Unit 5.5- Plant and Animal Responses Flashcards
Abiotic components definition:
Components of an ecosystem that are non-living
Alkaloids definition:
Organic, nitrogen-containing bases that have important physiological effects on animals.
Examples of alkaloids:
- Nicotine
- Quinine
- Strychnine
- Morphine
Biotic components definition:
Components of an ecosystem that are living
Pheremone definition:
Any chemical substance released by one living thing, which influences the behaviour or physiology of another living thing.
Tannins definition:
Phenolic compounds, located in a cell vacuole or in surface wax on plants
Tropism definition:
A directional growth response in which the direction of the response is determined by the direction of the external stimulus.
Nastic response definition:
Non-directional and quick response to external stimulus.
What chemicals are used by plants to protect themselves from herbivores?
- Tannins
- Alkaloids
- Pheremones
How do tannins protect plants from herbivores?
- Toxic to microorganisms and larger herbivores
- In leaves they are found in the upper epidermis and make the leaf taste bad
- In roots, they prevent infiltration by pathogenic microorganisms
How do alkaloids protect plants from herbivores?
- Derived from amino acids
- Taste bitter
- Located in growing tops and flowers and peripheral cell layers of stems and roots.
How do pheremones protect plants from herbivores?
Chemical released by plants that can affect the behaviour of physiology of herbivores.
What are examples of types of tropism?
- Phototropism
- Geotropism
- Chemotropism
- Thigmotropism
What is phototropism:
Shoots grow towards the light. This enables them to photosynthesise
What is geotropism?
Roots grow upwards towards the pull of gravity. This anchors them in the soil and helps them to take up water.
What is chemotropism?
On a flower, pollen tubes grow down the style, attracted by chemicals, towards the ovary where fertilisation can take place.
What is thigmotropism?
Shoots of climbing plants, such as ivy, wind around other plants or solid structures to gain support.
Positive tropic response definition:
When a plant responds towards a stimulus
Negative tropic response definition:
When a plant responds away from a stimulus
Example of thigmonastic response:
Venus fly trap closing leaves.
Where are plant hormones produced?
By cells in a variety of tissues in the plant
Examples of plant hormones:
- Cytokinins
- Abscisic acid
- Auxins
- Gibberellins
- Ethene
What do cytokinins do?
- Promote cell division
- Delay leaf senescence
- Overcome apical dominance
- Promote cell expansion
What does abscisic acid do?
- Inhibits seed germination and growth
- Causes stomatal closure when the plant is stressed by low water availability
What do auxins do?
- Promote cell elongation
- Inhibit growth of side-shoots
- Inhibit leaf abscission (leaf fall)
What do gibberellins do?
-Promote seed germination and growth of stems
What does ethene do?
Promote fruit ripening
How do hormones travel around the plant?
- Active transport
- Diffusion
- Mass flow in the phloem sap or xylem vessels
Apical dominance definition:
Inhibition of lateral buds further down the shoot by chemicals produced in the apical bud at the top of the plant shoot
Auxins definition:
Plant hormones which are responsible for regulating plant growth
Gibberellins definition:
Plant hormones which are responsible for stem elongation and seed germination
What happens when you break she shoot tip (apex) off the plant?
The plant starts to grow side branches from lateral buds that were previously dormant
What did researchers do the show that auxins in the apical bud prevent lateral buds from growing?
Applies a paste containing auxins to the cut end of a shoot and the lateral buds did not grow
How did scientists prove that it was auxin causing lateral buds not to grow, and not a hormone being produced when the tip was exposed to oxygen?
Applied a ring of auxin transport inhibitor below the apex of the shoot and the lateral buds grew.
What hormones other than auxin are involved in plant growth?
- Abscisic acid
- Gibberellins
What does abscisic acid do?
- Inhibits bud growth
- High auxin in the shoot may keep abscisic acid levels high in the bud
- When the tip is cut (source of auxin), abscisic acid levels will drop so the bud will start to grow.
What do cytokinins do?
-Promote bud growth
-Directly applying cytokinin to buds can overide apical dominance
-High levels of auxin in the shoot apex make most of the cytokinin go there
When the apex is removed, the cytokinin travels evenly around the plant, causing lateral growth.
What happens when gibberellic acid is applied to dwarf varieties of plants?
They grow taller
How was the function of gibberellin proved?
By comparing the concentrations of GA1 (gibberellin) in tall and short pea plants. Tall pea plants had a higher concentration
What converts GA20 to GA1?
An enzyme produced by the Le gene
How was it proven that GA20 can be converted into GA1?
- Researchers chose a pea plant that blocks part of gibberellin production so GA20 can not be made
- The researchers grafted a shoot onto a homozygous lele plant (which cannot convert GA20 into GA1) and it grew tall
- This is because although the shoot had no GA20, it still had the enzyme to convert GA20 into GA1
- Because this shoot grew tall, it confirms GA1 causes cell elongation
How does gibberelllin work?
- GA1 moves through plasma membrane
- Binds to receptor proteins as part of a chain reaction
- DELLA protein normally binds to transcription factors, rendering them useless, but the GA1 breaks down the DELLA
- Once the DELLA is gone, the transcription of a growth gene can occur
How does gibberellin promote seed germination?
- Gibberellin is released when the seed absorbs water
- The gibberellin travels to the aleurone layer on the endosperm region of the seed
- The gibberellin enables the production of amalayse, which breaks down starch into glucose
- This then enables the embryo to respire and grow
- The glucose is also used for protein synthesis
What are apical meristems?
Meristems at the tips or apices of roots and shoots. Responsible for roots and shoots getting longer
What are lateral bud meristems?
Meristems found in the buds. These can cause side shoots to grow
What are lateral meristems?
Form a cylinder near the outside of roots and shoots. Cause them to get wider
What are inrercalary meristems?
Found in some plants between the nodes where the leaves and buds branch off the stem. Growth between the nodes is responsible for the shoots getting longer
How did Darwin’s experiment to shoe that the growth stimulus is produced at the tip work?
- Control showing tip growing towards light
- Shoot with tip cut off doesn’t grow towards light
- Shoot with tip covered doesn’t grow towards light
What were the conclusions made from Darwin’s experiment to show the growth stimulus is produced at the tip?
- Light dependant stimulus in the tip
- Growth stimulus travels to zone of elongation
- The cells on the shaded side grow more than those on the sunny side
How did Boysen-Jensen prove that the thing causing shoots to bend (auxin) is soluble in water?
- Sheet of mica through shady half causes it to stop bending, but when in sunny half it still bends
- When tip is cut off and placed back on top of gelatin it still bends
What are the conclusions about Boysen-Jensen’s experiment about the thing causing plant shoots to bend (auxin) being soluble?
- Something has to travel to the shady side for the shoot to bend
- It’s soluble
How did Went prove that it was auxin causing shoots to bend and that the more auxin there was, the more the shoots would bend?
- Tips placed on agar so auxin diffuses into agar
- Agar blocks put on shoots with removed tips, in the dark
- The shoots bend
What are the conclusions made from Went’s experiment about auxin causing plant shoots to curve?
- Something in the tip which causes it to bend
- Concentration dependant as more blocks cause it to bend more
What can artificial auxins be used for?
- Prevent leaf and fruit drop
- Rooting powder
- Creating seedless fruit
- Herbicides
How can auxins be used to create seedless fruit?
Applying auxins promotes ovule growth which triggers the automatic production of auxin by tissues in the developing fruit, helping the complete the developmental process
How can auxins be used to create herbicides?
Because they are man made auxins, plants find them difficult to break down and they can act within the plant for longer. They promote shoot growth so much that the stem cannot support itself so it buckles and dies.