Introduction

Chloroplasts and cell walls are found in plant cells and not in animal cells. They are specialized structures that allow plants to function as autotrophs. Plants can make their own food by combining inorganic substances by using energy from the sun. The cell wall gives the plant structure.

Chloroplasts are organelles found only in plants and protists which are specialized at capturing energy from sunlight and converting it to chemical energy stored in glucose molecules (glucose).

Let’s take a closer look at these energy-capturing organelles and the plant cell wall now…

Learning

Chloroplast (plants and protists only)

Chloroplasts are plant (and protista)-specific organelles enclosed by a double membrane.  Inside, these organelles contain a series separate, internal membrane structures arranged like stacked pancakes called grana.   Each “pancake” within the grana is called a thylakoid; thylakoids are filled with a specialized, green-colored pigment called chlorophyll which captures sunlight. The green color of chlorophyll accounts for the green coloration found in most plants. Enzymes present in the space surrounding the thylakoids use the captured energy, water, and carbon dioxide to produce carbohydrates.

Chloroplasts are specialized at capturing energy from sunlight and converting it to chemical energy which is then stored in sugar molecules (glucose).  This chemical process is called photosynthesis. The energy in glucose is used by both plants and animals to generate ATP.

In addition to chemical energy, photosynthesis produces a critical by-product: oxygen. The oxygen that we breathe, and which many other organisms, including plants, require for life, is produced during photosynthesis.

In the manufacturing analogy, the chloroplast would represent a solar power plant, capturing sunlight energy which is converted for use within the cell.

Cell Wall

If you examine the plant cell diagram, you will see a structure external to the plasma membrane. This is the cell wall, a rigid covering that protects the cell, provides structural support, and gives shape to the cell. Fungal and some protistan cells also have cell walls. While the prokaryotic cell walls’ chief component is peptidoglycan, the major organic molecule in the plant (and some protists’) cell wall is cellulose a polysaccharide comprised of glucose units. Have you ever noticed that when you bite into a raw vegetable, like celery, it crunches? That’s because you are tearing the celery cells’ rigid cell walls with your teeth.

Important note! Not all Eukaryotic cells have a cell wall, in particular animal cells (like those that make up the human body!) do NOT have cell walls.

In the manufacturing analogy, the cell wall would represent the walls of the manufacturing plant, providing structure for the entire plant. Represented by the dark line surrounding the plant

Summary

Chloroplasts are plant (and protista)-specific organelles enclosed by a double membrane.

Chloroplasts are specialized at capturing energy from sunlight and converting it to chemical energy which is then stored in sugar molecules (glucose) through a process called photosynthesis.

Plant cell walls are located outside the plasma membrane in plant cells. They are composed of cellulose which is a long chain of glucose molecules bonded together.

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Sources:

“Plant Cell Walls and Chloroplasts.” By OpenStax Biology 2e. Retrieved from: https https://openstax.org/books/biology-2e/pages/4-3-eukaryotic-cells/ Licensed under: CC-BY: Attribution