Characteristics of Living Organisms » Growth and Development in Organisms

What you'll learn this session

Study time: 30 minutes

The difference between growth and development in organisms
How growth is measured in living things
Types of growth patterns (determinate and indeterminate)
Cell division and its role in growth
Growth factors and hormones
Environmental influences on growth and development
Real-world examples of growth and development across different organisms

Introduction to Growth and Development

Growth and development are two of the seven key characteristics of living organisms. While they're related, they're actually quite different processes that work together to transform a single cell into a complex organism like you!

Key Definitions:

Growth: An increase in size and mass due to an increase in cell number or cell size.
Development: The process by which an organism changes from a simple to a more complex form through cell differentiation and specialisation.

🌱 Growth

Growth is all about getting bigger! It happens when:

Cells increase in number through cell division (mitosis)
Cells increase in size
Materials are deposited between cells (like in plant cell walls)

Growth can be measured by changes in height, length, mass, volume, or number of cells.

🔬 Development

Development is about becoming more complex and specialised:

Cells differentiate to perform specific functions
Tissues and organs form from groups of specialised cells
Changes in form and function occur throughout an organism's life

Development isn't always about getting bigger it's about becoming more organised and complex!

Measuring Growth

Scientists use different methods to measure growth depending on the organism they're studying:

💪 Animals

Measured by:

Height/length
Mass (weight)
Volume

🌿 Plants

Measured by:

Height
Stem diameter
Leaf area
Dry mass

🦠 Microorganisms

Measured by:

Population count
Colony diameter
Optical density

Growth Patterns

Not all organisms grow in the same way. There are two main patterns of growth:

🟢 Determinate Growth

This is growth that stops once an organism reaches a certain size or age.

Most animals, including humans, show determinate growth
We grow rapidly during childhood and adolescence, then stop
Growth follows an S-shaped (sigmoid) curve when plotted on a graph
Example: A butterfly grows as a caterpillar, then stops growing once it becomes an adult

🟡 Indeterminate Growth

This is continuous growth throughout an organism's life.

Most plants show indeterminate growth
Some animals like fish and reptiles can grow throughout their lives
Growth is concentrated in specific areas called meristems in plants
Example: Trees can continue growing taller and wider for hundreds of years

Cell Division and Growth

At the cellular level, growth happens through cell division, primarily through a process called mitosis.

The Cell Cycle

The cell cycle is a series of events that leads to cell division and includes:

Interphase: The cell grows, replicates its DNA and prepares for division
Mitosis: The nucleus divides, creating two identical nuclei
Cytokinesis: The cytoplasm divides, creating two separate cells

This process allows organisms to grow by increasing their cell number. In humans, millions of cells divide every second to replace old or damaged cells and enable growth!

Case Study Focus: Human Growth

Human growth doesn't happen at a steady rate throughout life. We experience growth spurts during specific periods:

Infancy (0-2 years): Rapid growth where babies typically triple their birth weight in the first year
Childhood (2-puberty): Steady growth of about 5-7 cm per year
Puberty: A second growth spurt where teens can grow 8-12 cm per year
Adulthood: Growth stops as growth plates in bones close

This pattern shows how growth is regulated by hormones that are released at specific stages of life.

Growth Factors and Hormones

Growth doesn't just happen on its own it's carefully controlled by chemical messengers:

👤 Animal Growth Regulators

Key hormones include:

Growth Hormone (GH): Produced by the pituitary gland, stimulates overall body growth
Thyroid Hormones: Regulate metabolism and are essential for normal growth
Insulin-like Growth Factors (IGFs): Mediate many effects of growth hormone
Sex Hormones: Trigger growth spurts during puberty

🌱 Plant Growth Regulators

Plants use hormones called phytohormones:

Auxins: Promote cell elongation and stem growth
Gibberellins: Stimulate stem elongation and seed germination
Cytokinins: Promote cell division and delay ageing
Ethylene: Controls fruit ripening and leaf fall

Environmental Influences on Growth and Development

Growth and development aren't just controlled by internal factors the environment plays a huge role too!

🌞 Light

Affects:

Photosynthesis in plants
Direction of plant growth (phototropism)
Flowering timing
Vitamin D production in animals

🍔 Nutrition

Affects:

Rate of growth
Final size
Health and development
Immune function

🌡 Temperature

Affects:

Enzyme activity
Metabolic rate
Development speed
Germination in plants

Amazing Growth Facts

The fastest growing plant is bamboo, which can grow up to 91 cm in a single day!
Humans grow about 1 cm taller during sleep and shrink back down during the day due to spinal compression.
The blue whale calf gains about 90 kg per day during its first year of life.
Some bacteria can double their population every 20 minutes under ideal conditions.
The human brain reaches 80% of its adult size by age 2, but continues developing until the mid-20s.

Growth vs Development: Examples in Different Organisms

Metamorphosis: A Dramatic Example of Development

Some animals undergo dramatic changes in form during their life cycle through a process called metamorphosis:

Complete metamorphosis: Insects like butterflies change completely from egg to larva (caterpillar) to pupa (chrysalis) to adult
Incomplete metamorphosis: Insects like grasshoppers develop gradually, with the young looking like smaller versions of adults
Amphibian metamorphosis: Frogs transform from aquatic tadpoles with gills to terrestrial adults with lungs

These transformations involve both growth (increase in size) and development (change in form and function).

🌱 Plant Growth and Development

Plants show fascinating patterns:

Growth occurs at specific regions called meristems
Primary growth makes plants taller (from apical meristems)
Secondary growth makes stems and roots thicker (from lateral meristems)
Development includes germination, vegetative growth, flowering, fruiting and senescence

🧠 Human Brain Development

The brain shows how growth and development differ:

Growth: Brain reaches 80% of adult size by age 2
Development: Neural connections continue forming and being pruned throughout childhood and adolescence
The prefrontal cortex (responsible for decision-making) isn't fully developed until the mid-20s

Summary: Key Points About Growth and Development

Growth is quantitative (increase in size or number) while development is qualitative (increase in complexity)
Growth can be measured in various ways depending on the organism
Growth patterns can be determinate (stops at maturity) or indeterminate (continues throughout life)
Cell division through mitosis is essential for growth
Hormones and growth factors regulate growth and development
Environmental factors like light, temperature and nutrition influence growth rates
Different organisms show unique patterns of growth and development

Understanding growth and development helps us appreciate how living organisms change throughout their lives and adapt to their environments. These processes are fundamental to life itself!

🧠 Test Your Knowledge!