exploring life
A student says:
"A car is living because it moves."
What is wrong with this statement?
Movement alone does not mean something is living. Living things have multiple characteristics of life.
What is the basic unit of life?
cell
What do we call an organism made of one cell?
unicellular
What is the major difference between prokaryotic and eukaryotic cells?
Eukaryotic cells have a lining; prokaryotic cells do not have a membrane-bound lining.
A seed looks dry and does not move.
Is it necessarily nonliving? Explain
No. A seed is living. It can remain dormant and begin growing when conditions are suitable
Robert Hooke observed thin pieces of __________using a microscope.
What did he call the tiny structures he observed?
cork
What do we call an organism made of many cells?
multicellular
A cell has DNA, cytoplasm, ribosomes, and a cell membrane.
However, its DNA is not enclosed in a lining.
What type of cell is it?
Prokaryotic.
A plant bends toward sunlight.
Which characteristic of life does this demonstrate?
Responding to stimuli.
Why did Robert Hooke use the word "cell"?
The small compartments reminded him of the small rooms occupied by monks.
Classify each organism:
Bacterium — Human — Amoeba — Tree
Which organism is prokaryotic?
A. Human
B. Oak tree
C. Bacterium
D. Mushroom
bacterium
A crystal gets larger over time.
A student says:
"The crystal is alive because it grows."
Why is the student's conclusion incorrect?
Growth alone does not prove something is alive. A crystal is not made of cells and does not perform all the characteristics of life.
Robert Hooke observed cork and described the tiny structures as cells.
Did he actually observe living cells?
No. The cork cells were dead. He mainly observed their cell walls.
A unicellular organism has only one cell.
How can that one cell survive if it doesn't have organs like a human?
Its single cell performs all the necessary life processes, such as obtaining energy, responding to stimuli, growing, and reproducing.
A scientist discovers a unicellular organism.
It has:
What can the scientist conclude?
The organism has a prokaryotic cell and is most likely a bacterium.
A newly discovered object:
What evidence gives scientists the strongest reason to classify it as living?
It demonstrates multiple characteristics of life, including using energy, growth, response to stimuli, reproduction, and being made of cells.
Why was the development of microscopes so important to the study of life?
Microscopes allowed scientists to observe structures too small to see with the naked eye, including cells, helping scientists understand that living things are made of cells.
A student says:
"If an organism is unicellular, it must be prokaryotic."
Is the statement correct?
Answer:
No.
Some unicellular organisms are eukaryotic. For example, an amoeba is unicellular but eukaryotic.
Organism A
Organism B
Question:
Both organisms are unicellular. Why are they classified differently?
Organism A is prokaryotic because it lacks lining.
Organism B is eukaryotic because its DNA is enclosed inside a lining.