How do cells divide for growth, and how is growth measured?
The cell cycle and mitosis, the role of mitosis in growth, repair and asexual reproduction, growth in animals and plants, and the use of percentile charts to monitor growth.
A focused answer to Edexcel GCSE Combined Science Topic 2 (CB2), covering the cell cycle and mitosis, the role of mitosis in growth, repair and asexual reproduction, how animals and plants grow, and the use of percentile charts.
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What this dot point is asking
Edexcel wants you to describe the stages of the cell cycle including mitosis, explain the role of mitosis in growth, repair and asexual reproduction, describe how growth happens in animals and plants, and interpret percentile charts used to monitor growth.
The cell cycle
Mitosis is the part of the cycle in which the nucleus divides. The duplicated chromosomes line up in the centre of the cell, then one copy of each is pulled to opposite ends. Finally the cytoplasm and membrane divide (cytokinesis), giving two cells each with the full set of chromosomes.
Why mitosis matters
Mitosis is used for:
- Growth of a multicellular organism from a fertilised egg.
- Repair and replacement of damaged or worn-out cells.
- Asexual reproduction, where one parent produces genetically identical offspring (for example in some plants and simple organisms).
Growth in animals and plants
In animals, growth happens mainly by cell division followed by differentiation, where cells become specialised. Most cell division stops once an animal is fully grown, although some cells (such as those replacing skin and blood) keep dividing.
In plants, growth happens in two stages: cell division at the tips of roots and shoots (in regions of dividing cells called meristems), then cell elongation, where the new cells get longer. Plant cells keep the ability to divide and differentiate throughout life, which is why cuttings can grow into whole new plants.
The cell cycle is normally tightly controlled. If the control is lost and cells divide uncontrollably by mitosis, they can form a lump called a tumour. This shows why the rate of mitosis matters: too little and tissues cannot grow or repair, too much and abnormal growths can form. Differentiation also matters during growth, because cells must not only multiply but also become the right specialised types, such as muscle, nerve or xylem cells, in the right places.
Monitoring growth with percentile charts
Doctors plot a baby's mass, length or head circumference on a percentile chart. A point on the 50th percentile is the median for that age. The chart compares one child against a large sample, and a child that suddenly crosses several percentile lines may need investigation.
Try this
Q1. Name the type of cell division that produces two genetically identical cells. [1 mark]
- Cue. Mitosis.
Q2. State two uses of mitosis in a multicellular organism. [2 marks]
- Cue. Any two of: growth, repair or replacement of cells, asexual reproduction.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20194 marksDescribe what happens during the cell cycle to produce two genetically identical daughter cells.Show worked answer →
A 4-mark describe question rewards the stages in order.
During the longest stage (interphase), the cell grows and makes more sub-cellular structures such as mitochondria and ribosomes, and the DNA is copied so each chromosome becomes two identical strands (2 marks). During mitosis, the chromosomes line up in the middle of the cell, and one copy of each is pulled to each end (1 mark). The cytoplasm and cell membrane then divide to form two daughter cells, each genetically identical to the parent (1 mark).
Markers reward DNA replication before division, the separation of chromosome copies, and the two identical cells.
Edexcel 20213 marksA baby's mass is plotted on a growth chart and follows the 75th percentile line. Explain what the 75th percentile means and why percentile charts are useful.Show worked answer →
A 3-mark interpretation question on percentile charts.
The 75th percentile means that 75% of babies of that age have a mass below this value and 25% have a mass above it (1 mark). Percentile charts are useful because they let doctors compare a baby's growth with a large sample of children of the same age and sex (1 mark), and a sudden change in which percentile a baby follows can be an early sign of a health or feeding problem (1 mark).
Markers reward the percentage interpretation and the idea of monitoring growth against a population to spot problems.
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Sources & how we know this
- Edexcel GCSE (9-1) Combined Science (1SC0) specification — Pearson (2016)