Answer:
A factor that is purposely left the same.
Explanation:
A controlled variable should not be changed throughout an experiment or else it will affect the outcome of each individual trial.
Characteristics of Lancelets:
Small
Elongated
Marine invertebrate
Lacks a jaw
No sense organs
Has a notochord
Example: Lamprey
Characteristics of Tunicates:
Marine invertebrate
Has an outer coat that is rubbery or hard
Has two siphons
Examples: sea squirts, salps
Answer:
For regulating activities of cell.
Explanation:
Ad nucleus consists of genetic materials like DNA,RNA which is responsible for controlling and directing all the activities of cell.
The sediments rub together to become smoother. Sediments which are transported in a mass by water or stream are in motion with respect to the motion of the stream water. They bump into each other which makes extruding parts vulnerable to getting knocked off which makes these particles round after a while.
Answer:
D. They define geological periods because scientists use them as reference points for tracking the history of the earth.
Explanation:
Catastrophic events related to changes in geological timeline are very useful in defining geological periods.
These events have very significant appearance in the geological record and can be used to determine the history of the earth.
The catastrophic events usually culminates into extinction cycles or termination of some organisms from the earth surface.
Geologists use these events that are often wide spread to delineate geological periods.
