Biology: Nature and Variety of Organisms

Plants, Animals and Fungi

  • Living organisms are categorized based on shared features.
    • Key groups include plants, animals, and fungi.

Features of Plants, Animals, and Fungi

  • Eukaryotic Organisms
    • All three groups are composed of eukaryotic cells.
    • Eukaryotic cells are characterized by having a nucleus.

Characteristics of Plants

  1. Multicellularity: Plants are multicellular organisms.
  2. Presence of Chloroplasts: Includes chloroplasts which enable photosynthesis.
  3. Cell Wall Composition: Cells possess cell walls made of cellulose.
  4. Carbohydrate Storage: Store carbohydrates primarily as sucrose or starch.

Characteristics of Animals

  1. Multicellularity: Animals are also multicellular organisms.
  2. Lack of Chloroplasts: They do not possess chloroplasts and cannot perform photosynthesis.
  3. Absence of Cell Walls: Animal cells lack cell walls.
  4. Nervous Coordination: Majority exhibit nervous coordination, allowing rapid responses to environmental changes.
  5. Mobility: Animals have the ability to move from place to place.
  6. Carbohydrate Storage: They typically store carbohydrates in the form of glycogen.

Characteristics of Fungi

  1. Cellularity: Some fungi are unicellular while others are multicellular, forming a body known as mycelium composed of hyphae (thread-like structures).
  2. Cell Wall Composition: Their cell walls are made of chitin.
  3. Inability to Photosynthesize: Fungi cannot perform photosynthesis.
  4. Nutritive Method: Most fungi engage in saprotrophic nutrition, where they secrete extracellular enzymes to digest food prior to absorption.
  5. Carbohydrate Storage: Fungi can also store carbohydrates as glycogen.

Examples of Organisms

  • Plants: Flowering plants like cereals (e.g., maize), herbaceous legumes (peas, beans).
  • Animals: Mammals (humans), insects (houseflies, mosquitoes).
  • Fungi:
    • Yeast: A unicellular fungus.
    • Mucor: A multicellular fungus with mycelium and hyphae.

Protoctists, Bacteria, and Viruses

  • Additional groups beyond plants, animals, and fungi include protoctists, bacteria, and viruses.

Characteristics of Protoctists

  • Eukaryotic Nature: Protoctists are classified as eukaryotic organisms.
  • Cell Structure: Can be single-celled like certain algae or resemble animal cells like amoeba.

Characteristics of Bacteria

  • Prokaryotic Nature: Bacteria are prokaryotic organisms, meaning they consist of single prokaryotic cells.
  • Lack of Nucleus: Bacteria do not contain a nucleus and possess a circular chromosome of DNA.
  • Feeding Mechanism: Some may photosynthesize; most feed on other organisms, both living and dead.

Characteristics of Viruses

  • Nature: Viruses are not classified as cells and are smaller than bacteria.
  • Replication: Viruses can only reproduce inside living cells, acting as parasites.
  • Structure: Composed of a protein coat surrounding genetic material (either DNA or RNA).
  • Diversity: Viruses exhibit a vast array of shapes and sizes.

Examples of Organisms

  • Protoctists: Chlorella (plant-cell-like), Amoeba (animal-cell-like).
  • Bacteria:
    • Lactobacillus bulgaricus: Used in yogurt production, rod-shaped.
    • Pneumococcus: Spherical bacterium, causes pneumonia.
  • Viruses:
    • Influenza Virus: Causes flu.
    • Tobacco Mosaic Virus: Affects tobacco plants by disrupting chloroplast production.
    • HIV: Causes AIDS.

Pathogens

  • Definition of Pathogens: Organisms that cause disease, including certain fungi, protoctists, bacteria, and viruses.
  • Specific Examples of Pathogenic Organisms:
    • Protoctist: Plasmodium, causes malaria.
    • Bacterium: Pneumococcus, causes pneumonia.
    • Viruses: Influenza virus and HIV.

Key Characteristics of Living Organisms

  • All living organisms share eight fundamental characteristics:
    1. Nutrition: Organisms require nutrients for energy and growth, including proteins, fats, carbohydrates, vitamins, and minerals.
    2. Respiration: Energy is released from food through the process of respiration.
    3. Excretion: Waste removal, such as carbon dioxide and urine, is an essential process known as excretion.
    4. Response to Surroundings: Organisms can react to environmental changes.
    5. Movement: Organisms move towards essential resources like water and food, while avoiding dangers such as predators and toxins.
    6. Homeostasis: Ability to regulate internal conditions, including temperature and water balance.
    7. Reproduction: Organisms must reproduce to maintain their species.
    8. Growth and Development: All organisms, regardless of size, grow and transition to their adult forms.

Properties of Solids, Liquids, and Gases

  • Differentiation of states of matter is based on various properties:

Properties of Solids

  1. Volume: Solids have a definite volume.
  2. Shape: Solids maintain a fixed shape.
  3. Density: Typically have high density (heavy relative to size).
  4. Compressibility: Not easily compressed.
  5. Flow: Solids do not flow.

Properties of Liquids

  1. Volume: Liquids possess a definite volume but match the shape of their containers.
  2. Density: Usually exhibit medium density.
  3. Compressibility: Not easily compressed.
  4. Flow: Liquids flow easily.

Properties of Gases

  1. Volume: Gases do not have a definite volume and take on the volume of their containers.
  2. Shape: Gases take the shape of the container.
  3. Density: Have very low density (light relative to size).
  4. Compressibility: Gases are easily compressed.
  5. Flow: Gases flow easily.