Classfying Living Things 5°

Eukaryotic and Prokariotic Cells

By Beatriz Cortes

All organisms are made of cells and can be grouped according to the number and type of cells they have. Do you know which types of cells there are, an how organisms can be classified according to the number of cells they have?

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The cell is the basic unit of living things, which ca be classified as unicellular if they are made up of only one cell-like bacteria or multicellular if they are made up of more than one.

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One or many?

Eukaryotic Cells

The world eukaryotic means true nucleus. Eukaryotic cells have small inner structures called organelles, meaning small organs. Because they have a lot of organelles, this type of cell is very complex, but very functional. In a eukaryotic cell the nucleus controls the cell’s activities and is very important in cell reproduction. The DNA stored in the nucleus is the structure that contains all the organism’s information. Other organelles, like mitochondria, lysosomes and the endoplasmic reticulum, have different Jobs such as reparation or digestion. Most organisms, like animals and plants, are made of eukaryotic cell. Let´s read about some examples of eukaryotic organisms!

Diatoms are unicellular organisms that have strong cell wall. They are very sensitive to environmental changes, so diatoms are often used to study the quality of water.

​Yeasts are unicellular fungi. They are used in many food products, for example to make bread.

Euglenas are a microscopic unicellular organism that can survive in fresh or salt water. They can make food by photosynthesis –like plants- or eat other organisms –like animals.

Multiple Choice

What is the basic unit of all living organisms?

• Organ

• Cell

• Tissue

Multiple Choice

What does it mean when an organism is classified as unicellular?

• It is made of tissues.

• It refers to organisms that can only live in water.
• It means the organism is made up of only one cell.

Multiple Choice

What does the word "eukaryotic" mean?

• No nucleus

• With a fake nucleus

• True nucleus

Multiple Choice

What is the main role of the nucleus in a eukaryotic cell?

• To digest food

• To control the cell's activities

• To produce oxygen

Multiple Choice

Which of the following is an example of a unicellular eukaryotic organism?

• Dog

• Yeast

• Tree

All bacteria are prokaryotic. Prokaryotic cells don’t have a nucleus as do eukaryotic cells. Instead, they have a long string of DNA. Prokaryotic cells do not have many organelles either, so digestion or respiration are controlled by plasma membrane and the few organelles which are protected by a cell wall. Prokaryotic cells are much smaller than eukaryotic cells. Prokaryotic cells have different shapes, but the three basic ones are round called cocci, rod-shaped cells called bacilli, and spiral-shaped cell called spirochete.

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Prokaryotic cells

​Some kinds of bacteria are helpful. This means they do things that are good for other organisms, for example, to make yogurt and cheese to feed humans. Other kinds of bacteria are harmful, which means that they affect other organisms negatively. For example, some bacteria can produce diseases like tuberculosis and other are responsible for dental caries.

Bacteria: Friend or Foe

Multiple Choice

What is one main difference between prokaryotic and eukaryotic cells?

• Prokaryotic cells have many organelles.

• Prokaryotic cells do not have a nucleus.

• Eukaryotic cells have a spiral shape.

Multiple Choice

Which of the following statements about bacteria is true?

• All bacteria cause diseases in humans.

• All bacteria are eukaryotic.

• Some bacteria are helpful and used to make food.

Multiple Choice

Which of the following is an example of helpful bacteria?

• Bacteria that cause dental caries.

• Bacteria used to make yogurt.

• Bacteria that produce tuberculosis.

Scientists divide organisms into groups to make them easier to study according to their characteristics. Organisms with characteristics in common are put into the same group.

​We are all different

To classify organisms, first they are divided into very large general groups, then each group is divided into several smaller groups. The smaller the groups, the more characteristic the organisms in that group have in common. The classification criteria are: Kingdom, phylum, class, order, family, genus and species.

The Classification criteria

The kingdom of archaebacteria is a large group of prokaryotes. Archaebacteria are some of the oldest and simplest organisms found on Earth. They are usually found in unconventional environment with extremely salty, hot or acidic conditions. Archaebacteria are harmless to other organisms and scientists have not found any archaebacteria that cause any disease.

​​Archaebacteria

Eubacteria

​​Protists

​​Fungi

The six kingdom

​The kingdom of eubacteria, sometimes called “true bacteria”, is a large group made up of prokaryotic organisms. Eubacteria can be found in food, soil, water and even inside the human body. Did you know that you have over 1,000 kinds of bacteria that help you digest food?

​Protist are simple organisms made up of eukaryotic cells. They can live anywhere there is water. Protists are made up of one call or a small group of cells; they do not have tissues. Euglena and amoeba are examples of protists.

Fungi are eukaryotic organisms. There are unicellular fungi like yeasts and molds, and multicellular fungi like mushrooms. Fungi are decomposers because they use nutrients from dead organisms to survive. Fungi reproduce using spores. Fungi reproduce using spores. Fungi are used in many ways.

Plantae is a kingdom of multicellular eukaryotic organisms. They make their own food during the process of photosynthesis, in which they use water, carbon dioxide and sunlight to produce food and oxygen. This is why plants are called producers because they are the only organisms that can produce food from the sun to feed the ecosystem, except for algae. Most importantly, plants produce the oxygen that most living things need to survive.

Plants

Animals

The six kingdom

In the animalia kingdom all organisms are eukaryotic. They can move from one to another, but they cannot make their own food. They must eat plants or other animals to survive; this is why they are called consumers. Animals breathe in the oxygen produced by plants, and breathe out carbon dioxide in a process called respiration. Humans depend on other animals for food, work and companionship. Food like beef, pork, chicken, eggs and milk comes from animals.

The animal kingdom can be divided into two groups: vertebrates and invertebrates. Vertebrates are subdivided into 5 classes, while invertebrates have more than 30 different phyla.

Animal Classification

​Sponges have soft, jelly-like bodies that filter plankton plants (plants or bacteria) and particles from the water for food. Sponges do not move but live attached to the floor of their habitat.

​​Sponges

​​Cnidarians

Worms

Mollusks

​Mollusks are legless and have soft bodies. Some mollusks have shells that protect their bodies, like-snails. Others have tentacles, like the octopus.

Segmented worms have soft, ringed bodies. They usually live-in soil or water. Segmented worms are very important because they process dead plants and animals and make fertilizers or compost.

Cnidarians have soft, jelly-like bodies and long poisonous tentacles that help them capture their food. Most jellyfish and corals live in the ocean. Jellyfish swim around in the water, but corals live in colonies attached to the floor or their habitat.

INVERTEBRATES

​Arthropods have an exoskeleton, a rigid structure that protects and gives support to their bodies from the outside. Scientists divide this group into four: centipedes/millipedes, insects, spiders and crustaceans.

​​Arthropods

​​Echinoderms

Echinoderms are also known as starfish. Starfish usually have five legs and small jaws. Their bodies are covered with spines.

​Fish are vertebrates whose skin is covered with scales; they breathe under water through gills and have fins for moving. They are cold-blooded and oviparous.

​​What are fish and amphibians?

Reptiles are vertebrates whose skins covered with scales; they breathe through lungs. They are cold-blooded and oviparous. Birds are vertebrates whose skin is covered with feathers. They are warm-blooded and oviparous.

Reptiles and birds

​Mammals are vertebrates whose skins covered with fur; they breathe through lungs. They are warm-blooded and viviparous.

​​Mammals

VERTEBRATES

Multiple Choice

Why do scientists classify organisms into groups?

• To create new organisms

• To make them easier to study based on their characteristics

• To separate animals from plants

Multiple Choice

What is the correct order of classification from the largest to the smallest group?

• Kingdom, class, order, genus, family, species, phylum

• Kingdom, phylum, class, order, family, genus, species

• Phylum, kingdom, class, species, genus, family, order

Multiple Choice

Where are archaebacteria typically found?

• Inside the human body

• In extreme environments like salty, hot, or acidic areas

• In freshwater lakes and rivers

Multiple Choice

Which statement is true about eubacteria?

• They can live in soil, water, food, and inside the human body

• They are only found in extreme environments

• They are multicellular and have tissues

Multiple Choice

What do fungi use to reproduce?

• Seeds

• Buds

• Spores

Multiple Choice

Why are plants called producers?

• Because they feed on fungi

• Because they consume sunlight for heat

• Because they make their own food through photosynthesis

Multiple Choice

Which of the following are invertebrates?

• Mollusks

• Birds

• Mammals

Multiple Choice

What makes mammals different from birds and reptiles?

• They are oviparous and cold-blooded

• They are viviparous and warm-blooded

• They breathe through gills