Q:

Why do onion cells lack a chloroplast?

A:

Quick Answer

Plant cells from an onion bulb lack chloroplasts because this part of the plant grows below ground, making it incapable of absorbing the light needed to photosynthesize. Most subterranean root and bulb structures in plants do not have chloroplasts for this reason.

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Full Answer

Although cells at the very top of the bulb that peek through the soil may develop chloroplasts, the main function of these cells is to protect the plant against harmful pathogens in the soil and to store energy. These functions are made possible by the cell wall, cell membrane, cytoplasm, nucleus and large vacuum of the cell.

Light microscopy renders the nucleus of an onion cell visible at the edge of the cytoplasm. The vacuole is visible in the middle of the cell. This vacuole is transparent in the cells of white onions, making them invisible to light microscopy unless they are stained. Cells of red onions are naturally pigmented and do not require the addition of a staining agent.

The best samples for viewing through a light microscope are prepared from thin slices of small, firm onions. The orientation of the cells under a light microscope can increase or decrease their visibility. The more light that is allowed to pass through, the better the resolution becomes.

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Related Questions

  • Q:

    Why don't onion cells have chloroplasts?

    A:

    Onion cells lack chloroplasts because the onion is part of the plant that is not involved in photosynthesis. The part of the plant eaten by humans is called the bulb, and it resides at the base of the plant. The bulb’s primary purpose is energy storage and holding the flower for the second growing season. Growing near the ground, the bulb is in poor position to collect sunlight.

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  • Q:

    Why is chloroplast important?

    A:

    Chloroplasts are important because they are the sites where photosynthesis occurs. Photosynthesis is the process in which chemical energy is obtained by converting solar energy.

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  • Q:

    What is a plant node?

    A:

    A plant node, also known as a leaf node or stem node, is the part of the plant that causes leaf growth. Nodes are located along the plant's stem. Finding plant nodes is important to effective pruning maintenance and also to regenerating plants by planting new roots.

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  • Q:

    How do plant and animal cells differ?

    A:

    Plant cells differ from animal cells in their possession of chloroplasts, a cell wall, a large central vacuole and their relative lack of an internal cytoskeleton. Plant cells gain their form and rigidity from the pressure of their large, water-filled vacuoles against their tough cellulose cell walls. Animal cells must rely on protein-based skeletal structures within the cell to maintain their shape.

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