Note to teacher: Have students read through the first two sections of Background Information, Mitosis and Growth and Human Chromosomes, and review the questions and answers provided for each section to ensure understanding.

GET FOCUSED

Mitosis is the process that cells use to make exact copies of themselves. It happens so our bodies can grow, repair injuries, and replace old or damaged cells. During mitosis, one cell divides to form two new cells, each with the same number of chromosomes (genetic information in the form of DNA) as the original. The process has several steps: the DNA is copied, the chromosomes line up in the middle, they are pulled apart, and then the cell splits into two. This way, every new cell has the same exact instructions to do its job in the body!

Inform students that the Investigation is designed to help them to answer the following questions:

• What are the major differences between asexual and sexual reproduction? In your answer, describe both the advantages and disadvantages of asexual and sexual reproduction. Do humans reproduce asexually or sexually?Asexual reproduction involves one parent and produces offspring that are genetically identical. It’s quick and doesn’t require a mate, but it doesn’t create variety. Sexual reproduction involves two parents and creates genetically different offspring. It takes more time and energy, but increases genetic diversity. Humans reproduce sexually.
• Why is it important that each new cell gets an exact copy of the DNA during mitosis? Each new cell needs the same instructions to work properly. If the DNA isn’t copied exactly, the new cell might not function correctly, which could lead to problems in growth or repair.
• How do chromosomes ensure that genetic information is accurately passed from one cell to another during cell division? Chromosomes organize the DNA and help it separate evenly during mitosis. They make sure each new cell gets a full and correct set of instructions.
• How does mitosis help organisms grow and heal? Mitosis makes new cells that replace old or damaged ones. It also adds more cells so the organism can grow bigger.

As a class or independently as homework, have students read the first two sections of the Background Information section, Reproduction and Growth and Human Chromosomes.

Extended answers to the following questions are found on the Teacher Portal PostLab page. Go over these concepts and questions as a class prior to the lab to encourage students to look for answers as they proceed through the Lab and PostLab. In PostLab, you may review the questions again to address any misconceptions.

Mitosis and Meiosis

• What is the primary purpose of mitosis? To make new, identical cells for growth, repair, and replacing old cells.
• What is the number of daughter cells produced in mitosis? Two daughter cells.
• How does the chromosome number of daughter cells compare to the parent cell in mitosis? They have the same number — in humans, that’s 46 chromosomes.
• In which types of cells does mitosis occur? Body cells (also called somatic cells), like skin, bone, and muscle.
• What are the main stages of mitosis? Prophase, Metaphase, Anaphase, Telophase (and followed by Cytokinesis).
• Why is maintaining the full chromosome number important in mitosis? Because it keeps the genetic information complete, so the new cells can work just like the original one.
• Summarize the functions of mitosis in one sentence. Mitosis allows organisms to grow, heal, and replace cells by creating two identical copies of a parent cell.

Human Chromosomes

• How many chromosomes are found in almost every human cell, and how are they organized? There are 46 chromosomes, arranged in 23 pairs.
• Where do humans inherit their chromosomes from, and how is this reflected in chromosome pairs? One chromosome of each pair comes from the mother, and the other from the father.
• How is the 23rd pair of chromosomes different between males and females? Females have two X chromosomes (XX); males have one X and one Y chromosome (XY).
• Where do humans inherit their chromosomes, and how is this reflected in chromosome pairs? One chromosome of each pair comes from the mother, and the other from the father.
• What is the significance of organizing chromosomes into pairs for scientific studies? It helps scientists look for abnormalities or missing pieces in chromosomes and better understand genetic disorders.
• How do scientists use high-magnification slides to study chromosomes, and what can they learn from them?  They use microscopes to view stained chromosomes during cell division. They can see size, shape, and number, which helps diagnose conditions and understand genetics.

Note: These concepts are integrated into the Student Guide Backgrounds and CELL Introduction and are used to deepen students’ comprehension of the big ideas. You will find succinct answers to these questions in the PostLab; reading through these questions in PreLab will help students focus on important information during the Investigation.