As described in the beginning of this question, collenchyma cells are found in young stems and petioles (leaves) and function to provide flexible support to the plant. This is because chollenchyma cells lack secondary cell walls and do not produce lignin to harden them—this protein is characteristic of sclerenchyma cells, which are also used to provide support/strength to the plant. 

Due to their lack of rigidity, collenchyma cells a also capable of elongating with the stems and leaves they support, allowing them to remain alive at maturity. Sclerenchymal cells lack this ability.

As described in the background to the question, sclerenchyma cells are specialized to support the plant as it grows. These cells have thick secondary walls that are further strengthened by the hardening agent called lignin.  As a result, these cells are highly rigid and inflexible.  

At maturity, these cells cannot elongate and are found in regions of the plant that have stopped growing. In some parts of the plant, the sclerenchyma cells may even be dead; however, the rigid walls remain and act like a skeleteon that supports the remainder of the plaint over its lifetime.  

Sclerenchyma cells can also further differentiate into two types called sclereids and fibers. Sclerids can provide hardness to nut shells. Fibers, as their name suggests, are usually arranged in long threads and have commercial uses, such as being made into rope.

The vascular system in plants is designed to transport materials (water, nutrients, food) between the roots and shoots. There are two primary types of tissue dedicated to these processes. Xylem transports water and dissolved minerals upward from the roots; phloem transports sugars—the products of photosynthesis—from where they are synthesized to where they are needed, such as roots and new growth areas of leaves and fruits.

Both xylem and phloem are comprised of a variety of cell types that are specialized for transport and support. 

Cellulose, a polymer of glucose, is the main component of plant cell walls. 

Collagen is found in the connective tissues of animals. Chitin is found in the cell walls of fungi. Actin and myosin are the proteins responsible for contraction in muscle cells; actin is also a microfilament in the cytoskeleton. Peptidoglycan is found in the cell walls of bacteria.

The plant cell wall is made of cellulose, which makes it rigid. The cell wall offers structural support and protection to the cell and it’s rigid nature maintains the regular shape of the cell. The cell wall is also permeable and allows small molecules, proteins, and nutrients to pass, including water and carbon dioxide.

Plant cells contain one very large vacuole that occupies a large percentage of the cell space. The central function of this vacuole is to maintain the turgor pressure of the cell through the continual transport of water and ions in and out of the cell, as needed. Vacuoles store and transport water, waste, and ions too.

Plant cells contain most of the membrane-bound organelles that animal cells do; they do not have cilia, and only some plant cells contain centrioles. Plant cells have additional organelles that animal cells do not, namely chloroplasts and cell walls, for photosynthesis and support, respectively. Virtually all cells have cell membranes.

Stomata are the microscopic pores on the surface of leaves. Their function is to allow carbon dioxide into the plant while also allowing oxygen to leave the plant.

The correct answer to this question is Only plant cells have cell walls

Animals notably do not have cell walls. Animal cells, not plant cells, have plasma membranes that contain cholesterol. Both animals and plants have cells with mitochondria and have ribosomes attached to the endoplasmic reticulum. Also only animal cells contain flagella and plant cells do not contain flagella at all.