How are new cells produced, and how do cells become specialised and organised into tissues and organs?
The stages of mitosis and its role in growth, repair and maintaining the diploid chromosome number, stem cells and meristems as sources of unspecialised cells, and the specialisation of cells into tissues, organs and systems.
An SQA National 5 Biology answer on producing new cells, covering the stages of mitosis and its role in growth and repair, the diploid chromosome number, stem cells and meristems as sources of unspecialised cells, and the specialisation of cells into tissues, organs and systems.
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What this dot point is asking
The SQA wants you to describe the stages of mitosis and its role in growth and repair and in keeping the diploid chromosome number, explain what stem cells (in animals) and meristems (in plants) are, and describe how cells become specialised and are organised into tissues, organs and systems.
Mitosis and the diploid number
Mitosis is used for growth (making more cells as an organism gets bigger) and repair (replacing damaged or worn-out cells). Because the daughter cells are identical to the parent, the diploid chromosome number is maintained.
The stages of mitosis
Duplication has to come first so that, when the cell splits, each new cell receives a complete, identical set of chromosomes.
Stem cells and meristems
In animals, stem cells provide new cells for the growth and repair of tissues. In plants, the equivalent regions are meristems, where mitosis happens and unspecialised cells are produced that can then differentiate into specialised plant cells, allowing the plant to grow.
Specialisation: cells, tissues, organs and systems
Most cells in a multicellular organism are specialised: their structure suits one particular job. Specialised cells are organised in a hierarchy:
For example, muscle cells form muscle tissue, which (with other tissues) forms the heart, an organ, which is part of the circulatory system.
Examples in context
Example 1. Healing a cut. When you cut your skin, the skin cells around the wound divide by mitosis to make new, identical skin cells that close the gap. This is repair, and it keeps the diploid chromosome number so the new skin works exactly like the old.
Example 2. Stem cells in medicine. Bone marrow transplants give a patient healthy blood stem cells, which can keep dividing and specialise into red and white blood cells. This treats some blood cancers, and relies on the stem cells being unspecialised and able to become different cell types.
Try this
Q1. State the two main roles of mitosis in a multicellular organism. [1 mark]
- Cue. Growth and repair.
Q2. Name the regions in plants where unspecialised cells are produced by mitosis. [1 mark]
- Cue. Meristems.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 style4 marksDescribe the stages of mitosis, and state why the chromosomes must duplicate first.Show worked answer →
A 4-mark answer should give the ordered stages and the reason for duplication.
Before mitosis, the chromosomes duplicate, forming pairs of chromatids. This is so that each new cell can receive a full, identical set of chromosomes.
The chromosomes then line up at the equator (middle) of the cell, attached to spindle fibres.
The spindle fibres pull the chromatids apart to opposite ends of the cell.
Finally the nuclear membrane reforms around each set and the cytoplasm divides, giving two genetically identical daughter cells.
Markers reward (1) duplication into chromatids, (2) lining up at the equator on spindle fibres, (3) chromatids pulled to opposite ends, and (4) two identical daughter cells. The reason for duplication is to keep the diploid chromosome number.
SQA N5 style2 marksExplain what a stem cell is and why stem cells are useful in the body.Show worked answer →
Two ideas are needed: what makes a stem cell special, and its role.
A stem cell is an unspecialised cell that can keep dividing and has the potential to become different types of specialised cell.
Stem cells are useful because they provide new cells for the growth and repair of tissues, replacing cells that are lost or damaged.
Markers reward (1) unspecialised and able to become different cell types, and (2) their role in growth and repair.
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Sources & how we know this
- SQA National 5 Biology Course Specification — SQA (2019)