Organisms and Life Processes

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.

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.

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 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.

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.

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.

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 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.

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 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 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 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 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.