Characteristics of Living Organisms

Characteristics of Living Organisms

1. Unifying Characteristics of Living Organisms

To determine if an entity is 'living', it must meet specific criteria common to all living organisms. These criteria can be summarized using the acronym MRS C GREN, standing for:

  • Movement

  • Respiration

  • Sensitivity

  • Control

  • Growth

  • Reproduction

  • Excretion

  • Nutrition

All living entities must perform these life processes; otherwise, they can be classified as dead or non-living. For example, viruses are classified as non-living particles or agents.

2. Nutrition

2.1. Importance of Nutrition

Organisms must obtain food to generate energy and acquire the necessary materials for growth and development. This energy is crucial for various life processes such as movement and excretion.

2.2. Nutrition in Plants

  • Plants produce their own food through photosynthesis using sunlight, carbon dioxide, and water to synthesize oxygen and glucose.

2.3. Nutrition in Animals

  • Animals consume other living organisms to obtain energy and essential nutrients. They utilize digestion to break down larger complex molecules into simpler ones. These simpler molecules are absorbed into the bloodstream and utilized for processes such as respiration, which provides energy and supports growth and repair.

3. Respiration

3.1. Definition and Process

Respiration is a chemical process fundamental to all living organisms for energy production. Energy is released from glucose in two forms:

  • Aerobic respiration: occurs in the presence of oxygen.

  • Anaerobic respiration: occurs in the absence of oxygen.

Both processes ultimately lead to the production of carbon dioxide and water as waste products, with energy being transferred in the form of ATP.

4. Excretion

4.1. Definition and Need for Excretion

Excretion is the removal of toxic materials and substances produced from metabolic reactions in living cells. Waste products that must be eliminated to maintain health include:

  • Carbon dioxide from aerobic respiration.

  • Water from aerobic respiration and other reactions.

  • Urea, containing nitrogen from protein breakdown.

4.2. Excretion in Humans

Waste products expelled by humans include carbon dioxide and urea.

4.3. Excretion in Plants

Plants release:

  • Oxygen during photosynthesis.

  • Carbon dioxide during respiration.

5. Sensitivity and Response to Surroundings

5.1. Sensitivity

Sensitivity entails the ability of organisms to detect and respond to environmental stimuli. This capability enhances survival chances.

5.2. Sensitivity Responses in Animals

Humans utilize a nervous system composed of receptors, neurons, and effectors to detect and respond to stimuli via electrical impulses. The endocrine system also responds to stimuli through hormones in the bloodstream.

5.3. Sensitivity Responses in Plants

Plant responses are typically slower than animals and are regulated by chemicals.

6. Movement

6.1. Definition of Movement

Movement refers to actions by organisms that result in a change of position or location. Animal movement from one place to another is called locomotion.

6.2. Plant Movement

While plants cannot relocate, they can change orientation. For example, sunflowers exhibit movement by tracking the sun throughout the day.

7. Control

7.1. Homeostasis

Living organisms must regulate their internal environments within specific limits, a process known as homeostasis.

7.2. Homeostasis in Humans

  • Thermoregulation is the control of body temperature, typically maintained at 37°C. If temperature rises, mechanisms like sweating or vasodilation will prompt a return to optimal conditions.

  • Another mechanism is osmoregulation, in which water levels are controlled.

7.3. Homeostasis in Plants

Plants employ transpiration to maintain temperature and facilitate water loss from stomata on leaves.

8. Reproduction

8.1. Importance of Reproduction

Reproduction is essential for the survival of populations and species, leading to the creation of more individuals of the same kind.

8.2. Types of Reproduction

  1. Sexual Reproduction

    • Involves fusion of male and female gametes (sperm and egg in humans, pollen grains and ovules in plants). The resulting zygote contains DNA from both parents.

  2. Asexual Reproduction

    • Involves a single parent creating a clone via processes such as mitosis.

    • Common in bacteria and can occur in plants through natural or artificial methods, such as cuttings.

9. Growth

9.1. Definition of Growth

Growth is characterized by a permanent increase in size.

  • In animals, growth occurs from the zygote stage to adulthood.

  • In plants, growth is a continuous process with the development of new shoots and leaves.

10. Common Features: Eukaryotic Organisms

10.1. Definition and Groups

Eukaryotic organisms are categorized into:

  • Plants

  • Animals

  • Fungi

  • Protoctists

Eukaryotes can be unicellular or multicellular. They possess cells containing a nucleus with a distinct membrane.

10.2. Eukaryotic Cells

  • Comparison between animal and plant cells showing similarities and differences in structure, including the presence or absence of membranes and organelles.

11. Common Features: Prokaryotic Organisms

11.1. Definition

Prokaryotic organisms include bacteria, which are always unicellular with no membrane-bound nucleus. Genetic material is in the cytoplasm as a single, circular chromosome of DNA.

11.2. Characteristics of Bacteria

Biological characteristics include:

  • Microscopic size

  • Presence of cell walls, membranes, cytoplasm, and plasmids

  • No mitochondria or membrane-bound organelles.

11.3. Types of Pathogens

  • Bacteria: Example is Pneumococcus which causes pneumonia.

  • Fungi: Commonly infects plants; specific species can be pathogenic.

  • Protoctists: Such as Plasmodium, which causes malaria.

  • Viruses: Are not categorized as living due to their parasitic nature and inability to function independently.

11.4. Examples of Viruses

  1. Tobacco Mosaic Virus (TMV): Affects numerous plants, leading to discolored leaves.

  2. HIV: Causes AIDS and is transmitted through bodily fluids.

  3. Influenza Virus: Infects humans resulting in flu-like symptoms.

12. Pathogen Transmission and Impact

12.1. Tobacco Mosaic Virus

  • Effects include stunted growth due to disrupted photosynthesis. Control measures include maintaining field hygiene.

12.2. HIV

  • Symptoms include flu-like illness and can lead to AIDS if untreated.

12.3. Influenza Virus

  • Infects respiratory cells, resulting in high infectivity and symptoms like fever and fatigue.

By understanding these characteristics and processes, students can gain insights into the diversity of life and the fundamental principles underlying biological functioning.