Polysaccharide: This is a type of carbohydrate that consists of a number of sugar molecules bonded together. Cellulose is an example of a polysaccharide.
Hemicellulose: This is another component found in plant cell walls but it's less rigid than cellulose. It's like the cement between our brick analogy above, helping to fill gaps and provide additional support.
Lignin: This is an organic substance binding the cells, fibres and vessels which constitute wood and the lignified elements of plants. Think about it as extra reinforcement for our brick building.