Characteristics of Life
A sunflower bends toward sunlight during the day. Which characteristic of life is being demonstrated?
Response to stimuli
What is the main purpose of biological classification?
To organize organisms based on shared characteristics so scientists can identify, compare, and study them.
Name the three domains.
Archaea, Bacteria, and Eukarya
Why is a dichotomous key called “dichotomous”?
Each step gives two choices.
Aristotle originally divided living things into what two major groups?
Plants and Animals
A puppy increases in size and changes as it becomes an adult dog. Which characteristic of life is demonstrated?
Growth and development
Put these levels in order from broadest to most specific:
Species, Kingdom, Family, Domain, Genus, Phylum, Order, Class
Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species
Which kingdom includes mushrooms, molds, and yeast?
Fungi
What kind of characteristics should a dichotomous key primarily use?
Observable characteristics that clearly distinguish organisms.
Which scientist is often called the Father of Taxonomy?
Carl Linnaeus
After running outside, Jamal begins sweating. His body is trying to maintain a stable internal temperature. What characteristic of life does this demonstrate?
Homeostasis
Which classification level is more specific: Family or Genus?
Genus
Which kingdom includes humans?
Animalia
A key says:
1a. Has wings → Go to 2
1b. Does not have wings → Go to 3
Your organism has wings. Where should you go?
Step 2
Why did classification systems change as scientists learned more?
New evidence revealed similarities and differences that earlier systems could not account for.
A plant uses sunlight to make food, while a rabbit eats plants. What characteristic of life do BOTH demonstrate?
Living things obtain and use energy.
Two organisms belong to the same genus but different species. Would you expect them to have many characteristics in common?
Yes
An organism makes its own food. Which term describes it?
Autotroph
Which characteristic would be more useful in a dichotomous key?
A. Is pretty
B. Has six legs
C. Looks weird
D. Is my favorite
B
Aristotle grouped animals partly according to where they lived. What is one limitation of this system?
Very different organisms can live in the same habitat.
A student says fire is alive because it grows, uses energy, and can spread. Why is this evidence NOT enough to classify fire as living?
Something must demonstrate all of the characteristics of life to be considered living. Fire only shows some life-like characteristics.
Organisms A and B share the same kingdom, phylum, class, order, family, and genus. Organism C shares only kingdom and phylum with A. Which organism is more similar to A?
Organism B
A scientist discovers an organism that absorbs nutrients from dead material. Which kingdom should the scientist investigate first?
Fungi
A student follows a key and identifies an organism as a butterfly. However, the organism has no wings. What should the student do FIRST?
Restart/check the key and verify each choice.
A whale and shark both live in the ocean and have similar body shapes. Why shouldn't scientists classify them together using only this evidence?
Habitat and appearance alone are not enough. Multiple characteristics should be compared.
A seed has not grown for several months. A student concludes that it must be nonliving. What is wrong with the student's reasoning?
Living things do not have to demonstrate every characteristic at every moment. A dormant seed is still living.
Animal X and Animal Y share the same classification through FAMILY. Animal X and Animal Z share only DOMAIN and KINGDOM. Which pair should have more characteristics in common?
X and Y
A student places a mushroom in Plantae because mushrooms grow from the ground and cannot walk. What evidence shows the classification is incorrect?
Fungi are heterotrophs, while plants are autotrophs.
You need to separate a spider, butterfly, snake, and fish. Which would make a useful first pair of choices?
A. Cute/not cute
B. Has legs/does not have legs
C. Big/small
D. Scary/not scary
B
A scientist develops a classification model. Years later, new evidence contradicts part of the model. What should scientists do?
Evaluate the evidence and revise the model if supported.
A lizard moves from a hot rock into the shade when its body becomes too warm. Identify TWO characteristics of life demonstrated.
Response to stimuli and homeostasis
Organism A: Animalia → Chordata → Mammalia → Carnivora → Felidae
Organism B: Animalia → Chordata → Mammalia → Carnivora → Canidae
At what level do their classifications first become different?
Family
An unknown organism is multicellular, heterotrophic, and able to move from place to place. Which kingdom is most strongly supported?
Animalia
A key begins:
1a. Lives outside → Go to 2
1b. Lives inside → Go to 3
Why might this be a poor first step?
Organisms can live in different environments, so a consistent physical characteristic would be better.
Which system is stronger?
System A: Groups organisms by color and size.
System B: Groups organisms using several shared biological characteristics.
System B
A robot can move toward light, use electricity, and respond when someone touches it. Why should scientists NOT classify the robot as living based only on these observations?
It only demonstrates some life-like behaviors. Scientists must consider all characteristics of life.
A student says two organisms must be closely related because both belong to Animalia. Why is that evidence weak?
Kingdom is very broad. More specific classification levels should be compared.
A scientist finds a mostly unicellular organism that has characteristics unlike typical plants, animals, and fungi. Which kingdom should be considered?
Protista
Two students use the same dichotomous key on the same organism but reach different answers. What is the most reasonable explanation?
At least one student incorrectly identified a characteristic or followed the wrong pathway.
A student says, “Aristotle's classification system was wrong, so it had no scientific value.” Evaluate this statement.
The statement is inaccurate. His system helped organize organisms based on the knowledge available and contributed to later classification systems.
Scientists discover an unknown object. It grows larger, uses energy, and responds when exposed to light. What should scientists do before declaring it living?
Collect additional evidence to determine whether it demonstrates the other characteristics of life.
Four organisms share the same domain and kingdom. Only two also share the same phylum, class, order, family, and genus. Which two would you predict have the greatest number of characteristics in common? Explain.
The two sharing the most classification levels because they remain together through more specific groups.
Student A groups plants and fungi together because neither normally moves from place to place. Student B separates them based on how they obtain food. Which model is stronger and why?
Student B's because plants are autotrophs while fungi are heterotrophs.
You must make a key for an eagle, snake, dog, and fish. Develop a useful FIRST split and explain why it works.
Answers vary. Example: Has legs/does not have legs because it creates two groups using an observable characteristic.
Scientists discover organisms that do not fit an existing classification model. Explain how this could eventually cause the model to change.
Scientists would collect evidence, compare characteristics, and revise the model if the evidence shows the current system is inadequate.
Student A says, “If something moves, it is alive.” Student B says, “Movement alone cannot determine whether something is alive.” Whose claim is stronger? Defend your answer.
Student B. Nonliving things can move, and some living organisms do not visibly move. Multiple characteristics are needed.
Defend this statement: “The farther down the classification system two organisms remain together, the more similar they are expected to be.”
Classification becomes increasingly specific, so organisms sharing the more specific levels share more characteristics.
A scientist finds an organism with characteristics that seem to fit more than one kingdom. What is the BEST response?
A. Choose whichever looks closest.
B. Classify it based on habitat.
C. Collect additional evidence.
D. Create a new kingdom.
C
Evaluate this key:
1a. Organism is awesome → Go to 2
1b. Organism is boring → Go to 3
Explain the problem and revise it.
Awesome/boring are opinions. Replace them with objective characteristics such as has wings/does not have wings.
Give one strength, one limitation, and one improvement.
Strength: It organizes organisms using a characteristic.
Limitation: Habitat does not necessarily indicate important similarities.
Improvement: Use multiple biological characteristics.