Answer:
A.The hole in the ozone layer
Explanation:
• Montreal protocol is an international treaty that was signed to control the use of substances that are resulting in the depletion of the ozone hole.
This treaty was signed in the year 1987 and became effective form 1989.
• Since the time that this treaty has come into force, there has been a significant improvement in the ozone hole that was observed over Antarctic as it's size has decreased.
• This improvement has been possible because the treaty helped to phase out chemicals such as chlorofluorocarbons, carbon tetrachloride, etc. that are responsible for ozone hole depletion.
Answer:
Tropism can be called positive or negative. Positive tropism is movement or growth towards a stimulus, whereas negative tropism is the movement or growth away from a stimulus.
Explanation:
Solution:
The most appropiate unit of measurement fro most types of cells is CD4 counts are measured in cells per cubic millimetre = cells/mm3. A cubic millimetre (mm3) = mm3 = 1 mm x 1 mm x 1 mm.
This is the required answer.
The process of turning off and on of genes is known as gene regulation.
Explanation:
When the gene is turned on, it instructs the cells to construct a particular protein. The proteins are the molecules that build your body with collagen, tendons, and bones or keratin in your hair.
The gene regulatory proteins allow the individual genes of an organism to be turned on or off . in different cell types there are different selections of gene regulatory proteins. The patterns of the gene expression gives each cell its unique characteristics.
Each cell produces or turns on only a fraction of its genes. the remaining genes are repressed or turned off. this process is known as gene regulation. The signals from the environment or from other cells activate proteins called transcription factors.
