2.2 Growth and Differentiation

A free GCSE Biology lesson for AQA (8461) from OBA School: how animals and plants grow, where differentiation happens, and how cells build tissues and organs. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe the processes involved in growth: cell division, differentiation and (in plants) cell elongation
• Explain why most animal cells differentiate early, while many plant cells can differentiate all through life
• Describe where meristems are found and what they do
• Describe the levels of organisation from cells to organisms
• Calculate growth rates and percentage increases from data

Key words

• Growth: A permanent increase in size or mass.
• Differentiation: The process by which a cell becomes specialised for a particular job.
• Meristem: Plant tissue, at the tips of roots and shoots, where cells keep dividing by mitosis.
• Cell elongation: Plant cells getting longer as they take in water. A big part of how plants grow.
• Tissue: A group of cells with a similar structure and function working together.

Growth in animals

An animal grows by cell division (mitosis makes more cells) and differentiation (cells become specialised). A fertilised egg divides again and again to form an embryo; its cells then differentiate into the 200 or so types of cell in the human body.

• Most animal cells differentiate at an early stage of development and lose the ability to become other cell types.
• In mature animals, cell division is mainly for repair and replacement, for example new skin cells, blood cells and the lining of the gut.
• Animals stop growing when they reach adult size, and cannot regrow a lost limb.

Key fact: Uncontrolled cell division can form a mass of cells called a tumour. Cancer is caused by changes in cells that lead to uncontrolled growth and division.

Growth in plants

Plants grow by cell division, cell elongation and differentiation. Cell division happens only in meristems at the tips of shoots and roots (and in rings in stems that grow wider). New cells then take in water and get longer, pushing the tip forward, before they differentiate.

• Many plant cells keep the ability to differentiate throughout the life of the plant.
• This is why a cutting (a piece of stem) can grow new roots, and why gardeners can make clones of plants cheaply.
• Plants keep growing all their lives, mainly in height (at shoot tips) and in root length.

From cells to organisms

Differentiated cells work together in groups. Large multicellular organisms are organised in levels.

• When do most cells differentiate?; Animals early in development; Plants throughout life
• Where does cell division happen?; Animals all over the body, mainly for repair; Plants mainly in meristems at root and shoot tips
• Is cell elongation important?; Animals no; Plants yes, a major part of growth

Measuring growth

Growth can be measured as an increase in length, height or mass. The rate of growth is the change divided by the time taken.

Worked example: growth rate and percentage increase

A bean root is 12 mm long on day 0 and 33 mm long on day 7.
Increase = 33 − 12 = 21 mm. Rate = 21 ÷ 7 = 3 mm per day
Percentage increase = 21 ÷ 12 × 100 = 175%

Answer: 3 mm per day; a 175% increase

Common mistakes

• Saying plants grow only by cell division. Elongation and differentiation matter too.
• Saying all plant cells divide. Division happens only in the meristems.
• Thinking adult animals have no dividing cells. Cells still divide to repair and replace tissue.
• Working out percentage increase using the final value instead of the starting value.

Revision questions

Try these, then check your answers below each one.

Question 1. Where are meristems found in a plant? (Choose from: In the leaf veins only, At the tips of roots and shoots, In the flowers only, In the xylem.)

Answer: At the tips of roots and shoots

Working: Meristems are at the tips of shoots and roots, where cells divide by mitosis.

Question 2. True or false? Most animal cells differentiate at an early stage of development.

Answer: True

Working: True. Most animal cells become specialised early and then lose the ability to differentiate.

Question 3. In mature animals, what is cell division mainly used for? (Choose from: Growth in height, Repair and replacement of cells, Making new organs, Elongation of cells.)

Answer: Repair and replacement of cells

Working: In adults, mitosis mainly repairs damaged tissue and replaces worn-out cells such as skin and blood cells.

Related lessons

• Previous lesson: 2.1 Cell Division
• Next lesson: 2.3 Stem Cells
• In this chapter: 2.4 Stem Cell Dilemmas

Continue in the full course

This lesson is section 2.2 (AGCBH0202) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.