Tropism

A chemical which is a plant growth factor belonging to the group called auxins

A plants directional response towards gravity (Positive gravitropism = Towards gravity) (Negative gravitropism = Away from gravity)

A plants directional response towards light (Positive phototropism = Towards light) (Negative phototropism = Away from light)

1) IAA is synthesised in the root tip of the plant and transported throughout the root 2) IAA is moved on to the lower side of the roots ( The lower side is indicated by the presence of amyloplasts which gather at the bottom of cells due to their density) 3) IAA in roots inhibits cell elongation so the lower side elongates slower than the upper side 4) Root bends towards gravity

1) IAA is produced at the shoot tip and transported throughout the shoot 2) IAA moves towards the shaded side of the root setting up an IAA gradient across the shoot 3) IAA in the shoots causes cell elongation so the shaded side elongates at a faster rate than the side with light 4) Causes the shoot to bend towards light

Organelle in plant cells that store starch

Use the scalpel to cut a 1 cm section from the root tip of each seedling Mark the root tips at 2 mm intervals Divide the root tips into three groups and place them in test tubes of water The water helps to keep the plant tissue alive Group A receives treatment 1: Remove the ends of the root tips using the scalpel Transfer root cuttings with the end removed to an agar block Illuminate the seedlings equally on all sides Group B receives treatment 2: Transfer intact root tips to an agar block Place a light-proof container over the seedlings Group C receives treatment 3: Transfer intact root tips to an agar block Apply a directional light source to one side of the root tips Leave all the roots in their treatment conditions for 3 hours Use the 2 mm marker lines to determine whether growth has occurred Measure growth Observe whether the growth has been even on both sides Results and analysis In group A (tips removed) we would expect the roots to grow evenly IAA is synthesised in the root tips so removing them means that no IAA is produced There is no inhibition of cell elongation In group B (no light) we would expect the roots to grow less than group A, but still to grow evenly on both sides The roots do not grow as long as those in group A due to the presence of IAA, which inhibits elongation IAA does not redistribute in response to light so there is an equal concentration of IAA on both sides of the root tip In group C (directional light) we would expect the root to bend away from light There is a greater concentration of IAA on the shaded side, so there is inhibition of cell elongation The illuminated side grows at a faster rate The root bends away from the light; this is negative phototropism