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Plant Cell Structures

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Plant Cell Structures

What do plants have to do that animals don't?

Many plant cells are green. Why? Plant cells also usually have a distinct shape. The rigid exterior around the cells is necessary to allow the plants to grow upright. Animal cells do not have these rigid exteriors. There are other distinct differences between plant and animal cells. These will be the focus of this concept.

Plant Cells

Special Structures in Plant Cells

Most organelles are common to both animal and plant cells. However, plant cells also have features that animal cells do not have: a cell wall, a large central vacuole, and plastids such as chloroplasts.

Plants have very different lifestyles from animals, and these differences are apparent when you examine the structure of the plant cell. Plants make their own food in a process called photosynthesis . They take in carbon dioxide (CO 2 ) and water (H 2 O) and convert them into sugars. The features unique to plant cells can be seen in Figure below .

In addition to containing most of the organelles found in animal cells, plant cells also have a cell wall, a large central vacuole, and plastids. These three features are not found in animal cells.

The Cell Wall

A cell wall is a rigid layer that is found outside the cell membrane and surrounds the ce ll. The cell wall contains not only cellulose and protein, but other polysaccharides as well. The cell wall provides structural support and protection . Pores in the cell wall allow water and nutrients to move into and out of the cell. The cell wall also prevents the plant cell from bursting when water enters the cell.

Plastids

Plant plastids are a group of closely related membrane-bound organelles that carry out many functions.

  • One Example : Chloroplasts are the organelle of photosynthesis. They capture light energy from the sun and use it with water and carbon dioxide to make food (sugar) for the plant. The arrangement of chloroplasts in a plant’s cells can be seen in Figure below

Plant cells with visible chloroplasts (left). Starch-storing potato leucoplasts (right).

Chloroplasts

Chloroplasts capture light energy from the sun and use it with water and carbon dioxide to produce sugars for food. Chloroplasts look like flat discs and are usually 2 to 10 micrometers in diameter and 1 micrometer thick. A model of a chloroplast is shown in Figure below . The chloroplast is enclosed by an inner and an outer phospholipid membrane. Between these two layers is the intermembrane space. The fluid within the chloroplast is called the stroma , and it contains one or more molecules of small, circular DNA. The stroma also has ribosomes. Within the stroma are stacks of thylakoids , sub-organelles that are the site of photosynthesis. The thylakoids are arranged in stacks called grana (singular: granum). A thylakoid has a flattened disk shape. Inside it is an empty area called the thylakoid space or lumen. Photosynthesis takes place on the thylakoid membrane.

The internal structure of a chloroplast, with a granal stack of thylakoids circled.

Vocabulary

  • cell wall : Rigid layer that surrounds the plasma membrane of a plant cell; helps support and protect the cell; also characteristic of many prokaryotes.
  • central vacuole : Large saclike organelle in plant cells; stores substances such as water; helps keep plant tissues rigid.
  • chloroplast : Organelle in the cells of plants and algae; site of photosynthesis.
  • chromoplast : Plastid that makes and stores pigments.
  • grana (singular: granum ): Stacks of thylakoid membranes within the chloroplast.
  • leucoplast : Plastid used for bulk storage of starch, lipid, or protein; also makes molecules such as fatty acids and many amino acids.
  • photosynthesis : Process of using the energy in sunlight to make food (glucose).
  • plastids : A group of closely related membrane-bound plant cell organelles; includes chloroplasts, chromoplasts and leucoplasts.
  • stroma : Space outside the thylakoid membranes of a chloroplast; site of the Calvin cycle of photosynthesis.
  • thylakoid : Sub-organelle within the chloroplast; site of photosynthesis.
  • tonoplast : Membrane that surrounds the central vacuole.

Summary

  • Plant cells have a cell wall, a large central vacuole, and plastids such as chloroplasts.
  • The cell wall is a rigid layer that is found outside the cell membrane and surrounds the cell, providing structural support and protection.
  • The central vacuole maintains turgor pressure against the cell wall.
  • Chloroplasts capture light energy from the sun and use it with water and carbon dioxide to produce sugars for food.

Practice I

Use this resource to answer the questions that follow.

  1. List the three distinguishing features of a plant cell. Describe their roles.
  2. In addition to plants, what other organisms have chloroplasts?
  3. How is the vacuole related to plant death?

Practice II

Review

1. List three structures that are found in plant cells but not in animal cells.

2. Identify two functions of plastids in plant cells.

3. What is the role of the cell wall?

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