Plant Responses - 5.1 Flashcards
Name four plant hormones
- Auxin
- Gibberellins
- Ethene
- Abscisic Acid
Role of auxin?
Causes cell elongation in stems and inhibits growth in roots. Prevents leaves from dropping and promotes apical dominance
Role of Gibberellins?
Stimulates seed germination, stem elongation and pollen tube growth in fertilisation
Role of ethene?
A gas that causes fruit to ripen
Role of abscisic acid?
Stimulates stomatal closure and maintains dormancy of seeds
What are pheromones?
Gases that influence the behavior of the same species or herbivores, e.g ethene
What is a tropism?
Directional growth in response to a stimulus
State the four types of tropisms and explain the function of each
-Phototropism - growth towards light to obtain light energy for photosynthesis
-Geotropism - roots grow towards force of gravity to gain water and mineral ions from soil
-Hydrotropism - growth towards water (water is needed for photosynthesis)
-Thigmotropism - response to touch
What is a nastic response?
A non-directional response to a stimulus
What is apical dominance?
Auxin released from apical shoot tip / branch to inhibit growth of lateral banches / shoots. This ensures trees grow tall and obtain as much light energy as possible
How do gibberellins work in germination?
Water is absorbed by the seed which softens seed coat and allows young root and young shoot to break out of seed. Gibberellins are activated in the embryo - diffuse from embryo to aleurone layer, bind to specific receptors on plasma membrane which initiates transcription and translation of genes encoding digestive enzymes
How does stomatal closure happen?
When there is a low water potential in soil, detected by roots. ABA is synthesised and travels up the xylem via transpiration stream to leaves. ABA binds to receptors on plasma membrane of guard cells and stimulates stomatal closure
