Plant Hormones

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Plant Hormones

- Auxin is a hormone that controls plant growth near the tips of shoots and roots

- It controls the growth in response to light (phototropism) or in response to gravity (gravitropism)

- Extra auxin promotes growth in the shoot but inhibits growthin the root - producing the desired result

SHOOTS GROW TOWARDS LIGHT. Shoot tip exposed to light - more auxin on side in shade - cells grow faster on shaded side so shoot bends towards light

SHOOTS GROW AWAY FROM GRAVITY. Shoot growing sideways - gravity produces unequal distribution of auxin in tip - more auxin on lower side - lower side grows faster - shoot bends upwards

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Plant Hormones 2

ROOTS GROW TOWARDS GRAVITY. Root growing sideways - more auxin on lower side - extra auxin in root inhibits growth - meaning cells on top grow (elongate) faster - root bends downwards

ROOTS GROW TOWARDS MOISTURE. Uneven amount of moisture either side of a root - more auxin on side with more moisture - inhibits growth on that side - root bends in that direction towards moisture


1) Selective weedkillers are made of plant growth hormones - disrupt normal growth patterns - kills them

2) Plant cuttings don't grow in soil - add rooting powder which contains auxin - produce roots rapidly - start growing as new plants - help growers produce clones very quickly

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Homeostasis - all thr functions of your body which try and maintain a 'constant internal environment'

Bodily levels that need to be controlled include: Ion content, water content, sugar content, temperature.

Ion content -  regulated by the kidneys. Ions are taken into body in food then absorbed in blood. Some ions are lost in sweat, kidneys remove excess in urine

Water - taken into body as food and drink. Lost: through skin as sweat, via lungs in breath, via kidneys as urine. Cold day or not exercising - don't sweat much - produce more urine - urine more diluted so is pale. Hot day or exercising - sweat a lot - produce less urine - urine more concentrated so is deeper in colour - Lose more water through breath when exercising because you breathe faster

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Homeostasis 2

Body temperature - controlled by brain - enzymes in human body work best at 37 degrees celcius - body tries to maintain this temperature -part of brain acts as personal thermostat - sensitive to blood temperature in brain - recieves messages from skin about skin temperature too

Blood sugar levels - eating foods containing carbohydrates puts glucose into the blood from the gut - normal cell metabolism removes glucose from the blood - vigorous exercise = much moe glucose removed - insulin hormone helps maintain right level of glucose in blood - so cells get constant supply of energy

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