This prevents ripening.
What is the cerebrum?
Largest and most recognisable part of the brain.
Responsible for unique human features such as thought, imagination and reasoning.
Label cerebrum, cerebellum, medulla oblongata and hypothalamus on a diagram.
Describe the gross structure of the brain.
Two hemispheres of the cerebrum, joined via the corpus callosum.
The outermost layer consists of a thin layer I nerve cells known as the cerebral cortex.
What are the areas of the cerebral cortex?
Sensory areas - receive impulses from receptors.
Association areas - compare input with previous experiences in order to interpret it and judge a response.
Motor areas - send impulses to effectors (muscles or glands).
What is the job of the cerebellum?
Controls coordination of movement and posture.
Neurones from here carry impulses to the motor areas.
It processes sensory information from:
Balance organs in the inner ear.
Spindle fibres (muscle tension).
What is the job of the hypothalamus?
Controls the autonomic nervous system and the endocrine glands.
Controls homeostatic mechanisms.
What is the job if the medulla oblongata?
Controls the action of smooth muscle in the gut wall, and controls breathing movements and heart rate.
Controls non skeletal muscles (cardiac and involuntary muscles).
Effectively In control of autonomic nervous system?
Cardiac centre and respiratory centre are here.
What makes up the central nervous system?
grey matter - billions of non myelinated neurones.
White matter - longer myelinated axons and dense one that carry impulses. Myelin makes it white.
What does the peripheral nervous system consist of?
All the sensory and motor neurones that are outside the central nervous system, connecting the receptors and effectors to the CNS.
How is the motor system sub divided?
Somatic motor neurones carry impulses from the CNS to skeletal muscles, which are under voluntary control.
Autonomic motor neurones carry impulses from the CNS to cardiac muscle, to smooth muscle in the gut wall and to glands, which are controlled involuntarily.
Describe the autonomic nervous system.
Mostly non myelinated, somatic are myelinated.
Connections to effectors consist of at least two neurones, only one in somatic.
The two neurones connect at a ganglion.
Two types of autonomic motor neurones - sympathetic and parasympathetic.