Page 1: Abiotic Factors

Definition of Abiotic Factors

• Distribution, abundance, growth, and reproduction of organisms are controlled by environmental factors.

• Environmental factors are external forces, substances, or conditions that affect the life of organisms.

Page 2: Importance of Light

Role of Light

• Critical for life on Earth.

• Producers use light for photosynthesis, providing food for life.

• Light intensity is influenced by:

  • Water vapor

  • Dust particles

  • Geographic location (latitude)

Seasonal Variations

• Light availability changes with seasons:

  • Summer

  • Fall/Autumn

  • Winter

  • Spring

Page 3: Effect of Light on Plants

Light-Driven Responses

1. Heliotropism/Phototropism: Sunlight effects on plant movement.

2. Long Day Plants: Bloom when light exceeds 12 hours/day (e.g., Onion, Beetroot).

3. Short Day Plants: Bloom when light is less than 12 hours/day (e.g., Tobacco, Chrysanthemum).

4. Day Neutral Plants: Bloom with little response to light duration (e.g., Cucumber, Potato).

Impacts of Light on Plant Physiology

• Affects chlorophyll synthesis, chloroplast positioning, photosynthesis, respiration, transpiration, hormone production, flower/fruit development, and pigmentation.

Page 4: Effect of Light on Animals

Metabolic Influence

• Light enhances metabolic rates, enzyme activity, and mineral solubility; decreases gas solubility at high intensities.

Reproductive Influence

• Many animals require light to activate gonads and initiate reproductive cycles.

Developmental Effects

• Light can accelerate or retard development depending on the species (e.g., promotes salmon larvae, inhibits Mytilus larvae).

Pigmentation Effects

• Influences skin pigmentation in various species; lack of light can lead to loss of pigmentation.

Protoplasm Effects

• Ultraviolet rays can excite and ionize protoplasm, potentially causing mutations.

Page 5: Light and Animal Behavior

Phototaxis

• Orientation of animals towards (positive phototaxis) or away (negative phototaxis) from light sources.

Photoperiodism

• Organisms exhibit rhythms matching environmental light and darkness: cycles consist of periods (rise and fall) and amplitudes (fluctuations).

• Understanding photoperiodism is crucial for studying biological clocks in various species.

Page 6: Biological Rhythms

Examples of Rhythms

• Annelids exhibit a 29-day cycle.

• Insects display a 24.8 hours or 12.8 hours cycle.