0
Q
Describe the point played by auxins in apical dominance in a plant shoot. (7)
A
- Plant growth regulator
- Synthesised in growing tips / apical buds / meristems
- Moves by diffusion or active transport
- From cell to cell
- Also mass flow in phloem
- Stimulate cell elongation
- Inhibits side / lateral buds / growth
- Plant grows upwards / taller (allows stem to grow up to light instead of sprouting)
- Auxin not solely responsible for apical dominance (interaction between auxin and other plant growth regulators)
- Concentration gradient down shoot so effect of dominance decreases
- Role of ABA and lateral bud inhibition / cytokinins antagonistic to IAA / gibberellins enhance IAA
1
Q
Describe the roles of gibberellins in stem elongation. (5)
A
- Plant growth regulator
- Stimulates cell division
- Stimulates cell elongation
- Changes plasticity of cell wall
- Plant grows tall
- Apply GA to dwarf plants and they grow taller (GA promotes bolting of some rosette plants)
- Active and inactive forms
- Dwarf planets lack active form of GA
- Dominant allele causes synthesis of enzyme
- Enzyme catalyses the production of the active form of GA
- Recessive allele only inactive form of GA formed (dominant results in active form)
- Interaction between GA and other plant growth regulators
2
Q
Describe the part played by glucagon in the control of glucose in the blood. (3)
A
- Affects liver cells
- Promotes glycogenolysis
- Promotes use of fatty acids in respiration
- Promotes gluconeogenesis
- Results in rise in blood glucose concentration
- Back to norm (set point)
3
Q
Explain what is meant by endocrine gland. (2)
A
- A ductless gland
- Excrete hormones in the blood
- To target organ / tissues
4
Q
Describe how the liver reduces blood glucose concentration, when insulin is secreted. (3)
A
- Binds to receptors on membrane of liver cells
- Conversion glucose to glycogen (glycogenesis)
- Because insulin activates enzyme (glucokinase)
- Increased use of glucose in respiration
- Increased uptake of glucose into liver cells
