IGCSE Biology Notes

Characteristics: To be considered 'living', an organism must meet certain criteria collectively referred to as MRS C GREN:
- Movement: Ability of an organism to change position or place.
- Respiration: Process of breaking down glucose for energy (aerobic vs anaerobic).
- Sensitivity: Ability to respond to external stimuli (environmental changes).
- Control: Maintaining internal conditions (homeostasis).
- Growth: Increase in size or mass.
- Reproduction: Ability to produce offspring (asexual vs sexual reproduction).
- Excretion: Removal of toxic waste products.
- Nutrition: Energy acquisition through feeding (autotrophs vs heterotrophs).
Viruses: Classified as non-living as they lack the MRS C GREN criteria.

Nutrition:
- Autotrophic (e.g., plants) produce food via photosynthesis: ext{6CO}2 + ext{6H}2 ext{O} ightarrow ext{C}6 ext{H}{12} ext{O}6 + ext{6O}2
  - Uses sunlight, carbon dioxide, water to produce glucose and oxygen.
- Heterotrophic (e.g., animals), must consume organic matter.
  - Involves digestion to convert complex molecules into simpler forms for energy.
Respiration:
- Process to release energy from glucose, can be:
  - Aerobic (with oxygen), producing ext{CO}2 and ext{H}2 ext{O}.
  - Anaerobic (without oxygen), also produces waste but in different forms.
- Confusion between respiration (energy releasing) and gas exchange (oxygen in, carbon dioxide out).

Definition: Removal of toxic byproducts from metabolic reactions.
- In Animals:
  - Waste includes carbon dioxide, water, and urea.
- In Plants:
  - Waste includes oxygen from photosynthesis, excess water, and CO2.

Sensitivity: The ability to detect and respond to stimuli.
- In Animals:
  - Nervous system allows quick response through electrical impulses.
  - Endocrine system uses hormones to influence responses.
- In Plants:
  - Responses are chemical and slower (e.g., phototropism towards light, geotropism towards gravity).

Movement: Action that changes position (locomotion in animals, orientation in plants like sunflowers).
Control: Homeostasis necessary for survival; examples include:
- Thermoregulation: Maintaining ideal body temperature at 37°C in humans.
- Transpiration in plants maintains temperature through water loss.

Reproduction: Essential for species survival.
- Sexual Reproduction: Involves two gametes (sperm and egg) combining genetic material.
- Asexual Reproduction: Involves a single parent (e.g., mitosis, cloning).
Growth: Permanent size increase; differences between animals (growth until maturity) and plants (continuous growth).

Classification System (Five Kingdoms):
- Animals
- Plants
- Fungi
- Protoctists
- Prokaryotes (bacteria).

Common Features:
- Multicellular or single-celled with membrane-bound nuclei.
- Includes animals (lack cell walls, feed on organics) and plants (have cell walls, undergo photosynthesis).

Characteristics:
- Always single-celled, lack a nucleus, smaller than eukaryotes.
- E.g., bacteria: can be pathogenic or beneficial, utilize various modes of nutrition.

Definition: Microorganisms that cause diseases.
- Includes bacteria, fungi, protoctists, and viruses.
- Examples of diseases: Tuberculosis (bacterial), athlete's foot (fungal), malaria (protoctist), flu (viral).

Bacteria: E.g., M. tuberculosis causes TB, N. meningitidis leads to meningitis.
Fungi: E.g., Black Sigatoka affects banana plants, leading to decreased photosynthesis.
Protoctists: E.g., Plasmodium causes malaria; its lifecycle involves mosquitoes.
Viruses: Classified separately from living organisms; require host cells for reproduction (e.g., HIV, influenza).