plant is a kind of oragnism & a lemon tree is a kind of plant ->  a lemon tree is a kind of organism  a lemon tree is a kind of organism & cold temperatures usually have a negative impact on organisms ->  cold temperatures have a negative impact on the lemon trees  cold temperatures have a negative impact on the lemon trees & a greenhouse is used to protect plants by keeping them warm & a lemon tree is a kind of plant -> a greenhouse can be used to protect the lemon trees by keeping them warm