Core N - Homeostasis

Question 0

Describe the point played by auxins in apical dominance in a plant shoot. (7)

Answer 0

• 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

Question 1

Describe the roles of gibberellins in stem elongation. (5)

Answer 1

• 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

Question 2

Describe the part played by glucagon in the control of glucose in the blood. (3)

Answer 2

• 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)

Question 3

Explain what is meant by endocrine gland. (2)

Answer 3

• A ductless gland
• Excrete hormones in the blood
• To target organ / tissues

Question 4

Describe how the liver reduces blood glucose concentration, when insulin is secreted. (3)

Answer 4

• 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