GROWTH

Growth is defined as a permanent increase in the size of an organism.
Development refers to genetically programmed changes in form, which can be influenced by the environment.
Growth stages in an organism consist of:
- Cell division: Increase in the number of cells.
- Cell enlargement: Increase in size of cells.
- Cell differentiation: Specialization of cells.
Growth can also be observed and measured within populations.

Growth of organisms can be measured by various indicators, including:
- Length
- Height
- Wet mass
- Dry mass
- Surface area
- Number of leaves
- Circumference
Growth can be represented graphically by plotting growth parameters on the y-axis against time on the x-axis, creating a growth curve.

In certain organisms, growth is uniform across most parts throughout life (e.g., fish, some insects).
In other organisms, different body parts grow and develop at varying rates (e.g., mammals).
Focus will include:
- Growth in insects
- Growth in humans
- Growth in plants
- Growth in populations

Characterized by a gradual transition from larva to adult.
Larvae undergo several moults, each termed an instar, with the insect referred to as a nymph.
Each nymph stage becomes larger and more similar to the adult, with functional wings only in the adult stage.
Examples of insects: locusts, grasshoppers, cockroaches.

Eggs hatch into miniature, sexually immature nymphs.
Initially, the cuticle/exoskeleton is soft; soon it hardens into a rigid exoskeleton.
- The hardened cuticle restricts size/length increase, but dry mass grows through cell division.
At the end of each instar, the exoskeleton splits and is shed (ecdysis/moulting), allowing the nymph to grow in length while the new exoskeleton is soft.
Just before the final instar ends, sexual organs develop and wings are nearly formed.
The adult insect emerges fully developed after the final moult, initiating the life cycle again upon mating and fertilization of eggs.

Life cycle stages differ significantly; the intermediate stages do not resemble the adult.
No moulting occurs during these transitions.
Stages include egg, larva, pupa, and adult.
Common examples: butterflies, houseflies, mosquitoes.

Eggs are laid in environments conducive to warmth, moisture, and access to food.
Larvae emerge and actively seek food, facilitating rapid growth.
The pupal stage involves no feeding, with internal rearrangement occurring in the pupal case.
The adult emerges as the pupal case splits, starting the cycle anew after mating and egg-laying.

Epicotyl: The embryonic shoot above the cotyledons that develops into leaves, elongating during hypogeal germination.
Hypocotyl: The section below the cotyledon attachment, developing into the radicle, elongating during epigeal germination.
Tegmen: Inner seed coat.

Seeds require:
- Water
- Oxygen
- Suitable temperature
Water enters through the micropyle, activating enzymes that break down stored food:
- Proteins → amino acids
- Starch → simple sugars (e.g., glucose)
- Lipids → fatty acids and glycerol
Glucose, fatty acids, and glycerol are utilized in aerobic respiration and for cellulose formation at the tips of the embryonic root.

Germination is the transition of a seed into a seedling.
- Epigeal germination: Cotyledons expand above ground, become photosynthetic (e.g., red bean).
- Hypogeal germination: Cotyledons remain below ground, non-photosynthetic (e.g., lentils).

A population is a group of organisms of the same species sharing a specific area.
Population size can increase or decrease based on environmental conditions.
Growth occurs in phases, depicted in a sigmoid (S-shaped) growth curve with five phases observed.

Lag phase: Minimal growth.
Log phase: Birth rates exceed death rates, leading to rapid growth.
Decelerating phase: Growth slows; birth rate still exceeds death rate but by a lesser margin.
Stationary phase: Birth rate equals death rate.
Phase of decline/Death: Death rates exceed birth rates.

Human populations are influenced by the same factors as other organisms (e.g., disease, space, food, water).
However, humans can modify environments (e.g., building skyscrapers, boats) to reside in previously inhospitable areas.
Agricultural technology has increased food production capacity, reducing scarcity.
Medical advancements have improved life expectancy and reduced infant mortality, offsetting the impact of diseases.
Superior weaponry has led to the domination of larger animals, eliminating natural predators in human populations.

Increased population correlates with higher pollution, resource exploitation, and global issues (e.g., climate change).
Extinction rates among organisms are escalating.
Natural habitats are being compromised for housing and agricultural development.
Human interventions in ecosystems through pet trading, pest control, and overhunting are disrupting ecological balance.

Describe four methods to control mosquito populations (including one biological control method).
Describe four methods for controlling housefly populations.
Discuss the importance of managing these populations.