Mitosis root tip squash - Required practical A level Biology. Method explained & exam questions

Summary

In this informative video, Miss Estrich guides viewers through the mitosis root tip squash practical, detailing the essential equipment and step-by-step method required to prepare and analyze stained cell slides. She explains the significance of using specific materials, such as hydrochloric acid for softening root tissues and acetic orcein for staining chromosomes. The video also emphasizes safety measures, observations of cell stages during mitosis, and how to calculate the mitotic index. Common exam questions related to the practical are discussed, ensuring viewers are well-prepared for assessments.

Takeaways

• 😀 The practical involves preparing a stained squash of root tip cells to observe mitosis.
• 😀 Key equipment includes hydrochloric acid, acetic orcein stain, a mounted needle, and the root tip of an onion or garlic.
• 😀 Hydrochloric acid softens root tissues, making it easier to squash them.
• 😀 The root tip used should be the last five millimeters, where active cell division occurs.
• 😀 The root tips need to be soaked in hydrochloric acid and heated to 60°C for 10 minutes to soften the cells.
• 😀 Staining with acetic orcein makes chromosomes visible under the microscope.
• 😀 A gentle squashing technique is crucial to create a thin layer of cells for optimal viewing.
• 😀 Safety precautions include using goggles when handling hydrochloric acid and cutting away from the body with the scalpel.
• 😀 The mitotic index is calculated as the number of cells in mitosis divided by the total number of cells, multiplied by 100.
• 😀 Exam questions often focus on the rationale behind equipment use, methods, and safety precautions.

Q & A

What is the main purpose of the mitosis root tip squash practical?

The main purpose is to prepare a stained squash of cells from the root tip of an onion or garlic and to calculate the mitotic index, allowing observation of cells undergoing mitosis.

Why is hydrochloric acid used in this experiment?

Hydrochloric acid is used to soften the root tissues, making it easier to squash the cells for observation under a microscope.

What role does acetic orcein play in the practical?

Acetic orcein is a stain that colors the chromosomes in the nucleus, making them visible under the microscope.

What part of the root is used for the squash, and why?

The last five millimeters of the root tip are used because this is the region where cell division, or mitosis, is actively occurring.

What is the procedure after the root tip is softened in hydrochloric acid?

After softening, the acid is poured off, and the root tip is rinsed in distilled water to remove any remaining acid before staining.

How can air bubbles be prevented when placing the cover slip on the slide?

Using a mounted needle to gently lower the cover slip helps prevent air bubbles from forming under the slip.

What is the significance of squashing the cells gently?

Squashing gently creates a thin layer of cells, allowing light to pass through for better visibility under the microscope. Applying too much pressure can break the cover slip or damage the cells.

What are some hazards associated with this practical, and how can they be mitigated?

Hazards include cuts from the scalpel and irritation from hydrochloric acid. These can be mitigated by cutting away from the body and wearing goggles when handling acid.

How is the mitotic index calculated?

The mitotic index is calculated by dividing the number of cells in mitosis by the total number of cells and then multiplying by 100 to get a percentage.

What should you do to ensure an accurate count when calculating the mitotic index?

To ensure accuracy, examine multiple fields of view and count cells from several areas of the slide to get a representative sample of the entire root tip.