Many species of orchids are known as epiphytes. these are organisms which grow upon or are attached to other plants. epiphytic orchids use trees or shrubs for physical support, and do not or harm the trees or shrubs in any way.
what type of relationship does an epiphytic orchid have with its host plant?
commensalistic
mutualistic
competitive
parasitic

The orchid derives the benefit of physical support from the tree, while the tree receives neither benefit nor harm. This is an example of a COMMENSALISTIC relationship.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products

measuring light intensity

light meters can be used to measure light intensity. the meter is held at the soil surface and pointed in the direction of the maximum light intensity, and then the meter is read.

errors can be made when measuring light intensity by accidentally shading the light meter. the reliability of the results can be checked by taking many samples.