#127 Growth and development
Growth - permanent increase in size and dry mass, by an increase in cell number or cell size or both.
Development - increase in complexity
Development - increase in complexity
1. Growth
- due to an increase in cells, produced by mitosis.
- controlled by hormones (in animals) and growth substance like auxins (in plants).
Dry mass
Example: Changes of dry mass during the growth of a plant from a seed.
- due to an increase in cells, produced by mitosis.
- controlled by hormones (in animals) and growth substance like auxins (in plants).
Dry mass
- Often used as a measure of growth, because wet mass varies from day to day (e.g. plant will take up more water on a wet day than on a dry day, but the water does not all become part of the biomass – living material of the plant).
- Obtained by drying out the organism in an oven (killing it).
- Many individual have to be germinated at the same time and grown in the same conditions.
- Samples are dried at various times during the growth period.
Example: Changes of dry mass during the growth of a plant from a seed.
- ↓ slightly when the seed germinates, at day 2 (some of the stores in the cotyledon are being used in respiration).
- ↑ when the plumule stars to photosynthesise, and foliage leaves form to continue the process.
- ↓ at the end of the growth period (loss of seeds and fruits; leaves die).
2. Development
- increase in complexity of an organism as it grows. As the number of cells increases, they become differentiated (specialized for different tasks).
- change in shape to adapt for a specific function.
Examples:
- nerve cells are very elongated and can transmit electrical impulses
- xylem cells are elongated and lose their cell contents, with the cell walls becoming lignified so the cells conduct water efficiently.
Try this
1. Figure below shoes a section through a seed of a dicotyledon.
- ↑ when the plumule stars to photosynthesise, and foliage leaves form to continue the process.
- ↓ at the end of the growth period (loss of seeds and fruits; leaves die).
2. Development
- increase in complexity of an organism as it grows. As the number of cells increases, they become differentiated (specialized for different tasks).
- change in shape to adapt for a specific function.
Examples:
- nerve cells are very elongated and can transmit electrical impulses
- xylem cells are elongated and lose their cell contents, with the cell walls becoming lignified so the cells conduct water efficiently.
Try this
1. Figure below shoes a section through a seed of a dicotyledon.
i) What is the role of part A? [1 mark]
ii) What do parts B and C of the seed develop into after germination? [2 marks]
2. Figure below shows changes in mass of sets of pea seeds as they germinate and grow into seedlings, after germination set B was grown in the dark and set Q in the light.
ii) What do parts B and C of the seed develop into after germination? [2 marks]
2. Figure below shows changes in mass of sets of pea seeds as they germinate and grow into seedlings, after germination set B was grown in the dark and set Q in the light.