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Do onion cells have chromoplasts — Reading Comprehension

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This engaging middle school science passage explores the different types of plastids found in plant cells: chloroplasts, chromoplasts, and leucoplasts. It explains the specific functions of each, such as photosynthesis in chloroplasts and pigment storage in chromoplasts. The passage then focuses on the onion, a common example studied in biology, to explain why its cells primarily contain leucoplasts for starch storage rather than chromoplasts or chloroplasts. The content is directly aligned with life science and biology topics for grades 6-8, addressing concepts related to cell structure and function. It uses clear, concise language and bolded key terms to enhance learning, making it an excellent resource for students studying plant cells and organelles. The passage encourages students to connect cellular structures to the observable characteristics and functions of different plant parts, supporting a deeper understanding of NGSS standards.

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A microscopic illustration of different plastids found in plant cells, including a chloroplast (green), a chromoplast (red-orange), and a leucoplast (clear with starch grains).

Plant cells contain specialized organelles called plastids, which are responsible for various functions, including photosynthesis and pigment storage. There are several types of plastids, but three main types are commonly discussed: chloroplasts, chromoplasts, and leucoplasts. Chloroplasts are the most well-known, as they contain the green pigment chlorophyll and are the sites of photosynthesis. This is why leaves and other green parts of plants appear green.

Chromoplasts are a type of plastid that stores non-photosynthetic pigments. These pigments, such as carotenoids, are responsible for the vibrant red, orange, and yellow colors seen in fruits, flowers, and some roots. For example, the brilliant red of a ripe tomato or the bright orange of a carrot are due to the presence of chromoplasts. Their main function is to attract pollinators, like bees and birds, to flowers and to aid in seed dispersal by making fruits more appealing to animals.

Leucoplasts are colorless plastids. They are primarily used for storing starches, lipids, and proteins. They are abundant in the non-photosynthetic parts of plants, such as roots, seeds, and stems. A prime example is the potato tuber, which is packed with leucoplasts storing starch for the plant. Because they lack pigments, parts of the plant with a high concentration of leucoplasts often appear white or clear.

Now, let's consider the onion. The bulb of an onion grows underground and its cells are not exposed to sunlight. Therefore, the onion's primary function is not to perform photosynthesis, but rather to store energy and nutrients for the plant. Because of this, onion cells do not have chloroplasts. Similarly, since the onion bulb is not a fruit or flower and does not need to attract pollinators, its cells also lack chromoplasts. Instead, onion cells are rich in leucoplasts, which are essential for storing starch and other nutrients. This is why onion cells are generally clear or translucent and do not display vibrant colors.

Fun Fact: While onion bulbs are usually white or yellow, some varieties of red onions get their color not from chromoplasts, but from a different type of pigment called anthocyanin, which is stored in the cell's large central vacuole.

Which of the following is the primary function of leucoplasts in a plant cell?

Performing photosynthesisAttracting pollinatorsStoring starch and nutrientsGiving the cell a green color

What is the main reason why onion cells do not have chloroplasts?

They are located in the leavesThey are not exposed to sunlightThey store red pigmentsThey are too small to have them

What is the role of chromoplasts in a plant?

To store waterTo produce energyTo give a cell a red, orange, or yellow colorTo help the plant stand upright

Based on the passage, what can be inferred about the location of leucoplasts in a plant?

They are mainly found in a plant's leaves.They are concentrated in parts not exposed to direct sunlight.They are used to make flowers colorful.They are the primary organelles for photosynthesis.

A scientist observes a plant cell that is green. Based on the passage, which organelle is most likely abundant in this cell?

ChromoplastsLeucoplastsChloroplastsThe nucleus

Why do the cells of an onion bulb lack chromoplasts?

The onion is a fruit.The cells need to perform photosynthesis.The onion is not a flower or a fruit.The cells are responsible for attracting pollinators.

Which of the following best summarizes the main idea of the passage?

Plant cells contain different types of plastids for various functions.Onion cells are different from other plant cells.Chromoplasts are responsible for all plant colors.Leucoplasts are the most important type of plastid.

If a student found a plant part that was bright red, which type of plastid would they most likely find in its cells?

LeucoplastsChloroplastsAnthocyanoplastsChromoplasts