Organisms & Their Habitats
A Look at How Living Things Interact in Their Habitats and How Energy is Passed Along in an Ecosystem
What makes something "living"? If I ask you to name some living things, you most likely will say "person, dog, cat", or any list of animals. But there's a great deal more living things on our planet then just animals - all of the following are living things, or ORGANISMS.
Can you name the major types of living things in the pictures below?
Levels of Classification
There is an estimated 8.7 million different species of living things on our planet, with 6.5 million found on land, and 2.2 million found in our oceans. Scientists need to have a classification system that divides all these organisms into categories based on similar characteristics. There are 8 different categories, or groups, in the classification system: Domain, Kingdom, Class, Order, Family, Genus, Species. The largest of these categories begins with the Domain, and as each category gets more and more specific, the numbers of organisms in each category gets smaller and smaller, until there is only one specific living thing in the Species category.
To the right, you can see how dogs are classified (LOOK AT THE IMAGE TO THE RIGHT).
1) Dogs are in the largest KINGDOM of "Animalia", which includes all of the animals on our planet.
2) The next group is PHYLUM, and the dog belongs to the phylum "Chordata". You can see that the butterfly is no longer in this group because it doesn't have characteristics of the others.
3) Next is the CLASS "Mammalia", which humans also belong to, but you can see that fish are not part of this group.
4) The groups get smaller and more specific in their characteristics, and the next is the ORDER of carnivores, so now the elephant is removed.
5) The FAMILY "Canidae" includes all dog-like carnivores, and so the lion is removed.
6) Finally, we get to the GENUS and the SPECIES, and in that last group, we only have the ONE organism, which is the common dog.
Scientists use the GENUS and SPECIES names for the organism's SCIENTIFIC NAME. So, the scientific name for the dog is: Canis familiaris
Watch the 4 videos BELOW to better understand how living things are classified into this system.
Starting at the Top: The Three Domains
The three MAJOR groups of living things are called DOMAINS. The domains of living things are: Bacteria, Archaea, and Eukarya.
Organisms classified as Bacteria are single-celled (aka 'uni-cellular), meaning they consist of only one cell. Bacterial cells are prokaryotic, which means they do not contain a nucleus, and they come in mainly three different shapes: spherical, rod-shaped, or spiral-shaped. Often associated with causing diseases, there are more helpful bacteria in this domain.
Archaea are similar to bacteria, since they are also single-celled and prokaryotes, but they are quite different in their genetic and chemical makeup, along with where they live. Archaea are found in harsh environments, where no other living things could live, such as extreme salt, heat, cold, and acid. One type of Archaea lives in hot environments, like deep-sea hydrothermal vents. These are called thermophiles. Another type is the halophile, which lives in salty conditions like in the Dead Sea.
Organisms in the Domain Eukarya are different from the other two, starting with their cells being eukaryotes, or cells containing a nucleus. This domain is further broken down into four kingdoms: Protists, Fungi, Plants, and Animals. We humans belong to this domain.
Watch the TWO videos below that compare prokaryotic cells and eukaryotic cells.
What do all living things have in common?
All living things - bacteria, protists, fungi, plants and animals - share the same important characteristics:
They are all composed of one or many cells.
They all contain similar chemicals (water, carbohydrates, proteins, lipids, and nucleic acids).
They all need to obtain and use energy to undergo life processes. (This means they need some type of 'food'.)
They all respond to changes in their environment (stimulus/response) and can adapt.
They all grow and develop, and have a life-span (which means they eventually all die).
They can all reproduce.
They all contain DNA and can change and evolve over time.
In addition, all living things must satisfy their basic needs for water, food, living space, and stable internal conditions (homeostasis).
The Four Major Characteristics Used to Classify Organisms Into a Kingdom
Number of Cells:
a) unicellular - made of only one cell
b) multicellular - made out of many cells
Type of Cells:
a) prokaryotic cells - do not have a nucleus and lack major organelles
b) eukaryotic cells - have a nucleus and membrane-bound organelles inside (these are usually much larger than prokaryotic cells)
Ability to make food through photosynthesis:
a) autotroph - able to make food (sugar) in cells
b) heterotroph - can NOT make food in cells, and instead needs to obtain food for its body
Type of Reproduction Used:
a) asexual - requires only ONE parent cell, which will make a copy of its DNA, and then split into two, making an exact copy of the original parent, 100% of the DNA is from the parent
Examples of organisms that reproduce asexually: bacteria, archaea, protists, some plants (sweet potatoes, spider plant), some fungi (yeasts), and hydra (an animal)
b) sexual - requires two parent cells (sperm and egg) that combine 50% of their DNA to create a new unique organism. The offspring will receive half of its DNA from the egg and half from the sperm.
Examples of organisms that reproduce sexually: most plants (trees, flowers), animals (mice, humans), and fungi (mushrooms)
More examples of asexual and sexual reproduction:
Bacteria reproduce asexually. They will make an exact copy of their DNA, and then split into an exact replica of the original cell. Both bacterial cells are clones.
Trees reproduce sexually. There are male and female parts or cones that produce sperm and egg, and after fertilization occurs, a seed forms. The seed protects the baby plant embryo until conditions are just right for it to sprout.
The Six Kingdoms of Life
After the domain, the kingdom is the second largest group in the classification of living things. The six kingdoms consist of: Archaebacteria, Eubacteria, Protists, Fungi, Plants, and Animals.
Archaebacteria:
Extreme bacteria found in the domain Archaea. Their name means "ancient things" because they often live in conditions that resemble earth 3.5 billion years ago.
Cell type: prokaryotic (no nucleus)
Cell number: single-celled
Ability to make food: mostly autotrophic, but some heterotrophic
Type of reproduction: asexual
Eubacteria:
Bacteria found in the domain Bacteria, and those that are more commonly found everywhere. They have three main shapes: spherical, spiral, and rod.
Cell type: prokaryotic (no nucleus)
Cell number: single-celled
Ability to make food: some autotrophic, some heterotrophic
Type of reproduction: asexual
Protists:
The single-celled organisms in this kingdom are further classified as being plant-like, animal-like, or fungus-like. They look similar to bacteria, but are larger in size, and protists contain a nucleus in their cells. They use structures to move around in their environment, such as pseudopods, flagella, and cilia.
Cell type: eukaryotic (have a nucleus)
Cell number: mostly single-celled
Ability to make food: some autotrophic, some heterotrophic
Type of reproduction: mostly asexual
Fungi:
This kingdom includes the mushrooms, molds, mildews, and yeast. They obtain nutrients by absorbing their food using thin threadlike tubes called hyphae, and they reproduce by spores. Fungi play a key role in recycling decaying material (decomposers).
Cell type: eukaryotic (have a nucleus)
Cell number: single-celled yeasts only, all other fungi are multi-cellular
Ability to make food: heterotrophs
Type of reproduction: both asexual and sexual
Plants:
All plants are multi-cellular autotrophs that make their own food (a type of sugar) in their cells, using the sun's energy, in a process called photosynthesis. Plants are divided into two groups: non-vascular (have no roots or leaves, like moss) and vascular (roots, stems, and leaves).
Cell type: eukaryotic
Cell number: multi-celled
Ability to make food: autotrophic
Type of reproduction: mostly sexual
Animals:
All animals are multi-cellular heterotrophs, consuming food as herbivores (plant-eaters), omnivores (plant & meat eaters), or carnivores (meat-eaters), or as decomposers or scavengers. Animals have adaptations for finding food, habitats, mates, and as predators or prey. They can be invertebrates (lack a backbone) or vertebrates (have a backbone).
Cell type: eukaryotic
Cell number: multi-celled
Ability to make food: all heterotrophs
Type of reproduction: mostly sexual, hydra is asexual
Living Things and Their Environment
Have you ever walked through a forest and noticed all the amazing sights and sounds - birds nesting in the trees, butterflies and dragonflies fluttering by, a stream rolling over rocks, the sun's beams coming down through the trees? If you open your senses to the world around you, you will notice that there's a lot more going on out there than just human life. Both living and non-living things interact and make up the surroundings of organisms - this is called an ECOSYSTEM.
Think of that forest ecosystem again - can you list all the living and non-living things that make it up? Scientists call all the living parts of an ecosystem the BIOTIC FACTORS, while all the non-living parts are called the ABIOTIC FACTORS. Both the living and non-living things are important in the lives of organisms.
How Do Living Things Obtain Food Energy?
Organisms (living things) are classified by how they obtain food energy. Those organisms that can make their own food energy within their bodies are called AUTOTROPHS, whereas those organisms that can NOT make their own food are called HETEROTROPHS.
In an ecosystem, organisms have specific energy roles - those that can make their own food using the sun's energy through the process called PHOTOSYNTHESIS are called PRODUCERS ("produce own food"), which include plants, algae, seaweed, plant plankton (phytoplankton) and some bacteria and protists. Those organisms that need to obtain energy by eating other organisms are called CONSUMERS ("consume others for food"). The third role are those organisms, such as worms and some fungi and bacteria, which eat dead and decaying organisms, returning the nutrients back into the ecosystem - the DECOMPOSERS.
So, to sum it up, producers produce their own food using the sun's energy, which then pass on that energy when they get eaten by a consumer (the "primary consumer"), which continues to pass on the energy when they are consumed, or eaten by another consumer (the "secondary consumer"), until the last consumer in the 'chain' of food energy dies, and the decomposers take over, returning energy and nutrients back into the ecosystem.
This is called a FOOD CHAIN - it shows the linear transfer of food energy through an ecosystem, whereas a more realistic diagram, called a FOOD WEB, truly shows how all organisms interconnect when it comes to the transfer of food energy:
Consumers are further classified by what they eat:
HERBIVORES eat only plants, such as rabbits and deer.
CARNIVORES eat only other consumers (or meat), such as lions and wolves. Carnivores in nature hunt and eat other animals, making them PREDATORS, while the animal they hunt and eat is called the PREY.
OMNIVORES eat both plants and meat, such as raccoons, bears, and humans.
