Law of Superposition
a basic law of geochronology, stating that in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom, each layer being younger than the one beneath it and older than the one above it.
Answer:
The correct answer will be option-accurate and complete DNA replication.
Explanation:
The cell cycle of a cell is controlled by the internal checkpoints where the cell cycle halts until the favourable conditions appear. These checkpoints are G1 checkpoint, G2 checkpoint and M checkpoint.
The G2 checkpoint asses that the DNA replication has been completed, all the chromosomes have been replicated and the replicated DNA is not damaged. The cell cycle stops if the replicated DNA is found damaged.
Thus, option-accurate and complete DNA is the correct answer.
Answer:
All of these choices are correct.
Explanation:
Cell cycle is the process of growth and division of cell. It comprises of interphase and mitosis. In interphase the cell grows, replicates its genomic content and prepares itself for division. In mitosis the division occurs.
Cell cycle is controlled by a group of kinases called as Cyclin dependent Kinases (CDKs). They act by phosphorylating their substrates. They are of various types like Cdk1, Cdk2, Cdk4 etc. They become active when they bind to a regulatory protein called cyclin. They are also of various types like Cyclin A, Cyclin B, Cyclin C etc. Level of cyclin and corresponding CDK increases and decreases according to the stage of cell cycle. For example in S phase of cell cycle concentration of cyclin A and E shoots up. CDK2 is able to bind to these cyclin molecules and hence it becomes active.
Cell cycle has major checkpoints where the condition of cell is analysed before it proceeds to the next stage of cycle. If any abnormality is detected, repair mechanism is activated or the cell is killed. Checkpoints do not allow cell cycle to proceed in damaged cells.
p53 is a tumor suppressor protein which can halt cell cycle when it detects some abnormality in cell. It usually acts in G1/S checkpoint (before the DNA replication starts in cell) and G2/M checkpoint (before the cell division begins). Hence, all of the above statements are true.
Answer:
Biodiversity: Tropical rainforests are areas of extremely high biodiversity compared to other ecosystems. Biologists estimate that tropical rainforests contain about 50% of the world's terrestrial plant and animal species, yet they encompass only about 6% of the world's land area.
Explanation:
