Antidiuretic hormone provides a means of controlling output. During dehydration blood volume declines and concentration rises. The increased osmolarity of the blood stimulates the hypothalamus to stimulate the pituitary to release ADH. ADH will work on the kidneys to water into the bloodstream. A negative feedback system is used until the blood and osmolarity return to normal levels.

1. Water

2. Sodium

3. Posterior

4. Reabsorb

5. Volume

Explanation:

1. ADH or anti-diuretic hormone is the hormone which maintains the level of water in the body as ADH helps in reabsorption of water in the kidney and produces concentrated urine.

2. During dehydration, the level of the water in the blood declines but the concentration of sodium ions increases which increases the osmolarity of the blood.

3. The increased osmolarity are sensed by the osmoreceptors which send the signals to the hypothalamus which stimulates the posterior pituitary to release the ADH or vasopressin hormone.

4. The ADH hormone binds the ADH receptors in the collecting tubule of the kidney which opens the aquaporins to reabsorb the water from the urine.

5. This process in negative feedback as the volume of the blood and osmolarity returns to the normal. Once the level is normal, sends the signals to inhibit the synthesis of ADH from the posterior pituitary.

Species richness is species diversity and IUCN status of species is threat perception to any species.

Explanation:

Species richness is varieties of species present in a geographical region. It can be understood as simply number of different type of species present in a region. It does not provide any information about the vulnerability of any species to any factor such as anthropogenic factor. E.g. Tropical rainforests are characterised by a high amount of species diversity.

IUCN status of species refers to the categorisation of species based on threat perceptibility to the species in nature. Different types of status are provided to different species such as Endangered, Near threatened, Extinct and Least concern. This status serves as the primary benchmark for the increased susceptibility of any species to natural or anthropogenic actions. E.g. Sumatran Rhinos are listed amongst critically endangered species by the IUCN.

Human disturbances and actions of late have caused an imbalance in nature and the atmosphere. This has affected tundra climate and biodiversity severely in the following way-

Increased greenhouse gas emissions have led to global warming thus increasing temperature. This has led to the melting of the permafrost and thus plants accustomed to living in tundra climate are finding it difficult to live in a warmer climate and with melted permafrost. Rising temperature has led to the invasion of tundra biome by temperate plants thus decreasing biodiversity. This has been similar both in floral as well as a faunal biome.  Melting of ice caps has increased man’s presence in the otherwise frozen region. This has been associated with disappearances of some species such as blue whale from the polar region since Human’s have hunted them to a critically dangerous level. Melting of ice caps has altered the tundra ecology and biome and is transforming into temperate biome.  e.g. Walrus and polar bear are finding it difficult to sustain themselves due to declining ice cover and incresed competition from temperate animal species who have migrated into polar region in search of prey.