Growth response of plants title Growth response of plants

18.2 How do shoots respond to light? content Growth response of plants 18.1 Tropism 18.2 How do shoots respond to light? 18.3 How do roots and shoots respond to gravity? 18.4 How do roots respond to water? 18.5 What substances cause tropisms in plants? 18.6 How do auxins cause phototropism and geotropism?

18.1 Tropism nervous system Plants can still sense external stimuli and respond by movement endocrine system stimulus coming from one certain direction TROPISM unidirectional stimulus grow towards/ away from the stimulus plant will

18.2 How do shoots respond to light? Phototropism growth movement of a part of a plant in response to light growing towards the stimulus Shoots positive phototropism leaves can get more light for photosynthesis more food is made

To investigate phototropism in shoots Carry out Practical 18.1 To investigate phototropism in shoots

18.3 How do roots and shoots respond to gravity? Geotropism growth movement of a part of a plant in response to gravity growing away from the stimulus Shoots Roots negative geotropism positive geotropism leaves will grow away from the soil leaves can get more light for photosynthesis roots can get more water and dissolved minerals from the soil roots can grow deeper for better anchorage

To investigate geotropism in roots Carry out Practical 18.2 To investigate geotropism in roots

18.4 How do roots respond to water? Hydrotropism growth movement of a part of a plant in response to water Roots positive hydrotropism roots can get enough water and dissolved minerals for growth

18.5 What substances cause tropisms in plants? Auxins plant growth hormones produced at tips of shoots and roots diffuse to regions of elongation to promote growth (but effects vary with concentration & parts of plants concerned) one common auxin is indole acetic acid (IAA) cause tropism

Region of elongation in plants more auxins growth occurs in region of elongation no increase in length fewer auxins plumule after 1 to 2 days

increasing concentration of auxins -100 -50 50 100 150 200 10-6 10-4 10-2 1 102 104 ppm (parts per million) GROWTH RESPONSE most auxin concentrations which increase root growth are too low to increase shoot growth lower auxin concentrations increase the growth of roots percentage stimulation percentage inhibition shoots roots increasing concentration of auxins

increasing concentration of auxins higher auxin concentrations increase shoot growth but slow down root growth -100 -50 50 100 150 200 10-6 10-4 10-2 1 102 104 ppm (parts per million) GROWTH RESPONSE percentage stimulation percentage inhibition shoots roots increasing concentration of auxins

increasing concentration of auxins -100 -50 50 100 150 200 10-6 10-4 10-2 1 102 104 ppm (parts per million) GROWTH RESPONSE the concentration which produces the greatest root growth is lower than the one which produces the greatest shoot growth percentage stimulation percentage inhibition shoots roots increasing concentration of auxins

increasing concentration of auxins -100 -50 50 100 150 200 10-6 10-4 10-2 1 102 104 ppm (parts per million) GROWTH RESPONSE very high auxin concentrations slow down both root and shoot growth percentage stimulation percentage inhibition shoots roots increasing concentration of auxins

18.6 How do auxins cause phototropism and geotropism? Both tropisms are caused by an uneven distribution of auxins. How auxins cause phototropism of shoots How auxins cause geotropism of roots

Concept diagram Tropism auxins growth response of plants caused by auxins is a consists of growth response of plants work by produced by regulating plant growth tips of shoots and roots in response to a stimulus phototropism geotropism hydrotropism in response to in response to in response to unilateral light gravity water

Concept diagram unilateral light gravity water causes causes therefore different concentration of auxins in the shaded and unshaded sides of a plant different distribution of auxins on the upper and lower sides of a horizontally placed root therefore therefore bending of shoots towards light bending of roots downwards bending of roots towards water hence shoots are hence roots are hence roots are positively phototropic positively geotropic positively hydrotropic