Can anyone help me with a test

It’s science

Below are the three main organs that make up the plant body. what is the main function of the structure that is identified as b in the picture above? it anchors the plant.it produces food.it absorbs nutrients.it supports the plan

Which of these parts of the membrane large moecules pass through it ?

What type of plant is good for a bioassay and where can i buy it? i only have a month.