a) Can move slowly in the direction of light (illustrated below)
b) Are sensitive to gravity, enabling them to always send roots downwards and green shoots upwards
c) Respond to temperature changes in many ways. Exposure to heat causes stomata to open and allow water inside leaves to evaporate, so cooling the plant. Leaves may wilt, which reduces the surface area exposed to the sun. Some plants can orientate their leaves so that they hang vertically, again reducing the surface area exposed to the hot sun. In cold conditions, some plants can produce an organic “antifreeze”.
d) Are sensitive to touch: one example is the way some plants can wrap their stems around cane sticks or trellises. Certain plants have tendrils that are particularly sensitive and enable them to cling on to objects.
Have specialised sensory cells and sense organs:
a) Eyes respond to light to provide vision (below)
b) Ears respond to sound to provide hearing
c) Nerve endings in the skin provide the sense of touch
d) “Taste buds” in our tongues and other parts of the mouth provide a keen sense of taste
e) Millions of sensory neurons on a strip of tissue called the olfactory in the back of the nose give many animals an acute sense of smell. Fish have a similar system, although it works in water rather than air.