Organisms and Life Processes

Organisms and Life Processes

The Variety of Living Organisms

Learning Objectives

• Understand the difference between eukaryotic and prokaryotic organisms.
• Describe the features common to plants and recognize examples of flowering plants such as maize, peas, and beans.
• Describe the features common to animals and recognize examples such as mammals and insects.
• Describe the features common to fungi and recognize examples such as Mucor and yeast.
• Describe the features common to protoctists and recognize examples such as Amoeba, Chlorella, and Plasmodium.
• Describe the features common to bacteria and recognize examples such as Lactobacillus bulgaricus and Pneumococcus.
• Describe the features common to viruses and recognize examples such as the influenza virus, the HIV virus, and the tobacco mosaic virus.
• Understand the term 'pathogen' and know that pathogens may include fungi, bacteria, protoctists, or viruses.

Overview

• There are over ten million species of organisms alive on Earth today, with many more extinct.
• Biologists classify organisms into groups based on structure and function.
• Members of each group share common ancestry and similarities in structure and function.

Kingdoms

• The five major groups (kingdoms) of living organisms are:
  • Plants
  • Animals
  • Fungi
  • Protoctists
  • Bacteria

Plants

• All plants are multicellular.
• Plant cells contain chloroplasts and photosynthesize, converting water and carbon dioxide into complex organic compounds using light energy.
• Plant cells are surrounded by a cellulose cell wall.
• Plants make glucose (food) using light energy from CO_2 and water, which is called photosynthesis.
• The storage carbohydrate in plants is starch.
• Sucrose is transported around the plant.
• Examples include maize, peas, and beans.

Animals

• Animals are multicellular organisms.
• Animal cells do not contain chloroplasts, so they do not photosynthesize.
• Animals obtain nutrition by feeding on plants or other animals.
• Animal cells lack a cell wall, allowing them to change shape and move.
• Movement is often coordinated by a nervous system.
• The storage carbohydrate in animal cells is glycogen.
• Animals are divided into two main groups:
  • Invertebrates (no vertebral column or backbone) e.g., insects
  • Vertebrates (with a backbone) e.g., fish, amphibians, reptiles, birds, and mammals
• Insects make up the largest subgroup of animals, accounting for about 60% of all animal species.

Fungi

• Some fungi are multicellular, e.g., mushrooms and molds; others are unicellular, e.g., yeast.
• Fungal cells do not contain chloroplasts, so they do not photosynthesize.
• Fungal cells have cell walls made of chitin, not cellulose.
• Storage carbohydrate is glycogen.

Structure of Fungi

• Mushrooms and toadstools are reproductive structures called fruiting bodies.
• Under the soil, mushrooms have thread-like filaments called hyphae.
• A mold consists of a network of hyphae called a mycelium.
• Molds feed by absorbing nutrients from dead or living material.
• Hyphae secrete digestive enzymes onto the food, breaking it down into soluble substances such as sugars, which are then absorbed.
• This is called saprotrophic nutrition, and the enzymes are called extracellular enzymes.

Mucor

• The hyphae of Mucor have cell walls surrounding their cytoplasm.
• The cytoplasm contains many nuclei but is not divided into separate cells.

Saprotrophic Nutrition

• Extracellular digestive enzymes are secreted onto dead organic material.
• The material is digested into soluble products and absorbed for respiration.
• Decomposers break down dead organic material and recycle nutrients back into the soil.

Protoctists

• Protoctists are a mixed group of organisms that don't fit into plants, animals, or fungi.
• Most are microscopic single-celled organisms.
• Some protoctists are like animal cells (protozoa), such as Amoeba, which lives in pond water.
• Some contain chloroplasts and carry out photosynthesis (algae), like plant cells, such as Chlorella.
• Some algae, like seaweeds, are multicellular.
• Some protoctists are agents of disease, such as Plasmodium, which causes malaria.

Eukaryotic and Prokaryotic Organisms

• Plants, animals, fungi, and protoctists are composed of eukaryotic cells.
• Eukaryotic cells have a nucleus surrounded by a membrane, along with other membrane-bound organelles like mitochondria and chloroplasts.
• Eukaryotic cells have linear DNA
• Prokaryotic cells are simpler cells with no nucleus, mitochondria, or chloroplasts.
• The main forms of prokaryotic organisms are bacteria.
• Prokaryotic cells have no membrane bound nucleus or organelles.

Bacteria

• Bacteria are small single-celled organisms.
• Bacterial cells are much smaller than eukaryotic cells.
• A typical animal cell is 10 to 50 μm in diameter, whereas a typical bacterium is 1 to 5 μm in length.
• The shapes of bacteria include spheres (cocci), rods (bacilli), and spirals (spirilla).
• All bacteria are surrounded by a cell wall made of peptidoglycan (sugars and proteins).
• Some species have a capsule or slime layer outside the cell wall for extra protection.
• Inside the cell wall is the cell membrane.
• The cytoplasm contains a single circular loop of DNA (chromosome) instead of a nucleus.
• Some bacteria can swim using flagella.
• Plasmids are small circular rings of DNA that carry some of the bacterium's genes.
• Some bacteria contain chlorophyll and can carry out photosynthesis.
• Many bacteria are decomposers, recycling dead organisms and waste products.
• Some bacteria are used by humans to make food, such as Lactobacillus bulgaricus, used in yogurt production.
• Some bacteria are pathogens, which cause disease.
• Despite their simple structure, bacteria carry out life processes such as respiration, feeding, excretion, growth, and reproduction.
• Bacteria can move towards food or away from poisonous chemicals.

Viruses

• Viruses are parasites that can only reproduce inside living cells (hosts).
• Viruses are much smaller than bacterial cells, typically between 0.01 and 0.1 μm in diameter.
• Viruses are not made of cells.
• A virus particle consists of a core of genetic material (DNA or RNA) surrounded by a protein coat.
• The genetic material makes up just a few genes needed for reproduction inside the host cell.
• Sometimes, a membrane (envelope) surrounds the virus particle, stolen from the host cell's surface membrane.
• Viruses do not feed, respire, excrete, move, grow, or respond to their surroundings.
• Viruses reproduce by entering the host cell and using its genetic machinery to make more virus particles.
• The host cell dies and releases the virus particles to infect more cells.
• Many human diseases are caused by viruses, such as influenza, colds, measles, mumps, polio, and rubella.
• The body's immune system usually destroys the virus, but sometimes the virus causes permanent damage or death.
• HIV attacks cells of the immune system, causing AIDS.
• Viruses also infect plant cells, such as the tobacco mosaic virus, which interferes with chloroplast production.

Pathogens

• Pathogens are organisms that cause disease.
• Pathogens can include fungi, bacteria, protoctists, or viruses.
• Examples:
  • Plasmodium (a protoctist) causes malaria.
  • Some species of fungi cause diseases like athlete's foot.

AIDS and HIV

• AIDS is a syndrome (a set of symptoms caused by a medical condition).
• HIV damages the person's immune system, making them more likely to get other diseases like tuberculosis or develop unusual cancers.