Ineed with a few biology questions.

Answer No 1:

As soon as the fertilization of an egg takes place, the egg or the zygote starts to divide, giving rise to cells. The cells keep on differentiating until they become specialized cells.

Cell specialization can be described as a process by which cells become specialized to perform particular tasks in the body. Cell specialization is important because for an organism to work properly, different functions are to be done by cells, tissues, organs and organ system. Specialized cells are specific to do certain functions. Without a cell becoming specialized, the body will not be able to perform its functions.

Answer No 2:

All somatic cells are made up of the same chromosomes and the same genes in an organism. But different genes are activated in different types of cells. The genes which are active in one type of cell usually will not be active in other type of cell. These genes code for different proteins. Hence, this phenomenon allows all somatic cells to have the same karyotype but different specialized functions.

Answer No 3:

An environmental stimulus can be described as any environmental event which is detected by the body of an organism. For example, some plants tend to bend in the direction of the Sun. The Sun is the environmental stimuli and the movement of the plant in the direction of the Sun is the response.  

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.