- Growth in an organism is the increase in the number of cells and cell size. There are three ways growth can be measured:
- Size: height, width, length, circumference
- Wet mass: the mass of the organism including all the water in the body. It can vary from day to day.
- Dry mass: Mass of an organism with no water in its body. It can only be measured once the organism is dead. It can be dried out in a hot oven and weighed.
- Growth charts are used to assess a child’s growth over time so that an overall pattern in development can be seen and any problems highlighted (e.g. obesity, malnutrition, dwarfism etc.)
- For example, a baby’s growth is monitored after birth to check they are growing normally. They are plotted onto percentile charts so they can be compared with other babies.
- For example a baby in the 75th percentile means 75% of babies his age are lighter than him and 25% are heavier.
- There is usually no concern unless the baby’s size is above the 98th percentile or below the 2nd
Growth in plants
- Plants grow throughout their lives. There are three processes which occur:
- Cell differentiation: cells change to become specialised for its job.
- Cell division: by mitosis.
- Cell elongation: when a plant cell expands making the cell bigger so the plant can grow (only in plants).
- Plants have meristems (stem cells) behind the tip of their roots and shoots and these can differentiate into any plant cell. These meristems exist throughout the entire plant’s life.
- This is how old trees can keep growing new branches.
Growth in animals
- Animals tend to grow when they’re young and then they reach their full growth and stop growing.
- This means cell division is at a fast rate when they are young but in adults cell division is for repair.
Adults do have stem cells but they have a limited range that they can turn into: blood cells and skeletal tissue. This is why most animals cannot regrow a damaged limb or body part but plants can grow new shoots, roots and leaves.