Co-ordination and response - Introduction & Flowering plants

homeostasis

regulation of the internal conditions of a cell or organism

examples of internal conditions regulated by homeostasis

water content, temperature, pH, BP, blood glucose concentration

why is homeostasis important

to stay healthy and maintain optimum conditions to allow the organism to function and respond to changes

how does homeostasis keep us alive

it maintains optimal conditions for enzyme action and all cell functions

examples of homeostasis in humans

control of body temperature, control of body water content

is homeostasis involuntary or voluntary

involuntary

what parts of our body are involved in maintaining homeostasis

the brain stem and the spinal cord

responses of automatic control systems

nervous or chemical responses

3 main parts to a coordinated response

• stimulus

• receptor

• effector

stimulus

change in the environment (internal/external)

receptor

cells that detect stimuli

coordination centre

receives and processes information from receptors

effector

part of the body that brings about the response to a stimulus (muscle, gland)

control systems helping humans respond to stimuli

• nervous system

• hormonal system (endocrine system)

tropisms

directional growth responses

phototropism

plant response to light

geotropism / gravitoprism

plant response to gravity

positive tropism

growth towards stimulus

negative tropism

growth away from stimulus

shoots growing upwards

• positively phototropic

• negatively geotropic (away from gravity and towards light)

roots growing downwards

• negatively phototropic

• positively geotropic (away from light and towards gravity)

auxins

plant growth regulators that control directional growth responses

effect of auxin on the shoot

promote cell elongation

effect of auxin on the root

inhibit cell elongation

unequal distributions of auxin

unequal growth rates in shoot and root

distribution of auxin in the shoots

affected by light and gravity

distribution of auxin in the roots

affected by gravity

where is auxin made

it is mostly made in the tips of growing shoots and then diffuses down to the region where cell division occurs (below the tip)

more auxin

cells elongate and grow faster

light all around the tip (shoot)

auxin is distributed evenly throughout and the cells in the shoot grow at the same rate

light on the shoot predominantly from one side

auxin produced in the tip concentrates on the shaded side making the cells on that side elongate and grow faster than the cells on the sunny side

unequal growth on either side of the shoot

shoot bends and grows in the direction of the light