6.1- responses to stimuli

responses to stimuli flashcards

What are plant growth factors and where are they produced

• they are chemicals that regulate plant growth in response to directional stimuli

• They are produced in the growing regions of the plants

• They diffuse between cells

Explain how shoots show positive phototropism.

• IAA diffuses to the shaded side of the tip

• As it diffuses it causes H+ ions to be actively transported into the cell wall

• That causes disruption to the H-bonds betweeen the cellulose molecules which make the cell walls more permeable to water

• The cells on the shaded side are then able to elongate faster as there is a higher turgor pressure

• The shoot then bends towards light

contrast mammalian hormones and plant growth factors

Define taxis and kinesis , state their advantage

• taxis - directional movement in response to an external stimuli

• Kinesis - non-directional response to the presence and intensity of an external stimuli

• They allow mobile organisms to stay in their optimal environment

Why do organisms respond to temperature and humidity with kinesis instead of taxis?

Temperature and humidity don’t tend to be directional and there doesn’t tend to be a clear gradient

Outline a simple reflex arc.

Stimulus —> receptor —> sensory neurone —> relay neurone coordinates the response —> motor neurone —> effector —> response

What features are common to all sensory receptors?

• act as energy transducers to establish a generator potential

• They only respond to specific stimuli

Describe the basic structure of a pacinian corpuscle

• single nerve fibre that is surrounded by layers of connective tissue

  • The connective tissue layers are surrounded by gel and contained by a capsule

• Stretch mediated sodium channels on a plasma membrane

• A capillary goes along the base layer of tissue

Where are rods and cones located in the retina?

• rods - evenly distributed around the periphery

• Cones- mainly in the central fovea

• There are no photoreceptors at the blind spot