Module 5.1.5 Plant & Animal Responses Flashcards
What are the 4 types of plant growth & development?
Seed germination
Cell elongation
Apical dominance
Stem elongation
What are the 5 plant hormones?
Auxins (IAAs)
Gibberellins
Ethene
ABA
Cytokinins
What 2 processes is auxins involved in?
Cell elongation
Apical dominance
What happens in cell elongation?
Auxins are released by the meristem of the plant which bind to receptors on the cell surface membrane. H+ ions are then pumped into the cell through proton channels, decreasing the pH of the cell. This causes the cell to be more permeable to water so it becomes more flexible. The cell will end up absorbing more water, expanding the cell wall & causing cell elongation. The cell wall will then become turgid when the auxins are broken down as the cell matures
What is apical dominance?
Favouring apical shoot growth and inhibiting lateral shoot growth, caused by auxins
What is the apical shoot?
The main stem
What are the lateral shoots?
Shoots that branch off of the main stem
Why is apical dominance beneficial for the plant?
The shoots are better for competing for light since they are taller and get receive the maximum amount of light for photosynthesis & respiration
Why are the lateral shoots longer down the plant?
Auxins inhibit lateral shoot growth, as there is a smaller concentration of them down the plant, the lateral shoots are longer, makes a greater surface area for light to be absorbed
What is phototropism?
How a plant responds to light
What is geotropism?
How a plant responds to gravity
How are auxins involved in positive & negative phototropism?
Auxins molecules in a plant’s shoot move towards the shaded side which stimulates cell elongation. This causes the shaded side to grow at a faster rate than the rest of the plant, and as a result, bend towards the light. This ensures can get the maximum amount of sunlight it can, to increase respiration and produce more glucose. This is positive phototropism. The roots, however, will bend away from the light as they do not photosynthesise and have no stimulus, in a process known as negative phototropism.
How are auxins involved in positive & negative geotropism?
The plastids in the root cap of the roots will settle on the bottom side of the cell. This stimulates auxins to be produced which will cause cell elongation, causing the roots to bend towards the ground, due to gravity, as there is most likely water and nutrients there. This is called positive geotropism. However, the shoots will exhibit negative geotropism, as they will grow away from the gravitational pull of the ground, as there is most likely little sunlight there. This is known as negative geotropism
What 2 processes does auxins inhibit?
Fruit ripening
Abscission
What is abscission?
When leaves fall off the trees e.g. in autumn season
What processes does gibberellins help?
Stem elongation
Germination of cells
Stimulates pollen tube growth in fertilisation
How do gibberellins aid in seed germination?
Water is absorbed which stimulates seed germination. Due to the water uptake, the embryo synthesises gibberellin production. The aluerone layer then synthesises amylase in response to gibberellin production. Amylase then mobilises energy reserves and hydrolyses starch into maltose. Maltose is then hydrolysed into glucose which is respired to release ATP
How do gibberellins play a role in stem elongation?
Gibberellins increase the internode length so plants can get more sunlight -> maximum photosynthesis can occur
How are gibberellins linked to genes regarding height of the plant?
Some plants’ height is partially controlled by the Le gene. The dominant allele Le produces tall plants if present whereas the recessive allele le produces shorter plants if present in a homozygous plant. This gene regulates enzyme production that is involved in a pathway that for active gibberellin. Homozygous recessive plant end up being dwarves because no active gibberellin is formed so plants are unable to grow tall however, farmers may apply active gibberellin to stimulate growth in shorter plants
How may farmers have a role in preventing stem elongation?
Farmers may reduce the height of a plant because the stem isnt always eaten so it is useless for them. They may also reduce the stem to prevent crop damage in bad weather as taller plants are more prone to damage. Reducing the stem also reduces waste production
What processes does Ethene promote in a plant?
Abscission & fruit ripening
What type of relationship do auxins & Ethene have?
An antagonistic relationship -> they both oppose each other
What type of relationship do auxins & gibberellins have?
A synergic relationship -> both hormones work together
What does ABA (abscisic acid) do in a plant?
Maintains the dormancy of seeds & buds
Stimulates protective responses under stress -> (e.g. if its too cold, ABA may stimulate antifreeze production)
What type of relationship does ABA & gibberellins have?
An antagonistic relationship
What does cytokinins do in a plant?
Promotes cytokinesis & is produced in cells that are actively growing.
Reduces plant senescence & promotes lateral growth
What is Plant senescence?
Gradual ageing of a plant
How are cytokinins beneficial for plant growth?
Cytokinins increases more mitosis which makes more cells which increases plant growth
What type of relationship does cytokinins & auxins have?
A synergistic relationship
What are some commercial use of auxins?
Sprayed on developing fruits to prevent abscission & fruit ripening
Sprayed onto flowers to initiate fruit growth without fertilisation (parthenocarpy -> promotes growth of seedless fruits)
Applied to cut end of a shoot to stimulate root production
Synthetic auxins -> used as selective herbicides
What are the commercial use of gibberellins?
Sprayed onto fruit crops to promote growth
Sprayed onto citrus trees -> allows fruit to stay on the trees longer
Sprayed onto sugar cane to increase the yield of sucrose
Brewing -> GA sprayed onto barley seeds to make them germinate, amylase is produced, starch is broken down into maltose, the action of yeast on the maltose produces alcohol