Amodel organism is a species that researchers study to better understand certain biological processes. mollusks and arthropods are commonly used as model organisms for studying mechanisms of learning and memory, while sponges and jellyfish are not. why is this? a. mollusks and arthropods can detect stimuli from their environment, while jellyfish and sponges cannot. b. mollusks and arthropods exhibit cephalization, while jellyfish and sponges do not. c. mollusks and arthropods exhibit segmentation, while jellyfish and sponges do not. d. mollusks and arthropods can respond to changes in their environment, while jellyfish and sponges cannot.

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They can respond to changes in their environment which the answer is  

D. Mollusks and arthropods can respond to changes in their environment, while jellyfish and sponges cannot.

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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.